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Neuroanatomy This page intentionally left blank Second Edition

Neuroanatomy Draw It to Know It

Adam Fisch, MD JWM Neurology and Adjunct Professor of Neurology Indiana University School of Medicine Indianapolis, IN

1 1

Oxford University Press, Inc., publishes works that further Oxford University’s objective of excellence in research, scholarship, and education. Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offi ces in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Th ailand Turkey Ukraine Vietnam Copyright © 2012 by Adam Fisch Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York 10016 www.oup.com Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. ______Library of Congress Cataloging-in-Publication Data Fisch, Adam. Neuroanatomy : draw it to know it/Adam Fisch.—2nd ed. p.; cm. Includes bibliographical references and index. ISBN 978-0-19-984571-2 (pbk.) I. Title. [DNLM: 1. Nervous System—anatomy & histology. 2. Anatomy, Artistic—methods. 3. Medical Illustration. WL 101] 611.’8—dc23 2011037944 ______Th is material is not intended to be, and should not be considered, a substitute for medical or other professional advice. Treatment for the conditions described in this material is highly dependent on the individual circumstances. And, while this material is designed to off er accurate information with respect to the subject matter covered and to be current as of the time it was written, research and knowledge about medical and health issues is constantly evolving and dose schedules for medications are being revised continually, with new side eff ects recognized and accounted for regularly. Readers must therefore always check the product information and clinical procedures with the most up-to-date published product information and data sheets provided by the manufacturers and the most recent codes of conduct and safety regulation. Th e publisher and the authors make no representations or warranties to readers, express or implied, as to the accuracy or completeness of this material. Without limiting the foregoing, the publisher and the authors make no representations or warranties as to the accuracy or effi cacy of the drug dosages mentioned in the material. Th e authors and the publisher do not accept, and expressly disclaim, any responsibility for any liability, loss or risk that may be claimed or incurred as a consequence of the use and/or application of any of the contents of this material.

9 8 7 6 5 4 3 2 1 Printed in the United States of America on acid-free paper Th e fi rst edition of this book was dedicated to the memory of my younger brother, David.

Th is edition is dedicated to my children, Ava and Ezra, who were born during the rewrite of this book and who renew my faith that good things still happen. This page intentionally left blank Foreword from the First Edition

Neuroanatomy is a nightmare for most medical students. Th e complex array of nuclei, ganglia, tracts, lobes, Brodmann areas and cortical layers seem to the uninitiated as the height of useless trivia. My own memory of my neuroanatomy class in medical school is vivid. Our professor ordered each member of the class to buy a set of colored pencils—the kind you had in third grade. Each color was coded for particular structures (red for the caudate, green for the putamen, yellow for the claustrum and burnt sienna for the globus pallidus). At our senior play, which poked fun at our professors, a beleaguered medical student was asked to name the components of the basal ganglia. Without knowing what the structures even were or did, he responded “red, green, yellow, and burnt sienna.” Almost forty years later, this remains a class joke. Except for the handful of us who went into neurology, neurosurgery, and psychiatry, the basal ganglia to the rest of my class is just a fading joke from the distant past. And yet, no one can practice even rudimentary neurology without some basic understanding of the neuroanatomy. Non-neurologists in particular, many of whom see large numbers of patients with neurological complaints, have no hope of sorting out common problems such as headache, dizziness, tiredness, fatigue, sleep disorders, numbness and tingling, and pain, without a reasonable grasp of how the nervous system is organized. Despite all of the marvelous advances in neuroscience, genetics, and neuroimaging, the actual practice of neurology, whether it is done by a neurologist or a non-neurologist, involves localizing the problem. Th e nervous system is just too complicated to skip this step. Without an organized approach based on a reasonable understanding of functional neuroanatomy, clinical neurology becomes incomprehensible. In his wonderful book, Neuroanatomy: Draw It to Know It , neurologist Adam Fisch applies my old neuroanatomy professor’s colored pencil idea in a manner that actually works, and it’s fun! Over the course of 39 chapters, most of the clinically important neu- roanatomically important subjects are covered, ranging through the overall organization of the nervous system, the coverings of the brain, the peripheral nervous system, the spinal cord, the brainstem, the cerebellum, and the cerebral cortex. It is clear that the book was written by an experienced neurologist, as the topics are organized in a fashion that illumi- nates the principle of anatomical pathophysiological correlation, which is the tool with which neurologists approach clinical problems. Th is book should be of great interest to all neurologists, neurosurgeons, neurology residents, and students of neurology. Others who see patients with neurological complaints, such as internists, emergency physicians and obstetrician-gynecologists should also review their neuroanatomy if they wish to provide excellent care to their patients. viii Foreword

As any experienced teacher knows, one only really knows a subject when one can teach it oneself. By drawing the anatomy, the reader of this book literally teaches the subject to himself. By making it clinically relevant, the information learned in this manner is likely to stick. Adam Fisch has done us all a great service by rekindling the enjoyment in learning the relevant, elegant anatomy of the nervous system.

Martin A. Samuels, MD, DSc(hon), FAAN, MACP Chairman, Department of Neurology Brigham and Women’s Hospital Professor of Neurology Harvard Medical School Boston, MA Preface

Neuroanatomy is at once the most fascinating and most diffi cult subject in the fi eld of anatomy. When we master it, we can resolve the most perplexing diagnostic riddles in medicine, and yet we struggle with the numerous neuroanatomical structures and pathways, the intertextual inconsistencies in nomenclature and opinion, and the complex spatial relationships. So here, we bring the diff erences in nomenclature and opinion to the forefront to mitigate them and we present the material in an active, kinesthetic way. In this book, we approach each neuroanatomical lesson by beginning fresh with a blank page, and from there we build our diagram in an instructive, rather than a didactic format. With each lesson, we create a schema that provides a unique place for each neuroanatomical item. Th is, then, allows us to rehearse the schema and in the process memorize the fundamental neuroanatomical items. And because we are all students of anatomy— and not art—our purpose with each lesson is to learn a schematic that we can reproduce in the classroom, the laboratory, or at the bedside in a way that is especially designed for the “left -brained” among us. Some of us possess pigeon-like navigational skills, whereas others of us fi nd ourselves getting lost in our own houses. Th e ease with which we learn anatomy is inherently related to the strength of our spatial cognition, which makes it harder for those of us who struggle with complex spatial relationships to master the subject matter1 . When it comes to the task of deciphering a complicated illustration, specifi cally in studying the details of an illustration, it has been shown that we rely heavily on the right frontoparietal network2 – 4. In Neuroanatomy: Draw It to Know It , we shift the process of learning neuroanatomy away from the classic model of spatial de-encoding, away from the right frontoparietal network, to the formulation of memorizable scripts or schemas, which task the prefrontal cortices more intensively, instead 5 , 6 . In so doing, we provide the less spatially-inclined with a diff erent entry zone into the world of neuroanatomy. Th is book reconciles the most burdensome impasses to our learning: we highlight inconsistencies, remove spatial complexities, and create an active, instructive text that adheres to the principle—when we can draw a pathway step by step, we know it. x Preface

References 1 . Garg, A. X., Norman, G. & Sperotable, L. How medical students learn spatial anatomy. Lancet 357 , 363–364 (2001). 2 . Walter, E. & Dassonville, P. Activation in a frontoparietal cortical network underlies individual diff erences in the performance of an embedded fi gures task. PLoS One 6 (2011). 3 . Walter, E. & Dassonville, P. Visuospatial contextual processing in the parietal cortex: an fMRI investigation of the induced Roelofs eff ect. Neuroimage 42 , 1686–1697 (2008). 4 . Aradillas, E., Libon, D. J. & Schwartzman, R. J. Acute loss of spatial navigational skills in a case of a right posterior hippocampus stroke. J Neurol Sci 308 (2011). 5 . Knutson, K. M., Wood, J. N. & Grafman, J. Brain activation in processing temporal sequence: an fMRI study. Neuroimage 23 , 1299–1307 (2004). 6 . Rushworth, M. F., Johansen-Berg, H., Gobel, S. M. & Devlin, J. T. Th e left parietal and premotor cortices: motor attention and selection. Neuroimage 20 Suppl 1, S89–100 (2003). Acknowledgments

I’d like to thank my wife, Kate, and the rest of my family and friends for putting up with my decision to rewrite this book, and I’d like to thank my editor, Craig Panner, and the rest of the Oxford University Press team for all of their hard work. To rewrite this book, I started over entirely. I spent the fi rst year creating a muscle– nerve directory and the following year creating a brain atlas, and then I went to work on rewriting the book, itself. I threw out all of the original illustrations and redraft ed them as I wrote the individual tutorials. Taking advantage of the ability to keyword search the massive library of books now available online and taking advantage of several fundamental reference materials I'd used during the creation of the muscle–nerve directory and brain atlas, I was able to create detailed illustrations and scripts that maintained the simplicity of the original book but greatly improved upon its level of detail. As well, feedback from the fi rst edition helped me understand how to provide the information a student of neuroanatomy needs without sacrifi cing the clinical relevance a clinician is looking for. In creating the tutorials, I came to understand that the text should serve as a play-by-play manual that tersely defi nes each step in the drawing—only aft er the steps were solidifi ed did I fl esh out the material, itself. When the tutorials were written and fi nalized, I then broke them down into their individual steps, which served as an invaluable editorial process. Rewriting this book was all-consuming and I am eternally grateful to those closest to me for giving me the time and space to see it to completion. Th ere are many, many people who have helped me along the way and I hope the end product of this book will prove your patience and eff orts worthwhile. I believe this book represents the best that neuroanatomy education has to off er and I am exceedingly grateful to those around me who gave me the opportunity and freedom to have a second crack at it. This page intentionally left blank Contents

1. General Organization 3

2. Meninges and Ventricular System 13

3. Peripheral Nervous System—Upper Extremity 27

4. Peripheral Nervous System—Lower Extremity 55

5. Peripheral Nervous System—Sensory Maps 71

6. Peripheral Nervous System—Autonomic Nervous System 91

7. Spinal Cord 105

8. Spinal Canal and Muscle–Nerve Physiology 127

9. Brainstem—Part One 139

10. Brainstem—Part Two 159

11. Cranial and Spinal Nerve Overview and Skull Base 173

12. Cranial Nerves 3, 4, 6, 12 195

13. Cranial Nerves 5, 7, 9, 10 211

14. Vestibular and Auditory Systems 231 xiv Contents

15. Cerebellum 247

16. Cerebral Gray Matter 267

17. Cerebral White Matter 287

18. Basal Ganglia 303

19. Arterial Supply 317

20. Diencephalon 339

21. Limbic and Olfactory Systems 357

22. Vision 379

23. Eye Movements 409

24. Cognition 425

25. Sleep and Wakefulness 439

Index 451 Neuroanatomy This page intentionally left blank 1 General Organization

Overview of Neuroanatomy

Orientational Terminology

Divisions & Signs 4 Neuroanatomy: Draw It to Know It

Know-It Points

Orientational Terminology

■ Th e top of the cerebral hemisphere is dorsal and the ■ Towards midline is medial and towards the outside is bottom is ventral. lateral. ■ Th e anterior aspect of the cerebral hemisphere is ■ Sagittal view is side-on. rostral and the posterior aspect is caudal. ■ Coronal view is front-on. ■ Th e top of the brainstem is rostral and the bottom is ■ Axial view is horizontal. caudal. ■ Th e anterior aspect of the brainstem is ventral and the posterior aspect is dorsal.

Divisions & Signs

■ Cerebral cortical pyramidal cells are upper motor ■ Lower motor neuron injury causes fl accid muscle neuron. tone, hypoactive muscle stretch refl exes, and absent ■ Cranial nerve nuclei and spinal motor neurons are pathologic refl exes (eg, negative Babinski’s sign). lower motor neuron. ■ Upper motor neuron injury causes spastic muscle tone, hyperactive muscle stretch refl exes, and pathologic refl exes (eg, positive Babinski’s sign). 1. General Organization 5

FIGURE 1-1 Plate 4 (top) and plate 8 (bottom) from the 1810 atlas of Franz Joseph Gall and Johann Kaspar Spurzheim —Anatomie et physiologie du systeme nerveux. 6 Neuroanatomy: Draw It to Know It

Overview of Neuroanatomy

To begin, we will draw an overview of the anatomy of segments of the spinal cord from top to bottom as fol- the nervous system. First, we will address the brain, lows: cervical, thoracic, lumbosacral, and coccygeal. Th e brainstem, and cerebellum. Begin with a coronal section cervical segment mostly communicates with the upper through the brain. From outside to inside, label the extremities, upper trunk, head, and neck; the thoracic meninges, which protect and nourish the nervous segment mostly communicates with the trunk and abdo- system; the cortex, which constitutes the outer, cellular men; and the lumbosacral segment communicates with gray matter portion of the brain; the subcortical white the abdominal-pelvic region and the lower extremities. matter, which constitutes the underlying nerve axons; Draw a dorsal nerve root off of the posterior spinal the basal ganglia, which are most notably involved in cord; identify it with its dorsal root ganglion, which motor function but are also important for behavioral houses the sensory cell bodies. Th en, draw the ventral and cognitive functions; the thalamus, which in combi- root from the anterior surface of the spinal cord; it con- nation with the metathalamus relays most of the aff erent tains the motor fi bers that exit from the gray matter of information that enters the nervous system to various the spinal cord. Next, show that the motor and sensory regions throughout the cerebral cortex; the hypothala- roots meet to form a mixed spinal nerve within a neural mus, which lies along the third ventricle and is the center foramen. Th en, show that the cervical nerves interweave for autonomic nervous system function; and the cere- to form the cervical and brachial plexuses. Now, indicate brospinal fl uid system, which assists the meninges in that the lower lumbosacral nerve roots descend through supporting and nourishing the nervous system. the lumbar cistern and exit the spinal canal to form the Below the brain, draw the brainstem. From superior lumbosacral plexus. Next, indicate that the majority of to inferior, show the midbrain, identifi ed by its crus cere- the thoracic nerves remain unmixed. Th en, show that bri, then the pons, identifi ed by its bulbous basal out- aft er the nerves exit their plexuses, they continue as pouching, and fi nally the medulla. Th e brainstem peripheral nerve fi bers. Now, draw a representative neu- contains cranial nerve nuclei, which command oculob- romuscular junction and a sensory cell receptor and ulbar motility, facial sensation, and many craniofacial attach muscle fi bers to them. Neurotransmissions pass and thoracoabdominal autonomic functions. And the across the neuromuscular junctions to stimulate muscle brainstem also contains many additional neuronal pools fi bers, and peripheral nerve receptors detect sensory essential for survival as well as the fi ber tracts that pass impulses from the musculoskeletal system and skin. between the brain and spinal cord. On the posterior Lastly, to represent the divisions of the autonomic aspect of the brainstem, draw the leafy hemispheres of nervous system, draw a parasympathetic ganglion and a the cerebellum; the cerebellum is important for balance sympathetic paravertebral chain segment; the parasym- and orientation, postural stability, and coordination. pathetic nervous system is active in states of rest whereas Next, we will address the spinal cord and peripheral the sympathetic nervous system is active in states of nervous system. Draw the long, thin spinal cord with heightened awareness— it produces the “fi ght-or-fl ight” its cervical and lumbosacral enlargements. Label the response. 1. General Organization 7

Brain, Brainstem, & Cerebellum Spinal Cord & Peripheral Nervous System Dorsal root Spinal Meninges ganglion cord Cortex Peripheral nerve Subcortical Ventral white matter Cervical root Cervical Sensory Basal & brachial receptor ganglia Cerebro- plexuses spinal Thalamus Hypo- fluid Thoracic thalamus Thoracic Neuro- spinal nerve muscular Midbrain junction Muscle Lumbo- fibers Cere- Pons sacral bellum & Lumbosacral Medulla Coccygeal plexus

Cauda Peripheral Autonomic Nervous System equina

Sympathetic Parasympathetic chain ganglion

DRAWING 1-1 Overview of Neuroanatomy 8 Neuroanatomy: Draw It to Know It

Orientational Terminology

Here, we will draw the orientational planes of the ner- Next, draw a coronal section through the brain — a vous system. To begin, draw intersecting horizontal and coronal view of the brain bears resemblance to an ornate vertical lines. Label the left side of the horizontal line as crown . Indicate that the top of the brain is dorsal (also anterior and right side as posterior. Label the top of the superior) and the bottom is ventral (also inferior). For vertical line as superior and the bottom as inferior. this view, we need to additionally introduce the lateral– Th roughout the nervous system, front is always anterior medial and left -right planes of orientation. Label the and behind is always posterior, top is always superior and midline as medial and the outside edges of the hemi- bottom is always inferior. Th e anteroposterior and super- spheres as lateral. For the left –right planes of orientation oinferior planes and medial-lateral planes, which we will we need to include both the anatomic and radiographic introduce later, are static: they do not change orienta- perspectives. Label the left -hand side of the page as radio- tion— unlike the rostral-caudal and dorsal-ventral planes, graphic right and anatomic left and the right-hand side as which we introduce next. radiographic left and anatomic right. Th ese planes refer Next, let’s draw a side-on, sagittal view of the oblong to the standardized ways in which coronal radiographic cerebral hemisphere. Label the top of the cerebral hemi- images and anatomic sections are viewed: in radiographic sphere as dorsal and the bottom as ventral: the dorsal fi n images, the head is viewed face-forward and in anatomic of a shark is on its back whereas a shark’s underbelly is its sections, the head is viewed from behind. ventral surface. Label the anterior portion of the cerebral Lastly, draw an axial (aka horizontal or transverse) sec- hemisphere as rostral and the posterior portion as caudal. tion through the brain — the top of the page is the front Rostral relates to the word “beak” and caudal relates to of the brain and the bottom is the back. Label the front of the word “tail.” the section as rostral (also anterior) and the back as caudal Now, draw a sagittal view of the brainstem at a nega- (also posterior). Label the left -hand side of the section as tive 80-degree angle to the cerebral hemisphere. During radiographic right and anatomic left and the right-hand embryogenesis, human forebrains undergo an 80-degree side as radiographic left and anatomic right. Radiographic fl exion at the junction of the brainstem and the cerebral axial images are viewed from below (as if the patient’s feet hemispheres. Label the posterior aspect of the brainstem are coming out at you) whereas anatomic axial sections as dorsal and the anterior aspect as ventral. Th en, label are viewed from above (as if the patient’s head is coming the superior aspect of the brainstem as rostral and the up at you). Label the center of the cerebral hemispheres as inferior aspect as caudal. medial and their periphery as lateral. 1 – 8 1. General Organization 9

CORONAL Dorsal (superior) Superior Radiographic Radiographic right & left & Anterior Posterior anatomic anatomic left right

Inferior Lateral Medial Lateral Ventral (inferior)

SAGITTAL AXIAL Dorsal Rostral (anterior)

Rostral Caudal Radiographic Radiographic right & left & anatomic anatomic Rostral Dorsal Ventral left right Ventral Caudal Lateral Medial Lateral

Caudal (posterior)

DRAWING 1-2 Orientational Terminology 10 Neuroanatomy: Draw It to Know It

Divisions & Signs

Here, we will learn the central and peripheral divisions (eg, the Babinski sign). Now, for the fi rst injury type, of the nervous system and the meaning of upper and show that injury to the cerebral cortex, such as from a lower motor neuron signs; note that we exclude the stroke, disrupts the brain and the related white matter autonomic division of the nervous system, here, for sim- tracts. Indicate that it causes an upper motor neuron pat- plicity. First, let’s draw the central nervous system. Draw tern of injury: there is spastic muscle tone, hyperactive a brain, brainstem and cerebellum, and spinal cord. Next, muscle stretch refl exes, and the presence of pathologic in order to label the upper motor neuron and nerve com- refl exes. Second, show that injury to the spinal nerve ponents of the central nervous system, draw a cerebral fi ber, such as from neuropathy, causes a lower motor cortical neuron and label it as an upper motor neuron, neuron pattern of injury: there is fl accid muscle tone, and then show a white matter tract descend from it, and hypoactive muscle stretch refl exes, and the absence of label the tract as an upper motor neuron fi ber. pathologic refl exes. Now, let’s draw the peripheral nervous system. From Th e third pattern of injury, spinal cord injury, is the brainstem, draw a cranial nerve and from the spinal mixed. Transect the cervical spinal cord. Th en, indicate cord, draw a spinal nerve. Next, in order to label the that above the level of lesion, the patient is normal. Below lower motor neuron and nerve components of the the level of lesion, there is damage to the upper motor peripheral nervous system, draw a spinal motor neuron neuron fi bers, so show that below the level of lesion, and label it as a lower motor neuron and label the spinal there is an upper motor neuron pattern of injury. Th en, nerve as a lower motor neuron fi ber. Note that a common at the level of lesion, the spinal motor neuron and its point of confusion is when the lower motor neuron lies emanating fi bers are aff ected, so show that at the level of within the central nervous system, as it does here. For lesion, there is a lower motor neuron pattern of injury. this reason, it’s easier to determine whether a neuron is Note that upper motor neuron fi ndings oft en evolve upper motor or lower motor, if we think about the fi ber over hours to weeks. Initially, in a spinal cord injury, for type the neuron projects rather than the location of the instance, the observed pattern of defi cit below the level neuron, itself. Generally, cerebral cortical pyramidal cells of injury may be more characteristic of lower motor are upper motor neuron whereas cranial nerve nuclei neuron injury than upper motor neuron injury— there and spinal motor neurons are lower motor neuron. may be loss of muscle tone and arefl exia; however, over Next, we will use three diff erent locations of nervous hours to weeks, the patient’s tone and refl exes will system injury to learn the exam fi ndings in upper and become pathologically increased and take on a more lower motor neuron lesions. Let’s start by creating a small typical upper motor neuron injury pattern. Th is initial table. Across the top, write the words: injury type, muscle phase is called spinal shock in acute spinal cord injury tone, muscle stretch refl exes, and pathologic refl exes and cerebral shock in acute brain injury.1 – 4 , 6 , 7 , 9 1. General Organization 11

EXAM FINDINGS CENTRAL NERVOUS SYSTEM Injury Muscle Muscle Stretch Pathologic Upper motor Type Tone Reflexes Reflexes neuron (UMN) UMN Spastic Hyperactive Present UMN injury LMN Flaccid Hypoactive Absent Brain UMN fiber

PERIPHERAL NERVOUS SYSTEM Brainstem & Cerebellum Cranial nerve

Lower motor Normal neuron (LMN) LMN fiber LMN injury Spinal nerve UMN injury LMN injury Spinal cord

White matter tract

DRAWING 1-3 Divisions & Signs 12 Neuroanatomy: Draw It to Know It

References 1 . B r u n i, J . E . & M o n t e m u r r o, D . G . Human neuroanatomy: a text, 6 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., Plates brain atlas, and laboratory dissection guide ( Oxford University Press , 4–7 (Novartis , 1997 ). 2009 ). 7 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 2 . C a m p b e l l, W. W., D e J o n g, R . N . & H a e r e r, A . F. DeJong’s the clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). neurologic examination: incorporating the fundamentals of 8 . Troncoso , J. C., Rubio , A. & Fowler , D. R. Essential forensic neuroanatomy and neurophysiology, 6th ed. (Lippincott Williams & neuropathology (Wolters Kluwer Lippincott Williams & Wilkins, Wilkins, 2005 ). 2010 ). 3 . D e M y e r, W. Neuroanatomy, 2nd ed. ( Williams & Wilkins , 1998 ). 9 . Nielsen , J. B. , Crone , C. & Hultborn , H. Th e spinal pathophysiology 4 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and of spasticity — from a basic science point of view . Acta Physiol (Oxf) clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). 189 , 171 – 180 (2007 ). 5 . L e e s t m a, J . E . Forensic neuropathology, 2nd ed. ( CRC Press/Taylor & Francis, 2009 ). 2 Meninges and Ventricular System

Meninges

Cerebrospinal Fluid Flow

Cerebral Ventricles

Cisterns, Sinuses, & Veins (Advanced)

Hemorrhages & Innervation (Advanced) 14 Neuroanatomy: Draw It to Know It

Know-It Points

Meninges

■ From outside to inside, the meningeal layers are the ■ Th e falx cerebelli separates the cerebellar dura mater, arachnoid mater, and pia mater. hemispheres. ■ From outside to inside, the meningeal spaces are the ■ Th e superior sagittal dural venous sinus forms within epidural space, subdural space, and subarachnoid the falx cerebri. space. ■ Th e transverse sinuses form within the tentorium ■ Th e falx cerebri separates the cerebral hemispheres. cerebelli. ■ Th e tentorium cerebelli separates the cerebellum ■ Th e tentorium cerebelli divides the cranial vault into from the overlying occipital lobes. supratentorial and infratentorial compartments.

Cerebrospinal Fluid Flow

■ C e r e b r o s p i n a l fl uid fl ow pattern: foramen of Magendie, in midline, and the foramina – Th e lateral ventricles empty through the paired of Luschka, laterally, into the subarachnoid space. foramina of Monro into the third ventricle. ■ Cerebrospinal fl uid is produced and reabsorbed at a – Th e third ventricle empties into the fourth ventricle. rate of roughly 0.35 milliliters per minute. – Th e fourth ventricle empties down the central ■ Th ere is roughly 150 milliliters of cerebrospinal fl uid canal of the spinal cord and also through the in the nervous system at any given time.

Cerebral Ventricles

■ Each lateral ventricle has a frontal horn, occipital the inferior medullary velum, cerebellar peduncles, horn, and temporal horn. and cerebellum. ■ Th e bend of the lateral ventricle is the body. ■ Choroid plexus lies centrally within the cerebral ■ Th e atrium of the lateral ventricle is the confl uence ventricles: in the body, atrium, and temporal horn of where the body and the occipital and temporal horns the lateral ventricle, third ventricle, and fourth meet. ventricle. ■ Th e borders of the fourth ventricle include the fl oor of the fourth ventricle, the superior medullary velum,

Cisterns, Sinuses, & Veins (Advanced)

■ Collectively, the subarachnoid cisterns at the base of transverse sinuses, inferior sagittal sinus, straight the brain are referred to as the basal cisterns. sinus, and also the sigmoid sinuses, which drain into ■ Th e notable cisterns are the suprasellar, the internal jugular veins. interpeduncular, ambient, quadrigeminal, ■ Th e notable deep cerebral veins are the vein of Galen, prepontine, pontocerebellar, premedullary, lateral the basal veins of Rosenthal, and the internal cerebral cerebellomedullary, and posterior cerebellomedullary veins. cisterns, and the cistern of the velum interpositum. ■ Th e superfi cial cerebral veins drain the superfi cial ■ Th e notable dural venous sinuses are the superior c e r e b r u m . sagittal sinus, confl uence of sinuses, bilateral 2. Meninges and Ventricular System 15

Hemorrhages & Innervation (Advanced)

■ In epidural hematoma, blood collects between the ■ Th e trigeminal nerve innervates the supratentorial periosteal dura and skull. meninges, which includes the meninges of the ■ Epidural hematoma assumes a biconvex lens shape. anterior and middle cranial fossae. ■ In subdural hematoma, blood collects within the ■ Posterior cranial fossa meningeal innervation is dural border cell layer, external to the underlying derived, most notably, from the second and third arachnoid layer. cervical spinal nerves and a minor branch of the ■ Subdural hematoma assumes a crescent shape. v a g u s n e r v e . ■ Epidural hematomas are unaff ected by the dural folds whereas subdural hematomas pool at the site of dural refl ections.

A Arachnoid Superior granulations sagittal sinus 20 1 2 Interventricular foramen Corpus callosum 19 3 Interthalamic adhesion

Fornix 18 4 Third ventricle

Septum Cerebral 17 5 pellucidum aqueduct

Straight 6 sinus Frontal pole 16 Occipital 7 Pituitary gland 15 pole Cerebellum, 8 vermis Midbrain 14 Cerebellum, 9 Pons 13 hemisphere 10 Fourth ventricle Medulla oblongata 12 11 Fourth ventricle, median aperture

B Central sulcus Choroid plexus Lateral ventricle, body 40 21 22 of lateral ventricle Third ventricle 39 23 Lateral sulcus Interventricular foramen 38 Lateral 24 ventricle, Lateral trigone ventricle, 37 Lateral frontal horn ventricle, 25 occipital horn Frontal pole 36 Lateral Choroid ventricle, plexus of 26 temporal lateral 35 horn ventricle, Fourth temporal horn 27 ventricle Cerebral 34 Cerebellum, aqueduct 28 hemisphere Pons 33 Choroid plexus of 29 Fourth ventricle, fourth ventricle 32 lateral aperture 31 30 Medulla Fourth ventricle, oblongata median aperture

FIGURE 2-1 A. Flow pattern of cerebrospinal fl uid. B. Anatomy of the ventricular system. Used with permission from Woolsey, Th omas A., Joseph Hanaway, and Mokhtar H. Gado. Th e Brain Atlas: A Visual Guide to the Human Central Nervous System . 3rd ed. Hoboken, NJ: Wiley, 2008. 16 Neuroanatomy: Draw It to Know It

Meninges

Here, we will draw the meninges, which comprises divides the cranial vault into a supratentorial compart- the dura mater, arachnoid mater, and pia mater. First ment, which contains the cerebral hemispheres (note draw an outline of the skull and upper spinal canal. that we grossly distort the cerebral hemispheric propor- Intracranially, draw the outermost meningeal layer: the tions for diagrammatic purposes, here), and an infraten- dura mater, directly underlying the skull. Th en, within torial compartment, which contains the cerebellum and the spinal canal, show that space exists between the dura brainstem. Intracranial herniation syndromes involve mater and the vertebral column, which creates a true epi- pathologic displacement of central nervous system struc- dural space. Epidural hematoma more commonly occurs tures. Th ree forms of supratentorial herniation exist. in the spinal canal, because of its true epidural space, Indicate that in subfalcine herniation, one hemisphere than in the cranial vault, where the dura mater directly herniates underneath the falx cerebri (this shift is also adheres to the skull. Th e classic example of intracranial called cingulate herniation because it is the cingulate epidural hematoma is that which occurs from trauma to gyrus that fi rst herniates under the falx); next, show that the temporal bone — the fractured bone severs the under- in uncal herniation, the medial temporal lobe (the uncus) lying middle meningeal artery and the high pressure of herniates over the tentorium cerebelli; and then, show this arterial vessel rips the dura away from the skull so that in central herniation (aka transtentorial herniation), that blood collects between the dura and the cranium. the diencephalon herniates directly down through the Clinically, we commonly discuss the dura mater as a tentorium cerebelli. Next, let’s show the two forms of single layer, but within the cranium, it actually comprises infratentorial herniation that exist. Indicate that in two separate anatomic sublayers. Label the layer we just upward cerebellar herniation, the cerebellum herniates drew as the periosteal dural sublayer, which tightly upward into the supratentorial cavity, and then, show adheres to the skull. Next, label the underlying menin- that in tonsillar herniation, the cerebellar tonsils undergo geal sublayer. Th e periosteal layer ends within the cra- downward herniation through the foramen magnum.2 , 3 nium; within the spinal canal, only the meningeal dural Now, label the next innermost meningeal layer as the sublayer exists. Indicate that for much of the cranial dura arachnoid mater and then show that a potential space mater, the periosteal and meningeal sublayers closely exists between the dura and arachnoid mater layers: the adhere; however, show that meningeal dural sublayer subdural space. Show that this space is actually fi lled refl ections also exist. Th ese refl ections form the falx cere- with the loosely arranged dural border cell layer. Th e clas- bri, which separates the cerebral hemispheres; the tento- sic cause of subdural hematoma is from rupture of low- rium cerebelli, which separates the cerebellum from the pressure bridging veins as they run within this space. overlying occipital lobes; and the falx cerebelli (not Next, show that the pia mater directly contacts the shown here), which separates the cerebellar hemispheres. central nervous system parenchyma; it is the delicate, Th en, show that the superior sagittal dural venous sinus innermost layer of the meninges. Th en, label the space forms within the falx cerebri and that the transverse between the pia and arachnoid mater layers as the suba- sinuses form within the tentorium cerebelli. Th ese dural rachnoid space. Unlike the subdural space, this is a true venous sinuses function in cerebrospinal fl uid absorp- (actual) space, which bathes the nervous system. Th e tion and blood-fl ow return; we discuss them in detail subarachnoid space contains cisternal fl uid collections, elsewhere. 1 Next, indicate that the tentorium cerebelli which we draw in Drawing 2-4 . 4 – 8 2. Meninges and Ventricular System 17

Periosteal sublayer (dura) Sup. sag. sinus Falx cerebri Meningeal Subarachnoid sublayer (dura) Subdural space space Arachnoid mater (dural Pia mater border Subfalc. Skull cell layer) SUPRATENTORIAL

Central Uncal Transverse Tentorium cerebelli Transverse sinus sinus INFRATENTORIAL Cerebellar

Tonsillar

Epidural Spinal canal space

DRAWING 2-1 Meninges 18 Neuroanatomy: Draw It to Know It

Cerebrospinal Fluid Flow

Here, we will draw the fl ow of cerebrospinal fl uid canal, which is mostly obliterated by middle adulthood. through the nervous system in coronal view. First, estab- Next, show that cerebrospinal fl uid empties from the lish the relevant meningeal layers: draw the outermost fourth ventricle through the foramen of Magendie, in dural sublayer — the periosteal sublayer, and then the midline, and the foramina of Luschka, laterally, to enter innermost layer— the meningeal sublayer. Show that the subarachnoid space. Th en, show that fl uid descends together they form the dura mater, which contains dural into the spinal canal to bathe the spinal cord, and show venous sinuses within the dural refl ections. Next, move that it also ascends into the cranial vault to bathe the rest inward and draw the arachnoid mater. Between the of the brain. arachnoid mater and the overlying meningeal sublayer, Next, show a representative arachnoid villus extend label the subdural space, which is constituted by the from the subarachnoid space through the subdural dural border cell layer. Now, draw the pia mater as the space into a dural venous sinus. Finally, indicate that layer directly adhering to the nervous system paren- cerebrospinal fl uid passes into the arachnoid villus to be chyma. Between the pia mater and the arachnoid mater, reabsorbed within the dural venous sinus. Neoplastic label the subarachnoid space. arachnoid villi cells form meningiomas, a common brain Next, let’s draw the cerebral ventricles. Show a tumor type; the greatest concentration of meningiomas T-shaped coronal view of the paired lateral ventricles, is found where there is the greatest concentration of third ventricle, and fourth ventricle, and then, show the arachnoid villi: at the cerebral convexity, falx cerebri, central canal of the spinal cord. Also, show some repre- and base of the skull. sentative choroid plexus, the secretory epithelial tissue Note that although we have highlighted the cerebro- that produces cerebrospinal fl uid, in the lateral ventri- spinal fl uid resorption into the dural venous sinuses, cles; we show the ventricular locations of the choroid here, the majority of fl uid within these dural venous plexus in Drawing 2-3 . Th e choroid plexus is formed channels is blood. Th is is because the rate of cerebrospi- where invaginations of vascularized meninges, called tela nal fl uid production and resorption is far slower than the choroidea, merge with ventricular ependyma. Th e tela rate of blood entrance and reabsorption into and out of choroidea are variably defi ned histologically as either the cranial vault. Cerebrospinal fl uid is produced and combinations of pia and ependyma or double pial layers. reabsorbed at a rate of roughly 0.35 milliliters per minute, Th e tight junctions within the choroid plexus cuboidal which equals about 20 milliliters per hour. In a typical epithelium form an important blood–cerebrospinal lumbar puncture, anywhere from 10 to 20 milliliters fl uid barrier.9 – 12 of fl uid are withdrawn; thus, this fl uid is replaced within Now, show that cerebrospinal fl uid empties through a half-hour to one hour aft er the procedure. Th ere is the paired foramina of Monro into the third ventricle, roughly 150 milliliters of cerebrospinal fl uid in the ner- then into the fourth ventricle, and then down the central vous system at any given time.4 – 8 2. Meninges and Ventricular System 19

Periosteal sublayer (dura)

Meningeal sublayer (dura) Arachnoid mater Pia mater Dura Subdural Subarachnoid mater space space Choroid Lateral plexus ventricle

Arachnoid 3rd vent. F. of villus Monro

4th Dural venous L MLM = Magendie sinus L = Luschka

Central canal

DRAWING 2-2 Cerebrospinal Fluid Flow 20 Neuroanatomy: Draw It to Know It

Cerebral Ventricles

Here, we will draw the cerebral ventricles in sagittal view. then the inferior–posterior border as the inferior medul- First, draw the C-shaped appearance of one of the bilat- lary velum (aka posterior medullary velum). Th e cerebel- eral lateral ventricles and include its posterior tail. Next, lar peduncles form the lateral borders of the fourth label the individual horns of the representative lateral ventricle and the cerebellum helps form the rest of the ventricle. Label the supero-anterior-lying horn as the posterior border (the roof ). Medulloblastoma tumors frontal horn, the posterior-lying horn as the occipital oft en lie along the superior medullary velum. horn, and the infero-anterior-lying horn as the temporal Now, let’s include the choroid plexus. Show that it lies horn. Th e head of the caudate constitutes the majority of within the central regions of the cerebral ventricles: in the lateral wall of the frontal horn, the occipital horn the body and atrium of the lateral ventricle, temporal extends deep into the occipital lobe, and the hippocam- horn of the lateral ventricle, third ventricle, and fourth pus constitutes the anterior medial wall of the temporal ventricle. Th e lack of choroid plexus in the frontal and horn (the amygdala sits just in front of it and forms the occipital horns allows neurosurgeons to place intraven- anterior border of the temporal horn). Next, label the tricular drains in these horns without injuring the highly long superior bend of the lateral ventricle as its body and vascularized choroid plexus. label the region where the temporal and occipital horns Th e shape of the lateral ventricles bears resem- and body come together as the atrium (aka trigone). blance to many major cerebral structures— the cerebral Now, show that through the bilateral foramina of Monro, hemispheres, the caudate–putamen, and the fornix– the lateral ventricles empty into the third ventricle, hippocampus. During embryogenesis, all of these which lies in the midline of the nervous system and structures undergo a backward, downward, and forward which is fl anked by the hypothalamus, inferiorly, and the migration, which we will demonstrate with our arms, bilateral thalami, superiorly. Next, show that the third now. First, create a coronal view of the developing brain ventricle empties into the narrow cerebral aqueduct (of as follows. Hold your arms together with your elbows Sylvius), which empties into the diamond-shaped fourth bent and extend your wrists so you could set a plate on ventricle. Th en, show that at the inferior angle of the your palms. Your hyper-extended palms represent the fourth ventricle, at the level of the gracile tubercle (the fl at surface of the brain when it fi rst forms. Next, curl swelling formed by the gracile nucleus in the posterior your fi ngertips to demonstrate that during early develop- wall of the medulla), the fourth ventricle becomes the ment, there is inrolling of the walls of the hemispheres. obex, and descends as the central canal of the spinal Th en, continue to curl your fi ngers in so that they touch cord. 13 your palms to form the bilateral lateral ventricles and the Next, let’s label the midline borders of the fourth ven- small midline third ventricle. Next, initiate the backward, tricle. First, label the anterior border as the fl oor of the downward, and forward evagination of the ventricles. fourth ventricle. Th e fl oor of the fourth ventricle is an Bring your forearms back toward your chest, then fan your important anatomic site because it forms the posterior elbows apart as you bring your hands downward, and then border of the tegmentum of the pons and medulla and extend your arms forward. Th is completes our demonstra- many important anatomic structures lie within or near tion. We can imagine how each of the horns takes shape to it, including certain lower cranial nerve nuclei and during the diff erent steps of lateral ventricular develop- certain neurobehavioral cell groups (eg, the locus coer- ment: the frontal horns take shape during the origination uleus and the area postrema). Next, label the superior– of the ventricular system, the occipital horns are created posterior border of the fourth ventricle as the superior during the backward migration, and the temporal horns medullary velum (aka anterior medullary velum) and form during the downward and forward migration.4 – 8 2. Meninges and Ventricular System 21

Body Lateral Choroid ventricle plexus

Frontal horn

3rd ventricle Atrium Occipital Foramen horn of Monro

Temporal horn

Cerebral aqueduct Superior medullary velum

4th ventricle Floor

Inferior medullary velum = Choroid plexus Obex Central canal

DRAWING 2-3 Cerebral Ventricles 22 Neuroanatomy: Draw It to Know It

Cisterns, Sinuses, & Veins (Advanced)

Here, we will draw the subarachnoid cisterns, dural midline surface of the cerebrum. Th en, indicate that at venous sinuses, and cerebral veins. Begin with the cis- the occiput, lies the confl uence of sinuses (torcular terns. Draw a few key anatomic landmarks; fi rst, the Herophili). Next, show that the confl uence of sinuses brainstem: label the midbrain, pons, and medulla; then, merges with the bilateral transverse sinuses, which the thalamus; next, the splenium of the corpus callosum; wrap horizontally along the tentorium cerebelli. and lastly, the sella turcica. First, above the sella turcica, Note that oft en the right transverse sinus is larger than label the suprasellar cistern. Th e optic chiasm lies within the left . Now, show that the confl uence of sinuses this cistern and, thus, it is also referred to as the chias- also receives the straight sinus, which as we will later matic cistern. Next, in front of the midbrain, in between indicate, drains the deep cerebral veins. Note that an the cerebral peduncles, label the interpeduncular cistern; occipital sinus also exists, which drains inferiorly from then, along the lateral midbrain, label the ambient cis- the confl uence of sinuses; we leave it out of our diagram tern; and fi nally, behind the midbrain, label the quadri- for simplicity. geminal cistern, which is also called the cistern of the Next, draw the inferior sagittal sinus; it runs inferior great vein because it contains the great cerebral vein (aka to the superior sagittal sinus along the same midline vein of Galen). course, just above the corpus callosum, and it empties Next, label the cistern of the velum interpositum in into the straight sinus. Now, indicate that each transverse between the thalamus and the splenium of the corpus sinus empties into a sigmoid sinus, which forms an callosum. Note that this small cistern actually lies S-shaped curve along the intracranial surface of the mas- between the tela choroidea that lines the inferior surface toid portion of the temporal bone. Th en, show that at of the fornix and splenium of the corpus callosum and the jugular bulb, each sigmoid sinus empties into its the superior surface of the third ventricle and thalamus. respective internal jugular vein. Within the velum interpositum lie the internal cerebral Now, let’s introduce a few key deep cerebral veins. veins (drawn later). Now, in front of the pons, label the First, show that the vein of Galen (aka the great cerebral prepontine cistern and lateral to it, label the pontocere- vein) lies posterior to the splenium of the corpus callo- bellar cistern. Next, in front of the medulla, label the sum and drains directly into the straight sinus. Th en, premedullary cistern and, lateral to it, label the lateral indicate that each of the bilateral basal veins of Rosenthal cerebellomedullary cistern. Th en, underneath the cere- passes around the midbrain to drain into the vein of bellum, label the posterior cerebellomedullary cistern Galen, and that each of the bilateral internal cerebral (aka cisterna magna); this is the cerebrospinal extraction veins passes through the cistern of the velum interposi- site during cisternal puncture.14 – 16 tum to drain into the vein of Galen, as well. Collectively, the subarachnoid cisterns at the base of Finally, show a representative superfi cial cerebral the brain are referred to as the basal cisterns. Obliter- vein— the superior cerebral vein, which drains into the ation of the basal cisterns on radiographic imaging superior sagittal sinus. Th e superfi cial cerebral veins suggests brainstem swelling or compression, which is divide into superior, middle, and inferior groups of veins, life-threatening — see Figures 2-3 and 2-4 . which drain the superfi cial cerebrum. 4 – 8 , 17 Next, let’s draw the dural venous sinuses. First show that the superior sagittal sinus runs along the superfi cial 2. Meninges and Ventricular System 23

DURAL SINUSES & VEINS SUBARACHNOID CISTERNS

Superior sagittal sinus Cistern Splenium Thalamus of the velum interpositum Superior Quadri- cerebral vein geminal cistern Inferior sagittal sinus Midbrain Inter- Suprasellar peduncular Ambient cistern cistern cistern Internal cerebral vein Sella turcica Pons Vein of Straight Prepontine Galen Basal vein of Rosenthal sinus cistern Pontocerebellar cistern

Sigmoid sinus Transverse Confluence sinus of sinuses Medulla Internal Premedullary Posterior jugular cistern cerebello- Lateral vein medullary cerebello- cistern medullary cistern

DRAWING 2-4 Cisterns, Sinuses, & Veins 24 Neuroanatomy: Draw It to Know It

Hemorrhages & Innervation (Advanced)

Here, let’s learn a few important clinical correlates to the Next, let’s consider the innervation pattern of the meninges. First, let’s learn how to distinguish epidural meninges. Most meningeal innervation comes from the and subdural hematomas (Fig. 2-2 ). In epidural hema- trigeminal nerve, which innervates the supratentorial toma, blood collects between the periosteal dura and meninges, including the meninges of the anterior and skull. As it collects, it pushes aside the spongy brain middle cranial fossae. Posterior cranial fossa meningeal parenchyma and forms a biconvex lens-shaped fl uid col- innervation is derived, most notably, from the second lection with one side of the convexity displacing brain and third cervical spinal nerves and a minor branch of matter and the other side layering against the cranium. the vagus nerve. Note that the facial and glossopharyn- In subdural hematoma, blood collects within the dural geal nerves potentially play a role in meningeal innerva- border cell layer, external to the underlying arachnoid tion, as well.8 , 11 layer. Th e dural border cell layer is less resistant than the brain tissue, so blood spreads along the border cell layer in a crescent shape. Next, let’s distinguish these two hematoma types based on whether or not they respect the dural folds. Epidural hematomas form external to the periosteal sublayer, and therefore, they are unaff ected by the dural folds (the falx cerebri, tentorium cerebelli, and falx cerebelli), which lie deep to them. On the contrary, subdural hematomas form underneath the meningeal sublayer and pool at the site of the dural refl ections: they do not cross the dural folds. Lastly, consider the eff ect of the cranial sutures (the junctions between the skull bones) on both types of hematoma. Because epidural hematomas lie between the dura and skull, they are stopped at the cranial sutures; in contrast, subdural hematomas lie underneath the dura mater and are unaff ected by the cranial sutures.18 , 19 Figures 2-3 and 2-4 , each contain subarachnoid hemorrhage; the subarachnoid space was described in the FIGURE 2-2 Subdural hematoma on left side of page (right side of brain) previous lesson — CISTERNS, SINUSES, & VEINS. and epidural hematoma on right side of page (left side of brain). 2. Meninges and Ventricular System 25

FIGURE 2-3 Subarachnoid hemorrhage. Hemorrhage fi lls the subarachnoid space but spares the cerebral aqueduct and temporal horns of the lateral ventricles.

FIGURE 2-4 Subarachnoid hemorrhage. Th e “white star” pattern of hemorrhage in the basilar cisterns is outlined. 26 Neuroanatomy: Draw It to Know It

References 1 . Watson , C. , Paxinos , G. , Kayalioglu , G. & Christopher & Dana 1 1. J i n k i n s, R . Atlas of neuroradiologic embryology, anatomy, and Reeve Foundation . Th e spinal cord: a Christopher and Dana Reeve variants ( Lippincott Williams & Wilkins , 2000 ). Foundation text and atlas, 1st ed. ( Elsevier/Academic Press , 2009 ). 1 2. K i e r n a n, J . A . & B a r r, M . L . Barr’s the human nervous system: an 2 . Gilroy , J. Basic neurology, 3rd ed., Chapter 2 (McGraw-Hill , Health anatomical viewpoint, 9th ed. (Wolters Kluwer/Lippincott, Professions Division , 2000 ). Williams & Wilkins , 2009 ). 3 . Schünke , M. , Schulte , E. & Schumacher , U. Th ieme atlas of anatomy. 13 . Sekhar , L. N. a. F. , Richard G. Atlas of neurosurgical techniques: Head and neuroanatomy (Th ieme, 2007 ). Brain (Th ieme, 2006 ). 4 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 1 4. D u v e r n o y, H . M . & C a t t i n, F. Th e human hippocampus: functional atlas, 2nd ed. (Lange Medical Books/ McGraw-Hill , 2005 ). anatomy, vascularization and serial sections with MRI, 3rd ed. 5 . D e M y e r, W. Neuroanatomy, 2nd ed. ( Williams & Wilkins , 1998 ). (Springer , 2005 ). 6 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 15 . Ryan , S. , McNicholas , M. & Eustace , S. J. Anatomy for diagnostic clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). imaging, 2nd ed. ( Saunders , 2004 ). 7 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., 1 6. Th a p a r, K . Diagnosis and management of pituitary tumors (H u m a n a Plates 4–7 (Novartis , 1997 ). Press, 2001 ). 8 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 1 7. S w a r t z, J . D . & L o e v n e r, L . A . Imaging of the temporal bone, 4th ed., clinical practice, 40th ed. ( Churchill Livingstone / Elsevier , 2008 ). Chapter 4 ( Th ieme, 2009 ). 9 . B r u n i, J . E . & M o n t e m u r r o, D . G . Human neuroanatomy: a text, 1 8. E v a n s, R . W. Neurology and trauma, 2nd ed., Chapter 3 (Oxford brain atlas, and laboratory dissection guide ( Oxford University Press , University Press, 2006 ). 2009 ). 19 . Zasler , N. D., Katz , D. I. & Zafonte , R. D. Brain injury medicine: 1 0. C o t t r e l l, J . E . & Yo u n g, W. L . Cottrell and Young’s neuroanesthesia, principles and practice (Demos , 2007 ). 5th ed. (Mosby / Elsevier , 2010 ). 3 Peripheral Nervous System Upper Extremity

Brachial Plexus

Median Nerve

Ulnar Nerve

Radial Nerve

Cervical Plexus (Advanced) 28 Neuroanatomy: Draw It to Know It

Know-It Points

Brachial Plexus

■ R a m i . Th e brachial plexus is most commonly formed forms the medial cord; the anterior division (upper from the C5–T1 ventral rami. trunk) and the anterior division (middle trunk) form ■ Trunks. C7 makes up the middle trunk; C5 and C6 the lateral cord. form the upper trunk; and C8 and T1 form the lower ■ Major terminal nerves. Th e lateral and medial cords trunk. form the median nerve; the medial cord becomes the ■ Divisions & Cords. Th e posterior divisions form the ulnar nerve; the posterior cord becomes the radial posterior cord; the anterior division (lower trunk) n e r v e .

Median Nerve

■ Th e median nerve is formed from the lateral cord ■ Th e thenar group (C8, T1) comprises abductor (C6, C7) and the medial cord (C8, T1). pollicis brevis, opponens pollicis, and fl exor pollicis ■ Th e superfi cial forearm group comprises pronator brevis. teres and fl exor carpi radialis (C6, C7) and fl exor ■ Th e terminal motor group (C8, T1) comprises the digitorum superfi cialis and palmaris longus (C7, C8). fi rst and second lumbricals. ■ Th e anterior interosseous group (C7–T1) comprises pronator quadratus, fl exor pollicis longus, and fl exor digitorum profundus 2 and 3.

Ulnar Nerve

■ Th e ulnar nerve is formed from the medial cord ■ Th e deep branch is purely motor and innervates (C8, T1). muscle groups across the hand: ■ Th e forearm muscle group comprises fl exor – Th e hypothenar group: abductor digiti minimi, carpi ulnaris and fl exor digitorum profundus opponens digiti minimi, and fl exor digiti minimi 4 and 5. – Th e intrinsic hand group: lumbricals 3 and 4, ■ Th e superfi cial sensory division is purely sensory palmar interossei, and dorsal interossei except that it provides motor innervation to palmaris – Th e thenar group: fl exor pollicis brevis and brevis. adductor pollicis

Radial Nerve

■ Th e radial nerve is formed from the posterior cord ■ Th e posterior interosseous nerve branch supplies the (C5–C8). supinator muscle (C6, C7), extensor carpi ulnaris ■ Th e radial nerve innervates the triceps muscle (C7, C8) abductor pollicis longus (C7, C8), and the (primarily, C6, C7). fi nger and thumb extensors (C7, C8). ■ Th e elbow group comprises brachioradialis (C5, C6), extensor carpi radialis longus and brevis (C6, C7), and anconeus (C6–C8). 3. Peripheral Nervous System—Upper Extremity 29

Cervical Plexus (Advanced)

■ Th e cervical plexus (C1–C4) innervates the anterior ■ Th e phrenic nerve innervates the diaphragm; it is and posterior cervical triangles and the fl oor of the supplied by C3 and C4 from the cervical plexus and mouth. C5 from the brachial plexus. ■ Th e four major sensory nerves of the cervical plexus ■ Th e cervical spinal ventral rami form the cervical are the lesser occipital, greater auricular, and plexus; the dorsal ramus of C2 supplies the greater transverse cervical nerves (C2, C3), and the occipital nerve. supraclavicular nerve (C3, C4).

FIGURE 3-1 Th e brachial plexus. Used with permission from Mendell, FIGURE 3-2 Cervical plexus. Used with permission from Mendell, Jerry Jerry R., John T. Kissel, and David R. Cornblath. Diagnosis and R., John T. Kissel, and David R. Cornblath. Diagnosis and Management of Management of Peripheral Nerve Disorders , Contemporary Neurology Peripheral Nerve Disorders , Contemporary Neurology Series. Oxford: Series. Oxford: Oxford University Press, 2001. Oxford University Press, 2001.

FIGURE 3-3 Th e brachial plexus and the axillary artery. 30 Neuroanatomy: Draw It to Know It

Brachial Plexus

Here, we will draw the brachial plexus. First, draw three Next, just distal to the lateral cord, label the musculo- horizontal lines. Label them from top to bottom as the cutaneous nerve, which most notably innervates the upper, middle, and lower trunks. Next, indicate that C7 biceps brachii (C5, C6). Biceps brachii is an important makes up the middle trunk, and then that C5 and C6 elbow fl exor and also an important supinator. Th e role of form the upper trunk (C5 and C6 join at Erb’s point the biceps brachii in supination explains why supination and a shoulder injury here is called an Erb’s palsy). is at least partially preserved in radial nerve injury (when Th en, show that C8 and T1 form the lower trunk. Th e the radial-innervated supinator muscle, itself, becomes brachial plexus is typically formed from the C5–T1 ven- weakened). We’ll include the lesser muscles innervated tral rami. by the musculocutaneous nerve later. Th e trunks divide into anterior and posterior divisions Now, show that C5, C6, and C7 derive the long tho- as follows. Show that the posterior divisions all join to racic nerve, which innervates the serratus anterior form the posterior cord. At the bottom, label the anterior muscle: it pulls the scapula forward (protracts it). Th en, division (lower trunk) and then the medial cord. Next, show that the dorsal scapular nerve originates from C5 label the anterior division (upper trunk) and show that and C4 (not shown) and that it innervates the rhomboid the anterior division (middle trunk) joins it to form the muscles, which pull the scapula in the opposite direction lateral cord. Th e cords are named by their relationship to of the serratus anterior muscle: toward midline and the second portion of the axillary artery: the lateral cord downward. Injury to either serratus anterior, the rhom- lies lateral to the axillary artery, the medial cord lies boids, or the trapezius, which cranial nerve 11 inner- medial to it, and the posterior cord lies posterior to it. vates, results in scapular winging. Note that the nerves to Now, connect the distal lateral and medial cords and the serratus anterior and rhomboids are derived directly label their union as the median nerve. Th en, show that from the nerve roots, themselves— not from the brachial the medial cord becomes the ulnar nerve and that the plexus, which means that in a pure brachial plexopathy, posterior cord becomes the radial nerve. the serratus anterior and rhomboids are spared.

FIGURE 3-4 Biceps brachii. FIGURE 3-5 Serratus anterior.

FIGURE 3-6 Rhomboids. 3. Peripheral Nervous System—Upper Extremity 31

Dorsal scapular nerve (rhomboid m.) C5 Upper trunk Anterior division Lateral cord Musculocutaneous nerve upper trunk (biceps brach.,

Long thoracic nerve (serratus anteiror m.)

C6 Anterior division Posterior division middle trunk upper trunk

Middle trunk C7 Posterior division Posterior cord Radial nerve middle trunk

Median nerve

Posterior division C8 lower trunk Lower trunk Anterior division Medial cord Ulnar nerve lower trunk

DRAWING 3-1 Brachial Plexus — Partial 32 Neuroanatomy: Draw It to Know It

Brachial Plexus (Cont.)

Next, show that the suprascapular nerve originates from cord, draw the medial pectoral nerve; they innervate the the upper trunk and indicate that it innervates the pectoralis major muscle, which as a whole, provides supraspinatus muscle (C5, C6), which is responsible for shoulder adduction and shoulder internal rotation. Th e the fi rst 20 to 30 degrees of arm abduction, and also lateral pectoral nerve innervates the clavicular head of show that the suprascapular nerve innervates the infraspi- pectoralis major (C5 (most notably) and C6), which natus muscle (C5, C6), which is the primary external additionally provides shoulder fl exion and the medial rotator of the arm (the other is teres minor). pectoral nerve innervates the sternal head of the pecto- Draw the axillary nerve off the posterior cord and ralis major muscle (C6, C7 (most notably), C8, and T1), show that it innervates the deltoid muscle. Whereas which additionally provides shoulder extension. For supraspinatus is responsible for the fi rst 20 to 30 degrees completeness, show that the pectoral nerves (mostly the of arm abduction, the deltoid muscle (C5, C6) is respon- medial pectoral nerve) also innervate pectoralis minor, sible for the latter 70 to 80 degrees of arm abduction. We which provides scapula depression. will complete the musculature innervated by the axillary Now, draw the medial brachial cutaneous and medial nerve at the end. antebrachial cutaneous nerves; they are sensory nerves Next, more proximally off the posterior cord, draw that cover the medial aspect of the upper arm and fore- the thoracodorsal nerve; it innervates latissimus dorsi arm, respectively. In ulnar nerve injuries, medial arm (C6, C7, C8), which provides shoulder adduction, most and forearm sensation is spared due to sparing of these notably. cutaneous nerves; in contrast, in medial cordopathies, Now, we will draw the pectoral nerves. Off the lateral these nerves are oft en injured and medial upper arm and cord, draw the lateral pectoral nerve, and off the medial forearm sensation is impaired.

FIGURE 3-7 Infraspinatus. FIGURE 3-8 Deltoid.

FIGURE 3-9 Latissimus dorsi. FIGURE 3-10 Pectoralis major. 3. Peripheral Nervous System—Upper Extremity 33

Dorsal scapular nerve Suprascapular nerve Lateral pectoral nerve (rhomboid m.) (supraspinatus and infraspinatus m.) (clavicular pec. major C5 & pec. minor m.) Upper trunk Anterior division Lateral cord Musculocutaneous nerve upper trunk (biceps brach.,

Long thoracic nerve (serratus anteiror m.)

C6 Anterior division Posterior division middle trunk Axillary nerve upper trunk (deltoid

Middle trunk C7 Posterior division Posterior cord Radial nerve middle trunk

Thoracodorsal n. Median nerve (lat. dorsi m.) Posterior division C8 lower trunk Lower trunk Anterior division Medial cord Ulnar nerve lower trunk Medial pectoral n. (sternal T1 pec. major & pec. minor m.) Medial brachial cutaneous nerve Medial antebrachial cutaneous nerve

DRAWING 3-2 Brachial Plexus — Partial 34 Neuroanatomy: Draw It to Know It

Brachial Plexus (Cont.)

Now, let’s include some of the less oft en clinically tested teres major, which assists in shoulder internal rotation, brachial plexus structures. First, where the fi ft h and sixth as well. cervical roots join together, indicate the nerve to the sub- Next, return to the axillary nerve and show that the clavius muscle. Th e subclavius provides clavicle depression. more "minor" muscle it innervates is teres minor, which Next, show that in addition to the biceps brachii, the assists in shoulder external rotation. Th e action of teres musculocutaneous nerve also innervates the brachialis minor is best remembered by its relationship to the muscle, which lies deep within the anterior upper arm, action of the axillary-innervated deltoid muscle, which and fl exes the elbow with the forearm in any position; provides shoulder abduction. also show that the musculocutaneous nerve innervates Lastly, show that if the brachial plexus is shift ed up the coracobrachialis muscle, which assists the clavicular one level and receives substantial innervation from C4, head of the pectoralis major muscle in shoulder fl exion. it is called a prefi xed plexus, and if it is shift ed down one Proximal and distal to the thoracodorsal nerve, respec- level and receives substantial innervation from T2, it is tively, draw the upper subscapular and lower subscapular called a postfi xed plexus. nerves. Show that they both innervate the subscapularis Note that we have only listed the major actions of muscle, which assists in shoulder internal rotation. Th en, each muscle— refer to a kinesiology textbook for a list- show that the lower subscapular nerve also innervates ing of additional muscle actions.1 – 6

FIGURE 3-11 Coracobrachialis. FIGURE 3-12 Subscapularis.

FIGURE 3-13 Te r e s m a j o r . FIGURE 3-14 Teres minor. 3. Peripheral Nervous System—Upper Extremity 35

C4 (prefixed) Dorsal scapular nerve Suprascapular nerve Lateral pectoral nerve (rhomboid m.) (supraspinatus and infraspinatus m.) (clavicular pec. major C5 N. to subclavius m. & pec. minor m.) Upper trunk Anterior division Lateral cord Musculocutaneous nerve upper trunk (biceps brach., brachialis,

Long thoracic nerve (serratus anteiror m.) coracobrachialis m.) C6 Anterior division Posterior division middle trunk Axillary nerve upper trunk (deltoid & teres minor m.)

Middle trunk C7 Posterior division Posterior cord Radial nerve middle trunk Upper subscapular n. (subscap. m.) Thoracodorsal n. Median nerve (lat. dorsi m.) Lower subscap. n. Posterior division (subscap. & teres C8 lower trunk major m.) Lower trunk Anterior division Medial cord Ulnar nerve lower trunk Medial pectoral n. (sternal T1 pec. major & pec. minor m.) T2 (postfixed) Medial brachial cutaneous nerve Medial antebrachial cutaneous nerve

DRAWING 3-3 Brachial Plexus — Complete 36 Neuroanatomy: Draw It to Know It

Median Nerve

Here, we will draw the median nerve. To localize each we will keep track of the muscle groups, their nerve roots, form of median nerve injury, learn at least one muscle from and the muscles they comprise. Show that the superfi cial each muscle group. First, divide the page into the ventral forearm group is derived from roots C6 and C7 and also rami and brachial plexus, upper arm, forearm, and hand. from roots C7 and C8. Th e C6, C7 innervated muscles Next, draw a line across the page to represent the course of are pronator teres and fl exor carpi radialis. Pronator teres the median nerve down the upper extremity. At the left - provides forearm pronation when the elbow is extended hand side of the page, underneath the brachial plexus seg- and fl exor carpi radialis provides wrist fl exion with lat- ment, show that the lateral and medial cords form the eral deviation (towards the radius bone). median nerve. Indicate that the lateral cord rami that Next, show that the C7, C8 innervated muscles are supply the median nerve are C6 and C7, which are mostly fl exor digitorum superfi cialis and palmaris longus. Flexor sensory, and that the medial cord rami that supply the digitorum superfi cialis fl exes digits 2 through 5 at their median nerve are C8 and T1, which are mostly motor. proximal interphalangeal joints. It receives additional Next, show that the median nerve does not innervate supply from T1. Palmaris longus corrugates the skin over any of the muscles of the upper arm or provide any of its the wrist; you can see the palmaris longus tendon pop sensory coverage. out in midline when you fl ex your wrist. Now, in the proximal forearm, draw the branch to the superfi cial forearm group. At the bottom of the page,

FIGURE 3-15 Pronator teres. FIGURE 3-16 Flexor carpi radialis.

FIGURE 3-17 Flexor digitorum superfi cialis. FIGURE 3-18 Palmaris longus. 3. Peripheral Nervous System—Upper Extremity 37

Ventral rami & Upper arm Forearm Hand brachial plexus

C6 and C7 (mostly sensory) Superficial Upper & middle trunks forearm Lateral cord group

Medial cord Middle & lower trunks C8 - T1 (mostly motor)

Superficial forearm group (C6, C7) Pronator teres Flexor carpi radialis

(C7, C8) Flexor digitorum sublimis Palmaris longus

DRAWING 3-4 Median Nerve— Partial 38 Neuroanatomy: Draw It to Know It

Median Nerve (Cont.)

Th ere are two important proximal entrapment sites for Indicate that the anterior interosseous group is derived the median nerve, which we will indicate now. First, from roots C7–T1, which comprises pronator quadra- show that proximal to the superfi cial forearm group, lies tus, fl exor pollicis longus, and fl exor digitorum profun- the ligament of Struthers. All of the components of the dus 2 and 3. Pronator quadratus pronates the forearm median nerve lie downstream of this ligament; therefore, with the elbow in fl exion. Flexor pollicis longus fl exes when the median nerve is entrapped in the ligament of the interphalangeal joint of the thumb; it is the “long” Struthers, all of the median nerve components are fl exor of the thumb in that it passes the metacarpal– aff ected. Next, indicate the heads of the pronator teres phalangeal joint to fl ex the interphalangeal joint. Flexor muscles. When the median nerve becomes entrapped in digitorum profundus 2 and 3 fl exes the distal interpha- these muscle heads, everything downstream of them is langeal joints of the second and third digits. aff ected. Note, however, that the components of the Now, draw the carpal tunnel at the wrist; this is the superfi cial forearm group, including the pronator teres most common entrapment site of the median nerve. muscle, itself, are unaff ected when the nerve is entrapped Show that the median sensory branch to the proximal in the heads of the pronator teres muscles, because inner- palm, the palmar cutaneous nerve, takes off proximal vation to the superfi cial forearm group lies proximal to to the carpal tunnel, and therefore it and everything the entrapment site. else we have drawn so far is unaff ected in carpal tunnel Now, draw the anterior interosseous nerve branch. syndrome. Show that it innervates the anterior interosseous group.

FIGURE 3-19 Pronator quadratus. FIGURE 3-20 Flexor pollicis longus.

FIGURE 3-21 Flexor digitorum profundus 2 and 3. 3. Peripheral Nervous System—Upper Extremity 39

Ventral rami & Upper arm Forearm Hand brachial plexus

Anterior Median palmar C6 and C7 (mostly sensory) Superficial interosseous group cutaneous nerve Upper & middle trunks forearm Lateral cord group Anterior interosseous nerve

Ligament of Pronator teres Carpal tunnel Struthers heads Medial cord Middle & lower trunks C8 - T1 (mostly motor)

Superficial forearm group Anterior interosseous group (C6, C7) (C7 - T1) Pronator teres Pronator quadratus Flexor carpi radialis Flexor pollicis longus Flexor digitorum (C7, C8) profundus (2,3) Flexor digitorum sublimis Palmaris longus

DRAWING 3-5 Median Nerve— Partial 40 Neuroanatomy: Draw It to Know It

Median Nerve (Cont.)

Next, show that the recurrent motor branch of the supplies the opponens pollicis muscle, which directs the thumb innervates the thenar group, supplied by C8 and thumb to the little fi nger, and the ulnar nerve supplies T1. Show that this group comprises abductor pollicis the opponens digiti minimi muscle, which directs the brevis, opponens pollicis, and fl exor pollicis brevis. little fi nger to the thumb. Flexor pollicis brevis attaches Abductor pollicis brevis provides thumb abduction per- to the proximal phalanx of the thumb and fl exes the pendicular to the plane of the palm (in other words, thumb against the palm. Its tendon length is shorter when the palm is up, it raises the thumb toward the ceil- (more "brief ") than that of fl exor pollicis longus, which ing). Abductor pollicis brevis provides the Up component acts at the more distal-lying interphalangeal joint. Both of the Up, In, Out triad, which is as follows. Th e median- the median and ulnar nerves supply fl exor pollicis brevis. innervated abductor pollicis brevis moves the thumb per- Now, show the most distal median nerve motor pendicular to the plane of the palm: with the palm up, it group: the terminal motor group. Indicate that it is raises the thumb up toward the ceiling. Th e ulnar-inner- derived from C8–T1 and that it comprises the fi rst and vated adductor pollicis and the radial-innervated abductor second lumbricals, which have dual actions on the second pollicis longus move the thumb in the plane of the palm: and third digits; they extend their proximal interphalan- adductor pollicis draws the thumb in toward the side of geal joints and fl ex their metacarpal–phalangeal joints. the palm and abductor pollicis longus moves the thumb Finally, show that the median nerve provides distal out away from the side of the palm. sensory innervation via digital sensory branches, which Both the median and ulnar nerves produce the action we map along with the rest of the median nerve’s sensory of thumb to little fi nger opposition; the median nerve coverage of the hand in Drawing 5-1. 1 – 4 , 7 – 11

FIGURE 3-22 Abductor pollicis brevis. FIGURE 3-23 Opponens pollicis.

FIGURE 3-24 Flexor pollicis brevis. FIGURE 3-25 L u m b r i c a l s . 3. Peripheral Nervous System—Upper Extremity 41

Ventral rami & Upper arm Forearm Hand brachial plexus

Anterior Median palmar C6 and C7 (mostly sensory) Superficial interosseous group cutaneous nerve Upper & middle trunks forearm Thenar group Lateral cord group Anterior Recurrent motor interosseous nerve branch of the thumb

Digital branches (cutaneous)

Ligament of Pronator teres Carpal tunnel Terminal group Struthers heads Medial cord Middle & lower trunks C8 - T1 (mostly motor)

Superficial forearm group Anterior interosseous group Thenar group Terminal group (C6, C7) (C7 - T1) (C8, T1) (C8, T1) Pronator teres Pronator quadratus Abductor pollicis brevis Lumbricals (1,2) Flexor carpi radialis Flexor pollicis longus Opponens pollicis Flexor digitorum Flexor pollicis brevis (C7, C8) profundus (2,3) Flexor digitorum sublimis Palmaris longus

DRAWING 3-6 Median Nerve— Complete 42 Neuroanatomy: Draw It to Know It

Ulnar Nerve

Here, we will draw the ulnar nerve. To localize each form Next, at the elbow, draw the cubital tunnel— the most of ulnar nerve injury, learn at least one muscle from each common ulnar nerve entrapment site. All of the motor muscle group. First, divide the page into the ventral rami and sensory components of the ulnar nerve lie distal to and brachial plexus, upper arm, forearm, and hand. Draw the cubital tunnel; therefore, in a cubital tunnel syn- a line across the page to represent the course of the ulnar drome, all of the components of the ulnar nerve are nerve. Indicate that the ulnar nerve is formed from the aff ected. medial cord of the brachial plexus, which the C8–T1 Now, at the wrist, show that the ulnar nerve passes nerve roots of the lower trunk supply. Th e C8–T1 nerve through Guyon’s canal (aka Guyon’s tunnel). Th is is the roots supply all of the ulnar nerve-innervated muscles. other major ulnar nerve entrapment site. Variations of First, show that the medial cutaneous nerves to the Guyon’s canal entrapments exist aff ecting a variety of arm and forearm (aka medial brachial and medial ante- diff erent distal ulnar components. brachial cutaneous nerves) are direct branches from the Next, show that proximal to Guyon’s canal, the ulnar medial cord (and are not part of the ulnar nerve); they nerve derives the palmar and dorsal ulnar cutaneous provide sensory coverage to the medial arm and forearm. nerves; these branches are unaff ected in Guyon’s canal Th e ulnar nerve sensory coverage, itself, is confi ned to entrapments because they lie upstream from it. We map the medial hand. their sensory coverage, along with the sensory coverage Now, show that the most proximal muscle group the of the rest of the hand, in Drawing 5-1. ulnar nerve innervates is the forearm muscle group, As the ulnar nerve enters the hand, it splits into the which comprises fl exor carpi ulnaris and fl exor digitorum superfi cial sensory division, which is purely sensory profundus 4 and 5. Flexor carpi ulnaris fl exes the wrist except that it provides motor innervation to palmaris with medial deviation (in the direction of the ulna bone). brevis, which corrugates the hypothenar eminence, and Flexor digitorum profundus 4 and 5 fl exes the distal the deep branch, which is purely motor and innervates interphalangeal joints of the fourth and fi ft h digits. muscle groups across the hand.

FIGURE 3-26 Flexor carpi ulnaris. FIGURE 3-27 Flexor digitorum profundus 4 and 5.

FIGURE 3-28 Palmaris brevis. 3. Peripheral Nervous System—Upper Extremity 43

Ventral rami & Upper arm Forearm Hand brachial plexus

Medial Medial cutaneous cutaneous Dorsal ulnar nerve of nerve of cutaneous nerve the arm the forearm Deep branch Forearm muscle group Medial cord Guyon’s Superficial branch (sensory Lower trunk canal except palmaris brevis) (C8 -T1) Cubital tunnel Palmaris Palmar ulnar brevis muscle cutaneous nerve

Forearm muscle group Palmaris brevis Flexor carpi ulnaris Flexor digitorum profundus (4,5)

DRAWING 3-7 Ulnar Nerve— Partial 44 Neuroanatomy: Draw It to Know It

Ulnar Nerve (Cont.)

First, indicate that the deep branch innervates the closure) whereas the dorsal interossei spread them apart. hypothenar group, which comprises abductor digiti We focus on the fi rst dorsal interosseous muscle because minimi, opponens digiti minimi, and fl exor digiti it is commonly clinically tested; it provides fi nger abduc- minimi. Abductor digiti minimi abducts the fi ft h digit tion of the second digit. in the plane of the palm. In regards to opponens digiti Lastly, show that the deep branch innervates the minimi, both the median and ulnar nerves produce the thenar group, which comprises fl exor pollicis brevis and action of thumb to little fi nger opposition: the median adductor pollicis. Flexor pollicis brevis fl exes the thumb nerve supplies the opponens pollicis muscle, which against the palm; the median nerve also innervates it. directs the thumb to the little fi nger, and the ulnar nerve Adductor pollicis adducts the thumb against the side of innervates the opponens digiti minimi muscle, which the palm. It is the In component of the Up, In, Out triad, directs the little fi nger to the thumb. Flexor digiti minimi which is as follows. Th e median-innervated abductor fl exes the fi ft h digit toward the palm. pollicis brevis moves the thumb perpendicular to the Now, show that the deep branch innervates the intrin- plane of the palm: with the palm up, it raises the thumb sic hand group, which comprises lumbricals 3 and 4, the up toward the ceiling. Th e ulnar-innervated adductor palmar interossei, and dorsal interossei muscles. Th e pollicis and the radial-innervated abductor pollicis third and fourth lumbricals have dual actions on digits 4 longus move the thumb in the plane of the palm: adduc- and 5: they extend their proximal interphalangeal joints tor pollicis draws the thumb in toward the side of the and fl ex their metacarpal–phalangeal joints. Th e palmar palm and abductor pollicis longus moves the thumb out interossei bring the fi ngers together (they provide fi nger away from the side of the palm.1 – 4 , 9 , 11 , 12

FIGURE 3-29 Abductor digiti minimi. FIGURE 3-30 Palmar interossei.

FIGURE 3-31 First dorsal interosseous. FIGURE 3-32 Adductor pollicis. 3. Peripheral Nervous System—Upper Extremity 45

Ventral rami & Upper arm Forearm Hand brachial plexus

Thenar group

Medial Medial cutaneous cutaneous Dorsal ulnar Intrinsic hand group nerve of nerve of cutaneous nerve the arm the forearm

Deep branch Hypothenar group Forearm muscle group Medial cord Guyon’s Superficial branch (sensory Lower trunk canal except palmaris brevis) (C8 -T1) Cubital tunnel Palmaris Palmar ulnar brevis muscle cutaneous nerve

Forearm muscle group Palmaris brevis Hypothenar group Intrinsic hand group Thenar group Flexor carpi ulnaris Abductor digiti minimi Lumbricals (3,4) Flexor pollicis brevis Flexor digitorum Opponens digiti minimi Palmar interossei Adductor pollicis profundus (4,5) Flexor digiti minimi Dorsal interossei

DRAWING 3-8 Ulnar Nerve— Complete 46 Neuroanatomy: Draw It to Know It

Radial Nerve

Here, we will draw the radial nerve. To localize each the triceps. When the radial nerve is compressed within form of radial nerve injury, learn at least one muscle from the axilla, such as from using crutches, the triceps is each muscle group. To draw the radial nerve, divide the aff ected because it lies downstream from the axilla. Next, page into the ventral rami and brachial plexus, upper show that the spiral groove lies distal to the triceps. arm, forearm, and hand. First, show the proximal seg- Along the spiral groove, the radial nerve opposes the ment of the radial nerve. Next, indicate that the radial humerus and is susceptible to compression; injury here is nerve is derived from the C5–C8 nerve roots via the called “Saturday night palsy.” Th e triceps is unaff ected in posterior cord. Indicate that the axillary nerve originates Saturday night palsy because the take-off for the triceps from the posterior cord just proximal to the derivation is proximal to the spiral groove. of the radial nerve; the axillary nerve innervates the del- Where the upper arm and forearm meet, label the toid and teres minor muscles. Because the axillary nerve elbow and show the elbow group, which the C5–C8 lies upstream from the radial nerve, it is unaff ected in nerve roots supply. It comprises brachioradialis, which radial nerve palsy; we show it here because its anatomic C5 and C6 supply, extensor carpi radialis longus and proximity to the radial nerve makes it useful to test for brevis, which C6 and C7 supply, and anconeus, which clinical localization. C6–C8 supply. In regards to brachialis, the musculocu- Unlike the median and ulnar nerves, the radial nerve taneous nerve innervates the C5 and C6 portion and the does provide important motor and sensory branches to radial nerve innervates the small C7 portion. the upper arm. First, show that the radial nerve inner- Brachioradialis fl exes the elbow with the forearm in mid- vates the triceps muscle, which is supplied primarily by pronation/supination position whereas brachialis fl exes C6 and C7 but also by C8; it provides elbow extension. the elbow with the arm in any position. Th e extensor Now, show two key anatomic sites so we can under- carpi radialis longus and brevis muscles extend the wrist stand how to use the triceps as a localizing tool in radial with lateral deviation (toward the radius bone). Anconeus nerve palsy. First, show that the axilla lies proximal to assists in elbow extension.

FIGURE 3-33 Triceps. FIGURE 3-34 Brachioradialis.

FIGURE 3-35 Extensor carpi radialis. 3. Peripheral Nervous System—Upper Extremity 47

Ventral rami & Upper arm Forearm Hand brachial plexus

Deltoid & teres minor m. Elbow group Axillary nerve Triceps

Posterior cord Upper, middle, Axilla Spiral groove Elbow & lower trunks C5 - C8

Triceps Elbow group (C6-C8) (C5-C8) Brachioradialis (C5, C6) Brachialis (partial) (C5-C7) Extensor carpi radialis (longus & brevis) (C6, C7) Anconeus (C6 - C8)

DRAWING 3-9 Radial Nerve— Partial 48 Neuroanatomy: Draw It to Know It

Radial Nerve (Cont.)

Next, show that the radial nerve branches into the poste- Finally, indicate the posterior interosseous nerve rior interosseous nerve. In the proximal segment of the innervation of fi nger and thumb extensors, supplied by posterior interosseous nerve, indicate the supinator C7, C8; they are extensor indicis proprius, extensor digi- muscle. Th e C6, C7 nerve roots supply the supinator; it torum communis, and extensor digiti minimi (for the provides outward rotation (supination) of the forearm. fi ngers), and extensor pollicis longus and extensor polli- Note that the biceps brachii is also a major supinator of cis brevis (for the thumb). Extensor indicis proprius the elbow, and therefore, forearm supination is oft en extends the second digit; extensor digitorum communis preserved in radial neuropathy because of the unaff ected extends the third and fourth digits; and extensor digiti musculocutaneous-innervated biceps brachii. minimi extends the fi ft h digit. Th e extensor pollicis mus- Now, show that the posterior interosseous nerve inner- cles extend the thumb (with the palm down, they raise it vates extensor carpi ulnaris and abductor pollicis longus, up). Extensor pollicis brevis extends the thumb at the which are both supplied by C7, C8. Extensor carpi ulnaris metacarpal–phalangeal joint whereas extensor pollicis extends the wrist with medial deviation (towards the ulna longus extends the thumb at the interphalangeal joint. bone) and abductor pollicis longus abducts the thumb in Th is completes the motor innervation of the radial the plane of the palm. It is the Out component of the Up, nerve; now, let’s address the sensory innervation. First, In, Out triad, which is as follows. Th e median-innervated just distal to the axilla, show the take-off for the proximal abductor pollicis brevis moves the thumb perpendicular radial nerve branches. Th e proximal radial sensory nerves to the plane of the palm: with the palm up, it raises the are the posterior cutaneous nerves to the arm and fore- thumb up toward the ceiling. Th e ulnar-innervated arm and the lower lateral cutaneous nerve of the arm. adductor pollicis and the radial-innervated abductor pol- Th ese nerves cover the lower upper arm and the midline licis longus move the thumb in the plane of the palm: posterior arm and forearm, shown in Drawing 5-4. Next, adductor pollicis draws the thumb in toward the side of at the take-off of the posterior interosseous nerve, draw the palm and abductor pollicis longus moves the thumb the superfi cial sensory radial nerve; it provides distal out away from the side of the palm. radial sensory coverage, shown in Drawing 5-1. 1 – 4 , 9

FIGURE 3-36 S u p i n a t o r . FIGURE 3-37 Abductor pollicis longus.

FIGURE 3-38 Extensor digitorum communis. 3. Peripheral Nervous System—Upper Extremity 49

Ventral rami & Upper arm Forearm Hand brachial plexus Supinator Posterior cutaneous nerves to arm and forearm & lower lateral Extensor carpi ulnaris & Deltoid & cutaneous nerve of arm abductor pollicis longus teres minor m. Elbow group Finger & thumb extensors Axillary nerve Posterior interosseous nerve Triceps

Posterior cord Superficial radial Upper, middle, Axilla Spiral groove Elbow nerve (cutaneous) & lower trunks C5 - C8

Triceps Elbow group Supinator Extensor carpi ulnaris Finger & thumb extensors (C6-C8) (C5-C8) (C6, C7) Abductor pollicis longus (C7, C8) Brachioradialis (C5, C6) (C7, C8) Extensor indicis proprius Brachialis (partial) (C5-C7) Extensor digitorum communis Extensor carpi radialis Extensor digiti minimi (longus & brevis) (C6, C7) Extensor pollicis longus Anconeus (C6 - C8) Extensor pollicis brevis

DRAWING 3-10 Radial Nerve— Complete 50 Neuroanatomy: Draw It to Know It

Cervical Plexus (Advanced)

Here, we will draw the cervical plexus; it is constituted muscle also exist, which we leave out of our diagram for by ventral rami from C1–C4, which emerge from under- simplicity. neath the sternocleidomastoid muscle and innervate Next, let’s draw the motor nerves of the cervical structures of the anterior and posterior cervical triangles plexus. For this, we begin with the phrenic nerve. Show and the fl oor of the mouth. Begin our diagram with a that it originates from C3 and C4 from the cervical few key anatomic structures: fi rst, draw the clavicle; plexus and C5 from the brachial plexus. It descends then, the trapezius muscle; and then, the inferior attach- through the thoracic cavity to innervate the diaphragm. ment of the sternocleidomastoid muscle to the anterior Although not part of the cervical plexus, for regional clavicle; and fi nally, the superior attachment of the purposes also include the hypoglossal nerve, which tra- sternocleidomastoid muscle to the mastoid bone. We verses the hypoglossal canal. It innervates all of the cut out the sternocleidomastoid muscle belly because it intrinsic tongue muscles and the majority of the extrin- would obstruct the view of our diagram. sic tongue muscles, shown in Drawing 12-6. Next, in midline of the page, draw seven small foram- Next, show that for a portion of its course, C1 joins ina: the jugular foramen, the hypoglossal canal, and the cranial nerve 12 as part of the hypoglossal nerve. Th en, foramina of C1 through C5. As mentioned, the cervical show that C1 innervates both the geniohyoid and plexus is formed from the C1–C4 spinal nerves, but we thyrohyoid muscles and that it forms the superior (aka include the jugular foramen, hypoglossal canal, and C5 descending) root of the ansa cervicalis, which innervates foramen, here, because they are the exit sites of related the superior belly of the omohyoid muscle. anatomic structures. Now, show that C2 and C3 together form the infe- First, let’s draw the four major sensory nerves of the rior root of the ansa cervicalis, and show that where the cervical plexus, three of which we show by fi rst drawing superior and inferior roots meet, the ansa cervicalis an anastomosis between C2 and C3. Th is connection innervates sternohyoid, sternothyroid, and the inferior forms the lesser occipital, greater auricular, and transverse belly of omohyoid. cervical nerves. Show that the lesser occipital nerve pro- We can group the aforementioned muscles based on vides sensory coverage to the superior pole of the pinna their anatomic compartments. Sternohyoid, sternothy- and posterolateral head; the greater auricular nerve pro- roid, omohyoid, and thyrohyoid are all infrahyoid mus- vides sensory coverage to the inferior pole of the pinna cles (meaning they lie below the hyoid bone) and they and the angle of the mandible; and the transverse cervical are collectively referred to as strap muscles. On the con- nerve (aka the anterior cutaneous nerve of the neck) pro- trary, geniohyoid is a suprahyoid muscle (meaning it lies vides sensory coverage to the anterolateral neck. Next, above the hyoid bone); the other suprahyoid muscles are for the fourth sensory nerve, draw an anastomosis mylohyoid, stylohyoid, and the digastric. Th e digastric between C3 and C4 and show that it derives the supra- and stylohyoid muscles lie within the anterior triangle of clavicular nerve, which provides sensory coverage to the the neck whereas geniohyoid and mylohyoid lie within posterolateral neck, upper chest, and shoulder. Note that the fl oor of the mouth. minor C3 and C4 sensory branches to the trapezius 3. Peripheral Nervous System—Upper Extremity 51

Superior pinna/ post.lat. head Jugular Inferior pinna/ foramen mandible Sternocleidomastoid muscle Tongue muscles: intrinsic & Hypoglossal nerve extrinsic (majority) Hypoglossal canal Greater auricular n. C1 Genio- and thyrohyoid (cutaneous) Transverse Superior Antero- C2 Lesser cervical n. root lateral occipital n. Trapezius (cutaneous) Inferior neck (cutaneous) muscle root C3 Superior omhyoid Ansa cervicalis C4 Sternothyroid, sternohyoid, and inferior omohyoid C5 Phrenic Supraclavicular Sternocleidomastoid nerve nerve (cutaneous) muscle Clavicle Diaphragm Posterolateral neck, upper chest, and shoulder

DRAWING 3-11 Cervical Plexus — Partial 52 Neuroanatomy: Draw It to Know It

Cervical Plexus (Advanced) (Cont.)

We have completed the cervical plexus innervation of nerve; and therefore, in spinal accessory nerve palsy, the the muscles of the anterior cervical triangle and the fl oor trapezius muscle is partially spared. of the mouth, so now let’s show how the cervical plexus Now, in the corner of the diagram, make a notation derives the majority of cranial nerve 11, the spinal acces- that the cervical plexus also provides innervation to the sory nerve, which innervates the sternocleidomastoid deep anterior vertebral muscles, which comprise the and trapezius muscles. Motor cells from the medulla to anterior and lateral rectus capitis muscles (C1, C2), the sixth cervical segment are responsible for the com- longus capitis (C1, C2, C3), and longus colli (C2–C6) plete supply of the spinal accessory nerve, but we will muscles, and that the cervical plexus also helps innervate only show the cervical plexus contribution, here. Show the scalene and levator scapulae muscles. that branches from C2–C4 ascend the spinal canal, pass As a fi nal note, keep in mind that it is the cervical through the foramen magnum, and exit the cranium spinal ventral rami that form the cervical plexus; on the through the jugular foramen as the spinal accessory contrary, the cervical dorsal rami supply the posterior nerve. Th e spinal accessory nerve innervates the trape- scalp and suboccipital region. Th e primary motor inner- zius, supplied by C3 and C4, and the sternocleidomas- vator of this region is the suboccipital nerve and the pri- toid, supplied by C2–C4. Trapezius elevates the shoulders mary sensory innervator of this region is the greater (most notably) and sternocleidomastoid turns the head. occipital nerve. Th e dorsal ramus of C1 supplies the sub- Note that the trapezius receives additional innerva- occipital nerve whereas the dorsal ramus of C2 supplies tion from cervical sources other than the spinal accessory the greater occipital nerve — see Drawing 5-6. 1 – 4

FIGURE 3-39 Tr a p e z i u s . FIGURE 3-40 Sternocleidomastoid.

FIGURE 3-41 Levator scapulae. 3. Peripheral Nervous System—Upper Extremity 53

Cervical plexus also provides innervation to the Superior pinna/ anterior vertebral muscles, scalene muscles, Jugular post.lat. head and the levator scapulae. Inferior pinna/ foramen mandible Sternocleidomastoid muscle (C2-C4) Tongue muscles: intrinsic & Hypoglossal nerve extrinsic (majority) Hypoglossal canal Greater Spinal auricular n. accessory C1 Genio- and thyrohyoid (cutaneous) nerve Transverse Superior Antero- C2 Lesser cervical n. root lateral occipital n. Trapezius (cutaneous) Inferior neck (cutaneous) muscle root C3 Superior (C3, C4) omhyoid Ansa cervicalis C4 Sternothyroid, sternohyoid, and inferior omohyoid C5 Phrenic Supraclavicular Sternocleidomastoid nerve nerve (cutaneous) muscle Clavicle Diaphragm Posterolateral neck, upper chest, and shoulder

DRAWING 3-12 Cervical Plexus — Complete 54 Neuroanatomy: Draw It to Know It

References 1 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 8 . R a t h a k r i s h n a n, R ., Th erimadasamy, A. K., Chan , Y. H. & Wilder- clinical practice , 40th ed. ( Churchill Livingstone / Elsevier , 2008 ). S m i t h, E . P. Th e median palmar cutaneous nerve in normal subjects 2 . Preston , D. C. & Shapiro , B. E. Electromyography and neuromuscular and CTS . Clin Neurophysiol 118 , 776 – 780 ( 2007 ). disorders: clinical-electrophysiologic correlations, 2nd ed. (Elsevier 9 . Martinoli , C., et al . US of nerve entrapments in osteofi brous Butterworth-Heinemann, 2005 ). tunnels of the upper and lower limbs . Radiographics 2 0 S p e c 3 . P e r o t t o, A . & D e l a g i, E . F. Anatomical guide for the No. S199–213; discussion S213–197 ( 2000 ). electromyographer: the limbs and trunk, 4th ed. ( Charles C Th omas , 10 . Jablecki , C. K., et al . Practice parameter: Electrodiagnostic studies 2005 ). in carpal tunnel syndrome. Report of the American Association of 4 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., Plates Electrodiagnostic Medicine, American Academy of Neurology, and 4–7 (Novartis , 1997 ). the American Academy of Physical Medicine and Rehabilitation . 5 . Martin , R. M. & Fish , D. E. Scapular winging: anatomical review, Neurology 58 , 1589 – 1592 ( 2002 ). diagnosis, and treatments . Curr Rev Musculoskelet Med 1 , 1 – 1 1 11 . Furuya , H. Usefulness of manual muscle testing of pronator teres (2008 ). and supinator muscles in assessing cervical radiculopathy . Fukuoka 6 . Wilbourn , A. J. & Aminoff , M. J. AAEM minimonograph #32: the Acta Med . 96 , 319 – 325 (2005 ). electrodiagnostic examination in patients with radiculopathies. 12 . Palmer , B. A. & Hughes , T. B. Cubital tunnel syndrome . J Hand American Association of Electrodiagnostic Medicine . Muscle Nerve Surg Am 35 , 153 – 163 ( 2010 ). 21 , 1612 – 1631 (1998 ). 7 . Stevens , J. C. AAEM minimonograph #26: the electrodiagnosis of carpal tunnel syndrome. American Association of Electrodiagnostic Medicine. Muscle Nerve 20 , 1477 – 1486 ( 1997 ). 4 Peripheral Nervous System Lower Extremity

Lumbosacral Plexus

The Leg & Foot

The Thigh 56 Neuroanatomy: Draw It to Know It

Know-It Points

Lumbosacral Plexus

■ Th e lumbosacral plexus is formed from L1–S4. ■ Th e tibial nerve (L4–S3) innervates the posterior leg ■ Th e sciatic nerve (L4–S3) innervates the posterior and plantar foot. thigh. ■ Th e lateral cutaneous nerve of the thigh (L2, L3) ■ Th e femoral and obturator nerves (L2–L4) innervate provides sensory coverage to the lateral thigh. the anterior thigh. ■ Th e peroneal nerve (L4–S2) innervates the anterior and lateral leg and dorsal foot.

The Leg & Foot

■ Th e common peroneal nerve divides into the deep ■ Th e major tibial-innervated muscles are the peroneal nerve and superfi cial peroneal nerve. gastrocnemius and soleus (S1, S2), tibialis posterior, ■ Th e deep peroneal nerve innervates tibialis anterior fl exor digitorum longus, and fl exor hallucis longus (L4, L5), extensor digitorum longus, extensor hallucis (L5, S1). longus, peroneus tertius, extensor digitorum brevis, ■ Th e sural nerve is formed from branches of the and extensor hallucis brevis (L5, S1). common peroneal nerve and the tibial nerve. ■ Th e superfi cial peroneal nerve innervates peroneus longus and peroneus brevis (L5, S1).

The Thigh

■ Th e femoral nerve innervates the anterior ■ Th e obturator nerve innervates the adductor compartment (L2–L4). muscles. ■ Th e obturator nerve innervates the medial ■ Th e sciatic nerve innervates the hamstrings muscles. compartment (L2–L4). ■ Within the femoral triangle, the nerve lies most ■ Th e sciatic nerve innervates the posterior laterally; medial to it is the artery; and medial to it is compartment (L4–S2). the vein: use the mnemonic NAVY. ■ Th e femoral nerve innervates the quadriceps femoris muscles and we also consider it to innervate the iliopsoas (see text for details). 4. Peripheral Nervous System—Lower Extremity 57

FIGURE 4-1 Th e lumbar plexus. Used with permission from Mendell, Jerry R., John T. Kissel, and David R. Cornblath. Diagnosis and Management of Peripheral Nerve Disorders , Contemporary Neurology Series. Oxford: Oxford University Press, 2001.

FIGURE 4-2 Th e sacral plexus. Used with permission from Mendell, Jerry R., John T. Kissel, and David R. Cornblath. Diagnosis and Management of Peripheral Nerve Disorders , Contemporary Neurology Series. Oxford: Oxford University Press, 2001. 58 Neuroanatomy: Draw It to Know It

Lumbosacral Plexus

Here, we will draw the lumbosacral plexus. First, label from L5–S2, innervates gluteus maximus; and that one the top of the page from left to right as follows: ventral level above it, the superior gluteal nerve, derived from rami; pelvis, gluteal region, and hip; thigh; leg; and foot. L4–S1, innervates gluteus medius, gluteus minimus, and Nine spinal nerves (L1–S4) form the lumbosacral plexus. tensor fasciae latae. Gluteus medius inserts into the ilium Although more spinal nerves are involved in the lum- slightly higher than gluteus maximus, which helps us bosacral plexus than in the brachial plexus, their courses remember that the superior gluteal nerve innervates glu- are, generally, much simpler, which makes learning the teus medius whereas the inferior gluteal nerve innervates lumbosacral plexus comparatively easier. gluteus maximus. Gluteus maximus provides hip exten- First, draw the innervator of the posterior thigh: the sci- sion and gluteus medius provides hip abduction. atic nerve, which is derived from L4–S3. Show that it Regarding the other superior gluteal nerve-innervated passes through the pelvis and posterior thigh and then muscles, gluteus minimus provides hip abduction and branches into the peroneal and tibial nerves, which are the tensor fasciae latae provides hip abduction when the hip innervators of the leg and foot. Th e peroneal nerve wraps is in fl exion. around the fi bular neck and innervates the anterior and lat- Above the femoral and obturator nerves, draw the lateral leg and dorsal foot whereas the tibial nerve innervates eral cutaneous nerve of the thigh (aka lateral femoral the posterior leg and plantar foot. Indicate that the L4–S2 cutaneous nerve), derived from L2 and L3, which pro- roots supply the peroneal nerve and that the L4–S3 roots vides sensory coverage to the lateral thigh. supply the tibial nerve. We draw the details of the sciatic, At the bottom, draw the pudendal nerve, which is peroneal, and tibial nerves in Drawings 4-3 and 4-4 . primarily supplied by S4 but which also receives contri- Now, draw the innervators of the anterior thigh: the butions from S2 and S3. Th e pudendal nerve branches femoral and obturator nerves, derived from L2–L4. We into the inferior rectal nerve, perineal nerve, and dorsal draw their innervation pattern in Drawings 4-5 and 4-6 . nerve to the penis or clitoris. Th e pudendal nerve pro- Note that an accessory obturator nerve branch occasion- vides motor innervation to the external urethral and anal ally exists. sphincters and external genitalia and it provides sensory Next, draw the innervators of the hip: the gluteal coverage to the anus and external genitalia, as shown in nerves. Show that the inferior gluteal nerve, derived Drawing 5-6.

FIGURE 4-3 Gluteus maximus. FIGURE 4-4 Gluteus medius. 4. Peripheral Nervous System—Lower Extremity 59

Ventral rami Pelvis, gluteal region, & hip Thigh Leg Foot

L2 - L3 Lateral cutaneous nerve of the thigh Obturator nerve L2 - L4 Femoral nerve L4 - S1 Superior gluteal nerve (gluteus med. & min., and tensor fasc. lat. m.) Inferior gluteal nerve (gluteus maximus muscle) L5 - S2 L4 - S2 Peroneal nerve Sciatic nerve L4 - S3 L4 - S3 Tibial nerve

S4 & S2/S3 Pudendal nerve (perineum and external genitalia)

DRAWING 4-1 Lumbosacral Plexus — Partial 60 Neuroanatomy: Draw It to Know It

Lumbosacral Plexus (Cont.)

Next, go back beneath the sciatic nerve and draw the upper-lateral gluteal areas, and the ilioinguinal nerve posterior cutaneous nerve of the thigh (aka the posterior provides sensory coverage to the superior-medial por- femoral cutaneous nerve), derived from S1–S3. It tion of the thigh and proximal external genitalia. provides sensory coverage to the midline back of the Next, show that L5–S2 supplies the short rotators of thigh. the hip. Th e short rotators provide external rotation of Now, we will draw the less commonly considered the hip when it is in extension and hip abduction when neuroanatomic components of the lumbosacral plexus. it is in fl exion. Th eir innervation is as follows: the nerve Above the lateral cutaneous nerve of the thigh, draw the to quadratus femoris innervates quadratus femoris and genitofemoral nerve, derived from L1–L2. Show that gemellus inferior; the nerve to obturator internus inner- the genital branch innervates the cremaster muscle and vates obturator internus and gemellus superior; the nerve provides sensory coverage to the scrotum or labia and to piriformis innervates piriformis; and the obturator that the femoral branch is purely sensory; it provides nerve innervates obturator externus (note that obturator sensory coverage to the femoral triangle. externus is supplied by L3, L4). Next, at the top of the diagram, draw the iliohypogas- Now, from S2 and S3 show the pelvic splanchnic tric and ilioinguinal nerves, derived from L1. Both nerves and the perforating cutaneous nerve. And from nerves provide motor innervation to the internal oblique S4 show the nerves to levator ani and coccygeus, which and transversus abdominis muscles. Th e iliohypogastric form the pelvic diaphragm, and also show the sphincter nerve provides sensory coverage to the suprapubic and ani externus. 1 – 5 4. Peripheral Nervous System—Lower Extremity 61

Ventral rami Pelvis, gluteal region, & hip Thigh Leg Foot Iliohypogastric nerve L1 (Internal oblique and transversus abdominus muscles) Ilioinguinal nerve Genitofemoral nerve (genital branch - cremaster muscle) L1 - L2 (femoral branch - sensory only) L2 - L3 Lateral cutaneous nerve of the thigh Obturator nerve L2 - L4 Femoral nerve L4 - S1 Superior gluteal nerve (gluteus med. & min., and tensor fasc. lat. m.) Inferior gluteal nerve (gluteus maximus muscle) L5 - S2 Short rotators of the hip L4 - S2 Peroneal nerve Sciatic nerve L4 - S3 L4 - S3 Tibial nerve S1 - S3 Posterior cutaneous nerve of the thigh Pelvic splanchnic nerves S2 - S3 Perforating cutaneous nerve

S4 & S2/S3 Pudendal nerve (perineum and external genitalia)

S4 Nerves to levator ani, coccygeus, and sphincter ani externus

DRAWING 4-2 Lumbosacral Plexus — Complete 62 Neuroanatomy: Draw It to Know It

The Leg & Foot

Here, we will draw the innervation of the leg and foot. Now, show that the deep peroneal nerve innervates To localize each form of peroneal or tibial nerve injury, tibialis anterior, supplied by L4, L5. Tibialis anterior learn at least one muscle from each muscle group. Label provides foot dorsifl exion and to a lesser extent foot the top of the page from left to right as thigh, leg, and inversion. Next, show that the deep peroneal nerve foot. First, show that the innervation of the leg and foot also innervates extensor digitorum longus, extensor hal- is derived from the sciatic nerve, supplied by L4–S3. lucis longus, and peroneus tertius, supplied by L5, S1. Th en, defi ne two key anatomic structures. Indicate that Extensor digitorum longus extends the toes (except the the popliteal fossa is the depression behind the knee and great toe); extensor hallucis longus extends the great toe, that the fi bular neck is the continuation of the head of only; and peroneus tertius assists in foot eversion. To a the fi bula (the top of the lateral leg bone). lesser extent, all three of these muscles also provide foot Now, proximal to the popliteal fossa, let’s show how dorsifl exion. the sciatic nerve unbundles to innervate the anterior, lat- Next, show that the superfi cial peroneal nerve inner- eral, and posterior leg compartments. Show that the vates peroneus longus and peroneus brevis, supplied by common peroneal nerve leaves the path of the sciatic L5, S1. Th ey provide foot eversion and to a lesser extent nerve; passes inferolaterally through the popliteal fossa; foot plantar fl exion. wraps around the fi bular neck; and then splits into the Th en, show that in addition to the aforementioned deep peroneal nerve, which innervates the muscles of the muscles, the deep peroneal nerve also innervates the anterior leg and dorsum of the foot, and the superfi cial short extensor muscles of the foot: extensor digitorum peroneal nerve, which innervates the muscles of the lat- brevis and extensor hallucis brevis, supplied by L5, S1. eral leg. Next, show that the tibial nerve continues Extensor digitorum brevis extends the middle three toes straight down the posterior leg to innervate the muscles and extensor hallucis brevis extends only the great toe of the posterior leg and plantar foot. and only at the proximal phalanx.

FIGURE 4-5 Tibialis anterior. FIGURE 4-6 Peroneus longus.

FIGURE 4-7 Extensor digitorum brevis. 4. Peripheral Nervous System—Lower Extremity 63

Thigh Leg Foot Peroneus longus & peroneus brevis (L5, S1)

Superficial Tibialis anterior (L4, L5) peroneal nerve Ext. digit. brevis & Ext. digit. longus, ext. hallucis longus, ext. hallucis brevis Fibular & peroneus tertius (L5, S1) (L5, S1) neck Deep peroneal nerve

Common peroneal nerve

Sciatic nerve (L4 - S3) Tibial nerve

Popliteal fossa

DRAWING 4-3 Th e Leg & Foot— Partial 64 Neuroanatomy: Draw It to Know It

The Leg & Foot (Cont.)

Now, let’s show the tibial nerve-innervated muscles. First, both the lateral sural cutaneous nerve and also the sural indicate the superfi cial posterior compartment muscles: communicating branch. Show that the tibial nerve pro- gastrocnemius and soleus, supplied by S1, S2. Both mus- duces the medial sural cutaneous nerve, which joins the cles provide foot plantar fl exion: we test gastrocnemius sural communicating branch to form the sural nerve. with the knee extended and soleus with the knee fl exed. Th en, show that when the sural nerve passes through the Next, show the deep posterior compartment muscles: ankle, it produces both the lateral calcaneal nerve branch tibialis posterior and fl exor digitorum longus and fl exor and also the lateral dorsal cutaneous nerve. Th e lateral hallucis longus, supplied by L5, S1, primarily. Note that calcaneal branch is the lateral corollary of the medial cal- some texts indicate that L4 also innervates tibialis poste- caneal branch, which we will draw in a moment. But rior and some texts indicate that S2 also innervates the fi rst, show another important anatomic region, the tarsal fl exor digitorum and hallucis muscles. Tibialis posterior tunnel, which is the medial entry zone of the tibial nerve provides foot inversion; fl exor digitorum longus fl exes through the ankle into the foot. the toes (except the great toe); and fl exor hallucis longus Th e medial malleolus and medial calcaneus form the fl exes the great toe. superior and inferior boundaries of the tarsal tunnel, Now, add the lesser muscles that the tibial nerve respectively, and the fl exor retinaculum forms its roof. innervates: popliteus and plantaris. Popliteus unlocks Show that within the tarsal tunnel, the tibial nerve divides the knee at the beginning of knee fl exion and plantaris into the plantar nerves (medial and lateral) and also the acts in concert with gastrocnemius. medial calcaneal sensory nerve. Th e plantar nerves inner- Finally, let’s begin to address the sensory innervation vate the plantar intrinsic foot muscles, supplied by S1–S3, of the leg and foot. First, show that the common peroneal and the plantar nerves and medial calcaneal nerve pro- nerve derives a common sensory trunk that produces vide sensory coverage to the sole of the foot. 1 – 4 , 6 – 8

FIGURE 4-8 G a s t r o c n e m i u s . FIGURE 4-9 Tibialis posterior.

FIGURE 4-10 Flexor digitorum longus. 4. Peripheral Nervous System—Lower Extremity 65

Thigh Leg Foot Peroneus longus & peroneus brevis (L5, S1)

Lateral sural cutaneous nerve Lateral calcaneal branch & lateral dorsal cutaneous Common Sural communicating branch nerves peroneal Sural nerve (cutaneous) nerve Medial sural cutaneous nerve Medial calcaneal branch Superficial m. - gastrocnemius & soleus (S1, S2) (cutaneous) Sciatic nerve Deep m. - tibialis post., flexor digit. longus, (L4 - S3) Tibial nerve & flexor hallucis longus (L5, S1) Plantar instrinsic (additional m. - popliteus and plantaris) Tarsal foot muscles (S1- S3) Popliteal fossa tunnel Medial and lateral plantar nerves

DRAWING 4-4 Th e Leg & Foot— Complete 66 Neuroanatomy: Draw It to Know It

The Thigh

Here, we will draw the innervation of the thigh. To local- minor muscles. Iliopsoas is the primary hip fl exor and ize each form of femoral, sciatic, or obturator nerve attaches within the "iliac region;” when it is weak, injury, learn at least one muscle from each muscle group. patients have diffi culty climbing upstairs or rising from a First, label across the top of the page from left to right: low chair. Next, indicate that distally, the femoral nerve abdomen and pelvis, thigh, and leg. Th e thigh divides innervates the quadriceps femoris muscles, which are into three compartments: anterior, medial, and poste- rectus femoris and the vastus muscles: vastus medialis, rior, which supply the extensor, adductor, and fl exor vastus intermedius, and vastus lateralis. Th e quadriceps muscles, respectively. In accordance with the “one femoris muscles provide knee extension, and when they compartment — one nerve” principle, indicate that the are weak, patients have diffi culty walking downstairs. femoral nerve innervates the anterior compartment, Next, show that the obturator nerve innervates the which the L2–L4 nerve roots supply; the obturator adductor muscles, which are adductor longus, adductor nerve innervates the medial compartment, which is also brevis, and adductor magnus; note that adductor magnus supplied by L2–L4; and the sciatic nerve innervates the is also supplied by the sciatic nerve, as we will later show. posterior compartment, which, again, is supplied by We test the adductor muscles through hip adduction but L4–S2. Note, though, that the tibial division of the sci- these muscles provide a variety of actions intrinsic to gait atic nerve receives additional supply from S3 for its and stability. innervation of the foot. Now, show that the sciatic nerve innervates the ham- Now, let’s show the innervation of each compart- strings muscles, which are semimembranosus, semiten- ment’s primary muscle groups. First, indicate that dinosus, and the short and long heads of the biceps proximally, the femoral nerve innervates the iliopsoas femoris muscle. Th e hamstrings muscles provide knee muscle, which comprises iliacus and the psoas major and fl exion and hip extension.

FIGURE 4-11 Iliopsoas. FIGURE 4-12 Quadriceps femoris.

FIGURE 4-13 Adductor muscles. FIGURE 4-14 H a m s t r i n g s . 4. Peripheral Nervous System—Lower Extremity 67

Abdomen & pelvis Thigh Leg

Iliopsoas

Femoral nerve Quadriceps femoris: rectus femoris, vastus medialis, (L2 - L4) vastus intermedius, & vastus lateralis Anterior compartment

Obturator nerve (L2 - L4) Adductor muscles: longus, brevis, (magnus) Medial compartment

Sciatic nerve Hamstrings: semimembranosus, semitendinosus, (L4 - S2) biceps femoris (short and long heads) Posterior compartment

DRAWING 4-5 Th e Th igh— Partial 68 Neuroanatomy: Draw It to Know It

The Thigh (Cont.)

Next, let’s consider some of the fi ner details regarding the Th en, show that the femoral nerve innervates the primary muscles of the thigh. First, note that in regards to pectineus muscle, which lies in the femoral triangle; the iliopsoas muscle, the psoas muscles (psoas major and occasionally, the obturator nerve helps innervate the minor) are actually innervated by direct branches from pectineus muscle, as well. Th e pectineus assists in both ventral lumbar rami from L1 to L3 (and not the femoral hip fl exion and adduction. It cannot be isolated and nerve). However, because the psoas muscles cannot be tested clinically. isolated and tested clinically, they are lumped in with the Finally, show that the obturator nerve innervates the iliacus muscle, and all three are considered collectively as obturator externus muscle, which is one of the short rota- the femoral nerve-innervated iliopsoas muscle. tors of the hip and which provides external rotation of the Now, show the sciatic nerve’s innervation to the hip in hip extension and hip abduction in hip fl exion. adductor magnus muscle, and indicate that the adductor Now, let’s include the sensory branches of the thigh; magnus has both an adductor portion, supplied by we map their sensory coverage in Drawing 5-5. First, L2–L4, and a hamstrings portion, supplied by L4, L5. draw the lateral femoral cutaneous nerve (aka the lateral Finally, note that the peroneal division of the sciatic cutaneous nerve of the thigh), supplied by L2, L3. It pro- nerve innervates the short head of the biceps femoris and vides sensory coverage to the lateral aspect of the thigh. that the tibial division innervates the other hamstrings Th en, from the femoral nerve, draw the medial and muscles: the long head of biceps femoris, semitendino- intermediate cutaneous nerves of the thigh, which cover sus, and semimembranosus. Th e peroneal innervation of the anterior thigh and which are collectively known as the short head of the biceps femoris is especially impor- the anterior femoral cutaneous nerve. Th en, draw the tant in localization because a peroneal neuropathy at the saphenous nerve, which extends down the medial leg to fi bular head (the most common peroneal nerve entrap- the instep of the foot and provides sensory coverage to ment site) will spare the short head of the biceps femoris, that same area. Lastly, show that the saphenous nerve but a peroneal neuropathy proximal to the fi bular head produces the small but clinically important sensory will aff ect the short head of the biceps femoris. branch called the infrapatellar branch, which innervates Now, let’s include the lesser clinical muscles of the the anterior knee and which can be injured in knee thigh. First, show that the femoral nerve innervates the arthroscopy. sartorius muscle, which is the longest muscle in the body. Now, draw the posterior cutaneous nerve of the thigh, It is a superfi cial muscle that crosses the thigh: it spans which S1–S3 supply; it covers the posterior thigh, and from the anterior superior iliac spine to the medial knee. also some of the pelvic and proximal leg regions. Finally, Th ink of someone checking the bottom of his or her note that the obturator nerve, itself, covers a small cuta- shoe to imagine the sartorius’ action; it provides knee neous area on the medial thigh. fl exion in combination with hip abduction and lateral Before we conclude, let’s consider the anatomic rela- rotation. Functionally, it serves to decelerate the lower tionships of the neurovascular structures of the femoral extremity during climbing movements. triangle because they are critical to know when perform- Next, show that the obturator nerve innervates the ing femoral venous cannulation. Within the femoral tri- gracilis muscle, supplied by L2, L3. It also lies superfi - angle, the nerve lies most laterally; medial to it is the cially and spans the medial line of the thigh, and it pro- artery; and medial to it is the vein. Th e mnemonic NAVY vides hip adduction and also knee fl exion and medial is helpful because it incorporates the position of the rotation. midline genitalia, the “Y,” into the acronym.1 – 4 4. Peripheral Nervous System—Lower Extremity 69

Abdomen & pelvis Thigh Leg (L2, L3) Lateral femoral cutaneous nerve Iliopsoas Sartorius (psoas direct from L1-L3) Medial and intermediate cutaneous nerves of the thigh Saphenous nerve (cutaneous) (and infrapatellar branch)

Femoral nerve Quadriceps femoris: rectus femoris, vastus medialis, (L2 - L4) vastus intermedius, & vastus lateralis Anterior compartment Pectineus Obturator externus Gracilis Obturator nerve (L2 - L4) Adductor muscles: longus, brevis, (magnus) Medial compartment Adductor portion (L2-4) Adductor magnus Hamstrings portion (L4, L5)

Sciatic nerve Hamstrings: semimembranosus, semitendinosus, (L4 - S2) biceps femoris (short and long heads) Posterior compartment (peroneal - short head; tibial - all other hamstrings m.)

(S1 - S3) Posterior cutaneous nerve of the thigh

DRAWING 4-6 Th e Th igh— Complete 70 Neuroanatomy: Draw It to Know It

References 1 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of American Association of Electrodiagnostic Medicine . Muscle Nerve clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). 21 , 1612 – 1631 ( 1998 ). 2 . Preston , D. C. & Shapiro , B. E. Electromyography and neuromuscular 6 . Ta k a k u r a, Y ., K i t a d a, C ., S u g i m o t o, K ., Ta n a k a, Y . & Ta m a i, S . Ta r sal disorders: clinical-electrophysiologic correlations, 2nd ed. (Elsevier tunnel syndrome. Causes and results of operative treatment . J Bone Butterworth-Heinemann, 2005 ). Joint Surg Br 73 , 125 – 128 (1991 ). 3 . P e r o t t o, A . & D e l a g i, E . F. Anatomical guide for the electromyographer: 7 . Stewart , J. D. Foot drop: where, why and what to do? Pract Neurol 8 , the limbs and trunk, 4th ed. (Charles C Th omas, 2005 ). 158 – 169 , doi:10.1136/jnnp.2008.149393 ( 2008 ). 4 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., Plates 8 . Antoniadis , G. & Scheglmann , K. Posterior tarsal tunnel syndrome: 4–7 (Novartis , 1997 ). diagnosis and treatment. Dtsch Arztebl Int 105 , 776 – 781 , 5 . Wilbourn , A. J. & Aminoff , M. J. AAEM minimonograph #32: the doi:10.3238/arztebl.2008.0776 (2008 ). electrodiagnostic examination in patients with radiculopathies. 5 Peripheral Nervous System Sensory Maps

Sensory Map of the Hand

Sensory Map of the Foot

Dermatomes

Cutaneous Nerves — Upper Limb

Cutaneous Nerves — Lower Limb

Cutaneous Nerves — Trunk (Advanced)

Referred Pain 72 Neuroanatomy: Draw It to Know It

Know-It Points

Sensory Map of the Hand

■ Th e median nerve covers the ball of the thumb, the ■ Th e radial nerve covers the dorsal lateral two thirds of lateral palm, and the palmar surface and dorsal tips of the hand and proximal dorsal surface of the lateral the lateral digits. d i g i t s . ■ Th e ulnar nerve covers the palmar and dorsal surfaces of the medial one third of the hand and digits.

Sensory Map of the Foot

■ Tibial nerve branches cover the plantar foot. covers the webbing between the great toe and second ■ Peroneal nerve branches cover the dorsal foot. digit and except for the distal sural branches. ■ Th e plantar nerves cover the plantar foot and the ■ Th e distal branches of the sural nerve cover the lateral medial calcaneal nerve covers the heel. malleolus, lateral foot, and little toe. ■ Th e superfi cial peroneal nerve covers the dorsum ■ Th e saphenous nerve covers the instep of the foot. of the foot, except that the deep peroneal nerve

Dermatomes

■ C7 covers the middle fi nger, C8 the medial hand, ■ Th e coccyx covers the center of the anus; S5 through C6 the lateral hand and lateral forearm, C5 the S1 form rings around it. upper lateral arm, T1 the medial forearm, and ■ S2 covers the posteromedial lower limb and S1 covers T2 the medial upper arm. the posterolateral lower limb. ■ T4 covers the nipple line and T10 the umbilicus. ■ C2 covers the back of the head. ■ L3 and L4 cover the knee, L5 covers the great toe, and S1 covers the ankle and little toe.

Cutaneous Nerves — Upper Limb

■ Th e medial and lateral cutaneous nerves of the ■ Th e supraclavicular nerve covers the shoulder. forearm and arm cover the medial and lateral forearm ■ Th e posterior cutaneous nerves to the forearm and and arm, respectively. arm cover the midline posterior forearm and arm, ■ Th e intercostobrachial nerve covers the axilla. r e s p e c t i v e l y .

Cutaneous Nerves — Lower Limb

■ Th e lateral femoral cutaneous nerve covers the ■ Th e lateral sural cutaneous nerve and the superfi cial lateral thigh, the posterior femoral cutaneous nerve peroneal nerve cover the upper lateral and lower covers the posterior thigh, and the anterior femoral lateral leg, respectively. cutaneous nerve covers the anterior and medial ■ Th e sural nerve covers the posterior leg. thigh. ■ Th e saphenous nerve covers the medial leg. 5. Peripheral Nervous System—Sensory Maps 73

Cutaneous Nerves — Trunk (Advanced)

■ Th e posterior ramus derives the posterior cutaneous ■ Th e iliohypogastric, ilioinguinal, genitofemoral, branch. and pudendal nerves cover the abdomino-pelvic ■ Th e anterior ramus derives the intercostal nerve, region. which provides the lateral cutaneous branch and the ■ Th e posterior cutaneous rami cover the posterior anterior cutaneous branch. trunk, posterior neck, and posterior head. ■ Th e thoracic anterior and lateral cutaneous branches ■ Th e greater occipital nerve, specifi cally, covers cover the midline thorax and abdomen and the the back of the head. lateral thorax and abdomen, respectively.

Referred Pain

■ Innervation of the diaphragm comes from C3, C4, ■ Innervation of the heart comes from T1–T5, which and C5, which cover the neck, shoulders, and upper cover the chest and medial upper arm and forearm. lateral arm. ■ Innervation of the appendix comes from T10, which ■ Use the mnemonic: C3, C4, C5 keeps the diaphragm covers the umbilicus. alive!

FIGURE 5-1 Dermatomal maps based on O. Foerster’s work (1933).Used with permission from Haymaker, Webb, and Barnes Woodhall. Peripheral Nerve Injuries, Principles of Diagnosis . 2nd ed. Philadelphia: Saunders, 1953. FIGURE 5-2 Dermatomal maps based on Keegan & Garrett’s work (1948). Used with permission from Haymaker, Webb, and Barnes Woodhall. Peripheral Nerve Injuries, Principles of Diagnosis . 2nd ed. Philadelphia: Saunders, 1953.

FIGURE 5-3 Anterior peripheral nerve map. Used with permission from Haymaker, Webb, and Barnes Woodhall. Peripheral Nerve Injuries, Principles of Diagnosis . 2nd ed. Philadelphia: Saunders, 1953. 5. Peripheral Nervous System—Sensory Maps 75

FIGURE 5-4 Posterior peripheral nerve map. Used with permission from Haymaker, Webb, and Barnes Woodhall. Peripheral Nerve Injuries, Principles of Diagnosis . 2nd ed. Philadelphia: Saunders, 1953. 76 Neuroanatomy: Draw It to Know It

Sensory Map of the Hand

Here, we will create a diagram for the sensory coverage Th en, on the palm-up tracing, show that the palmar of the hand. Begin with the median nerve’s sensory cover- ulnar cutaneous nerve covers the hypothenar eminence. age. Trace both sides of your hand. On the palm-up trac- Remember that both of these sensory nerves branch ing, square off the ball of the thumb to indicate the sensory proximal to Guyon’s canal. Lastly, still on the palm-up coverage of the palmar cutaneous nerve. Th en, show that tracing, show that the superfi cial sensory division covers the median nerve digital sensory branches cover the lat- the medial half of the fourth digit and the fi ft h digit. eral palm, lateral half of the ring fi nger, middle and index Th is sensory branch passes through Guyon’s canal. fi ngers, and the palmar thumb. Next, on the dorsal sur- Now, to map the superfi cial sensory radial nerve cov- face of the hand, show that the median nerve provides erage, fi rst, on the dorsal surface tracing, show that the sensory coverage to the dorsal tips of the thumb, index superfi cial sensory radial nerve covers the lateral two and middle fi ngers, and lateral half of the ring fi nger. thirds of the dorsum of the hand, the proximal thumb, Next, let’s show the ulnar nerve’s sensory coverage. proximal second and third digits, and proximal lateral On the dorsal surface tracing, show that the dorsal ulnar half of the fourth digit. And then on the palm-up trac- cutaneous nerve covers the medial one third of the hand ing, show that the radial nerve’s sensory coverage wraps and the medial half of the fourth digit and fi ft h digit. around to the proximal palmar thumb.1 – 8 5. Peripheral Nervous System—Sensory Maps 77

Median digital sensory branches

Median digital Ulnar sensory branches Superficial superfic. radial nerve sensory Dorsal division ulnar cutaneous nerve Median Palmar Superficial palmar ulnar radial nerve cutaneous cutan. nerve nerve

Dorsal hand Palmar hand

DRAWING 5-1 Sensory Map of the Hand 78 Neuroanatomy: Draw It to Know It

Sensory Map of the Foot

Here, let’s sketch the sensory coverage of the feet. Despite Next, turn to the dorsal foot tracing. Indicate that the the following details, bear in mind that generally, quite superfi cial peroneal nerve covers the dorsum of the foot simply, the tibial nerve covers the plantar foot and the except for the following areas: the deep peroneal nerve peroneal nerve covers the dorsal foot. Now, trace your covers the webbing between the great toe and second feet. Label one tracing as the dorsal foot and the other as digit, and the distal branches of the sural nerve (the lat- the plantar foot. On the plantar foot, show that the medial eral calcaneal branch and lateral dorsal cutaneous nerve) calcaneal nerve covers the heel. Th en, draw a line down cover the lateral malleolus, lateral foot, and little toe. the center of the fourth toe and through the sole. Indicate Finally, on the plantar and dorsal surfaces, show that that the medial plantar nerve covers the medial foot and the femoral-derived saphenous nerve covers the instep that the lateral plantar nerve covers the lateral foot. (or medial surface) of the foot. 1 – 4 , 8 5. Peripheral Nervous System—Sensory Maps 79

Deep peroneal nerve

Medial Distal plantar Superficial sural Lateral nerve peroneal branches plantar nerve nerve

Saphenous branch (femoral nerve) Distal sural branches Medial calcaneal nerve

Plantar foot Dorsal foot

DRAWING 5-2 Sensory Map of the Foot 80 Neuroanatomy: Draw It to Know It

Dermatomes

Here, we will draw the dermatomal sensory innervation descent from the superolateral anterior lower extremity; of the limbs and trunk. Note that the dermatomal maps then, indicate that the coverage of L3 and L4 crosses the have broader clinical signifi cance and are simpler than knee; then, show that L5 covers the great toe; and then, the cutaneous nerve maps of the limbs and trunk. that S1 covers the ankle and little toe. Draw the anterior and posterior outlines of the body. Next, let’s draw the posterior lower extremity and Th en begin with the hand; show that C7 covers the gluteal coverage. First, show that the coccyx covers the middle fi nger, C8 the medial hand, and C6 the lateral center of the anus and then show the dermatomal rings hand and lateral forearm. Next, show that C5 covers the that surround it: the innermost is S5, then going out- upper lateral arm. Th en, show that T1 covers the medial ward is S4, then S3, and then show that S2 encircles S3 forearm and T2 the medial upper arm. but also extends down the posteromedial lower limb. Next, to show the important dermatomes of the And lastly, show that S1 extends down the posterolateral thorax, abdomen, and pelvis, indicate that T4 covers lower limb and covers the Achilles. the nipple line, T10 covers the umbilicus, T12 covers Finally, show that C2 covers the back of the head, C3 the suprapubic area, L1 covers the inguinal region, S2 and C4 cover the posterior neck, and T2–L5 cover the covers the proximal external genitalia, and S3 covers the upper back to the buttocks (note that L2 is sometimes distal external genitalia. listed as the lowest lumbar dermatome). Now, show the sloping dermatomal coverage of the We show the trigeminal nerve sensory innervation to anterior lower extremity. First, indicate that L2 begins its the face in Drawing 13-1. 1 – 4 , 8 5. Peripheral Nervous System—Sensory Maps 81

Anterior dermatomal map Posterior dermatomal map

C3 C5 C4 T4 T2 T2 C5 C6 T1 T10 T2 L1 L5 T12 C6 C7 C8 L2 S2 T1 S3 S3 S4 L3 C7 C8 Co. S5 S2 L4 S1 L5

DRAWING 5-3 Dermatomes 82 Neuroanatomy: Draw It to Know It

Cutaneous Nerves — Upper Limb

Here, we will draw the cutaneous nerve innervation of lateral forearm; the radial nerve-derived lower lateral the upper limb. First, draw an anterior upper limb. cutaneous nerve of the arm covers the lower lateral anterior Show that the medial cord-derived medial cutaneous upper arm; the axillary nerve-derived upper lateral cutane- nerves of the forearm and arm cover the medial forearm ous nerve of the arm covers the upper lateral anterior arm; and arm, respectively. And then show that the intercos- and the supraclavicular nerve covers the shoulder. tobrachial nerve covers the axilla. In our discussion of Next, draw the posterior upper limb. Th e posterior the sensory innervation of the trunk, we discuss the T2 upper limb sensory coverage is nearly identical to the lateral cutaneous intercostal origins of the intercostobra- anterior upper limb coverage, so, fi rst, simply redraw the chial nerve. anterior limb. Next, indicate that the radial nerve-derived Next, show that the musculocutaneous nerve-derived posterior cutaneous nerves to the forearm and arm cover lateral cutaneous nerve of the forearm covers the anterior the midline forearm and arm, respectively.1 – 4 , 8 5. Peripheral Nervous System—Sensory Maps 83

Anterior upper limb

Upper lateral Lateral cutaneous n. of forearm Lower lateral cut. n. of arm (musculocutaneous) cut. n. of arm Supra- (axillary) (radial) clavicular n.

Medial cutaneous n. of forearm & arm Intercosto- (medial cord) brachial nerve (T2)

Posterior upper limb Upper lateral cut. n. of arm Low. lat. cut. (axillary) Supra- Lat. cut. n. of forearm (musculocut.) n. of arm (radial) clavicular n.

Posterior cutaneous n. of forearm & arm (radial)

Medial cutaneous n. of forearm & arm Intercosto- (medial cord) brachial nerve (T2)

DRAWING 5-4 Cutaneous Nerves — Upper Limb 84 Neuroanatomy: Draw It to Know It

Cutaneous Nerves — Lower Limb

Here, we will map the cutaneous innervation of the peroneal nerve, covers the upper lateral aspect of the leg lower limb. First, let’s draw the anterior and posterior and that the superfi cial peroneal nerve covers the lower aspects of the lower limb and label their medial and lat- lateral aspect of the leg. Th e superfi cial peroneal nerve eral surfaces. Begin with the thigh. Indicate that the also covers the dorsum of the foot except as follows: lateral cutaneous nerve of the thigh (aka lateral femoral the deep peroneal nerve covers the webbing between the cutaneous nerve) covers the lateral aspect of the com- great toe and second digit, and the distal sural branches plete thigh. Th en, show that the posterior cutaneous cover the extreme lateral foot. Next, indicate that the nerve of the thigh (aka posterior femoral cutaneous medial calcaneal nerve covers the heel. nerve) covers the back of thigh. Next, show that the Show that the sural nerve, which is derived from both anterior femoral cutaneous nerve covers the anterior and the common peroneal and tibial nerves, covers the pos- medial thigh. And fi nally, show that the obturator nerve terior leg. Th e medial sural cutaneous branch of the tibial covers a small sensory patch on the medial aspect of the nerve provides the upper sural coverage and the distal thigh. Note that the lateral and posterior cutaneous sural branches (the lateral calcaneal and lateral dorsal nerves of the thigh are direct branches from the lum- cutaneous nerves) provide the distal coverage. bosacral plexus, whereas the anterior femoral cutaneous To complete the leg, show that the femoral-derived nerve is a branch of the femoral nerve. Th e anterior fem- saphenous nerve covers the medial aspect of the leg and oral cutaneous nerve is oft en subdivided into the inter- instep of the foot. Include the clinically important infra- mediate and medial femoral cutaneous nerves. patellar branch of the saphenous nerve, which covers the Now, move to the leg. Show that the lateral sural anterior knee; this small branch is sometimes injured cutaneous nerve, which is derived from the common during arthroscopic knee surgery. 1 – 4 , 8 – 10 5. Peripheral Nervous System—Sensory Maps 85

Anterior lower limb Lateral Lateral cutaneous nerve of the thigh

Lateral sural Superficial cutaneous n. peroneal n. Anterior femoral cutaneous n. 2nd digit Infrapatellar Saphenous nerve branch (knee) Great Obturator n. toe Deep Medial peroneal nerve

Posterior lower limb Lateral Lateral cut. n. of the thigh Lateral sural cut. n. Posterior cutaneous (Distal Sup. per. n. nerve of the thigh sural n.) (Medial sural cut. n.) Sural nerve Saphenous n. Anterior femoral cut. n. Medial Medial calcaneal nerve

DRAWING 5-5 Cutaneous Nerves — Lower Limb 86 Neuroanatomy: Draw It to Know It

Cutaneous Nerves — Trunk (Advanced)

Here, we will map the cutaneous innervation of the Now, show that the iliohypogastric nerve provides trunk and related anatomic regions. Before sketching sensory coverage to the suprapubic area and the upper- their sensory coverage, let’s address the origins of the lateral gluteal region. Next, show that the ilioinguinal sensory nerves of the thorax, abdomen, and back. Show nerve provides sensory coverage to the superior-medial that the anterior and posterior nerve roots form a mixed thigh and proximal external genitalia. Th en, show that spinal nerve, which splits into posterior and anterior the genital branch of the genitofemoral nerve provides rami. Th e posterior ramus derives the posterior cutane- additional sensory coverage to the proximal external ous sensory branch and the anterior ramus derives the genitalia and that the femoral branch of the genitofemo- intercostal nerve, which provides the lateral cutaneous ral nerve covers the femoral triangle. Next, show that the branch and the anterior cutaneous branch. lateral cutaneous nerve of the thigh covers the lateral Now, draw the anterior trunk (the thorax and abdo- thigh. And fi nally, show that the pudendal nerve covers men) and posterior trunk (the back). Also include the the distal external genitalia, provides even further cover- pelvic and gluteal junctional zones in our posterior trunk age to the proximal external genitalia, and also covers diagram and also the back of the head and neck, as well, the anus. given their regional relevance. Show that the supraclavic- Next, show that the posterior cutaneous rami provide ular nerve covers the supraclavicular chest and also the most of the sensory innervation to the posterior trunk. posterior shoulders. Th en, show that thoracic anterior First, indicate that the thoracic rami cover from the scap- cutaneous branches cover the midline thorax and abdo- ulae to the iliac crests and then that the lumbosacral and men, and then that the thoracic lateral cutaneous coccygeal rami cover the buttocks. Note that the sensory branches cover the lateral thorax and abdomen. Note innervators of the buttocks are oft en called the cluneal that T1 is uninvolved in sensory coverage of the trunk: it nerves. Now, show that the inferior aspect of each but- supplies the medial cutaneous nerves of the arm and tock receives additional coverage from the anterior rami- forearm, instead; also, note that the lateral cutaneous derived posterior cutaneous nerve of the thigh and branch of T2 is called the intercostobrachial nerve and it perforating cutaneous nerve. covers the axilla; and, fi nally, note that T12 is called the Finally, show that the posterior cervical rami cover subcostal nerve, which innervates the upper/lateral but- the back of the neck and that the greater occipital nerve, tock, and has important connections with the cutaneous which is supplied by the posterior ramus of C2, covers branches of the lower abdomen, which we draw next. the back of the head. 1 , 2 , 4 , 8 , 11 5. Peripheral Nervous System—Sensory Maps 87

Anterior trunk Posterior trunk (and head & neck)

Posterior G.O.N. (C2) cutaneous branch Supraclavicular nerve Cervical Post. Supraclavic. ramus Post. root Anterior Lateral cutaneous cutaneous (Posterior cutaneous rami) Ant. thoracic thoracic Ant. root branches branches ramus Thoracic Lateral cut. Intercostal branch Iliohypogastric nerve Ilio- Inguinal Lat. cut. Fem. hypo. lumbosacral, Gen. n. thigh & coccygeal (Cluneal) Anterior Perf. Post. cutaneous Pud. Pud. branch cut. n. cut. n. thigh

DRAWING 5-6 Cutaneous Nerves — Trunk 88 Neuroanatomy: Draw It to Know It

Referred Pain

Here, we will draw a map for referred pain, which is the this innervation pattern by the mnemonic: C3, C4, C5 physiologic process whereby internal organs manifest keeps the diaphragm alive! In accordance with the vis- with body surface pain. Since Sir Henry Head wrote ceral-dermatomal rule we have established, diaphrag- about this subject in the late 1800s and early 1900s, matic pain is felt in the neck and upper shoulder: the many accounts of the dermatomal distribution of vis- dermatomal distribution of these cervical levels. Next, ceral pain have been published; however, the true let’s consider the visceral map for the heart. Show that, pathophysiologic mechanism of visceral pain remains to generally, the T1 to T5 spinal nerves innervate this be determined. It results either from direct intermin- organ; the upper thoracic spinal nerves cover the chest gling of visceral and somatic aff erent fi bers or from indi- and medial upper arm and forearm. Again, in accordance rect somatic fi ber sensitization. Also, it either occurs with the referred pain principle, myocardial ischemia is peripherally (ie, in the peripheral nerves) or centrally commonly felt along this upper thoracic dermatomal (ie, in the spinal cord). Regardless of the exact pathophys- distribution: the left side of the chest and inside of the iologic mechanism of referred pain, it is clear that vis- left arm. Note that classic cardiac pain does not extend ceral organs refer pain to their related dermatomal into the fi ngers, which are supplied by the C6 to C8 distributions. spinal nerves. Finally, consider the appendix, which is Using this rule, let’s consider the somatotopic map of innervated by T10. Appendicitis is fi rst felt as a vague, referred pain for a few important organs. Draw the trunk painful sensation at the umbilicus — the dermatomal and upper left arm. Indicate that innervation of the dia- distribution of T10. Only later, when the appendicitis phragm comes from C3, C4, and C5, which cover the worsens, does the pain become somatic, at which time it neck, shoulders, and upper lateral arm. We remember moves to the right lower quadrant. 12 5. Peripheral Nervous System—Sensory Maps 89

C4 Diaphragm

T3 Heart C5 T4

T5 T2

T1 T10 Appendix

DRAWING 5-7 R e f e r r e d P a i n 90 Neuroanatomy: Draw It to Know It

References 1 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 7 . R a t h a k r i s h n a n, R ., Th erimadasamy, A. K., Chan , Y. H. & Wilder- clinical practice, 40th ed. ( Churchill Livingstone / Elsevier , 2008 ). S m i t h, E . P. Th e median palmar cutaneous nerve in normal subjects 2 . Preston , D. C. & Shapiro , B. E. Electromyography and neuromuscular and CTS . Clin Neurophysiol 118 , 776 – 780 (2007 ). disorders: clinical-electrophysiologic correlations, 2nd ed. (Elsevier 8 . H a y m a k e r, W. & Wo o d h a l l, B . Peripheral nerve injuries; principles of Butterworth-Heinemann, 2005 ). diagnosis, 2d ed. ( Saunders , 1953 ). 3 . P e r o t t o, A . & D e l a g i, E . F. Anatomical guide for the 9 . Ta k a k u r a, Y ., K i t a d a, C ., S u g i m o t o, K ., Ta n a k a, Y . & Ta m a i, S . electromyographer: the limbs and trunk, 4th ed. ( Charles C Th omas , Tarsal tunnel syndrome. Causes and results of operative treatment . 2005 ). J Bone Joint Surg Br 73 , 125 – 128 (1991 ). 4 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., Plates 10 . Stewart , J. D. Foot drop: where, why and what to do? Pract Neurol 4–7 (Novartis , 1997 ). 8 , 158 – 169 (2008 ). 5 . Furuya , H. Usefulness of manual muscle testing of pronator teres and 1 1. B r o d a l, P. Th e central nervous system: structure and function, 4th ed. supinator muscles in assessing cervical radiculopathy . Fukuoka Acta ( Oxford University Press , 2010 ). Med . 96 , 319 – 325 (2005 ). 12 . Snell , R. S. Clinical neuroanatomy, 7th ed., Chapter 14 (Wolters 6 . Stevens , J. C. AAEM minimonograph #26: the electrodiagnosis of Kluwer Lippincott Williams & Wilkins, 2010 ). carpal tunnel syndrome. American Association of Electrodiagnostic Medicine. Muscle Nerve 20 , 1477 – 1486 (1997 ). 6 Peripheral Nervous System Autonomic Nervous System

Autonomic Fiber Arrangements

Parasympathetic Nervous System

Sympathetic Nervous System

The Urinary System (Advanced)

The Cardiac Reﬂ ex (Advanced) 92 Neuroanatomy: Draw It to Know It

Know-It Points

Autonomic Fiber Arrangements

■ Th e parasympathetic nervous system originates ■ Preganglionic parasympathetic and sympathetic within the cranial nerve nuclei and the sacral neurons release acetylcholine. intermediolateral cell column from S2 to S4. ■ Postganglionic parasympathetic fi bers release ■ Th e sympathetic nervous system originates within the acetylcholine. thoracolumbar intermediolateral cell column from ■ Postganglionic sympathetic fi bers release T1 to L2. norepinephrine (except for those fi bers to the sweat ■ Parasympathetic ganglia lie close to (or within) their glands and adrenal gland, which release acetylcholine target organ. and epinephrine, respectively). ■ Sympathetic ganglia lie far from their target organ.

Parasympathetic Nervous System

■ Th e Edinger-Westphal nucleus of cranial nerve 3 pharyngeal and thoracoabdominal glands and innervates the ciliary ganglion. organs. ■ Th e superior salivatory nucleus of cranial nerve 7 ■ Th e nucleus ambiguus of cranial nerves 9 and 10 innervates both the pterygopalatine and innervates ganglia related to the carotid body and submandibular ganglia. carotid sinus and the cardiac ganglion. ■ Th e inferior salivatory nucleus of cranial nerve 9 ■ Sacral nuclei of the intermediolateral cell column innervates the otic ganglion. (S2–S4) project to abdomino-pelvic ganglia. ■ Th e dorsal motor nucleus of the vagus nerve of cranial nerve 10 innervates the ganglia of numerous

Sympathetic Nervous System

■ Th e paravertebral chain lies just lateral to the ■ Sympathetic splanchnic nerves innervate the four vertebral column. prevertebral ganglia. ■ Superior cervical ganglion fi bers ascend the carotid ■ Certain preganglionic sympathetic fi bers synapse artery to innervate the head and neck. directly in adrenal medullary chromaffi n c e l l s . ■ Loss of sympathetic tone to the face results in Horner’s syndrome: ptosis, miosis, and anhidrosis. 6. Peripheral Nervous System—Autonomic Nervous System 93

The Urinary System (Advanced)

■ Th e sympathetic and somatomotor eff erents inhibit and tonically inhibit the parasympathetic urination. ganglion. ■ Th e parasympathetic fi bers activate urination. ■ Somatomotor eff erents provide tonic activation of ■ Parasympathetic fi bers excite bladder wall contraction the external urethral sphincter. and inhibit internal urethral sphincter constriction. ■ Male reproductive mnemonic: Parasympathetic— ■ Sympathetic fi bers inhibit bladder wall contraction, Point and Sympathetic — Shoot. excite internal urethral sphincter constriction,

The Cardiac Reﬂ ex (Advanced)

■ Th e glossopharyngeal nerve carries aff erents from ■ Th e rostral ventrolateral medulla provides tonic the carotid body and carotid sinus. sympathetic stimulation to the intermediolateral cell ■ Th e vagus nerve carries aff erents from the aortic column of the spinal cord to produce heart rate bodies and aortic arch baroreceptors. a c c e l e r a t i o n . ■ Th e glossopharyngeal and vagus nerves project to the solitary tract nucleus, which, via the nucleus ambiguus, induces heart rate deceleration. 94 Neuroanatomy: Draw It to Know It

Autonomic Fiber Arrangements

Here, we will draw the motor fi ber arrangements for the Th en, indicate that all postganglionic parasympathetic parasympathetic and sympathetic divisions of the auto- fi bers release acetylcholine and also that most post- nomic nervous system. First, indicate that the parasym- ganglionic sympathetic fi bers release norepinephrine pathetic nervous system brings the body into a rest state (noradrenaline). Th e exceptions are the postganglionic whereas the sympathetic nervous system is activated in sympathetic fi bers to sweat glands, which release acetyl- states of physical and psychological stress: it produces choline, and the adrenal medullary cells, which mostly the so-called “fi ght-or-fl ight” response. Next, draw rep- release epinephrine (adrenaline). 1 resentative preganglionic neurons for both the parasym- In addition to the neurotransmitters, neuropeptides pathetic and sympathetic nervous systems. Indicate that also exist within autonomic neurons. In comparison to the visceral neurons of the parasympathetic nervous the neurotransmitters, neuropeptides are generally pack- system lie within cranial nerve nuclei and the sacral aged into larger vesicles and have more wide-reaching intermediolateral cell column of the spinal cord, from S2 and long-lasting eff ects. Th e neuropeptides are organized to S4, and that the visceral neurons of the sympathetic into many diff erent classes, such as the calcitonin family, nervous system lie within the thoracolumbar interme- hypothalamic hormones, hypothalamic- releasing and diolateral cell column, from T1 to L2. Next, in the para- -inhibiting hormones, neuropeptide Y family, opioid sympathetic arrangement show a long preganglionic peptides, pituitary hormones, tachykinins, VIP-glucagon axon synapse on a ganglion within its eff ector tissue: cra- family, and additional peptides that do not fall into any nial and sacral parasympathetic ganglia lie either very of these categories. 2 , 3 close to or within the wall of their target organ. Th en, Lastly, consider that the digestive tract also contains show a postganglionic parasympathetic fi ber project its own autonomic system, called the enteric nervous deep into the target organ. system. Th e enteric nervous system comprises numerous Now, let’s draw the axons of the sympathetic nervous neurons distributed in myenteric and submucosal plex- system. Show a preganglionic sympathetic axon synapse uses. Th e enteric nervous system and the pacemaker on a nearby peripheral ganglion. Other than the pregan- cells of the digestive system wall (the interstitial cells of glionic sympathetic fi bers that travel to the adrenal Cajal) generate and propagate patterns of depolarization gland, sympathetic preganglionic axons are short and that result in waves of peristaltic muscle contraction. synapse close to their site of origin: either in the paraver- Food ingestion triggers the peristaltic refl ex, which pro- tebral chain or one of the prevertebral ganglia. Next, pels food through the digestive tract, and the enteric show a postganglionic sympathetic fi ber travel a long neural circuits adjust intestinal blood fl ow and secreto- distance to its target organ and also to the body walls motor activity for absorption. Notably, psychopharma- and limbs, where the sympathetic nervous system inner- cologic drugs oft en aff ect the neurotransmitters and vates sweat glands, hair fi bers, and blood vessels of skel- neuromodulators of the enteric nervous system. For etal muscle and skin. instance, acetylcholine is an important peristaltic pro- Now, let’s label the relevant neurotransmitters moter, so cholinesterase inhibitors, which increase circu- involved in these autonomic fi ber pathways. As a class, lating levels of acetylcholine, promote gastrointestinal neurotransmitters are small molecules with transient activity and can result in diarrhea. In contrast, tricyclic eff ects. Indicate that both the preganglionic parasympa- antidepressants contain anticholinergic properties and, thetic and sympathetic neurons release acetylcholine. as a result, can cause constipation.4 – 8 6. Peripheral Nervous System—Autonomic Nervous System 95

PARASYMPATHETIC Postganglionic neuron near to or within the target organ Preganglionic Cranial nerves & neuron Sacral inter- Acetylcholine Acetylcholine REST mediolateral cell column

Target organs + sweat glands, SYMPATHETIC hair fibers, & blood vessels of skeletal muscle & skin Norepinephrine except Preganglionic Postganglionic Acetylcholine for sweat glands Thoracolumbar neuron neuron Acetylcholine Epinephrine for adrenal medulla inter- ACTION mediolateral cell column

DRAWING 6-1 Autonomic Fiber Arrangements 96 Neuroanatomy: Draw It to Know It

Parasympathetic Nervous System

Here, will draw the motor division of the parasympa- laryngeal mucosa, lungs, esophagus, liver, pancreas, gall- thetic nervous system. First, draw a coronal view through bladder, stomach, small intestine, and colon to the splenic the brainstem and label the midbrain, pons, and medulla; fl exure. It induces bronchoconstriction and increases indicate that the brainstem contains the cranial compo- gut peristalsis. As we will show in a moment, however, nent of the parasympathetic system. Th en, draw a coro- the dorsal motor nucleus of the vagus provides minimal, nal view of the sacral spinal cord and label it as the sacral if any, innervation to the heart; nucleus ambiguus is component. responsible for that, instead. In the midbrain, draw the Edinger-Westphal nucleus Next, draw the nucleus ambiguus of cranial nerves 9 of cranial nerve 3. Show that it innervates the ciliary and 10. Show that through its glossopharyngeal nerve ganglion, which innervates the ciliary body and pupil- parasympathetic fi bers, nucleus ambiguus innervates lary constrictor muscles. ganglia that lie within and act on the carotid body and Next, in the pons, draw the superior salivatory nucleus carotid sinus, and then show that through its vagus nerve of cranial nerve 7, which innervates both the pterygo- parasympathetic fi bers, nucleus ambiguus innervates the palatine and submandibular ganglia, which innervate cardiac ganglion, which induces heart rate deceleration. the majority of the major glands of the face. Indicate that Note that although not drawn as such here, nucleus the pterygopalatine ganglion innervates the major glands ambiguus and the dorsal motor nucleus of the vagus of the upper face except for the parotid gland (which the both lie at the same rostro-caudal level of the medulla otic ganglion innervates). Specifi cally, the pterygopala- (see Drawing 11-4, for details). tine ganglion innervates the nasal, lacrimal, pharyngeal, Now, let’s turn our attention to the sacral component and palatine glands. Th en, show that the submandibular of the parasympathetic nervous system. Draw the sacral ganglion innervates the submandibular and sublingual nuclei of the intermediolateral cell column for sacral glands. levels 2–4. Th ese nuclei reside in lamina 7 in the inter- Now, in the medulla, draw the inferior salivatory mediate gray matter horn of the spinal cord. Show nucleus of cranial nerve 9. Show that it innervates the that the visceromotor axons from sacral levels 2–4 travel otic ganglion, which, as mentioned, innervates the as pelvic splanchnic nerves, which relay in the ganglia parotid gland. Th en, draw the dorsal motor nucleus of of their target organs in the abdomen and pelvis. Th eir the vagus nerve of cranial nerve 10. Show that it inner- targets are the hindgut derivatives: the distal transverse vates the ganglia of numerous pharyngeal and thora- colon, descending colon, sigmoid colon, and rectum; and coabdominal glands and organs. Notably, it innervates also the anal canal, lower urinary tract, and reproductive the abdominal foregut and midgut derivatives (but not organs. Sacral parasympathetic activation increases blood the hindgut derivates: its innervation stops at the splenic fl ow to the gut, increases gut peristalsis and secretion, fl exure of the colon). Th e target organs of the dorsal provides urinary bladder detrusor muscle tone, and motor nucleus of the vagus include the pharyngeal and induces genital engorgement.4 – 8 6. Peripheral Nervous System—Autonomic Nervous System 97

CRANIAL COMPONENT

Edinger-Westphal nucleus, Ciliary ganglion Ciliary body & pupillary cranial nerve 3 constrictor muscles Midbrain Pterygopalatine ganglion Nasal, lacrimal, pharyngeal & Superior salivatory nucleus, Pons palatine glands cranial nerve 7

Inferior salivatory nucleus, Submandibular ganglion Submandibular & sublingual glands cranial nerve 9 Medulla Nucleus ambiguus, cranial Otic ganglion Parotid gland nerves 9, 10 CrN 9 Dorsal motor nucleus Carotid body & sinus of vagus, cranial nerve 10 CrN 10

Cardiac ganglion Heart

SACRAL COMPONENT Pharyngeal & Thoracoabdominal targets thoracoabdominal minus hindgut derviatives Intermediolateral cell ganglia & minus the heart column of sacral levels 2 − 4 Pelvic splanchnic nerves Wall of abdomino- Hindgut derivatives plus pelvic targets anal canal, lower urinary tract, & reproductive organs

DRAWING 6-2 Parasympathetic Nervous System 98 Neuroanatomy: Draw It to Know It

Sympathetic Nervous System

Here, we will draw the motor division of the thora- cilisopinal center of Budge is innervated by the postero- columbar sympathetic nervous system. Across the top of lateral hypothalamus via the hypothalamospinal path- the page, write nucleus, ganglion, and eff ector tissue. way. Next, show that postganglionic superior cervical Next, draw an outline of the spinal cord; show that the ganglion fi bers ascend the carotid arteries to innervate origins of the sympathetic nervous system lie in the the head and neck. Notable causes of injury along this intermediolateral cell column from T1 to L2. Now, sympathetic pathway are medullary brainstem strokes, draw the paravertebral chain; it resembles a string of paravertebral masses, such as Pancoast tumor (a form of pearls and lies just lateral to the vertebral column: we apical lung tumor), and carotid dissection. Loss of sym- draw it as four circles and a long tail because only 4 of pathetic tone to the face results in Horner’s syndrome: the roughly 24 sympathetic ganglia are worth specifying ptosis, miosis, and anhidrosis. for our purposes, here. Label them now from superior to Next, we will draw the innervation to the rest of the inferior as the superior cervical ganglion, the middle cer- abdomen and pelvis, which is derived from sympathetic vical ganglion, the inferior cervical ganglion, and, lastly, splanchnic nerves, which generally originate from the the fi rst thoracic ganglion. Th e inferior cervical and fi rst T5 to L2 level of the spinal cord. Rather than relay in the thoracic ganglia combine to form the stellate ganglion. paravertebral ganglia, show that these nerves, instead, Next, show that there are 10 additional thoracic para- synapse in the four prevertebral ganglia, which span vertebral ganglia (for a total of 11), and 4 lumbar para- from the lower thoracic to the sacral vertebral column. vertebral ganglia, and 4 or 5 sacral paravertebral ganglia, Indicate that the prevertebral ganglia are, from superior and the ganglion impar, the most caudal paravertebral to inferior: the celiac, aorticorenal, superior mesenteric, ganglion, which neighbors the coccyx.9 and inferior mesenteric ganglia. Th en, show that the Now, let’s divide the sympathetic motor innerva- celiac ganglion innervates the spleen and foregut derivation into its diff erent anatomic segments. First, draw tives; the aorticorenal ganglion innervates the renal ves- the innervation to the thorax and upper abdomen: sels; the superior mesenteric ganglion innervates the show that preganglionic sympathetic fi bers synapse in midgut derivatives; and the inferior mesenteric ganglion the paravertebral chain and then project the long dis- innervates the hindgut derivatives, the lower urinary tance to their thoracoabdominal targets. Th e targets system, and the reproductive organs.5 within this anatomic segment include the lungs, trachea, As our last anatomic segment, show that pregangli- heart, and esophagus; the preganglionic sympathetic onic sympathetic fi bers synapse directly in the adrenal fi bers that innervate this segment originate in the inter- gland, most commonly on adrenal medullary chromaffi n mediolateral cell column from T1 to T5. cells, which predominantly release epinephrine (and to a Next, let’s show the innervation pattern to the upper much lesser extent norepinephrine).1 extremity. Indicate that it stems from postganglionic Finally, within the sympathetic nervous system, we fi bers of the middle cervical and stellate paravertebral need to show that both divergence and convergence of ganglia. Th en, also show that the stellate ganglion plays preganglionic sympathetic fi bers occurs. Indicate that in an important supplementary role in sympathetic inner- divergence, fi bers from one preganglionic axon form vation to the heart. synapses on multiple postganglionic neurons, whereas in Now, in regards to the head and neck, show that the convergence, there is a confl uence of fi bers from diff er- superior cervical ganglion receives innervation from ent preganglionic axons onto a single postganglionic the C8 to T2 spinal cord level: this region is called neuron.4 – 8 , 10 the cilisopinal center of Budge; and then, show that the 6. Peripheral Nervous System—Autonomic Nervous System 99

Nucleus Ganglion Effector tissue Hypothalamus Carotid arteries Head & neck Paravertebral chain Superior cervical Middle cervical Upper extremity Spinal cord Inferior cervical (Stellate) First thoracic Heart Ciliospinal center of Budge C8 - T2 Divergence Convergence Intermediolateral 10 additional thoracic, 4 lumbar, Thoracoabdominal cell column 4 sacral, & ganglion impar targets of T1 - L2 Preganglionic sympathetic fibers Adrenal gland Splanchnic nerves Prevertebral ganglia Spleen & foregut Celiac Renal vessels Aorticorenal Midgut Superior mesenteric Hindgut, lower urinary Inferior mesenteric & reproductive organs

DRAWING 6-3 Sympathetic Nervous System 100 Neuroanatomy: Draw It to Know It

The Urinary System (Advanced)

Here, we will draw the innervation of the bladder and sphincter constriction, and tonically inhibit the para- urethra, which are responsible for micturition (urina- sympathetic ganglion. Lastly, show that the somatomo- tion). We will address three classes of fi ber circuitry: tor eff erents provide tonic activation of the external parasympathetic, sympathetic, and somatomotor. We urethral sphincter. will address the urinary system in detail, but quite simply, Now, we need to address the supraspinal control of the sympathetic and somatomotor eff erents inhibit uri- urination. Th e command center for bladder emptying nation and the parasympathetic fi bers activate it. First, (micturition) and the command center for bladder fi ll- draw a bladder and urethra; then, label the bladder wall ing (continence) lie within neighboring regions of the as the detrusor muscle; next, draw the internal and exter- pons. Th e pontine micturition center lies in the medial nal urethral sphincters; and then, draw viscerosensory (M) region of the dorsolateral pontine tegmentum and aff erents from the bladder and urethra— aff erents pass the pontine continence center lies ventro-lateral to it in through the hypogastric, pelvic splanchnic, and puden- the lateral (L) region. Th ese regions receive aff erents dal nerves to innervate select spinal cord and supraspinal from many brain regions, including the periaqueductal nervous system regions. Now, let’s draw the eff erent gray area, the hypothalamus, cerebellum, and certain pathways of the lower urinary system; we will draw the limbic system regions. Barrington fi rst described the pathways, fi rst, and then label their function.11 pontine micturition center, so it is oft en referred to as First, indicate that S2 to S4 parasympathetic eff erents the Barrington nucleus. project to the parasympathetic vesical ganglion. Th en, Lastly, let’s add to our diagram the peripheral nerves show that postganglionic parasympathetic fi bers inner- that carry the aforementioned autonomic and somatic vate the bladder wall and also the internal urethral fi bers. Show that postganglionic thoracolumbar sympa- sphincter. Next, indicate that preganglionic sympathetic thetic fi bers initially travel within the superior hypogas- eff erents from T12 to L2 synapse in the paravertebral tric plexus and then emerge as hypogastric nerves. Next, chain and the inferior mesenteric prevertebral ganglion, show that the sacral parasympathetic fi bers travel via the and then show that postganglionic fi bers from these pelvic splanchnic nerve. Th en, indicate that both the ganglia project to three separate targets: the bladder wall, hypogastric and pelvic splanchnic nerves join within the parasympathetic ganglion, and the internal urethral the inferior hypogastric plexus (aka the pelvic plexus), sphincter. Finally, show that somatomotor neurons in which provides both sympathetic and parasympathetic Onuf ’s nucleus, a circumscribed region of the sacral ven- innervation to the bladder and urethra. Finally, show tral horn from S2 to S4, project to the external urethral that somatomotor eff erent fi bers travel as the pudendal sphincter. nerve to provide somatomotor innervation to the exter- Next, let’s include the function of each of these fi ber nal urethral sphincter. types (parasympathetic, sympathetic, and somatomo- Note that the inferior hypogastric plexus innervates tor), but again, we can reason out these functions if we the reproductive organs, as well. In regards to sexual remember that the sympathetic and somatomotor fi bers function, the parasympathetic nervous system is respon- inhibit urination and the parasympathetic fi bers activate sible for penile and clitoral engorgement and the sympa- it. First, show that the parasympathetic fi bers excite blad- thetic nervous system is responsible for penile ejaculation. der wall contraction and inhibit internal urethral sphinc- We remember this functional relationship with the ter constriction. Th en, show that the sympathetic fi bers mnemonic Parasympathetic— Point and Sympathetic— inhibit bladder wall contraction, excite internal urethral Shoot. 4 – 8 , 10 , 12 – 14 6. Peripheral Nervous System—Autonomic Nervous System 101

Pontine micturition center Superior hypogastric & Pontine continence center Hypogastric plexus nerve Paravertebral Inferior chain & Sympathetic hypogastric Inferior efferents plexus mesenteric T12- ganglion L2 Viscerosensory afferents Detrusor muscle

Parasympathetic Bladder Parasympathetic efferents (vesical) Pelvic S2- ganglion splanchnic S4 nerve Onuf’s Urethra nucleus Somatomotor efferents Pudendal Internal nerve urethral External sphincter urethral sphincter

DRAWING 6-4 Th e Urinary System 102 Neuroanatomy: Draw It to Know It

The Cardiac Reﬂ ex (Advanced)

Here, we will draw the cardiovascular refl ex, which projects to the parasympathetic cardiac ganglion and maintains blood pressure and cardiac output. It involves induces heart rate deceleration. Note that the dorsal a wide range of autonomic receptors, fi bers, and nuclei, motor nucleus of the vagus may play a parallel but very so we will limit our drawing to a few fundamental nuclei minor role to that of nucleus ambiguus in cardiac inner- and fi ber types. To begin, let’s draw some of the key vation. Now, show that the rostral ventrolateral medulla involved structures. First, draw the heart; aorta and provides tonic sympathetic stimulation to the interme- aortic arch; and the common carotid artery— include its diolateral cell column of the spinal cord, which produces bifurcation into the internal carotid and external carotid heart rate acceleration. Th en, indicate that the solitary arteries (denote the internal carotid artery, for reference). tract nucleus excites the caudal ventrolateral medulla, Next, draw the inferior ganglia of the glossopharyngeal which inhibits the rostral segment of the ventrolateral and vagus nerves. Th en, draw the medulla; then, the medulla, which provides further means for heart rate spinal cord; and lastly, the adjacent thoracic paraverte- deceleration. Note that we have left out some of the bral ganglia. nuclei and regions involved in this refl ex for simplicity; Now, let’s draw the specifi c components of the cardio- they are the parabrachial pontine nucleus, sensorimotor vascular refl ex. First, draw the carotid body at the bifur- cortex, amygdala, and hypothalamus. cation of the common carotid artery and then the aortic A simple way to test the cardiovascular response is by bodies below the arch of the aorta. Next, draw the carotid varying your pulse. Take your pulse and get a good sense sinus in the proximal walls of the internal carotid artery of your heart rate. Th en, take a deep breath and hold it and then the aortic arch baroreceptors in the aortic arch. for 5 or 6 seconds. Your heart rate should speed up Th e carotid body and aortic bodies are chemorecep- because when you inhale deeply, you open up lung tissue tors that respond to arterial oxygen and carbon dioxide and shunt blood into the lung capillaries, which reduces levels and blood acidity. Th e carotid sinus and aortic your eff ective circulating blood volume (ie, your stroke arch baroreceptors are baroreceptors, which respond to volume). Cardiac output is stroke volume multiplied by stretch changes in the arterial vasculature due to changes heart rate; therefore, to compensate for a decreased in blood pressure. Now, show that the glossopharyngeal stroke volume, your heart rate increases (typically by 8 nerve carries aff erents from the carotid body and carotid beats per minute). sinus and that the vagus nerve carries aff erents from the An additional, slower response to a reduced stroke aortic bodies and aortic arch baroreceptors. volume is to increase the eff ective circulating blood Next, within the lateral dorsal medulla, label the soli- volume, itself. For instance, when we stand, blood pools tary tract nucleus, and within the central medulla, label in our veins, so aft er we stand upright for a full minute, the nucleus ambiguus. Th en, draw a coronal view through T5 sympathetic splanchnic fi bers command our abdom- the ventrolateral medullary reticular formation, called inal vessels to shunt roughly 1.5 units of blood from simply the ventrolateral medulla. Divide the ventrolat- our abdomen into our peripheral vasculature. Because eral medulla into rostral and caudal segments for reasons there is a delay in the shunting of blood between systems, we will show soon. Now, indicate that the glossopharyn- when we check orthostatic blood pressure, we must geal and vagus nerves project their central processes to wait at least a few minutes in between measuring supine the solitary tract nucleus. Th en, show that the solitary and standing blood pressure (and possibly longer, tract nucleus innervates the nucleus ambiguus, which even). 4 – 9 , 15 – 17 6. Peripheral Nervous System—Autonomic Nervous System 103

(Internal carotid) Inferior ganglia: Solitary tract nuc. glossopharyngeal Carotid MEDULLA Carotid & vagus nerves body Glossopharyngeal nerve sinus Nucleus ambiguus Aortic arch (Rostral) baroreceptors Vagus nerve Ventrolateral medulla Aortic bodies (Caudal) Heart rate Preganglionic deceleration parasympathetic Heart rate acceleration Parasympathetic cardiac ganglion Thoracic paravertebral ganglia Intermedio- Pre- lateral Postganglionic cell column sympathetic ganglionic sympathetic of spinal cord

DRAWING 6-5 Th e Cardiac Refl e x 104 Neuroanatomy: Draw It to Know It

References 1 . Sherwood , L. Fundamentals of physiology: a human perspective, 10 . Cohen , H. S. Neuroscience for rehabilitation, 2nd ed. ( Lippincott ; 3rd ed. (Brooks/Cole; Th omson Learning distributor, 2006 ). Williams & Wilkins , 1999 ). 2 . N e s t l e r, E . J ., H y m a n, S . E . & M a l e n k a, R . C . Molecular neuro- 1 1. O s t e r g a r d, D . R ., B e n t, A . E ., C u n d i ff , G . W. & S w i ft , S . E . pharmacology: a foundation for clinical neuroscience, pp. 183 – 184 Ostergard’s urogynecology and pelvic fl oor dysfunction, 6th ed., ( McGraw-Hill, Medical Publishing Division , 2001 ). Chapter 4 (Wolters Kluwer/Lippincott Williams & Wilkins, 3 . P e r r y, E . K ., A s h t o n, H . & Yo u n g, A . H . Neurochemistry of 2008 ). consciousness: neurotransmitters in mind (J. Benjamins Pub. Co., 12 . Siegel , A. & Sapru , H. N. Essential neuroscience, 2nd ed. (Wolters 2002 ). Kluwer Health/Lippincott Williams & Wilkins, 2011 ). 4 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 1 3. S t o k e r, J ., Ta y l o r, S . A . & D e L a n c e y, J . O . L . Imaging pelvic fl oor atlas, 2nd ed. ( Lange Medical Books/McGraw-Hill , 2005 ). disorders, 2nd rev. ed. (Springer , 2008 ). 5 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 14 . Yamada , S. & American Association of Neurological Surgeons. clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). Tethered cord syndrome in children and adults, 2nd ed., pp. 12 – 13 6 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., Plates (Th ieme; American Association of Neurosurgeons, 2010 ). 4–7 (Novartis , 1997 ). 1 5. K i e r n a n, J . A . & B a r r, M . L . Barr’s the human nervous system: an 7 . S n e l l, R . S . Clinical neuroanatomy, 7th ed., Chapter 14 (Wolters anatomical viewpoint, 9th ed. (Wolters Kluwer/Lippincott, Kluwer Lippincott Williams & Wilkins, 2010 ). Williams & Wilkins , 2009 ). 8 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 1 6. P o s n e r, J . B . & P l u m, F. Plum and Posner’s diagnosis of stupor and clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). coma, 4th ed. ( Oxford University Press , 2007 ). 9 . R o b e r t s o n, D . Primer on the autonomic nervous system, 2nd ed. 1 7. L o e w y, A . D . & S p y e r, K . M . Central regulation of autonomic (Elsevier Academic Press, 2004 ). functions, Chapter 9 ( Oxford University Press , 1990 ). 7 Spinal Cord

Spinal Cord Overview

Ascending Pathways

Descending Pathways (Advanced)

Major Ascending & Descending Tracts

Spinocerebellar Pathways (Advanced)

Spinal Cord Disorders 106 Neuroanatomy: Draw It to Know It

Know-It Points

Spinal Cord Overview

■ Th e posterior, middle, and anterior white matter form ■ Laminae VIII and IX are the motor laminae. the posterior, lateral, and anterior funiculi, respectively. ■ Lamina X surrounds the central canal. ■ Th e gray matter of the spinal cord divides into the ■ In the lumbosacral cord, white matter is small and posterior horn, intermediate zone, and anterior horn. gray matter is large. ■ Th e gray matter of the spinal cord comprises Rexed ■ In the thoracic cord, white matter is moderately large laminae, which are numbered I to X. and gray matter is small. ■ Laminae I–VI are the sensory laminae. ■ In the cervical spinal cord, both the gray and white ■ Lamina VII is the spinocerebellar and autonomic matter regions are large. lamina.

Ascending Pathways

■ Th e posterior column pathway comprises large sensory ■ Th e anterolateral system includes the spinothalamic fi bers, which carry vibration, two-point discrimination, tract and the spinal-hypothalamic and spinal- and joint position sensory information. brainstem pathways. ■ Th e gracile fasciculus carries large fi ber sensory ■ Th e spinocerebellar tracts comprise large sensory information from the lower body. fi bers, which carry joint proprioception to the ■ Th e cuneate fasciculus carries large fi ber sensory cerebellum for the coordination of movement. information from the upper body. ■ Th e anterolateral system comprises small fi ber sensory pathways, which carry pain, itch, and thermal sensory information.

Descending Pathways (Advanced)

■ Th e anterior corticospinal tract innervates proximal ■ Th e tectospinal tract innervates the upper musculature for gross motor movements. cervical spinal segments to produce contralateral ■ Th e lateral corticospinal tract innervates distal head turn. musculature for fi ne motor movements. ■ Th e reticulospinal tracts and vestibulospinal tracts ■ Th e hypothalamospinal tract carries hypothalamic maintain posture through the activation of control of autonomic function. antigravity muscles. ■ Th e rubrospinal tract innervates the upper cervical spinal cord to produce arm fl exion. 7. Spinal Cord 107

Major Ascending & Descending Tracts

■ P o s t e r i o r c o l u m n fi bers ascend the spinal cord ■ Anterolateral system: 1st order neuron in the dorsal ipsilateral to their side of origin. root ganglion, 2nd order neuron in the dorsal horn of ■ A n t e r o l a t e r a l s y s t e m fi bers ascend the spinal cord the spinal cord, 3rd order neuron in the ventrolateral contralateral to their side of origin. posterior nucleus of the thalamus. ■ Lateral corticospinal tract fi bers descend the spinal ■ Corticospinal tract: 1st order neuron in the motor cord contralateral to their side of origin. cortices (primarily), 2nd order neuron in the anterior ■ Posterior column pathway: 1st order neuron in the horn of the spinal cord. dorsal root ganglion, 2nd order neuron in the gracile and cuneate nuclei, 3rd order neuron in the ventrolateral posterior nucleus of the thalamus.

Spinocerebellar Pathways (Advanced)

■ Th e posterior spinocerebellar tract originates from ■ Th e cuneocerebellar tract originates in the upper limb aff erents of the lower trunk and lower limb, synapses and upper trunk and enters the cerebellum via the in the dorsal nucleus of Clarke, and enters the ipsilateral inferior cerebellar peduncle. cerebellum via the ipsilateral inferior cerebellar ■ Th e rostral spinocerebellar tract originates in the peduncle. upper limb and enters the cerebellum via the ■ Th e anterior spinocerebellar tract originates from ipsilateral inferior cerebellar peduncle. aff erents of the lower limb and enters the cerebellum via the superior cerebellar peduncle. 108 Neuroanatomy: Draw It to Know It

A Cervical Dorsal median septum Fasciculus gracilis Fasciculus cuneatus Dorsal funiculus Dorsomedial tract Dorsolateral (Lissauer's) tract Dorsal root Marginal layer Substantia gelatinosa Dorsal horn Nucleus proprius Reticulated area Lateral Intermediate funiculus gray Central canal Ventral horn Far-lateral Ventral funiculus Near-lateral Motor Central Medial columns Ventromedial Ventral median sulcus funiculus B Thoracic

Dorsal horn Clarke's column

Lateral horn Central canal

Ventral horn Medial motor columns

C Lumbar Fasciculus gracilis

Myelinated afferents Dorsal horn Central gray

Lateral funiculus Intermediate gray

Far-lateral Ventral horn Near-lateral Central Motor 1 mm columns Medial

FIGURE 7-1 Histologic axial sections through cervical, thoracic, and lumbosacral spinal cord. Used with permission from Altman, Joseph, and Shirley A. Bayer. Development of the Human Spinal Cord: An Interpretation Based on Experimental Studies in Animals . Oxford ; New York: Oxford University Press, 2001. 7. Spinal Cord 109

Dorsal funiculus

Dorsal root

Dorsal root entry zones I II III

V VI

Intermediate gray Lateral funiculus

Ventral horn motoneurons (far-lateral) Ventral horn motoneurons (medial)

FIGURE 7-2 Gray matter horns. Used with permission from the estate of Dr. William DeMyer. 110 Neuroanatomy: Draw It to Know It

Spinal Cord Overview

Here, we will draw the spinal cord in axial cross-section. the central processes of sensory fi bers in a complicated Show that the spinal cord is ovoid and has a thin fi ssure way; generally, laminae I, II, and V receive small, poorly on its anterior surface. Next, draw the internal gray myelinated or unmyelinated fi bers, which carry pain and matter, which resembles a butterfl y. Th en, draw the cen- temperature sensation, and laminae III and IV receive tral canal in the center of the gray matter; it is mostly large cutaneous sensory fi bers— note, however, that the obliterated by the second decade of life. Th e white matter majority of large fi bers do not synapse within the Rexed of the spinal cord is segmented into posterior, lateral, laminae at all but instead directly ascend the posterior and anterior funiculi (aka columns). Label the posterior columns.1 white matter as the posterior funiculus, the middle white Laminae V and VI receive descending motor fi bers matter as the lateral funiculus, and the anterior white and assist in sensorimotor integration. Lamina VII con- matter as the anterior funiculus. Lastly, show that inter- tains the dorsal nucleus of Clarke, a key spinocerebellar spinal rostro-caudal white matter projections travel via nuclear column, and the intermediolateral column, a key the proprius fasciculus, which surrounds the gray matter autonomic nuclear column. Laminae VIII and IX con- horns. Next, introduce the posterior median septum, tain motor neurons. Lamina X surrounds the central which divides the posterior white matter into two halves, canal.2 , 3 and label the anterior median fi ssure in parallel along the Now, let’s illustrate the relative size of the white and anterior surface of the spinal cord. gray matter regions of the spinal cord at diff erent ana- Th e gray matter of the spinal cord divides into three tomic heights. Show that in the lumbosacral cord, the diff erent regions, which are further classifi ed as Rexed amount of white matter is small, because the ascending laminae. First, label the regions from posterior to ante- fi bers have yet to coalesce and the descending motor rior as the posterior horn, intermediate zone, and ante- fi bers have already terminated on their anterior horn rior horn. Th en, label the Rexed laminae, which are cells. Indicate that the amount of gray matter is large numbered from I to X. In the posterior horn, label lami- because of the numerous neurons needed to innervate nae I–VI: they are the sensory laminae; then, in the the lower limbs. Th en, show that in the thoracic cord, intermediate zone, label lamina VII, which is the spinoc- the amount of white matter is moderately large because erebellar and autonomic lamina; next, in the anterior of the presence of the lumbosacral aff erents and eff er- horn, label laminae VIII and IX, which are the motor ents, and then show that the amount of gray matter is laminae; and fi nally, label lamina X around the central small, because thoracic innervation to the trunk requires canal. far fewer neurons than lumbosacral or cervical innerva- Now, let’s address a few neuroanatomic highlights of tion to the limbs. Finally, in the cervical spinal cord, the Rexed laminae. Lamina I is the marginal nucleus (aka indicate that both the gray and white matter regions are posteromarginal nucleus); lamina II is the substantia large: the white matter bundles are dense with ascending gelatinosa — so named because its lack of myelinated and descending fi bers from throughout the spinal cord fi bers gives it a gelatinous appearance on myelin staining; and the gray matter horns are large because of the large and laminae III and IV comprise nucleus proprius (the populations of neurons required to innervate the upper proper sensory nucleus). Laminae I through V receive limbs. 2 , 4 – 12 7. Spinal Cord 111

CERVICAL Posterior median septum

Posterior I Funiculus II Posterior III horn IV V THORACIC VI Lateral Central canal Funiculus VII X Intermediate zone

VIII & IX Anterior horn

Proprius fasciculus LUMBOSACRAL Anterior funiculus Anterior median fissure

DRAWING 7-1 Spinal Cord Overview 112 Neuroanatomy: Draw It to Know It

Ascending Pathways

Here, we will draw the ascending spinal cord pathways in cape-like distribution in the arms and upper trunk but is axial cross-section. Draw an outline of a spinal cord in preserved in the legs. We can imagine that as the central axial cross-section and include the gray matter horns. We fl uid collection expands outward, it aff ects the arms and start with the posterior column pathway, which com- upper trunk fi rst, and only later the legs. In regards to the prises large sensory fi bers that carry vibration, two-point sensory information carried by the anterolateral system, discrimination, and joint position sensory information. the lateral regions subserve pain and temperature and Within the posterior column, draw the posterior median the anterior regions subserve tactile and pressure sensa- septum, which divides the posterior white matter into tion. Indeed, texts oft en further subdivide the anterolat- right and left posterior columns. Th en, label the poste- eral system into separate ventral and lateral pathways. rior intermediate septum, which further subdivides each Next, label the ventral commissure, which lies in between posterior column into medial and lateral segments. Label the anterior horns; it is the white matter pathway through the medial segment as the gracile fasciculus and the lat- which the anterolateral system fi bers decussate. eral segment as the cuneate fasciculus. Write thoracic Lastly, along the posterior lateral wall of the spinal level 6 (T6) over the posterior intermediate septum to cord, label the posterior spinocerebellar tract, and along indicate that the gracile fasciculus carries large fi ber sen- the anterior lateral wall, label the anterior spinocerebel- sory information from the lower body (from below T6) lar tract. Th ese tracts comprise large sensory fi bers that and the cuneate fasciculus carries sensory information carry joint proprioception to the cerebellum for the from the upper body (from T6 and above).4 S e n s o r y coordination of movement; we address the spinocerebel- aff erents from the face travel via the trigeminal sensory lar pathways in Drawing 7-5 . system. A mnemonic to remember the function of the Now, show that the cell bodies for spinal sensory gracile fasciculus is that ballerinas must have good sen- fi bers lie within dorsal root ganglia, which are situated sory input from their feet to twirl grace fully. just proximal to where the anterior and posterior roots Now, label the anterolateral system as a long pathway merge, within the intervertebral foramina. Indicate that that lies just outside of the anterior gray matter horn and spinal sensory axons are pseudo-unipolar, meaning they extends between the anterior and lateral white matter contain a single short axon that emanates from the cell funiculi. It comprises small fi ber sensory pathways that body and divides into processes that extend peripherally carry pain, itch, and thermal sensory information. Th e (eg, to the skin’s surface) and centrally (eg, to the spinal anterolateral system includes the spinothalamic tract cord). and the spinal-hypothalamic and spinal-brainstem path- Finally, let’s draw the anterolateral system and poste- ways. In regards to the anterolateral system’s somatotopic rior column projections. Label Lissauer’s tract along the organization, the lower-most spinal levels comprise its dorsal edge of the dorsal horn. Indicate that the central outermost somatotopic layer and the upper-most spinal processes of the anterolateral system pass through levels comprise its innermost somatotopic layer; thus, Lissauer’s tract, synapse within the ipsilateral dorsal indicate that the arms lie along the inner aspect of the horn, and cross within the ventral commissure to ascend anterolateral system and the legs lie along the outer the spinal cord within the anterolateral system. Th en, aspect. As a helpful mnemonic, consider that in cervical indicate that the posterior column pathway fi bers enter syringomyelia, a fl uid-fi lled cavity within the central the spinal cord medial to Lissauer’s tract and directly cord (see Drawing 7-8 ), there is oft en a suspended ascend the spinal cord within the ipsilateral posterior sensory level wherein small fi ber sensation is lost in a column. 2 , 4 – 12 7. Spinal Cord 113

Cell body Posterior column fiber Thoracic Axon level 6 Anterolateral system Posterior fiber Anterolateral column system Gracile fiber Cuneate Fasciculus Posterior Lissauer Fasciculus intermediate tract septum

Posterior median Posterior septum spinocerebellar tract

Periphery Anterior spinocerebellar tract Ventral commissure

Arms Legs Anterolateral system

DRAWING 7-2 Ascending Pathways 114 Neuroanatomy: Draw It to Know It

Descending Pathways (Advanced)

Here, we will draw the descending spinal cord pathways spinal cord and label the lateral reticulospinal tract and in axial cross-section. First, draw one half of an outline of lateral vestibulospinal tract in the lateral funiculus (the an axial cross-section of the spinal cord and include a lateral vestibulospinal tract borders the anterior funicu- gray matter horn. Th en, label the following terms across lus). Next, indicate that the medial reticulospinal tract the top of the page: tract, origin, termination, and func- originates in the medial zone of the pontine reticular tion. Next, label the lateral corticospinal tract in the lat- formation and passes predominantly ipsilaterally to acti- eral funiculus and then the anterior corticospinal tract vate the axial and proximal limb extensors. Th en, indi- along the anterior median fi ssure. Indicate that the ante- cate that the lateral reticulospinal tract originates in the rior corticospinal tract fi bers originate in the motor cor- medial zone of the medullary reticular formation and tices (most notably), terminate in contralateral spinal passes predominantly ipsilaterally to inhibit the axial and motor neurons, and innervate proximal musculature for proximal limb extensors (and to a lesser degree it also gross motor movements. Next, outside of our table, make excites axial and proximal limb fl exors). Now, make a a notation that the lateral corticospinal tract fi bers inner- notation that the vestibulospinal tracts excite the axial vate distal musculature for fi ne motor movements (we and proximal limb extensors. Specifi cally, the medial draw this pathway in Drawing 7-4 ). Th en, label the vestibulospinal tract acts on the cervical spinal cord to somatotopic organization of the lateral corticospinal excite neck extensor musculature and the lateral ves- tract: indicate that the medial aspect of the lateral corti- tibulospinal tract projects along the height of the spinal cospinal tract carries the arm fi bers and the lateral aspect cord to excite paravertebral and proximal limb extensor carries the leg fi bers. muscles. 7 , 9 , 13 , 14 Next, label the hypothalamospinal tract alongside the Next, consider that normally the cerebral cortex lateral corticospinal tract in the lateral funiculus. Indicate inhibits the rubrospinal and reticulo- and vestibulospi- that this tract originates in the hypothalamus, descends nal tracts, but when cortical inhibition is lost, these three ipsilaterally, and carries hypothalamic control of auto- tracts are left unchecked, which results in upper extrem- nomic function. Now, label the rubrospinal tract near to ity fl exion and lower extremity extension, referred to as the lateral corticospinal tract. Indicate that it originates decorticate posturing. Th en, consider that a lesion that from the red nucleus in the midbrain, crosses in the ven- cuts off both the cortical and rubrospinal tracts (ie, a tral tegmental area of the brainstem, and innervates the lesion below the level of the midbrain) leaves the retic- upper cervical spinal cord to produce arm fl exion. Next, ulo- and vestibulospinal tracts unchecked, which results label the tectospinal tract in the anterior-medial spinal in neck and limb extension, referred to as decerebrate cord. Indicate that it originates in the superior colliculus posturing. of the midbrain, decussates in the dorsal midbrain teg- Finally, in regards to the somatotopy of the anterior mentum, and innervates the upper cervical spinal seg- gray matter horns, show that the posterior nuclei inner- ments to produce contralateral head turn. vate the fl exor muscles and the anterior nuclei innervate Now, let’s address the reticulospinal tracts and ves- the extensor muscles, and then show that the medial nuclei tibulospinal tracts, both of which maintain posture innervate the proximal muscles and the lateral nuclei through the activation of antigravity muscles. In our innervate the distal muscles. Notice how the somatotopic axial cross-section, label the medial reticulospinal tract organization of the gray matter parallels the positions of and medial vestibulospinal tract in the anterior-medial the functionally-related white matter pathways.2 , 4 – 12 7. Spinal Cord 115

TRACT ORIGIN TERMINATION FUNCTION Anterior corticospinal Motor cortices (mostly) Contralateral Proximal muscle activation Hypothalamospinal Hypothalamus Ipsilateral Autonomic function Rubrospinal Red nucleus Contralateral Activates upper limb flexion Tectospinal Superior colliculus Contralateral Neck movement - head turn Medial reticulospinal Pontine reticular formation Ipsilateral (mostly) Activates limb extension Lateral reticulospinal Medullary reticular formation Ipsilateral (mostly) Inhibits limb extension

Hypothalamospinal *Lateral corticospinal - tract innervate distal muscles Legs Arms Lateral cortico- *Vestibulospinal - spinal tract activate axial & Rubrospinal tract proximal limb extensors Flexors Lateral Distal Proximal reticulospinal tract Tectospinal tract Extensors Medial Medial vestibulospinal tract reticulospinal Lateral tract vestibulospinal tract Anterior corticospinal tract *Further details drawn elsewhere

DRAWING 7-3 Descending Pathways 116 Neuroanatomy: Draw It to Know It

Major Ascending & Descending Tracts

Here, we will draw the posterior column pathway, the the medial lemniscus and synapse in the third-order anterolateral system (which includes, most notably, the neuron in the ventroposterior lateral nucleus of the thal- spinothalamic tract), and the lateral corticospinal tract. amus. Finally, indicate that the thalamus projects to the First, draw an axial cross-section through the spinal cord. sensory cortex. Next, label the origin and termination points of our Now, let’s draw the cell bodies and fi ber pathway pathway; label the right peripheral nerve and the left for the anterolateral system. Indicate that the fi rst- cerebral hemisphere’s primary motor cortex and primary order neuron lies within the dorsal root ganglion; then, sensory cortex. show that the second-order neuron lies within the dorsal Now, label the posterior column of the right side of horn of the spinal cord; and fi nally, show that the third- the posterior white matter. Posterior column fi bers ascend order neuron lies within the contralateral thalamus (also the spinal cord ipsilateral to their side of origin. Next, within the ventroposterior lateral nucleus). Now, draw label the anterolateral system bundle on the left side of the anterolateral system pathway, itself. Show that ante- the spinal cord — the anterolateral system fi bers ascend rolateral system central processes project from the dorsal the spinal cord contralateral to their side of origin. Finally, root ganglion to the dorsal horn. Th ese inputs ascend draw the lateral corticospinal tract on the right side of the and descend a variable number of spinal cord levels spinal cord— the lateral corticospinal tract fi bers descend before synapsing in the spinal cord. Th en, show that at or the spinal cord contralateral to their side of origin. near their level of entry into the spinal cord, the antero- Next, let’s label cell bodies for each pathway and then lateral system fi bers decussate via the ventral commissure draw each pathway’s course. We will abbreviate the cell and bundle in the anterolateral spinal cord, where they bodies for each pathway as follows: posterior column ascend the spinal cord and brainstem to synapse in the pathway cell body as PCP, anterolateral system cell body thalamus. Finally, show that the thalamus projects to the as ALS, and lateral corticospinal tract cell body as CST. sensory cortex. Note that whereas the posterior column Show that the fi rst cell body (the fi rst-order sensory pathway ascends the spinal cord ipsilateral to its side of neuron) for the posterior column pathway lies in the origin, the anterolateral system ascends the spinal cord dorsal root ganglion. Th is cell body is pseudo-unipolar: contralateral to its side of origin. indicate that it projects a single axon bundle over a very Lastly, let’s draw the cell bodies and pathway for the short distance, which divides into a peripheral process lateral corticospinal tract. Indicate that the fi rst-order (the peripheral nerve) and a central process (the poste- neuron lies in the motor cortex, most notably, but also in rior nerve root). Next, show that the second-order sen- the premotor and sensory cortices, and then that the sory neurons lie in the gracile and cuneate nuclei in the second-order neuron lies within the contralateral ante- medulla. Th en, draw the third-order sensory neuron in rior gray matter horn of the spinal cord. Now, show the contralateral thalamus. Now, draw the posterior that lateral corticospinal fi bers descend from the motor column pathway, itself. Indicate that the central process cortex through the ipsilateral brainstem, decussate enters and ascends the posterior column without form- within the medullary pyramids at the cervicomedullary ing a synapse in the spinal cord and that it instead fi rst junction, and then descend through the spinal cord in synapses in the gracile and cuneate nuclei in the medulla. the lateral corticospinal tract to synapse in spinal motor Next, show that the gracile and cuneate nuclei send neurons. Th en, show that motor neurons project nerve decussating fi bers across the medulla via the internal fi bers via the anterior nerve root, which joins the poste- arcuate fasciculus; these fi bers ascend the brainstem via rior nerve root to form a mixed spinal nerve.2 , 4 – 12 7. Spinal Cord 117

Posterior column pathway - PCP Primary motor cortex Primary sensory cortex (Left) Anterolateral system - ALS (1CST) Lateral corticospinal tract - CST Corticospinal tract Thalamus (3 PCP)(3ALS)

Internal arcuate fasciculus Gracile & (2PCP) Medial cuneate nuclei lemniscus Cervico-medullary junction

Posterior column fiber Anterolateral system fiber Posterior Posterior nerve root (2ALS) column

(1ALS) Lateral (1PCP) corticospinal Axon tract Spinal Anterolateral nerve (2CST) system Ventral commissure Motor Peripheral Anterior neuron (Right) Nerve nerve root

DRAWING 7-4 Major Ascending & Descending Tracts 118 Neuroanatomy: Draw It to Know It

Spinocerebellar Pathways (Advanced)

Here we will draw the spinocerebellar pathways, which anterior spinocerebellar tract projects from L3 to L5 carry proprioceptive sensory information to the cerebel- across midline within the ventral commissure, ascends lum for the coordination of movement and the mainte- the spinal cord and brainstem within the anterior spi- nance of posture. Th e spinocerebellar pathways comprise nocerebellar tract, enters the cerebellum within the supe- the posterior, anterior, and rostral spinocerebellar tracts, rior cerebellar peduncle, and then decussates again within and the cuneocerebellar tract. Except for the cuneocere- the cerebellum to terminate on its side of origin (although bellar tract, all of the spinocerebellar tracts synapse a small portion of fi bers terminate in the contralateral within the spinal cord (generally within the intermedi- cerebellum and do not make this last decussation). Th us, ate zone of the gray matter) prior to reaching the cerebel- through this double decussation, the anterior spinocere- lum. Th e posterior and anterior spinocerebellar pathways bellar tract remains ipsilateral to its side of origin. Note are the best understood of these pathways; we will draw that, generally, the inferior and middle cerebellar pedun- them fi rst. cles are the infl ow pathways into the cerebellum and the Draw an axial cross-section through the spinal cord. superior cerebellar peduncle is the outfl ow pathway for In the corner of the diagram, write the words “tract” and fi bers from the cerebellum — the anterior spinocerebellar “origin.” We will list the origin of each spinocerebellar pathway is an important exception to this rule. pathway as we complete our diagram. First, indicate that Now, let’s draw the cuneocerebellar tract. Indicate the posterior spinocerebellar tract originates from aff er- that the cuneocerebellar tract originates in the upper ents of the lower trunk and lower limb. Now, to draw the limb and upper trunk. Th en, just beneath the inferior posterior spinocerebellar tract course, draw a peripheral cerebellar peduncle, label the lateral cuneate nucleus nerve and show its central process synapse in the inter- (aka accessory cuneate nucleus)— the fi rst synapse of the mediate zone of the spinal cord from T1 to L2 in a region cuneocerebellar tract. Next, to draw the cuneocerebellar called the dorsal nucleus of Clarke. Th e majority of the tract course, show the central process of a peripheral posterior spinocerebellar tract aff erent fi bers arise from nerve fi ber enter the posterior column and directly below the L2 spinal level, ascend in the posterior funicu- ascend the spinal cord to the lateral cuneate nucleus. lus, and then make their synapse in the dorsal nucleus of Th en, indicate that the cuneocerebellar fi bers project Clarke. Now, show that the dorsal nucleus of Clarke from the lateral cuneate nucleus through the ipsilateral projects via the ipsilateral inferior cerebellar peduncle to inferior cerebellar peduncle to enter the cerebellum. enter the cerebellum. Finally, let’s draw our last pathway, the rostral spinoc- Next, let’s draw the anterior spinocerebellar tract. erebellar tract. Indicate that it originates in the upper Indicate that it originates from aff erents of the lower limb. Th en, to draw the rostral spinocerebellar tract limb. Th en, to draw the anterior spinocerebellar tract course, show the central process of a peripheral nerve course, show the central process of a peripheral nerve synapse at the C4 to C8 spinal levels. Indicate that along fi ber synapse at the L3 to L5 levels of the spinal cord. a poorly described course, fi bers project from the C4 to Th e course of the anterior spinocerebellar tract is quite C8 spinal levels to the cerebellum via the ipsilateral infe- long and involves a double decussation. Indicate that the rior cerebellar peduncle.2 , 4 – 12 7. Spinal Cord 119

Cerebellum Superior cerebellar peduncle Inferior cerebellar Lateral peduncle cuneate nucleus Rostral spino- Cuneo- cerebellar tract cerebellar tract (from C4 to C8)

Posterior spinocerebellar tract

TRACT ORIGIN Posterior Lower limb & T1 C4 L3 lower trunk to to to L2 C8 L5 Anterior Lower limb Anterior spino- Cuneo- Upper limb & cerebellar tract upper trunk Rostral Upper limb

DRAWING 7-5 Spinocerebellar Pathways 120 Neuroanatomy: Draw It to Know It

Spinal Cord Disorders

Case I Patient presents with years of progressive “lightning-like” cord involvement. Th e lower extremity arefl exia suggests pain in the lower extremities. Exam reveals profound lower lower motor neuron involvement, so also show that there extremity loss of vibration/proprioception sensation with is dorsal root involvement. Th e dorsal root involvement preserved pain/temperature sensation and preserved causes the lancinating pain — presumably from irritation strength in the lower extremities. Th ere is arefl exia in the of the pain/temperature fi bers. lower extremities. Th e upper extremities are normal. Indicate that this constellation of defi cits suggests a Show that the loss of vibration/proprioception sensa- diagnosis of tabes dorsalis (aka syphilitic myelopathy), tion with preserved pain/temperature sensation and pre- in which the posterior columns and dorsal roots are served motor function suggests posterior column spinal aff ected.15 – 21

Case II Patient presents with an abrupt onset of interscapular the longitudinal loss of pain/temperature sensation sug- pain, lower extremity weakness, sensory disturbance, gests involvement of the anterolateral system with pres- and bowel and bladder incontinence. Exam reveals ervation of the posterior columns. arefl exia of the lower extremities; paraparesis; loss of Indicate that this constellation of defi cits suggests pain/temperature sensation with preserved vibration/ anterior spinal artery ischemia, in which the anterior proprioception sensation in the lower extremities; anal two thirds of the spinal cord are aff ected. Note that sphincter atonia; and a normal motor, sensory, and refl ex this syndrome variably aff ects the lateral corticospinal exam in the upper extremities. tracts. Th e most common site of anterior spinal artery Show that the sudden weakness and arefl exia suggests ischemia is at the T4 level. 18 – 22 bilateral anterior motor horn cell involvement, and that

Case III Patient presents with sudden weakness on the right side right-side posterior column tract involvement; that the of the body and sensory disturbance. Exam reveals right- left -side loss of pain/temperature sensation suggests side weakness, right-side loss of vibration/proprioception right-side anterolateral system involvement; and that sensation, and left -side loss of pain/temperature sensa- the right-side arefl exia suggests right-side lower motor tion. Refl exes are absent on the right side and normal on neuron involvement, which could occur from either the left . anterior or posterior horn injury. Show that the right-side hemi-body weakness sug- Indicate that this constellation of defi cits suggests a gests right-side corticospinal tract involvement; that hemi-cord syndrome involving the right half of the spinal the right-side loss of vibration/proprioception suggests cord, called Brown-Séquard syndrome.18 – 21 7. Spinal Cord 121

Tabes dorsalis Anterior spinal artery ischemia Brown Sequard syndrome (Syphilitic myelopathy)

DRAWING 7-6 Spinal Cord Disorders — Partial 122 Neuroanatomy: Draw It to Know It

Spinal Cord Disorders (Cont.)

Case IV Patient presents with a few-month course of progressive Indicate that this constellation of defi cits suggests a burning pain across the shoulders. Exam reveals weak- central cord syndrome, oft en a syringomyelia. ness of the upper extremities; absent biceps refl exes with Syringomyelia is a fl uid-fi lled cavity within the hyperrefl exia of lower extremities; pathologic (ie, posi- spinal cord, which may be limited to a dilatation of the tive) Babinski’s; absent pain/temperature sensation central canal, may extend outside of the central canal, or across the upper chest and limbs with preserved vibra- may be separate from the central canal, entirely. It causes tion/proprioception sensation. lower motor neuron signs at the level of the lesion, Show that the dissociation of loss of pain/temperature impaired pain/temperature sensation but preserved sensation with preserved vibration/proprioception sen- vibration/proprioception in a segmental distribution sation in a suspended sensory level suggests damage to the (classically, in a cape-like distribution across the arms crossing anterolateral system fi bers. Show that the loss of and upper trunk): a so-called suspended sensory level, strength and arefl exia of the upper limbs in that same seg- and upper motor neuron signs below the level of the ment suggests bilateral anterior motor horn damage. lesion.18 – 21

Case V Patient presents with a few-month course of trunk and Indicate that this combination of defi cits is oft en lower limb sensory dysesthesias. Exam reveals hyperre- found in subacute combined degeneration due to vitamin fl exia throughout except for absent ankle jerks; patho- B12 defi ciency. Subacute combined degeneration aff ects logic (ie, positive) Babinski’s; loss of vibration/ the posterior and lateral columns. Although not men- proprioception sensation in the lower extremities with tioned, gait ataxia is oft en present in this disorder and preserved pain/temperature sensation; and mild, diff use may be due to the profound vibration/proprioception lower extremity weakness. sensory loss or due to posterior spinocerebellar tract Show that the loss of vibration/proprioception sensa- involvement from lateral column pathology. B12 defi - tion with preserved pain/temperature sensation suggests ciency also oft en causes a superimposed neuropathy, posterior column involvement. Th en, show that the diff use which explains the absent ankle jerks. 18 – 21 , 23 , 24 motor weakness is due to corticospinal tract involvement.

Case VI (Advanced ) Patient presents with longstanding gait disturbance and the vibration/proprioception sensory loss with preserved weakness. Exam shows lower extremity arefl exia with pain/temperature sensation suggests posterior column preserved upper extremity refl exes; pathologic (ie, posi- involvement. Next, show that the profound ataxia sug- tive) Babinski’s; profound ataxia; vibration/propriocep- gests spinocerebellar tract involvement. And fi nally, tion sensory loss out of proportion to pain/temperature indicate that the motor weakness suggests corticospinal sensory loss; and motor weakness of the upper and lower tract involvement. extremities. Indicate that this constellation of defi cits is found in First, show that the mixed refl ex pattern in the pres- Friedreich’s ataxia, an inherited progressive ataxia with ence of pathologic Babinski’s suggests a mixed upper and pathology that fi rst appears in the dorsal roots. lower motor neuron disease pattern with pathology of Spinocerebellar tract involvement is an important dis- the dorsal nerve roots and dorsal horns. Th en, show that tinguishing feature of this disorder.18 – 21 7. Spinal Cord 123

Tabes dorsalis Anterior spinal artery ischemia Brown Sequard syndrome (Syphilitic myelopathy)

Central cord syndrome Subacute combined degeneration Friedreich’s ataxia (often Syringomyelia) (Vitamin B12 deficiency)

DRAWING 7-7 Spinal Cord Disorders — Partial 124 Neuroanatomy: Draw It to Know It

Spinal Cord Disorders (Cont.)

Case VII Patient presents with a several-month course of weak- Show that the presence of motor weakness in con- ness that began in the left arm and has since spread junction with mixed hyperrefl exia and arefl exia with to both arms and legs. Exam reveals asymmetric but bilateral pathologic Babinski’s and a normal sensory diff use upper and lower extremity weakness. Th ere is exam suggests both corticospinal tract and anterior mixed hyperrefl exia and arefl exia throughout the bilat- motor horn involvement. eral upper and lower extremities. Th ere are bilateral Indicate that this constellation of defi cits is oft en pathologic (ie, positive) Babinski’s. Sensory exam is found in amyotrophic lateral sclerosis (aka ALS or Lou normal. Gehrig’s disease).18 – 21

Case VIII (Advanced) Patient presents with muscle pains and slowly progres- Many illnesses cause select anterior horn cell loss. sive muscle wasting. Exam reveals asymmetric lower Indicate that two common illnesses that cause this pathol- extremity weakness; hyporefl exia in the lower extremi- ogy are polio syndrome and spinal muscular atrophy.18 – 21 ties; the absence of pathologic Babinski’s (ie, negative Babinski's); and normal sensation. Show that the weakness in conjunction with hyporefl exia and a normal sensory exam suggests anterior motor horn involvement, only.

Case IX (Advanced ) Patient presents with slowly progressive lower extremity Show that the weakness in conjunction with spasticity, weakness. Exam reveals spastic weakness of the lower hyperrefl exia, bilateral pathologic Babinski’s, and a normal extremities more so than the upper extremities; hyper- sensory exam suggests corticospinal tract involvement. refl exia; bilateral pathologic (ie, positive) Babinski’s; gait Indicate that select corticospinal tract involvement ataxia; and a normal sensory exam. suggests a diagnosis of primary lateral sclerosis. 18 – 21 7. Spinal Cord 125

Tabes dorsalis Anterior spinal artery ischemia Brown Sequard syndrome (Syphilitic myelopathy)

Central cord syndrome Subacute combined degeneration Friedreich’s ataxia (often Syringomyelia) (Vitamin B12 deficiency)

Amyotrophic lateral sclerosis Spinal muscular atrophy, Primary lateral sclerosis (aka ALS or Lou Gehrig’s disease) Polio syndrome

DRAWING 7-8 Spinal Cord Disorders — Complete 126 Neuroanatomy: Draw It to Know It

References 1 . S i e g e l, A . & S a p r u, H . N . Essential neuroscience (L i p p i n c o t t neuroanatomy and neurophysiology, 6th ed. ( Lippincott Williams & Williams & Wilkins , 2006 ). Wilkins, 2005 ). 2 . S i e g e l, A . & S a p r u, H . N . Essential neuroscience, 2nd ed. (Wolters 1 4. B e n a r r o c h, E . E . Basic neurosciences with clinical applications Kluwer Health/Lippincott Williams & Wilkins, 2011 ). ( Butterworth Heinemann Elsevier , 2006 ). 3 . Shimoji , K. O. & Willis , W. D. Evoked spinal cord potentials: an 1 5. L a r n e r, A . J . A dictionary of neurological signs, 2nd ed. (Springer , illustrated guide to physiology, pharmacology, and recording 2006 ). techniques (Springer , 2006 ). 16 . Chilver-Stainer , L. , Fischer , U. , Hauf , M. , Fux , C. A. & 4 . Watson , C. , Paxinos , G. , Kayalioglu , G. & Christopher & Dana Sturzenegger , M. Syphilitic myelitis: rare, nonspecifi c, but treatable . Reeve Foundation. Th e spinal cord: a Christopher and Dana Reeve Neurology 72 , 673 – 675 ( 2009 ). Foundation text and atlas, 1st ed. ( Elsevier/Academic Press , 2009 ). 17 . Berger , J. R. & Sabet , A. Infectious myelopathies. Semin Neurol 2 2, 5 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 133 – 142 (2002 ). clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). 18 . Samuels , M. A. , Feske , S. & Daff n e r, K . R . Offi ce practice of 6 . Pierrot-Deseilligny , E. & Burke , D. J. Th e circuitry of the human neurology, 2nd ed. ( Churchill Livingstone , 2003 ). spinal cord: its role in motor control and movement disorders 1 9. R o w l a n d, L . P., P e d l e y, T. A . & K n e a s s, W. Merritt’s neurology, ( Cambridge University Press , 2005 ). 12th ed. (Wolters Kluwer Lippincott Williams & Wilkins, 2010 ). 7 . P a t e s t a s, M . A . & G a r t n e r, L . P. A textbook of neuroanatomy 20 . Ropper , A. H., Adams , R. D., Victor , M. & Samuels , M. A. Adams (Blackwell Pub., 2006 ). and Victor’s principles of neurology, 9th ed. (McGraw-Hill Medical, 8 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., 2009 ). Plates 4–7 (Novartis , 1997 ). 21 . Merritt , H. H. & Rowland , L. P. Merritt’s neurology, 10th ed. 9 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and ( Lippincott Williams & Wilkins , 2000 ). clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). 22 . Takahashi , S. O. Neurovascular imaging: MRI & microangiography 1 0. D e M y e r, W. Neuroanatomy, 2nd ed. ( Williams & Wilkins , 1998 ). (Springer , 2010 ). 11 . Baehr , M. , Frotscher , M. & Duus , P. Duus’ topical diagnosis in 23 . Paul , I. & Reichard , R. R. Subacute combined degeneration neurology: anatomy, physiology, signs, symptoms, 4th completely rev. mimicking traumatic spinal cord injury . Am J Forensic Med Pathol ed., Chapter 3 (Th ieme, 2005 ). 30, 47 – 48 (2009 ). 1 2. A l t m a n, J . & B a y e r, S . A . Development of the human spinal cord: an 24 . Kumar , A. & Singh , A. K. Teaching NeuroImage: Inverted V sign in interpretation based on experimental studies in animals (Oxford subacute combined degeneration of spinal cord . Neurology 72 , e4 University Press, 2001 ). (2009 ). 1 3. C a m p b e l l, W. W., D e J o n g, R . N . & H a e r e r, A . F. DeJong’s the neurologic examination: incorporating the fundamentals of 8 Spinal Canal and Muscle– Nerve Physiology

The Spinal Canal

The Muscle Stretch Reﬂ ex

Muscle–Nerve Physiology ( Advanced )

Nerve Roots & Rami 128 Neuroanatomy: Draw It to Know It

Know-It Points

The Spinal Canal

■ Th e vertebral column contains 33 vertebrae and 31 ■ Th e collection of nerve fi bers in the caudal spinal spinal nerves. canal is the cauda equina. ■ Th e spinal cord ends at the L1–L2 vertebral column ■ Th e distal, bulbous region of the spinal cord is the level. conus medullaris. ■ Motor and sensory roots combine within an ■ Th e site of fl uid collection during a lumbar puncture intervertebral neural foramen at each level to form a is the lumbar cistern, which is the subarachnoid space mixed spinal nerve. below the level of the spinal cord. ■ Only the C1 through C7 nerve roots exit above their related vertebral bodies, the rest exit beneath them.

The Muscle Stretch Reﬂ ex

■ Th e muscle spindle sends an excitatory volley along basis for the termination of the muscle stretch the type Ia sensory aff erent, which directly innervates refl ex. the motor neuron. ■ Th e biceps refl ex involves C5, C6. ■ Th rough the inhibitory neurotransmitter glycine, ■ Th e triceps refl ex involves C7, C8. Renshaw cells inhibit the antagonist refl ex from ■ Th e patellar refl ex involves L2–L4. fi ring. ■ Th e Achilles refl ex involves S1, S2. ■ Muscle spindle fi bers have a lower threshold to fi re than Golgi tendon organs, which is the

Muscle–Nerve Physiology (Advanced )

■ A γ motor neurons project to the muscle spindles to ■ Th e largest peripheral nerve fi bers are 12 to 22 stimulate muscle tone. micrometers in diameter and conduct at 70 to 120 ■ Initially, when supraspinal input to the Aγ motor meters per second. neurons is disrupted, muscle tone becomes fl accid; ■ Th e smallest peripheral nerve fi bers are less than 1 days or weeks later, spasticity develops. micrometer in diameter and conduct at less than 2 ■ Skeletal muscle fi bers outside of the capsule are meters per second. extrafusal fi bers and are innervated by the Aα motor ■ Saltatory conduction is the fi ring of impulses in the nerves. interspaces between segments of myelin: the nodes of ■ I n t r a f u s a l fi bers lie within the muscle spindle and are R a n v i e r . innervated by the Aγ motor nerves. 8. Spinal Canal and Muscle–Nerve Physiology 129

Nerve Roots & Rami

■ Th e ventral root carries motor fi bers and the dorsal ■ Dorsal rami innervate the paraspinal muscles and root carries sensory fi bers. provide sensory coverage to the back of the head and ■ Th e dorsal root ganglion lies within the intervertebral posterior trunk. foramen along the posterior nerve root; it houses the ■ Ventral rami provide motor and sensory innervation cell bodies of sensory nerves. to a widespread group of muscles and sensory areas, ■ Sensory cell bodies are pseudo-unipolar: they contain including the anterior trunk and upper and lower a short axon with bipolar processes that pass both limbs. centrally and peripherally. ■ Impulses travel up the white ramus (myelinated) to ■ Just distal to the dorsal root ganglion, the anterior the paravertebral sympathetic ganglion and then and posterior roots join to form a mixed spinal nerve, down the gray ramus (unmyelinated) back to the which then separates into dorsal and ventral rami. v e n t r a l r a m u s .

4 5 6 C7 7 C8 8 T1 1 2

VERTEBRAE SPINAL CORD VERTEBRAE NERVES 3 C1 4 I I 2 5 II Cervical II 3 6 III III plexus IV IV 4 7 V V 5 8 VI VI 6 Brachial 9 L1 VII VII 7 plexus 10 8 T1 T1 11 S1 II II T1 2 12 1 III III 3 2 IV IV 3 V 4 V 4 5 1 2 VI 5 VI VII 6

VII VIII 7 8 VIII IX 9 IX X 10 X XI 11 XI XII 12 XII L1 L1 L1 II II 2 Lumbar III plexus III 3 IV IV 4 V V 5 S1 Sacral 2 3 plexus 4 5 Coccyx 1 L5

FIGURE 8-1 Segmental organization of the spinal canal and the peripheral nerves. Used with permission from Altman, Joseph, and Shirley A. Bayer. Development of the Human Spinal Cord: An Interpretation Based on Experimental Studies in Animals . Oxford; New York: Oxford University Press, 2001. 130 Neuroanatomy: Draw It to Know It

The Spinal Canal

Here, we will draw a sagittal view of the spinal canal, the coccyx. Only C1 through C7 exit above their related which encases the spinal cord and spinal nerve roots. To vertebral bodies; the rest exit beneath them. begin, draw a sagittal section through the brainstem and Now, let’s label a few important caudal spinal canal then the spinal cord. Indicate that the cervical segment structures. Indicate that the collection of nerve fi bers of the spinal cord angles anteriorly; the thoracic segment that traverses the caudal spinal canal is the cauda equina, angles posteriorly; and the lumbosacral and coccygeal which is the Latin term “tail of the horse.” Th en, indicate segments angle anteriorly, again. that the anatomically related, threadlike fi brous tissue Th e vertebral column contains 33 vertebrae: 7 cervi- that extends from the distal tip of the spinal cord through cal, 12 thoracic, and 5 lumbar vertebrae, and then the the caudal spinal canal is the fi lum terminale. Finally, vertebral fusions that constitute the sacrum and coccyx. label the most distal, bulbous region of the spinal cord Th e spinal cord ends at the L1–L2 vertebral column as the conus medullaris. Th e cauda equina and conus level; thus the spinal cord is shorter than the spinal canal, medullaris each have related syndromes, which are self- and therefore, at any vertical height, the spinal cord level named. Cauda equina syndrome is a lower motor neuron is lower than the surrounding vertebral level. Now, show syndrome, whereas conus medullaris syndrome is an the following vertebral bodies: C1, C2, C7, T1, T12, upper motor neuron syndrome. Injury to both the cauda and L1; then, show that there is hyperfl exion of the sacral equina and conus medullaris causes mixed upper and column at the clinically important L5–S1 junction, a lower motor neuron disease. common site of nerve root compression; then, show that Next, let’s label the meningeal coverings of the spinal S5 angles further posteriorly; and fi nally show that the canal. First, label the surface of the spinal cord as the coccyx angles back anteriorly. 1 pia mater. Th en, draw a combined layer of dura and A pair of motor and sensory roots exit the spinal cord underlying arachnoid mater. Show that there is plenty of at each level and combine within an intervertebral neural separation between these meningeal coverings and the foramen to form a spinal nerve. Th ere are a total of 31 underlying pia mater. Label the naturally occurring space spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, between the arachnoid and pia mater layers as the suba- and 1 coccygeal. Show that the fi rst cervical spinal nerve, rachnoid space. Th en, show that the site of fl uid collec- C1, exits below the skull (beneath the foramen magnum) tion during a lumbar puncture is in the lumbar cistern, and above the fi rst cervical vertebra. Th en, indicate that the subarachnoid space below the level of the spinal cord. C2 exits above its vertebra, and so on— show that C7 Finally, draw the vertebral arch (the posterior portion of exits above the C7 vertebra, which is the lowermost cer- the vertebral column), and between it and the dura vical vertebra. As mentioned, however, there are 8 cervi- mater, label the epidural space. Note that although we cal spinal nerves, so show that C8 exits underneath the have only labeled the posterior aspect of the epidural C7 vertebra and above the T1 vertebra. Where, then, space, here, throughout the spinal canal, the spinal epi- must the T1 nerve exit? Show that the T1 spinal nerve dural space exists superfi cial to the dura mater and inter- exits below its corresponding vertebra because C8 fi lls nal to the periosteal lining of the vertebral canal. Th e the space above it. Th en, show that T12 exits beneath spinal epidural space is a common site for hematoma, the T12 body, L1 beneath L1, L5 under L5, S1 under S1, infection, and spread of neoplastic disease.2 – 4 S5 under S5, and the coccygeal nerve exits underneath 8. Spinal Canal and Muscle–Nerve Physiology 131

Foramen Vertebral bodies magnum C 1 nerve C1 body C 2 nerve Dura & C2 body arachnoid C 7 nerve layers C7 body C8 nerve T1 body Subarachnoid T1 nerve space

Epidural Pia space mater T12 body Vertebral arch T12 nerve L1 body L1 nerve Conus medullaris Cauda equina L5 body Lumbar cistern L5 nerve S1 body Filum terminale = S5 body S1 nerve fibrous tissue Coccyx S5 nerve Coccygeal nerve

DRAWING 8-1 Th e Spinal Canal 132 Neuroanatomy: Draw It to Know It

The Muscle Stretch Reﬂ ex

Here, we will draw a muscle stretch refl ex (aka myotatic fl exion of the aff ected foot (aka foot dorsifl exion) with or deep tendon refl ex). First, draw an axial cross-section simultaneous fl exion of the knee and the hip. In order through the spinal cord. Th en, draw a lower extremity for us to remain upright when we undergo the triple that is fl exed at the knee and show a knee extensor muscle fl exor refl ex, our opposite leg must bear our weight. Th us, fi ber of the quadriceps muscle group at the top of the through a simultaneous but opposing refl ex in our oppo- thigh and a knee fl exor fi ber of the hamstrings muscle site leg, the crossed extension refl ex, our non-aff ected group at the bottom of the thigh: we use the knee exten- foot fl exes downward and our non-aff ected hip and knee sor refl ex as our example, here. Next, denote the location extend. of the related motor neurons within the anterior horn of Now, let’s show how to terminate the muscle stretch the spinal cord. Now, draw a muscle spindle and show a refl ex; bear in mind that there are a number of neurobio- type Ia sensory fi ber project from it to the extensor motor logical infl uences on the relaxation of muscle contrac- neuron. Th en, draw an Aα motor fi ber projection from tion, which include myosin ATPase and calcium the extensor motor neuron to the representative extra- re-accumulation into the endoplasmic reticulum, which fusal extensor fi ber. In large muscle groups, such as the we will not draw, here. Delay in the relaxation phase of quadriceps, a single motor neuron commands as many as the muscle stretch refl ex (aka Woltman’s sign) is observed 1,000 extrafusal muscle fi bers, whereas in small muscle in symptomatic hypothyroidism. Re-draw our muscle groups, such as the extraocular muscles, a motor neuron stretch refl ex arrangement but exclude the fl exor neuron commands as few as 10 extrafusal muscle fi bers. Show and its motor fi ber. Th en, label a Golgi tendon organ that when the patellar tendon is stretched with the tap of where the quadriceps tendon inserts into the patella. a refl ex hammer, the muscle spindle sends an excitatory Next, show that a type Ib fi ber projects from the Golgi volley along the type Ia sensory aff erent, which excites tendon organ to the Renshaw interneuron. Now, show the extensor motor neuron and nerve, and the muscle an inhibitory fi ber project from the interneuron to the extensor contracts so the knee extends.5 , 6 quadriceps (extensor) motor neuron. Th e type Ia and Ib If the hamstrings were also activated (meaning, if the fi bers fi re at the same rate, but muscle spindle fi bers have extensor and fl exors shortened simultaneously), the a much lower threshold to fi re than Golgi tendon organs. thigh would only stiff en and not move. So, now, draw a Th us, the muscle spindle fi res fi rst, and then later the Renshaw cell (an interneuron) in the anterior horn of Golgi tendon organ fi res, which terminates the muscle the gray matter of the spinal cord, and show that through stretch refl ex. Th is completes our diagram. the inhibitory neurotransmitter glycine, the Renshaw For reference, the commonly tested muscle stretch cell inhibits the fl exor motor neuron from fi ring. refl exes are the biceps, which involves the C5, C6 nerve Interneurons are the lynchpins to more complicated roots; the triceps, which involves the C7, C8 nerve roots; spinal refl exes, as well, such as the triple fl exor refl ex, the patella (drawn here), which involves the L2 to L4 which has the following sequential mechanics: a painful nerve roots; and the Achilles, which involves the S1, S2 stimulus to the bottom of the foot causes refl ex upward nerve roots.2 , 4 , 7 – 10 8. Spinal Canal and Muscle–Nerve Physiology 133

*The Renshaw cell lies in the anterior horn Type Ia Muscle sensory nerve spindle

*Renshaw cell Extensor Flexor

Flexor Extensor Aα motor nerve

Type Ia Type Ib sensory nerve sensory nerve

*Renshaw cell

Extensor Golgi Aα tendon motor nerve organ

DRAWING 8-2 Th e Muscle Stretch Refl e x 134 Neuroanatomy: Draw It to Know It

Muscle–Nerve Physiology (Advanced )

Here, let’s address muscle tone, the muscle spindle, and and bag2 — the latter shares many similarities with nuclear peripheral nerve classifi cation. We begin with muscle chain fi bers. Indicate, now, that in addition to attaching tone. Re-draw our Aα motor refl ex loop: draw the spinal to chain fi bers, the type II sensory aff erents also attach to cord and lower extremity and then show the muscle bag 2 fi bers. spindle project via a type Ia sensory aff erent to excite the Now, let’s address the eff erent innervation of the motoneuron, which projects via an Aα motor nerve to muscle spindle. Th e Aγ motor nerves terminate in either excite the extrafusal muscle fi ber. Next, label an Aγ motor plate or trail endings in the polar region of the muscle neuron in the anterior gray matter and show that it proj- spindle along the intrafusal muscle fi bers. Indicate that, ects to the muscle spindle. Th e Aγ motor neurons stimu- generally, plate endings lie along nuclear bag fi bers late muscle tone. Finally, draw a supraspinal projection and trail endings lie along nuclear chain fi bers and bag2 γ to the A motor neuron to show that supraspinal centers fi bers. Th e bag 1 fi bers act when there is a change in muscle send descending excitatory inputs to the A γ motor neu- fi ber length, during the dynamic phase, whereas the γ rons. Initially, when supraspinal input to the A motor chain fi bers and bag2 fi bers act when muscle length is neurons is disrupted, muscle tone becomes fl accid; it is unchanged, during the static phase. not until days or weeks later that spasticity develops. Lastly, let’s address the classifi cation of peripheral Now, let’s draw the muscle spindle anatomy. Begin nerves. Two classifi cation schemes are commonly used: with the connective tissue-enclosed muscle spindle cap- the Gasser scheme, which applies to all nerve types— sule. Next, label the skeletal muscle fi bers outside of the motor, sensory, and autonomic, and the Lloyd scheme, capsule as extrafusal fi bers; these fi bers produce limb which applies to sensory nerves, only. Th e two schemes movement and they are innervated by the Aα motor are fairly redundant, however, and can be learned nerves. Now, draw several intrafusal fi bers within the together. We will only list the largest and smallest fi bers, muscle spindle; they are innervated by the A γ motor here, but the table in Drawing 8-3 is complete for refer- nerves. Th en, within the central, non-contractile portion ence. Label the top row of our table as the Gasser nerve of the muscle spindle, draw nuclei clustered together like class, Lloyd nerve class, diameter, and speed (ie, conduc- marbles in a bag and label this as the nuclear bag fi ber; tion velocity). Make a notation that the diameter units next, draw a row of nuclei like pearls on a chain and label are micrometers and the speed units are meters per this as the nuclear chain fi ber. Both fi ber types exist second. List the largest fi ber type as Gasser class Aα and within the muscle spindle and they each are attuned to Lloyd class Ia and Ib; indicate that they are 12 to 22 diff erent aspects of muscle tone. micrometers (μ m) in diameter and conduct at 70 to 120 Next, let’s address the type Ia and type II sensory meters per second (m/s). Th en, label the smallest fi bers aff erents of the muscle spindle. Show an annulospiral as Gasser class C and Lloyd class IV, and show that they sensory nerve ending around the non-contractile, cen- are less than 1 μ m in diameter and conduct at less than tral portion of both the nuclear bag and nuclear chain 2 m/s. Impulses slowly ascend the small unmyelinated fi bers; the annulospiral nerve ending connects to the nerve axons, whereas they quickly ascend the large, heav- type Ia sensory aff erent fi ber. Th en, show that fl ower ily myelinated nerve fi bers because impulses of myeli- spray sensory nerve endings connect the type II fi bers to nated fi bers fi re only in the interspaces between segments the nuclear chain fi bers. However, to complicate mat- of myelin — the nodes of Ranvier; this pattern of fi ring is 1,2,4,5,9–16 ters, two forms of nuclear bag fi ber actually exist, bag1 called saltatory conduction. 8. Spinal Canal and Muscle–Nerve Physiology 135

MUSCLE TONE Supraspinal input

Type Ia Muscle sensory nerve spindle

Extafusal Aγ motor nerve Gamma Motoneuron Aα PERIPHERAL NERVE motor nerve CLASSIFICATION Gasser Lloyd Diameter Speed MUSCLE SPINDLE A α Ia 12-22 70-120 Type Ia, annulospiral (sensory) Muscle spindle Ib Plate ending A β II 5-12 30-70 (motor) - dynamic Nuclear bag A γ - 2-8 15-30

Aδ III 1-5 5-30 Extrafusal Nuclear chain Bag2 fiber muscle B - <3 3-15 fiber Trail ending C IV <1 <2 Intrafusal Type II, (motor) - static muscle fiber flower spray Diameter = micrometers(μm) (sensory) Speed = meters/second (m/s)

DRAWING 8-3 Muscle–Nerve Physiology 136 Neuroanatomy: Draw It to Know It

Nerve Roots & Rami

To draw the anatomy of the nerve roots and rami, fi rst In brief, dorsal rami innervate the paraspinal muscles draw an outline of an axial cross-section through the and provide sensory coverage to the back of the head and spinal cord. Th en, draw the spinal cord dorsal and ven- posterior trunk, whereas the ventral rami provide motor tral gray matter horns. Next, draw the anterior-lying ver- and sensory innervation to a far more widespread group tebral body. Th en, draw the pedicle on the right side of of muscles and sensory areas, including the anterior the page but leave out the pedicle on the left ; otherwise trunk and upper and lower limbs. we would obstruct our view of the dorsal root ganglion, Show a representative thoracic nerve originate from which sits in the intervertebral foramen, underneath the the anterior ramus and pass along the chest wall to form pedicle. Next, draw the transverse processes, then the an intercostal nerve. Now, turn your attention back to laminae, and fi nally the spinous process. We leave out where the rami split to draw the sympathetic ganglion the articular processes, which form facet joints between and related autonomic rami. Along the ventral ramus, the vertebral arches. attach the white ramus, so named because it is myeli- Now, draw an anterior horn cell on the right side of nated. Th en, more proximally, just past the takeoff of the the spinal cord (the left side of the page) and show a ven- dorsal ramus, attach the gray ramus, which is unmyeli- tral root emerge from it. Th e ventral root carries motor nated. Indicate that the gray and white rami meet in a fi bers. Next, show a dorsal root enter the dorsal horn: it paravertebral sympathetic ganglion. Sympathetic ganglia carries sensory fi bers. As mentioned, underlying the pedi- form two long chains that fl ank the vertebral column; cle is the intervertebral foramen. Within the interverte- the sympathetic cell bodies lie within the intermediolat- bral foramen, attach a dorsal root ganglion to the posterior eral cell column of the spinal cord and project to the nerve root. Th e dorsal root ganglion houses the cell paravertebral sympathetic chains. bodies of sensory nerves. Sensory cell bodies are pseudo- Finally, show an impulse travel along the ventral unipolar because they contain a short axon with bipolar ramus and then up the white ramus to the paravertebral processes that pass both centrally and peripherally. Next, sympathetic ganglion. Th en, show it pass down the gray just distal to the dorsal root ganglion, indicate that the ramus back to the ventral ramus. From there, the impulse anterior and posterior roots join to form a mixed spinal disseminates along either the dorsal ramus or the ventral nerve, which then separates into dorsal and ventral rami. ramus.2 , 4 , 7 , 17 8. Spinal Canal and Muscle–Nerve Physiology 137

Paraspinal innervation Spinous process Lamina Transverse process Dorsal ramus Dorsal root Dorsal ganglion root Ant. horn Pedicle Spinal cell Sympathetic Gray nerve ganglion ramus Ventral root White ramus

Vertebral Ventral body ramus

Intercostal nerve

DRAWING 8-4 Nerve Roots & Rami 138 Neuroanatomy: Draw It to Know It

References 1 . B r u n i, J . E . & M o n t e m u r r o, D . G . Human neuroanatomy: a text, brain 10 . Nielsen , J. B., Crone , C. & Hultborn , H. Th e spinal pathophysiology atlas, and laboratory dissection guide (Oxford University Press, 2009 ). of spasticity — from a basic science point of view . Acta Physiol (Oxf) 2 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 189 , 171 – 180 (2007 ). clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). 11 . Siegel , A. & Sapru , H. N. Essential neuroscience, 2nd ed. (Wolters 3 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed., Plates Kluwer Health/Lippincott Williams & Wilkins, 2011 ). 4–7 (Novartis , 1997 ). 1 2. R o b i n s o n, A . J . & S n y d e r - M a c k l e r, L . Clinical electrophysiology: 4 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and electrotherapy and electrophysiologic testing, 3rd ed. (Wolters clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). Kluwer/Lippincott Williams & Wilkins, 2008 ). 5 . MacIntosh , B. R. , Gardiner , P. F. & McComas , A. J. Skeletal muscle: 13 . Pierrot-Deseilligny , E. & Burke , D. J. Th e circuitry of the human form and function, 2nd ed. (Human Kinetics, 2006 ). spinal cord: its role in motor control and movement disorders 6 . C o n n, P. M . Neuroscience in medicine, 3rd ed. (Humana Press, 2008 ). ( Cambridge University Press , 2005 ). 7 . Preston , D. C. & Shapiro , B. E. Electromyography and neuromuscular 1 4. K h u r a n a, I . Textbook of medical physiology (Elsevier , 2006 ). disorders: clinical-electrophysiologic correlations, 2nd ed. (Elsevier 1 5. E n o k a, R . M . Neuromechanics of human movement, 4th ed. Butterworth-Heinemann, 2005 ). (Human Kinetics, 2008 ). 8 . P e r o t t o, A . & D e l a g i, E . F. Anatomical guide for the electromyographer: 16 . DiGiovanna , E. L. , Schiowitz , S. & Dowling , D. J. An osteopathic the limbs and trunk, 4th ed. (Charles C Th omas, 2005 ). approach to diagnosis and treatment, 3rd ed. ( Lippincott Williams 9 . Mendell , J. R., Kissel , J. T. & Cornblath , D. R. Diagnosis and manage- and Wilkins , 2005 ). ment of peripheral nerve disorders ( Oxford University Press , 2001 ). 1 7. D e M y e r, W. Neuroanatomy, 2nd ed. ( Williams & Wilkins , 1998 ). 9 Brainstem Part One

Brainstem Composite — Axial View

The Midbrain

The Pons

The Medulla 140 Neuroanatomy: Draw It to Know It

Know-It Points

Brainstem Composite — Axial View

■ Th e axial plane of the brainstem divides from anterior ■ In the posterior tegmentum lie the cranial nerve to posterior into a basis, tegmentum, and tectum. nuclei and neurobehavioral cells. ■ Within the basis lie the corticopontine, ■ Additional tegmental structures are the reticular corticonuclear, and corticospinal tracts, and most of formation, supplementary motor and sensory tracts, the supplementary motor nuclei. and the brainstem auditory components. ■ In the anterior tegmentum lie the medial lemniscus, ■ Th e tectum is the roof of the brainstem and includes anterolateral system, and trigeminothalamic tracts. the superior and inferior colliculi.

The Midbrain

■ Th e substantia nigra contains dopaminergic nuclei; it ■ Th e central tegmental tract carries ascending reticular lies within the basis just posterior to the white matter fi bers to the rostral intralaminar nuclei of the pathways. thalamus as part of the ascending arousal system and ■ Th e superior cerebellar peduncle decussates in the descending fi bers from the red nucleus to the inferior central midbrain tegmentum in the inferior midbrain. olive as part of the triangle of Guillain-Mollaret. ■ Th e periaqueductal gray area contains opioids, which ■ Th e superior colliculi lie in the upper midbrain and function in pain suppression. are involved in visual function. ■ Th e reticular formation divides into lateral, medial, ■ Th e inferior colliculi lie in the lower midbrain and and median zones. are involved in auditory function. ■ Th e raphe nuclei populate the median zone of the reticular formation and are primarily serotinergic.

The Pons

■ Th e pontine nuclei send pontocerebellar tracts into ■ Th e cerebrospinal fl uid space of the pons is the fourth the cerebellum via the middle cerebellar peduncle as ventricle and the central gray area surrounds it. part of the corticopontocerebellar pathway. ■ Locus coeruleus nuclei are most heavily concentrated ■ Corticospinal tract fi bers descend through the in the pons and they are nearly entirely pontine basis. noradrenergic.

The Medulla

■ Th e descending corticospinal tract fi bers populate the ■ Th e olivary nuclei send climbing fi bers to the medullary pyramids. contralateral dentate nucleus of the cerebellum, ■ In the lower medulla, internal arcuate fi bers originate which projects back to the contralateral red nucleus from the gracile and cuneate nuclei and form the to complete the triangle of Guillain-Mollaret. great sensory decussation. ■ Along the anterior border of the fourth ventricle ■ Th e inferior olive receives tracts from the spinal cord (in its inferior fl oor) lies the area postrema. (from below) and from the red nucleus (from above). 9. Brainstem—Part One 141

FIGURE 9-1 Anterior aspect of brainstem, thalamus, and striatum. Used with permission from Woolsey, Th omas A., Joseph Hanaway, and Mokhtar H. Gado. Th e Brain Atlas: A Visual Guide to the Human Central Nervous System, 3rd ed. Hoboken, NJ: Wiley, 2008. 142 Neuroanatomy: Draw It to Know It

FIGURE 9-2 Posterior aspect of brainstem, thalamus, and striatum. Used with permission from Woolsey, Th omas A., Joseph Hanaway, and Mokhtar H. Gado. Th e Brain Atlas: A Visual Guide to the Human Central Nervous System, 3rd ed. Hoboken, NJ: Wiley, 2008. 9. Brainstem—Part One 143

FIGURE 9-3 Axial section through the midbrain: the sections are in radiographic orientation. Used with permission from Woolsey, Th omas A., Joseph Hanaway, and Mokhtar H. Gado. Th e Brain Atlas: A Visual Guide to the Human Central Nervous System, 3rd ed. Hoboken, NJ: Wiley, 2008. 144 Neuroanatomy: Draw It to Know It

FIGURE 9-4 Axial section through the pons: the sections are in radiographic orientation. Used with permission from Woolsey, Th omas A., Joseph Hanaway, and Mokhtar H. Gado. Th e Brain Atlas: A Visual Guide to the Human Central Nervous System, 3rd ed. Hoboken, NJ: Wiley, 2008. 9. Brainstem—Part One 145

FIGURE 9-5 Axial section through the medulla: the sections are in radiographic orientation. Used with permission from Woolsey, Th omas A., Joseph Hanaway, and Mokhtar H. Gado. Th e Brain Atlas: A Visual Guide to the Human Central Nervous System, 3rd ed. Hoboken, NJ: Wiley, 2008. FIGURE 9-6 Axial section through the midbrain: the section is in anatomic orientation. Used with permission from DeArmond, Stephen J., Madeline M. Fusco, and Maynard M. Dewey. Structure of the Human Brain: A Photographic Atlas, 3rd ed. New York: Oxford University Press, 1989.

FIGURE 9-7 Axial section through the inferior midbrain and high pons: the section is in anatomic orientation. Used with permission from DeArmond, Stephen J., Madeline M. Fusco, and Maynard M. Dewey. Structure of the Human Brain: A Photographic Atlas, 3rd ed. New York: Oxford University Press, 1989. 9. Brainstem—Part One 147

FIGURE 9-8 Axial section through the medulla: the section is in anatomic orientation. Used with permission from DeArmond, Stephen J., Madeline M. Fusco, and Maynard M. Dewey. Structure of the Human Brain: A Photographic Atlas, 3rd ed. New York: Oxford University Press, 1989. 148 Neuroanatomy: Draw It to Know It

Brainstem Composite — Axial View

Here, we will draw an axial composite of the brainstem: Moving posteriorly, label the supplementary motor a consolidation of the diff erent brainstem levels into a nuclei, which in the midbrain include the substantia single general organizational pattern. First, draw an nigra and red nucleus; in the pons, the pontine nuclei; ovoid outline of the brainstem. Th en, show the axes of and in the medulla, the inferior olive. Next, in the ante- our diagram: indicate that the anterior pole is at the rior tegmentum, label the medial lemniscus pathway — bottom of the page and that the posterior pole is at the the major large fi ber sensory pathway from the body. top and then show the anatomic left –right orientational Th en, lateral to it, label the anterolateral system pathway, plane. Next, label the left side of the page as nuclei and which, most notably, carries the spinothalamic tract— the right side of the page as tracts. the major small fi ber sensory pathway from the body. Now, divide the brainstem from anterior to posterior Next, posterior to the anterolateral system, label the into its basis, tegmentum, and tectum. Th e basis com- trigeminothalamic tracts, which carry sensory informa- prises descending white matter tracts and certain supple- tion from the face. mentary motor nuclei. Th e tegmentum is the central Now, in the posterior tegmentum, label the cranial bulk of the brainstem; it contains the cranial nerve nerve nuclei. Th e cell bodies for cranial nerves 3–10 and nuclei, neurobehavioral cells, ascending sensory tracts, cranial nerve 12 lie within the brainstem (cranial nerve additional supplementary motor nuclei, and the supple- 11 lies in the upper cervical spinal cord). Next, label the mentary motor and sensory tracts. Th e tectum is the neurobehavioral cells, which include the periaqueductal roof of the brainstem. In the midbrain, the tectum is gray area in the midbrain; the locus coeruleus in the the quadrigeminal plate, whereas in the pons and pons; and the raphe nuclei, which span much of the medulla, by at least one commonly held defi nition, the height of the midline brainstem. Th en, label the broad tectum is limited to the nonfunctioning medullary reticular formation in the tegmentum. velum. Note, however, that select authors include the Now, label the supplementary motor and sensory superior cerebellar peduncles as part of the pontine tracts, which include the medial longitudinal fasciculus tectum, as well.1–3 and tectospinal tracts, which run the midline height of Within the basis, show the ventral-lying corticofugal the brainstem, and the central tegmental and rubrospinal tracts, which comprise the eff erent fi ber tracts from the tracts. Next, label the brainstem auditory components, cerebral cortex; they include the corticopontine, corti- which are the cochlear nucleus, superior olivary nucleus, conuclear (aka corticobulbar), and corticospinal tracts. trapezoid body, inferior colliculus, and lateral lemniscus. Th e corticonuclear tracts peel off and synapse in target We address these components in detail in Drawing 14-4. nuclei as they descend the brainstem; the corticopontine Now, label the cerebrospinal fl uid space, which in the tracts synapse in the pontine basis; and the corticospinal midbrain is the cerebral aqueduct and in the pons and tracts pass through the medullary pyramids to reach medulla is the fourth ventricle. Lastly, label the cerebellar their targets in the spinal cord. peduncles: superior, middle, and inferior.1 – 11 9. Brainstem—Part One 149

NUCLEI TRACTS TECTUM CSF space Cerebellar Supplementary Cranial nerve nuclei peduncles motor & sensory Neurobehavioral tracts cells Auditory Trigemino- Auditory system system Reticular thalamic formation TEGMENTUM tracts Antero- lateral Medial system lemniscus

Supplementary motor nuclei Supplementary motor nuclei BASIS Corticofugal tracts Posterior Right Left Anterior

DRAWING 9-1 Brainstem Composite— Axial View 150 Neuroanatomy: Draw It to Know It

The Midbrain

Here, we will draw an anatomic, axial cross-section relationship to the red nucleus, rubral tremor can occur through the midbrain. First, show the anterior–posterior from injury to other brainstem areas, as well, and also and left –right axes of our diagram and then label the left from injury to the cerebellum and thalamus. side of the page as nuclei and the right side as tracts. Th en, Now, show that fi bers from the superior cerebellar label the basis, tegmentum, and tectum. Next, anteriorly, peduncle (the major outfl ow tract of the cerebellum) draw the bilateral crus cerebri. Divide the center of the decussate in the central midbrain tegmentum, and indi- crus into the corticonuclear tracts (aka corticobulbar cate that this decussation occurs in the inferior midbrain tracts), medially, and the corticospinal tracts, laterally. (below the level of the red nuclei). Injury to these cross- Next, in the most medial portion of the crus, draw the ing fi bers produces cerebellar ataxia on the side of the frontopontine tracts, and in the most lateral portion, body that the fi bers originated from (regardless of where draw the additional corticopontine tracts, which ema- they are injured along their path). For instance, whether nate from the occipital, parietal, and temporal cortices. it happens pre- or post-decussation, injury to superior Now, label the substantia nigra as the long stretch of cerebellar fi bers from the right cerebellum produces dopaminergic nuclei just posterior to the white matter ataxia on the right side of the body. pathways in the base of the midbrain. Loss of dopamin- Next, draw a red nucleus on the opposite side of the ergic cells in the dark, melanin-rich pars compacta divi- midbrain so we can see how its presence forces the sion of the substantia nigra results in Parkinson’s disease. ascending sensory pathways out laterally. Immediately Th e reddish, iron-rich, pars reticulata division of the lateral to the red nuclei, draw the medial lemniscus, and substantia nigra plays an important role in the direct and posterolateral to it, draw the anterolateral system. Next, indirect basal ganglia pathways (see Drawing 18-4). Th e along the posterior wall of the medial lemniscus, label substantia nigra helps initiate movement, and pathology the anterior trigeminothalamic tract (we draw the poste- to it, either from degeneration or injury, produces bra- rior trigeminothalamic tract later). Th en, along the pos- dykinesia, a slowness and stiff ness of movement. terolateral wall of the anterolateral system, label the Next, in the anterior aspect of the midbrain tegmen- lateral lemniscus. tum, draw the circular red nucleus just off midline. Th e Now, label the cerebral aqueduct as the small cerebro- red nuclei receive fi bers from both the motor cortex and spinal fl uid space in the dorsum of the midbrain. Th en, cerebellum. Each red nucleus connects with the ipsilat- label the surrounding periaqueductal gray area. Th e eral inferior olive as part of the triangle of Guillain- periaqueductal gray area is packed with neuropeptides, Mollaret (via the central tegmental tract), and each red monoamines, and amino acids, but it most notably con- nucleus also sends rubrospinal tract fi bers down the tains opioids, which help in pain suppression. Electrical brainstem and spinal cord to produce fl exion movements stimulation of the periaqueductal gray area to produce of the upper extremities (see Drawing 7-3). Make a nota- analgesia was fi rst attempted in the 1970s but has had tion that the red nuclei span the mid and upper mid- mixed results. Of note, the periaqueductal gray area brain. Injury in the vicinity of the red nucleus can receives ascending spinomesencephalic fi bers via the produce a low-frequency, coarse postural and action anterolateral system, which play a role in the emotional tremor on the contralateral side of the body, called a aspect of pain, and it receives descending fi bers from the rubral tremor. Despite its name, which suggests a close hypothalamus via the dorsal longitudinal fasciculus. 9. Brainstem—Part One 151

NUCLEI TRACTS Tectum Cerebral aqueduct AT = Ant. trigemino- Periaqueductal thalamic tract Tegmentum gray LL LL = Lateral lemniscus ALS = Antero- ALS lateral system AT Medial Basis lemniscus Superior cerebellar peduncle Red fiber decussation (Red Addl. nucleus (lower midbrain) nucleus) (mid-/upper cortico- midbrain) pontine tracts Substantia nigra Cortico- spinal (Crus tract cerebri) Cortico- Fronto- nuclear pontine tract Posterior tract Right Left Anterior

DRAWING 9-2 Th e Midbrain— Partial 152 Neuroanatomy: Draw It to Know It

The Midbrain (Cont.)

Periaqueductal gray area functions include far-reaching and 4 in the lateral midbrain, here, this is only because of modulation of sympathetic responses (ie, pupillary dilation the constraints of our diagram; they actually lie in the and cardiovascular responses); parasympathetic-induced midline midbrain, as shown more accurately in Chapters micturition; modulation of reproductive behavior; and 11 and 12. even aff ect locomotion and vocalization. However, its Next, let’s address the supplementary motor and sen- most widely recognized function is in pain modulation. sory fi ber tracts. In midline, just in front of the periaque- Next, in front of the periaqueductal gray area, label ductal gray area, label the medial longitudinal fasciculus, the reticular formation. Initially, the indistinct histology which plays an important role in conjugate horizontal of the reticular formation led people to believe it was eye movements (see Drawing 23-1). Th en, in the central, simply a “diff use arousal network,” but now the func- dorsal tegmentum, label the central tegmental tract. It tional specialization of the reticular formation is well carries ascending reticular fi bers to the rostral intralami- recognized. Th e reticular formation divides into lateral, nar nuclei of the thalamus as part of the ascending arousal medial, and median zones, and the raphe nuclei popu- system and descending fi bers from the red nucleus to the late the last — the median zone. Th e raphe nuclei are pri- inferior olive as part of the triangle of Guillain-Mollaret. marily serotinergic and are heavily modulated by Along the posterior wall of the central tegmental tract, label psychotropic medications. Th ey aff ect sleep–wake cycles, the posterior trigeminothalamic pathway: it originates in pain management, and motor activity but are most com- the upper pons and ascends through the midbrain. monly referenced for their role in mood disorders and Now, let’s draw the key contents of the tectum. First, the hallucinatory eff ects of illicit drugs. Th e raphe nuclei draw the colliculi, which divide into paired bilateral lie along much of the height of the midline brainstem as superior and inferior colliculi. Th e superior colliculi lie six separate subnuclei, which divide into rostral and caudal in the upper midbrain and are involved in visual func- nuclear groups based on whether they lie above or below tion and the inferior colliculi lie in the lower midbrain the mid-pons. Th e rostral raphe group (aka oral raphe and are involved in auditory function. Th en, draw the group) comprises the upper pontine and midbrain raphe posterior commissure. Th e pathway for the pupillary nuclei: the caudal linear, dorsal raphe, and median raphe light refl ex passes through the posterior commissure and nuclei. Th e caudal raphe group comprises the lower pon- the nucleus of the posterior commissure helps control tine and medullary raphe nuclei: the raphe magnus, raphe vertical eye movements. obscurus, and raphe pallidus nuclei. Note that additional Next, label the tectospinal tract just anterior to the serotinergic reticular formation areas are also categorized medial longitudinal fasciculus. Th e tectospinal tract as part of the raphe nuclei. Eff erent projections from the originates in the superior colliculus and decussates in the rostral raphe group mostly ascend into the upper brain- midbrain tegmentum and descends in front of the medial stem and forebrain, whereas projections from the caudal longitudinal fasciculus. Both the medial longitudinal raphe group primarily descend into the lower brainstem fasciculus and the tectospinal tract maintain their poste- and spinal cord. Aff erents to the raphe nuclei also exist, rior, midline position throughout the height of the which generally originate from behavioral brain areas.7 brainstem. Regional stimulation of the superior collicu- Now, label the presence of the cranial nerve 3 and 4 lus stimulates eff erent impulses through the tectobulbar nuclei and also a portion of the cranial nerve 5 nuclei— tract to the brainstem for eye movements and through subnuclei of cranial nerve 5 lie along the height of the the tectospinal tract to the upper cervical nuclei for visu- brainstem. Note that although we show cranial nerves 3 ally directed neck and head movements.1 – 11 9. Brainstem—Part One 153

NUCLEI TRACTS Colliculi: Posterior commissure MLF = Medial longitudinal Tectum superior fasiculus & inferior Cerebral aqueduct Post. trigemino- AT = Ant. trigeminothalamic tract Periaqueductal M thalamic tract Tegmentum gray L Central LL LL = Lateral lemniscus F tegmental ALS = Antero- *Cranial nerve Reticular Raphe ALS tract lateral system nuclei: 3, 4, (5) formation nuclei AT Tectospinal Medial tract Basis lemniscus Superior cerebellar peduncle Red fiber decussation (Red Addl. nucleus (lower midbrain) nucleus) (mid-/upper cortico- midbrain) pontine tracts Substantia nigra Cortico- spinal (Crus tract cerebri) Cortico- Fronto- nuclear pontine tract Posterior *Note: cranial nerves tract Right Left 3 & 4 lie in midline Anterior

DRAWING 9-3 Th e Midbrain— Complete 154 Neuroanatomy: Draw It to Know It

The Pons

Here, we will draw an anatomic, axial cross-section of Next, show that in the pons, the medial lemniscus lies the pons. First, show the axes of our diagram: indicate medially— unlike in the midbrain, where the red nuclei that the anterior pole is at the bottom of the page and push the medial lemniscus out laterally. Th en, lateral to that the posterior pole is at the top and then show the the medial lemniscus, draw the anterolateral system, and anatomic left –right orientational plane. Next, in the along the posterior wall of the medial lemniscus, draw opposite corner, draw a small axial pons section and sep- the anterior trigeminothalamic tract. arate the large basis from the comparatively small teg- Now, let’s show the supplementary motor and sensory mentum. For our main diagram, exclude the bulk of the tracts of the pontine tegmentum. Indicate that the basis to make room for the complexity of the tegmen- medial longitudinal fasciculus and the tectospinal tract tum. Next, label the left side of the page as nuclei and the continue to descend through the dorsal midline tegmen- right side as tracts. tum and that the central tegmental tract descends First, in the basis, draw the corticofugal tracts, which through the dorsal, central tegmentum. Also, include we pare down to the corticospinal and corticonuclear the rubrospinal tract just posterior to the anterolateral tracts because the corticopontine fi bers synapse within system. Now, label the cerebrospinal fl uid space of the the pons, itself. Draw the pontine nuclei within the pon- pons as the fourth ventricle and show that the central tine basis; the frontopontine and additional corticopon- gray area surrounds it. Next, label the locus coeruleus in tine fi bers synapse within these nuclei. Next, show that the posterior tegmentum, just in front of the central gray the pontine nuclei send pontocerebellar tracts into the area. cerebellum via the middle cerebellar peduncle (aka Although technically the locus coeruleus spans from brachium pontis) as part of the corticopontocerebellar the caudal end of the periaqueductal gray area in the pathway. lower midbrain to the facial nucleus in the mid-pons, Now, draw the inferior cerebellar peduncle, which locus coeruleus nuclei are most heavily concentrated in comprises the restiform and juxtarestiform bodies. the pons. Th e locus coeruleus nuclei are nearly entirely Spinocerebellar, reticulocerebellar, and olivocerebellar noradrenergic and, thus, are far more uniform in their fi bers pass through the restiform body, whereas the jux- neurotransmitter makeup than the periaqueductal gray tarestiform body is primarily reserved for fi bers that pass area and even more uniform than the raphe nuclei, which between the vestibular nucleus and vestibulocerebel- are mostly serotinergic. lum.8 Next, show that the superior cerebellar peduncle Next, label the reticular formation and raphe nuclei (aka brachium conjunctivum) lies posterior to the infe- and then label the nuclei of cranial nerves 5, 6, 7, and rior cerebellar peduncle. Th e middle and inferior cere- 8 in the dorsal pontine tegmentum. Cranial nerves 6 and bellar peduncles are the main infl ow pathways into the 7 lie within the mid to low pons; cranial nerve 8 lies cerebellum and the superior cerebellar peduncle is the within both the pons and medulla; and portions of cra- main outfl ow pathway. Th e superior cerebellar peduncle nial nerve 5 lie along the height of the brainstem. Again, attaches to the upper pons and midbrain; the middle note that our diagram does not refl ect the medial-lateral cerebellar peduncle attaches to the pons and extends to position of the cranial nerve nuclei. Next, draw the the pontomedullary junction; and the inferior cerebellar pontine components of the auditory system: the lateral peduncle attaches to the lower pons and medulla. Now, lemniscus in the lateral tegmentum and the trapezoid draw the anterior spinocerebellar fi bers in the postero- body and superior olivary nucleus in the anterolateral lateral pons; the other spinocerebellar pathways enter tegmentum. 1 – 11 the cerebellum below the pons through the inferior cerebellar peduncle (see Drawing 7-5). 9. Brainstem—Part One 155

NUCLEI TRACTS Superior cerebellar *Position of cranial nuclei Inferior peduncle NOT accurately depicted cerebellar Middle 4th ventricle peduncle cerebellar peduncle TEGMENTUM Medial Locus Central gray Central tegmental longitudinal *Cranial nerve nuclei: coeruleus area tract Ant. spino (5), 6, 7, (8) fasciculus cerebellar Reticular Rubrospinal tract Superior Tectospinal formation Raphe tract olivary nuc. tract nuclei Trapezoid Medial lemniscus body Lateral Ant. trigemino- Antero- lemniscus thalamic tract lateral system BASIS

Pontocerebellar fibers Pontine Corticonuclear Corticospinal nuclei tracts Tegmentum tracts Posterior Basis Right Left Anterior

DRAWING 9-4 Th e P o n s 156 Neuroanatomy: Draw It to Know It

The Medulla

Here, we will draw an anatomic, axial cross-section of cerebellum, which projects back to the contralateral red the medulla. First, show the axes of our diagram: indi- nucleus to complete the triangle of Guillain-Mollaret. cate that the anterior pole is at the bottom of the page Now, let’s focus on the lateral wall of the medulla. and that the posterior pole is at the top and then show First, posterior to the inferior olive, draw the anterolat- the anatomic left –right orientational plane. Next, on eral system. At the medullary level, the anterolateral one side, label the nuclei and, on the other, the tracts. system contains many ascending sensory pathways in Now, draw an outline of the medulla. Show that the bulk addition to the spinothalamic fi bers, including the spino- of the medulla is tegmentum and that the basis is reserved reticular, spinomesencephalic, and spinotectal pathways. for the descending corticospinal tract fi bers, which pop- It also carries spino-olivary and spinovestibular fi bers, ulate the medullary pyramids. Most of the classes of cor- which disperse within the medulla, itself. Next, poste- ticofugal fi bers (corticonuclear and corticopontine) rior to the anterolateral system, draw the spinocerebellar synapse above or at the level of the medulla; the only tracts: both the anterior and posterior spinocerebellar corticofugal pathway within the medulla is the corti- pathways are found within the medulla. Th en, medial to cospinal tract. the anterolateral system and spinocerebellar tracts, label Now, let’s draw the large fi ber sensory system. In the the rubrospinal tract. dorsal medulla, label the gracile nucleus, medially, and Now, draw the other main supplementary pathways: the cuneate nucleus, laterally; they receive the ascending the medial longitudinal fasciculus in the posterior mid- gracile and cuneate posterior column tracts from the line and the tectospinal tract anterior to it (the anterior- spinal cord. Th en, draw the medial lemniscus tract along posterior and medial-lateral positions of these pathways the midline of the medulla and indicate that in the lower remain roughly unchanged throughout their course medulla, internal arcuate fi bers decussate from the grac- through the brainstem). Next, along the outer, posterior ile and cuneate nuclei to the opposite side of the medulla wall of the medulla, label the inferior cerebellar peduncle. in what is referred to as the great sensory decussation Now, indicate that the fourth ventricle is the cerebrospi- (see Drawing 10-1). Next, along the outside of the medial nal fl uid space of most of the medulla. A small tissue fold, lemniscus, label the anterior trigeminothalamic tract. called the obex, exists where the fourth ventricle funnels We fi nd anterior trigeminothalamic projections through- inferiorly into the central canal. At the rostral–caudal out the brainstem because the anterior trigeminotha- level of the obex lies the gracile tubercle— the swelling lamic tract is formed from fi bers of the spinal trigeminal formed by the gracile nucleus in the posterior wall of the nucleus, which extends inferiorly into the upper cervical medulla. Along the anterior border of fourth ventricle spinal cord. On the contrary, fi bers from the posterior (in its inferior fl oor) label the area postrema, which is an trigeminothalamic tracts originate and ascend from the important chemoreceptor trigger zone for emesis (vom- principal sensory nucleus in the pons, so no posterior iting). Next, indicate that the central gray area surrounds trigeminothalamic tract fi bers are found within the the fourth ventricle. Th en, show that within the central medulla. medullary tegmentum lies the reticular formation, in the Next, label the inferior olive (aka inferior olivary median zone of which lies the raphe nuclei. complex), which comprises the main inferior olivary Lastly, label the nuclei of cranial nerves 5, 8, 9, 10, and nucleus and the accessory olivary nuclei. Th e inferior 12 in the dorsal medulla. Again, note that our diagram olive receives many diff erent fi ber pathways, including does not refl ect the medial-lateral position of the cranial tracts from the spinal cord (from below) and from the nerve nuclei. Th e cochlear nucleus of cranial nerve 8 red nucleus (from above). Th e inferior olive sends climb- represents the medulla’s contribution to the auditory ing fi bers to the contralateral dentate nucleus of the system. 1 – 11 9. Brainstem—Part One 157

NUCLEIArea 4th ventricle TRACTS postrema Inferior cerebellar peduncle Tegmentum Gracile Central gray Medial Cuneate Nucleus area nucleus longitudinal fasciculus Spinocerebellar *Cranial nerve Reticular Raphe Tecto- tracts nuclei: formation nuclei spinal Rubrospinal (5), (8), tract tract 9, 10, 12 Internal arcuate fibers Antero- lateral Anterior system Medial trigemino- lemniscus thalamic tract

Inferior olive

(Pyramid) Corticospinal tracts

Posterior Base Pyramidal decussation *Position of cranial nuclei Right Left NOT accurately depicted Anterior

DRAWING 9-5 Th e Medulla 158 Neuroanatomy: Draw It to Know It

References 1 . Campbell , William, W. , DeJong , Russell N. , Haerer , Armin F. 6 . D e M y e r, W. Neuroanatomy, 2nd ed. ( Williams & Wilkins , 1998 ). DeJong's Th e Neurologic Examination, 6th ed., Chapter 11 7 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and ( Lippincott, Williams, & Wilkins , 2005 ). clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). 2 . Jinkins , J. R. Atlas of Neuroradiologic Embryology, Anatomy, & 8 . Jacobson , S. & Marcus , E. M. Neuroanatomy for the neuroscientist Variants, Chapter 2H ( Lippincott, Williams, & Wilkins , 2000 ). (Springer , 2008 ). 3 . Arslan , O . Neuroanatomical Basis of Clinical Neurology, Chapter 4 9 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human (Parthenon Publishing, 2001 ). brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal 4 . Baehr , M. , Frotscher , M. & Duus , P. Duus’ topical diagnosis in structure, vascularization and 3D sectional anatomy ( Springer , 2009 ). neurology: anatomy, physiology, signs, symptoms, 4th completely 10 . Paxinos , G. & Mai , J. K. Th e human nervous system, 2nd ed. rev. ed., Chapter 3 (Th ieme, 2005 ). (Elsevier Academic Press, 2004 ). 5 . B o g o u s s l a v s k y, J . & C a p l a n, L . R . Stroke syndromes, 2nd ed. 1 1. N o b a c k, C . R . Th e human nervous system: structure and function, ( Cambridge University Press , 2001 ). 6th ed. (Humana Press, 2005 ). 1 0 Brainstem Part Two

Major Sensory Projections

Major Motor Projections

Midbrain Syndromes ( Advanced )

Pontine Syndromes ( Advanced )

Medullary Syndromes ( Advanced ) 160 Neuroanatomy: Draw It to Know It

Know-It Points

Major Sensory Projections

■ Th e leg fi bers of the medial lemniscus originate in ■ Th e arm and leg fi bers project to the ventroposterior the gracile nucleus of the medulla. lateral thalamic nucleus. ■ Th e arm fi bers of the medial lemniscus originate in ■ Th e facial fi bers project to the ventroposterior medial the cuneate nucleus of the medulla. thalamic nucleus. ■ Th e gracile nucleus lies medial to the cuneate nucleus. ■ Th e leg, arm, and face fi bers project from medial to ■ Within the internal arcuate decussation, the leg fi bers lateral along the posterior paracentral gyrus and shift anterior to the arm fi bers. p o s t c e n t r a l g y r u s . ■ As the medial lemniscus ascends the brainstem, the arm fi bers shift medial to the leg fi bers.

Major Motor Projections

■ Th e leg, arm, and face fi bers originate from medial ■ Th e motor fi ber arrangement in the brainstem, from to lateral along the anterior paracentral gyrus and medial to lateral, is the face, arm, and leg fi bers. precentral gyrus. ■ During the corticospinal tract decussation at the ■ Th e descending fi bers bundle in the internal medullo-cervical junction, the arm and leg fi bers shift capsule from anterior to posterior as face, arm, so that despite the decussation, the arm fi bers remain and leg fi bers. medial to the leg fi b e r s .

Midbrain Syndromes (Advanced )

■ Weber’s syndrome results from injury to the ■ Benedikt’s syndrome is a syndrome of ipsilateral third paramedian midbrain. nerve palsy and contralateral choreiform movements. ■ Weber’s syndrome is a syndrome of ipsilateral ■ Claude’s syndrome results from injury to the post- third nerve palsy and contralateral face and body decussation superior cerebellar fi bers and weakness. neighboring third nerve fi bers. ■ Benedikt’s syndrome results from injury to the red ■ Claude’s syndrome is a syndrome of ipsilateral third nucleus and neighboring third nerve fi bers. nerve palsy and contralateral ataxia.

Pontine Syndromes (Advanced )

■ Locked-in syndrome results from injury to the – Destruction of the paramedian pontine reticular pontine basis and ventral paramedian pontine formation (the PPRF) tegmentum. – Spared third nerve innervation of the levator palpebrae ■ In locked-in syndrome, there is: ■ Dysarthria-clumsy hand syndrome is due to restricted – Damage to the descending corticospinal and paramedian pontine injury. corticonuclear tracts ■ Dysarthria-clumsy hand syndrome is a syndrome of – Preservation of most of the reticular formation contralateral face and upper extremity weakness with – Destruction of the exiting facial motor nerve fi bers preserved lower extremity strength. 10. Brainstem—Part Two 161

Medullary Syndromes (Advanced )

■ Wallenberg’s syndrome results from lateral medullary – Th e hypothalamospinal tract injury; it most commonly occurs from a posterior – Th e vestibular nucleus inferior cerebellar artery territory infarct. ■ Dejerine’s syndrome results from injury to the ■ In Wallenberg’s syndrome, there is injury to: midline medulla. – Th e inferior cerebellar peduncle ■ In Dejerine’s syndrome, there is injury to the – Th e spinal trigeminal tract and nucleus hypoglossal nucleus, medial lemniscus tract, and – Th e anterolateral system (spinothalamic tract) medullary pyramid. – Th e nucleus ambiguus 162 Neuroanatomy: Draw It to Know It

Major Sensory Projections

Th ere are three main somatosensory pathways within anterior–posterior: the leg fi bers go from medial to ante- the brainstem: the medial lemniscus tract, the spinotha- rior and the arm fi bers go from lateral to posterior. Post- lamic tract of the anterolateral system, and the trigemi- decussation, these fi bers bundle as the medial lemniscus nothalamic tract. Th e medial lemniscus carries input tract. from the large sensory fi bers from the body, which Next, show that as the medial lemniscus ascends transmit vibration, two-point discrimination, and joint the pons and midbrain, it fl ips back to medial–lateral position sensory information. Th e spinothalamic tract orientation but with the arm fi bers medial, leg fi bers lat- carries input from the small sensory fi bers from the body, eral. Indicate that within the thalamus, the body fi bers which transmit pain, itch, and thermal sensory informa- (arms and legs) project to the ventroposterior lateral tion. Th e trigeminothalamic tract projects sensory infor- nucleus and the facial fi bers project to the ventroposte- mation from the face. All three pathways ascend the rior medial nucleus. Next, draw the twisting thalamo- brainstem separately and then bundle within the ventro- cortical sensory projections to the cerebral cortex. In posterior thalamus before they project to the somatosen- their ascent, the sensory fi bers again reverse their orien- sory cortex. Th e position of the spinothalamic tract is tation: the leg fi bers project medially to terminate in the largely unchanged throughout its spinal cord and brain- posterior paracentral gyrus, the arm fi bers project lateral stem ascent, so we will not draw it here, and we draw the to the legs and terminate in the upper convexity of the trigeminothalamic tracts in detail where we discuss the postcentral gyrus, and the facial fi bers project lateral to trigeminal nucleus, itself (see Drawing 13-3), so we will both of them and terminate in the lower lateral postcen- not draw them here either. Here, we will focus on the tral gyrus. medial lemniscus tract; specifi cally, we will draw the ori- Now, demonstrate this multi-step rotational ascent gins of the medial lemniscus tract in the gracile and with your hand for easy reference. Place your right hand cuneate nuclei, the internal arcuate decussation of the in front of you, palm down, with your fi ngers pointing to gracile and cuneate projection fi bers, the medial lemnis- your right. Your thumb represents the leg fi bers and your cus brainstem ascent, and the thalamocortical projec- little fi nger represents the arm fi bers. To demonstrate the tions to the parietal lobe. decussation of the internal arcuate fi bers, move your First, draw the lower medulla and show that the hand across midline and bring it in towards you. In the leg fi bers of the medial lemniscus tract originate in the process, rotate your hand into anterior–posterior orien- gracile nucleus in the posteromedial medulla and, then, tation with your little fi nger behind your thumb: arm that the arm fi bers of the medial lemniscus tract origi- fi bers posterior to leg fi bers. Next, to demonstrate the nate in the cuneate nucleus in the posterolateral medulla. orientation reversal that occurs during the medial lem- Th e gracile nucleus receives aff erents from the spinal niscus ascent to the thalamus, rotate your hand back into cord posterior column gracile tract and the cuneate medial–lateral orientation (the little fi nger [the arm] is nucleus receives aff erents from the posterior column medial and the thumb [the leg] is lateral) and simultane- cuneate tract. Next, indicate that the gracile and cuneate ously raise it. Th en, to demonstrate the thalamocortical fi bers decussate (ie, cross midline) as internal arcuate projection to the somatosensory cortex, twist your hand fi bers in the lower medulla; in the process, they rotate over so that the thumb (the leg) is medial and the little their somatotopic orientation from medial–lateral to fi nger (the arm) is lateral. 1 – 6 10. Brainstem—Part Two 163

Arms Legs

Face

Cerebrum Legs Arms Face Legs Thalamus Arms

Gracile (legs) Cuneate Midbrain Legs Arms (arms) Arms Internal Legs arcuate Pons

Medulla

DRAWING 10-1 Major Sensory Projections 164 Neuroanatomy: Draw It to Know It

Major Motor Projections

Here, let’s draw the corticonuclear and corticospinal motor they are called lateral corticospinal tract fi bers due to fi ber descent through the brainstem. Most of the motor their position in the lateral spinal cord. Th e remaining fi bers originate in parallel to the sensory fi bers just in front fi bers travel ipsilaterally through the anteromedial spinal of the central sulcus in the precentral gyrus and anterior cord as the anterior corticospinal tract and remain paracentral gyrus, from lateral to medial as the face, arm, uncrossed as they leave the brainstem. Th ese fi bers and leg fi bers. Show the origins of the diff erent somatomo- descend the spinal cord through the anterior funiculus, tor fi bers: the facial fi bers in the lateral cortex, the arm and when they reach the level of their target neuron, fi bers in the upper convexity, and the leg fi bers in the para- they cross within the anterior commissure. 1 G e n e r a l l y , central frontal lobe. Draw the twisting descent of each lateral corticospinal tract fi bers innervate distal muscula- fi ber group through the subcortical white matter. Th e ture for fi ne motor movements, whereas anterior corti- facial fi bers descend medially, the leg fi bers descend later- cospinal tract fi bers innervate proximal musculature for ally, and the arm fi bers descend in between the two. Show gross motor movements. these descending fi bers bundle in the internal capsule and With our drawing complete, let’s demonstrate the pass into the ipsilateral cerebral peduncle in the midbrain. rotation and descent of the motor fi bers with our hand. Next, show that the motor fi ber arrangement in the During the sensory fi ber demonstration, we used our midbrain, from medial to lateral, is as follows: face, arm, thumb as the leg fi bers and our little fi nger as the arm and leg. Th e facial fi bers are called corticonuclear fi bers fi bers; let’s use the same representation here. We begin (aka corticobulbar fi bers) and they synapse on diff erent where we ended our sensory fi ber rotation — in the cere- cranial nerve nuclei throughout their descent. Th e arm bral cortex with our hand turned palm towards us and and leg fi bers form the corticospinal tract. In the pons, as our arm across our body. To demonstrate the twist and the motor fi bers descend through the pontine nuclei, the bundling of the motor fi bers as they descend through face, arm, and leg fi bers maintain their same orientation. the subcortical white matter and into the internal cap- Show that they are positioned as follows, from medial to sule, lower your hand and turn it over (palm away lateral: face, arm, and leg. At the most inferior level of from you) as you bring your fi ngers together. Your pinky the medulla, by defi nition, the corticonuclear fi bers have (the arm fi bers) should be medial to your thumb (the completed their descent, so only the arm and leg corti- leg fi bers). To demonstrate the motor fi ber descent cospinal fi bers are found; they descend through the base through the brainstem, simply continue to drop your of the medulla in the ipsilateral medullary pyramid: hand. Now, we need to demonstrate the pyramidal indicate that the arms are still medial to the legs. decussation at the medullo-cervical junction and the As the corticospinal tract descends through the second twist of the corticospinal fi bers. Th is rotation is medullo-cervical junction, show it decussate and shift important because it keeps the leg fi bers lateral to the posterolaterally to enter the lateral funiculus of the cervi- arm fi bers when the corticospinal tract crosses midline cal spinal cord. Indicate that during the decussation, the in the upper cervical cord. For this step, bring your hand arm and leg fi bers twist so that the arms remain medial across midline and turn your palm back towards you so to the legs. Seventy-fi ve to ninety percent of the corti- that your thumb is lateral and your little fi nger is medial cospinal fi bers undergo the aforementioned decussation; when your hand crosses midline.1 – 6 10. Brainstem—Part Two 165

Legs Arms

Face Internal capsule

Cerebrum Legs Arms Face Midbrain

Legs Arms Face

Pons Legs Arms

Medulla Arms Legs

Cervico- medullary junction

DRAWING 10-2 Major Motor Projections 166 Neuroanatomy: Draw It to Know It

Midbrain Syndromes (Advanced )

Case I Patient presents with sudden onset of double vision and the corticonuclear and corticospinal tracts responsible right-side weakness. Exam reveals left eye third nerve for face, arm, and leg strength on the opposite side of the ophthalmoplegia with impaired pupillary constriction body (the right side). Now, encircle the paramedian and also right face, arm, and leg weakness. midbrain, which is involved in Weber’s syndrome: a syn- Draw an axial section through the midbrain. Th en, drome of ipsilateral third nerve palsy and contralateral draw the left -side oculomotor nucleus and its exiting third face and body weakness.2 , 3 , 5 , 7 , 8 nerve. Next, label the left -side crus cerebri: it encompasses

Case II Patient presents with sudden onset of double vision and through the rostral midbrain. To keep track of the ros- right-side involuntary movements. Exam reveals left eye tral–caudal plane, draw a sagittal brainstem and include third nerve ophthalmoplegia with impaired pupillary the superior colliculus in the rostral midbrain and also constriction and also right-side choreiform movements. the red nucleus. Draw an axial section through the midbrain. Next, Now, in the axial diagram, encircle the red nucleus and draw the left -side oculomotor nucleus and its exiting neighboring third nerve. Show that both are involved in third nerve. Th en, label the left red nucleus. Label the Benedikt’s syndrome: a syndrome of ipsilateral third nerve superior colliculus to show that this axial section is palsy and contralateral choreiform movements.2 , 3 , 5 , 7 – 9

Case III Patient presents with double vision and right-side inco- fi bers exit the pons, ascend the brainstem, and decussate ordination. Exam reveals left eye third nerve ophthal- in the caudal midbrain beneath the red nuclei. moplegia with impaired pupillary constriction and also Now, encircle the post-decussation superior cerebel- right-side ataxia. lar fi bers and neighboring third nerve. Injury to these Draw an axial section through the midbrain. Next, two structures produces Claude’s syndrome: a syndrome draw the left -side oculomotor nucleus and its exiting third of ipsilateral third nerve palsy and contralateral ataxia. nerve. Th en, show that the superior cerebellar peduncle Note that the superior cerebellar peduncle fi bers form a fi bers exit the right cerebellum and decussate in the mid- compact bundle along the dorsolateral wall of the fourth brain. Now, label the inferior colliculus in the axial dia- ventricle in the pons, and then decussate at the level of gram to establish that our section is in the caudal midbrain, the inferior colliculus. We discuss the superior cerebellar and also do so in the sagittal brainstem diagram, as well. decussation again as part of the corticopontocerebellar In the sagittal diagram, show that the superior cerebellar pathway in Drawing 15-7.2 , 3 , 5 , 7 , 8 , 10 – 13 10. Brainstem—Part Two 167

Superior colliculus

3rd nerve 3rd nerve

Red nucleus

Crus cerebri

Weber’s syndrome Benedikt’s syndrome

Superior Inferior colliculus cerebellar Superior colliculus Red nucleus peduncle 3rd nerve Inferior colliculus Decussation Superior cerebellar peduncle

Claude’s syndrome Sagittal brainstem

DRAWING 10-3 Midbrain Syndromes 168 Neuroanatomy: Draw It to Know It

Pontine Syndromes (Advanced )

Case I Patient is found in an apparent comatose state. Exam tegmentum. Th en, show the medial longitudinal fascic- reveals normal pupil reactivity, normal vertical eye move- ulus (MLF) in the contralateral dorsal tegmentum. ments, volitional blinks, complete bilateral face and Indicate that the PPRF stimulates the abducens nucleus, body paralysis, normal sleep–wake states, and an absent which sends eff erent nerve fi bers through the medial gag refl ex. pons to produce ipsilateral eye abduction. Th en, also First, draw an axial section through the pons and show that the abducens nucleus sends ascending establish the anterior–posterior plane of orientation; interneuronal fi bers up the contralateral MLF, which this is an axial, anatomic view of the pons, with the ante- innervate the oculomotor nucleus and cause the ipsilat- rior surface of the brainstem at the bottom of the page eral eye (the eye contralateral to the abducens nucleus) and the posterior surface at the top. Th en, separate the to adduct. Paralysis of horizontal eye movements in this basis from the tegmentum. Next, in the basis, draw the case results from destruction of the PPRF; note that scattered descending corticonuclear (aka corticobulbar) although most of the reticular formation is spared, this and corticospinal tracts. Paralysis of the body and of the small portion is injured. Volitional vertical eye move- lower cranial nerves (tongue movements, gag, and swal- ments are spared because the center for volitional verti- low) results from damage to the descending corticospi- cal eye movements lies within the midbrain (above the nal and corticonuclear tracts. level of the lesion). Next, draw the reticular formation in the pontine teg- Th e patient’s ability to blink results from the ability mentum; the normal sleep–wake states are maintained to elevate and retract the upper eyelids through spared because the majority of the reticular formation is spared. third nerve innervation of the levator palpebrae and Now, draw the abducens nucleus of cranial nerve 6. through third nerve relaxation, which passively closes And then draw the facial nucleus of cranial nerve 7 and the eyelids. Orbicularis oculi is required for forced eyelid show that cranial nerve 7 forms an internal genu around closure; it is innervated by the facial nerve, which is the abducens nucleus, which creates a bump in the fl oor injured in this syndrome. of the fourth ventricle, called the facial colliculus. Finally, encircle the pontine basis and ventral parame- Paralysis of the face results from destruction of the exit- dian pontine tegmentum and indicate that injury here ing facial motor nerve fi bers. Th e facial nucleus, itself, produces the aforementioned constellation of symptoms, lies within the dorsal pons and is spared. called locked-in syndrome. In locked-in syndrome, the Next, show the pontine circuitry for horizontal eye pontine basis and ventral tegmentum are injured, causing movements. First draw the paramedian pontine reticular devastating paralysis, which is oft en misperceived as coma formation (PPRF) in the paramedian ventral pontine when in reality consciousness is preserved.2 , 3 , 5 , 7 , 8 , 14 – 16

Case II Patient presents with slurred speech and clumsiness of separate the basis from the tegmentum. Indicate that within the right hand. Exam reveals impaired smile on the right; the basis of the pons, from medial to lateral, lie the face, dysarthria; dysphagia; loss of fi ne motor movements in arm, and leg fi bers. Encircle the face and arm fi bers and the right hand; and mild weakness of the right arm with show that injury here results in dysarthria-clumsy hand normal right leg strength. syndrome: a syndrome of contralateral face and upper Draw another axial section through the pons and estab- extremity weakness with preserved lower extremity strength lish the anatomic right–left planes of orientation. Now, due to restricted paramedian pontine injury.2 , 3 , 5 , 7 , 8 , 12 , 15 , 17 10. Brainstem—Part Two 169

4th ventricle Reticular 6 MLF formation 7 Tegmentum Posterior Basis Right Left PPRF Anterior

CrN 7 Corticobulbar CrN 6 & corticospinal tracts

4th ventricle

Locked-in syndrome

Face Arm Leg

Dysarthria-clumsy hand syndrome

DRAWING 10-4 Pontine Syndromes 170 Neuroanatomy: Draw It to Know It

Medullary Syndromes (Advanced )

Case I Patient presents with dizziness, incoordination, double Now, show that the hoarseness and dysphagia is mostly vision, trouble swallowing, sensory disturbance, and from involvement of the left nucleus ambiguus. Next, pupillary asymmetry. Exam reveals left -side cerebellar show that the left -side Horner’s syndrome is from injury ataxia; loss of pain and temperature sensation in the left to descending hypothalamospinal tract fi bers on the left . face; loss of pain and temperature sensation on the right Indicate that the descending hypothalamospinal fi bers side of the body; left -side Horner’s syndrome (ptosis, are believed to lie ventral to the solitary tract; injury to anhidrosis, and miosis); dysarthria and impaired gag the solitary tract, itself, produces taste disturbance. refl ex; ocular skew with the left eye lower than the right; Next, show that the ocular skew deviation — the left and right-beating nystagmus (slow phase to the left , fast eye being more inferior that the right, and the right-beat- phase to the right). ing nystagmus (slow phase to the left ) — results from Draw the left half of the medulla and defi ne the planes injury to the left vestibular nucleus and cerebellar system. of the diagram. Th is is an axial, anatomic view of the To understand the nystagmus, point your index fi ngers medulla with the anterior surface of the brainstem at the toward midline to demonstrate the tonic drive that each bottom of the page and the posterior surface at the top. side of the medulla places on the eyes. Th en drop your First, show that the left cerebellar ataxia results from left hand to indicate a left medullary lesion: the right injury to the left inferior cerebellar peduncle. Next, show side now forces the eyes to the left , which is the slow that the loss of sensation on the left side of the face results phase. Th e direction of the nystagmus, itself, refers to the from spinal trigeminal tract and nucleus involvement. fast phase: the right-beating compensatory mechanisms Th en, show that the loss of pain and temperature sensa- that respond to the slow phase. tion on the right side of the body is from injury to the Encircle the aforementioned structures; injury to this anterolateral system bundle (spinothalamic fi bers) on lateral medullary region is called Wallenberg’s syndrome. the left . Note that this case represents the classic pattern Wallenberg’s syndrome most commonly occurs from a of sensory loss for this injury type but depending on the posterior inferior cerebellar artery territory infarct rostral-caudal level of the lesion, variation in sensory loss caused by a branch occlusion of a vertebral artery. As a exists; most notably, the facial sensory loss can occur fi nal note, through not fully determined pathophysio- contralaterally or bilaterally rather than ipsilaterally (as logic mechanisms, hiccups are also commonly encoun- shown here). tered in Wallenberg’s syndrome.2 , 3 , 5 , 7 , 8 , 18 – 23

Case II Patient presents with dysarthria, right-side weakness, side large fi ber sensory defi cit is from injury to the left and sensory disturbance. Exam reveals dysarthric speech; medial lemniscus tract; and that the right side weakness right hemibody loss of vibration and proprioception is from injury to the left medullary pyramid. Encircle sensation; and right arm and leg weakness. And with these structures and label this syndrome as Dejerine’s tongue protrusion, there is tongue deviation to the left . syndrome, which results from injury to the medial Facial sensation and facial strength is spared. medulla.2 , 3 , 5 , 7 , 8 , 24 – 26 Show that the dysarthria and tongue deviation result from injury to the left hypoglossal nucleus; that the right 10. Brainstem—Part Two 171

Solitary Hypoglossal Inferior cerebellar tract Wallenberg’s nucleus Vestibular peduncle nucleus syndrome Hypothalamo- spinal fibers Spinal trigeminal tract & nucleus Dejerine’s Nucleus syndrome ambiguus Medial Anterolateral lemniscus system

Posterior Pyramid Right Left Anterior

DRAWING 10-5 Medullary Syndromes 172 Neuroanatomy: Draw It to Know It

References 1 . Baehr , M. , Frotscher , M. & Duus , P. Duus’ topical diagnosis in 1 5. S c h m a h m a n n, J . D ., K o, R . & M a c M o r e, J . Th e human basis pontis: neurology: anatomy, physiology, signs, symptoms, 4th completely rev. motor syndromes and topographic organization . Brain 127 , ed., Chapter 3 (Th ieme, 2005 ). 1269 – 1291 (2004 ). 2 . D e M y e r, W. Neuroanatomy, 2nd ed. ( Williams & Wilkins , 1998 ). 16 . Al-Sardar , H. & Grabau , W. Locked-in syndrome caused by basilar 3 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and artery ectasia. Age Ageing 31 , 481 – 482 (2002 ). clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). 17 . Arboix , A. , et al . Clinical study of 35 patients with dysarthria- 4 . Jacobson , S. & Marcus , E. M. Neuroanatomy for the neuroscientist clumsy hand syndrome . J Neurol Neurosurg Psychiatry 75 , 231 – 234 (Springer , 2008 ). (2004 ). 5 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human 1 8. F u r m a n, J . M . a . C ., S t e p h e n P. Vestibular disorders: a case-study brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal approach, 2nd ed. ( Oxford University Press , 2003 ). structure, vascularization and 3D sectional anatomy (S p r i n g e r, 19 . Walsh , F. B., Hoyt , W. F. & Miller , N. R. Walsh and Hoyt’s clinical 2009 ). neuro-ophthalmology: the essentials, 2nd ed. ( Lippincott Williams & 6 . Paxinos , G. & Mai , J. K. Th e human nervous system, 2nd ed. Wilkins, 2008 ). (Elsevier Academic Press, 2004 ). 20 . Brodsky , M. C. , Donahue , S. P. , Vaphiades , M. & Brandt , T. Skew 7 . B o g o u s s l a v s k y, J . & C a p l a n, L . R . Stroke syndromes, 2nd ed. deviation revisited. Surv Ophthalmol 51 , 105 – 128 ( 2006 ). ( Cambridge University Press , 2001 ). 21 . Cerrato , P. , et al . Restricted dissociated sensory loss in a patient 8 . Roach , E. S. , Toole , J. F. , Bettermann , K. & Biller , J. Tool e’s with a lateral medullary syndrome: A clinical-MRI study. Stroke 3 1, cerebrovascular disorders, 6th ed. ( Cambridge University Press , 3064 – 3066 (2000 ). 2010 ). 22 . Kim , J. S. Pure lateral medullary infarction: clinical-radiological 9 . Vidailhet , M. , et al. Dopaminergic dysfunction in midbrain correlation of 130 acute, consecutive patients . Brain 126 , dystonia: anatomoclinical study using 3-dimensional magnetic 1864– 1872 (2003 ). resonance imaging and fl uorodopa F 18 positron emission 23 . Zhang , S. Q., Liu , M. Y., Wan , B. & Zheng , H. M. Contralateral tomography. Arch Neurol 56 , 982 – 989 (1999 ). body half hypalgesia in a patient with lateral medullary infarction: 10 . Coppola , R. J. Localization of Claude’s syndrome. Neurology 5 8, atypical Wallenberg syndrome . Eur Neurol 59 , 211 – 215 (2008 ). 1707 ; author reply 1707-1708 (2002 ). 24 . Kim , J. S., et al. Medial medullary infarction: abnormal ocular 11 . Seo , S. W. , et al . Localization of Claude’s syndrome . Neurology 5 7, motor fi ndings. Neurology 65 , 1294 – 1298 (2005 ). 2304 – 2307 (2001 ). 2 5. N a n d h a g o p a l, R ., K r i s h n a m o o r t h y, S . G . & S r i n i v a s, D . 12 . Querol-Pascual , M. R. Clinical approach to brainstem lesions. Neurological picture. Medial medullary infarction . J Neurol Semin Ultrasound CT MR 31 , 220 – 229 (2010 ). Neurosurg Psychiatry 77 , 215 (2006 ). 1 3. A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 26 . Nakajima , M. , Inoue , M. & Sakai , Y. Contralateral pharyngeal atlas , 2nd ed. ( Lange Medical Books/McGraw-Hill , 2005 ). paralysis caused by medial medullary infarction . J Neurol Neurosurg 14 . Lim , H. S. & Tong , H. I. Locked-in syndrome— a report of three Psychiatry 76 , 1292 – 1293 (2005 ). cases . Singapore Med J 19 , 166 – 168 (1978 ). 1 1 Cranial and Spinal Nerve Overview and Skull Base

Spinal & Cranial Nerve Origins

Spinal & Cranial Nuclear Classiﬁ cation

Cranial Nerve Nuclei

Cranial Nerve Nuclei ( Simpliﬁ ed )

Skull Base

Skull Foramina

Cavernous Sinus 174 Neuroanatomy: Draw It to Know It

Know-It Points

Spinal & Cranial Nerve Origins

■ Th e trilaminar developing embryo contains ■ An artery and nerve pair corresponds to each ectoderm, mesoderm, and endoderm. somite segment, and wherever the products of ■ Th e neural crests are neural tube derivatives that give that somite go, the nerve and artery pair follows. rise to, amongst other things, the peripheral nervous ■ Th e sulcus limitans separates the basal and alar plates. system. ■ Th e basal plates, which produce the ventral roots, ■ Sclerotome diff erentiates into bone; dermatome house motor cell columns. derives the dermis; the myotomal masses derive ■ Th e alar plates, which receive the dorsal roots, house skeletal muscle. s e n s o r y c e l l c o l u m n s .

Spinal & Cranial Nuclear Classiﬁ cation

■ In the spinal cord: ■ In the brainstem: – Th e general somatic aff erent column lies in the – Th e general somatic eff erent column lies medial to posterior horn. the general visceral eff erent column. – Th e general somatic eff erent column lies in the – Th e general visceral aff erent column lies medial to the anterior horn. general somatic aff erent column. – Th e general visceral aff erent column lies in the – Within the upper medulla, the special somatic posterior intermediate horn. aff erent column spans the width of the alar plate. – Th e general visceral eff erent column lies in the – Th e special visceral cell columns hug the sulcus anterior intermediate horn. l i m i t a n s .

Cranial Nerve Nuclei

■ Th e somatomotor set is nearly exclusively general ■ Th e somatomotor set lies in midline and comprises somatic eff erent, but it also includes a single general cranial nerves 3, 4, 6, 12, and 11. visceral eff erent nucleus. ■ Th e solely special sensory set comprises cranial nerves ■ Th e solely special sensory set is exclusively special 1, 2, and 8. somatic aff erent. ■ Th e pharyngeal arch set comprises cranial nerves 5, 7, ■ Th e pharyngeal arch derivatives contain all of the cell 9, and 10. column types except for the general somatic eff erent and special somatic aff erent cell columns. 11. Cranial and Spinal Nerve Overview and Skull Base 175

Skull Base

■ Th e anterior cranial fossa comprises the frontal bone, ■ Th e basal portions of the temporal lobes lie within ethmoid bone, jugum sphenoidale, and lesser wing of the middle cranial fossae. the sphenoid bone. ■ Th e posterior cranial fossa comprises the posterior ■ Th e basal portions of the frontal lobes lie within portion of the petrous bone, the occipital bone, and anterior cranial fossae. the clivus. ■ Th e middle cranial fossa comprises the greater wing ■ Th e cerebellum and brainstem lie within the of the sphenoid bone, a portion of the squamous posterior cranial fossae. temporal bone, a portion of the petrous temporal ■ Th e occipital and parietal lobes lie superior to the bone, and the sella turcica of the sphenoid bone. plane of the skull base.

Skull Foramina

■ Th e foramina of the cribriform plate of the ethmoid ■ Th e third division of the trigeminal nerve (the bone contain the olfactory nerve bundles (cranial mandibular nerve [5(3)]) traverses foramen ovale. nerve 1). ■ Th e facial nerve (cranial nerve 7) and ■ Th e optic nerve (cranial nerve 2) traverses the optic vestibulocochlear nerve (cranial nerve 8) pass canal. through the internal acoustic meatus. ■ Th e oculomotor, trochlear, and abducens nerves ■ Th e glossopharyngeal nerve (cranial nerve 9), vagus (cranial nerves 3, 4, and 6, respectively) and the fi rst nerve (cranial nerve 10), and spinal accessory nerve division of the trigeminal nerve (the ophthalmic (cranial nerve 11) pass through the jugular foramen. nerve [5(1)]) pass through the superior orbital ■ Th e hypoglossal nerve (cranial nerve 12) passes fi ssure. through the hypoglossal canal. ■ Th e second division of the trigeminal nerve ■ Th e spinal accessory nerve enters the cranium (the maxillary nerve [5(2)]) traverses foramen through the foramen magnum (and exits through the rotundum. jugular foramen).

Cavernous Sinus

■ Th e cavernous sinus is a major venous confl uence ■ Within the medial aspect of the cavernous sinus lies with many venous communications. the internal carotid artery. ■ Along the lateral wall of the cavernous sinus, from ■ Th e posterolateral cavernous sinus dura forms the superior to inferior, lie cranial nerves 3 and 4 and the medial upper third of Meckel’s cave, which envelops fi rst and second divisions of cranial nerve 5. the trigeminal ganglion. ■ Medial to the fi rst division of cranial nerve 5 lies cranial nerve 6. 176 Neuroanatomy: Draw It to Know It

A 1 Neural plate Open neuroepithelium

Mesoderm Notochordal plate Closing neuroepithelium Neural groove 2

Somite

Closed neuroepithelium Spinal canal Neural tube

Notochord

B GW3.0 C GW3.0 BRAIN VESICLES Lip of neural groove

Neural groove Open neuroepithelium

Otic placode

SPINAL CORD Closing neuroepithelium

Closed neuroepithelium

Somites

Open neuroepithelium

Posterior neuropore

FIGURE 11-1 A. Axial section through the developing embryo and B. Neural tube model and axial section. Used with permission from Altman, Joseph, and Shirley A. Bayer. Development of the Human Spinal Cord: An Interpretation Based on Experimental Studies in Animals . Oxford; New York: Oxford University Press, 2001. 11. Cranial and Spinal Nerve Overview and Skull Base 177

Inner and outer laminae of compact bone

Frontal crest Diploe Cribriform plate Foramen cecum (ethmoid bone) Groove made by Crista galli meningeal artery

Orbital plate of Anterior cranial fossa frontal bone

Sphenoid bone

Optic canal Sella turcica Foramen rotundum Superior orbital fissure Anterior clinoid process Posterior clinoid process

Middle cranial fossa Foramen ovale Foramen spinosum Internal acoustic meatus Foramen lacerum

Jugular foramen Clivus

Hypoglossal canal Foramen magnum

Posterior cranial fossa

Internal occipital Internal occipital protuberance crest

FIGURE 11-2 Th e skull base. Used with permission from Bruni, J. E. & Montemurro, D. G. Human Neuroanatomy: A Text, Brain Atlas, and Laboratory Dissection Guide. New York: Oxford University Press, 2009. 178 Neuroanatomy: Draw It to Know It

Spinal & Cranial Nerve Origins

To understand the origins of the spinal and cranial nerves, it sclerotome: the sclerotome diff erentiates into bone. we will draw the developing embryo. First, draw a coro- Indicate that the sclerotome around the notochord nal section through the dorsal half of the embryo. Label becomes vertebral bone. Next, draw another arrow dor- the outer layer as the ectoderm; it derives the epidermis sally to the surface of the embryo and label it dermatome, and neuroectoderm. Th en, draw endoderm at the bottom which derives the dermis: the skin layer underlying the of the diagram; it comprises most of the ventral half of epidermis. Th en, direct the last arrow laterally to the the embryo and it forms the gut and respiratory contents myotomal masses, which derive skeletal muscle. of the developing embryo. Next, draw the notochord and An artery and nerve pair corresponds to each somite indicate that it is mesoderm-derived. We have thus estab- segment, and wherever the products of that somite go, lished the three main layers of the trilaminar developing the nerve and artery pair follows. Th is is the anatomic embryo: the ectoderm, mesoderm, and endoderm. basis of how we systematically assess dermatomal and Th e developing embryo forms around the notochord myotomal levels during the neurologic exam. From the and the notochord eventually degenerates into the jelly- peripheral distribution of the defi cit, we localize the like substance of the intervertebral discs, called nucleus rostral–caudal level of the lesion. pulposus. If the notochord persists in its primitive state, With that embryogenesis as a background, let’s take it is considered chordoma— notochord tumor. Th e a closer look at the origin of the cranial and spinal notochord induces the overlying ectoderm to develop nerves. Separate the tissue within the neural tube into a into the neural plate. Its neural folds then invaginate to ventral-lying basal plate and a dorsal-lying alar plate. become the oval-shaped neural tube, which has a long, Along the horizontal meridian, label the sulcus limitans: narrow cerebrospinal fl uid space in its center, and, as a small sulcus, which cuts into the lateral walls of the mentioned, is ectoderm-derived. We will draw the details central-lying cerebrospinal fl uid space and separates of the neural tube later. the basal and alar plates. Somite nerve pairs emanate Dorsolateral to the neural tube, draw the neural crests, from these neural plates as nerve roots: the ventral roots which are neural tube derivatives that give rise to, carry motor fi bers and the dorsal roots carry sensory amongst other things, the peripheral nervous system. fi bers (in accordance with the law of Bell and Magendie). Next, draw somite tissue masses lateral to the notochord; Th is ventral–dorsal functional division applies to the they, like the notochord, are mesoderm-derived. Th e neural tube, as well. Th e basal plates, which produce the neural crest cells and somite tissue masses develop early ventral roots, house motor cell columns, and the alar in embryogenesis and the somite masses derive scleroto- plates, which receive sensory roots, house sensory cell mal, myotomal, and dermatomal cells. We will include columns. Th e ventral–motor/dorsal–sensory division the somites in our diagram along with their derivatives, that exists early in embryogenesis in the neural tube per- albeit an anachronism, for simplicity. sists throughout development. Th is division provides Draw three arrows from one of the somite masses the basis for the organization of the spinal and cranial as follows. Direct one to the notochord and label nerves. 1 – 4 11. Cranial and Spinal Nerve Overview and Skull Base 179

Neural crests: neural tube-derived Ectoderm

Dermatome Neural tube: ectoderm-derived

Alar plate Somite: Sulcus mesoderm- Limitans derived Basal plate

Myotome Sclerotome

Notochord: mesoderm-derived, becomes vertebrae

Endoderm

DRAWING 11-1 Spinal & Cranial Nerve Origins 180 Neuroanatomy: Draw It to Know It

Spinal & Cranial Nuclear Classiﬁ cation

Here, we will draw the spinal neurons and the brainstem the head and neck. Th e pharyngeal arches produce cra- cranial nerve nuclei in axial view. Draw an axial cross- nial nerve, arterial, and musculoskeletal derivatives.5 section through the spinal cord. First, divide the spinal Now, let’s draw the cranial nuclear columns of the cord gray matter into alar (sensory) and basal (motor) brainstem. Draw one side of an axial brainstem compos- plates. Th en, divide the gray matter into three anatomic ite: a compression of all three brainstem levels. Divide it horns: posterior, intermediate, and anterior. Now, label from posterior to anterior into tectum, tegmentum, and the cell columns: general somatic aff erent in the poste- basis. Th e cranial nuclear cell columns lie within the rior horn, general somatic eff erent in the anterior horn, dorsal tegmentum, just in front of the cerebrospinal fl uid general visceral aff erent in the posterior intermediate space. Next, label the sulcus limitans in the fourth ventri- horn, and general visceral eff erent in the anterior inter- cle; it separates the eff erent from the aff erent cell columns. mediate horn. Now, begin with the cranial homologues of the spinal Next, let’s draw the cranial nerve nuclear cell columns. nerves: in the basal plate, from medial to lateral, draw the Th ey share the same general layout as the spinal neurons general somatic eff erent and general visceral eff erent cell but have two key anatomic diff erences. One diff erence is columns, and in the alar plate, from medial to lateral, that in the brainstem, the posterior-lying alar plate shift s draw the general visceral aff erent and general somatic laterally to make room for the fourth ventricle; there- aff erent cell columns. Next, include the special somatic fore, all of the cranial nerve nuclei end up oriented along aff erent column; within the upper medulla, its constella- the horizontal axis of the dorsal brainstem tegmentum. tion of subnuclei spans the width of the alar plate. Now, To understand this shift , imagine opening an orange — we need to address the special visceral cell columns, both the dorsum of the orange swings out laterally. A second of which hug the sulcus limitans. Draw the special visceral diff erence between the brainstem cell columns and the eff erent cell column in the space between the general vis- spinal cord is that the brainstem involves additional cell ceral eff erent cell column and the sulcus limitans. Th en, columns— the special visceral eff erent and aff erent cell join the special visceral aff erent cell column with the gen- columns and the special somatic aff erent cell column. eral visceral aff erent column in the medial alar plate. Th e special visceral cell columns are part of the pharyn- Note that some texts substitute the word “somatic” geal arch (aka branchial arch) cranial nerve derivatives, with the word "sensory" when referring to the general which appear early in embryogenesis as bar-like ridges somatic aff erent and special somatic aff erent columns that contain the ectoderm, endoderm, and mesoderm and refer to them, instead, as the general sensory and that form the skeletal tissue, musculature, and linings of special sensory aff erent columns. 6 , 7 11. Cranial and Spinal Nerve Overview and Skull Base 181

SPINAL CORD BRAINSTEM Tectum Sulcus limitans GSA Posterior SSA SVA GVA GSA horn GSE GVE SVE

ALAR GVA Intermediate horn Tegmentum BASAL GVE

GSE Anterior horn

Basis

GSE - General Somatic Efferent GSA - General Somatic Afferent GVE - General Visceral Efferent GVA - General Visceral Afferent SVE - Special Visceral Efferent SSA - Special Somatic Afferent SVA - Special Visceral Afferent

DRAWING 11-2 Spinal & Cranial Nuclear Classifi c a t i o n 182 Neuroanatomy: Draw It to Know It

Cranial Nerve Nuclei

Here, we will draw the organization of the cranial nerve your tongue using cranial nerve 12; and shrug your nuclei in coronal view. Draw a coronal section through shoulders using cranial nerve 11. Notice that these move- the brainstem and upper cervical spinal cord and mark ments involve midline muscles, which helps us remem- the boundaries of the midbrain, pons, and medulla. ber that the general somatic eff erent cell column lies near Th en, denote the sulcus limitans, which divides the to midline. brainstem into basal and alar plates. Along the top of Now, in the general somatic eff erent column, in the brainstem, list the positions of the cell columns. At descending order, draw the nuclei of the somatomotor the medial end of the basal plate (ie, at the midline of the set. Label the oculomotor nucleus of cranial nerve 3 (the brainstem), label the general somatic eff erent column; oculomotor nerve): it extends from the upper to the lateral to it, label the general visceral eff erent column; lower midbrain, spanning the height of the superior col- continuing laterally, label the special visceral eff erent liculus and reaching the level of the inferior colliculus. column; then, label the combined general visceral aff er- Th en, underneath the oculomotor nucleus, label the tro- ent and special visceral aff erent columns; then, label the chlear nucleus of cranial nerve 4 (the trochlear nerve): it special somatic aff erent column; and fi nally, label the is a small nucleus that lies in the caudal midbrain at the general somatic aff erent column. level of the inferior colliculus. Next, label the abducens We organize the cranial nerves into three groups of nucleus of cranial nerve 6 (the abducens nerve): it spans nerves: the somatomotor (aka somitic), solely special from the mid to the lower pons. Now, show the hypo- sensory, and pharyngeal arch derivatives. Each of the dif- glossal nucleus of cranial nerve 12 (the hypoglossal ferent cranial nerve sets involves various populations of nerve), which spans most of the height of the medulla. cell columns. Th e somatomotor set is nearly exclusively Th en, label the accessory nucleus of cranial nerve 11 (the general somatic eff erent, but also includes a single gen- accessory nerve) in the upper cervical spinal cord: it eral visceral eff erent nucleus; the solely special sensory spans the fi rst fi ve cervical spinal cord levels. set is exclusively special somatic aff erent; and the pha- Next, in the general visceral eff erent cell column, draw ryngeal arch derivatives contain all of the cell column the Edinger–Westphal nucleus of cranial nerve 3 (the types except for the general somatic eff erent and special oculomotor nerve), which lies in the rostral midbrain. somatic aff erent cells. Note that although we distinguish this nucleus from the Begin with the somatomotor set. It lies in midline oculomotor nucleus, it is actually a rostral subnucleus of and comprises cranial nerves 3, 4, 6, 12, and 11. Th e the oculomotor complex, which comprises all of the somatomotor set is considered the brainstem extension nuclei of cranial nerve 3. of the spinal neurons because it innervates somite tissue Now, we will draw the solely special sensory set, which derivatives. However, whereas the spinal neurons con- comprises cranial nerves 1, 2, and 8, all of which are tain general somatic eff erent and aff erent and general purely sensory. Cranial nerve 1 is involved in olfaction, visceral eff erent and aff erent cells, the somatomotor cra- cranial nerve 2 in vision, and cranial nerve 8 in vestibular nial nerve set comprises only general somatic eff erent and auditory function. Only cranial nerve 8 resides cells and a single general visceral eff erent nucleus— the within the brainstem. Cranial nerve 1 comprises tiny Edinger–Westphal nucleus. To demonstrate the actions nerve fi laments that traverse the cribriform plate, and of the somatomotor cranial nerve set, move your eyes in cranial nerve 2 is the set of optic nerves that run under- all directions using cranial nerves 3, 4, and 6; protrude neath the base of the brain. 11. Cranial and Spinal Nerve Overview and Skull Base 183

Abducens PONS nucleus, Vestibulo- CrN 6 cochlear nucleus, CrN 8

Hypoglossal nucleus, MEDULLA CrN 12

Accessory CERVICAL nucleus, SPINAL CrN 11 CORD

DRAWING 11-3 Cranial Nerve Nuclei— Partial 184 Neuroanatomy: Draw It to Know It

Cranial Nerve Nuclei (Cont.)

Next, in the special somatic aff erent column, label the cell column. Indicate that the superior salivatory nucleus vestibulocochlear nucleus of cranial nerve 8 (the vestib- of cranial nerve 7 (the facial nerve) is a small nucleus that ulocochlear nerve), which spans from the upper pons to sits at the inferior border of the pons. Th en, underneath the mid-medulla. Although not shown as such, here, the superior salivatory nucleus, show that the inferior within the upper medulla, its constellation of subnuclei salivatory nucleus of cranial nerve 9 (the glossopharyn- spans the width of the alar plate: from the sulcus limi- geal nerve) is a small nucleus in the upper medulla. Now, tans to the lateral edge of the brainstem. underneath the inferior salivatory nucleus, draw the Now, let’s draw the pharyngeal arch set, which com- dorsal motor nucleus of the vagus nerve, cranial nerve prises the remaining cranial nerve nuclei: cranial nerves 10, as spanning from the inferior salivatory nucleus to 5, 7, 9, and 10. According to the simplest, most common the bottom of the medulla. defi nition, the fi rst pharyngeal arch derives cranial nerve Next, let’s draw the special visceral eff erent cell 5, the second pharyngeal arch derives cranial nerve 7, column. Begin with the motor trigeminal nucleus of cra- the third pharyngeal arch derives cranial nerve 9, and nial nerve 5 (the trigeminal nerve) in the upper pons. the fourth and sixth pharyngeal arches derive cranial Th en, draw the facial nucleus of cranial nerve 7 (the nerve 10. Charles Judson Herrick's early 1900s observa- facial nerve), which spans from the lower pons to the tions about the role of these cranial nerves in the gill pontomedullary junction. Next, draw the nucleus arches of fi sh provides insight into their purpose in ambiguus of cranial nerves 9 and 10, which spans the humans. Fish use these nerves to coordinate jaw move- height of the medulla. Note that the nucleus ambiguus ments that pump water across their gills for oxygen trans- actually has both special visceral and general visceral fer. In humans, oxygen transfer occurs in the lungs, so we eff erent components. use the special visceral eff erent component of these cra- Now, turn to the sensory cells in the alar plate. Begin nial nerves, instead, for other purposes, including chew- with the combined special and general visceral aff erent ing (cranial nerve 5), facial expression (cranial nerve 7), cell column; draw the solitary tract nucleus of cranial and speaking and swallowing (cranial nerves 9 and 10). nerves 7, 9, and 10, which spans the height of the Taste is carried by special visceral aff erents of cranial medulla. Th en, move to the general somatic aff erent cell nerve 7 from the anterior two thirds of the tongue and column at the lateral end of the alar plate; draw the three by cranial nerves 9 and 10 from the posterior one third subnuclei of the trigeminal nucleus: the mesencephalic of the tongue and the epiglottis, respectively. Facial sen- trigeminal nucleus, which spans from the midbrain to sation is mostly carried by cranial nerve 5, but it is also the upper pons; the principal sensory trigeminal nucleus, carried by cranial nerves 7, 9, and 10, to a lesser extent. which is restricted to the upper pons; and the spinal Finally, cranial nerves 7, 9, and 10 also provide parasym- trigeminal nucleus, which spans from the upper pons to pathetic innervation to the glands and viscera of the face the upper cervical spinal cord. Cranial nerve 5 contrib- and thoracoabdomen. utes to all three subdivisions of the trigeminal nucleus, Now, let’s draw the nuclei of the pharyngeal arch and cranial nerves 7, 9, and 10 help supply the spinal set. Start with the nuclei of the general visceral eff erent trigeminal nucleus, only. 3 , 4 , 6 – 12 11. Cranial and Spinal Nerve Overview and Skull Base 185

General General Special Sulcus Special General Special General MIDLINE somatic visceral visceral limitans visceral visceral somatic somatic efferent efferent efferent afferent afferent afferent afferent Oculomotor Edinger- MIDBRAIN nucleus, Westphal CrN 3 nucleus, Mesencephalic trigeminal Trochlear CrN 3 nucleus, CrN 5 nucleus, Motor CrN 4 trigeminal Principal nucleus, sensory Abducens CrN 5 trigeminal PONS nucleus, Facial Vestibulo- nucleus, CrN 5 CrN 6 nucleus, cochlear Sup. salivatory nuc. CrN 7 Spinal CrN 7 nucleus, trigeminal CrN 8 Inf. salivatory nuc. CrN 9 nucleus, Dorsal Solitary CrNs 5, 7, Hypoglossal motor Nucleus tract 9, & 10 nucleus, nucleus ambiguus, nucleus, MEDULLA CrN 12 of the CrNs 9 &10 CrNs 7, 9, vagus, &10 CrN 10 Accessory CERVICAL nucleus, SPINAL CrN 11 CORD

DRAWING 11-4 Cranial Nerve Nuclei— Complete 186 Neuroanatomy: Draw It to Know It

Cranial Nerve Nuclei (Simpliﬁ ed)

Here, we will consolidate the cranial nerve nuclei into a show that it receives additional aff erent innervation simple diagram we can recall at the bedside. Note that from cranial nerves 7, 9, and 10. this compression is not a depiction of the complete cra- Th e cranial nuclei are numbered by their rostral– nial nerve nuclei but instead provides an easy way to caudal positions as they exit the base of the brain. Cranial remember the relative positions of the cranial nerves. nerve 1 lies rostral to 2, 2 to 3, 3 to 4, and so on. Th e only Draw another coronal brainstem. Across the top, use the exception is cranial nerve 11, which originates from sulcus limitans to divide the brainstem into a medial, below cranial nerve 12. One way to recall this rostral– motor division and a lateral, sensory division. Th en caudal organization is to imagine that you are a primor- divide the rostral–caudal axis of the brainstem into the dial fi sh swimming through the great sea. First, you midbrain, pons, and medulla. Along the medial half of smell food (cranial nerve 1, the olfactory nerve); then, the motor division, draw the cranial nerve nucleus of cra- you visualize it (cranial nerve 2, the optic nerve); next, nial nerve 3 in the rostral midbrain, 4 in the caudal mid- you fi x your eyes on it, for which you use your extra- brain, 6 in the mid- to lower pons, 12 spanning the height ocular eye muscles — innervated by cranial nerve 3 (the of the medulla, and 11 in the cervical spinal cord. In the oculomotor nerve), cranial nerve 4 (the trochlear nerve), lateral motor area, draw the eff erent cranial nerve nucleus and cranial nerve 6 (the abducens nerve); you chew the of cranial nerve 5 in the rostral pons, 7 in the caudal food using cranial nerve 5 (the trigeminal nerve) and pons, and 9 and 10 spanning the height of the medulla. then taste it and smile using cranial nerve 7 (the facial Next, in the medial sensory region, draw the aff erent nerve). Th en, you listen for predators with cranial nerve cranial nerve nuclei of cranial nerves 7, 9, and 10 span- 8 (the vestibulocochlear nerve) while you swallow the ning the height of the medulla. Th en, draw the cranial meal with cranial nerves 9 (the glossopharyngeal nerve) nerve nucleus of cranial nerve 8 from the pons into the and 10 (the vagus nerve); you lick your lips with cranial medulla. Next, at the lateral edge of the brainstem, show nerve 12 (the hypoglossal nerve); and toss your head that the aff erent nucleus of cranial nerve 5 spans from from side to side with cranial nerve 11 (the accessory the midbrain to the upper cervical spinal cord, and also nerve). 3 , 4 , 6 – 12 11. Cranial and Spinal Nerve Overview and Skull Base 187

SULCUS MIDLINE MOTORLIMITANS SENSORY

3 MIDBRAIN

5 6 PONS 7 8 5

12 9 & 10 7, 9, & 10 MEDULLA 7, 9, & 10

11 CERVICAL SPINAL CORD

DRAWING 11-5 Cranial Nerve Nuclei (Simplifi ed) 188 Neuroanatomy: Draw It to Know It

Skull Base

Here, we will draw the skull base in axial view. Draw an Now, let’s draw a sagittal section of the skull to illus- outline of one half of an axial view of the skull base and trate how the peaks and valleys within the skull base form label its anterior one third as the frontal bone. Next, in diff erent fossae. Draw a downward-sloping line with two midline, demarcate the ethmoid bone, which comprises peaks. Label the anterior depression as the anterior cra- the steeply peaked crista galli and the surrounding cribri- nial fossa, the middle depression as the middle cranial form plate. Th en, posterior to the frontal bone, draw the fossa, and the posterior depression as the posterior cra- sphenoid bone, which subdivides into a body and lesser nial fossa. 1 and greater wings. First, label the midline portion of the Next, let’s defi ne the borders of these fossae in our sphenoid bone as the sphenoid body. Show that it subdi- axial diagram. First, let’s include the major peaks within vides into the jugum sphenoidale, anteriorly, and the the skull base (the fossae comprise the valleys between sella turcica, posteriorly. Th e posterior end of the mid- these peaks). Dot a line along the lesser wing of the sphe- line sphenoid bone and the neighboring anterior occipi- noid bone. Anterior to it, label the anterior cranial fossa, tal bone (drawn later), together, form the clivus. Now, which comprises the frontal bone, ethmoid bone, jugum draw the sphenoid wings. Label the lesser wing, anteri- sphenoidale, and lesser wing of the sphenoid bone — the orly, and the greater wing, posteriorly. Topographically, basal portions of the frontal lobes lie within this fossa. the lesser sphenoid wing angles up over the greater sphe- Next, dot a diagonal line through the petrous temporal noid wing, which rolls downward. Label the protuber- bone. Indicate that the middle cranial fossa lies between ance along the posteromedial ridge of the lesser wing as the lesser wing of the sphenoid bone and the petrous the anterior clinoid process, an important anatomic ridge of the temporal bone. Th e middle cranial fossa landmark. comprises the greater wing of the sphenoid bone, a por- Next, draw the temporal bone posterior to the greater tion of the squamous temporal bone, a portion of the wing of the sphenoid bone. Label the squamous part, petrous temporal bone, and the sella turcica of the sphe- laterally, and the petrous part, medially. Th e squamous noid bone— the basal portions of the temporal lobes lie part makes up the bulk of the external surface of the tem- within this fossa. Lastly, posterior to the petrous ridge, poral bone, whereas the petrous part makes up the bulk label the posterior cranial fossa, which comprises the of the internal surface. Next, posteromedial to the tem- posterior portion of the petrous bone, the occipital bone, poral bone, draw the occipital bone; it extends back to and the clivus— the cerebellum and brainstem lie within the occiput. In the anterior one third of the occipital this fossa. Note that the occipital and parietal lobes lie bone, draw the foramen magnum, which is the entry superior to the plane of the skull base.13 zone of the brainstem. Now, label the combined anterior Next, we will draw the foramina of the skull base. occipital bone and posterior sphenoid bone as the clivus, Skull base injuries and diseases present with unique pat- which is steeply sloped. Next, along the lateral edge of terns of neurologic defi cit, so we need a good under- the skull base, label the parietal bone. Th e parietal bones standing of the skull foramina and their neurovascular make up much of the lateral and superior surfaces of the contents to diagnose the various presentations of skull skull. base injury.3 , 4 , 6 , 13 , 14 11. Cranial and Spinal Nerve Overview and Skull Base 189

Sphenoid Lesser wing of the body sphenoid bone Frontal bone Ethmoid Anterior bone Anterior clinoid process cranial Greater wing of Jugum fossa Anterior the sphenoid bone Middile Middle cranial Sella cranial Squamous cranial fossa turcica fossa part fossa Posterior Clivus Petrous Posterior cranial part cranial fossa Tenporal fossa bone Foramen magnum SKULL BASE - SAGITTAL VIEW

Parietal bone Occipital bone

SKULL BASE - AXIAL VIEW

DRAWING 11-6 Skull Base 190 Neuroanatomy: Draw It to Know It

Skull Foramina

Here, we will draw the skull foramina. First, draw the think of the “Star Wars” character R2D2 , whose round anterior half of the skull base in axial view; include the head and name (R2D2 ) should serve as a helpful mne- following topographic landmarks: the frontal bone, eth- monic. Note that within the mandible is foramen moid bone, lesser wing of the sphenoid bone (include its mentum, which houses the distal mandibular nerve anterior clinoid process), and the ridge of the petrous branch — the mental nerve, which provides sensory cov- portion of the temporal bone. Next, we will label the erage to the mentum (the chin). Lastly, indicate that major neurovascular structures and cranial nerves that foramen spinosum contains the meningeal branch of the pass through the foramina; we will denote the cranial mandibular nerve (aka nervus spinosus) and also the nerves in brackets. Show that the foramina of the cribri- middle meningeal artery— injury to this vessel can lead form plate of the ethmoid bone contain the olfactory to intracranial epidural hematoma.9 , 16 nerve bundles (cranial nerve 1). Next, medial to the Now, draw the posterior surface of the skull base in anterior clinoid process, label the optic canal and lateral axial view; include the posterior extension of the petrous to it label the superior orbital fi ssure. Show that the optic ridge and the foramen magnum as topographic land- nerve (cranial nerve 2) traverses the optic canal and marks. 17 First, along the petrous apex, draw the internal that the oculomotor, trochlear, and abducens nerves acoustic meatus. Indicate that both the facial nerve (cra- (cranial nerves 3, 4, and 6, respectively) and the fi rst divi- nial nerve 7) and vestibulocochlear nerve (cranial nerve sion of the trigeminal nerve (the ophthalmic nerve 8) and the internal auditory artery (aka labyrinthine [5(1)]) pass through the superior orbital fi ssure. Next, artery) pass through the internal acoustic meatus. Next, show that the ophthalmic artery traverses the optic canal below the internal acoustic meatus, draw the jugular and that the superior ophthalmic vein passes through foramen, which lies at the border of the temporal and the superior orbital fi ssure. Th e ophthalmic artery is a occipital bones. Show that the glossopharyngeal nerve direct branch of the internal carotid artery, which tra- (cranial nerve 9), vagus nerve (cranial nerve 10), and verses the carotid canal; indicate that the carotid canal spinal accessory nerve (cranial nerve 11) pass through lies along the petrous ridge. Note that adjacent to the the jugular foramen; and also show that the internal jug- carotid canal is the foramen lacerum, which the internal ular vein passes through the jugular foramen— it receives carotid artery runs above in its lacerum segment (see the sigmoid sinus and inferior petrosal sinus.18 N o w , Drawing 11-8 ). 15 along the foramen magnum, label the hypoglossal canal Next, posterior to the superior orbital fi ssure, within and show that both the hypoglossal nerve (cranial nerve the greater wing of the sphenoid bone, from anterior to 12) and also a venous plexus pass through the hypoglos- posterior, label foramen rotundum, foramen ovale, and sal canal. Th en, indicate that in addition to traversing the foramen spinosum. Indicate that the second division of jugular foramen, the spinal accessory nerve also runs the trigeminal nerve (the maxillary nerve [5(2)]) tra- through foramen magnum; it originates in the cervical verses foramen rotundum and that the third division of spinal cord, passes up through foramen magnum, and the trigeminal nerve (the mandibular nerve [5(3)]) tra- then passes out of the cranium through the jugular fora- verses foramen ovale. To remember that foramen rotun- men. Finally, indicate that the vertebral arteries and dum houses the second division of the trigeminal nerve, spinal vessels traverse the foramen magnum as well.3 , 4 , 6 – 11 11. Cranial and Spinal Nerve Overview and Skull Base 191

Internal acoustic meatus Cribriform [7, 8], (internal plate [1] auditory artery) Hypoglossal canal [12], (venous plexus) Superior orbital fissure [3, 4, 5(1), 6], Jugular foramen Foramen (superior ophthalmic vein) Optic canal [9, 10, 11], magnum [11], Foramen rotundum [5(2)] [2], (ophthalmic (internal jugular vein) (vertebral & artery) spinal vessels) Foramen ovale [5(3)] Foramen spinosum Carotid canal (meningeal branch of (internal carotid artery) 5(3) and middle meningeal artery)

ANTERIOR SKULL BASE - AXIAL VIEW POSTERIOR SKULL BASE - AXIAL VIEW

[ ] - indicates cranial nerve #

DRAWING 11-7 Skull Foramina 192 Neuroanatomy: Draw It to Know It

Cavernous Sinus

Here, we will draw the cavernous sinus in coronal and Next, indicate that cranial nerve 2 passes through the oblique views. Begin with the coronal diagram; show its optic canal and then that cranial nerves 3, 4, and 6 pass planes of orientation. Next, let’s draw a few related ana- through the superior orbital fi ssure. Th en, show that cra- tomic landmarks: the sella turcica of the sphenoid bone nial nerve 5(1) passes through the superior orbital fi ssure, and related pituitary body, the base of the brain and 5(2) passes through foramen rotundum, and 5(3) (which underlying optic nerves, and the medial edge of the tem- does not pass through the cavernous sinus) passes through poral lobe. Th en, draw one of the paired sphenoid sinuses foramen ovale, and that all of these divisions of the trigem- within the sphenoid bone and indicate that it is air-fi lled. inal nerve join together as the trigeminal ganglion. Next, draw one of the bilateral cavernous sinuses Now, let’s draw the course of the internal carotid between the sella turcica and the temporal lobe. Indicate artery. Here, we follow Bouthillier’s 1996 classifi cation that the cavernous sinuses are fi lled with venous trabecu- scheme. First, show that within the cervical segment, the lations; the cavernous sinus is a major venous confl uence artery ascends from the carotid bifurcation through the with many venous communications. Next, let’s draw the carotid space to the carotid canal; in the petrous seg- contents of one of the cavernous sinuses (we will label ment, the carotid artery rises and passes forward within the cranial nerves in brackets). Along the lateral wall of the carotid canal; in the lacerum segment, it exits the the cavernous sinus, from superior to inferior, label cra- carotid canal and rises into the cavernous sinus; in the nial nerves 3 and 4 and then the fi rst and second divi- cavernous sinus segment, it rises within the cavernous sions of cranial nerve 5. Next, medial to the fi rst division sinus, then passes forward through it, and then rises out of cranial nerve 5, label cranial nerve 6. Th en, within the of the cavernous sinus, where it becomes the clinoid seg- medial aspect of the cavernous sinus, label the internal ment, which curves posteriorly; in the ophthalmic seg- carotid artery. Finally, draw another portion of the inter- ment, the artery passes posteriorly and gives off the nal carotid artery in between the roof of the cavernous ophthalmic artery, which traverses anteriorly through sinus and the ipsilateral optic nerve— the carotid artery the optic canal; lastly, within the communicating seg- doubles back across the top of the cavernous sinus, as we ment, the carotid artery rises into the suprasellar cistern will show in our oblique view, next. Within the cavern- and gives off the anterior choroidal and posterior com- ous sinus, the pupillosympathetic fi bers run across cra- municating artery branches and bifurcates into the ante- nial nerve 6 when they leave the internal carotid artery rior and middle cerebral arteries.20 – 22 to join the fi rst division of the fi ft h cranial nerve. Finally, let’s defi ne the walls of the dura-enclosed cav- Now, we will draw an oblique view of the cavernous ernous sinus. Show that its roof underlies the level of the sinus. Begin with our planes of orientation and then let’s anterior clinoid process; that anteriorly, the cavernous draw the skull landmarks. Draw the anterior clinoid pro- sinus extends to the superior orbital fi ssure; that posteri- cess, which is the posteromedial edge of the lesser wing orly, it reaches the apex of the petrous bone/upper clivus; of the sphenoid bone, and then draw the relevant foram- that medially, it neighbors the lateral sella turcica; and ina: medial to the anterior clinoid process, label the optic that laterally, it neighbors the medial temporal lobe. canal, and lateral to it, draw the superior orbital fi ssure; Finally, show that the posterolateral cavernous sinus dura posterior to the superior orbital fi ssure, draw foramen also forms the medial upper third of Meckel’s cave, which rotundum, and posterior to it, draw foramen ovale.19 envelops the trigeminal ganglion.7 , 23 11. Cranial and Spinal Nerve Overview and Skull Base 193

Base of the brain CAVERNOUS SINUS - OBLIQUE VIEW Internal carotid art. Superior (double-back) Optic nerves Lateral Temporal Anterior lobe CAVERNOUS Posterior Medial [3] SINUS Pituitary Inferior (Venous) body (Suprasellar [4] Anterior Internal cistern) [5(1)] Sella turcica clinoid carotid Optic of sphenoid bone process [2] Communicating [6] art. canal [5(2)] Sphenoid Ophthalmic Ophthalmic branch Clinoid (Air) sinus Cavernous Superior Superior orbital fissure [3] [5(1)] [4] Lateral Medial [6] Lacerum Foramen [5(2)] Inferior rotundum (Carotid canal) CAVERNOUS CAVERNOUS SINUS - CORONAL VIEW Petrous SINUS Meckel’s [5(3)] cave Foramen Cervical [ ] - indicates cranial nerve # ovale (Carotid space) Internal carotid artery

DRAWING 11-8 Cavernous Sinus 194 Neuroanatomy: Draw It to Know It

References 1 . J i n k i n s, R . Atlas of neuroradiologic embryology, anatomy, and 1 2. B u c k, A . H . & S t e d m a n, T. L . A Reference handbook of the medical variants ( Lippincott Williams & Wilkins , 2000 ). sciences: embracing the entire range of scientifi c and practical medicine 2 . Donkelaar , H. J. T., Lammens , M. , Hori , A. & Cremers , C. W. R. J. and allied science, 3rd ed. ( W. Wood , 1913 ). Clinical neuroembryology: development and developmental disorders 1 3. N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatom, 2nd ed., Plates of the human central nervous system (Springer , 2006 ). 4–7 (Novartis , 1997 ). 3 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 1 4. S w a r t z, J . D . & L o e v n e r, L . A . Imaging of the temporal bone. 4th ed., clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). p. 58 (Th ieme, 2009 ). 4 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 15 . Mafee , M. F. , Valvassori , G. E. & Becker , M. Imaging of the head and clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). neck, 2nd ed. (Th ieme, 2005 ). 5 . Rosen , C. J. & American Society for Bone and Mineral Research . 1 6. Vo g l, T. J . Diff erential diagnosis in head and neck imaging: a Primer on the metabolic bone diseases and disorders of mineral systematic approach to the radiologic evaluation of the head and neck metabolism, 7th ed., p. 953 (American Society for Bone and region and the interpretation of diffi cult cases (Th ieme, 1999 ). Mineral Research , 2008 ). 1 7. F o s s e t t, D . T. & C a p u t y, A . J . Operative neurosurgical anatomy 6 . Wilson-Pauwels , L. Cranial nerves: function and dysfunction, 3rd ed. (Th ieme, 2002 ). ( People’s Medical Pub. House , 2010 ). 1 8. P e n s a k, M . L . Controversies in otolaryngology (Th ieme, 2001 ). 7 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human 1 9. C a p p a b i a n c a, P. , C a l i f a n o, L . & I a c o n e t t a, G . Cranial, craniofacial brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal and skull base surgery (Springer , 2010 ). structure, vascularization and 3D sectional anatomy (S p r i n g e r, 2 0. S a n n a, M . Atlas of microsurgery of the lateral skull base, 2nd ed. 2009 ). (Th ieme, 2008 ). 8 . Sundin , L. & Nilsson , S. Branchial innervation . J Exp Zool 293 , 2 1. M a c d o n a l d, A . J . Diagnostic and surgical imaging anatomy. Brain, 232 – 248 (2002 ). head & neck, spine, 1st ed., pp. 282 – 283 ( Amirsys , 2006 ). 9 . Binder , D. K. , Sonne , D. C. & Fischbein , N. J. Cranial nerves: 22 . Osborn , A. G. & Jacobs , J. M. Diagnostic cerebral angiography, anatomy, pathology, imaging (Th ieme, 2010 ). 2nd ed. ( Lippincott Williams & Wilkins , 1999 ). 1 0. A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 2 3. B r u n i, J . E . & M o n t e m u r r o, D . G . Human neuroanatomy: a text, atlas, 2nd ed. ( Lange Medical Books/McGraw-Hill , 2005 ). brain atlas, and laboratory dissection guide ( Oxford University Press , 1 1. N i e u w e n h u y s, R ., Vo o g d, J . & H u i j z e n, C . V. Th e human central 2009 ). nervous system, 4th ed. (Springer , 2008 ). 1 2 Cranial Nerves 3, 4, 6, 12

Cranial Nerves 3, 4, & 6: Anatomy

Extraocular Movements

Extraocular Muscles: Recti Muscles

Extraocular Muscles: Oblique Muscles

Oculomotor Nuclei ( Advanced )

Cranial Nerve 12 196 Neuroanatomy: Draw It to Know It

Know-It Points

Cranial Nerves 3, 4, & 6: Anatomy

■ Cranial nerve 3 emerges from the anterior, medial orbital fi ssure to enter the orbit to innervate the midbrain and enters the interpeduncular cistern; superior oblique muscle on the side opposite its then, it passes through the prepontine cistern, nucleus of origin. the lateral dural wall of the cavernous sinus, and ■ Cranial nerve 6 exits the brainstem at the through the superior orbital fi ssure to enter the pontomedullary sulcus, climbs the clivus, passes over orbit. the petrous apex, and then passes through the cavernous ■ Cranial nerve 4 passes dorsally out of the posterior sinus and superior orbital fi ssure to enter the orbit. aspect of the midbrain and courses around the ■ Th e posterior communicating artery, which connects outside of the opposite cerebral peduncle through the the internal carotid artery and ipsilateral posterior ambient cistern; then, it passes through the lateral cerebral artery, passes just above the oculomotor dural wall of the cavernous sinus and the superior n e r v e .

Extraocular Movements

■ Cranial nerve 3 innervates the majority of the rectus—depression (with eye in abduction), superior extraocular muscles: the medial rectus, superior oblique—depression (with eye in adduction), inferior rectus, inferior rectus, and inferior oblique. oblique—elevation (with eye in adduction). ■ Cranial nerve 6 innervates the lateral rectus. ■ Each muscle’s chief action in primary position ■ Cranial nerve 4 innervates the superior oblique. (ie, looking straight ahead) is its primary action. ■ All of the extraocular muscles except for the inferior ■ Each muscle’s secondary and tertiary actions are its oblique attach at the orbital apex in a common additional rotational eff ects on the eye. tendinous ring: the annulus of Zinn. ■ Th e mnemonic “SUPERIOR people do NOT extort” ■ Cardinal positions of gaze: medial rectus— indicates that the superior muscles are both intorters. adduction, lateral rectus—abduction, superior ■ Th e mnemonic “OBLIQUE muscles rotate the eye rectus—elevation (with eye in abduction), inferior OUT” indicates that the oblique muscles are abductors.

Oculomotor Nuclei (Advanced )

■ Th e superior rectus subnuclei project contralaterally, through lens thickening, pupillary constriction, and the single levator palpebrae subnucleus projects inward rotation of the eyes — eye convergence. bilaterally, and the remaining subnuclei project ■ Th e preganglionic perioculomotor cell group lies ipsilaterally. along the dorsal aspect of the oculomotor nucleus. ■ Superior rectus subnucleus lesions produce bilateral ■ Th e motoneuron division of the perioculomotor cell palsies because when the superior rectus fi bers exit group lies along the medial aspect of the oculomotor their subnucleus, they immediately pass through the nucleus. contralateral subnucleus. ■ Th e accommodation refl ex (or near-response) is a three-part refl ex that brings near objects into focus 12. Cranial Nerves 3, 4, 6, 12 197

Cranial Nerve 12

■ Th e hypoglossal nucleus spans most of the height of four extrinsic tongue muscles: styloglossus, the medulla. hyoglossus, and genioglossus. ■ Cranial nerve 12 exits the medulla between the ■ Palatoglossus is the only extrinsic tongue muscle not medullary pyramid and the inferior olive, passes innervated by cranial nerve 12; its innervation comes through the premedullary cistern, and exits the skull from cranial nerve 10, the vagus nerve. base through the hypoglossal canal; then, it passes ■ When one side of the genioglossus is denervated, the through the medial nasopharyngeal carotid space and tongue moves forward and toward the weakened side terminates in the tongue musculature. (away from the intact side). ■ Th e hypoglossal nerve innervates the large intrinsic tongue muscle mass, and it innervates three of the

Superior oblique m.

Levator palpebrae m. Superior rectus m. Cavernous Medial rectus m. sinus Internal carotid a. III

Sphenoid bone Inferior oblique m. Superior Clivus Lateral rectus m. orbital fissure

Inferior rectus m. Tendinous ring (opened)

FIGURE 12-1 Sagittal view of cranial nerves 3, 4, and 6. Used with permission from Baehr, Mathias, M. Frotscher, and Peter Duus. Duus’ Topical Diagnosis in Neurology: Anatomy, Physiology, Signs, Symptoms, 4th completely rev. ed. Stuttgart; New York: Th ieme, 2005. 198 Neuroanatomy: Draw It to Know It

Cranial Nerves 3, 4, & 6: Anatomy

Here, we will draw the course of cranial nerves 3, 4, and direction of the eyes. To demonstrate a right fourth nerve 6 in sagittal view. First, draw a midsagittal section palsy, elevate your right hand. Now, tilt your head both through the brainstem from the midbrain to the pon- ways; tilting your head toward the elevated (aff ected) tomedullary sulcus; be sure to include a cerebral pedun- side worsens the disconjugate lines of vision whereas tilt- cle. Next, label the cavernous sinus, the superior orbital ing it the opposite way (towards the normal side) brings fi ssure, and the orbit. Note that cranial nerves 3 and 4 the lines of vision into alignment: patients with a fourth pass through the lateral dural wall of the cavernous sinus, nerve palsy tilt their head away from the aff ected eye. whereas cranial nerve 6 passes through the cavernous Now, draw the clivus; it is a fusion of the sphenoid sinus, itself. Also note that all of the extraocular muscles and occipital bones that sits directly across from the except for the inferior oblique share a common tendi- brainstem. Th en, draw the abducens nucleus of cranial nous ring, called the annulus of Zinn; cranial nerves 3 nerve 6 in the dorsal, inferior pons. Show that the sixth and 6 pass through this ring to innervate their respective nerve exits the brainstem at the pontomedullary sulcus, muscles, whereas cranial nerve 4 passes above it to inner- climbs the clivus, passes over the petrous apex, and then vate the superior oblique muscle. passes through the cavernous sinus and superior orbital Now, draw the oculomotor complex of cranial nerve fi ssure to enter the orbit. Next, also indicate that as part 3 within the dorsal, center of the midbrain and indicate of its path into the cavernous sinus (aft er crossing over that it lies at the level of the superior colliculus. In axial the petrous apex), the sixth nerve passes through view, show that the oculomotor fascicles emerge from Dorello’s canal: a dural channel within a basilar venous the anterior, medial midbrain and enter the interpedun- plexus. In this stretch, the abducens nerve is in close cular cistern. Th en, in the sagittal diagram, show that the proximity to the fi rst division of cranial nerve 5, and oculomotor nerve passes through the prepontine cistern, injury to both nerves, here, is called Gradenigo’s syn- the lateral dural wall of the cavernous sinus, and the drome. Note that cranial nerve 6 dysfunction is oft en a superior orbital fi ssure to enter the orbit. harbinger of increased intracranial pressure because the Next, draw the trochlear nucleus of cranial nerve 4 at abducens nerve is fi xed where it pierces the dura and can the level of the inferior colliculus. In axial view, indicate be stretched when there is downward herniation of the that the fourth nerve passes dorsally out of the posterior brainstem. aspect of the midbrain and courses around the outside of Next, let’s show the arteries that can compress the the opposite cerebral peduncle through the ambient cis- aforementioned cranial nerves. First, show that the pos- tern. Th en, in sagittal view, complete its course through terior cerebral artery (PCA) sits above both the third the lateral dural wall of the cavernous sinus and through and fourth cranial nerves, and then that the superior cer- the superior orbital fi ssure to enter the orbit to innervate ebellar artery (SCA) sits below them. Next, show that the superior oblique muscle on the side opposite its the anterior inferior cerebellar artery (AICA) lies in nucleus of origin. Th e trochlear nerve is the only cranial close relation to the sixth cranial nerve as it exits the nerve to exit posteriorly from the brainstem and the only pontomedullary sulcus. Th en, show that the internal cranial nerve to send all of its fi bers to the contralateral carotid artery (ICA) lies within the cavernous sinus, and side. When the long, thin trochlear nerve is injured, the show that the posterior communicating artery (Pcomm) aff ected eye is elevated (aka hypertropic). Hold your fi sts passes just above the oculomotor nerve to connect the with your index fi ngers straight out to demonstrate the ICA and PCA.1 – 7 12. Cranial Nerves 3, 4, 6, 12 199

MIDBRAIN: AXIAL VIEW Cranial CrN 4 nerve 3 Superior CrN 3 Cerebral colliculus PCA peduncle Inferior colliculus Superior P. comm. orbital fissure Cavernous sinus Cranial nerve 4

Orbit ICA SCA Dorello’s Superior canal Lateral Cranial Clivus nerve 6 Anterior Posterior

Medial Inferior

AICA

DRAWING 12-1 Cranial Nerves 3, 4, & 6: Anatomy 200 Neuroanatomy: Draw It to Know It

Extraocular Movements

Here, we will draw the six cardinal positions of gaze and diff erent actions on the eye in primary position: vertical, create a table for the complete extraocular muscle actions. rotational, and horizontal. Cranial nerve 3 innervates the majority of the extraocu- Next, let’s complete our eye muscle actions table. lar muscles: the medial rectus, superior rectus, inferior Across the top row, write cranial nerve (CrN), muscle, rectus, and inferior oblique; cranial nerve 6 innervates primary action, secondary action, and tertiary action. the lateral rectus; and cranial nerve 4 innervates the Th e muscle’s chief action in primary position (ie, looking superior oblique. We will draw the cardinal positions in straight ahead) is its primary action, and the muscle’s coronal section, so fi rst label the superior–inferior and secondary and tertiary actions are its additional rota- lateral–medial axes and then identify our perspective as tional eff ects on the eye. Begin with the medial rectus from the left eye. Show that the lateral rectus directs the muscle, innervated by cranial nerve 3, and show that its eye laterally (called abduction) and that the medial primary action is adduction and that it does not have rectus directs the eye medially (called adduction). Th en, secondary or tertiary actions. Th en, show that the cra- show that when the eye is abducted, the superior rectus nial nerve 6-innervated lateral rectus muscle’s primary directs the eye superiorly and the inferior rectus directs action is abduction, and show that it also does not have the eye inferiorly. Next, show that when the eye is either secondary or tertiary actions. In the next row, adducted, the superior oblique directs the eye inferiorly write that the cranial nerve 3-innervated superior rectus and the inferior oblique directs the eye superiorly. muscle’s primary action is elevation, its secondary action Now, in order to understand the complete move- is intorsion, and its tertiary action is adduction. Th en, ments, beyond just the six cardinal directions of gaze, write that the cranial nerve 3-innervated inferior rectus let’s fi rst learn the relationship between the eye and the muscle’s primary action is depression, its secondary eye muscle plane. Draw an axial view of the eye within action is extorsion, and its tertiary action is adduction. the orbit. Show the optical axis of the eye and then the Next, show that the cranial nerve 4-innervated superior eye muscle plane. Th e muscle plane originates from the oblique muscle’s primary action is intorsion, its second- orbital apex, which lies anterior to the orbital opening of ary action is depression, and its tertiary action is abduc- the optic canal; all of the extraocular muscles except for tion. Finally, show that the cranial nerve 3-innervated the inferior oblique attach at the orbital apex in a inferior oblique muscle’s primary action is extorsion, its common tendinous ring: the annulus of Zinn. Th e infe- secondary action is elevation, and its tertiary action is rior oblique, instead, attaches to the medial orbital fl oor. abduction. Now, show that the primary position of the eye, the posi- Now, include the following two mnemonics: tion of the eye when it is looking straight ahead, is “SUPERIOR people do NOT extort,” which means that 23 degrees nasal to the eye muscle plane. Th is angle the superior muscles are both intorters, and “OBLIQUE results in the vertical eye muscles (superior and inferior muscles rotate the eye OUT,” which means that the rectus and superior and inferior oblique) all having three oblique muscles are abductors.8 , 9 12. Cranial Nerves 3, 4, 6, 12 201

SIX CARDINAL POSITIONS OF GAZE Superior TABLE OF EXTRAOCULAR MOVEMENTS Medial Lateral CRN MUSCLE PRIMARY SECONDARY TERTIARY ACTION ACTION ACTION Inferior Inferior Superior Left eye 3 Medial rectus Adduction XX oblique rectus

Medial 6 Lateral rectus Abduction XX rectus 3 Superior rectus Elevation Intorsion Adduction Lateral rectus 3 Inferior rectus Depression Extorsion Adduction

Superior Inferior 4 Superior oblique Intorsion Depression Abduction oblique rectus 3 Inferior oblique Extorsion Elevation Abduction EYE IN THE ORBIT: AXIAL VIEW 23 degrees “SUPERIOR people do NOT EXTORT” optical axis muscle plane “OBLIQUE muscles move the eye OUT”

Orbital apex

DRAWING 12-2 Extraocular Movements 202 Neuroanatomy: Draw It to Know It

Extraocular Muscles: Recti Muscles

Here, we will draw the actions of the recti muscles: hori- are mixed. Start with the eyes in abduction: superior zontal (ie, medial and lateral) and vertical (ie, superior rectus inserts on the top of the eyeball and inferior rectus and inferior). First, establish the anterior–posterior and inserts on the bottom. Show that in this position, supe- medial–lateral axes. Th en, draw two eyeballs in primary rior rectus rotates the eye up and inferior rectus rotates it position in axial section. On one, attach a medial rectus down. Next, show that in adduction, superior rectus muscle; on the other, attach a lateral rectus muscle. rotates the eye internally around the anterior–posterior Indicate that the medial rectus, which is innervated by axis: it intorts it, meaning the medial aspect of the eye cranial nerve 3, rotates the eye medially and that the lat- lowers and the lateral aspect of the eye elevates. Th en, eral rectus, which is innervated by cranial nerve 6, rotates show that in adduction, inferior rectus externally rotates it laterally. Next, draw axial sections with the eyes rotated the eye: it extorts it, meaning the medial aspect of the medially (adducted) and also laterally (abducted), and eye raises and the lateral aspect of the eye lowers. Finally, show that in both of these positions, the medial rectus in primary position, show that superior rectus produces still adducts the eye and the lateral rectus still abducts it. elevation, intorsion, and adduction, and that inferior Th e horizontal recti only move the eye within the hori- rectus produces depression, extorsion, and adduction. zontal plane. As a clinical corollary, when the lateral Now, let’s use our hands again to feel the vertical recti rectus fails, the eye has trouble turning outward and the rotations. Use your right fi st as your right eye and hook patient has diffi culty with far vision, whereas when the your left index fi nger (the right superior rectus) over the medial rectus fails, the patient has diffi culty with eye top of it at an angle. First, with your hand fully abducted convergence and near vision. pull on your wrist: the fi st rotates superiorly. Th en posi- Now, we will use our hands to feel the horizontal recti tion your fi st straight ahead and pull: you can feel your rotational pull on the eye. Th e medial and lateral recti fi st adduct (note, however, that superior rectus has mul- muscles are the simplest. Make a fi st with your right hand tiple actions in this position). Finally, position your fi st to represent your right eyeball. Your thumb is your right in full adduction and continue to pull. Th e fi st is unable medial rectus. Grip your thumb with your left hand and to rotate medially any farther, and instead it intorts. pull on it (not so hard that you pull the eye out of its Note that the eye muscle always overpowers the eye (ie, orbit!). Notice that whether your fi st is directed straight your left fi nger should overpower your right fi st). Next, ahead, adducted, or abducted, the force from your left let’s do the same for the inferior rectus. Flip your right hand always rotates your wrist medially along the horizon- hand over (knuckles down) and hook your left index tal plane. To demonstrate the lateral rectus rotational pull, fi nger underneath your fi st. Fully abduct your fi st and fl ip your fi st over and pull your thumb backward. Again, pull; the downward/backward force of the inferior rectus whether your fi st is directed straight ahead, adducted, or depresses the eye. Th en, direct your fi st straight ahead abducted, the lateral rectus rotates it laterally. and pull to feel your fi st adduct (note, however, that Next, let’s learn the vertical recti muscles: superior inferior rectus has multiple actions in this position). and inferior. For this drawing, add the superior–inferior Finally, in full adduction, continue to pull down and axis. At the extremes of horizontal gaze, the vertical recti back: the fi st is unable to rotate medially any farther, and produce pure actions, but in primary position, the actions instead it extorts.6 , 8 , 9 12. Cranial Nerves 3, 4, 6, 12 203

Anterior Superior

Medial Lateral

Inferior Posterior

Medial rectus Superior rectus

Lateral rectus Inferior rectus

DRAWING 12-3 Extraocular Muscles: Recti Muscles 204 Neuroanatomy: Draw It to Know It

Extraocular Muscles: Oblique Muscles

Here, we will draw the oblique muscles. Once again, Now, let’s use our fi st to demonstrate the rotational establish the anterior–posterior, medial–lateral, and pull of these eye muscles; we’ll start with the superior superior–inferior axes. First, draw an axial view of the oblique. Your right fi st is again the eyeball. Hook your superior oblique muscle in adduction. Show that the left thumb around your right index fi nger. Th e left thumb superior oblique muscle runs across the superior surface is the trochlea and the right index fi nger is the superior of the eyeball, hooks around the trochlea, which is Latin oblique. Pay attention to the spread between your index for “pulley,” and runs along the medial wall of the orbit. and middle fi ngers. When the eye is fully adducted, Next, show that in this position, the superior oblique force along the trochlea depresses the eye; when the eye rotates the eye down. Th en, show that when the eye is is abducted, force along the trochlea intorts the eye; use fully abducted, superior oblique force causes the eye to primary position to feel the superior oblique cause intort. With the eye looking straight ahead, show that eye abduction (although the superior oblique has multi- the superior oblique causes intorsion, depression, and ple actions in this position). For the inferior oblique, we also abduction. have to reverse our anterior–posterior plane: here, the For the inferior oblique, let’s use a coronal plane knuckles are posterior and the wrist is anterior; thus, because the inferior oblique attaches to the medial nasal when the wrist is facing toward the body, it is in adduc- fl oor (unlike the other extraocular muscles, which attach tion, and when it is facing away from the body, it is in at the orbital apex at the annulus of Zinn). Draw the abduction. With your wrist adducted, grip your right inferior oblique fi rst in adduction. Show that in this index fi nger and pull; the eye elevates; then, in full position, the inferior oblique causes elevation; then, abduction, feel the inferior oblique cause the eye to show that in abduction, it causes extortion; and lastly, extort; use primary position to feel the inferior oblique show that in primary position, it causes extorsion, eleva- cause eye abduction (although the inferior oblique has tion, and abduction. multiple actions in this position).6 , 8 , 9 12. Cranial Nerves 3, 4, 6, 12 205

Anterior Superior

Medial Lateral

Inferior Posterior

Superior oblique

Superior Medial Lateral Inferior

Inferior oblique

DRAWING 12-4 Extraocular Muscles: Oblique Muscles 206 Neuroanatomy: Draw It to Know It

Oculomotor Nuclei (Advanced )

Here, we will draw the Warwick model of the oculomo- through lens thickening, pupillary constriction, and tor complex and the perioculomotor cell group model. inward rotation of the eyes — eye convergence. First, Let’s begin with the oculomotor complex. In the 1950s, indicate that our diagram is in coronal view. Th en, draw R. Warwick created a classic model for the oculomotor a large, long nucleus to represent a consolidation of complex, and although details of this model have been the oculomotor complex; note that this representation updated over time, its basic construct remains unchanged. excludes the visceral nuclei, which will be drawn as Th e model shows that the superior rectus subnuclei proj- part of the perioculomotor cell group. Next, along ect contralaterally, the single levator palpebrae subnu- the dorsal aspect of the oculomotor nucleus, draw the cleus projects bilaterally, and the remaining subnuclei preganglionic perioculomotor cell group; show that project ipsilaterally. As an important clinical corollary, the Edinger–Westphal nucleus lies within this part of levator palpebrae subnucleus lesions naturally cause the perioculomotor cell group. Th e preganglionic cell bilateral eye muscle palsies and superior rectus subnu- group is responsible for producing the lens thickening cleus lesions also produce bilateral palsies because when and pupillary constriction responses of the accommoda- the superior rectus fi bers exit their subnucleus, they tion refl ex. Next, along the rostral–caudal length of the immediately pass through the contralateral subnucleus. medial aspect of the oculomotor nucleus, draw the Now, let’s draw Warwick’s model of the oculomotor motoneuron division of the perioculomotor cell group; complex in sagittal view. Label the rostral–caudal and it innervates the multiply innervated muscle fi bers of the dorsal–ventral planes of orientation. First, let’s draw the accommodation refl ex, which produce the eye conver- lateral subnuclei from ventral to dorsal. Draw the long, gence response. Show that the motoneuron division of narrow ventral subnucleus; designate it as innervating the perioculomotor cell group encompasses the antero- the medial rectus (although in actuality, three separate median nucleus, anteriorly, and the nucleus of Perlia in oculomotor regions supply the medial rectus muscle). mid-anteroposterior position. Note that due to the actual Above the ventral subnucleus, draw the intermediate sub- complexity of this nuclear complex, we should not nucleus, which innervates the inferior oblique; and above attempt to draw discrete functional meaning from the it, draw the dorsal subnucleus, which innervates the infe- positions of the Edinger–Westphal nucleus, anterome- rior rectus. Medial to these subnuclei, draw the medial dian nucleus, and nucleus of Perlia from this diagram— subnucleus, which innervates the contralateral superior these nuclei are included, here, only to provide historical/ rectus (note: this subnucleus is commonly unnamed). anatomic context to our perioculomotor cell group Th en, on the dorsocaudal surface, draw the small central model, and we should still simply consider them to caudal subnucleus, which innervates the bilateral levator broadly enact the visceral actions of the oculomotor palpebrae. On the rostral surface, draw the visceral nuclei, nerve. which include the Edinger–Westphal nucleus, anterome- Finally, in regards to the accommodation refl ex, itself, dian nucleus, and the nucleus of Perlia.10 consider that supranuclear control of the perioculomo- Next, let’s draw the perioculomotor cell group, which tor cell group comes from widely distributed areas, places the Edinger–Westphal nucleus, anteromedian which include the supraoculomotor area (which lies nucleus, and nucleus of Perlia into a larger context of within the mesencephalic reticular formation just dorsal neural substrate responsible for the accommodation to the oculomotor complex) and numerous cerebral refl ex. Th e accommodation refl ex (or near-response) is a and cerebellar smooth pursuit centers described in three-part refl ex that brings near objects into focus Chapter 23. 2 , 6 – 9 , 11 , 12 12. Cranial Nerves 3, 4, 6, 12 207

OCULOMOTOR COMPLEX - PERIOCULOMOTOR CELL GROUP - SAGITTAL VIEW CORONAL VIEW Rostral Rostral Visceral nuclei Dorsal Ventral Medial Lateral Caudal Caudal

Perioculomotor cell group Medial (preganglionic cell group) Dorsal nucleus nucleus (SR) Edinger-Westphal (IR) nucleus Nucleus of Perlia Intermediate (mid anterior- posterior) nucleus Ventral (IO) nucleus Anteromedian Central (MR) nucleus (anterior) caudal (LP) nucleus Perioculomotor cell group (multiply innervated muscle fiber motoneurons) Oculomotor nucleus

DRAWING 12-5 Oculomotor Nuclei 208 Neuroanatomy: Draw It to Know It

Cranial Nerve 12

Here we will draw the hypoglossal nerve (cranial nerve 12) its innervation comes from cranial nerve 10, the vagus course in sagittal view and then we will create a diagram nerve. Genioglossus is the most clinically important of to understand the actions of the extrinsic tongue muscles these three extrinsic tongue muscles because whereas the that it innervates. We begin with the hypoglossal nerve other tongue muscles receive bilateral cortical innerva- path from the medulla to the tongue. First, draw an axial tion, genioglossus receives predominately contralateral view of the medulla and label the hypoglossal nucleus cortical innervation; therefore, it is the most helpful for within the posterior medulla; it spans from the upper to clinical localization, as we discuss at the end. 13 the lower regions of the medulla. Next, label a few key To understand the action of all of these muscles, we structures along the hypoglossal nerve course: the infe- will draw a sagittal schematic of their innervation. Show rior olive, the vertebral artery, and the hypoglossal canal. that styloglossus attaches the tongue to the styloid pro- Now, show that the hypoglossal nerve passes anteriorly cess; indicate that it pulls the tongue up and back. Th en, through the medulla and exits between the medullary show that hyoglossus attaches the tongue to the hyoid pyramid and the inferior olive at the ventrolateral (aka bone; indicate that it depresses the tongue. Finally, show preolivary) sulcus. Th en, show that the hypoglossal nerve that genioglossus attaches the tongue to the anterior passes through the premedullary cistern, lateral to the mandible; indicate that it provides tongue protrusion. vertebral artery, to exit the skull base through the hypo- Now, in axial section, show that both genioglossi glossal canal. point towards the center of the anterior mandible. Th eir Now, show that aft er the hypoglossal nerve exits the opposing horizontal angles cancel, and so the tongue is hypoglossal canal, it passes through the medial nasopha- directed forward when it is activated (you can also feel ryngeal carotid space, where it descends in close proxim- the tongue curl when you protrude it because the genio- ity to the carotid and internal jugular vasculature before glossi pull the center of the tongue downward, as well). approaching the hyoid bone and terminating in the Th us, when one side of the genioglossus is impaired tongue musculature. Th e proximity of cranial nerve 12 to (either from genioglossus atrophy or from hypoglossal the internal carotid artery makes it susceptible to injury nerve or nucleus injury), the tongue moves forward and from carotid dissection, because clot formed from dissec- toward the side of the lesion (away from the intact side). tion can expand the carotid wall enough to compress the Demonstrate this with your index fi ngers. Hold your adjacent nerves. Cranial nerves 9, 10, and 11 also run fi sts in front of you and point your index fi ngers toward within this space, so a combined cranial nerve 9, 10, 11, midline. Now drop one of your fi sts: the tongue pro- and 12 injury suggests a possible carotid dissection. trudes toward the side of the lesion (away from the intact Next, let’s show the termination of the hypoglossal side). Corticonuclear innervation to the portion of each nerve under the tongue, or “glossus” (hence the name hypoglossal nucleus that innervates the genioglossus is “hypoglossal nerve”). Th e hypoglossal nerve innervates predominantly contralateral, however. Th erefore, with the large intrinsic tongue muscle mass, which comprises lesions proximal to the hypoglossal nucleus, tongue pro- the superior and inferior longitudinal muscles and the trusion is either normal or it points away from the side of transverse and vertical muscles, and it innervates three the lesion: for instance, in a right-side hemispheric lesion, of the four extrinsic tongue muscles: styloglossus, hyo- the left genioglossus will be weak, so the tongue will glossus, and genioglossus. Palatoglossus is the only extrin- deviate toward the left (away from the injured side of the sic tongue muscle not innervated by cranial nerve 12; brain). 1 – 4 , 6 , 7 12. Cranial Nerves 3, 4, 6, 12 209

Medulla: axial view Hypoglossal nucleus

Styloid process Vertebral artery Styloglossus Genioglossi Hypoglossal Styloglossus Tongue canal

Genioglossus Intrinsic tongue Carotid artery muscles in medial Hyoglossus nasopharynx Tongue

Hyoglossus Posterior Genioglossus Right Left Mandible Hyoid Anterior bone

DRAWING 12-6 Cranial Nerve 12 210 Neuroanatomy: Draw It to Know It

References 1 . Binder , D. K. , Sonne , D. C. & Fischbein , N. J. Cranial nerves: 8 . Leigh , R. J. & Zee , D. S. Th e neurology of eye movements (Oxford anatomy, pathology, imaging (Th ieme, 2010 ). University Press, 2006 ). 2 . Brazis , P. W. , Masdeu , J. C. & Biller , J. Localization in clinical 9 . Wo n g, A . M . F. Eye movement disorders ( Oxford University Press , neurology, 5th ed. ( Lippincott Williams & Wilkins , 2007 ). 2008 ). 3 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 10 . Warwick , R. A study of retrograde degeneration in the oculomotor clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). nucleus of the rhesus monkey, with a note on a method of recording 4 . M a c d o n a l d, A . J . Diagnostic and surgical imaging anatomy. Brain, its distribution. Brain 73 , 532 – 543 (1950 ). head & neck, spine, 1st ed., pp. 282 – 283 ( Amirsys , 2006 ). 11 . Horn , A. K. , et al . Perioculomotor cell groups in monkey and man 5 . Takahashi , S. O. Neurovascular imaging: MRI & microangiography defi ned by their histochemical and functional properties: (Springer , 2010 ). reappraisal of the Edinger-Westphal nucleus . J Comp Neurol 507 , 6 . Wilson-Pauwels , L. Cranial nerves: function and dysfunction, 3rd ed. 1317 – 1335 (2008 ). ( People’s Medical Pub. House , 2010 ). 12 . Miller , N. R., Walsh , F. B. & Hoyt , W. F. Walsh and Hoyt’s clinical 7 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human neuro-ophthalmology, 6th ed. ( Lippincott Williams & Wilkins , brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal 2005 ). structure, vascularization and 3D sectional anatomy (Springer , 2009 ). 1 3. C o n n, P. M . Neuroscience in medicine, 3rd ed. (Humana Press, 2008 ). 1 3 Cranial Nerves 5, 7, 9, 10

Cranial Nerve 5: Peripheral Innervation

Cranial Nerve 5: Nuclei

Cranial Nerve 5: Tracts ( Advanced )

Cranial Nerve 7: Innervation

Cranial Nerve 7: Anatomy

Cranial Nerves 9 & 10

The Gag Reﬂ e x 212 Neuroanatomy: Draw It to Know It

Know-It Points

Cranial Nerve 5: Peripheral Innervation

■ Th e peripheral divisions of the trigeminal nerve are trigeminally innervated medial and lateral pterygoids, division 1 — the ophthalmic division, which covers masseter, and temporalis muscles. the eyes; division 2 — the maxillary division, which ■ In a lower trigeminal motor neuron lesion (eg, when covers the cheeks; and division 3 — the mandibular a trigeminal motor nucleus or nerve is injured or division, which covers the jaw. when a lateral pterygoid is damaged), the jaw deviates ■ Th e main function of the trigeminal motor system is toward the injured side. mastication (ie, chewing), which requires the

Cranial Nerve 5: Nuclei

■ Th e trigeminal ganglion lies in Meckel’s cave: a ■ Th e trigeminal motor nucleus and the principal dural-based, cerebrospinal fl uid-fi lled cavern that lies sensory nucleus lie in parallel just above the abducens along the posterolateral aspect of the cavernous sinus. nucleus in the upper pons. ■ Th e ophthalmic division traverses the superior orbital ■ Th e mesencephalic nucleus spans from the upper fi ssure; the maxillary division traverses foramen pons to the level of the superior colliculus (in the rotundum; and the mandibular division traverses midbrain). foramen ovale. ■ Th e spinal trigeminal nucleus and tract span from ■ Th e ophthalmic and maxillary divisions (divisions 1 the upper pons to the upper cervical spinal cord. and 2, respectively) pass through the lateral wall of ■ Th e motor division of the trigeminal nerve passes the cavernous sinus and then merge together along through the cerebellopontine angle cistern and joins with the mandibular division to form the trigeminal the mandibular division as it exits the middle cranial ganglion within Meckel’s cave. fossa through foramen ovale.

Cranial Nerve 5: Tracts (Advanced )

■ Th e central sensory aff erents of the trigeminal nerve large fi ber sensory modality trigeminal nerve fi bers relay to the cortex through two diff erent project to the principal sensory nucleus. trigeminothalamic pathways: anterior and posterior. ■ Th e spinal trigeminal nucleus divides from superior ■ S m a l l fi ber sensory modality trigeminal nerve fi bers to inferior into pars oralis, pars interpolaris, and pars project to the spinal trigeminal tract and nucleus and c a u d a l i s .

Cranial Nerve 7: Innervation

■ Th e upper division of the facial nucleus receives ■ In a right cerebral cortical stroke, the left upper face is bilateral corticonuclear projections and the lower strong and the left lower face is weak. division receives contralateral projections, only. ■ In a left Bell’s palsy, both the left upper face and left ■ Fibers from the upper division innervate the upper lower face are weak. face and fi bers from the lower division innervate the lower face. 13. Cranial Nerves 5, 7, 9, 10 213

Cranial Nerve 7: Anatomy

■ Th e facial nucleus houses special visceral eff erent ■ Th e pars caudalis portion of the spinal trigeminal (SVE) cells and innervates the muscles of facial nucleus receives the general sensory aff erent (GSA) expression. fi bers of cranial nerve 7, which carry sensory ■ Th e superior salivatory nucleus houses general information from select portions of the external ear. visceral eff erent cells (GVE) and provides ■ Th e facial nerve divides into four segments: an parasympathetic innervation to the pterygopalatine extracranial segment — where the nerve emerges from and submandibular ganglia. the petrous portion of the temporal bone; an ■ Th e solitary tract nucleus receives the special visceral intratemporal segment — where it passes through the aff erent (SVA) fi bers of cranial nerve 7, which carry petrous bone; a cisternal segment — where it passes taste sensation from the anterior two thirds of the through the cerebellopontine angle cistern; and an tongue. intra-axial segment — its brainstem course.

Cranial Nerves 9 & 10

■ Th e inferior salivatory nucleus innervates the otic reception from the glossopharyngeal and vagus ganglion, which provides parasympathetic nerves. innervation to the parotid gland. ■ Th e solitary tract nucleus receives sensory aff erents ■ Th e dorsal motor nucleus of the vagus provides for taste, sensory aff erents from the epiglottis, and parasympathetic innervation to smooth muscle of the parasympathetic aff erents from widespread oropharynx and parasympathetic innervation to thoracoabdominal regions. viscera within the thoracoabdomen. ■ Th e glossopharyngeal and vagus nerves exit the ■ Nucleus ambiguus innervates the throat muscles and medulla through the post-olivary sulcus to enter the provides parasympathetic innervation to select cerebellomedullary cistern, and they traverse the skull cardiovascular structures. base through the jugular foramen. ■ Th e spinal trigeminal nucleus, pars caudalis receives a small portion of its cutaneous sensory

The Gag Reﬂ ex

■ Th e gag refl ex relies on the glossopharyngeal nerve ■ In a lower motor neuron injury (such as a direct for its aff erent loop and the vagus nerve for its lesion to the nucleus ambiguus itself or its exiting eff erent loop. fi bers), there is unilateral palatal paralysis on the side of the lower motor neuron lesion. 214 Neuroanatomy: Draw It to Know It

Cranial Nerve 5: Peripheral Innervation

Here, we will draw the peripheral sensory coverage of the Th e main function of the trigeminal motor system is trigeminal nerve and the trigeminal motor innervation mastication (chewing). Mastication requires the trigem- of the muscles of mastication. Th e peripheral divisions of inally innervated medial and lateral pterygoids, masseter, the trigeminal nerve are division 1— the ophthalmic and temporalis muscles. Feel just above and in front of division, which covers the eyes; division 2 — the maxil- the angle of your mandible and clench and relax your lary division, which covers the cheeks; and division 3 — jaw. Th e contracting muscles under your fi ngertips are the mandibular division, which covers the jaw. First, the masseters. Next, look at your temples and cheeks; the draw a head. Next, mark a dot on the superior-posterior temporalis muscles fi ll out your facial contour. Atrophy curvature of the head, then mark one at the corner of the to these muscles is an important potential clue of trigem- eye, and then the tip of the nose. Now, connect these inal neuronal degeneration. Th e medial pterygoids, tem- dots and label the region supero-anterior to this line as poralis, and masseter muscles elevate the mandible to division 1— the ophthalmic division. Next, midway close the jaw, whereas the lateral pterygoids help to open along that line make another dot, then make a dot at the it (although much of the work in jaw opening actually maxilla, and then the corner of the mouth. Join these relies on the digastric muscle, which is partially inner- dots and label the region between this line and division vated by the trigeminal nerve, and the geniohyoid 1 as division 2— the maxillary division. Finally, mark a muscle). Open your jaw and extend your mandible for- dot at the original superior-posterior point, then at the ward to activate your lateral pterygoids. tragus, and then at the mentum. Connect these dots and Next, draw the lateral pterygoids at an angle to one label the region between this line and division 2 as divi- another; show that they push the mandible forward. sion 3— the mandibular division. Now tap these points Th en, point your index fi ngers towards one another on your own face for sense-memory. to represent the lateral pterygoids. Drop one of your Two key details of facial sensory coverage are that fi ngers to represent a weakened lateral pterygoid; the division 3 of the trigeminal nerve covers neither the intact fi nger points toward the weak side. In a lower outer ear nor the angle of the mandible. Th e coverage of motor neuron lesion (eg, when a trigeminal motor the outer ear is complex: it involves the great auricular nucleus or nerve is injured or when a lateral pterygoid is nerve (supplied by C2, C3) and cranial nerves 7, 9, and damaged), the jaw deviates toward the injured side. 10; the angle of the mandible is covered by the great Cortical innervation of the trigeminal motor nuclei is auricular nerve. Th us, sensory examination of the outer bilateral with contralateral predominance; thus, in corti- ear and angle of the mandible should be normal in iso- cal injury, if jaw deviation occurs, it is directed away from lated peripheral trigeminal nerve injury. Lastly, note that the injured side. For instance, in a right hemispheric the coverage of the trigeminal nerve extends posteriorly stroke, the left trigeminal nucleus is unable to activate past the superior pole of the head, and thus the sensory the left lateral pterygoid and so the jaw may deviate to loss in peripheral trigeminal nerve injury should con- the left (away from the right cerebral hemispheric tinue posterior to the superior pole of the head. injury).1 – 8 13. Cranial Nerves 5, 7, 9, 10 215

Lateral pterygoids

Division 1 (Ophthalmic)

Division 2 (Maxillary) Jaw

Posterior Division 3 (Mandibular) Left Right

DRAWING 13-1 Cranial Nerve 5: Peripheral Innervation 216 Neuroanatomy: Draw It to Know It

Cranial Nerve 5: Nuclei

Here, we will draw the trigeminal nuclei in sagittal view. upper pons to the level of the superior colliculus (in the First, draw the trifurcated sensory ganglion of the midbrain), and then show that the spinal trigeminal trigeminal nerve, called the trigeminal ganglion, which nucleus and tract span from the upper pons to the upper means the “three twins.” It lies in a low depression known cervical spinal cord (their termination is variably listed as the trigeminal impression at the apex of the petrous as anywhere from C2 to C4). Trigeminal sensory aff er- temporal bone. Th e trigeminal ganglion is enveloped in ents descend the spinal trigeminal tract and then synapse Meckel’s cave: a dural-based, cerebrospinal fl uid-fi lled in the adjacent spinal trigeminal nucleus in a specifi c cavern that lies adjacent to the posterolateral aspect of somatotopic pattern (see Drawing 13-3 ). Th e caudal end the cavernous sinus. Now show that from rostral to of the spinal trigeminal nucleus is continuous with the caudal, the divisions of the trigeminal ganglion are the substantia gelatinosa, which lies within the dorsal horn ophthalmic, maxillary, and mandibular divisions — their of the spinal cord, and the spinal trigeminal tract is con- central projections terminate in the various trigeminal tinuous with the posterolateral fasciculus (aka Lissauer's nuclei. Next, show that the ophthalmic division traverses tract), which lies along the dorsal edge of the dorsal horn the superior orbital fi ssure; the maxillary division tra- of the spinal cord (see Drawings 7-1 and 7-2). verses foramen rotundum; and the mandibular division Next, show that the motor division of the trigeminal traverses foramen ovale. As they proceed centrally, the nerve passes ventrolaterally through the cerebellopon- ophthalmic and maxillary divisions (divisions 1 and 2, tine angle cistern to exit the brainstem (all of the pha- respectively) pass through the lateral wall of the cavern- ryngeal arch derivatives leave the brainstem along a ous sinus; they then merge together along with the man- ventrolateral path) and joins the mandibular division as dibular division to form the trigeminal ganglion within it exits the middle cranial fossa through foramen ovale to Meckel’s cave.9 innervate the muscles of mastication. Now, let’s draw a sagittal section through the brain- Th e mesencephalic nucleus contains the primary sen- stem in order to show the four diff erent trigeminal sory neurons for proprioceptive aff erents from the mus- nuclei: one motor, three sensory. We will use the upper cles of mastication, which ascend through the mandibular pons as the central point of the trigeminal nuclei, so also division of the trigeminal nerve. Th us, the mesenceph- draw an axial cross-section through the upper pons for alic nucleus is the only central nervous system nucleus to reference. Next, establish the position of the trigeminal house primary sensory neurons (the primary sensory motor nucleus and the principal sensory nucleus in the neurons of the mesencephalic sensory aff erents do not lie upper pons. Th ey lie in parallel just above the abducens within a peripheral ganglion). Th e mesencephalic nucleus. Show that the trigeminal motor nucleus lies nucleus projects to other sensory nuclei and also to the medial to the principal sensory nucleus— their positions trigeminal motor nucleus to produce the masseter refl ex follow the general organization of the cranial nerves (see (ie, the jaw jerk). When the muscles of mastication are Drawings 11-2 and 11-4). Whereas the principal sensory stretched, they activate the mesencephalic nucleus, and motor trigeminal nuclei are restricted to this upper which triggers the jaw jerk. A brisk jaw jerk can suggest pontine level, the two other trigeminal sensory nuclei pathologic disinhibition of suppressive corticopontine combined span the height of the brainstem and upper fi bers to cranial nerve 5. cervical spinal cord. Return, now, to the sagittal diagram We discuss the principal sensory and spinal trigemi- and show that the mesencephalic nucleus spans from the nal nuclei next. 1 – 6 , 10 13. Cranial Nerves 5, 7, 9, 10 217

Motor trigeminal nucleus Principal sensory nucleus

Posterior Superior colliculus Upper pons: axial section Inferior colliculus Anterior Mesencephalic Superior nucleus of CrN 5 orbital fissure Trigeminal motor Principal sensory Opthalmic nerve & nerve Motor trigeminal Trigeminal nuclei ganglion Petrous apex Maxillary nerve Cerebellopontine Spinal Foramen angle cistern Foramen trigeminal ovale rotundum nucleus Mandibular nerve Upper cervical spinal cord

DRAWING 13-2 Cranial Nerve 5: Nuclei 218 Neuroanatomy: Draw It to Know It

Cranial Nerve 5: Tracts (Advanced )

Here, we will draw the trigeminothalamic tracts and the trigeminal nucleus spans from the pons to the upper cer- somatotopic organization of the spinal trigeminal vical spinal cord. Indicate that within the spinal trigemi- nucleus. Th e central sensory aff erents of the trigeminal nal nucleus, pars oralis is the superior-most subnucleus: nerve relay to the cortex through two diff erent trigemi- it spans from the pons to the mid-medulla; show that nothalamic pathways: anterior and posterior. Draw a pars interpolaris is the middle subnucleus: it lies in the coronal view of the brainstem. Th en, draw the trigemi- mid-medulla; and, fi nally, indicate that pars caudalis is nal ganglion and show that the small fi ber sensory the inferior-most subnucleus: it spans from the lower modality trigeminal nerve fi bers project to the spinal medulla to the upper cervical spinal cord. Its inferior trigeminal tract and nucleus and that the large fi ber sen- extent is variably listed as anywhere from C2 to C4. sory modality trigeminal nerve fi bers project to the prin- Next, show that the somatotopic features of the face in cipal sensory nucleus. Note that although the principal the spinal trigeminal somatotopic map are stretched and sensory nucleus is oft en considered the trigeminal func- distorted to fi t into the proportions of the long, colum- tional equivalent of the gracile and cuneate nuclei and the nar spinal trigeminal nucleus (imagine pulling a rubber spinal trigeminal nucleus is oft en considered the trigemi- mask off of your face to visualize the distortion). Th e nal functional equivalent of the anterolateral system (ie, superior features of the face (eg, the eyes) lie anterior and spinothalamic tract), postsynaptic interconnections the inferior features (eg, the jaw) lie posterior; the most within the trigeminal system make this an imperfect rela- superior portion of the pars caudalis subnucleus receives tionship and we are unable to use it, clinically. 3 the lips and perioral area and the most inferior compo- Now, let’s draw the trigeminothalamic projections. nent receives the outer ears. Note that our somatotopic First, show that the anterolateral portion of the principal discussion of the spinal trigeminal nucleus refers to the sensory nucleus projects via the anterior trigeminotha- pars caudalis subnucleus, only; therefore, the most supe- lamic tract to the contralateral ventroposterior medial rior area is the inferior medulla and the most inferior nucleus of the thalamus, and then show that the postero- area is the upper cervical spinal cord. Clinically, when we medial portion of the principal sensory nucleus projects discuss the spinal trigeminal nucleus, we generally are via the posterior trigeminothalamic tract to the ipsilat- referring to the pars caudalis subnucleus of the spinal eral ventroposterior medial nucleus of the thalamus. trigeminal nucleus, only. Th en, indicate that the spinal trigeminal nucleus projects Now, let’s draw the onion-skin layers of the spinal via the anterior trigeminothalamic tract to the contralat- trigeminal somatotopic map: the central sensory pro- eral ventroposterior medial nucleus of the thalamus. cessing map for pain/temperature information in the Note that in regards to the somatotopy of the principal face. Draw an undistorted face. Show that the lips and sensory nucleus, the mandibular division of the trigemi- perioral area constitute the outermost layer of the nal nerve synapses posteriorly within the principal sen- onion — they lie within the most superior area of the pars sory nucleus and the ophthalmic division synapses caudalis subnucleus of the spinal trigeminal nucleus; the anteriorly; the maxillary division synapses intermediately next innermost layer, moving inferiorly within pars cau- between the mandibular and ophthalmic divisions.3 dalis, comprises the nose, eyes, and outer oral areas; then, Next, let’s draw the spinal trigeminal nucleus. It runs continuing downward, lies the cheeks and forehead; medial to the spinal trigeminal tract, has an onionskin then the vertical band just in front of the ears; and fi nally somatotopy, and divides into three diff erent cytoarchi- lies the partial spinal trigeminal sensory coverage of the tectural regions. In sagittal view, show that the spinal external ear (from cranial nerves 7, 9, and 10).1 – 6 , 8 , 10 13. Cranial Nerves 5, 7, 9, 10 219

TRIGEMINAL THALAMIC PROJECTIONS SPINAL TRIGEMINAL SOMATOTOPY Ipsilateral Contralateral thalamus thalamus

Posterior Anterior trigemino- trigemIno- thalamic thalamic Oralis tract tract Anterolateral Interpolaris projection Posteromedial Caudalis projection

Principal sensory nucleus

Trigeminal Spinal ganglion trigeminal tract & nucleus

DRAWING 13-3 Cranial Nerve 5: Tracts 220 Neuroanatomy: Draw It to Know It

Cranial Nerve 7: Innervation

Here, we will address the corticonuclear innervation of right hemisphere to indicate damage from the stroke. In cranial nerve 7, the facial nerve. We focus on this subject this situation, contralateral facial nuclear innervation is in particular because testing facial weakness can help us lost. However, show that ipsilateral upper division facial diff erentiate an upper motor neuron injury (eg, cortical nuclear innervation is preserved. As a result, show that stroke) from a lower motor neuron injury (eg, Bell’s the left upper face is strong and the left lower face is palsy). First, draw the left half of a face; label its upper weak. Th us, in cerebral cortical injury, there is contralat- and lower divisions. At the bedside, we test the upper eral lower facial weakness with preserved upper facial face with forehead wrinkle and the lower face with forced strength. As a small clinical pearl, when there is facial smile. Note that an involuntary smile (aka mimetic or weakness due to upper motor neuron injury, the palpe- emotional smile) has a diff erent innervation pattern than bral fi ssure on the paretic side of the face will oft en be what we will draw, here, so be careful not to make your wider than on the normal side of the face because the patients laugh at this point in the exam. facial droop will pull down the lower eyelid. Next, draw the bilateral cerebral hemispheres. Th en, Vignette two involves a left Bell’s palsy. Again, redraw draw the left facial nucleus and divide it into its upper the hemispheres, facial nucleus, and face. Here, encircle and lower divisions. First, show that the upper division the facial nucleus, itself, to indicate damage from the receives bilateral corticonuclear projections and then Bell’s palsy. Show that in this clinical circumstance, show that the lower division receives contralateral pro- innervation to the facial nucleus is preserved bilaterally, jections, only. Now, draw fi bers from the upper division but peripheral innervation to the face is lost. As a to the upper face and then show fi bers from the lower result, show that both the left upper face and left division to the lower face. Th e fact that the upper face lower face are weak. In Bell’s palsy, there is paralysis of receives bilateral corticonuclear innervation and the the complete ipsilateral side of the face. Note that Bell’s lower face receives contralateral corticonuclear innerva- palsy can occur anywhere along the seventh cranial tion allows us to distinguish upper motor neuron from nerve; therefore, the full clinical presentation of a lower motor neuron lesions, as we will see when we walk Bell’s palsy depends on where along its course the facial through the two clinical vignettes, next.2 nerve is aff ected. Th e next diagram will help us to under- Vignette one involves a right cerebral cortical stroke stand why there are such a wide variety of presentations that aff ects the facial fi bers. Redraw the hemispheres, for Bell’s palsy and what those potential presentations facial nucleus, and face. Th en encircle the cortex of the can be.1 – 6 , 8 , 10 13. Cranial Nerves 5, 7, 9, 10 221

NORMAL INNERVATION PATTERN UPPER MOTOR NEURON LESION LOWER MOTOR NEURON LESION

Right hemisphere Left hemisphere Right hemisphere Left hemisphere Right hemisphere Left hemisphere

Upper Upper Upper divsion divsion divsion Lower Lower Lower Left facial division division division nucleus (STRONG) (WEAK) Upper Upper Upper Left face face face face Lower Lower Lower face face face (WEAK) (WEAK)

DRAWING 13-4 Cranial Nerve 7: Innervation 222 Neuroanatomy: Draw It to Know It

Cranial Nerve 7: Anatomy

Here, we will draw the four components of cranial nerve fl oor of the fourth ventricle, called the facial colliculus. 7, the facial nerve. To begin, divide the nerve into four Next, in the cisternal segment, at the level of the pon- segments: an extracranial segment — where the nerve tomedullary junction, label the motor root, which con- emerges from the petrous portion of the temporal bone sists of special visceral eff erent (SVE) fi bers, only, and (the petrous bone); an intratemporal segment — where it then label the nervus intermedius (of Wrisberg), which passes through the petrous bone; a cisternal segment— consists of the remaining three fi ber types. Now, label where it passes through the cerebellopontine angle cis- the internal acoustic meatus (aka internal auditory tern; and an intra-axial segment — its brainstem course. canal), which is where the facial nerve enters the petrous Now, let’s establish the relevant cranial nerve 7 nuclei bone. Th e motor root and nervus intermedius merge and their end targets, and then we’ll illustrate their together within the internal acoustic meatus. Next, label paths. the geniculate ganglion, which houses the cell bodies for First, for reasons that will become clear later, draw the the pseudo-unipolar facial sensory aff erents. Th en, label abducens nucleus of cranial nerve 6, which spans from the nerve to the stapedius muscle (an SVE branch). Th is the mid to lower pons. Th en, draw the facial nucleus, small muscle contracts the neck of the stapes to prevent which spans from the lower pons to the pontomedullary the transmission of high-energy sounds through the junction and houses special visceral eff erent (SVE) cells. middle ear ossicles; note that it may also serve to extract Indicate that this component innervates the muscles of meaningful sound from background noise. Now, label facial expression. Next, draw the superior salivatory the greater petrosal nerve, which carries the GVE (upper nucleus, which lies just above the pontomedullary junc- division) fi bers. Next, label the chorda tympani, which is tion and houses general visceral eff erent cells (GVE). the nerve bundle of the combined GVE (lower division) Indicate that this component provides preganglionic and the SVA fi bers. And fi nally, draw the stylomastoid parasympathetic innervation to the pterygopalatine and foramen, which is the opening through which the SVE submandibular ganglia. Now, draw the solitary tract and GSA fi bers exit the petrous bone. nucleus, which spans the height of the medulla and Before we draw the nerve paths, themselves, let’s sub- receives the special visceral aff erent (SVA) fi bers of cra- divide the intratemporal segment of the facial nerve into nial nerve 7. Indicate that these fi bers carry taste sensa- four descriptive segments. First, label the meatal seg- tion from the anterior two thirds of the tongue. Next, ment, which is the segment wherein the facial nerve draw the pars caudalis portion of the spinal trigeminal passes through the internal acoustic meatus. Next, label nucleus, which spans from the inferior medulla to the the labyrinthine segment, which is the segment wherein upper cervical spinal cord and receives the general sen- the facial nerve exits the meatal segment and enters the sory aff erent (GSA) fi bers of cranial nerve 7. Indicate facial canal. Th is segment terminates at the geniculate that these fi bers carry sensory information from select ganglion, which is identifi ed by its abrupt bend, the portions of the external ear. external genu. Next, label the horizontal (aka tympanic) Now, let’s establish several key anatomic features of segment, wherein the facial nerve runs posteriorly (hori- the facial nerve course. First, label the internal genu; this zontally). Lastly, label the mastoid segment. In this seg- is the sweeping path the facial nerve takes over the top of ment, the facial nerve drops straight down and exits the the abducens nucleus — it generates a small bump in the skull through the stylomastoid foramen. 13. Cranial Nerves 5, 7, 9, 10 223

EXTRACRANIAL INTRATEMPORAL CISTERNAL INTRA-AXIAL SEGMENT SEGMENT SEGMENT SEGMENT Internal Pterygopalatine Pons ganglion, GVE genu Internal Greater acoustic Abducen’s Motor nucleus petrosal nerve meatus root (Meatal (Labyrinthine Facial segment) segment) nucleus, Geniculate Nervus Superior SVE ganglion intermedius salivatory (Horizontal nucleus, GVE segment) Solitary Medulla Nerve Spinal tract Tongue: to stapedius trigeminal nucleus, Chorda anterior two- nucleus, SVA tympani (Mastoid thirds, SVA pars segment) Cervical spinal caudalis, Submandibular cord GSA ganglion, GVE Stylomastoid foramen

External ear, GSA Muscles of facial expression, SVE

DRAWING 13-5 Cranial Nerve 7: Anatomy— Partial 224 Neuroanatomy: Draw It to Know It

Cranial Nerve 7: Anatomy (Cont.)

Now, we will show the nerve path for each facial nerve and meatal segments, crosses the cerebellopontine angle fi ber type. Begin with the SVE fi ber component; show cistern within the nervus intermedius, enters the brain- that it originates from the facial nucleus, sweeps over the stem at the pontomedullary junction, and synapses in abducens nucleus in the internal genu, exits the brainstem the superior portion of the solitary tract nucleus. at the pontomedullary junction as the motor root, passes Next, let’s draw the GVE fi bers, which carry pregan- through the cerebellopontine angle cistern, enters the glionic parasympathetic fi bers. Th e GVE component petrous bone through the internal acoustic meatus, and originates from the superior salivatory nucleus; it exits then passes through the meatal, labyrinthine, and hori- the brainstem at the pontomedullary junction, traverses zontal segments. Show that it gives off the stapedius nerve the cerebellopontine angle cistern within the nervus branch at the beginning of the mastoid segment and then intermedius, passes through the meatal segment, and drops straight down and exits the skull through the stylo- divides at the end of the labyrinthine segment (ie, at the mastoid foramen and divides into several nerve branches, geniculate ganglion). Th e upper division exits the petrous which innervate the muscles of facial expression. bone through a hiatus along the anterior petrous surface Next, let’s draw the GSA fi bers; they originate from as the greater petrosal nerve; it passes through foramen small portions of the external ear, which comprises the lacerum and then the pterygoid canal to innervate the auricle (aka pinna) and external acoustic meatus (aka pterygopalatine ganglion, which provides parasympa- external ear canal). Th e peripheral process of the GSA thetic postganglionic innervation to the nasal, palatine, component enters the skull through the stylomastoid and lacrimal glands. Th e lower division continues with foramen, ascends the mastoid segment, and traverses the the rest of the facial nerve through the horizontal seg- horizontal segment, and its cell bodies reside in the genic- ment and then through the superior portion of the mas- ulate ganglion. Th e central process of the GSA compo- toid segment, where it joins the chorda tympani to nent emerges from the geniculate ganglion; passes through innervate the submandibular ganglion, which provides the labyrinthine segment, through the internal acoustic postganglionic parasympathetic innervation to the sub- meatus, and through the cerebellopontine angle cistern mandibular and sublingual glands. within the nervus intermedius; enters the brainstem at Finally, let’s include some associated nerve structures the pontomedullary junction; and descends the spinal that either join or run alongside the facial nerve. First, trigeminal tract to synapse in the inferior portion of the show that the vestibulocochlear nerve also passes through pars caudalis portion of the spinal trigeminal nucleus. the internal acoustic meatus along with the facial nerve. Now, let’s illustrate the SVA fi bers, which originate Th en, show that the chorda tympani merges with the from the anterior two thirds of the tongue. Indicate that lingual nerve, a branch of the mandibular division of the the peripheral process of the SVA component joins the trigeminal nerve, which carries sensory aff erent informa- chorda tympani, ascends the mastoid segment, and tra- tion from the fl oor of the mouth. Lastly, show that the verses the horizontal segment, and its cell bodies lie within sympathetic deep petrosal nerve joins the greater petrosal the geniculate ganglion. From the geniculate ganglion, nerve in the pterygoid canal; together they form the nerve show that its central process traverses the labyrinthine of the pterygoid canal (aka the vidian nerve).1 – 8 , 10 – 12 13. Cranial Nerves 5, 7, 9, 10 225

EXTRACRANIAL INTRATEMPORAL CISTERNAL INTRA-AXIAL SEGMENT SEGMENT SEGMENT SEGMENT Internal Pterygopalatine Nerve of the Pons ganglion, GVE genu pterygoid canal Internal Greater acoustic Abducen’s Motor nucleus petrosal nerve meatus root (Meatal (Labyrinthine Facial Deep petrosal segment) nucleus, nerve segment) Geniculate Nervus Superior SVE ganglion Vestibulocochlear intermedius salivatory (Horizontal nerve nucleus, GVE segment) Solitary Medulla Nerve Spinal tract Tongue: to stapedius trigeminal nucleus, Chorda anterior two- Lingual nucleus, SVA tympani (Mastoid thirds, SVA nerve pars segment) Cervical spinal caudalis, Submandibular cord GSA ganglion, GVE Stylomastoid foramen

External ear, GSA Muscles of facial expression, SVE

DRAWING 13-6 Cranial Nerve 7: Anatomy— Complete 226 Neuroanatomy: Draw It to Know It

Cranial Nerves 9 & 10

Here, we will draw the glossopharyngeal nerve (cranial and the tympanic membrane; also, the GSA component nerve 9) and the vagus nerve (cranial nerve 10), together. of the vagus nerve carries posterior cranial fossa dura First, draw a sagittal view of the brainstem. Begin with mater sensory input. the inferior salivatory nucleus, which is a small nucleus Finally, draw the solitary tract nucleus, which spans in the upper medulla. Indicate that it innervates the otic the height of the medulla. Show that within its upper ganglion with GVE fi bers of the glossopharyngeal nerve. (gustatory) region, it receives taste aff erents from the Th e otic ganglion provides parasympathetic innervation posterior third of the tongue via SVA fi bers of the to the parotid gland. Next, directly underneath the infe- glossopharyngeal nerve and from the epiglottis via SVA rior salivatory nucleus, draw the dorsal motor nucleus of fi bers of the vagus nerve. Th en, indicate that within its the vagus, which spans the remainder of the medulla. lower (cardiorespiratory) region, it receives GVA fi bers Indicate that it provides parasympathetic innervation to of the glossopharyngeal nerve from the carotid body smooth muscle of the oropharynx and parasympathetic chemoreceptors and the carotid sinus (aka carotid bulb) innervation to viscera within the thoracoabdomen baroreceptors. Lastly, indicate that the solitary tract through GVE fi bers of the vagus nerve. Its actions nucleus receives GVA fi bers of the vagus nerve from the include pulmonary bronchiole constriction, heart rate thoracoabdomen: specifi cally, from the heart, barore- reduction, and augmentation of gut peristalsis. Now, ceptors in the aortic arch, chemoreceptors in the aortic draw nucleus ambiguus, which spans the height of the bodies, pharynx, larynx, lungs, and proximal gut.13 medulla. Indicate that it innervates the throat muscles Next, note that both the glossopharyngeal and vagus with SVE fi bers of the glossopharyngeal and vagus nerves each have superior and inferior sensory ganglia nerves. Its glossopharyngeal innervation is to stylopha- that are protected by the skull base; they lie within or ryngeus, which elevates the pharynx during speech and near to the jugular foramen. Cell bodies of the GSA swallowing, and its vagal innervation is to the pharynx, fi bers lie in the superior ganglia and those of the GVA larynx, select palatine muscles, and one tongue muscle: and SVA fi bers lie in the inferior ganglia.10 palatoglossus. Next, show that nucleus ambiguus also Now, draw an axial view of the medulla. Show that provides parasympathetic GVE innervation to the the glossopharyngeal and vagus fi bers exit the medulla carotid body and carotid sinus through the glossopha- laterally through the post-olivary sulcus to enter the ryngeal nerve, and to the heart and aortic bodies through cerebellomedullary cistern (aka inferior cerebellopon- the vagus nerve. tine cistern). Th en, return to our sagittal diagram and Now, draw the spinal trigeminal nucleus, pars cauda- show that these nerve fi bers traverse the skull base lis, which spans from the inferior medulla to the upper through the jugular foramen along with the accessory cervical spinal cord. Indicate that inferiorly it receives nerve (cranial nerve 11) and the internal jugular vein. cutaneous sensory reception from GSA fi bers of the Next, show that within the periphery, within the carotid glossopharyngeal and vagus nerves (and the facial nerve). space, cranial nerves 9, 10, and 11 and also cranial nerve Its sensory aff erents originate from many sites of the 12 (the hypoglossal nerve) and the internal jugular vein head and neck, including the oropharynx, external ear, and internal carotid artery run together.1 – 8 , 10 – 12 13. Cranial Nerves 5, 7, 9, 10 227

MOTOR SENSORY BRAINSTEM - SAGITTAL VIEW Inf. salivatory nuc.: Spinal trigeminal nuc.: Inferior Otic ganglion Head & neck salivatory GVE - CrN 9 GSA - CrN 9 & 10 JUGULAR nucleus (Superior ganglion) FORAMEN CAROTID Dorsal MEDULLA SPACE CrN 9 motor nuc. Dorsal motor nuc. Solitary of vagus of the vagus: CrN 10 tract Solitary tract nuc.: CrN 9 CrN 11 Thoracoabdomen Nucleus nucleus Taste CrN 10 Internal GVE - CrN 10 CrN 11 ambiguus SVA - CrNs 9 & 10 jugular vein CERVICAL (Inferior ganglion) CrN 12 SPINAL Internal Spinal CORD Nucleus ambiguus: jugular v. Internal trigeminal Throat muscles carotid artery nucleus, SVE - CrNs 9 & 10 Solitary tract nuc.: pars caudalis Carotid body & sinus GVA - CrN 9 Postolivary Nucleus ambiguus: (Inferior ganglion) Carotid body & sinus sulcus CrNs 9 & 10 GVE - CrN 9 Cerebello- medullary Solitary tract nuc.: cistern Nucleus ambiguus: Thoracoabdomen MEDULLA: AXIAL VIEW Heart & aortic bodies GVA - CrN 10 GVE - CrN 10 (Inferior ganglion)

DRAWING 13-7 Cranial Nerves 9 & 10 228 Neuroanatomy: Draw It to Know It

The Gag Reﬂ ex

In neurology, the gag refl ex is oft en tested to assess the Now, we will use prototypical injury patterns to show integrity of the brainstem and cranial nerves. We brush what happens in both upper motor neuron and lower the patient’s soft palate and observe for the characteristic motor neuron lesions to solidify our understanding of gag response. Th e gag refl ex relies on the glossopharyn- this arrangement. Redraw the hemispheres and bilateral geal nerve for its aff erent loop and the vagus nerve for its nucleus ambiguus nuclei. Show that in an upper motor eff erent loop, and it also involves the motor division of neuron lesion (such as a cortical stroke), the side of the trigeminal nerve and the hypoglossal nerve for addi- the palate contralateral to the stroke is weak and the tional motor eff ects. Although certain details of the gag side contralateral to the intact hemisphere is strong: refl ex remain poorly understood, enough of its neuro- the majority of fi bers from the intact hemisphere go to anatomy has been elucidated that we are able create a the contralateral nucleus ambiguus and the minority go reliable diagram for it. to the ipsilateral nucleus ambiguus. Note, however, that First, show that soft palate stimulation sends a volley many texts deny that there is any diff erence in the inner- of aff erent impulse along the glossopharyngeal nerve; it vation to the ipsilateral and the contralateral nucleus is unclear whether this aff erent impulse is somatic or vis- ambiguus nuclei and simply state that cortical innerva- ceral. Next, draw the glossopharyngeal sensory nuclei; tion to the nucleus ambiguus nuclei is bilateral without include both the spinal trigeminal nucleus for the ipsilateral or contralateral predominance. When that is GSA fi bers and the solitary tract nucleus for the GVA the case, a unilateral upper motor neuron lesion (eg, fi bers (as either may be involved). Th en, show that these a cortical stroke) has no eff ect on the gag refl ex. nuclei excite motor neurons in nucleus ambiguus and Next, again draw the hemispheres and bilateral indicate that nucleus ambiguus sends eff erent impulse nucleus ambiguus nuclei. Show that in a lower motor via the vagus nerve for pharyngeal constriction. Th us, neuron injury (such as a direct lesion to the nucleus the glossopharyngeal nerve provides the aff erent limb of ambiguus, itself, or its exiting fi bers), the corticonuclear the gag refl ex and the vagus nerve provides the eff erent innervation is preserved but there is complete peripheral limb. However, the gag refl ex additionally involves jaw fi ber loss on the side of the lesion and, therefore, there is opening and tongue thrust, so also show that nucleus unilateral palatal paralysis on the side of the lower motor ambiguus stimulates the trigeminal motor nucleus in the neuron lesion.11 pons, which is largely responsible for jaw opening via cra- When we evaluate for palatal weakness, the side of nial nerve 5, and the hypoglossal nucleus in the medulla, the palate that hangs lower is the side that is weak; which provides tongue thrust via cranial nerve 12. dismiss trying to determine the directionality of the Next, let’s illustrate the supranuclear innervation of the uvula — this only adds an unnecessary layer of complex- palate in order to demonstrate the cortical innervation to ity to our assessment. Paralysis of the muscles of the soft the special visceral eff erent component of the glossopha- palate results in failure of closure of the nasopharyngeal ryngeal and vagus nerves. First, draw the bilateral nucleus aperture; as a consequence, air escapes through the nose ambiguus nuclei. Th en, show that each nucleus ambiguus during speech and liquids are regurgitated into the nasal innervates the ipsilateral side of the palate. Next, show cavity during swallowing. In amyotrophic lateral sclerosis that each cerebral hemisphere projects corticonuclear (ALS), there is oft en loss of corticonuclear innervation fi bers to each nucleus ambiguus, but show that the pre- to the nucleus ambiguus, with resultant characteristic dominance of fi bers go to the contralateral nucleus. nasal pattern speech. 13. Cranial Nerves 5, 7, 9, 10 229

NORMAL Cortico CORTICONUCLEAR nuclear INNERVATION

Upper motor neuron injury

THE GAG REFLEX Nucleus ambig. Sensory Loop Palate CrN 9 Soft palate Spinal trigeminal stimulus nucleus or Solitary tract (STRONG) (WEAK) nucleus

Motor Loop

Pharyngeal CrN 10 Nucleus ambiguus constriction Jaw opening CrN 5 Motor trigeminal nucleus Lower motor neuron injury (WEAK) (STRONG) Tongue thrust CrN 12 Hypoglossal nucleus

DRAWING 13-8 Th e Gag Refl e x 230 Neuroanatomy: Draw It to Know It

References 1 . Binder , D. K. , Sonne , D. C. & Fischbein , N. J. Cranial nerves: 7 . Willoughby , E. W. & Anderson , N. E. Lower cranial nerve motor anatomy, pathology, imaging (Th ieme, 2010 ). function in unilateral vascular lesions of the cerebral hemisphere . 2 . Brazis , P. W. , Masdeu , J. C. & Biller , J. Localization in clinical Br Med J (Clin Res Ed) 289 , 791 – 794 ( 1984 ). neurology, 5th ed. ( Lippincott Williams & Wilkins , 2007 ). 8 . S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 3 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic clinical practice, 40th ed. ( Churchill Livingstone/Elsevier , 2008 ). and clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 9 . M a f e e, M . F., Va l v a s s o r i, G . E . & B e c k e r, M . Imaging of the head and 2006 ). neck, 2nd ed. (Th ieme, 2005 ). 4 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human 1 0. M a c d o n a l d, A . J . Diagnostic and surgical imaging anatomy. Brain, brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal head & neck, spine, 1st ed. (Amirsys , 2006 ). structure, vascularization and 3D sectional anatomy (Springer , 2009 ). 1 1. C o n n, P. M . Neuroscience in medicine, 3rd ed. (Humana Press, 2008 ). 5 . N e t t e r, F. H . & D a l l e y, A . F. Atlas of human anatomy, 2nd ed. 12 . Sundin , L. & Nilsson , S. Branchial innervation . J Exp Zool 293 , (Novartis , 1997 ). 232 – 248 , doi:10.1002/jez.10130 (2002 ). 6 . Wilson-Pauwels , L. Cranial nerves: function and dysfunction, 3rd ed. 13 . Fritsch , H. & Kühnel , W. Color atlas of human anatomy. Volume 2, ( People’s Medical Pub. House , 2010 ). Internal organs, 5th ed., Chapter 11 (Th ieme, 2007 ). 1 4 Vestibular and Auditory Systems

The Ear

The Vestibular System

Central Auditory Pathways

Auditory Physiology ( Advanced ) 232 Neuroanatomy: Draw It to Know It

Know-It Points

The Ear

■ Th e external and middle ear canals lie within the ■ Reissner’s membrane separates the vestibular tympanic portion of the temporal bone. duct from the cochlear duct, and the basilar ■ Th e middle ear canal contains three ossicles — from membrane separates the cochlear duct from the lateral to medial: the malleus, incus, and stapes. tympanic duct. ■ Th e stapes abuts the oval window; when sound is ■ Th e vestibular and tympanic ducts are fi lled with transmitted through the ossicles, the stapes pushes perilymphatic fl uid, and the cochlear duct is fi lled the oval window into the inner ear. with endolymphatic fl uid. ■ Th e inner ear canal lies within the petrous portion of ■ Th e three semicircular canals (anterior, horizontal, the temporal bone. and posterior) lie perpendicular to one another and ■ Th e inner ear canal divides into three diff erent parts: detect rotational acceleration. the semicircular canals, which serve vestibular ■ From the observer’s perspective, the anterior canals function; the cochlea, which serves auditory produce upward eye movement; the posterior canals function; and the vestibule, which is involved in both produce downward eye movement; the right-side auditory and vestibular functions. canals produce clockwise torsional eye movement; ■ Th ree ducts form within the cochlea: the cochlear and the left -side canals produce counterclockwise duct (scala media), the vestibular duct (scala torsional eye movement. vestibuli), and the tympanic duct (scala tympani).

The Vestibular System

■ Th e vestibular nuclear complex excites the ■ Th e medial division of the vestibular nuclear contralateral abducens nucleus and the abducens complex comprises the superior nucleus and medial nucleus excites the contralateral oculomotor nucleus, nucleus. which is ipsilateral to the vestibular nuclear complex ■ Th e lateral division of the vestibular nuclear where the impulse originated. complex comprises the lateral nucleus and inferior ■ Th e vestibular nuclear complex spans from the nucleus. upper pons to the inferior fl oor of the fourth ventricle (in the medulla).

Central Auditory Pathways

■ Th e ventral cochlear nucleus lies at the ■ Each inferior colliculus projects to the ipsilateral pontomedullary junction. medial geniculate nucleus via the brachium of the ■ Th e dorsal cochlear nucleus lies in the upper medulla. inferior colliculus. ■ Th e superior olivary complex lies in the mid-pons. ■ Each medial geniculate nucleus projects to ■ Th e inferior colliculi lie in the inferior midbrain. the ipsilateral transverse temporal gyri (Heschl’s ■ Th e lateral lemniscus tracts project to the inferior gyri) — the primary auditory cortex. colliculi. 14. Vestibular and Auditory Systems 233

Auditory Physiology (Advanced )

■ Preservation of tone localization throughout the ■ Within the transverse temporal gyri (Heschl’s gyri), central auditory system is called tonotopy. low-frequency sounds localize laterally whereas ■ Th e base of the cochlea encodes high-frequency high-frequency sounds localize medially. sounds and the apex encodes low-frequency sounds. ■ When there is a unilateral lesion to the central ■ Low-frequency sounds lie anterior within the ventral auditory pathway, hearing is preserved from the and dorsal cochlear nuclei. duplication of auditory information in the ■ High-frequency sounds lie posterior within the contralateral cerebral hemisphere. ventral and dorsal cochlear nuclei.

Integument Epitympanic recess Facial Auditory ossicles musculature Squama of Semicircular ducts temporal bone (in canals)

Meninges Endolymphatic duct (in vestibular aqueduct) Endolymphatic sac Brain (in dura mater) Perilymphatic duct (in cochlear canaliculus) Scala tympani Auricle Cochlear duct Scala vestibuli External Mucous membrane acoustic meatus Auditory tube

Levator veli palatini Cartilages of external ear Secondary tympanic membrane Vestibule Mastoid process Tympanic membrane and cavity Mastoid air cells Styloid process

FIGURE 14-1 Outer, middle, and inner ear. Used with permission from Baloh, Robert W., and Vicente Honrubia. Clinical Neurophysiology of the Vestibular System, 3rd ed. Contemporary Neurology Series 63. Oxford; New York: Oxford University Press, 2001. 234 Neuroanatomy: Draw It to Know It

Nerve from anterior Scarpa’s Vestibular nerve canal ganglion Facial nerve Utricular nerve Auditory nerve

Internal auditory canal Nerve from horizontal canal

Nerve from posterior canal Round window Cochlea Saccular nerves Spiral ganglion

FIGURE 14-2 Inner ear. Used with permission from Baloh, Robert W., and Vicente Honrubia. Clinical Neurophysiology of the Vestibular System, 3rd ed. Contemporary Neurology Series 63. Oxford; New York: Oxford University Press, 2001.

OCCIPUT

RPC LPC

RHC LHC

RAC LAC

BROW

RAC + LAC =

RAC + RPC =

A RAC + RPC + RHC =

Stimulate Left Utricular Nerve

B RE LE

FIGURE 14-3 Oculomotor eff ects of semicircular canal stimulation. Used with permission from Leigh, R. J. & Zee, D. S. Th e Neurology of Eye Movements. Oxford; New York: Oxford University Press, 2006. 14. Vestibular and Auditory Systems 235

FIGURE 14-4 Summary of probable direct connections of vestibulo-ocular refl ex, based upon fi ndings from a number of species. Excitatory neurons are indicated by open circles, inhibitory neurons by fi lled circles. III: oculomotor nuclear complex; IV: trochlear nucleus; VI: abducens nucleus; XII: hypoglossal nucleus; AC: anterior semicircular canal; ATD: ascending tract of Deiters; BC: brachium conjunctivum; HC: "horizontal" or lateral semicircular canal; IC: interstitial nucleus of Cajal; IO: inferior oblique muscle; IR: inferior rectus muscle; LR: lateral rectus muscle; LV: lateral vestibular nucleus; MLF: medial longitudinal fasciculus; MR: medial rectus muscle; MV: medial vestibular nucleus; PC: posterior semicircular canal; PH: prepositus nucleus; SV: superior vestibular nucleus; SO; superior oblique muscle; SR: superior rectus muscle; V: inferior vestibular nucleus; VTP: ventral tegmental pathway. Used with permission from Leigh, R. J. & Zee, D. S. Th e Neurology of Eye Movements. Oxford; New York: Oxford University Press, 2006. 236 Neuroanatomy: Draw It to Know It

The Ear

Here, we will draw a coronal view of the ear with the Now, let’s draw the three ducts that form within the subject facing towards us. Begin with our planes of cochlea. First, draw the cochlear duct (scala media); orientation. First, draw the medial–lateral plane; then, then, label the vestibular duct (scala vestibuli), which is the anterior–posterior plane; and fi nally, the superior– continuous with the vestibule; and fi nally, label the tym- inferior plane. Now, draw the outer ear. Th en, draw the panic duct (scala tympani), which ends in the round external ear canal, which extends through the tympanic window (aka the secondary tympanic membrane). Show portion of the temporal bone, just in front of the mas- that the vestibular and tympanic ducts connect at the toid process. Next, draw the tympanic membrane. apex of the cochlea (aka the helicotrema). Reissner’s Indicate that sound waves pass through the external ear membrane separates the vestibular duct from the canal to vibrate the tympanic membrane. cochlear duct and the basilar membrane separates the Now, draw the middle ear canal, which also lies mostly cochlear duct from the tympanic duct. Th e vestibular within the tympanic portion of the temporal bone. and tympanic ducts are fi lled with perilymphatic fl uid, Indicate that it contains three ossicles— from lateral to whereas the cochlear duct is fi lled with endolymphatic medial, the malleus, incus, and stapes, which are the fl uid. Perilymphatic fl uid is like extracellular fl uid in that Latin terms for their shapes: “hammer,” “anvil,” and “stir- it is high in sodium and low in potassium, whereas endo- rup,” respectively. Next, indicate that the stapes abuts the lymphatic fl uid is like intracellular fl uid in that it is high oval window. When sound is transmitted through the in potassium and low in sodium. Patients with Ménière’s ossicles, the stapes pushes the oval window into the inner syndrome, which causes bouts of vertigo, low-frequency ear (drawn soon). Now, show that the eustachian tube hearing loss, and ear fullness, are commonly treated with extends from the middle ear into the nasopharynx; it salt-wasting diuretic medications because the syndrome is causes your middle ears to equilibrate with the atmo- thought to be due to pathologically elevated endolym- spheric pressure in your nasopharynx when you swallow. phatic sodium concentration. In more severe cases of Two important muscles exist within the middle ear Ménière’s syndrome, vestibular ablation is performed and, canal: the tensor tympani, which is innervated by the also, aminoglycosides (specifi cally gentamicin and strep- trigeminal nerve and which acts on the tympanic mem- tomycin) are used to destroy the vestibular end-organ brane, and the stapedius muscle, which is innervated by with relative preservation of the auditory cells. the facial nerve and which acts on the stapes. Now, indicate that when the oval window vibrates, a Next, we will draw the inner ear canal, which lies fl uid wave passes through the vestibule, which then within the petrous portion of the temporal bone. Divide passes through the vestibular duct, across the apex of the the inner ear into three diff erent parts. First, draw the cochlea into the tympanic duct, and then through the semicircular canals, which lie in superior-lateral position tympanic duct to push the round window into the air- and serve vestibular function; then, draw the cochlea, fi lled middle ear canal. In this process, the auditory sen- which is shaped like a snail’s shell, and which lies in ante- sory organ, the organ of Corti, which lies along the rior-inferior position and serves auditory function; and basilar membrane, is activated for sound detection. fi nally, draw the vestibule, which lies in between them High-frequency sounds activate hair cells at the base of and is involved in both auditory and vestibular func- the cochlea (near the oval and round windows) whereas tions — it transmits sound waves from the oval window low-frequency sounds activate hair cells at the apex of to the cochlea and contains the otolith organs, which the cochlea. Th e basilar membrane is thinnest at its base provide vestibular cues.1 and widest at its apex. 14. Vestibular and Auditory Systems 237

Tympanic duct

Cochlear duct Malleus OSSICLES Vestibular Incus Oval duct Vestibule Outer EXTERNAL Tymp Stapes window Apex ear EAR CANAL mbrn Round COCHLEA MIDDLE window EAR CANAL INNER EAR CANAL Superior Posterior Eustachian Lateral Medial tube Anterior Inferior

DRAWING 14-1 Th e Ear— Partial 238 Neuroanatomy: Draw It to Know It

The Ear (Cont.)

Next, return to the vestibule so we can show the otolith same diagonal, from left anterior to right posterior; then, organs. First, draw the saccule, which detects vertical show that the right anterior and left posterior canals movement (ie, gravity), and then draw the utricle, which drive the eyes along the same diagonal, from right ante- perceives horizontal (forward/backward) movement. rior to left posterior; and fi nally, indicate that the hori- Th e macula (the neuroepithelial sensory detection zontal canals drive the eyes laterally. 1 region) of the saccule is principally vertically oriented Next, we will divide the directionality of the eye and its attached hair cells are horizontally oriented to movements generated by the anterior and posterior detect vertical movement, whereas the macula of the semicircular canals (the vertical canals) based on whether utricle is principally horizontally oriented and its the canal is anterior or posterior, right or left . Label across attached hair cells are vertically oriented to detect hori- the top of the page that we will show the eye movement zontal movement. directionality from the observer’s perspective in coronal Now, let’s label the semicircular canals: the anterior view. Also, to avoid confusion, since eye movements are semicircular canal, horizontal semicircular canal, and pos- commonly addressed in regards to the nystagmus they terior semicircular canal. Th ese three semicircular canals produce, indicate that we are showing the slow phase of lie perpendicular to one another and detect rotational the nystagmus. Now, indicate that the anterior canals acceleration. To understand their directionality, include produce upward movements and that the posterior within our fi gure an axial view of them. Draw an oval- canals produce downward movements, and, again, from shaped cranium and label its anterior and posterior the observer’s perspective, indicate that the right-side aspects. Th en, draw the left anterior semicircular canal canals produce torsional movements in a clockwise direc- facing anterolaterally and the left posterior semicircular tion whereas the left -side canals produce torsional move- canal perpendicular to it. Th e posterior canal lies along ments in a counterclockwise direction.2 the axis of the petrous ridge. Next, include the laterally In benign paroxysmal positional vertigo, calcium car- facing left horizontal canal. In normal, upright head posi- bonate crystals from the utricle fall into one of the semi- tion, the horizontal canal is tilted upward about 30 degrees circular canals— most oft en the posterior canal— and to the horizontal plane and the anterior and posterior stimulate positional vertigo. If the right posterior canal is canals are roughly within the vertical plane. When sitting activated, then from the observer’s perspective, the slow upright, if the head is tilted down 30 degrees, the horizon- phase of the nystagmus is downward with clockwise tal canals are brought into the earth-horizontal plane. rotation. Th e fast phase, which is how the nystagmus is Now, draw the right-side semicircular canals as mirror actually named, is in the opposite direction: upward and images of the left . counterclockwise. 2 At the utricular end of each canal is a membranous To conclude our diagram, let’s draw the vestibuloco- enlargement, called the ampulla, which contains the sen- chlear nerve, which transmits the vestibular and auditory sory cell system of the semicircular canal. Attached to impulses from the inner ear to the vestibulocochlear the ampulla is the cupula, which is a gelatinous mass that nuclei in the brainstem. First, draw the vestibular seg- defl ects during angular acceleration. When the cupula ment of the vestibulocochlear nerve and then the cochlear bows, the hair cells are activated and, as a result, the segment. Indicate that the vestibulocochlear nerve passes semicircular canals generate eye movements in their through the internal acoustic meatus (along with the plane of orientation. Show that the left anterior canal facial nerve) and crosses the pontocerebellar cistern to and the right posterior canal drive the eyes along the enter the brainstem at the pontomedullary junction. 14. Vestibular and Auditory Systems 239

SEMICIRCULAR CORONAL, OBSERVER PERSPECTIVE - SLOW PHASE EYE MOVEMENTS CANALS LeftAnterior Right Anterior Posterior Right Left canals canals canals canals

VESTIBULOCOCHLEAR NERVE Anterior Vestibular Posterior canal segment Cochlear canal segment Internal Posterior acoustic Horizontal Tympanic duct meatus canal Cochlear duct Malleus OSSICLES Vestibular Incus Utricle Oval Saccule duct Vestibule Outer EXTERNAL Tymp Stapes window Apex ear EAR CANAL mbrn Round COCHLEA MIDDLE window EAR CANAL INNER EAR CANAL Superior Posterior Eustachian Lateral Medial tube Anterior Inferior

DRAWING 14-2 Th e Ear— Complete 240 Neuroanatomy: Draw It to Know It

The Vestibular System

Here, we will draw the vestibulo-ocular refl ex, vestibu- nuclear complex, which spans from the upper pons to lospinal pathways, and a few additional central vestibu- the inferior fl oor of the fourth ventricle (in the medulla). lar projections. We will begin with the vestibulo-ocular To draw the individual nuclei of the vestibular nuclear refl ex. Each of the semicircular canals has its own projec- complex, divide the complex into medial and lateral tion pattern (see Figure 14-4); here, we will draw the divisions. Label the top of the medial division as the horizontal canal’s excitation of the ocular nuclei because superior nucleus and the rest as the medial nucleus; then, it is the most clinically helpful pathway to learn. Draw a label the top half of the lateral division as the lateral coronal view of the brainstem and include an axial sec- nucleus and the bottom half as the inferior nucleus. Th e tion through a pair of eyes. Next, draw the left vestibular lateral nucleus is also called Deiters’ nucleus and the nuclear complex, which spans much of the height of the inferior nucleus is also called the descending nucleus. pons and the medulla. Now, label the left oculomotor Note that although not shown as such in our diagram, nucleus and also the right abducens nucleus. Show that the lateral and inferior nuclei actually overlap in the low the vestibular nuclear complex excites the contralateral pons and the medial and superior nuclei overlap in the abducens nucleus, which causes the right lateral rectus mid-pons. muscle to produce eye a b duction: it drives the right eye Now, to continue our vestibulospinal pathway dia- to the right. Th en, indicate that the abducens nucleus gram, include upper and lower levels of the spinal cord. also projects fi bers across midline that ascend the medial Indicate that the lateral vestibular nucleus projects longitudinal fasciculus and excite the contralateral ocul- uncrossed descending fi bers, which descend the ventral omotor nucleus, which causes the left medial rectus spinal cord and innervate extensor motor neurons muscle to produce eye a d duction: it drives the left eye to throughout the spinal cord, and label this projection as the right. Lastly, show that the vestibular nuclear com- the lateral vestibulospinal tract. Th en, indicate that the plex also sends direct projections to the ipsilateral oculo- medial vestibular nucleus projects crossed and uncrossed motor nucleus via the ascending tract of Deiters. Note fi bers that descend the medial spinal cord to innervate that the vestibular nuclear complex simultaneously extensor motor neurons in the upper spinal cord, only, inhibits the ipsilateral abducens nucleus and contralat- and label this as the medial vestibulospinal tract. Note eral oculomotor nucleus, and also note that of the four that the medial vestibulospinal tract also receives minor vestibular nuclei (drawn later), the medial and lateral inputs from the lateral and inferior vestibular nuclei, as nuclei have the most robust ocular projections.2 well. Th ese vestibulospinal pathways provide antigravity For a simple way to remember this circuitry at the movements for the maintenance of posture, as do the bedside, hold your fi sts in front of you and show that the reticulospinal tracts (see Drawing 7-3). left vestibular nuclear complex drives the eyes to the right Next, let’s list a few additional central vestibular func- and the right vestibular nuclear complex drive the eyes to tions. Indicate that the vestibular nuclei project to the the left . Next, drop one fi st to demonstrate that when thalamus for somatosensory detection of vestibular one vestibular nuclear complex is damaged, the eyes devi- movement and to the reticular formation, which induces ate toward the damaged side, away from the intact side. nausea and vomiting. Lastly, indicate that the vestibulo- Next, we will draw the vestibulospinal pathways. colic refl ex maintains the head at a level position during Redraw a brainstem. Include an outline of the vestibular movement. 2 – 4 14. Vestibular and Auditory Systems 241

VESTIBULOSPINAL TRACTS

HORIZONTAL CANAL PROJECTIONS - EXCITATORY Sup Lat Med Medial vestibulo- Inf spinal tract Medial Lateral rectus rectus Lateral Oculomotor vestibulo- Upper nucleus spinal Medial longitudinal tract Ascending fasciculus tract of Deiters Abducens Lower Vestibular nucleus nuclear complex ADDITIONAL CENTRAL VESTIBULAR PROJECTIONS Thalamic projections - somatosensory detection Reticular projections - nausea/vomiting Vestibulocolic reflex - level head

DRAWING 14-3 Th e Vestibular System 242 Neuroanatomy: Draw It to Know It

Central Auditory Pathways

Here, we will create a simplifi ed diagram of the central ventral stria. To begin, show projection fi bers from the auditory pathways. First, draw a coronal view of the left ventral cochlear nucleus to the bilateral superior oli- brainstem. On the left side, label the ventral cochlear vary complexes. Th en, add another pathway that projects nucleus at the pontomedullary junction and then, just from the ventral cochlear nucleus to the contralateral below it, in the upper medulla, label the dorsal cochlear inferior colliculus via the lateral lemniscus without syn- nucleus. Note that the ventral cochlear nucleus is oft en apsing in the superior olivary complex. Label the ventral further subdivided into its anterior and posterior subnu- cochlear to bilateral superior olivary complex and ven- clei. Next draw an axial view of the posterolateral wedge tral cochlear to contralateral inferior colliculus projec- of the upper medulla/pontomedullary junction to illus- tion fi bers as the ventral acoustic stria, and indicate that trate the anterior–posterior relationship of the ventral they are also referred to as the trapezoid body. Next, in and dorsal cochlear nuclei. Draw the restiform body of our axial diagram show that the ventral acoustic stria the inferior cerebellar peduncle and then show that the passes ventral to the restiform body. ventral cochlear nucleus lies along its ventrolateral sur- Now, return to the coronal diagram and show that face and that the dorsal cochlear nucleus lies along its the dorsal cochlear nucleus projects to the contralateral dorsolateral surface. 5 inferior colliculus via the lateral lemniscus without form- Now, in the coronal diagram, label the bilateral ing a synapse in the superior olivary complex, and label superior olivary complexes in the mid-pons. Each supe- this projection as the dorsal acoustic stria. In the axial rior olivary complex comprises three separate nuclei: a diagram, show that the dorsal acoustic stria emerges nucleus of the trapezoid body, medial superior olivary from the dorsal cochlear nucleus and passes dorsally nucleus, and lateral superior olivary nucleus. Surrounding around the restiform body. the superior olivary complexes are peri-olivary cells. Next, back in the coronal diagram, show that the ven- Next, in the inferior midbrain, label the bilateral inferior tral cochlear nucleus sends additional projection fi bers colliculi. Th en, show projection fi bers from the bilateral to the contralateral inferior colliculus, which ascend via superior olivary complexes to their respective inferior the lateral lemniscus tract without synapsing in the supe- colliculi and label these projections as the lateral lemnis- rior olivary complex. Label these fi bers as the intermedi- cus tracts. Next, label the left medial geniculate nucleus, ate acoustic stria. In our axial diagram, show that the which is part of the metathalamus, and then, label the intermediate acoustic stria emerges from the dorsal por- left transverse temporal gyri (aka Heschl’s gyri) continu- tion of the ventral cochlear nucleus and passes dorsally ous with the superior temporal gyrus in the Sylvian fi s- around the restiform body. sure. Now, draw a representative projection from the left A simple acronym for the central auditory pathways inferior colliculus to the left medial geniculate nucleus is “S-L-I-M,” which denotes a few of the key steps in via the brachium of the inferior colliculus. And fi nally, the pathway: superior olivary complex to lateral lemnis- draw a projection from the left medial geniculate nucleus cus to inferior colliculus to medial geniculate body. A to the ipsilateral transverse temporal gyri (Heschl’s common electrophysiologic test of the auditory system gyri) — the primary auditory cortex. Note that the same is the brainstem auditory evoked response, which helps projections exist on the right side, as well. localize central auditory pathway lesions and helps detect Next, let’s show the projection fi bers from the ventral asymptomatic central nervous system lesions in the diag- and dorsal cochlear nuclei. Th ree acoustic striae exist: nostic evaluation of multiple sclerosis.3 , 6 ventral, dorsal, and intermediate. First, let’s draw the 14. Vestibular and Auditory Systems 243

UPPER MEDULLA/PONTOMEDULLARY JUNCTION - AXIAL VIEW Posterior Lateral Medial Anterior Dorsal cochlear CENTRAL AUDITORY PATHWAYS nucleus CORONAL VIEW Dorsal Restiform acoustic stria Medial geniculate body Intermediate Transverse temporal nucleus (metathalamus) gyri (Heschl’s gyri) Ventral acoustic stria Brachium of inferior colliculus cochlear nucleus Ventral acoustic stria (also trapezoid body)

Inferior colliculi

SOCs Lateral lemniscus Ventral acoustic stria SOCs - Superior olivary complexes (also trapezoid body) Dorsal Ventral acoustic stria cochlear nucleus Intermediate Dorsal acoustic stria cochlear nucleus

DRAWING 14-4 Central Auditory Pathways 244 Neuroanatomy: Draw It to Know It

Auditory Physiology (Advanced )

Here, we will learn the physiology of tonotopy (the top- low-frequency sounds whereas level diff erences are best ographic organization of sound) and also the physiology detected for high-frequency sounds. of binaural and monaural sound localization. First, we Now, let’s incorporate these interaural diff erences will show the tonotopy of select regions of the auditory into the core pathways for binaural sound localization. pathway. Indicate that the base of the cochlea encodes First, in coronal view, on both sides of the brainstem, high-frequency sounds and that the apex encodes low- draw the following superior olivary complex nuclei: frequency sounds. Th en, within the ventral and dorsal the medial nucleus of the trapezoid body, medial supe- cochlear nuclei, show that low-frequency sounds lie rior olivary nucleus, and lateral superior olivary nucleus. anterior whereas high-frequency sounds lie posterior. Low-frequency sounds are encoded within the spheri- Finally, indicate that within the transverse temporal gyri cal bushy cells of the ventral cochlear nucleus. Indicate (Heschl’s gyri) (the primary auditory cortex), low-fre- that they project bilaterally to the medial superior quency sounds localize laterally whereas high-frequency olivary nuclei, which are sensitive to interaural time sounds localize medially. Th us, there is preservation of diff erences. tonotopy throughout the central auditory system.7 , 8 High-frequency sounds are encoded within the ven- Each cerebral hemisphere receives similar input from tral cochlear nucleus in both the spherical bushy cells each set of cochlear nuclei, so when there is a unilateral and globular bushy cells. Both cell types project to the lesion to any of the steps in the central auditory pathway, lateral superior olivary nucleus, which is sensitive to hearing is preserved from the duplication of auditory interaural level diff erences. Show that the spherical bushy information in the contralateral cerebral hemisphere. cells send exclusively ipsilateral, excitatory projections to Th e auditory system has this central duplication of sen- the lateral superior olivary nucleus. On the contrary, sory information whereas other sensory systems, such as using the ventral cochlear nucleus on the opposite side, the visual and somatosensory systems, do not because show that the globular bushy cells send excitatory pro- the peripheral receptors of the visual and somatosensory jections to the contralateral medial nucleus of the trape- systems are topographically arranged to encode for stim- zoid body, which in turn sends inhibitory projections ulus localization, whereas the cochlea is tonotopically to the ipsilateral lateral superior olivary nucleus (thus arranged, instead. the globular bushy cells inhibit the contralateral lateral Tonotopy informs the brain about sound frequency superior olivary nucleus via the medial nucleus of the but not location; therefore, sound localization must trapezoid body). 9 – 16 occur through other means. Sound reaches each ear (the Th ese pathways establish the physiology of binaural near ear and far ear) at slightly diff erent times and inten- sound localization, but plug one of your ears, close your sities. Th ese are the two main interaural (between ear) eyes, and snap your fi ngers at diff erent points in space. diff erences: the interaural time diff erence and the inter- Even with only one ear, you can still localize sound stim- aural level diff erence (where “time” refers to the time the uli fairly well because of your monaural sound localiza- sound reaches each ear and “level” refers to the sound tion skills. Monaural localization of sound relies on the intensity level at each ear). Sound reaches the near ear head-related transfer function, which shapes sound before it reaches the far ear to create the interaural time waves as they propagate toward the eardrum. Th rough diff erence, and the head, itself, attenuates the sound monaural sound localization mechanisms, the head, before it reaches the far ear to create the interaural level torso, and pinna distort sound waves into spectral pat- diff erence. In accordance with the duplex theory of terns that the central auditory system uses in the local- sound localization, time diff erences are best detected for ization of sound.15 14. Vestibular and Auditory Systems 245

TONOTOPY BINAURAL SOUND LOCALIZATION

Lateral MEDIAL superior olivary nucleus sensitive to interaural TIME difference LATERAL superior olivary nucleus sensitive to interaural LEVEL difference Low Medial High MNTB - medial nucleus of the trapezoid body TRANSVERSE TEMPORAL MSO - medial superior olivary nucleus GYRI (HESCHL’S GYRI) LSO - lateral superior olivary nucleus

Dorsal nucleus High LEFT RIGHT

Low Posterior COCHLEAR NUCLEI High Anterior LSO MSO MNTB MNTB MSO LSO Ventral nucleus Low

COCHLEA Low Spherical bushy cells Globular bushy cells High of the ventral of the ventral cochlear nucleus cochlear nucleus

Lateral Medial

DRAWING 14-5 Auditory Physiology 246 Neuroanatomy: Draw It to Know It

References 1 . S w a r t z, J . D . & L o e v n e r, L . A . Imaging of the temporal bone, 4th ed. 1 0. B e n a r r o c h, E . E . Basic neurosciences with clinical applications, p. 503 (Th ieme, 2009 ). ( Butterworth Heinemann Elsevier , 2006 ). 2 . Leigh , R. J. & Zee , D. S. Th e neurology of eye movements (Oxford 1 1. Wo o d i n, M . A . & M a ff e i, A . Inhibitory synaptic plasticity, pp. 40 – 42 University Press, 2006 ). (Springer Verlag, 2010 ). 3 . Wilson-Pauwels , L. Cranial nerves: function and dysfunction, 1 2. B r o n z i n o, J . D . Th e biomedical engineering handbook, 3rd ed., pp. 143 – 165 ( People’s Medical Publishing House , 2010 ). pp. 5 – 11 , 5 – 12 ( CRC/Taylor & Francis , 2006 ). 4 . Wa x m a n, S . G . Clinical neuroanatomy, 25th ed., p. 53 ( Lange 13 . Tollin , D. J. Encoding of interaural level diff erences for sound Medical Books/McGraw-Hill, Medical Pub. Division , 2003 ). localization . In Th e senses: a comprehensive reference ( e d A . I . 5 . Rajimehr , R. & Tootell , R. Organization of human visual cortex . Basbaum ) ( Elsevier Science , 2008 ). In Th e senses: a comprehensive reference (ed. A. I. Basbaum ) ( Elsevier 14 . Burger , R. M. & Rubel , E. W. Encoding of interaural timing for Inc., 2008 ). binaural hearing. In Th e senses: a comprehensive reference ( e d A . I . 6 . Covey , E. Inputs to the inferior colliculus. In Th e senses: a comprehensive Basbaum ) ( Elsevier Science , 2008 ). reference (ed A. I. Basbaum ) ( Elsevier Science , 2008 ). 15 . Middlebrooks , J. Sound localization and the auditory cortex. In Th e 7 . Winer , J. A. & Schreiner , C. Th e auditory cortex, p. 659 ( Springer , senses: a comprehensive reference ( e d A . I . B a s b a u m) (E l s e v i e r 2011 ). Science, 2008 ). 8 . E h r e t, G . & R o m a n d, R . Th e central auditory system, pp. 161 – 163 16 . Kaas , J. H. & Hackett , T. A. Th e functional neuroanatomy of the ( Oxford University Press , 1997 ). auditory cortex . In Th e senses: a comprehensive reference ( e d A . I . 9 . B u r k a r d, R . F., E g g e r m o n t, J . J . & D o n, M . Auditory evoked potentials: Basbaum ) ( Elsevier Inc. , 2008 ). basic principles and clinical application, pp. 217 – 218 (Lippincott Williams & Wilkins , 2007 ). 1 5 Cerebellum

Lobes, Zones, & Modules

Somatotopy & Lobules

Peduncles, Midline Structures, Arteries

Nuclei & Circuitry ( Advanced )

Corticopontocerebellar Pathway 248 Neuroanatomy: Draw It to Know It

Know-It Points

Lobes, Zones, & Modules

■ Th e primary fi ssure divides the corpus cerebelli into ■ Th e spinocerebellum plays a major role in postural anterior and posterior lobes. stability. ■ Th e posterolateral fi ssure separates the corpus ■ Th e pontocerebellum is geared towards goal-directed, cerebelli from the fl occulonodular lobe. fi ne motor movements. ■ Th e vestibulocerebellum is important for equilibrium and eye movements.

Somatotopy & Lobules

■ Unilateral cerebellar lesions aff ect the ipsilateral side ■ Th e midline, vermian cerebellum divides into ten of the body. diff erent lobules. ■ Th e midline cerebellum plays a role in posture ■ Th e cerebellar hemispheres divide into nine diff erent whereas the lateral cerebellum assists in fi ne motor, lobules. goal-oriented skills.

Peduncles, Midline Structures, Arteries

■ Th e middle and inferior cerebellar peduncles are – Select midline cerebellar tracts exit the cerebellum aff erent pathways into the cerebellum. through the inferior cerebellar peduncle ■ Th e superior cerebellar peduncle is an eff erent ■ Th e fl occulonodular lobe lies in anterior, mid- pathway out of the cerebellum. cerebellar position. ■ Notable exceptions to the aforementioned rules are: – Th e anterior spinocerebellar tract enters the cerebellum through the superior cerebellar peduncle

Nuclei & Circuitry (Advanced )

■ Th e two main classes of cerebellar nuclei are the ■ Th e fastigial nucleus plays a role in both the cerebellar cortical neurons and the deep cerebellar vestibulocerebellum and spinocerebellum. nuclei. ■ Th e interposed nuclei (the combined globose and ■ Th e cerebellar cortical cell layers, from outside to emboliform nuclei) are part of the spinocerebellum. inside, are the molecular layer, Purkinje layer, and ■ Th e dentate nucleus is part of the pontocerebellum. granule layer. ■ Climbing fi bers are excitatory fi bers that originate ■ From lateral to medial, the deep cerebellar nuclei solely from the inferior olive and project to the are the dentate, emboliform, globose, and fastigial cerebellum via the contralateral inferior cerebellar nuclei. peduncle. 15. Cerebellum 249

Corticopontocerebellar Pathway

■ Th e corticopontocerebellar fi bers descend to the ■ Th e dentate nucleus projects through the superior pontine nuclei. cerebellar peduncle across midline within the ■ Th e pontine nuclei project across midline through midbrain, inferior to the red nucleus, to synapse in the middle cerebellar peduncle into the contralateral the ventrolateral nucleus of the thalamus and also in cerebellar cortex. the red nucleus. ■ Th e cerebellar cortex projects to the dentate ■ Th e thalamus projects back to the primary motor nucleus. strip to complete the corticopontocerebellar pathway.

1 Superior medullary velum 12 Culmen 25 Inferior semilunar lobule 2 Superior cerebellar peduncle (brachium 13 Preculminate fissure 26 Ansoparamedian fissure conjunctivum) 14 Anterior quadrangular lobule 27 Gracile lobule 3 Fastigium 15 Central lobule 28 Prebiventral fissure 4 Inferior medullary velum 16 Ala (wing) of the central lobule 29 Biventral lobule 5 Inferior cerebellar peduncle (restiform 17 Lingula 30 Intrabiventral fissure body) 18 Primary fissure 31 Secondary fissure 6 Middle cerebellar peduncle (brachium 19 Posterior quadrangular lobule (lobulus 32 Tonsil pontis) simplex) 33 Nodulus 7 Intermediate nerve 20 Superior posterior fissure 34 Posterolateral fissure 8 Vestibulocochlear nerve 21 Superior semilunar lobule 35 Uvula 9 Lateral recess of the fourth ventricle 22 Floccular peduncle 10 Roofplate of the fourth ventricle 23 Flocculus 11 Choroid plexus of the fourth ventricle 24 Horizontal fissure

FIGURE 15-1 Anterior cerebellum. Used with permission from Nieuwenhuys, Rudolf, Christiaan Huijzen, Jan Voogd, and SpringerLink (Online service). “Th e Human Central Nervous System.” Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. 250 Neuroanatomy: Draw It to Know It

Spinocerebellum (medial [vermal] region)

Pontocerebellum, neocerebellum or cerebrocerebellum (lateral hemisphere region)

Spinocerebellum (intermediate [paravermal] region)

Vestibulocerebellum (frocculonodular lobe)

Pontocerebellum, neocerebellum or cerebrocerebellum (lateral hemisphere region)

Intermediate (paravermal) region Medial (vermal) region

FIGURE 15-2 Th e cerebellar modules: vestibulocerebellum, spinocerebellum, pontocerebellum. Used with permission from Bruni, J. E. & Montemurro, D. G. Human Neuroanatomy: A Text, Brain Atlas, and Laboratory Dissection Guide. New York: Oxford University Press, 2009. 15. Cerebellum 251

Anterior lobe Posterior lobe Flocculonodular lobe

FIGURE 15-3 Cerebellar somatotopy. Used with permission from Manni, E., and L. Petrosini. A Century of Cerebellar Somatotopy: A Debated Representation. Nat Rev Neurosci 5, no. 3 (2004): 241-9. 252 Neuroanatomy: Draw It to Know It

Lobes, Zones, & Modules

Here, we will use a fl attened perspective of the cerebel- its name because of its midline vestibulo- and olivocere- lum to learn the cerebellar anatomic lobes, zones, and bellar fi bers, which project to the deep, medial-lying cer- functional modules. To understand how unfolding the ebellar fastigial nuclei. Show that this functional module cerebellum aff ects our perspective of it, draw a sagittal is important for equilibrium and eye movements. section of the folded cerebellum and then show that we Next, show that the anterior lobe combines with peel back the anterior cerebellum so that the anterior the majority of the vermian and paravermian posterior lobe ends up at the top of the diagram and the fl occu- lobe to form the spinocerebellum. Th e spinocerebellum lonodular lobe ends up at the bottom. receives its name from its major input fi bers: the spinoc- Now, draw the corpus cerebelli, which comprises the erebellar tracts. Show that this functional module plays a anterior and posterior cerebellar lobes and constitutes major role in postural stability. the bulk of the cerebellum. On the right, we will draw Now, indicate that the remainder of the posterior the cerebellar lobes, and on the left , we will draw the cer- lobe forms the pontocerebellum, which receives its name ebellar zones. because it acts through the corticopontocerebellar path- Begin with the lobes: show that the primary fi ssure way. Show that this functional module is geared towards separates the corpus cerebelli such that the anterior one- goal-directed, fi ne motor movements. third of the corpus cerebelli forms the anterior lobe and In acute alcohol intoxication, the entire cerebellum is the posterior two-thirds forms the posterior lobe. Next, aff ected: show that in this setting, nystagmus occurs below the corpus cerebelli, draw the propeller-shaped from toxicity to the vestibulocerebellum, truncal ataxia fl occulonodular lobe: label its nodule in midline and occurs from toxicity to the spinocerebellum, and incoor- fl occulus out laterally. Show that the posterolateral fi s- dination occurs from toxicity to the pontocerebellum. In sure separates the corpus cerebelli from the fl occulonod- contrast, in alcoholic cerebellar degeneration, the pathol- ular lobe. ogy is predominantly restricted to the anterior superior Now, let’s draw the cerebellar zones. Indicate that the cerebellar vermis; therefore, truncal ataxia is sometimes midline cerebellum is the vermis (which means worm- the sole defi cit. We may miss this exam fi nding, if we fail like); then, lateral to it, denote the paravermis (aka the to ask our patients to stand during the exam. intermediate zone); and lateral to it, label the hemisphere As a fi nal note on nomenclature, indicate that each (aka the lateral zone). functional module is synonymously named based on Next, let’s address the functional modules; show that its stage of phylogenic development. Th e vestibulocere- we will specifi cally address the module name, its anatomy bellum is phylogenetically the oldest portion of the cer- and function, and the exam defi cit observed when the ebellum and is referred to as the archicerebellum; the module is injured. spinocerebellum is phylogenetically the next oldest and Indicate that the fl occulonodular lobe combines with is referred to as the paleocerebellum; and the pontocer- the anterior tip of the vermis (the lingula) to form the ebellum is phylogenetically the newest portion of the vestibulocerebellum. Th e vestibulocerebellum receives cerebellum and is referred to as the neocerebellum.1 – 11 15. Cerebellum 253

Module Anatomy Function Exam deficit Vestibulocerebellum Flocculonodular lobe (& Equilibrium & Nystagmus or archicerebellum lingula: ant. tip of vermis) eye movements

Spinocerebellum Anterior lobe & vermian Postural stability Truncal ataxia or paleocerebellum & paravermian posterior lobe

Pontocerebellum Lateral posterior lobe Fine motor movement Incoordination or neocerebellum Zones Lobes Anterior Primary fissure lobe

Anterior Hemisphere Para- Vermis Posterior lobe lobe vermian Posterior zone lobe Flocculo- nodular lobe Posterolateral fissure Nodule Flocculus Flocculonodular lobe

DRAWING 15-1 Lobes, Zones, & Modules 254 Neuroanatomy: Draw It to Know It

Somatotopy & Lobules

Here, we will use a fl attened perspective of the cerebellum role of the neocerebellar posterior lobe is to provide to learn the cerebellar somatotopic map and the classifi - goal-oriented, fi ne motor movements, such as those of cation of the cerebellar lobules. Once again, to under- the fi ngers and mouth. stand how unfolding the cerebellum aff ects our perspective Now, we will draw the classifi cation of the cerebellar of it, draw a sagittal section of the folded cerebellum and lobules — its numbering system and nomenclature is then show that we peel back the anterior cerebellum so quite confusing, so keep track. Th e midline, vermian cer- that the anterior lobe ends up at the top of the diagram ebellum divides into ten diff erent lobules and the hemi- and the fl occulonodular lobe ends up at the bottom. spheres divide into nine lobules. We’ll draw the vermian To begin our diagram, draw the corpus cerebelli and lobules, fi rst, and then the hemispheric lobules. show that the primary fi ssure separates the anterior lobe Indicate that vermian lobule 1 sits above the superior from the posterior lobe. Next, draw the fl occulonodular lip of the fourth ventricle and is named the lingula. Next, lobe and indicate that the posterolateral fi ssure separates show that lobules 2 and 3, together, form the central it from the corpus cerebelli. lobule and then that lobules 4 and 5 form the culmen. First, let’s address the somatotopic map of the cerebel- Posterior to the primary fi ssure, label lobule 6, which is lum. In clinical practice, remember the following: (1) the declive. Show that lobule 7A is the folium and that unilateral cerebellar lesions aff ect the ipsilateral side of lobule 7B is the tuber; then, indicate that lobule 8 is the the body and (2) the midline cerebellum plays a role in pyramis and that lobule 9 is the uvula. Lobule 10 is the posture whereas the lateral cerebellum assists in fi ne nodule of the fl occulonodular lobe. motor, goal-oriented skills. For instance, to stand upright, Now, let’s label the classifi cation of the cerebellar you need the midline cerebellum, and to play the piano, hemispheric lobules. Show that except for lobule 1, you need the lateral cerebellar hemispheres. each vermian lobule has a hemispheric counterpart. Now, show that the somatotopic map in the anterior Hemispheric lobules 2 and 3 form the wing (or ala) of lobe looks like someone lying in a bathtub— arms and the central lobule; lobules 4 and 5 form the anterior legs coming out of the water. Next, show that the hands quadrangular lobule; posterior to the primary fi ssure is extend into the posterior lobe. Th en, draw the mouth lobule 6, the simple lobule (aka the posterior quadrangu- beneath the fi ngers. Now, show that there is duplication lar lobule); lobule 7A is quite large and forms the supe- of the arms and legs in the posterior lobe. rior and inferior semilunar lobules (aka the ansiform As mentioned, the somatotopic map of the cerebel- lobule); lobule 7B is the gracile lobule; lobule 8 is the lum is in concert with its functional layout: the role of biventral lobule; lobule 9 is the tonsil. Finally, show the spinocerebellar anterior lobe is to provide postural that lobule 10 is the fl occulus of the fl occulonodular stability, which requires the limbs and trunk, and the lobe. 1 – 11 15. Cerebellum 255

Hemispheric lobules H 2 & 3 Wing of central lobule Anterior H 4 & 5 Anterior quadrangular lobule lobe H 6 Simple lobule Posterior H 7A Superior semilunar lobule Anterior lobe lobe Inferior semilunar lobule 1 Flocculo- Primary H 7B Gracile lobule H2 nodular lobe H 8 Biventral lobule 2 H3 fissure H 9 Tonsil 3 H4 Posterior H 10 Flocculus H5 lobe 4 H6 5 Corpus 6 cerebelli H7A Vermian lobules 7A 1 Lingula 7B 2 & 3 Central lobule 4 & 5 Culmen 8 6 Declive H7B 7A Folium 9 H8 7B Tuber H9 Posterolateral fissure 8 Pyramis 9 Uvula 10 H10 Flocculonodular lobe 10 Nodule

DRAWING 15-2 Somatotopy & Lobules 256 Neuroanatomy: Draw It to Know It

Peduncles, Midline Structures, Arteries

Here, we will draw the cerebellar peduncles, the fl occulonodular lobe and paired tonsils, and the cerebellar arterial supply.

I. Cerebellar Peduncles Begin with one of the saddle-shaped cerebellar hemi- the brainstem vestibular nucleus, and certain monosyn- spheres. Next, add the cerebellar peduncles: superior, aptic cerebello-spinal connections. middle, and inferior. To illustrate the fl ow through these Now, let’s expound upon the major pathways that do pathways, redraw the cerebellar peduncles adjacent to follow the general infl ow/outfl ow rule. Show that the the rest of our diagram. middle cerebellar peduncle comprises corticopontocer- First, show that the middle cerebellar peduncle is ebellar fi bers (see Drawing 15-7 ), which are critical for an aff erent pathway into the cerebellum; it is reserved the modulation of movement. Th en, indicate that three for fi bers that originate in pontine nuclei. Next, indi- of the four spinocerebellar pathways enter the cerebel- cate that the inferior cerebellar peduncle is also an lum through the inferior cerebellar peduncle: the poste- aff erent pathway into the cerebellum; it receives fi bers rior spinocerebellar tract, cuneocerebellar tract, and from throughout the brainstem and spinal cord. Now, rostral spinocerebellar tract. As mentioned, the fourth show that the cerebellum sends eff erent fi bers out spinocerebellar tract, the anterior spinocerebellar tract, through the superior cerebellar peduncle. Th us, the main defi es the general organization of cerebellar infl ow and infl ow pathways into the cerebellum are the middle enters the cerebellum through the superior cerebellar and inferior cerebellar peduncles and the main outfl ow peduncle. Next, show that the brainstem pathways that peduncle from the cerebellum is the superior cerebellar enter the cerebellum through the inferior cerebellar peduncle. peduncle are the reticulo- and trigeminocerebellar fi bers, Next, let’s list the main exceptions to this rule. the olivocerebellar fi bers (known as climbing fi bers), and Indicate that the anterior spinocerebellar tract enters fi bers from the vestibular nucleus and nerve, itself. the cerebellum through the superior cerebellar peduncle, Now, indicate that the pathways that exit the cerebel- which defi es this peduncle’s role as an outfl ow pathway. lum through superior cerebellar peduncle are the denta- Th en, indicate that select midline cerebellar tracts exit torubal and dentatothalamic tracts, which project the cerebellum through the inferior cerebellar peduncle, rostrally; the dentatoreticular tract, which projects cau- which defi es this peduncle’s role as an infl ow pathway. dally; and fi bers from the globose and emboliform nuclei, Specifi cally, these midline pathways are the fastigiobul- which reach the region of the red nucleus responsible for bar fi bers, the fi bers from the fl occulonodular lobe to the rubrospinal tract. 15. Cerebellum 257

MCP pathway Corticopontocerebellar ICP pathways Spinal cord: PST, CST, & RST Brainstem: Reticulo-, trigemino- olivo-, & vestibulocerebellar pathways, & direct vestibular nerve fibers SCP pathways Pathways from the dentate & interposed nuclei Sup. CP Middle cerebral General organization peduncle SCP Inf. CP Pontine MCP Cere- nuclei only bellum ICP Brainstem Spinal cord

Exceptions : 1. AST uses SCP for inflow 2. Select midline cerebellar pathways use ICP for outflow

DRAWING 15-3 Peduncles, Midline Structures, Arteries— Partial 258 Neuroanatomy: Draw It to Know It

Peduncles, Midline Structures, Arteries (Cont.)

II. Midline Structures Now, in order to draw the fl occulonodular lobe and cer- a wide-ranging syndrome divided into three diff erent ebellar tonsils, fi rst label the fourth ventricle and indi- subtypes: types I, II, and III. Type I is the most mild cate that the midline portion of the cerebellum is the and type III is the most severe. Chiari malformation vermis, and also show that the outer aspect of the cere- always involves downward displacement of the cerebel- bellum is the hemisphere. Next, include in our diagram lar tonsils through the foramen magnum, but what the two components of the fl occulonodular lobe: in the determines its morbidity is the degree of cerebellar hemisphere, show the fl occulus, and in the vermis, show displacement and the degree of displacement of addi- the nodule. We show these structures, here, because the tional brainstem structures. Also, what determines its unfolded schematic of the cerebellum, which is so com- morbidity is the associated pathologic involvement monly used to represent the cerebellum, places the fl oc- of other areas of the central nervous system. Notably, culonodular lobe at the bottom of the diagram, and we type I Chiari malformation is found in roughly two need to appreciate that the fl occulonodular lobe actually thirds of cases of syringomyelia (a central cavitation of lies in anterior, mid-cerebellar position. Also, above the the spinal cord), and type II Chiari malformation (aka fourth ventricle, include the lingula: the slender vermian Arnold-Chiari malformation) is almost universally asso- tip of the anterior cerebellar lobe. Th e lingula combines ciated with myelomeningocele (a protrusion of the with the fl occulonodular lobe to form the vestibulocer- spinal cord and meninges through a defect in the poste- ebellum (or archicerebellum), which infl uences equilib- rior vertebral column). Patients with Chiari malforma- rium and eye movements. tion range from being entirely asymptomatic (when the Next, include one of the paired cerebellar tonsils; we malformation is only incidentally found on radiographic include the cerebellar tonsils because this paired, midline imaging) to being severely aff ected with considerable structure is an important aspect of a common neurologic developmental delay and substantial motor–sensory condition, Chiari malformation. Chiari malformation is defi cits. 12 – 15

III. Arterial Supply Lastly, let’s show the basic arterial supply of the cerebel- upper portion of the basilar artery, show that the paired lum. First, let’s draw the vertebrobasilar arterial arrange- superior cerebellar arteries emerge. Now, show that on ment and then show its cerebellar perfusion pattern. the anterior surface of the cerebellum, the posterior infe- Show that paired vertebral arteries derive the basilar rior cerebellar arteries perfuse the inferior cerebellum; artery, which branches into the paired posterior cerebral the anterior inferior cerebellar arteries perfuse the mid- arteries. Th en, indicate that the posterior inferior cere- lateral cerebellum; and the superior cerebellar arteries bellar arteries emerge from the vertebral arteries. Next, perfuse the superior cerebellum. We show the discrete at the base of the basilar artery, show that paired anterior vascular cerebellar territories in Drawing 19-6.1 – 11 , 16 , 17 inferior cerebellar arteries emerge and, fi nally, at the 15. Cerebellum 259

MCP pathway Corticopontocerebellar

ICP pathways Posterior Spinal cord: PST, CST, & RST Vermis Hemisphere cerebral Brainstem: Reticulo-, trigemino- artery olivo-, & vestibulocerebellar pathways, & direct vestibular nerve fibers Superior Superior cerebellar SCP pathways cerebellar artery artery Pathways from the dentate & Basilar Lingula interposed nuclei Sup. CP artery 4th Middle cerebral Anterior General organization ventricle peduncle Anterior inferior inferior SCP Nodule Inf. CP Pontine cerebellar artery cerebellar MCP Cere- Flocculus nuclei only artery bellum Cerebellar ICP Posterior inferior Posterior tonsil Brainstem cerebellar artery inferior Spinal cord cerebellar artery Exceptions : 1. AST uses SCP for inflow Vertebral 2. Select midline cerebellar artery pathways use ICP for outflow

DRAWING 15-4 Peduncles, Midline Structures, Arteries — Complete 260 Neuroanatomy: Draw It to Know It

Nuclei & Circuitry (Advanced )

Here, we will draw the cerebellar nuclei and circuitry. Th e deep cerebellar nuclei parse into specifi c func- Label the left side of the page as the cerebellar nuclei. tional modules. Th e fastigial nucleus plays a role in both Begin this diagram with a saddle-shaped cerebellar hemi- the vestibulocerebellum and spinocerebellum; the inter- sphere. Include along the surface a single fold, called a posed nuclei are part of the spinocerebellum; and the folium. Th e folding of the cerebellum into lobes, lobules, dentate nucleus is part of the pontocerebellum. and folia allows it to assume a tightly packed, inconspic- Now, let’s show the fl ow of information through the uous appearance in the posterior fossa. Th e cerebellum cerebellum. Label the right-hand side of the page as cer- has a vast surface area, however, and when stretched, it ebellar circuitry. First, indicate that there are three main has a rostrocaudal expanse of roughly 120 centimeters, types of cerebellar aff erent fi bers: climbing fi bers, mossy which allows it to hold an estimated one hundred billion fi bers, and multilayered fi bers, which are also known as granule cells — more cells than exist within the entire monoaminergic fi bers. cerebral cortex. Note that this is in part due to the small Show that climbing fi bers are excitatory fi bers that size of the granule cells, themselves. It is presumed that originate solely from the inferior olive and pass via the the cerebellum’s extraordinary cell count plays an impor- contralateral inferior cerebellar peduncle to the cerebel- tant role in the remarkable rehabilitation commonly lum. Debate exists as to whether climbing fi bers use the observed in cerebellar stroke.8 , 9 , 18 excitatory neurotransmitter aspartate or glutamate, but it Now, indicate that the two main classes of cerebellar seems most probable that they use glutamate. Th ese olivo- nuclei are the cerebellar cortical neurons and the deep cerebellar fi bers are distinct in that each Purkinje cell is cerebellar nuclei. Draw a magnifi ed view of the folium in innervated by a single olivocerebellar climbing fi ber. Note order to show the diff erent cerebellar cortical cell layers. that this pathway represents the inferior arm of the tri- Indicate that on the outside is the molecular layer, under- angle of Guillain-Mollaret, discussed in Chapter 9. neath it is the interposed Purkinje layer, and on the inside Now, show that the mossy fi bers are excitatory fi bers is the granule layer with the subcortical white matter derived from diff use cell populations within the brain- underneath it. Show that the molecular layer primarily stem and spinal cord. Th ey, like the climbing fi bers, comprises cell processes but also contains stellate and mostly use the excitatory neurotransmitter glutamate. basket cells; the Purkinje layer contains a single layer of Lastly, show that the multilayered fi bers are derived large Purkinje cell bodies; and the granule layer is highly from neurobehavioral centers in the brainstem and dien- cellular: it contains granule cells, Golgi cells, and unipo- cephalon, such as the locus coeruleus, raphe nucleus, and lar brush cells. the tuberomammillary nucleus of the hypothalamus. Next, let’s address the centrally located deep cerebel- Whereas the climbing and mossy fi bers are unquestion- lar nuclei. At the bottom of the page, list their names. ably excitatory, the role of the multilayered fi bers is less From medial to lateral, they are the fastigial, globose, uniform. Th ey are considered monoaminergic because emboliform, and dentate nuclei. Show that together their cells of origin are generally associated with a single the globose and emboliform nuclei are also known as neurotransmitter type: the locus coeruleus is noradren- the interposed nuclei. An acronym for the lateral to ergic, the raphe nucleus is serotinergic, and the tubero- medial organization of the deep nuclei is “Don’t Eat mammillary nucleus is histaminergic. Greasy Food,” for dentate, emboliform, globose, and Now, show that all three fi bers innervate both the fastigial. deep cerebellar nuclei and cerebellar cortex. 15. Cerebellum 261

CEREBELLAR NUCLEI

Cortical cell layers CEREBELLAR CIRCUITRY Molecular: primarily cell processes Purkinje: solely Purkinje cell bodies Granule: highly cellular Subcortical white matter Cerebellar cortex Folium Cerebellar Inferior olivary Climbing cortex nucleus fibers

Deep cerebellar Brainstem & Mossy nuclei spinal cord fibers

Deep cerebellar nuclei Neurobehavioral Multilayered Deep cerebellar nuclei monoaminergic fibers Fastigial Globose Emboliform Dentate cell populations nucleus nucleus nucleus nucleus Interposed nuclei

DRAWING 15-5 Nuclei & Circuitry — Partial 262 Neuroanatomy: Draw It to Know It

Nuclei & Circuitry (Advanced ) (Cont.)

Next, show that the deep cerebellar nuclei send excit- transmitted to the Purkinje layer. Indicate that the atory fi bers to structures throughout the central nervous Purkinje layer, which is the sole recipient of this post- system. Th e majority of eff erent information that leaves processed information, sends inhibitory fi bers to the the cerebellum does so from the deep cerebellar nuclei, deep cerebellar nuclei. Th us the cerebellar cortex, acting which act through the excitatory neurotransmitter glu- through the Purkinje layer, is an important modulating tamate, most notably. force on the deep cerebellar nuclei. Th e Purkinje cells Now, indicate that the molecular and granule cell act through the inhibitory neurotransmitter gamma- layers fi lter and temporally pattern information as it is aminobutyric acid (GABA). 1 – 11 , 19 – 23

Molecular layer

Parallel fiber

Basket cell Purkinje cell layer

Purkinje cell

Granule cell layer

Golgi cell

Glomerulus

Climbing fiber (from inferior olivary nucleus) Granule cell Neuron in deep cerebellar nucleus

Mossy fiber (from pontine nuclei and most other sources)

JEB

(to thalamus)

FIGURE 15-4 Cerebellar histological architecture. Used with permission from Bruni, J. E. & Montemurro, D. G. Human Neuroanatomy: A Text, Brain Atlas, and Laboratory Dissection Guide. New York: Oxford University Press, 2009. 15. Cerebellum 263

CEREBELLAR NUCLEI

Deep cerebellar Brainstem & Mossy nuclei spinal cord fibers Central Deep cerebellar nervous nuclei system Neurobehavioral Multilayered targets Deep cerebellar nuclei monoaminergic fibers Fastigial Globose Emboliform Dentate cell populations nucleus nucleus nucleus nucleus Interposed nuclei

DRAWING 15-6 Nuclei & Circuitry — Complete 264 Neuroanatomy: Draw It to Know It

Corticopontocerebellar Pathway

Here, we will draw the corticopontocerebellar pathway. nucleus, to synapse in the ventrolateral nucleus of the For this diagram, we need to draw one side of the brain, thalamus. Th en, show that select fi bers synapse directly the brainstem, and then the opposite side of the cerebel- in the red nucleus, instead. Note that the red nucleus lum, and we need to establish the midline of the diagram. projections typically originate from the globose and Indicate that the bulk of the pathway originates in emboliform nuclei, which lie medial to the dentate the primary motor and sensory cortices; we exclude the nucleus, whereas the thalamic projections typically orig- lesser contributions from more wide-reaching brain inate from the dentate nucleus. Now, show that the thal- regions. To get a sense of the corticopontocerebellar amus projects back to the primary motor strip to pathway’s importance in movement, consider that nearly complete the corticopontocerebellar pathway. 20 million fi bers are dedicated to the corticopontocere- Th e clinical application of this pathway comes in the bellar pathway, whereas only 1 million fi bers are dedi- analysis of cerebellar defi cits. Cerebellar injuries cause cated to the corticospinal tract. 24 ipsilateral defi cits. If a person has a cerebellar defi cit (for Now, show that the corticopontocerebellar fi bers fi rst instance, incoordination), then either the ipsilateral cer- descend to the pontine nuclei, where they make their ebellum or a portion of this pathway (somewhere along primary synapse. Next, show that the pontine nuclei its course) is aff ected. If the area of injury localizes con- project across midline through the middle cerebellar tralateral to the side of the body that is aff ected, think of peduncle into the contralateral cerebellar cortex. As a a corticopontocerebellar pathway lesion. Consider a reminder, the inferior and middle cerebellar peduncles stroke in which there is a left third nerve palsy and right- are the main infl ow pathways into the cerebellum, and side hemiataxia. Where could the injury lie? On a sepa- the superior cerebellar peduncle is the main outfl ow rate sheet of paper, draw the midbrain. Defi ne right pathway from the cerebellum. and left . Draw the left third nerve and its exiting fascicles Th en, show that the cerebellar cortex projects to and then draw the right cerebellum. How can we con- the dentate nucleus, which lies deep within the cerebel- nect these disparate regions? Show that fi bers exit the lum. Now, draw the superior cerebellar peduncle, red right cerebellum through the superior cerebellar pedun- nucleus, and ventrolateral nucleus of the thalamus. cle and pass adjacent to the third nerve fi bers on the left . Indicate that the dentate projects fi bers out of the cere- Indicate that injury here produces the aforementioned bellum through the superior cerebellar peduncle, which defi cits (see Drawing 10-3, Claude's syndrome, for cross midline within the midbrain, inferior to the red details). 1 , 3 , 7 – 11 15. Cerebellum 265

Primary motor cortex Motor & sensory cortices

Ventrolat. Thalamus Midline Red nucleus

Superior cerebellar peduncle Dentate nucleus Cerebellar Middle cerebellar Pontine cortex peduncle nucleus

Cerebellum Cerebral hemisphere

Brainstem

DRAWING 15-7 Corticopontocerebellar Pathway 266 Neuroanatomy: Draw It to Know It

References 1 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 1 3. C h e n, H . Atlas of genetic diagnosis and counseling, pp. 157 – 159 atlas, 2nd ed. ( Lange Medical Books/McGraw-Hill , 2005 ). (Humana Press, 2006 ). 2 . D u v e r n o y, H . M . & B o u r g o u i n, P. Th e human brain: surface, 1 4. R o w l a n d, L . P., P e d l e y, T. A . & K n e a s s, W. Merritt’s neurology, 12th three-dimensional sectional anatomy with MRI, and blood supply, ed., p. 551 (Wolters Kluwer Lippincott Williams & Wilkins, 2010 ). 2nd completely rev. and enl. ed. (Springer , 1999 ). 15 . Sarnat , H. B. & Curatolo , P. Malformations of the nervous system, 3 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic p. 98 ( Elsevier , 2008 ). and clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 16 . Yokota , O. , et al. Alcoholic cerebellar degeneration: a clinicopatho- 2006 ). logical study of six Japanese autopsy cases and proposed potential 4 . Mai , J. K., Voss , T. & Paxinos , G. Atlas of the human brain, 3rd ed. progression pattern in the cerebellar lesion . Neuropathology 2 7, ( Elsevier/Academic Press , 2008 ). 99 – 113 (2007 ). 5 . Manni , E. & Petrosini , L. A century of cerebellar somatotopy: a 17 . Takahashi , S. O. Neurovascular imaging: MRI & microangiography debated representation . Nat Rev Neurosci 5 , 241 – 249 (2004 ). (Springer , 2010 ). 6 . Manto , M.-U. & Pandolfo , M. Th e cerebellum and its disorders 18 . Kelly , P. J., et al. Functional recovery aft er rehabilitation for ( Cambridge University Press , 2002 ). cerebellar stroke. Stroke 32 , 530 – 534 (2001 ). 7 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human 19 . Apps , R. & Hawkes , R. Cerebellar cortical organization: a one-map brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal hypothesis. Nat Rev Neurosci 10 , 670 – 681 (2009 ). structure, vascularization and 3D sectional anatomy (S p r i n g e r, 20 . Dietrichs , E. Clinical manifestation of focal cerebellar disease as 2009 ). related to the organization of neural pathways . Acta Neurol Scand, 8 . N i e u w e n h u y s, R ., Vo o g d, J . & H u i j z e n, C . V. Th e human central Suppl. (188 ) 186 – 111 (2008 ). nervous system, 4th ed. (Springer , 2008 ). 21 . Nakanishi , S. Synaptic mechanisms of the cerebellar cortical 9 . N o b a c k, C . R . Th e human nervous system: structure and function, network. Trends Neurosci 28 , 93 – 100 (2005 ). 6th ed. (Humana Press, 2005 ). 22 . Strick , P. L. , Dum , R. P. & Fiez , J. A. Cerebellum and nonmotor 10 . Paxinos , G. & Mai , J. K. Th e human nervous system, 2nd ed., function. Annu Rev Neurosci 32 , 413 – 434 (2009 ). Chapter 11 ( Elsevier Academic Press , 2004 ). 23 . Huang , C. M. & Huang , R. H. Ethanol inhibits the sensory 11 . Voogd , J. & Glickstein , M. Th e anatomy of the cerebellum . Trends responses of cerebellar granule cells in anesthetized cats . Alcohol Neurosci 21 , 370 – 375 (1998 ). Clin Exp Res 31 , 336 – 344 (2007 ). 12 . Bailey , B. J., Johnson , J. T. & Newlands , S. D. Head & neck 24 . Melillo , R. & Leisman , G. Neurobehavioral disorders of childhood: surgery — otolaryngology, 4th ed., p. 2311 ( Lippincott Williams & an evolutionary perspective, p. 55 ( Kluwer Academic/Plenum Wilkins, 2006 ). Publishers , 2004 ). 1 6 Cerebral Gray Matter

Cerebral Hemisphere — Lateral Face

Cerebral Hemisphere — Medial Face

Cerebral Hemisphere — Inferior Face

The Insula ( Advanced )

Cerebral Cytoarchitecture ( Advanced )

Brodmann Areas 268 Neuroanatomy: Draw It to Know It

Know-It Points

Cerebral Hemisphere — Lateral Face

■ Th e area anterior to the central sulcus is the frontal ■ Th e precentral gyrus lies in between the precentral lobe. sulcus and the central sulcus; it is the primary motor ■ Posterior to the lateral parietotemporal line lies the area. occipital lobe. ■ Th e postcentral gyrus lies in between the postcentral ■ Superior to the temporo-occipital line lies the sulcus and the central sulcus; it is the primary parietal lobe, and inferior to it lies the temporal lobe. sensory area. ■ Th e limbic lobe is present only on the brain’s inferior and medial surfaces.

Cerebral Hemisphere — Medial Face

■ Th e cingulate sulcus and collateral sulcus delineate ■ Th e temporal lobe lies anterior to the basal the bulk of the limbic lobe. parietotemporal line. ■ Th e frontal lobe lies anterior to the central sulcus. ■ Th e cuneus lies superior to the calcarine sulcus. ■ Th e parieto-occipital sulcus separates the parietal ■ Th e parahippocampal gyrus lies superior to the lobe, anteriorly, from the occipital lobe, posteriorly. collateral sulcus. ■ Th e subparietal sulcus demarcates the boundary ■ Th e fusiform gyrus lies in between the collateral and between the parietal and limbic lobes. occipitotemporal sulci.

Cerebral Hemisphere — Inferior Face

■ Th e frontal pole lies at the anterior end of the ■ Th e Sylvian fi ssure runs in between the frontal and frontal lobe. temporal lobes and ascends much of the lateral aspect ■ Th e temporal pole lies at the anterior end of the of the brain. temporal lobe. ■ Th e occipital pole lies at the posterior end of the occipital lobe.

The Insula (Advanced )

■ Th e insula underlies the cerebral opercula. ■ Th e frontal operculum lies in between the anterior ■ Th e circular sulcus circumscribes the insula. horizontal and anterior ascending Sylvian fi ssure rami. ■ Th e central sulcus extends through the insula and ■ Th e parietal operculum lies in between the anterior divides the insula into anterior and posterior lobules. ascending and posterior Sylvian fi ssure rami. ■ Th e orbital operculum lies inferior to the anterior ■ Th e temporal operculum lies inferior to the posterior horizontal ramus of the Sylvian fi ssure. ramus of the Sylvian fi s s u r e . 16. Cerebral Gray Matter 269

Cerebral Cytoarchitecture (Advanced )

■ Th ree diff erent histologic patterns of cerebral ■ A prominent example of a pyramidal cell are the cortex exist: neocortex, allocortex, and mesocortex. Betz cells, which lie primarily within the primary ■ Neocortex (aka isocortex) is the phylogenetically motor cortex. newest cortical cytoarchitecture and comprises six ■ Th e six cytoarchitectural layers of the neocortex, layers. from outside to inside, are the molecular, external ■ Allocortex is phylogenetically older and comprises granular, external pyramidal, internal granular layer, from three to fi ve layers. internal pyramidal, and multiform layers. ■ Mesocortex represents transitional cortex between neocortex and allocortex.

Brodmann Areas

■ Areas 3, 1, 2 lie within the postcentral and posterior of the inferior frontal gyrus; together, they make up paracentral gyri; they constitute the primary sensory Broca’s area —the speech output area. area. ■ Areas 41 and 42 lie in the transverse temporal gyri ■ Area 4 lies within the precentral and anterior (Heschl’s gyri); they make up the primary auditory paracentral gyri; it is the primary motor area. cortex. ■ Area 8 lies in front of area 6; it contains the human ■ Area 22 lies in the superior temporal gyrus and, homologue to the rhesus monkey frontal eye posteriorly, it contains Wernicke’s area — the language fi elds. reception area. ■ Area 44 lies in the pars opercularis of the inferior ■ Area 17 lies on the banks of the calcarine sulcus and frontal gyrus and area 45 lies in the pars triangularis is the primary visual cortex. 270 Neuroanatomy: Draw It to Know It

FIGURE 16-1 Lateral and medial cerebral surfaces. Used with permission from Devinsky, Orrin, and Mark D’Esposito. Neurology of Cognitive and Behavioral Disorders , Contemporary Neurology Series. Oxford; New York: Oxford University Press, 2004. 16. Cerebral Gray Matter 271

FIGURE 16-2 Inferior cerebral surface. Used with permission from Devinsky, Orrin, and Mark D’Esposito. Neurology of Cognitive and Behavioral Disorders , Contemporary Neurology Series. Oxford; New York: Oxford University Press, 2004. 272 Neuroanatomy: Draw It to Know It

FIGURE 16-3 Brodmann areas. Used with permission from Devinsky, Orrin, and Mark D’Esposito. Neurology of Cognitive and Behavioral Disorders, Contemporary Neurology Series. Oxford; New York: Oxford University Press, 2004. This page intentionally left blank 274 Neuroanatomy: Draw It to Know It

Cerebral Hemisphere — Lateral Face

Here, we will draw the lateral face of the cerebrum. First, Now, let’s draw the gyri and sulci of the lateral tempo- draw the lateral aspect of a cerebral hemisphere and show ral lobe. Again draw two sulci — label the top sulcus as the Sylvian fi ssure (aka the lateral sulcus) along a diago- the superior temporal sulcus and the bottom sulcus as nal. Th en, draw the central sulcus from the top of the the inferior temporal sulcus. Th en, label the superior brain to the Sylvian fi ssure. Label the area anterior to temporal gyrus above the superior temporal sulcus; the the central sulcus as the frontal lobe. Next, label the pre- middle temporal gyrus in between the superior and occipital notch along the posterior undersurface of the middle temporal sulci; and the inferior temporal gyrus brain and then the parieto-occipital sulcus along the below the inferior temporal sulcus. superior convexity of the brain; note that the parieto- Next, let’s draw a similar arrangement for the occipi- occipital sulcus terminates abruptly in the superolateral tal gyri of the lateral surface of the brain. Draw the supe- convexity— on the contrary, the parieto-occipital sulcus rior occipital sulcus (aka the intraoccipital sulcus), which is prominent on the medial surface of the brain. Now, follows the path of the intraparietal sulcus (drawn later), dot a vertical line from the termination of the parieto- and then draw the inferior occipital sulcus, which fol- occipital sulcus to the pre-occipital notch and label it as lows the path of the inferior temporal sulcus. Above the the lateral parietotemporal line. Posterior to this imagi- superior occipital sulcus, label the superior occipital nary line, label the occipital lobe. Next, dot a roughly gyrus; in between the superior and inferior occipital horizontal line from the posterior end of the Sylvian fi s- sulci, label the middle occipital gyrus (aka the lateral sure to the middle of the anterior border of the occipital occipital gyrus); and below the inferior occipital sulcus, lobe and label this line as the temporo-occipital line. label the inferior occipital gyrus. Th e middle occipital Superior to this line, label the parietal lobe, and inferior gyrus is the largest of the occipital gyri on the lateral sur- to it, label the temporal lobe. We have now drawn the face of the brain, and it is sometimes subdivided into four cerebral lobes visible on the lateral surface of the superior and inferior gyri. brain; the fi ft h lobe, the limbic lobe, is present only on Now, label the basal, anterior surface of the frontal the brain’s inferior and medial surfaces. lobe as the orbitofrontal cortex. Th en, in the posterior Next, let’s draw the gyri and sulci of the lateral surface aspect of the frontal lobe, draw the precentral sulcus, of the brain. Redraw a lateral hemisphere and include and in between it and the central sulcus, label the pre- the central sulcus and Sylvian fi ssure. Divide the anterior central gyrus, which is the primary motor area. frontal lobe into three horizontally distributed gyri using Next, let’s draw the gyri and sulci of the parietal lobe. two parallel sulci. Label the top sulcus as the superior First, draw the postcentral sulcus, and in between it and frontal sulcus and the bottom sulcus as the inferior fron- the central sulcus, label the postcentral gyrus, which is tal sulcus. Th en, indicate that the superior frontal gyrus the primary sensory area. Th en, draw the intraparietal lies above the superior frontal sulcus; that the middle sulcus, and show that it divides the remainder of the frontal gyrus lies in between the superior and inferior parietal lobe into the superior parietal lobule, superiorly, frontal sulci; and that the inferior frontal gyrus lies in and the inferior parietal lobule, inferiorly — the inferior between the inferior frontal sulcus and the inferior parietal lobule divides into the supramarginal gyrus and border of the frontal lobe. Note that the inferior frontal angular gyrus. Th e supramarginal gyrus caps the poste- gyrus is triangular, and it contains pars orbitalis, pars tri- rior end of the Sylvian fi ssure and the angular gyrus caps angularis, and pars opercularis divisions. the posterior end of the superior temporal sulcus.1 – 6 16. Cerebral Gray Matter 275

Central sulcus Parieto-occipital sulcus PARIETAL LOBE Lateral parietotemporal line FRONTAL LOBE Temporo- occipital line OCCIPITAL Precentral Central Sylvian TEMPORAL LOBE Postcentral LOBE sulcus sulcus fissure sulcus Pre-occipital notch Superior Sup. occipital Sup. frontal Pre- Post- parietal lobule sulcus gyr. central central Intra- Middle frontal gyrus gyrus Supramarginal parietal gyr. Superior gyrus Angular sulcus Inf. frontal frontal sulcus gyrus Sup. ocip. gyrus Inferior Sup. temporal gyr. gyr. frontal sulcus Sylvian Mid. ocip. fissure Middle temporal gyr. gyr. Orbitofrontal Superior Inf. temporal gyr. Inf. ocip. cortex temp. sulc. gyr. Inferior temp. sulc. Inferior occipital sulcus

DRAWING 16-1 Cerebral Hemisphere — Lateral Face 276 Neuroanatomy: Draw It to Know It

Cerebral Hemisphere — Medial Face

Here, we will draw the lobes, gyri, and sulci of the medial label the posterior paracentral gyrus — the medial exten- face of the cerebrum. Draw an outline of the medial face sion of the postcentral gyrus. Note that together the of a cerebral hemisphere. Label the cingulate sulcus anterior and posterior paracentral gyri are referred to as above and in parallel to the corpus callosum. Th en, label the paracentral lobule. the collateral sulcus in the temporal region in parallel to Now, posterior to the pars marginalis, draw the pari- the brain’s inferior border. Indicate that these sulci delin- eto-occipital sulcus, and in between these two sulci, label eate the limbic lobe. Next, draw the central sulcus, and the precuneus gyrus. Th en, show that the subparietal anterior to it, label the frontal lobe. Now, draw the pari- sulcus separates the precuneus from the cingulate gyrus. eto-occipital sulcus, and show that it separates the pari- Next, show that the calcarine sulcus extends directly pos- etal lobe, anteriorly, from the occipital lobe, posteriorly. terior from the inferior tip of the parieto-occipital sulcus, Next, use the subparietal sulcus to demarcate the bound- and then indicate that the anterior calcarine sulcus ary between the parietal and limbic lobes. Now, to sepa- extends anteriorly from the inferior tip of the parieto- rate the temporal and occipital lobes, dot a line between occipital sulcus to underneath the posterior corpus cal- the pre-occipital notch and the parieto-occipital sulcus, losum (the splenium). Within the occipital lobe, superior and label the line as the basal parietotemporal line. Th e to the calcarine sulcus, label the cuneus, and inferior to temporal lobe lies anterior to this line. Note that the it, label the lingual gyrus. Now, along the path of the basal parietotemporal line is alternatively drawn from anterior calcarine sulcus, draw the collateral sulcus, and the pre-occipital notch to the anterior end of the ante- superior to it, label the parahippocampal gyrus. Th en, rior calcarine sulcus (drawn later). inferior and in parallel to the collateral sulcus, label the Now, let’s draw the gyri and sulci of the medial sur- occipitotemporal sulcus, and in between these two sulci, face of the cerebral hemisphere. First, redraw the hemi- label the fusiform gyrus. Finally, inferolateral to the fusi- sphere— include the corpus callosum and thalamus. form gyrus, label the inferior temporal gyrus. Along the outer contour of the corpus callosum, label Note that there are substantial variations in the defi - the callosal sulcus, and in parallel to it, draw the cingu- nitions of the anatomy of the inferomedial temporal and late sulcus. In between these sulci, label the cingulate occipital gyri and substantially diff ering semantics used gyrus. to describe these areas. For instance, the lingual gyrus is Next, in the central, superior hemisphere, draw the sometimes referred to as the medial occipitotemporal central sulcus, and anterior to it, draw the paracentral gyrus and the fusiform gyrus is sometimes referred to as sulcus. Between these two sulci, draw the anterior para- the lateral occipitotemporal gyrus. Th e fusiform gyrus is central gyrus— the medial extension of the precentral also sometimes referred to as the combined medial and gyrus. Anterior to the paracentral sulcus label the supe- lateral occipitotemporal gyri or as a subportion of the rior frontal gyrus (aka the medial frontal gyrus). Th en, occipitotemporal gyrus. Also, the collateral sulcus is posterior to the central sulcus, continue the cingulate alternatively referred to as the medial occipitotemporal sulcus as the pars marginalis (the marginal branch of the sulcus and the occipitotemporal sulcus is sometimes cingulate sulcus), and between it and the central sulcus, called the lateral occipitotemporal sulcus. 1 – 6 16. Cerebral Gray Matter 277

Central sulcus

Parieto- Cingulate sulcus PARIETAL occipital sulcus FRONTAL LOBE LOBE LIMBIC Paracentral Central LOBE Sub-partl. Pars OCCIPITAL sulcus sulcus slcs. marginalis LOBE Anterior Posterior Collateral TEMPORAL paracentral paracentral Parieto- sulcus LOBE Preoccip. Superior frontal gyrus gyrus notch gyrus occipital Precuneus sulcus Basal parieto- Cingulate Cingulate gyrus temporal line sulcus Corpus callosum Callosal Subpar- ietal sulcus sulcus Thalamus Cuneus Ant. calc. Calcarine sulc. sulcus Parahippocampal Lingual gyrus Collateral gyrus sulcus Fusiform gyrus Occipitotemporal Inferior temporal sulcus gyrus

DRAWING 16-2 Cerebral Hemisphere — Medial Face 278 Neuroanatomy: Draw It to Know It

Cerebral Hemisphere — Inferior Face

Here, we will draw the lobes, gyri, and sulci of the infe- Now, we will draw the Sylvian fi ssure. First, further rior surface of the brain and we will also learn the defi ne the region surrounding the optic chiasm as the anatomy of the Sylvian fi ssure. Draw the undersurface anterior perforated substance, which is perforated by of the brain, but on one side, leave out the anterior short branches of the proximal middle cerebral artery. end of the temporal lobe. Include the following ana- Next, label the internal carotid artery just lateral to the tomic landmarks: the optic chiasm and neighboring optic chiasm. Th en, show that the proximal middle cere- pituitary body and mammillary bodies, the midbrain, bral artery (the M1 branch) originates from the internal and cerebellum. Next, in the anterior one third of carotid artery within the cistern of the vallecula cerebri the hemisphere, label the frontal lobe. Th en, in the pos- (aka the carotid cistern) and passes laterally within this terior one third of the hemisphere, draw the basal pari- cistern through the deep (or basal) portion of the Sylvian etotemporal line; anterior to it, label the temporal lobe, fi ssure between the frontal and temporal lobes. As the and posterior to it, label the occipital lobe. Finally, Sylvian fi ssure wraps around to the lateral convexity of include the collateral sulcus and label the limbic lobe the brain, the related cisternal space becomes the cistern medial to it. of the lateral cerebral fossa; exactly where this cisternal Now, on the opposite side of the brain, let’s draw the transition occurs is inconsistently defi ned. 1 , 7 – 11 gyri and sulci. First, within the medial frontal lobe, label Now, let’s continue with the lateral face of the Sylvian the olfactory sulcus. Medial to it, label the gyrus rectus, fi ssure. Draw an outline of the lateral cerebral hemi- and lateral to it, label the orbital gyri and orbital sulci. sphere and include the central sulcus for orientational Now, on the medial aspect of the occipital lobe, label the purposes. First, draw the anterior-inferior division of the lingual gyrus, and on the lateral aspect, label the inferior Sylvian fi ssure; then, at its midpoint, draw a “V” for the occipital gyrus. Next, within the temporal lobe, draw the rami extensions from the Sylvian fi ssure. Label the lower collateral and occipitotemporal sulci. Medial to the col- arm of the “V” as the anterior horizontal ramus and the lateral sulcus, label the parahippocampal gyrus, and in upper arm as the anterior ascending ramus: the anterior between the collateral and occipitotemporal sulci, label horizontal ramus runs roughly horizontally and the the fusiform gyrus. Th en, lateral to the fusiform gyrus, anterior ascending ramus runs roughly vertically. Th ese label the inferior temporal gyrus. Next, at the anterior rami subdivide the inferior frontal gyrus as follows: end of the collateral sulcus, label the rhinal sulcus — the beneath the anterior horizontal ramus, label the pars collateral sulcus either merges with this sulcus or runs in orbitalis; then, in between the two rami, label the trian- parallel to it (see Drawing 21-3). Now, show that the gular-shaped pars triangularis; and lastly, posterior to parahippocampal gyrus doubles back onto itself as the the anterior ascending ramus, label the pars opercularis. uncus; this is, generally, the fi rst portion of the brain to Next, let’s draw the posterior-superior division of the herniate over the tentorium cerebellum during uncal Sylvian fi ssure. At the distal end of the central sulcus, herniation. draw the horizontally directed posterior horizontal Next, let’s draw the anatomic poles of the brain: label ramus and then complete the Sylvian fi ssure with the the frontal pole at the anterior end of the frontal lobe; posterior ascending ramus. Th e supramarginal gyrus caps label the temporal pole at the anterior end of the tempo- this ramus. Note that a posterior descending ramus also ral lobe; and label the occipital pole at the posterior end exists, which lies along the vertical plane of the posterior of the occipital lobe. ascending ramus (we leave it out for simplicity).1 – 6 16. Cerebral Gray Matter 279

CEREBRAL Olfactory sulcus SYLVIAN FISSURE - LATERAL FACE HEMISPHERE - Frontal Central sulcus INFERIOR pole Anterior Gyrus Orbital FACE ascending FRONTAL LOBE rectus gyri ramus Supramarg. Internal Orbital sulci Anterior Oper. Posterior Proximal MCA carotid Optic horizontal Trg. Posterior ascending w/in deep Sylvian artery chiasm Temporal ramus Orb. horizontal fissure pole ramus ramus Rhinal Ant. perf. Uncus sulcus Orb. - pars orbitalis substance Trg. - pars triangularis Midbrain Fusiform LIMBIC Oper. - pars opercularis TEMPORAL Parahippo- gyrus LOBE Supramarg. - supramarginal gyrus LOBE campal gyrus Collateral sulcus Cerebellum Occipito- temporal Inferior Basal parietotemporal Collateral sulcus temporal line gyrus sulcus OCCIPITAL LOBE Lingual Inferior Occipital gyrus occipital gyrus pole

DRAWING 16-3 Cerebral Hemisphere — Inferior Face 280 Neuroanatomy: Draw It to Know It

The Insula (Advanced )

Here, we will draw the insula (aka the island of Reil), Next, draw a coronal view of the insula so we can, at which underlies the cerebral opercula. First, draw a lat- least partially, draw its diff erent opercular coverings. In eral hemisphere. Th en, carve out the center of the hemi- accordance with Nieuwenhuys' description, label the sphere and indicate that the circular sulcus circumscribes orbital operculum, which lies inferior to the anterior the insula (except in the antero-inferior region at the horizontal ramus of the Sylvian fi ssure; next, label the limen insulae— the insular apex). Next, show that the frontal operculum, which lies in between the anterior central sulcus extends through the insula and divides it horizontal and anterior ascending Sylvian fi ssure rami; into anterior and posterior lobules. Th en, indicate that then, label the parietal operculum, which lies in between the anterior lobule contains three short insular gyri and the anterior ascending and posterior Sylvian fi ssure rami; that the posterior lobule contains two long insular gyri. and fi nally, label the temporal operculum, which lies Within the anterior lobule, draw the precentral inferior to the posterior ramus of the Sylvian fi ssure. sulcus, and anterior to it, draw the short insular sulcus. Indicate that the temporal operculum is formed from In between the precentral and central sulci, label the both the superior temporal gyrus and transverse tempo- posterior short insular gyrus; in between the precentral ral gyri (Heschl’s gyri). and short insular sulci, label the middle short insular Th e insula has widespread intracortical connectivity, gyrus; and fi nally, anterior to the short insular sulcus, including connections to the hypothalamus, thalamus, label the anterior short insular gyrus. cortical sensory association areas, auditory cortex, and Now, within the posterior lobule, draw the postcen- limbic system. It has been shown to play a role in pain tral sulcus, and in between it and the central sulcus, label modulation, appetite, awareness of visceral sensation, the anterior long insular gyrus, and posterior to it, label anxiety and emotion, socialization, auditory processing, the posterior long insular gyrus. and much more.4 – 6 , 9 , 12 – 14

1 Central sulcus 2 Lateral sulcus, posterior branch 3 Lateral sulcus, ascending branch 4 Frontoparietal operculum 5 Circular sulcus of the insula 6 Lateral sulcus, anterior branch 7 Long gyrus of the insula 8 Central sulcus of the insula 9 Short gyri of the insula 10 Frontal operculum 11 Temporal operculum 12 Limen insulae 13 Anterior pole of the insula

FIGURE 16-4 Insular cortex. Used with permission from Nieuwenhuys, Rudolf, Christiaan Huijzen, Jan Voogd, and SpringerLink (Online service). “Th e Human Central Nervous System.” Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. 16. Cerebral Gray Matter 281

Precentral Parietal operculum sulcus Postcentral Central Circular sulcus sulcus sulcus Post. Frontal Middle short Posterior operculum short gyr. long gyr. gyr. Anterior Orbital Ant. short long gyr. operculum gyr. Transverse temporal Short Circular gyri (Heschl’s gyri) Frontal & parietal Temporal operculum insular sulcus opercula sulcus

Insula Transverse temporal gyri (Heschl’s gyri) Temporal operculum Anterior lobule - short insular gyri Posterior lobule - long insular gyri

DRAWING 16-4 Th e Insula 282 Neuroanatomy: Draw It to Know It

Cerebral Cytoarchitecture (Advanced )

Here, we will draw the cytoarchitecture of the cerebral Next, let’s label the six cytoarchitectural layers of the cortex. First, indicate that three diff erent histologic pat- neocortex from outside to inside. Label the outermost terns of cerebral cortex exist: neocortex, allocortex, and cytoarchitectural layer as layer I, the molecular (or plexi- mesocortex. Neocortex (aka isocortex) is the phyloge- form) layer; indicate that it is primarily a nerve fi ber netically newest cortical cytoarchitecture; it constitutes layer, meaning that it is cell sparse and predominantly roughly 90% of the cerebral cortex and comprises six his- comprises axons and dendritic processes. Th en, show tologically distinct layers. Allocortex is phylogenetically that the next innermost layer is layer II, the external older and comprises from three to fi ve layers (the actual granular layer; indicate that it predominantly contains number is inconsistently defi ned). Allocortex subdivides non-pyramidal cells and much fewer small pyramidal into paleocortex and archicortex. Th e most prominent cells. Next, label layer III, the external pyramidal layer; example of paleocortex is the olfactory cortex and the indicate that it predominantly contains pyramidal cells most prominent example of archicortex is the hippocam- of varying sizes. Also, layer III is sparsely populated with pus. Mesocortex represents transitional cortex between non-pyramidal cells. Now, label layer IV, the internal neocortex and allocortex and it subdivides into perial- granular layer; indicate that it is densely packed with locortex and proisocortex. Periallocortex further subdi- non-pyramidal cells. Layer IV is the narrowest cellular vides into peripaleocortex and periarchicortex. layer and it contains the horizontally oriented external Now, in order to learn the six histologic layers of the band of Baillarger, which is a prominent thalamocortical neocortex, let’s discuss the neocortical cell populations, nerve fi ber layer. In the primary visual cortex, this nerve themselves. Th e cerebral cortex contains roughly 50 bil- fi ber band is called the line of Gennari. Next, label layer V, lion neurons, which are commonly divided into pyrami- the internal pyramidal (or ganglionic) layer; indicate that dal and non-pyramidal cells. Indicate that pyramidal it contains the largest pyramidal cells, most notably the cells are 10 to 80 micrometers (μ m) in diameter and are Betz cells which are the major cortical motor neurons. shaped like a fl ask with a single thick, cortically oriented Th e horizontally oriented internal band of Baillarger lies apical dendrite and multiple basal dendrites. Indicate deep within this layer. Now, label layer VI, the multiform that one important pyramidal cell type is the Betz cell; (or fusiform) layer; indicate that it contains a wide variety by at least one commonly held defi nition, Betz cells lie of pyramidal and non-pyramidal cells. Layer VI blends primarily within the primary motor cortex but also into the underlying white matter.10 , 18 extend, to a lesser extent, into the premotor cortex— Although the specifi c cellular constitution and nerve note that select authors instead defi ne Betz cells as fi ber density of each histologic layer varies across the being solely confi ned to the primary motor cortex. Th en, cerebral cortex, certain areas of similarity exist. In indicate that the non-pyramidal cells are much smaller: 1909, Korbinian Brodmann published the most widely they are 5 to 15 μ m in diameter. Th e most notable recognized cytoarchitectural maps of the human brain, non-pyramidal cell type is the stellate (or granule) cell. which distinguish 52 diff erent cytoarchitectural areas. Other non-pyramidal cell types include the basket, Each area or group of areas subserves a unique function. fusiform, horizontal, Martinotti, and neurogliaform In the next diagram, we will draw select, fundamental cells. 15 – 17 Brodmann areas and learn their signifi cance. 16. Cerebral Gray Matter 283

CORTICAL CLASSIFICATION NEOCORTICAL CYTOARCHITECTURE

NEOCORTEX LAYER HISTOLOGY (Isocortex) I. Molecular Cell sparse, primarily axons & dendrites Paleocortex II. External granular Non-pyramidal & ALLOCORTEX few small pyramidal cells Archicortex III. External pyramidal Pyramidal cells Peripaleocortex of varying sizes

Periallocortex IV. Internal granular Non-pyramidal cells & MESOCORTEX Periarchicortex external band of Baillarger Proisocortex V. Internal pyramidal Large pyramidal cells & internal band of Baillarger

VI. Multiform Multitude of cell types, blends CELL NOMENCLATURE into underlying white matter Pyramidal cells - 10 to 80 μm; example - Betz cell Non-pyramidal cells - 5 to 15 μm; example - stellate cells

DRAWING 16-5 Cerebral Cytoarchitecture 284 Neuroanatomy: Draw It to Know It

Brodmann Areas

Here, we will draw select, fundamental Brodmann areas. Next, peel back the superior temporal gyrus and label First, draw lateral and medial surfaces of the cerebrum. areas 41 and 42 in the transverse temporal gyri (Heschl’s Next, include certain key sulci. On the lateral hemi- gyri); these gyri form the primary auditory cortex. Th en, spheric face, include the precentral, central, and postcen- label the superior temporal gyrus as area 22. Wernicke’s tral sulci, and then the Sylvian fi ssure with its anterior area, the language reception area, lies in the posterior horizontal and anterior ascending rami, and also include portion of area 22 (and it also extends into the angular the lateral parietotemporal line. On the medial face, gyrus, Brodmann area 39 [not drawn]).22 include the corpus callosum, cingulate sulcus, and pars Next, antero-inferior to area 8, along the surface of marginalis, and then the paracentral, central, parieto- the lateral and medial faces of the cerebrum, from supe- occipital, and calcarine sulci. rior to inferior, label areas 9, 10, and 11; then, in between Now, within the postcentral and posterior paracen- area 45 and area 10, label area 46; then, beneath area 46, tral gyri, from anterior to posterior, label Brodmann label area 47; and fi nally, in the anterior cingulate areas 3, 1, 2; they constitute the primary sensory area. gyrus, label area 24. Th ese areas form the prefrontal Th en, within the precentral and anterior paracentral cortex, which is subdivided into dorsolateral prefrontal, gyri, label area 4, which is the primary motor area. orbitofrontal, and anterior cingulate (medial frontal) Within the primary motor and sensory areas, cortical cortices; each subdivision governs a discrete cognitive representation of the face and body is somatotopically domain. Although the exact anatomy of these divisions arranged in what is referred to as the homunculus (see is inconsistently defi ned, there is consensus regarding Drawing 19-4). their functions. Indicate that, generally, the dorsolateral Now, in front of area 4, label area 6. On the lateral prefrontal cortex encompasses areas 9, 46, and a portion hemisphere, area 6 is called the premotor area, and it lies of area 10; the orbitofrontal cortex comprises areas 11, in the anterior precentral gyrus and posterior superior 47, and a portion of area 10; and the anterior cingulate and middle frontal gyri. On the medial hemisphere, area cortex comprises area 24. Indicate that dorsolateral pre- 6 is called the supplementary motor area, and it lies in frontal cortex mediates executive function and task the medial aspect of the superior frontal gyrus. Th e pre- sequencing— injury here results in organizational defi - motor and supplementary motor areas help assemble cits; that orbitofrontal cortex governs social behavior — complex motor programs. 19 damage here results in impulsivity; and that anterior Next, in front of area 6, label area 8. Th e most notable cingulate (medial frontal) cortex mediates motivation— feature of area 8 is that on its lateral surface it contains injury here results in a lack of motivation (abulia).23 , 24 the human homologue to the rhesus monkey frontal eye Finally, within the occipital lobe, label the visual fi elds — the animal model for human eye movements. In cortex. On the medial surface, indicate that area 17, the humans, however, volitional control of eye movements is primary visual cortex, lies on the banks of the calcarine derived from the anterior wall of the precentral sulcus sulcus; and then show that area 18, the secondary visual and portions of many additional disparate Brodmann cortex, lies above and below area 17; and then that area areas, including areas 4, 6, 8, and 9.14 , 20 , 21 19, the tertiary visual cortex, lies above and below area Now, label area 44 in the pars opercularis and area 45 18. On the lateral surface, show that area 17 lies at the in the pars triangularis of the inferior frontal gyrus. Areas occipital pole, that area 18 lies anterior to area 17, and 44 and 45 make up Broca’s area— the speech output area. that area 19 lies anterior to area 18. 25 , 26 16. Cerebral Gray Matter 285

LATERAL FACE MEDIAL FACE Paracentral Central Precentral Central Postcentral Pars sulcus sulcus sulcus sulcus sulcus marginalis 4 3 4 3 6 12 6 12 Parieto- 8 8 Lateral parieto- occipital sulcus 9 24 9 temporal line 19 4142 18 44 10 17 10 46 45 22 19 11 17 18 18 47 19 17 11 Sylvian Cingulate Calcarine fissure sulcus sulcus AREA ANATOMY FUNCTION AREA ANATOMY FUNCTION 3, 1, 2 Postcentral gyrus Primary sensory area 9, 46, 10 Dorsolateral prefrontal Executive function 4 Precentral gyrus Primary motor area 11, 47, 10 Orbitofrontal cortex Social behavior 6 Post. frontal lobe Premotor & supplementary motor 24 Anterior cingulate Motivation 8 Ant. frontal lobe Rhesus monkey frontal eye fields 17Calcarine sulcus Primary visual 44, 45 Broca’s area Language expression 18 Occipital lobe Secondary visual 41, 42 Heschl’s gyri Primary auditory cortex 19 Occipital lobe Tertiary visual 22 (& 39) Wernicke’s area Language reception

DRAWING 16-6 Brodmann Areas 286 Neuroanatomy: Draw It to Know It

References 1 . Stippich , C. & Blatow , M. Clinical functional MRI: presurgical 14 . Clark , D. L. , Boutros , N. N. & Mendez , M. F. Th e brain and functional neuroimaging, p. 242 ( Springer , 2007 ). behavior: an introduction to behavioral neuroanatomy, 3rd ed., p. 50 2 . O n o, M ., K u b i k, S . & A b e r n a t h e y, C . D . Atlas of the cerebral sulci ( Cambridge University Press , 2010 ). (G. Th ieme Verlag; New York: Th ieme Medical Publishers, 1990 ). 1 5. P r i t c h a r d, T. Medical neuroscience ( Fence Creek Publishing, LLC , 3 . D u v e r n o y, H . M . & B o u r g o u i n, P. Th e human brain: surface, 1999 ). three-dimensional sectional anatomy with MRI, and blood supply, 1 6. K r a u s e, W. J . Krause’s essential human histology for medical students, 2nd completely rev. and enl. ed. (Springer , 1999 ). 3rd ed., p. 320 (Universal Publishers, 2005 ). 4 . B r u n i, J . E . & M o n t e m u r r o, D . G . Human neuroanatomy: a text, 17 . Jacobson , S. & Marcus , E. M. Neuroanatomy for the neuroscientist, brain atlas, and laboratory dissection guide ( Oxford University Press , pp. 158 – 161 ( Springer , 2008 ). 2009 ). 18 . Dambska , M. & Wisniewski , K. E. Normal and pathologic 5 . Mai , J. K., Voss , T. & Paxinos , G. Atlas of the human brain, 3rd ed. development of the human brain and spinal cord (J o h n L i b b e y, ( Elsevier/Academic Press , 2008 ). 1999 ). 6 . Rhoton , A. L. , Jr . Th e cerebrum. Anatomy. Neurosurgery 6 1, 19 . Wyllie , E. , Gupta , A. & Lachhwani , D. K. Th e treatment of epilepsy: 37 – 118 ; discussion 118–119 ( 2007 ). principles & practice, 4th ed. ( Lippincott Williams & Wilkins , 7 . S e e g e r, W. Endoscopic and microsurgical anatomy of the upper basal 2006 ). cisterns (Springer , 2008 ). 20 . Leigh , R. J. & Zee , D. S. Th e neurology of eye movements (Oxford 8 . N i e u w e n h u y s, R ., Vo o g d, J . & H u i j z e n, C . V. Th e human central University Press, 2006 ). nervous system, 4th ed. (Springer , 2008 ). 2 1. B ü t t n e r - E n n e v e r, J . A . Neuroanatomy of the oculomotor system 9 . K u l k a r n i, N . V. Clinical anatomy for students: problem solving (Elsevier , 1988 ). approach, p. 949 ( Jaypee , 2006 ). 2 2. A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 10 . Kretschmann , H.-J. & Weinrich , W. Cranial neuroimaging and atlas, 2nd ed. ( Lange Medical Books/McGraw-Hill , 2005 ). clinical neuroanatomy: atlas of MIR imaging and computed 2 3. S a l l o w a y, S ., M a l l o y, P. & D u ff y, J . D . Th e fr ontal lobes and tomography, 3rd ed. ( Georg Th ieme Verlag; Th ieme Medical neuropsychiatric illness, 1st ed. ( American Psychiatric Press , 2001 ). Publishers , 2004 ). 2 4. C u m m i n g s, J . L . & M e g a, M . S . Neuropsychiatry and behavioral 1 1. F o s s e t t, D . T. & C a p u t y, A . J . Operative neurosurgical anatomy, p . 2 3 neuroscience, Chapter 18 ( Oxford University Press , 2003 ). (Th ieme, 2002 ). 25 . Grill-Spector , K. & Malach , R. Th e human visual cortex . Annu Rev 1 2. H a l i m, A . Human anatomy: volume III: Head, neck and brain Neurosci 27 , 649 – 677 (2004 ). ( I.K. International Publishing House Pvt. Ltd. , 2009 ). 26 . Rajimehr , R. & Tootell , R. Organization of human visual cortex . In 13 . Govaert , P. & De Vries, L. S. An atlas of neonatal brain sonography, Th e senses: a comprehensive reference (ed. A. I. Basbaum ) ( Elsevier 2nd ed., pp. 18 – 19 ( Mac Keith Press , 2010 ). Inc., 2008 ). 1 7 Cerebral White Matter

Cerebral White Matter — Overview

Long Association Fibers ( Advanced )

Internal Capsule

Commissures & Disconnections ( Advanced ) 288 Neuroanatomy: Draw It to Know It

Know-It Points

Cerebral White Matter — Overview

■ Association fi bers connect areas within a ■ Subcortical projection fi bers divide into the thalamic hemisphere. bundle and the pontine bundle. ■ S t r i a t a l fi bers provide communication between the ■ Th e deep white matter region between the cortex and cerebral cortex and the basal ganglia. the diencephalon is anatomically divided into the ■ C o r d fi bers either directly connect areas on opposite centrum semiovale and the corona radiata. sides of the neuroaxis or provide an important step in ■ Th e centrum semiovale lies above the level of the that cross-axis connection. lateral ventricles and the corona radiata lies at their ■ C o r d fi bers subdivide into commissural and l e v e l . subcortical fi ber bundles.

Long Association Fibers (Advanced )

■ Th e superior longitudinal fasciculus connects the ■ Th e inferior longitudinal fasciculus is the major white parietal and frontal cortices. matter bundle of the ventral occipitotemporal visual ■ Th e arcuate fasciculus originates in the posterior pathway, the so-called “what” pathway. superior temporal area and passes forward to the ■ Th e fronto-occipital fasciculus transmits visual spatial frontal lobe; it is classically considered the language information to the frontal motor areas to guide conduction pathway. movement via the “where” pathway. ■ Th e cingulum is the main white matter bundle of the limbic system. ■ Th e middle longitudinal fasciculus spans from the posterior end of the superior temporal gyrus to the temporal pole.

Internal Capsule

■ Th e internal capsule fi lls a V-shaped wedge within the ■ Th e posterior limb of the internal capsule lies in conglomeration of the basal ganglia and thalamus. between the thalamus and the lentiform nucleus. ■ Th e anterior limb of the internal capsule lies in ■ Both the sublenticular and retrolenticular limbs lie between the head of the caudate and the lentiform posterior to the posterior limb. nucleus. ■ Infarction to the genu and posterior limb of the ■ Th e genu of the internal capsule is the bend; it lies internal capsule produces a classic and common pure along the medial-lateral plane of the anterior motor stroke. thalamus. 17. Cerebral White Matter 289

Commissures & Disconnections (Advanced )

■ C o m m i s s u r a l fi bers connect corresponding areas ■ Th e anterior-inferior portion of the corpus callosum of the cerebrum; the two main commissural is the rostrum; the anterior-superior portion is the bundles are the anterior commissure and the corpus genu; the length of the corpus callosum is the body; callosum. and the posterior portion is the splenium. ■ Th e corpus callosum lies superior to the anterior ■ In alexia without agraphia, there is injury to the commissure and connects dorsal cortical areas, medial left posterior occipital lobe and also to the whereas the anterior commissure connects ventral right visual projection fi bers aft er they have crossed areas. midline within the splenium of the corpus callosum. ■ Th e anterior commissure connects the bilateral ■ Alien hand syndrome has three forms: the callosal ventral posterior frontal lobes and also the bilateral variant, which manifests with intermanual confl ict; anterior temporal lobes. the frontal variant, which manifests with involuntary ■ Th e corpus callosum connects the bilateral grasping; and the sensory variant, which manifests hemispheres from the frontal to the occipital poles. with limb ataxia. 290 Neuroanatomy: Draw It to Know It

FIGURE 17-1 Achille-Louis Foville’s illustrations of white matter, 1844. Used with permission from Schmahmann, Jeremy D., and Deepak N. Pandya. Fiber Pathways of the Brain . New York: Oxford University Press, 2006. 17. Cerebral White Matter 291

FIGURE 17-2 White matter organization. Used with permission from Schmahmann, Jeremy D., and Deepak N. Pandya. Fiber Pathways of the Brain. New York: Oxford University Press, 2006. 292 Neuroanatomy: Draw It to Know It

Cerebral White Matter — Overview

Here, we will draw an overview of the white matter path- Indicate that the two types of striatal fi ber bundles are ways in accordance with the organization described in the Muratoff bundle (aka subcallosal fasciculus) and the the 2006 white matter textbook Fiber Pathways of the external capsule. Brain . Begin with a coronal section through the brain, Now, we will draw the cord fi bers, which connect brainstem, and upper spinal cord. Include a sulcal inden- opposite sides of the nervous system: they subdivide into tation on the surface of the cerebral cortex as a point of commissural and subcortical fi ber bundles and they form reference and also include a thalamus and head of the the dense aggregate of deep white matter underneath the caudate. Th ree white matter pathway types exist: associa- cortical gray matter. Draw a transverse-oriented com- tion fi bers, which connect areas within a hemisphere; missural fi ber connection from one side of the cortex to cord fi bers, which either directly connect areas on oppo- the other. Th e key commissural fi bers are the anterior site sides of the neuroaxis or provide an important step commissure and corpus callosum— the latter contains in that cross-axis connection; and striatal fi bers, which roughly 300 million myelinated axons. 1 Next, draw two provide communication between the cerebral cortex and vertically oriented representative subcortical projection the basal ganglia. fi bers: an ascending one from the thalamus to the cortex, First, we will draw the association fi bers, which are called the thalamic bundle, and a descending one from subdivided in accordance with the distance they travel. the cortex to the opposite side of the brainstem, called Begin with a short association fi ber (aka U-fi ber or arcu- the pontine bundle. Th e thalamic bundle encompasses ate bundle). Short association fi bers travel between gyri such pathways as the somatosensory aff erents from the just underneath the innermost cerebral cortical gray spinal cord and the cerebellar projections of the cortico- matter layer (layer 6). Certain white matter diseases, pontocerebellar pathway; these pathways relay in the such as subtypes of multiple sclerosis, spare the short thalamus in their ascent to the cerebral cortex. Th e pon- association fi bers. Next, draw a mid-range association tine bundle encompasses such pathways as the corti- fi ber, called a neighborhood association fi ber. Neigh- cospinal tract, which descends through the internal borhood association fi bers extend into the deep white capsule and pons, and the corticopontine tract, which matter to connect areas a mid-distance away from one synapses in the pons. Note that although the thalamic another. Finally, draw a long-distance association fi ber, bundle and the corticopontine tract are actually ipsi- called a long association fi ber. Long association fi bers hemispheric projections, they both are steps in larger extend deep into the brain and connect distant ipsi- pathways that connect opposite sides of the neuroaxis. hemispheric regions. Note that we will draw the specifi c, Th e cord fi bers form the deep white matter region named long association fi bers in our sagittal diagram, between the cortex and the diencephalon, which is ana- separately. tomically divided into the centrum semiovale and corona Next, draw a prototypical striatal fi ber projection radiata. Th e name corona radiata stands for “radiating from the cerebral cortex to the basal ganglia. Projections crown”; however, its radiating appearance is appreciable from throughout the cortex synapse in the basal gan- only in detailed anatomic dissection. Indicate that the glia and are evidentiary of the widespread role of the centrum semiovale lies above the level of the lateral ven- basal ganglia in behavioral as well as motor functions. tricles and that the corona radiata lies at their level. 2 – 8 17. Cerebral White Matter 293

GENERAL ORGANIZATION - NOMENCLATURE GENERAL ORGANIZATION - CORONAL VIEW Short Long association Neighborhood association association fiber* Striatal Neighborhood Short fiber fibers ASSOCIATION association Subcortical association fiber cord bundles Long association*

Thalamic Commissural Commissural bundle cord fibers bundle CORD Pontine Thalamic bundle bundle Subcortical bundle Pontine bundle

Muratoff bundle CENTRUM SEMIOVALE & CORONA RADIATA Centrum semiovale - above lateral ventricles STRIATAL Corona radiata - at level of the lateral ventricles External capsule *Trajectory best viewed in sagittal section

DRAWING 17-1 Cerebral White Matter — Overview 294 Neuroanatomy: Draw It to Know It

Long Association Fibers (Advanced )

Here, we will draw the long association fi bers. Begin cingulum projects bidirectionally through the limbic with a sagittal section through a cerebral hemisphere. lobe: from the cingulate gyrus around the posterior end Th e fi rst fi bers we will draw are the superior longitudinal of the corpus callosum back forward through the para- fasciculus and the arcuate fasciculus. Note that histori- hippocampal gyrus. Indicate that the cingulum plays an cally and commonly these fi bers are classifi ed either syn- important role in emotional processing. Interestingly, onymously or as part of a single system. First, show that cingulotomy (ie, cingulum fi ber transection) was unsuc- the superior longitudinal fasciculus is a bidirectional cessfully used to treat psychosis in the mid-twentieth pathway that connects the parietal and frontal cortices— century and was abandoned, but is now sometimes used classically it is more broadly defi ned as involving the for the treatment of obsessive-compulsive disorder and temporal and occipital cortices, as well. Th e superior intractable pain. longitudinal fasciculus is further subcategorized into Now, draw the middle longitudinal fasciculus from three diff erent fasciculi, which, roughly, from rostral to the posterior end of the superior temporal gyrus to the caudal are SLF I, II, and III. In accordance with its broad temporal pole (note that this is not the medial longitudi- anatomy, the superior longitudinal fasciculus is involved nal fasciculus, which lies in the brainstem and transmits in a wide variety of cognitive functions, but indicate that, eye movements). Indicate that the middle longitudinal notably, it communicates spatial information between fasciculus connects paralimbic, associative, and prefron- the frontal and parietal lobes. tal cortices. Next, show that the arcuate fasciculus originates in Next, draw the inferior longitudinal fasciculus from the posterior superior temporal area and passes forward the antero-inferior temporal lobe to the parieto- occipital to the frontal lobe. Th e ability to repeat language, which lobe. Th e inferior longitudinal fasciculus is the major is called language conduction, has historically been white matter bundle of the ventral occipitotemporal assigned to the arcuate fasciculus (and still commonly visual pathway, which is responsible for object recogni- is). Language conduction requires the transmission of tion and identifi cation— the so-called “what” pathway. language from the superior temporal reception area to Next, draw the fronto-occipital fasciculus in the supe- the frontal motor speech output area. Despite its histor- rior cortex from the parieto-occipital area to the pre- ical assignment to the arcuate fasciculus, evidence sug- frontal area. Th e fronto-occipital pathway is the “where” gests that the arcuate fasciculus is actually more generally pathway corollary to the ventral occipitotemporal “what” involved in the spatial orientation of sound and that the pathway; it transmits visual spatial information to the superior longitudinal fasciculus (specifi cally, SLF III), frontal motor areas to guide movement. the middle longitudinal fasciculus, and the extreme cap- Lastly, show that the extreme capsule spans from the sule, instead, transmit language conduction. middle temporal area to the ventral prefrontal cortex. It Now, draw the uncinate fasciculus, which connects the is discretely situated between the claustrum and the orbital prefrontal cortex and anterior cingulate gyrus with insula (as opposed to the external capsule, which is situ- the anterior temporal lobe. Indicate that the uncinate fas- ated between the claustrum and the putamen) and is ciculus combines processed somatosensory information most easily viewed on coronal radiographic imaging. (auditory, visual, gustatory) with emotional response reg- Indicate that the extreme capsule plays a role in language, ulation to assist in decision-making processes. specifi cally in syntax and grammar, and as discussed pre- Next, we will draw the cingulum, which is the main viously, conduction aphasia may at least partially be due white matter bundle of the limbic system. Show that the to dysfunction within this white matter bundle.3 – 8 17. Cerebral White Matter 295

ABBREVIATION FIBER BUNDLE FUNCTION SLF Superior longitudinal Spatial awareness fasciculus

LONG ASSOCIATION FIBER BUNDLES - AF Arcuate Classic view - language conduction SAGITTAL VIEW fasciculus Modern view - sound orientation FOF SLF UF Uncinate Connects somatosensation & fasciculus emotion for decision-making CB CB Cingulum Emotional processing AF bundle EC ILF UF MLF Middle longitudinal Associative, paralimbic, MLF fasciculus prefrontal communication ILF Inferior longitudinal “What” visual pathway fasciculus

FOF Fronto-occipital “Where” visual pathway fasciculus

EC Extreme capsule Language syntax & grammar

DRAWING 17-2 Long Association Fibers 296 Neuroanatomy: Draw It to Know It

Internal Capsule

Here, we will draw the anatomy of the internal capsule in only a few key clinical highlights. Most important to both axial and sagittal views. Th e internal capsule com- clinical neurology is the position of the motor fi bers prises fi ber bundles that originate from widespread brain because infarction of the genu and posterior limb of the regions and it carries fi bers of many disparate functional internal capsule produces a classic and common pure modalities, including motor, sensory, cognitive, and motor stroke. Th e motor fi bers are arranged somatotopi- emotional fi ber pathways. We will begin by drawing an cally, meaning the facial fi bers pass through the genu, the axial view of the key basal ganglia structures (and the arm fi bers lie posterior to the facial fi bers in the anterior thalamus) because the internal capsule forms a wedge in portion of the posterior limb, and the leg fi bers descend between them. For orientational purposes, fi rst draw the posterior to the arm fi bers in the posterior portion of the posterior aspect of the lateral ventricle and then the fron- posterior limb. Importantly, the motor fi bers crowd tal horn of the lateral ventricle. Next, draw the head of together inferiorly within the internal capsule; thus, the the caudate; then, the thalamus; and next, the globus more inferior the infarct, the more broad the motor defi - pallidus and putamen, which together form the lenti- cit relative to the size of the infarct. form nucleus. Now, show that the internal capsule fi lls Draw a sagittal view of the internal capsule as a broad- the V-shaped wedge in between these nuclei. based triangle sitting on a pointed edge; the internal cap- Next, re-draw an axial view of the internal capsule so sule gradually dips down along the anterior–posterior we can label its individual limbs. Indicate that the ante- course of the anterior limb and then rises again along the rior portion, between the head of the caudate and the anterior–posterior course of the posterior limb. From lentiform nucleus, is called the anterior limb; then, show anterior to posterior, label the anterior limb, genu, poste- that the middle (bend) of the internal capsule, which rior limb, and sublenticular and retrolenticular limbs. occurs along the medial–lateral plane of the anterior Indicate that the anterior limb consists of fi bers from the thalamus, is called the genu; next, indicate that the por- prefrontal cortex, predominantly anterior thalamic radi- tion of internal capsule between the thalamus and the ation fi bers that connect the frontal cortex with the thal- lentiform nucleus is called the posterior limb; then, show amus and also frontopontine fi bers. Th en, show that the that the retrolenticular limb lies posterior to the poste- genu and posterior limbs comprise the motor fi bers. rior limb— its fi bers run posterior to the lentiform We commonly associate the facial fi bers purely with nucleus; and fi nally, label the sublenticular limb in the genu, but show that the facial fi bers actually begin parentheses— its fi bers run underneath the lentiform in the anterior limb, descend through the genu, and enter nucleus and lie inferior to the plane of this diagram. the posterior limb. Next, show that the arm fi bers descend Note that the relative anterior–posterior positions of the through the anterior portion of the posterior limb. Th en, sublenticular and retrolenticular limbs are inconsistently show that the leg fi bers originate posterior to the arm defi ned; therefore, we consider them both together as fi bers and pass anteriorly during their descent through lying posterior to the posterior limb. the posterior limb. Finally, indicate that the sublenticu- In sagittal view, we will now show the position of lar limb carries auditory fi bers from the medial genicu- a few fi ber bundles that pass through the internal cap- late body, and then show that both the sublenticular and sule; bear in mind that the fi bers we will draw represent retrolenticular limbs carry visual projection fi bers. 3 – 9 17. Cerebral White Matter 297

INTERNAL CAPSULE Caudate AXIAL VIEW Frontal Anterior (head) horn limb

Putamen Globus Genu pallidus Internal capsule

Thalamus Posterior limb (Sublenticular limb) Retrolenticular limb Lateral ventricle Retrolenticular Limbs: Anterior Sublenticular Genu Posterior Retrolent. Prefrontal MOTOR FIBERS Sublent. (visual) (auditory & Face Arm Leg visual) Anterior Posterior

INTERNAL CAPSULE SAGITTAL VIEW

DRAWING 17-3 Internal Capsule 298 Neuroanatomy: Draw It to Know It

Commissures & Disconnections (Advanced )

Here, we will draw the commissural fi bers and learn Th e function of the commissural fi bers has aroused about the major disconnection syndromes. Commissural great interest throughout the past several centuries, and fi bers connect corresponding areas of the cerebrum; the although the commissural fi bers have long been under- two main commissural bundles are the anterior commis- stood to provide interhemispheric communication, the sure and the corpus callosum. Th e corpus callosum lies full extent of their function is still not known. Functional superior to the anterior commissure and connects dorsal analysis of the corpus callosum suggests a role for it in cortical areas, whereas the anterior commissure connects both sensory integration and high-level cognitive pro- ventral areas. First, let’s use an axial plane through the cessing. Much of what is known about the commissural inferior surface of the brain. Hash the anterior commis- bundles, however, comes from callosal resection surger- sure bundle, which connects the bilateral ventral poste- ies, which are still done today to prevent the transmis- rior frontal lobes and also the bilateral anterior temporal sion of epileptic activity between the cerebral hemispheres lobes. Th en, draw the corpus callosum fi bers, which con- (ie, to stem the propagation of seizures), and also from nect the bilateral hemispheres from the frontal to the commissural fi ber disruption injuries, which can result occipital poles. Indicate that the frontal fi bers are called in disconnection syndromes. the anterior forceps (aka forceps minor, frontal forceps) Here, we will address two major disconnection syn- and that the occipital fi bers are called the posterior for- dromes: pure alexia without agraphia and alien hand ceps (aka forceps major, occipital forceps). syndrome. In 1892, Dejerine memorably described the Next, let’s draw a sagittal view of the corpus callosum syndrome of pure alexia without agraphia, which is a syn- to show its four regions. Label the anterior-inferior por- drome in which patients are unable to read but are still tion of the corpus callosum as the rostrum; the anterior- able to write. To illustrate the anatomic underpinnings of superior portion as the genu, which is the anterior bend; alexia without agraphia, draw an anatomic axial section the length of the corpus callosum as the body; and the through a mid-height of the cerebrum. Th en, label the posterior portion as the splenium. Indicate that the pre- language center in the left superior temporal gyrus. Next, frontal fi bers run through the rostrum and genu; the label the left visual cortex and show that it directly com- frontal fi bers run through the anterior body; the tem- municates with the language center. Th en, draw the right poro-parietal fi bers run through the posterior body; and visual cortex and then the splenium of the corpus callo- the temporo-occipital fi bers run through the splenium. sum. Indicate that the right visual cortex projects to the Now, return to our axial diagram and indicate that the language center through the splenium of the corpus cal- genu fi bers correspond to the anterior forceps; the sple- losum. Now, show that in pure alexia without agraphia, nial fi bers correspond to the posterior forceps; and the there is a posterior cerebral lesion that aff ects the medial body fi bers correspond to the midportion of the callo- left posterior occipital lobe and the related visual projec- sum. Th e rostral fi bers run beneath the genu and are infe- tion fi bers, and indicate that the lesion also involves the rior to the plane of this axial section. right visual projection fi bers aft er they have crossed mid- Additional smaller commissural fi ber pathways exist, line within the splenium of the corpus callosum. From including the hippocampal commissure, which lies infe- this lesion, the left visual center is directly cut off from rior to the splenium of the corpus callosum and connects the language center and the communication between the the bilateral hippocampal formations, and the posterior, right visual center and the language center is disrupted habenular, and supraoptic commissures. from the injury to the corpus callosum. 17. Cerebral White Matter 299

COMMISSURAL FIBERS - INFERIOR AXIAL VIEW

Anterior forceps (genu)

Anterior commissure

Corpus ALEXIA WITHOUT Posterior forceps callosum AGRAPHIA - (splenium) (body) ANATOMICAL, AXIAL VIEW

CORPUS CALLOSUM - SAGITTAL VIEW Language Frontal center Temporo-parietal Prefrontal Body Genu Temporo-occipital Left Right visual cortex visual cortex Rostrum Splenium

DRAWING 17-4 Commissures & Disconnections— Partial 300 Neuroanatomy: Draw It to Know It

Commissures & Disconnections (Advanced ) (Cont.)

Left posterior cerebral artery infarction is a common is most commonly aff ected. Left anterior cerebral artery cause of alexia without agraphia. Note that a coincident infarction is a notable cause of this variant of alien hand right homonymous hemianopia oft en occurs in this syn- syndrome.11 – 13 drome due to the left posterior occipital injury, and also Finally, label the sensory variant, which manifests note that our diagram is an anatomic drawing, in which with limb ataxia. To demonstrate the sensory variant of the left side of the brain is on the left -hand side of the alien hand syndrome, let your hand dangle out away from page; radiographic images have the opposite orientation your body and try to forget its existence. Patients with (see Drawing 1-2).10 the sensory variant are generally unaware of their limb or Another disconnection syndrome that receives atten- even frankly deny that it’s their own. Indicate that pari- tion from both neurologists and Hollywood, alike, is eto-occipital lobe lesions cause this iteration of alien called alien hand syndrome (aka alien limb sign). It hand syndrome and that the nondominant hemisphere was cinematized most memorably in Stanley Kubrick’s and hand are most commonly aff ected. Corticobasal Dr. Strangelove . Th ree forms of alien hand syndrome degeneration, a neurodegenerative cause of dementia, exist, each with a discrete anatomic localization; however, can cause this alien hand syndrome variant.11 – 13 patients commonly present with overlapping symptoms. Other important clinical aspects regarding the corpus Across the top of the page, label variant, manifestation, callosum are the frequency with which it fails to develop localization, and dominance. First, label the callosal vari- and the wide range of diseases that aff ect it. Congenital ant, which manifests with intermanual confl ict or so- failure of the corpus callosum to fully develop is known called self-oppositional behavior. In this alien hand as callosal agenesis and it occurs either in isolation or as syndrome variant, one hand is in direct confl ict with the part of a more complex syndrome, such as the Arnold- other, most commonly the left with the right. To show Chiari, Dandy-Walker, or Aicardi syndromes. Acquired yourself what is meant by self-oppositional behavior, forms of corpus callosum abnormalities occur from a open a desk drawer with your right hand and then imme- wide range of causes, including demyelinating disorders, diately slam it shut with your left . Indicate that this vari- such as multiple sclerosis, and head trauma. Also, certain ant is most commonly caused by a lesion in the anterior tumors characteristically invade the corpus callosum, corpus callosum and that the nondominant hand (ie, the such as glial tumors — most commonly glioblastoma left hand) is most commonly aff ected, meaning the left multiforme, lymphomas, and lipomas. Lastly, metabolic hand opposes the actions of the right. disorders can also aff ect the corpus callosum, such as Next, label the frontal variant, which manifests with Marchiafava-Bignami, which is a rare cause of necrotic involuntary grasping, groping, or manipulation of layering of the corpus callosum. Marchiafava-Bignami objects. To demonstrate what happens in this syndrome, was originally described from the autopsies of three with one hand involuntarily grasp at an object. Indicate Italian men known to have been heavy red wine drinkers that this variant is due to a lesion to the medial frontal but has subsequently been found in both alcoholics and lobe. Th e lesion is most commonly in the dominant non-alcoholics, alike, and is ascribed to vitamin B com- hemisphere and the dominant hand (ie, the right hand) plex defi ciency. 3 , 14 – 18 17. Cerebral White Matter 301

COMMISSURAL FIBERS - ALIEN HAND SYNDROME INFERIOR AXIAL VIEW VARIANT MANIFESTATION LOCALIZATION DOMINANCE Callosal Intermanual Corpus callosum- Non-dominant hand conflict anterior body Anterior Frontal Involuntary Medial frontal lobe Dominant hemisphere; forceps (genu) grasping dominant hand Sensory Limb ataxia Parieto-occipital lobe Non-dominant hemisphere; Anterior commissure non-dominant hand

Corpus ALEXIA WITHOUT Posterior forceps callosum AGRAPHIA - (splenium) (body) ANATOMICAL, AXIAL VIEW

CORPUS CALLOSUM - SAGITTAL VIEW Language Frontal center Temporo-parietal Prefrontal Body Genu Temporo-occipital Left Right visual cortex visual cortex Rostrum Splenium

DRAWING 17-5 Commissures & Disconnections— Complete 302 Neuroanatomy: Draw It to Know It

References 1 . F i l l e y, C . M . Th e behavioral neurology of white matter, C h a p t e r 2 1 0. F e s t a, J . R . & L a z a r, R . M . Neurovascular neuropsychology, ( Oxford University Press , 2001 ). pp. 32 – 33 ( Springer , 2009 ). 2 . J o y c e, C . Diagnostic imaging in critical care: a problem based approach 11 . Biran , I. & Chatterjee , A. Alien hand syndrome . Arch Neurol 6 1, ( Churchill Livingstone Elsevier , 2010 ). 292 – 294 (2004 ). 3 . S c h m a h m a n n, J . D . & P a n d y a, D . N . Fiber pathways of the brain 12 . Biller , J. , Fleck , J. D. & Pascuzzi , R. M. Practical neurology DVD ( Oxford University Press , 2006 ). review, pp. 43 – 44 (Lippincott Williams & Wilkins, 2005 ). 4 . Jones , D. K. Diff usion MRI: theory, methods, and application, 1 3. B o g o u s s l a v s k y, J . & C a p l a n, L . R . Stroke syndromes, 2nd ed., pp. 20 – 22 ( Oxford University Press , 2011 ). pp. 319 – 321 ( Cambridge University Press , 2001 ). 5 . M o r i t a n i, T. , E k h o l m, S . & We s t e s s o n, P. - L . Diff usion-weighted MR 1 4. A r b e l a e z, A ., P a j o n, A . & C a s t i l l o, M . A c u t e M a r c h i a f a v a - B i g n a m i imaging of the brain, 2nd ed., Chapter 2 ( Springer , 2009 ). disease: MR fi ndings in two patients . AJNR Am J Neuroradiol 2 4, 6 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 1955 – 1957 (2003 ). clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). 1 5. J i n k i n s, R . Atlas of neuroradiologic embryology, anatomy, and 7 . M e n d o z a, J . E . & F o u n d a s, A . L . Clinical neuroanatomy: a variants ( Lippincott Williams & Wilkins , 2000 ). neurobehavioral approach (Springer , 2008 ). 1 6. D o b b s, M . R . Clinical neurotoxicology: syndromes, substances, 8 . Jacobson , S. & Marcus , E. M. Neuroanatomy for the neuroscientist, environments, 1st ed., p. 93 ( Saunders/Elsevier , 2009 ). pp. 158 – 161 ( Springer , 2008 ). 1 7. M a h m u t G a z i Ya ş a r g i l, C . D . A . Microsurgery of CNS tumors, 9 . C h o w d h u r y, F. , H a q u e, M ., S a r k a r, M ., A r a, S . & I s l a m, M . W h i t e pp. 297 – 298 (Th ieme, 1996 ). fi ber dissection of brain; the internal capsule: a cadaveric study . Turk 18 . Prabhakar Rajiah , A. G. S. S. Paediatric radiology: clinical cases, C a s e Neurosurg 20 , 314 – 322 (2010 ). 5.15 (PasTest , 2008 ). 1 8 Basal Ganglia

Basal Ganglia: Anatomy

Basal Ganglia: Nomenclature

Direct & Indirect Pathways: Anatomy (Advanced)

Direct & Indirect Pathways: Circuitry 304 Neuroanatomy: Draw It to Know It

Know-It Points

Basal Ganglia: Anatomy

■ Th e caudate nucleus lies along the lateral wall of the ■ Th e putamen and head of the caudate are connected lateral ventricle. at the nucleus accumbens. ■ Th e lens-shaped lentiform nucleus subdivides into the ■ Th e lateral medullary lamina separates the putamen putamen, laterally, and the globus pallidus, medially. and the globus pallidus. ■ Th e internal capsule lies in between the lentiform ■ Th e medial medullary lamina subdivides the globus nucleus and the head of the caudate, anteriorly, and pallidus into an internal (or medial) segment and an the lentiform nucleus and the thalamus, posteriorly. external (or lateral) segment.

Basal Ganglia: Nomenclature

■ Th e term corpus striatum comprises the caudate, ■ Th e pale appearance of the globus pallidus gives it its putamen, and globus pallidus. name: pallidum. ■ Th e caudate nucleus divides into a head, body, and tail. ■ Th e subthalamic nucleus and substantia nigra are ■ Striations connect the caudate and the putamen; functionally but not developmentally associated with thus, collectively, they are the striatum. t h e b a s a l g a n g l i a .

Direct & Indirect Pathways: Anatomy (Advanced)

■ Field H lies medial to the subthalamic nucleus and ■ Th e lenticular fasciculus projects from the internal inferior to the zona incerta. segment of the globus pallidus through Fields H2, ■ Field H1 lies in between the thalamus and zona incerta. H, and H1 to enter the thalamus. ■ Field H2 lies lateral to the zona incerta and medial to ■ Where the ansa lenticularis and the lenticular the internal capsule. fasciculus run together in Field H1, they are ■ Th e ansa lenticularis originates in the globus pallidus collectively called the thalamic fasciculus. internal segment, projects inferomedially, passes ■ Th e subthalamic fasciculus refers to projections beneath the subthalamic nucleus, and then passes between the globus pallidus and subthalamic through Field H and Field H1 to enter the thalamus. nucleus. 18. Basal Ganglia 305

Direct & Indirect Pathways: Circuitry

■ Th e direct pathway: – Th e GPi/STNr inhibits the thalamus (the thalamus – Th e cortex excites the striatum excites the cerebral cortex) – Th e striatum inhibits the combined globus pallidus – Th e indirect pathway is overall inhibitory internal segment and the substantia nigra reticulata – A parallel circuit also exists within the indirect (GPi/STNr) pathway that passes through the subthalamic – Th e GPi/STNr inhibits the thalamus (the thalamus nucleus in which the globus pallidus external excites the cerebral cortex) segment inhibits the subthalamic nucleus and the – Th e direct pathway is overall excitatory subthalamic nucleus excites the GPi/STNr ■ Th e indirect pathway: – Th is parallel indirect pathway through the – Th e cortex excites the striatum subthalamic nucleus is also overall inhibitory – Th e striatum inhibits the globus pallidus external ■ Dopamine from the substantia nigra compacta segment excites the direct pathway (via dopamine 1 receptors) – Th e globus pallidus external segment inhibits the and inhibits the indirect pathway (via dopamine 2 GPi/STNr receptors); both of these eff ects promote movement.

Cingulate sulcus Cingulate gyrus Corpus callosum Lateral ventricle Septum pellucidum Septal nuclei Caudate nucleus

Internal capsule External capsule Insula Claustrum Lateral sulcus Extreme capsule

Superior temporal: Gyrus Sulcus Globus pallidus Middle temporal gyrus Diagonal band Inferior temporal: Sulcus Gyrus

Putamen Entorhinal cortex Collateral sulcus Accumbens nucleus Parahippocampal gyrus Optic nerves 10 mm

FIGURE 18-1 Coronal anatomic section through the anterior region of the basal ganglia. Used with permission from the Michigan State University: Brain Biodiversity Bank. https://www.msu.edu/∼brains/ 306 Neuroanatomy: Draw It to Know It

Cingulate sulcus 3rd ventricle Cingulate gyrus Corpus callosum Fornix Lateral ventricle Choroid plexus Caudate nucleus

Anterior commissure Internal capsule External capsule Insula Claustrum Extreme capsule Lateral sulcus Superior temporal: Globus pallidus Gyrus Sulcus Anterior Middle commissure temporal gyrus

Inferior temporal: Amygdaloid nuclei Sulcus Gyrus Collateral sulcus Putamen Optic chiasm Entorhinal cortex Preoptic area Parahippocampal gyrus Infundibular stalk 10 mm

FIGURE 18-2 Coronal anatomic section through the middle region of the basal ganglia. Used with permission from the Michigan State University: Brain Biodiversity Bank. https://www.msu.edu/∼brains/ 18. Basal Ganglia 307

Cingulate sulcus 3rd ventricle Cingulate gyrus Corpus callosum Fornix Lateral ventricle Thalamic nuclei: Choroid plexus Anteroprincipal Caudate nucleus Ventrolateral Reticular Medial dorsal thalamic nucleus

Lateral Internal capsule sulcus External capsule Claustrum Extreme capsule Insula Zona incerta Globus pallidus Superior Optic tract temporal: Gyrus Sulcus

Middle temporal gyrus

Inferior temporal: Lateral ventricle Sulcus Red nucleus Subthalamic nucleus Gyrus Collateral sulcus Putamen Substantia nigra Entorhinal cortex Hippocampus Interpeduncular fossa Parahippocampal gyrus Dentate gyrus Pons Cerebral peduncle 10 mm

FIGURE 18-3 Coronal anatomic section through the posterior region of the basal ganglia. Used with permission from the Michigan State University: Brain Biodiversity Bank. https://www.msu.edu/∼brains/ 308 Neuroanatomy: Draw It to Know It

Basal Ganglia: Anatomy

Here, we will draw the basal ganglia and its related struc- below it, draw the frontal horn of the lateral ventricle. tures in axial, coronal, and sagittal views. Note that Next, draw the combined putamen and head of the cau- we will not be able to show all of the structures in each date and show that they are connected at the base by view; however, through the combined views we will the nucleus accumbens. Th e nucleus accumbens is the draw the fundamental anatomy of the basal ganglia. bridge that persists between the head of the caudate and Also, note that the basal ganglia are more correctly putamen aft er the anterior limb of the internal capsule referred to as the basal nuclei because by defi nition a separates the head of the caudate from the putamen. ganglion is a neuronal aggregation within the peripheral Now, beneath the nucleus accumbens, draw the basal nervous system and the basal nuclei lie within the central forebrain. nervous system. Begin with an axial view. First, draw a Next, draw another coronal view just posterior to the few orientational landmarks: along the medial aspect previous section. To establish the anterior-posterior of the diagram, anteriorly, draw the frontal horn of the plane of this diagram, inferiorly, draw the optic tract lateral ventricle; then, posteriorly, draw the body of the and third ventricle; the hypothalamus immediately sur- lateral ventricle and the thalamus; next, along the lateral rounds the third ventricle. Next, draw the corpus callo- edge of the diagram, draw the insula and then medial to sum and frontal horn of the lateral ventricle. Along it, draw the claustrum. the lateral wall of the frontal horn, draw the head of the Next, let’s include a few key basal ganglia structures. caudate. Th en, draw the putamen, and medial to it, draw Along the lateral wall of the frontal horn of the lateral the globus pallidus; show that the lateral medullary ventricle, label the head of the caudate. Th en, at the pos- lamina separates them. Note that the medial medullary tero-lateral tip of the thalamus in the lateral wall of the lamina subdivides the globus pallidus into an internal body of the lateral ventricle, draw the tail of the caudate. (or medial) segment and an external (or lateral) segment. Note that the body of the caudate is not visible at this Next, in between the lentiform nucleus and the caudate, axial height. Now, in the center of the diagram, draw the draw the internal capsule. Now, beneath the globus pal- lens-shaped lentiform nucleus and subdivide it into the lidus, draw the basal forebrain and then draw the hori- putamen, laterally, and the globus pallidus, medially. zontally oriented anterior commissure in between them. Early in development, the globus pallidus migrates into Note that the globus pallidus actually extends beneath the medial wall of the putamen—we can envision the the anterior commissure as the ventral pallidum (see lentiform nucleus as a globus pallidus core surrounded Drawing 18-2 ). by a putaminal shell. Next, in between the lentiform Lastly, let’s draw the basal ganglia in sagittal view. nucleus and the head of the caudate and thalamus, label First, draw the corpus callosum and the subjacent lateral the internal capsule. Th en, in between the putamen ventricular system: label the frontal horn, atrium, and and the claustrum, label the external capsule, and in temporal horn divisions of the ventricular system. Next, between the claustrum and the insula, label the extreme draw the caudate and label the head and body. Note that capsule. the tail is not visible in this section. Th en, anteriorly, Now, let’s draw a coronal view through the anterior draw the putamen and, posteriorly, draw the thalamus. aspect of the basal ganglia. At the inferomedial aspect of In between these structures, label the internal capsule, the diagram, draw the optic chiasm; then, along the supe- and show that it funnels, inferiorly, into the cerebral rior aspect of the diagram, draw the corpus callosum; just peduncle. 18. Basal Ganglia 309

BASAL GANGLIA & RELATED CORONAL VIEW CORONAL VIEW STRUCTURES (ANTERIOR) (MID-ANTERIOR/POSTERIOR) AXIAL VIEW Corpus callosum Corpus callosum Internal Caudate Extreme capsule Internal capsule Frontal Insula Caudate Frontal (head) Claustrum capsule horn (head) horn External capsule Putamen Putamen Frontal Nucleus Globus horn accumbens pallidus Caudate Anterior commissure3rd (head) Basal forebrain ventricle Basal Optic chiasm Lateral forebrain medullary lamina Optic tract Putamen Globus Internal capsule pallidus SAGITTAL Corpus callosum VIEW (body) Thalamus Caudate (head) Internal Lateral Thalamus Lateral Caudate capsule (tail) ventricle, Putamen ventricle, frontal horn Cerebral atrium Lateral ventricle peduncle (body) Lateral ventricle, temporal horn

DRAWING 18-1 Basal Ganglia: Anatomy 310 Neuroanatomy: Draw It to Know It

Basal Ganglia: Nomenclature

Here, we will draw a fl ow diagram for the nomenclature the anteromedial portion of the globus pallidus that lies of the basal ganglia. Begin with the term corpus striatum, below the anterior commissure. However, although we which comprises the caudate, putamen, and globus pal- consider the ventral striatum and ventral pallidum to be lidus. Indicate that the caudate nucleus, itself, is divided divisions of the striatum and pallidum, here, certain texts into a head, body, and tail and that the globus pallidus is distinguish these ventral structures as entirely separate divided into external (lateral) and internal (medial) seg- nuclei (ie, they distinguish the ventral pallidum from the ments. Striations connect the caudate and the putamen, pallidum, itself ). Also, note that because the globus pal- which are collectively known as the striatum. Th e stria- lidus is derived from the phylogenetically older portion tum is further subdivided into dorsal and ventral divi- of the brain — the diencephalon, and the caudate and sions. Th e dorsal striatum comprises the bulk of the putamen are derived from the phylogenetically newer caudate and putamen, whereas the ventral striatum is lim- part of the brain — the telencephalon, the pallidum is ited to only the ventromedial caudate and putamen, but sometimes referred to as the paleostriatum, whereas the the ventral striatum also encompasses the nucleus accum- caudate and putamen are sometimes collectively referred bens and select basal forebrain structures. Th e dorsal to as the neostriatum. striatum is involved in a wide array of processes, including Th e corpus striatum also encompasses several fi ber the sensorimotor circuits, whereas the ventral striatum pathways that pass between the globus pallidus and the associates principally with the limbic system and is pri- subthalamic nucleus and thalamus: the ansa lenticularis, marily involved in emotional and behavioral processes. lenticular fasciculus, subthalamic fasciculus, and thal- Now, indicate that together the globus pallidus and amic fasciculus. Th ese fi bers comprise a considerable putamen are called the lentiform nucleus, due to their portion of the white matter region inferolateral to the collective lens-shaped appearance. Bundles of myeli- thalamus, which is called the fi elds of Forel (aka preru- nated fi bers traverse the globus pallidus, giving it a pale bral fi elds or Forel’s Field H). appearance, so the globus pallidus is also commonly As a fi nal note, the subthalamic nucleus and substan- called the pallidum. Just as the striatum divides dorsally tia nigra are functionally but not developmentally asso- and ventrally, so the pallidum is further subdivided into ciated with the basal ganglia; therefore, although they a dorsal pallidum and ventral pallidum. Similar to the are variably included as part of the basal ganglia, we do striatum, the dorsal pallidum refers to the bulk of the not include them in our defi nition of the basal ganglia, globus pallidus, whereas the ventral pallidum refers to here, in accordance with the Terminologia Anatomica. 18. Basal Ganglia 311

Caudate nucleus Corpus striatum 1. head 2. body 3. tail

Caudate Putamen Globus pallidus (pallidum, paleostriatum) Globus pallidus 1. external (lateral) segment 2. internal (medial) segment Striatum Lentiform nucleus (neostriatum)

Basal ganglia-diencephalic Dorsal Ventral Dorsal Ventral white matter connections striatum striatum pallidum pallidum 1. ansa lenticularis (eg, nucleus 2. lenticular fasciculus accumbens) 3. subthalamic fasciculus 4. thalamic fasciculus

DRAWING 18-2 Basal Ganglia: Nomenclature 312 Neuroanatomy: Draw It to Know It

Direct & Indirect Pathways: Anatomy ( Advanced )

Here, in coronal view, we will draw the anatomy of the defi nition of the thalamic fasciculus. Additional fi ber direct and indirect pathways and the anatomy of the pathways pass through Field H and H1 in their ascent fi elds of Forel. Note that we exclude the related corticos- into the thalamus; they include the cerebellothalamic triatal projections. First, draw the lentiform nucleus and fi bers from the corticopontocerebellar pathway, the divide it into the putamen and globus pallidus; then, fur- medial lemniscus, the nigrothalamic fi bers, and the spi- ther subdivide the globus pallidus into its internal and nothalamic fi bers of the anterolateral system pathway. external segments. Next, draw the thalamus, and infero- Th e term thalamic fasciculus is sometimes broadened to lateral to it, draw the zona incerta. Th en, inferior to the include the cerebellothalamic fi bers and it is also some- zona incerta, draw the subthalamic nucleus, and then times used synonymously with the term Field H1 , just as inferior to it, draw the substantia nigra. Finally, through the term lenticular fasciculus is sometimes used synony- the middle of the diagram draw the posterior limb of the mously with term Field H2 . Finally, note that the thal- internal capsule and indicate that it becomes the cerebral amic fasciculus projects to multiple thalamic nuclei, peduncle as it descends through the brainstem. including the ventroanterior nucleus, which most nota- Now, we are able to label the individual fi elds of Forel, bly communicates with the globus pallidus; the ventro- which are Fields H, H1, and H2. First, indicate that lateral nucleus, which most notably communicates with Field H lies medial to the subthalamic nucleus and infe- the cerebellum; the dorsomedial nucleus, which most rior to the zona incerta; then, show that Field H1 lies in notably communicates with the prefrontal cortex and between the thalamus and zona incerta (medial to the basal ganglia; and the centromedian and parafascicular zona incerta and inferolateral to the thalamus); and nuclei (the main intralaminar nuclei), which most nota- fi nally, indicate that Field H2 lies lateral to the zona bly communicate with the striatum and frontal lobes. incerta and medial to the internal capsule. Now, we will draw the globus pallidus external seg- Next, we will draw the direct pathway fi bers, which ment projections, which subserve the indirect pathway, comprise the pallidothalamic pathways, and which ema- and which involve the subthalamic nucleus and substan- nate from the internal segment of the globus pallidus. tia nigra. First, show that the external segment of the Start with the ansa lenticularis. Show that it projects inf- globus pallidus projects to the subthalamic nucleus, and eromedially from the globus pallidus internal segment, then show that the subthalamic nucleus projects back to courses beneath the subthalamic nucleus, then turns the external segment of the globus pallidus and also to the superiorly to pass through Field H and Field H1 to enter internal segment of the globus pallidus. Indicate that the the thalamus. Next, show that the lenticular fasciculus reciprocal pallidosubthalamic and subthalamopallidal projects from the internal segment of the globus pallidus projections are collectively called the subthalamic fascicu- across the internal capsule, through Field H2 and then lus. Next, show that the subthalamic nucleus also projects Field H, and then show that it courses superiorly through to the substantia nigra and that the substantia nigra proj- Field H1 to enter the thalamus. Now, indicate that where ects back to the subthalamic nucleus. Finally, show that the ansa lenticularis and the lenticular fasciculus run the globus pallidus external segment projects to the sub- together in Field H1, they are collectively called the stantia nigra and then that the substantia nigra projects thalamic fasciculus; note that this is the most limited fi bers through Fields H and H1 that enter the thalamus. 18. Basal Ganglia 313

THALAMUS ZONA Thalamic INCERTA fasciculus Internal capsule H1 (posterior limb) H2 PUTAMEN Lenticular fasciculus

GLOBUS PALLIDUS H EXTERNAL INTERNAL

SUBTHALAMIC Subthalamic NUCLEUS Ansa fasciculus lenticularis

SUBSTANTIA NIGRA Cerebral peduncle

DRAWING 18-3 Direct & Indirect Pathways: Anatomy 314 Neuroanatomy: Draw It to Know It

Direct & Indirect Pathways: Circuitry

Here, we will draw a fl ow diagram for the circuitry of selectively injured, patients develop wild ballistic, fl ing- the direct and indirect pathways; they involve medium ing movements, called hemiballismus, on the side con- spiny neuron projections from the striatum to the globus tralateral to the subthalamic nucleus lesion due to a loss pallidus and substantia nigra. Th e direct and indirect of motor inhibition. pathways are the best described of the numerous frontal- Lastly, we need to account for the role of the substan- subcortical pathways that project through the basal gan- tia nigra compacta in the direct and indirect pathways. glia. First, label the cerebral cortex, thalamus, and motor Parkinson’s disease results from loss of dopaminergic cells neurons. Th en, show that the thalamus excites the cere- within the substantia nigra compacta, and in Parkinson’s bral cortex, which stimulates the motor neurons. Next, disease, there is muscle rigidity, stiff ness, diffi culty with we will draw the direct pathway. Label the striatum — the initiation of movement, and slowness and decomposition combined caudate and putamen. Now, show that the of rapid alternating movements. In our fl ow diagram, cortex excites the striatum. Within the striatum, the sen- near the striatum, label the substantia nigra compacta, sorimotor cortex primarily targets the putamen; the and indicate that it releases dopamine. If dopamine acted putamen is the primary source of the direct and indirect equally on both the direct and indirect pathways, the pathways. Next, label the combined globus pallidus two pathways would equalize one another and the net internal segment and the substantia nigra reticulata; they eff ect would be nil. So, now, show that the two most comprise the fi nal output nuclei of the basal ganglia — prominent striatal dopamine receptors are the dop- hereaft er, we consider them as a single functional entity: amine 1 receptor, which is part of the direct pathway GPi/STNr. Next, show that the striatum inhibits the and is excited by dopamine, and the dopamine 2 recep- GPi/STNr and then show that the GPi/STNr inhibits tor, which is part of the indirect pathway and is inhib- the thalamus. Th us, indicate that the direct pathway is ited by dopamine. Th us, dopamine from the substantia overall excitatory. nigra compacta excites the direct pathway and inhibits Now, we will draw the indirect pathway. First, include the indirect pathway— both of these eff ects promote the globus pallidus external segment; show that it is movement. inhibited by the striatum and then show that the globus Note that many frontal-subcortical pathways project pallidus external segment inhibits the GPi/STNr— thus, through the basal ganglia in addition to the motor path- indicate that the indirect pathway is overall inhibitory. ways we have drawn; these pathways help drive a multi- A parallel circuit also exists within the indirect pathway tude of processes, including emotional, behavioral, that passes through the subthalamic nucleus. So, now, somatosensory, and cognitive functional modalities. add the subthalamic nucleus and show that it excites the Th rough the corticostriatal fi bers— the Muratoff bundle GPi/STNr; then, show that the globus pallidus external and the external capsule— the cerebral cortex targets the segment inhibits the subthalamic nucleus. Th erefore, striatum in a topographic manner. For instance, the pre- whether it is because of the globus pallidus external frontal cortex acts through innervation of the head and segment inhibition of the GPi/STNr or because of body of the caudate nucleus; the parietal lobes act through the globus pallidus external segment inhibition of the innervation of both the putamen and caudate; the pri- subthalamic nucleus, through both means, the end result mary auditory cortex projects to the caudoventral puta- of the indirect pathway is that it is overall inhibitory. As men and tail of the caudate; and the visual cortices project a clinical corollary, when the subthalamic nucleus is primarily to the nearest portion of the caudate nucleus. 18. Basal Ganglia 315

Thalamus

Direct Globus pallidus pathway internal segment/ substantia nigra reticulata D1 Striatum Cerebral Substantia nigra (caudate (Dopamine) cortex compacta & putamen) D2

Globus pallidus Subthalamic nucleus Indirect external segment pathway Motor neurons Direct pathway - overall excitatory Indirect pathway - overall inhibitory

DRAWING 18-4 Direct & Indirect Pathways: Circuitry 316 Neuroanatomy: Draw It to Know It

References 1 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and 10 . Koob , G. F. & Volkow , N. D. Neurocircuitry of addiction. atlas, 2nd ed. ( Lange Medical Books/McGraw-Hill , 2005 ). Neuropsychopharmacology 35 , 217 – 238 (2010 ). 2 . B r o d a l, P. Th e central nervous system: structure and function, 4th ed. 11 . Kopell , B. H. & Greenberg , B. D. Anatomy and physiology of the ( Oxford University Press , 2010 ). basal ganglia: implications for DBS in psychiatry . Neurosci Biobehav 3 . C a m p b e l l, W. W., D e J o n g, R . N . & H a e r e r, A . F. DeJong’s the neurologic Rev 32 , 408 – 422 (2008 ). examination: incorporating the fundamentals of neuroanatomy and 1 2. N i e u w e n h u y s, R ., Vo o g d, J . & H u i j z e n, C . V. Th e human central neurophysiology, 6th ed. (Lippincott Williams & Wilkins, 2005 ). nervous system, 4th ed. (Springer , 2008 ). 4 . DeLong , M. R. & Wichmann , T. Circuits and circuit disorders of 1 3. N o b a c k, C . R . Th e human nervous system: structure and function, the basal ganglia . Arch Neurol 64 , 20 – 24 (2007 ). 6th ed. (Humana Press, 2005 ). 5 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 1 4. P a t e s t a s, M . A . & G a r t n e r, L . P. A textbook of neuroanatomy clinical applications . 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). (Blackwell Pub., 2006 ). 6 . H a l l e t t, M . & P o e w e, W. Th erapeutics of Parkinson’s disease and other 15 . Paxinos , G. & Mai , J. K. Th e human nervous system, 2nd ed., movement disorders, Chapter 3 (Wiley-Blackwell , 2008 ). Chapter 21 ( Elsevier Academic Press , 2004 ). 7 . Heilman , K. M. & Valenstein , E. Clinical neuropsychology, 4th ed. 1 6. S t e i n e r, H . & Ts e n g, K . -Y . Handbook of basal ganglia structure and ( Oxford University Press , 2003 ). function, Chapter 24 ( Elsevier/Academic Press , 2010 ). 8 . Hirsch , M. C. Dictionary of human neuroanatomy , p. 149 ( Springer , 17 . Wieser , H. G. & Zumsteg , D. Subthalamic and thalamic stereotactic 2000 ). recordings and stimulations in patients with intractable epilepsy, 9 . K i e r n a n, J . A . & B a r r, M . L . Barr’s the human nervous system: an pp. 30 – 31 ( John Libbey Eurotext , 2008 ). anatomical viewpoint, 9th ed. (Wolters Kluwer/Lippincott, Williams & Wilkins, 2009 ). 1 9 Arterial Supply

The Circle of Willis

Leptomeningeal Cerebral Arteries

Deep Cerebral Arteries ( Advanced )

Arterial Borderzones

Brainstem Arteries ( Advanced )

Cerebellar Arteries

Spinal Cord Arteries ( Advanced )

Thalamic Arteries ( Advanced ) 318 Neuroanatomy: Draw It to Know It

Know-It Points

The Circle of Willis

■ Two main arterial systems exist: an anterior-lying ■ Th e two vertebral arteries join to form the basilar internal carotid artery system and a posterior-lying artery. vertebral-basilar arterial system. ■ Th e basilar artery ascends the brainstem and ■ Th e middle cerebral arteries originate from the bifurcates, superiorly, into the posterolaterally internal carotid arteries and extend laterally. directed posterior cerebral arteries. ■ Th e anterior cerebral arteries branch anteriorly from the internal carotid arteries.

Leptomeningeal Cerebral Arteries

■ Th e anterior cerebral artery supplies the medial one ■ Th e posterior cerebral artery supplies the posterior third of the mid/upper cerebrum. portion of the mid/lower cerebrum. ■ Th e middle cerebral artery supplies the lateral two ■ Th e superfi cial portion of the anterior choroidal thirds of the cerebrum. artery supplies the medial temporal lobe.

Deep Cerebral Arteries (Advanced )

■ Th e perforating branches of the middle cerebral ■ Th e perforating branches of the internal carotid artery supply the anterior-superior-lateral basal artery supply the genu of the internal capsule and the ganglia region. area that immediately surrounds it. ■ Th e perforating branches of the anterior cerebral ■ Th e perforating branches of the anterior choroidal artery supply the anterior-inferior-medial basal artery supply the posterior-inferior-medial basal ganglia region. g a n g l i a r e g i o n .

Arterial Borderzones

■ Infarcts in the borderzones in between the superfi cial, ■ Th e somatotopic organization of the homunculus, leptomeningeal arteries and the deep, perforating from inferolateral to superomedial, is as follows: the arteries are called “end-zone infarcts.” tongue, face, hand, arm, and hip; and hanging over ■ Infarcts in the borderzones in between the superfi cial, the medial face of the hemisphere are the leg and leptomeningeal arteries are called “watershed infarcts.” foot. 19. Arterial Supply 319

Brainstem Arteries (Advanced )

■ Th e key medullary arteries are the anterior spinal ■ Th e common source for the circumferential arteries is artery and the posterior inferior cerebellar arteries. the basilar artery. ■ Th e common source for the key medullary arteries is ■ Th e key arteries that supply the midbrain are the the vertebral arteries. paramedian mesencephalic and thalamoperforating ■ Most pontine arterial supply comes from arteries and the collicular, posteromedial choroidal, circumferential arteries: the pontine paramedian and superior cerebellar arteries. arteries, short pontine circumferential arteries, and ■ Th e common source for the key midbrain arteries is long pontine circumferential arteries. the posterior cerebral arteries (or distal basilar artery).

Cerebellar Arteries

■ Th e posterior inferior cerebellar artery divides into artery supplies the anterior middle cerebellum; the lateral and medial branches, which supply the lateral posterior inferior cerebellar artery supplies the and medial regions of the inferior cerebellum, posterior middle cerebellum, inferiorly, and the respectively. superior cerebellar artery supplies the posterior ■ Th e superior cerebellar artery divides into lateral and middle cerebellum, superiorly. medial branches, which supply the lateral and medial ■ Th e anterior inferior cerebellar artery supplies much superior cerebellum, respectively. of the middle cerebellar peduncle and commonly ■ Th e middle cerebellum is supplied by all three gives off the internal auditory artery. cerebellar arteries: the anterior inferior cerebellar

Spinal Cord Arteries (Advanced )

■ Th e anterior spinal artery supplies the anterior two connections that form an arterial meshwork around thirds of the spinal cord. the spinal cord. ■ Th e posterior spinal arteries supply the posterior one ■ Th e most important radiculomedullary artery is the third of the spinal cord. artery of Adamkiewicz, which in the majority of ■ Segmental arteries help supply the anterior and people arises from T9 to T12 and from the left side posterior spinal arteries throughout their descent. of the body. ■ Th e pial network is a ring of arterial supply that ■ Th e intrinsic arterial territories divide into the surrounds the spinal cord; it has longitudinal c e n t r i f u g a l a n d c e n t r i p e t a l s y s t e m s .

Thalamic Arteries (Advanced )

■ Th e thalamotuberal artery supplies the anterior ■ Th e thalamoperforating arteries supply the medial thalamus. thalamus. ■ Th e medial posterior choroidal artery supplies the ■ Th e thalamogeniculate arteries supply the lateral medial posterior thalamus. t h a l a m u s . ■ Th e lateral posterior choroidal artery supplies the posterior thalamus. 320 Neuroanatomy: Draw It to Know It

Anterior cerebral artery Middle cerebral artery

Internal carotid artery

FIGURE 19-1 Cerebral angiography of internal carotid system, which supplies the anterior circulation.

Posterior cerebral artery

Basilar artery

Vertebral artery

FIGURE 19-2 Cerebral angiography of vertebrobasilar system, which supplies the posterior circulation. 19. Arterial Supply 321

Anterior communicating artery Longitudinal cerebral fissure Anterior cerebral artery

Internal carotid artery

Posterior communicating artery Anterior cerebral artery Middle cerebral artery Posterior cerebral artery Anterior choroidal artery

Superior cerebellar artery Posterior communicating artery Basilar artery Posterior cerebral artery Superior cerebellar artery

Labyrinthine artery

Basilar artery

Anterior inferior cerebellar artery

Anterior spinal artery Vertebral artery

Posterior inferior cerebellar artery

FIGURE 19-3 Arteries of the base of the brain. Used with permission from Bruni, J. E. & Montemurro, D. G. Human Neuroanatomy: A Text, Brain Atlas, and Laboratory Dissection Guide. New York: Oxford University Press, 2009. 322 Neuroanatomy: Draw It to Know It

The Circle of Willis

Here, we will draw the circle of Willis, which Th omas that branches of the vertebral arteries combine inferi- Willis fi rst described in 1664. Let’s stage our diagram orly to form the anterior spinal artery. Next, connect so that we learn the most commonly discussed arteries the internal carotid and posterior cerebral arteries fi rst and then add the more advanced vasculature. As with the posterior communicating arteries. Th en, show we learn the details of the cerebral vasculature, keep in that the anterior communicating artery connects the mind that two main arterial systems exist: an anterior- two anterior cerebral arteries. Next, on one side of lying internal carotid artery system and a posterior-lying the diagram, we will draw the cerebellar vessels from vertebral-basilar system. Start our diagram with the inferior to superior. First, draw the posterior inferior cer- anterior-lying internal carotid arteries; show axial sec- ebellar artery off the vertebral artery; then, the anterior tions through them. Next, show that the middle cerebral inferior cerebellar artery off the inferior portion of the arteries originate from the internal carotid arteries and basilar artery; and lastly, the superior cerebellar artery off extend laterally. Th en, indicate that the anterior cerebral the superior portion of the basilar artery. Now, draw the arteries branch anteriorly from the internal carotids. lenticulostriate branches of the middle cerebral artery; Next, at the bottom of the diagram, show that the two then, draw the anterior choroidal branch of the internal vertebral arteries join to form the basilar artery, and then carotid artery. Finally, draw the basilar perforators: the show that the basilar artery ascends the brainstem. At its pontine paramedian arteries, the short pontine circum- apex, show that the basilar bifurcates into the posterolat- ferential arteries, and the long pontine circumferential erally directed posterior cerebral arteries. Now, show arteries. 1 – 3

FIGURE 19-4 Magnetic resonance angiography of the cerebral arterial system demonstrating the circle of Willis. 19. Arterial Supply 323

Anterior cerebral artery Lenticulostriate Anterior branches communicating Internal Middle artery cerebral carotid artery artery Posterior Anterior choroidal artery communicating artery Posterior cerebral Superior Pontine paramedian arteries artery cerebellar Basilar artery artery Short pontine circumferential arteries Anterior inferior cerebellar artery Long pontine circumferential arteries Posterior inferior cerebellar artery

Vertebral Anterior spinal artery artery

DRAWING 19-1 Th e Circle of Willis 324 Neuroanatomy: Draw It to Know It

Leptomeningeal Cerebral Arteries

We divide the arterial supply of the cerebral hemi- posterior cerebral artery (PCA) supplies a small portion spheres into the superfi cial, leptomeningeal arterial of the posterior cerebral hemisphere. For reference, indi- branches and the deep, perforating arterial branches. cate that the parieto-occipital sulcus is the anterior Here, we will address the vascular territories of the lep- boundary of the PCA. Now, indicate that at the inferior tomeningeal branches, which emanate from the anterior, level, the ACA covers the medial one third of the middle, and posterior cerebral arteries, and we will also cerebrum only as far posterior as the Sylvian fi ssure, and address the anterior choroidal artery. Note that because show that the MCA covers the lateral two thirds of the there is vast interpatient variability in the vascular terri- hemisphere — the MCA territory terminates just poste- tories, we should pay closer attention to the general vas- rior to the medial-lateral axis of the posterior midbrain. cular territory of each vessel than its specifi c territorial Th en, show that the PCA covers the posterior cerebrum. borders. Lastly, indicate that the superfi cial portion of the ante- Begin with axial sections through the cerebrum at rior choroidal artery covers the medial temporal lobe. three diff erent vertical heights: superior, middle, and Now, let’s draw the arterial territories in sagittal view. inferior. To denote the mid-vertical cerebrum, include Draw both the lateral and medial faces of the cerebrum. the lateral ventricles at the level of the body of the cau- Show that the MCA supplies the majority of the lateral date nucleus, and to denote the inferior cerebrum, cerebral hemisphere, except for a strip of the antero- include the midbrain. First, at the superior level, show superior hemisphere, which the ACA supplies, and also that the anterior cerebral artery (ACA) supplies the a strip of the postero-inferior hemisphere, which the medial one third of the superior cerebrum and that the PCA supplies. Next, let’s address the medial hemisphere; middle cerebral artery (MCA) supplies the lateral two draw a diagonal line from the parieto-occipital sulcus to thirds. For reference, indicate that the superior frontal the anterior pole of the temporal lobe. Show that the sulcus separates the MCA and ACA supply. Next, at the ACA supplies the antero-superior hemisphere and that mid-vertical level, show that the ACA supplies the the PCA supplies the postero-inferior hemisphere, and medial one third of the hemisphere and that the MCA also indicate that the anterior choroidal artery supplies supplies the lateral two thirds, and also indicate that the the medial temporal lobe.1 , 2 , 4 – 6 19. Arterial Supply 325

SUPERIOR MIDDLE INFERIOR Sup. frontal sulcus

ACA ACA ACA Sylvian MCA fissure AXIAL VIEW MCA MCA Midbrain Ant. choroidal PCA artery Parieto- PCA occipital sulcus

LATERAL MEDIAL ACA ACA MCA SAGITTAL VIEW PCA PCA Ant. chord. art.

DRAWING 19-2 Leptomeningeal Cerebral Arteries 326 Neuroanatomy: Draw It to Know It

Deep Cerebral Arteries (Advanced )

Here, we will draw the deep, perforating cerebral arterial see, there is substantial overlap in the lenticulostriate and territories. Label the right-hand side of the page as the anterior cerebral artery vascularization of the basal gan- deep cerebral structures and the left -hand side as the glia. To distinguish the arterial supply of these vessels, perforating arterial territories. Note that an attempt to denote that the lenticulostriate arteries supply the supe- draw the exact vascular supply of each deep structure rior portion of the overlapping structures, whereas the would be impractical due to the number of structures ACAs supply the inferior portion. we would have to account for and the multiplicity of Next, show that the perforating branches of the inter- their arterialization. Instead, here, we will label only the nal carotid artery supply the genu of the internal capsule vascularization of certain landmark structures. As we go and the areas that immediately surround it. Th en, show through our vertically compressed axial diagram we that the anterior choroidal artery supplies the posterior- must think in terms of three diff erent axes. Draw the inferior-medial basal ganglia region: the lower posterior anterior–posterior and medial–lateral axes, now, and we internal capsule, medial geniculate nucleus and related will denote the superior–inferior variations in arterial- acoustic radiations, medial globus pallidus, and tail of ization where appropriate in our diagram, itself. the caudate. Now, show that the anterior communicat- First, draw the key anatomic landmarks. Indicate the ing artery supplies the anterior hypothalamus and neigh- hypothalamus, which lies in the anterior midline; it bor- boring diencephalic structures. Th en, show that the ders the third ventricle. Next, label the thalamus, which posterior communicating artery supplies the posterior lies above the hypothalamus in midline. Th en, anterior hypothalamus, optic chiasm and mammillary bodies, to the hypothalamus, draw the head of the caudate and and also the anterior thalamus via the thalamotuberal then draw the lentiform nucleus, which is the globus pal- artery. Finally, show that many diff erent thalamic arter- lidus and putamen combination. Sandwiched in between ies supply the remainder of the thalamus (see Drawing the aforementioned structures, draw the internal capsule 19-8 ). and divide it into its central-lying genu and its anterior Next, let’s consolidate this information into a single and posterior limbs. perforating artery–single structure/region list so we Now, sketch this same arrangement on the arterial can simplify the aforementioned material. On the left - side of the page. Show that the perforating branches of hand side, label the deep, perforating arteries, and on the the MCA, which are known as the lenticulostriate arter- right-hand side, label the single structure or region. ies, supply the anterior-superior-lateral basal ganglia Indicate that the lenticulostriate arteries supply the region: they supply the putamen and lateral globus pal- antero-supero-lateral basal ganglia; the ACA supplies lidus, superior internal capsule, the body of the caudate, the antero-infero-medial basal ganglia; the internal and the superior caudate head. Th en, show that the ACA carotid artery supplies the genu of the internal capsule; perforating branches (including the recurrent artery of the anterior communicating artery supplies the anterior Heubner) supply the anterior-inferior-medial basal gan- hypothalamus; the posterior communicating artery sup- glia region: the anterior-inferior head of the caudate, plies the posterior hypothalamus; the anterior choroidal anterior-inferior portion of the anterior limb of the inter- artery supplies the posterior limb of the internal capsule; nal capsule, and the medial lentiform nucleus. As we can and the thalamic arteries supply the thalamus. 1 , 2 , 4 – 6 19. Arterial Supply 327

Anterior Perforating arterial territories Deep cerebral structures Medial Lateral Posterior Caudate Anterior cerebral artery (head) (inferior)

Ant. Lenticulo- Ant. comm. striate limb arteries Internal Hypo- Internal (superior) thalamus Post. carotid capsule comm. artery (genu) Lentiform nucleus

Post. Anterior limb Thalamic choroidal Thalamus arteries artery

DRAWING 19-3 Deep Cerebral Arteries 328 Neuroanatomy: Draw It to Know It

Arterial Borderzones

Here, let’s use coronal slices through the cerebrum to Now, let’s label the somatotopic cortical representa- draw the arterial borderzones. Vascular insuffi ciency tion of the body, known as the homunculus. We do so in within these arterial borders produces a clinically order to understand the clinical eff ect of an important important form of cerebral infarction, called borderzone type of watershed infarct — the MCA/ACA borderzone infarct. First, draw a coronal section through the cere- infarct, which produces the “man in a barrel” syndrome. brum and label the general superfi cial, leptomeningeal Th e homunculus lies along the pre- and post-central gyri, arterial supply, and then label the deep, perforating arte- laterally, and the paracentral gyri, medially. First, show rial supply. Th e anastomoses (ie, collateralizations) that that within the homunculus, the tongue lies inferiorly. exist between the superfi cial, leptomeningeal arteries and Th en, above it, show the face and then the hand above it. the deep, perforating arteries are limited to capillary con- Th e tongue, face, and hand take up a disproportionately nections, which cannot sustain arterial perfusion in low- large area within the cortex relative to their actual size in blood-fl ow states. Indicate that infarcts that occur within the body. Now, continue counterclockwise around the these borderzones are called “end-zone infarcts,” so convexity of the hemisphere, and include the arm and named because these arteries are essentially end arteries. hip. Th en, hanging over the medial face of the hemi- Now, draw another coronal section through the cere- sphere, draw the leg and foot. Note that the foot termi- brum. Here, we will focus on the borderzones that exist nates superior to the cingulate gyrus. in between the superfi cial arterial territories. Indicate Th e somatotopic sensorimotor area that corresponds that the ACA supplies the supero-medial hemisphere, to the borderzone between the MCAs and ACAs the PCA supplies the infero-medial hemisphere, and the encodes the proximal arms and legs. So when an ACA/ MCA supplies the lateral two thirds of the cerebral MCA borderzone infarct occurs, patients have weakness hemisphere. Next, label the borderzones between these of their proximal arms and legs with preservation of arteries. Again, the anastomoses that exist within these hand and feet strength; they act like a “man in a barrel.” borderzones are insuffi cient to maintain cerebral perfu- To demonstrate this clinical eff ect for yourself, sit with sion in low-blood-fl ow states, resulting in stroke; infarcts your arms at your side and wiggle your fi ngers and toes to these borderzones are called “watershed infarcts.” but be unable to raise your arms or your legs. 1 , 2 , 4 – 8

FIGURE 19-5 Coronal section of arterial borderzones. 1, middle cerebral artery; 2, perforating arteries; 3, medullary arteries; 4, anterior cerebral artery; 5, posterior cerebral artery. Used with permission from Bogousslavsky, J., and L. R. Caplan. Stroke Syndromes, 2nd ed. Cambridge and New York: Cambridge University Press, 2001. 19. Arterial Supply 329

CORONAL VIEW Borderzone ACA MCA Hip Arm Leg Leptomeningeal Hand territory Foot Face Perforator Borderzone territory Tongue

PCA MCA

Borderzone End-zone Infarct Watershed Infarct

DRAWING 19-4 Arterial Borderzones 330 Neuroanatomy: Draw It to Know It

Brainstem Arteries (Advanced )

Here, we will draw the brainstem arterial supply. We will lastly, the posterior group is supplied by the superior cer- begin with the four common brainstem arterial territo- ebellar arteries: note that the posterior group is found ries as originally defi ned in the 1960s by Gillian and only in the upper pons— it is not present in the mid- or Lazorthes. First, draw one half of an axial composite of lower pons. Th us, most of the pontine arterial supply the brainstem: a compression of all three brainstem comes in the form of circumferential arteries that origi- levels. Th en, designate the thin paramedian region as the nate from the basilar and either travel a short distance anteromedial group. Now, divide the remainder of the (the pontine paramedian arteries), a mid-distance (the brainstem from anterior to posterior into the anterolat- short pontine circumferential arteries), or a long distance eral, lateral, and posterior groups. (the long pontine circumferential arteries). Th e posterior Next, we will make a table of the specifi c vessels that portion of the pons receives additional supply from supply the brainstem. Note that although our list will the anterior inferior cerebellar artery, inferiorly, and not be exhaustive, it will cover the major arteries. First, the superior cerebellar artery, superiorly. Note that the indicate that within the medulla, the anteromedial group common source for these arteries is the basilar artery. is supplied by the anterior spinal artery and direct verte- Basilar ischemia can produce pontine basis strokes, bral artery branches; the anterolateral group is supplied which can cause locked-in syndrome. by the anterior spinal artery and the posterior inferior Next, let’s label the midbrain arteries. Th e anterome- cerebellar arteries; the lateral group is supplied by the dial group is supplied by basilar tip and proximal PCA posterior inferior cerebellar arteries; and the posterior branches; indicate that from inferior to superior, these group is supplied by the posterior inferior cerebellar and branches are called the inferior and superior paramedian posterior spinal arteries. Now, encircle the key medullary mesencephalic arteries and the thalamoperforate arter- arterial vessels: the anterior spinal artery and the poste- ies. Th en, show that the anterolateral group is supplied rior inferior cerebellar arteries. Next, note that the by PCA branches: the collicular and posteromedial common source for these arteries is the vertebral arteries. choroidal arteries. Next, indicate that the lateral and As a clinical corollary, ischemia to the posterior inferior posterior groups are also supplied by the collicular and cerebellar artery results in lateral medullary syndrome, posteromedial choroidal arteries in concert with the called Wallenberg’s syndrome. superior cerebellar arteries. Now, let’s encircle the key Now, let’s label the pontine arteries; the fi rst three arteries that supply the midbrain: the paramedian mes- groups are supplied by basilar branches that travel pro- encephalic and thalamoperforating arteries and the col- gressively farther distances to their targets. Indicate that licular, posteromedial choroidal, and superior cerebellar the anteromedial group is supplied by the pontine para- arteries. Note that the common source for these arteries median arteries; the anterolateral group is supplied by is the PCAs or distal basilar artery. When basilar clot the short pontine circumferential arteries; the lateral produces ischemia to the proximal PCAs, large midbrain group is supplied by the long pontine circumferential strokes can occur and produce a so-called “top of the arteries and the anterior inferior cerebellar arteries; and, basilar” syndrome.1 – 5 19. Arterial Supply 331

BRAINSTEM ARTERIAL BRAINSTEM ARTERIAL SUPPLY TERRITORIES: AXIAL VIEW MEDULLA PONS MIDBRAIN ANTEROMEDIAL Anterior spinal Pontine paramedian Paramedian mesen- artery arteries cephalic & thalamo- Vertebral artery perforating arteries

ANTEROLATERAL Anterior spinal Short pontine circum- Collicular & Posterior group artery ferential arteries Posteromedial Posterior inferior choroidal arteries cerebellar artery

Lateral LATERAL Posterior inferior Long pontine circum- Collicular, postero- group cerebellar artery ferential arteries medial choroidal, & Anterior inferior superior cerebellar cerebellar artery arteries Antero- medial POSTERIOR Posterior inferior Superior cerebellar Collicular, postero- Anterolateral group cerebellar artery artery medial choroidal, & group Posterior spinal superior cerebellar artery arteries SOURCE VERTEBRAL BASILAR POSTERIOR ARTERIES ARTERY CEREBRAL & DISTAL BASILAR ARTERIES

DRAWING 19-5 Brainstem Arteries 332 Neuroanatomy: Draw It to Know It

Cerebellar Arteries

Here, we will draw the cerebellar arterial supply. First, the inferior cerebellum, respectively. Next, show that the draw three axial sections through the cerebellum at dif- SCA supplies the superior cerebellum. Th en, further ferent heights: inferior, middle, and superior. Next, asso- indicate that it divides into lateral and medial branches ciate each height with a brainstem level: the inferior (similar to the PICA), which supply the lateral and cerebellum neighbors the medulla, the middle cerebel- medial superior cerebellum, respectively. Lastly, show lum borders the pons, and the superior cerebellum that the middle cerebellum is supplied by all three cere- neighbors the midbrain. Th ree arteries supply the cerebellar arteries: the AICA supplies the anterior, middle bellum: the posterior inferior cerebellar artery (PICA), cerebellum; the PICA supplies the posterior, middle cer- the anterior inferior cerebellar artery (AICA), and the ebellum, inferiorly; and the SCA supplies the posterior, superior cerebellar artery (SCA). First, show that the middle cerebellum, superiorly. Note that the AICA sup- PICA supplies the entire inferior cerebellum. Th en, fur- plies a large portion of the middle cerebellar peduncle, ther indicate that it divides into lateral and medial and also note that it commonly gives off the internal branches, which supply the lateral and medial regions of auditory artery, which supplies the inner ear. 1 – 4 , 9 19. Arterial Supply 333

Midbrain

(lateral branch)

anterior inferior Superior cereberllar cerebellar artery artery Pons (medial superior branch) cerebellar Posterior Medulla artery inferior (superior) cerebellar (lateral Posterior artery Superior cerebellum branch) inferior (medial (inferior) cerebellar branch) artery Middle cerebellum

Inferior cerebellum

DRAWING 19-6 Cerebellar Arteries 334 Neuroanatomy: Draw It to Know It

Spinal Cord Arteries (Advanced )

Here, we will draw the arterial supply of the spinal cord. Next, indicate that where the segmental artery divides Begin with the extrinsic system: on one side of the page, into ventral and dorsal branches, the dorsal branch is draw an axial section through the spinal cord, and on the called the dorsospinal artery, and it forms three types other, draw an oblique, coronal section. Indicate that a of radicular arteries. Show that the radicular arteries single anterior spinal artery descends the anterior median (proper)— anterior and posterior— supply the nerve fi ssure and that a pair of posterior spinal arteries descends roots; the radiculomedullary arteries supply the anterior the posterior spinal cord. Next, in the axial cut, show spinal artery; and the radiculopial arteries supply the that generally, the anterior spinal artery supplies the posterior spinal arteries and also the pial network. anterior two-thirds of the spinal cord and that the poste- Indicate that the pial network is a ring of arterial supply rior arteries supply the posterior one-third. Now, on that surrounds the spinal cord; it has superior–inferior the coronal side of the diagram, draw the vertebral interconnections that form an arterial meshwork around arteries. Show that near where they join as the basilar the cord. Note that the most important radiculomedul- artery, vertebral artery branches also join to form the lary artery is the artery of Adamkiewicz, which in the anterior spinal artery. Th en, indicate that each vertebral majority of people arises from T9 to T12 but which can artery produces a single posterior spinal artery. Note, originate anywhere from T8 to L3; it most commonly however, that in many instances, the posterior spinal originates from the left side of the body. Injury to this arteries originate from the PICAs, instead. Also, note artery can lead to paraplegia. At the C5 to C7 level, that in addition to these posterolaterally situated arter- another notable radiculomedullary artery exists — the ies, posteromedial spinal arteries can also exist. artery of the cervical enlargement. Segmental arteries help supply the anterior and poste- Now, let’s draw the intrinsic arterial territories in axial rior spinal arteries throughout their descent. In our axial view. Th ey divide into the centrifugal and centripetal diagram, show a source artery and an attached segmental systems. Show that the centrifugal system comprises artery. Th e source arteries and segmental arteries vary sulcal arteries from the anterior spinal artery, which along the superior–inferior length of the spinal canal. supply the spinal cord from central to peripheral; they Th roughout the cervical spinal cord, the source artery is primarily supply the gray matter horns. Th en, indicate the subclavian artery. Th e segmental arteries in the upper that the centripetal system comprises vasocoronal perfo- cervical spinal cord are the spinal segmental branches of rating arteries from the pial arterial network, which the vertebral arteries, and in the lower cervical spinal supply the spinal cord from peripheral to central; they cord, they are the ascending cervical artery (from the primarily supply the white matter funiculi. thyrocervical trunk) and the deep cervical artery (from We will not address the spinal cord venous system, the costocervical trunk). In the thoracic and lumbar here, except to note that extensive venous anastomoses spinal cord, the descending aorta is the source artery. Th e exist that communicate with surrounding venous plex- segmental branches in the thoracic cord are the posterior uses. Th e low-pressure state and valveless chambers of intercostal arteries; in the lumbar cord, they are the the spinal venous system expose the spinal canal to lumbar arteries. Finally, in the sacral spinal cord, the intrathoracic or intra-abdominal abscesses and neoplas- source artery is the internal iliac artery, most commonly, tic metastases. 2 , 10 , 11 and the segmental arteries are the lateral sacral arteries. 19. Arterial Supply 335

EXTRINSIC ARTERIAL SYSTEM AXIAL CORONAL Posterior spinal Basilar artery artery Posterior Pial arterial territory network Vertebral Radiculopial artery artery Posterior Anterior Anterior territory spinal artery spinal artery

Nerve Pial roots Vaso- Anterior spinal Radiculo- arterial coronal Sulcal artery medullary Radicular network artery proper artery Dorsal branch INTRINSIC ARTERIAL TERRITORIES Segmental Ventral AXIAL artery branch

Vaso- Sulcal Source artery coronal

DRAWING 19-7 Spinal Cord Arteries 336 Neuroanatomy: Draw It to Know It

Thalamic Arteries (Advanced )

In this diagram, we will draw the thalamic arterial supply. Now, lateral to the medial posterior choroidal artery, First, on the left -hand side of the page, draw two outlines draw the lateral posterior choroidal artery, which sup- of the thalamus: we will use these outlines to show the plies the lateral pulvinar, dorsomedial thalamic nucleus, arterial territories of the thalamus. Label one as dorsal and lateral geniculate body (of the metathalamus). Show and the other as ventral to distinguish the variation that dorsally its supply is restricted to the medial poste- in thalamic arterial supply at diff erent heights. Also, rior thalamus, whereas ventrally its supply extends out include the anterior–posterior and medial–lateral planes laterally. of orientation. Next, show that the thalamoperforating arteries On the right-hand side of the page, we will draw the emanate from the PCA medial to the posterior commu- arteries, themselves. First, draw the basilar artery and nicating artery. Like the thalamotuberal artery, the thal- show that it bifurcates into the bilateral PCAs. Next, amoperforating arteries have several alternate names; draw an axial cut through the left internal carotid artery. they include the following: the thalamic-subthalamic Th en, connect the left internal carotid artery and left arteries, paramedian arteries, posterior inferior optic PCA with the posterior communicating artery. arteries, and deep interpeduncular profunda arteries. Now, let’s show the vessels that supply the thalamus. Th e thalamoperforating arteries supply the medial por- Emanating from the posterior communicating artery, tion of the thalamus. Show that dorsally, the medial draw the thalamotuberal artery. Th e thalamotuberal extent of their supply ends at the medial posterior chor- artery has a few alternate names, which although cum- oidal artery territory, whereas ventrally, their supply bersome help us to understand its arterial distribution; extends to the medial edge of the thalamus. Much atten- they include the following: the anterior thalamoperfo- tion is given to the anatomic variant wherein a common rating artery, premammillary artery, and polar artery. stem, the artery of Percheron, emanates from one PCA Indicate that within the thalamus, both dorsally as well and provides thalamoperforating branches to the bilat- as ventrally, the thalamotuberal artery supplies the ante- eral medial thalamic and extra-thalamic thalamoperfo- rior thalamus: specifi cally, it supplies the ventroanterior rating territories. nucleus, ventrolateral nucleus, and the anterior portion Now, in between the posterior choroidal arteries, of the medial thalamic nuclei. draw the thalamogeniculate arteries, which supply the Next, we will draw the medial branch of the poste- lateral thalamus and help supply the geniculate bodies. rior choroidal artery. Show that it emerges from the Dorsally, show that their supply extends posteriorly, PCA lateral to the posterior communicating artery. Th e whereas ventrally, show that it extends anteriorly. medial posterior choroidal artery supplies the medial In addition to supplying the thalamus and metathala- thalamus: most notably, the medial posterior pulvinar mus, the thalamic arteries also help supply many other and medial geniculate body (of the metathalamus). diencephalic structures, such as the hypothalamus, sub- Indicate that dorsally, its arterial supply extends anteri- thalamus, optic tracts, and internal capsule; they also orly, whereas ventrally, its distribution is restricted to help supply certain upper brainstem structures, as well as being more posterior. the choroid plexus and hippocampus.2 , 4 , 12 – 16 19. Arterial Supply 337

(Dorsal) Thalamo- (Ventral) Internal tuberal carotid artery Thalamo- Thalamo- Thalamo- perforating tuberal tuberal Lateral Medial artery posterior posterior Medial Thalamo- choroidal choroidal Thalamo- posterior perforating artery artery geniculate choroidal Thalamo- Posterior geniculate Thalamo- communicating arteries geniculate artery

Lateral Medial posterior posterior Thalamo- choroidal choroidal perforating Lateral post. arteries Anterior Posterior choroidal Lateral cerebral artery Medial Basilar artery Posterior

DRAWING 19-8 Th alamic Arteries 338 Neuroanatomy: Draw It to Know It

References 1 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human 9 . Kelly , P. J., et al. Functional recovery aft er rehabilitation for brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal cerebellar stroke. Stroke 32 , 530 – 534 (2001 ). structure, vascularization and 3D sectional anatomy (Springer , 2009 ). 10 . Kudo , K. , et al. Anterior spinal artery and artery of Adamkiewicz 2 . Takahashi , S. O. Neurovascular imaging: MRI & microangiography detected by using multi-detector row CT . AJNR Am J Neuroradiol (Springer , 2010 ). 24 , 13 – 17 (2003 ). 3 . Ta t u, L ., M o u l i n, T. , B o g o u s s l a v s k y, J . & D u v e r n o y, H . A r t e r i a l 11 . Shimizu , S. , et al . Origins of the segmental arteries in the aorta: an territories of human brain: brainstem and cerebellum . Neurology 4 7, anatomic study for selective catheterization with spinal 1125 – 1135 (1996 ). arteriography . AJNR Am J Neuroradiol 26 , 922 – 928 (2005 ). 4 . B o g o u s s l a v s k y, J . & C a p l a n, L . R . Stroke syndromes, 2nd ed. 1 2. B o g o u s s l a v s k y, J ., R e g l i, F. & A s s a l, G . Th e syndrome of unilateral ( Cambridge University Press , 2001 ). tuberothalamic artery territory infarction . Stroke 17 , 434 – 441 5 . Mai , J. K., Voss , T. & Paxinos , G. Atlas of the human brain, 3rd ed. ( 1986 ). ( Elsevier/Academic Press , 2008 ). 1 3. C a r r e r a, E . & B o g o u s s l a v s k y, J . Th e thalamus and behavior: eff ects 6 . Ta t u, L ., M o u l i n, T. , B o g o u s s l a v s k y, J . & D u v e r n o y, H . A r t e r i a l of anatomically distinct strokes . Neurology 66 , 1817 – 1823 (2006 ). territories of the human brain: cerebral hemispheres . Neurology 5 0, 1 4. P e r r e n, F. , C l a r k e, S . & B o g o u s s l a v s k y, J . Th e syndrome of combined 1699 – 1708 ( 1998 ). polar and paramedian thalamic infarction . Arch Neurol 6 2, 7 . Roach , E. S. , Toole , J. F. , Bettermann , K. & Biller , J. Toole’s cerebro- 1212 – 1216 (2005 ). vascular disorders, 6th ed. ( Cambridge University Press , 2010 ). 15 . Schmahmann , J. D. Vascular syndromes of the thalamus. Stroke 3 4, 8 . Vo n K u m m e r, R ., B a c k, T. & A y, H . Magnetic resonance imaging in 2264 – 2278 (2003 ). ischemic stroke (Springer , 2006 ). 1 6. D o n k e l a a r, H . J . Clinical neuroanatomy (Springer , 2011 ). 2 0 Diencephalon

The Diencephalon

The Thalamus, Part 1 ( Advanced )

The Thalamus, Part 2 ( Advanced )

Thalamus: Anatomy & Function

Hypothalamus: Nuclei

Hypothalamus: Tracts 340 Neuroanatomy: Draw It to Know It

Know-It Points

The Diencephalon

■ Th e thalamus contains numerous thalamic nuclei and ■ Th e epithalamus comprises the habenula, pineal related fi ber tracts. gland, and the pretectal structures. ■ Th e metathalamus comprises the medial and lateral ■ Major white matter bundles that pass through the geniculate nuclei. diencephalon are the column of the fornix, stria ■ Th e subthalamus comprises the subthalamic nucleus, medullaris thalami, and the anterior, posterior, and zona incerta, and the nuclei of the fi elds of Forel. h a b e n u l a r c o m m i s s u r e s . ■ Th e hypothalamus contains numerous hypothalamic nuclei and related fi ber tracts, and it also contains the mammillary bodies, and neurohypophysis.

Thalamus: Anatomy & Function

■ Th e internal medullary lamina separates the medial ■ Th e dorsolateral nucleus communicates with the and lateral thalamic groups. limbic system. ■ Th e anterior group nuclei communicate with the ■ Th e pulvinar is important for visual attention. limbic system. ■ Th e medial geniculate nucleus is part of the auditory ■ Th e medial group nuclei (the most prominent of system. which is the dorsomedial nucleus) connect with the ■ Th e lateral geniculate nucleus is part of the visual prefrontal cortex. system. ■ Th e lateral group nuclei divide into ventral and dorsal ■ Th e most notable function of the posterior group subgroups. nuclei is nociceptive sensory processing. ■ Th e ventroanterior nucleus connects with the basal ■ Th e intralaminar group helps form the ascending ganglia. arousal system for wakefulness. ■ Th e ventrolateral nucleus connects primarily with the ■ Th e midline group nuclei function in limbic-related cerebellum. processes. ■ Th e ventroposterior lateral nucleus receives sensory ■ Th e thalamic reticular nucleus modulates thalamic aff erents from the body. o u t p u t . ■ Th e ventroposterior medial nucleus receives sensory aff erents from the face. 20. Diencephalon 341

Hypothalamus: Nuclei

■ Within the hypothalamus, from medial to lateral, are ■ Th e anterior (aka chiasmatic) group encompasses the the periventricular, intermediate, and lateral zones. region above and anterior to the optic chiasm and ■ Both the periventricular and intermediate zones are optic tract. highly cellular whereas the lateral zone contains a ■ Th e middle (aka tuberal) group encompasses the high degree of white matter fi bers. region between the optic chiasm and mammillary ■ Th e anteromedial hypothalamus is involved in bodies (ie, the region above the tuber cinereum). parasympathetic activity whereas the posterolateral ■ Th e posterior (aka mammillary) group encompasses hypothalamus is involved in sympathetic activity. the mammillary bodies and the region above them.

Hypothalamus: Tracts

■ Th e magnocellular neurons of the paraventricular via hypophysial veins: follicle-stimulating hormone, and supraoptic nuclei project to the capillary plexus luteinizing hormone, adrenocorticotropic hormone, of the neurohypophysis via the thyroid-stimulating hormone, prolactin, growth hypothalamohypophysial tract. hormone, and melanocyte-stimulating hormone. ■ Th e paraventricular and supraoptic nuclei release the Th e hypothalamus controls the release of the hormones vasopressin (aka antidiuretic hormone aforementioned hormones via a variety of [ADH]) and oxytocin. parvocellular neurons, the most notable of which is ■ Th e epithelial-cell–fi lled adenohypophysis releases the arcuate (aka infundibular) nucleus. the following hormones into the general circulation 342 Neuroanatomy: Draw It to Know It

Cingulate sulcus 3rd ventricle Cingulate gyrus Corpus callosum Fornix Thalamic nuclei: Lateral ventricle Choroid plexus Anteroprincipal Caudate nucleus Anteromedial Ventroanterior Reticular Paratenial thalamic Paraventricular nucleus Internal capsule External capsule Insula Claustrum Lateral Extreme capsule sulcus Superior Globus pallidus: temporal: Internal Gyrus External Sulcus Fornix

Middle Hypothalamus temporal gyrus Medial Inferior central temporal: Lateral ventricle Sulcus Cortical Gyrus Basomedial Collateral sulcus Basolateral Putamen Amygdaloid Lateral Entorhinal cortex Hippocampus nuclei Parahippocampal gyrus 10 mm

FIGURE 20-1 Coronal section through the diencephalon. Used with permission from the Michigan State University: Brain Biodiversity Bank. https://www.msu.edu/∼brains/ 20. Diencephalon 343

Cingulate gyrus Cingulate sulcus Precuneus Superior frontal gyrus Parieto-occipital sulcus

Cuneus Corpus callosum: Splenium Calcarine sulcus Body Genu

Interventricular Fornix foramen

Anterior commissure Lingual gyrus Thalamus Lateral ventricle Hypothalamus

Optic tract Mammillothalamic tract Mammillary nuclei 10 mm Red nucleus Cerebellum Superior colliculus Superior cerebellar peduncle Inferior colliculus Pontine nuclei Inferior olive Cerebellar tonsil

FIGURE 20-2 Sagittal section through the diencephalon. Used with permission from the Michigan State University: Brain Biodiversity Bank. https://www.msu.edu/∼brains/ 344 Neuroanatomy: Draw It to Know It

The Diencephalon

Here, we will draw the anatomy of the diencephalon. posterior part of the pituitary gland as the neural lobe; First, list the major groups of diencephalic structures: it is neurally connected to the hypothalamus via the the thalamus, metathalamus, subthalamus, hypothala- hypothalamohypophysial tract. Th en, label the anterior mus, and epithalamus. Now, include the major structures lobe of the pituitary gland as the adenohypophysis; it categorized within these groups. Indicate that the thala- forms from Rathke’s pouch — an outgrowth of the roof mus contains numerous thalamic nuclei and related fi ber of the mouth, and therefore, it is not a diencephalic tracts; the metathalamus comprises the medial and lat- structure. Th e adenohypophysis is linked to the hypo- eral geniculate nuclei; the subthalamus comprises the thalamus via the hypothalamohypophysial venous portal subthalamic nucleus, zona incerta, and the nuclei of the system. 4 , 5 fi elds of Forel; then, show that the hypothalamus con- Now, for anatomic reference, include the midbrain tains numerous hypothalamic nuclei and related fi ber and its superior and inferior colliculi. Th en, draw the tracts, and also contains the mammillary bodies, and epithalamic structures: fi rst, above the colliculi, draw the neurohypophysis, which is the posterior lobe of the pitu- pineal gland; anterior to it, draw the pretectal structures; itary body and which subdivides into a neural lobe and and then above them, draw the habenula and habenular infundibulum; then, show that the epithalamus com- commissure. Next, anterior to the epithalamus, draw the prises the habenula, pineal gland, and the pretectal struc- egg-shaped thalamus. Th en, indicate that the stria med- tures, which include the pretectal area, pretectal nuclei, ullaris thalami passes from the habenula along the dorso- posterior commissure, and subcommissural organ. medial thalamus to the septal nuclei, which lie above the Finally, let’s list some of the major white matter bundles anterior commissure (they are part of the limbic system). that pass through the diencephalon: the column of the Finally, show that the column of the fornix descends fornix, stria medullaris thalami, and the anterior, poste- through the hypothalamus and connects with the mam- rior, and habenular commissures. millary bodies. Now, let’s draw the diencephalon in sagittal view. Next, we will draw the central diencephalon in coro- First, label the central portion of the diagram as the nal view. For anatomic reference, superiorly, include the hypothalamus and then defi ne its borders. Draw the corpus callosum, body of the fornix, body of the lateral lamina terminalis as the anterior border of the hypothal- ventricle; then, laterally, include the internal capsule, amus; it separates the hypothalamus from the subcallosal which becomes the cerebral peduncle as it descends region of the limbic lobe and it is variably considered through the brainstem; next, inferiorly, draw the pons; either a diencephalic or telencephalic structure. Indicate in midline, lying medial to the cerebral peduncle, draw that the lamina terminalis spans from the anterior com- the interpeduncular cistern; and above it, draw the third missure, superiorly, to the optic chiasm, inferiorly.1 – 3 ventricle. Now let’s draw the major diencephalic struc- Next, draw the tuber cinereum as the inferior border of tures visible in this section: superiorly, draw the thala- the hypothalamus. Show that it ends, posteriorly, at the mus; ventrolateral to it, draw the subthalamus; and mammillary bodies. ventromedial to it, along the lateral wall of the third ven- Next, antero-inferiorly, draw the funnel-shaped dip in tricle, draw the hypothalamus and include its infero-lying the tuber cinereum called the median eminence; attach mammillary bodies. Finally, show that the supramam- to it the infundibulum (the pituitary stalk); and attach millary commissure stretches across midline above the to the infundibulum, the pituitary gland. Label the mammillary bodies.6 – 8 20. Diencephalon 345

Diencephalon structures SAGITTAL Stria medullaris thalami thalamus VIEW Habenula (& habenular comm.) thalamic nuclei Septal Thalamus thalamic fiber tracts Pineal gland nuclei metathalamus Superior colliculus medial geniculate nucleus Column of Pretectal Anterior Inferior lateral geniculate nucleus fornix structures commissure colliculus subthalamus Hypothalamus subthalamic nucleus Midbrain zona incerta Lamina terminalis Mammillary Forel’s fields nuclei Optic chiasm Tuber Lateral Median eminence cinereum bodies CORONAL VIEW ventricle, hypothalamus Infundibulum body hypothalamic nuclei Corpus callosum Adenohypophysis hypothalamic fiber tracts Internal Neural lobe mammillary bodies Body capsule neurohypophysis of fornix neural lobe Major white matter bundles infundibulum Thalamus column of fornix 3rd ventricle epithalamus stria medullaris thalami Sub- habenula commissures Hypothalamus thalamus pineal gland anterior Supramammillary pretectal structures posterior commissure pretectal area habenular Mammillary pretectal nuclei Interpeduncular bodies posterior commissure cistern Pons Cerebral subcommissural organ peduncle

DRAWING 20-1 Th e Diencephalon 346 Neuroanatomy: Draw It to Know It

The Thalamus, Part 1 (Advanced )

Here, in two separate parts, we will create a table to orga- the corticopontocerebellar pathway, most notably, but nize the many diff erent thalamic and metathalamic indicate that it also receives basal ganglia projections, as nuclei into several anatomic groups and briefl y discuss well. Both the ventroanterior and ventrolateral nuclei their functional roles. Across the top of the page, write project to the motor cortex. Note that there is inconsis- group, nucleus, function/connections. First, label the tency in the literature regarding whether the ventroante- anterior nuclear group. Indicate that it comprises the rior nucleus projects to primary motor cortex as well as principal anterior and anterodorsal nuclei; in nonhuman premotor cortex or simply premotor cortex and there is species, the principal anterior nucleus is subdivided into inconsistency as to whether its aff erent fi bers are primar- the anteromedial and anteroventral nuclei. 9 Show that ily from the basal ganglia or cerebellum.10 the anterior nuclear group communicates with the mam- Next, indicate that the ventroposterior nucleus sub- millary bodies and cingulate gyrus as part of the Papez divides into medial and lateral nuclei, and show that the circuit. ventroposterior medial nucleus receives sensory aff erents Now, label the medial nuclear group. Indicate that from the face and that the ventroposterior lateral nucleus the dorsomedial nucleus is the most prominent nucleus receives sensory aff erents from the body. Th e ventropos- within this group, and show that it has important con- terior inferior nucleus, a less commonly discussed nections with the prefrontal cortex. nucleus, also exists. Sensory information in the thalamus Next, label the lateral nuclear group, which divides has a very specifi c somatosensory map in which the fi st is into dorsal and ventral subgroups. Indicate that the adjacent to the mouth. Small ventroposterior strokes in dorsal subgroup comprises the dorsolateral, lateral pos- the lateral portion of the ventroposteromedial nucleus terior, and pulvinar nuclei. Th en, show that the dorsolat- and medial portion of the ventroposterolateral nucleus eral nucleus bundles functionally with the anterior result in the characteristic cheiro-oral syndrome in nuclear group and communicates with the limbic system. which there is loss of sensation around the mouth and in Next, indicate that the lateral posterior and pulvinar the fi st contralateral to the side of the thalamic infarct. nuclei collectively form the pulvinar–lateral posterior Now, label the posterior nuclear group, which lies complex, which is involved in visual attention. Th e pulv- beneath the pulvinar and spans posteriorly from the inar relays visual input from the superior colliculus to caudal pole of the ventroposterior nucleus to the medial the visual cortex as part of the extrageniculate visual geniculate nucleus and also extends medial to the medial pathway. geniculate nucleus. Show that it comprises the posterior, Now, show that the ventral subgroup of the lateral limitans, and suprageniculate nuclei. Th e posterior nuclear group comprises the ventroanterior, ventrolat- nuclear group has broad cortical connections; here, eral, and ventroposterior nuclei. Indicate that the ven- simply denote the commonly cited secondary somatosen- troanterior nucleus receives projections from the basal sory cortical projections of the posterior nucleus, which ganglia, most notably, and that the ventrolateral nucleus are involved in nociceptive sensory processing.3 , 8 , 11 , 12 receives cerebellar and red nucleus projections as part of We complete the table, next. 20. Diencephalon 347

THALAMUS (PART 1) GROUP NUCLEUS FUNCTION/CONNECTIONS Anterior nuclear Principal anterior Papez circuit Anterodorsal

Medial nuclear Dorsomedial Prefrontal cortex

Lateral nuclear Dorsal subgroup Dorsolateral Limbic system Lateral posterior Lateral posterior & pulvinar- Pulvinar subserve visual attention

Ventral subgroup Ventroanterior Basal ganglia Ventrolateral Cerebellum, red nucleus (& basal ganglia) Ventroposterior Medial Facial sensory fibers Lateral Body sensory fibers

Posterior nuclear Posterior Example: posterior nucleus- Limitans nociceptive sensation Suprageniculate

DRAWING 20-2 Th e Th alamus, Part 1 348 Neuroanatomy: Draw It to Know It

The Thalamus, Part 2 (Advanced )

Now, label the intralaminar nuclear group, which divides involved in limbic-related processes and that it has into caudal and rostral subgroups. Th e caudal subgroup important hippocampal connections.15 is the most notable; it comprises the centromedian and Now, label the thalamic reticular nucleus, which lies parafascicular nuclei. Th e rostral subgroup comprises along the rostral, ventral, and lateral aspects of the thala- a cluster of closely related nuclei: the central medial, par- mus in between the thalamic external medullary lamina acentral, and central lateral nuclei. Th e intralaminar and the posterior limb of the internal capsule. Show that it nuclei project to other thalamic nuclei, notably the contains GABAergic neurons, which modulate thalamic ventroanterior and ventrolateral nuclei; they have key output. Th e external medullary lamina is a white matter connections to the basal ganglia; and they project dif- layer that surrounds the lateral aspect of the thalamus. fusely to other cortical and subcortical areas. Th e intrala- Finally, indicate the metathalamus and show that it minar nuclei play an important role in a wide range of comprises the medial geniculate and lateral geniculate processes; as an important example, indicate that they nuclei. Indicate that the medial geniculate nucleus forms participate in the ascending arousal system, which is fun- an important step in the auditory system pathway; it damental to wakefulness.13 , 14 receives aff erents from the inferior colliculus, which it Next, indicate the midline nuclear group, which, by projects to the transverse temporal gyri (of Heschl). at least one defi nition, comprises the rhomboid, paratae- Th en, show that the lateral geniculate nucleus forms an nial, paraventricular, and reuniens nuclei— the reuniens important step in the visual system pathway; it receives nucleus lies immediately ventral to the interthalamic aff erents from the optic tract, which it projects to the adhesion. Show that this group of nuclei is reportedly primary visual cortex.8 20. Diencephalon 349

THALAMUS (PART 2) GROUP NUCLEUS FUNCTION/CONNECTIONS Intralaminar nuclear Caudal subgroup Centromedian Connects with other thalamic nuclei, Parafascicular basal ganglia, and diffuse cortical/ Rostral subgroup Central medial subcortical areas; example function - Paracentral ascending arousal system Central lateral

Midline nuclear Rhomboid Limbic-related processes/ Parataenial hippocampal connections Paraventricular Reuniens

Thalamic reticular Modulates thalamic output

METATHALAMUS NUCLEUS FUNCTION/CONNECTIONS Medial geniculate Auditory system Lateral geniculate Visual system

DRAWING 20-3 Th e Th alamus, Part 2 350 Neuroanatomy: Draw It to Know It

Thalamus: Anatomy & Function

Here, we will draw the egg-shaped anatomy of the thala- the pulvinar. Indicate that the pulvinar, which is part mus and metathalamus and review their functional high- of the extrageniculate visual pathway, is important for lights. First, draw the back end of the thalamus and then visual attention (as is the lateral posterior nucleus). the front; we leave the thalamus open so we can label its Now, let’s address the two metathalamic nuclei: draw interior nuclei. Now, draw the anterior–posterior and the medial geniculate nucleus underneath the medial medial–lateral planes of orientation. Next, along the aspect of the pulvinar and the lateral geniculate nucleus anterior–posterior axis of the thalamus, draw the inter- underneath the lateral aspect of the pulvinar. Show that nal medullary lamina. Show that anteriorly it bifurcates the medial geniculate nucleus is part of the auditory to envelop the anterior group nuclei; the length of the system and that the lateral geniculate nucleus is involved internal medullary lamina separates the medial and latin the visual system. eral thalamic groups. Now, indicate that the anterior Next, beneath the pulvinar, label the posterior group group nuclei communicate with the limbic system. Th en, nuclei; they span posteriorly from the caudal pole of the label the medial group nuclei (the most prominent of ventroposterior nucleus to the medial geniculate nucleus which is the dorsomedial nucleus) and show that they and they also extend medial to the medial geniculate connect with the prefrontal cortex. nucleus. Th e most notable function of the posterior Next, let’s label the lateral group nuclei, which divide group nuclei is nociceptive sensory processing. Although into ventral and dorsal subgroups. First, label the ventral it is not easy to appreciate the following from this dia- subgroup nuclei: anteriorly, label the ventroanterior gram, the pulvinar, which lies above the posterior group nucleus, which connects with the basal ganglia; in the nuclei, actually extends farther posterior than any of the middle, label the ventrolateral nucleus, which connects other thalamic nuclei or the metathalamic nuclei. with the cerebellum, red nucleus, and, to a lesser extent, Next, in the center of the diagram, label the intrala- the basal ganglia; and posteriorly, label the ventroposte- minar group, which has widespread connectivity and is rior nucleus. Show that the ventroposterior nucleus fur- involved in multiple functional roles but most notably ther divides into lateral and medial nuclei. Denote that helps form the ascending arousal system for wakefulness. the ventroposterior lateral nucleus receives sensory aff er- Now, draw the midline group nuclei along the ventro- ent projections from the body whereas the ventroposte- medial portion of the thalamus in the midline of the rior medial nucleus receives sensory aff erents from the central nervous system; they function in limbic-related face; both nuclei then relay these sensory projections to processes. Th en, lastly, write out that the thalamic reticu- the somatosensory cortex. lar nucleus forms a shell around the rostral/ventral/ Next, let’s label the dorsal subgroup of the lateral lateral thalamus, and indicate that it modulates thalamic group nuclei. First, anteriorly, label the dorsolateral output. Th e posterior limb of the internal capsule lies lat- nucleus, which communicates with the limbic system eral to the reticular nucleus and the external medullary along with the anterior group nuclei; in the middle, lamina lies in between the reticular nucleus and the lat- label the lateral posterior nucleus; and posteriorly, label eral border of the thalamus. 20. Diencephalon 351

Internal medullary lamina ASCENDING LIMBIC AROUSAL SYSTEM PREFRONTAL CORTEX SYSTEM Midline group Medial group nuclei nuclei Anterior VISUAL group ATTENTION nuclei Dorsolateral Medial geniculate Lateral Intra- nucleus - AUDITORY Ventroanterior posterior laminar SYSTEM nuclei Pulvinar Ventrolateral Posterior BASAL GANGLIA Ventroposterior group nuclei Lateral Medial CEREBELLUM, Body Face RED NUCLEUS, Lateral geniculate (& BASAL GANGLIA) nucleus - VISUAL SYSTEM SOMATOSENSORY CORTEX Thalamic reticular nucleus: shell around rostral/ventral/lateral thalamus - Medial Anterior MODULATES THALAMIC OUTPUT Posterior Lateral

DRAWING 20-4 Th alamus: Anatomy & Function 352 Neuroanatomy: Draw It to Know It

Hypothalamus: Nuclei

Here, we will draw the hypothalamic zones, nuclear Next, let’s draw the individual nuclei; begin with the groups, and the most prominent hypothalamic nuclei. hypothalamic nuclei of the medial zone (the collective First, draw the hypothalamic zones in coronal section. periventricular and intermediate zones). First, draw the Draw the third ventricle and the adjacent hypothalamus anterior (chiasmatic) group nuclei: from inferior to supe- and above it label the thalamus. Next, from medial to rior, starting just above the optic chiasm, draw the supra- lateral within the hypothalamus, label the periventricu- chiasmatic, anterior, and paraventricular nuclei. Next, in lar, intermediate, and lateral zones. Indicate that the the preoptic region, label the medial preoptic nucleus in column of the fornix lies in between the intermediate front of the anterior nucleus. Th e preoptic nucleus devel- and lateral zones and distinguishes them. Now, indicate ops as part of the telencephalon but is anatomically and that the periventricular and intermediate zones are oft en functionally related to the hypothalamus, so it is com- collectively referred to as the medial zone (as we will monly included as part of the hypothalamus. Note that routinely refer to them, here); however, the medial zone the preoptic region is oft en distinguished from the ante- is sometimes used to refer to the intermediate zone, only, rior group as its own nuclear group. Now, draw the instead. Both the periventricular and intermediate zones middle (tuberal) group nuclei: from inferior to superior, are highly cellular whereas the lateral zone contains a starting along the tuber cinereum, draw the infundibular high degree of white matter fi bers. (aka arcuate) nucleus and then the ventromedial and Now, we will draw hypothalamic nuclear groups. dorsomedial nuclei. Next, draw the posterior (mammil- Draw a sagittal outline of the hypothalamus: along lary) group nuclei: fi rst, within the mammillary body, the inferior border, include the pituitary stalk and mam- draw the medial mammillary nucleus, and then above it, millary bodies and in between them label the tuber draw the posterior nucleus. Finally, extending through cinereum; then, label the anterior border of the hypo- the inferior aspect of the middle (tuberal) and posterior thalamus as the lamina terminalis and antero-superiorly (mammillary) groups, draw the medial aspect of the draw the anterior commissure and antero-inferiorly draw tuberomammillary nucleus. the optic chiasm. Next, although it is an oversimplifi ca- Now, recreate a sagittal view of the hypothalamus so tion, include the following important physiologic prin- we can draw the lateral zone hypothalamic nuclei. First, ciple: the anteromedial hypothalamus is involved in anteriorly, in the preoptic region, draw the lateral preop- parasympathetic activity (eg, satiety, sleep, and heat tic nucleus. Th en, above the optic tract, draw the supraop- dissipation to decrease body temperature) and the poste- tic nucleus. Note that many texts list this nucleus as lying rolateral hypothalamus is involved in sympathetic activ- within the medial zone of the hypothalamus rather than ity (hunger, wakefulness, and heat conservation to the lateral zone. Next, draw the lateral aspect of the increase body temperature).3 , 16 Now, label the anterior tuberomammillary nucleus along the inferior aspect of (aka chiasmatic) group as encompassing the region above the hypothalamus extending through the middle and and anterior to the optic chiasm and optic tract; then, posterior groups. Now, draw a small nucleus in the pos- label the middle (aka tuberal) group as encompassing terior aspect of the tuberal region, called the lateral the region between the optic chiasm and mammillary tuberal nucleus. Th en, label the lateral mammillary bodies (ie, the region above the tuber cinereum); and nucleus. And fi nally, delineate the lateral hypothalamic then, label the posterior (aka mammillary) group as area, which spans from the posterior optic chiasm to the encompassing the mammillary bodies and the region posterior end of the hypothalamus; it, most notably, above them. contains the medial forebrain bundle.3 , 6 – 8 , 17 – 21 20. Diencephalon 353

MEDIAL (PERIVENTRICULAR & INTERMEDIATE) ZONE NUCLEI LATERAL ZONE NUCLEI - SAGITTAL VIEW SAGITTAL VIEW ANTERIOR MIDDLE POSTERIOR Lateral (CHIASMATIC) (TUBERAL) (MAMMILLARY) hypothalamic Anterior GROUP GROUP GROUP Lateral commissure area Paraventricular Dorso- Posterior preoptic nucleus nucleus medial nucleus Lateral mamm- nucleus illary nucleus Lamina Supraoptic Lateral terminalis nucleus tuberal nucleus Tuberomammillary Medial nucleus preoptic nucleus HYPOTHALAMIC ZONES - CORONAL VIEW Medial Anterior mammillary nucleus THALAMUS 3RD nucleus Tuberomammillary HYPOTHALAMUS nucleus VENTRICLE Suprachiasmatic Tuber Column Ventromedial nucleus cinereum of fornix nucleus Infundibular (arcuate) Optic chiasm nucleus Periventricular Simplified physiologic principle Intermediate zone Lateral Anteromedial - parasympathetic Medial zone zone Posterolateral - sympathetic zone

DRAWING 20-5 Hypothalamus: Nuclei 354 Neuroanatomy: Draw It to Know It

Hypothalamus: Tracts

Here, we will draw the prominent pathways of the hypo- the primary capillary plexus that serve as either releasing thalamus and in the process learn select highlights of its hormones or release-inhibiting hormones; the most physiology. Draw a sagittal view of the hypothalamus notable source of these neurochemicals is the arcuate and pituitary gland, midbrain, and thalamus. Th en (aka infundibular) nucleus. Oft en the name of the releas- divide the pituitary gland into the adenohypophysis, ing hormone contains the name of the hormone itself; anteriorly, and neurohypophysis, posteriorly. Next, label for instance, growth hormone-releasing hormone pro- the paraventricular and supraoptic nuclei (a more accu- motes the release of growth hormone.20 , 21 One clinically rate depiction of their anatomic positions is shown in important release-inhibiting hormone is dopamine, Drawing 20-5 ). Now, within the neurohypophysis, draw which inhibits the release of prolactin; therefore, exoge- a capillary plexus. Th en, show that the magnocellular nous dopamine agonists, such as bromocriptine, are used neurons of the paraventricular and supraoptic nuclei to help control prolactin levels and reduce tumor size in project to the capillary plexus of the neurohypophysis prolactin-secreting pituitary tumors (prolactinomas). 22 via the hypothalamohypophysial tract, and then show Now, let's show some additional hypothalamic tracts. that the neurohypophysis releases hormones into the Show that the amygdala, the emotional center, projects general circulation via the hypophysial veins. Indicate fi bers that pass over the thalamus to the bed nucleus of that through this pathway, the paraventricular and the stria terminalis, septal nuclei, and hypothalamus via supraoptic nuclei release the hormones vasopressin (aka the stria terminalis. 23 Th en, show that the fornix sends a antidiuretic hormone [ADH]) and oxytocin. Vasopressin descending column through the hypothalamus to the causes increased reabsorption of water in the collecting mammillary nuclei and that the mammillary nuclei proj- tubules of the kidneys. Oxytocin causes increased uter- ect to the anterior thalamic nuclei via the mammillotha- ine and mammillary gland contraction. Note that the lamic fasciculus; these two projections form a key portion hypothalamohypophysial tract is also referred to as the of the Papez circuit, an important limbic system path- combined supraopticohypophysial and paraventriculo- way for memory consolidation (see Drawing 21-4). hypophysial tracts. Next, indicate that the mammillary nuclei project via Now, within the median eminence of the hypothala- the mammillotegmental fasciculus to the brainstem teg- mus, draw the primary capillary plexus. Th en, within the mentum. Most texts indicate that the mammillotegmen- adenohypophysis, draw the secondary capillary plexus. tal fasciculus terminates in the midbrain, but select texts Next, connect the primary and secondary plexuses with indicate that it also projects to the pons.24 , 25 Th en, show the hypothalamohypophysial portal venous system. Th en, that the retino-hypothalamic pathway, which is funda- show that the epithelial-cell–fi lled adenohypophysis mental for the regulation of the light–dark circadian releases the following hormones into the general circula- cycle, synapses in the suprachiasmatic nuclei. Now, show tion via hypophysial veins: follicle-stimulating hormone, that diff use nuclei of the limbic system, including those luteinizing hormone, adrenocorticotropic hormone, thy- of the septal nuclei and the olfactory and periamygdaloid roid-stimulating hormone, prolactin, growth hormone, and areas, project through the lateral hypothalamus to the melanocyte-stimulating hormone. Note that the fi rst fi ve midbrain tegmentum as the medial forebrain bundle.20 , 25 hormones form the quirky yet memorable acronym Finally, show that the dorsal longitudinal fasciculus proj- FLATPiG. Th e hypothalamus controls the release of ects from the hypothalamus into the brainstem; it these hormones via a variety of parvocellular neurons, coalesces most prominently in the periaqueductal gray which release chemicals (peptides, most notably) into area (in the midbrain). 6 , 7 20. Diencephalon 355

Stria terminalis Septal nuclei & Anterior thalamic bed nucleus of nucleus stria terminalis Mammillothalamic fasciculus Dorsal longitudinal fasciculus (prominent in Medial forebrain periaqueductal gray area) bundle Column Limbic system Mammillo- of fornix tegmental fasciculus Suprachiasmatic Mammillary Midbrain nucleus nucleus tegmentum Optic Paraventricular chiasm & supraoptic nuclei Retino- Amygdala hypothalamic tract Primary capillary Neurohypophysis Adenohypophysis plexus Hypothalamohypophysial tract Hypothalamo- Vasopressin Follicle-stimulating hormone Neuro- hypophysial Oxytocin Luteinizing hormone Secondary hypophysis portal system capillary Adrenocorticotropic hormone pexus Thyroid stimulating hormone Capillary plexus Prolactin Adeno- Growth hormone hypophysis Melanocyte stimulating hormone

DRAWING 20-6 Hypothalamus: Tracts 356 Neuroanatomy: Draw It to Know It

References 1 . U p l e d g e r, J . E . A brain is born: exploring the birth and development 1 3. M e n d o z a, J . E . & F o u n d a s, A . L . Clinical neuroanatomy: a of the central nervous system, 1st pbk. ed., pp. 149 – 150 (North neurobehavioral approach , p. 204 ( Springer , 2008 ). Atlantic Books; Upledger Enterprises , 2010 ). 14 . Steriade , M. Th e intact and sliced brain , p. 255 ( MIT Press , 2001 ). 2 . B a d i e, B . Neurosurgical operative atlas. Neuro-oncology, 2nd ed., 15 . Dauber , W. & Feneis , H. Pocket atlas of human anatomy, 5th rev. pp. 42 – 44 (Th ieme; American Association of Neurosurgeons, ed., p. 364 (Th ieme, 2007 ). 2007 ). 1 6. B i l l e r, J . Th e interface of neurology & internal medicine, p. 466 3 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and (Wolters Kluwer Health/Lippincott Wiliams & Wilkins, 2008 ). atlas, 2nd ed., Chapter 21 ( Lange Medical Books/McGraw-Hill , 17 . Haines , D. E. & Ard , M. D. Fundamental neuroscience: for basic and 2005 ). clinical applications, 3rd ed. ( Churchill Livingstone Elsevier , 2006 ). 4 . R a m a m u r t i, R . Textbooks of operative neurosurgery, Vo l . 1 , C h a p t e r 1 8. S t a n d r i n g, S . & G r a y, H . Gray’s anatomy: the anatomical basis of 41 (BI Publications Pvt. Ltd., 2005 ). clinical practice, 40th ed., p. 318 ( Churchill Livingstone/Elsevier , 5 . Akalan , N. Neuroendocrine research models . Acta Neurochir Suppl 2008 ). 83 , 85 – 91 (2002 ). 19 . Waxman , S. G. Clinical neuroanatomy. 25th ed., p. 127 ( Lange 6 . Mai , J. K., Voss , T. & Paxinos , G. Atlas of the human brain, 3rd ed. Medical Books/McGraw-Hill, Medical Pub. Division , 2003 ). ( Elsevier/Academic Press , 2008 ). 20 . Moore , S. P. & Psarros , T. G. Th e defi nitive neurological surgery 7 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human board review, pp. 44 – 49 (Blackwell Pub., 2005 ). brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal 2 1. K i e r n a n, J . A . & B a r r, M . L . Barr’s the human nervous system: an structure, vascularization and 3D sectional anatomy ( Springer , 2009 ). anatomical viewpoint, 9th ed. (Wolters Kluwer/Lippincott, 8 . N i e u w e n h u y s, R ., Vo o g d, J . & H u i j z e n, C . V. Th e human central Williams & Wilkins , 2009 ). nervous system, 4th ed. (Springer , 2008 ). 2 2. B e c k e r, K . L . Principles and practice of endocrinology and 9 . Butler , A. B. & Hodos , W. Comparative vertebrate neuroanatomy: metabolism, 3rd ed., p. 238 ( Lippincott Williams & Wilkins , 2001 ). evolution and adaptation, 2nd ed., p. 435 ( Wiley-Interscience , 23 . Liddle , P. F. & Royal College of Psychiatrists. Disordered mind and 2005 ). brain: the neural basis of mental symptoms , p. 43 ( Gaskell; 1 0. C i t o w, J . S . Neuroanatomy and neurophysiology : a review, p. 35 Distributed in North America by American Psychiatric Press , (Th ieme, 2001 ). 2001 ). 11 . Jacobson , S. & Marcus , E. M. Neuroanatomy for the neuroscientist, 2 4. M a r t i n, J . H . Neuroanatomy: text and atlas, 3rd ed., p. 499 Chapters 6 & 7 ( Springer , 2008 ). ( McGraw-Hill Companies, Inc ., 2003 ). 1 2. A r s l a n, O . Neuroanatomical basis of clinical neurology, pp. 101 – 102 2 5. C o n n, M . Neuroscience in Medicine, 3rd ed., p. 389 ( Humana Press , ( Parthenon Pub. Group , 2001 ). 2008 ). 2 1 Limbic and Olfactory Systems

Limbic System, Part 1

Limbic System, Part 2 ( Advanced )

Hippocampus: Anatomy

Hippocampus: Circuitry

Olfactory System, Part 1

Olfactory System, Part 2 ( Advanced )

Olfactory Cortex & Basal Forebrain, Part 1

Olfactory Cortex & Basal Forebrain, Part 2 ( Advanced ) 358 Neuroanatomy: Draw It to Know It

Know-It Points

Limbic System, Part 1

■ Th e limbic system forms outer and inner rings around ■ Th e hippocampus lies along the anteroposterior the diencephalon. length of the superior aspect of the parahippocampal ■ Th e anterior cingulate gyrus is part of the anterior gyrus; it is the center for memory processing. network of motivation, attention, and behavior and is ■ Th e amygdala divides into corticomedial and associated with the amygdala. basolateral groups. ■ Th e posterior cingulate gyrus is part of the posterior ■ Th e corticomedial group of the amygdala connects, network of learning and memory and is associated most notably, to the olfactory system and with the hippocampus. hypothalamus for autonomic function. ■ Th e parahippocampal gyrus forms the inferior aspect ■ Th e basolateral group of the amygdala connects, most of the limbic gyrus; it channels information to and notably, to the thalamus and prefrontal cortex for from the hippocampus to help in memory such functions as sensory processing of visual, consolidation. auditory, and somatosensory stimuli.

Limbic System, Part 2 (Advanced )

■ Th e cingulum spans the cingulate and ■ Th e fornix emerges from the hippocampus, wraps parahippocampal gyri. around the thalamus, and passes anteriorly in midline ■ Th e cingulum, most notably, interconnects just below the corpus callosum. intracingulate areas and synapses in the hippocampus. ■ Via the stria terminalis, the amygdala projects to the septal nuclei, bed nucleus of the stria terminalis, and hypothalamus.

Hippocampus: Anatomy

■ Th e subdivisions of the cornu ammonis from the ■ Th e posterior parahippocampal gyrus is referred to dentate gyrus to the subiculum are CA4, CA3, CA2, as the parahippocampal cortex and corresponds to and CA1. Von Economo areas TF and TH. ■ CA1 forms the largest stretch of Ammon’s horn and ■ Th e uncus forms the anterior gyral thumb of the is distinctively susceptible to anoxic injury. parahippocampal gyrus. ■ Th e entorhinal and perirhinal cortices form the anterior parahippocampal gyrus. 21. Limbic and Olfactory Systems 359

Hippocampus: Circuitry

■ Th e Papez circuit (extrahippocampal circuitry): ■ Th e perforant pathway (intrahippocampal – Th e entorhinal cortex projects to the hippocampus. circuitry): – Th e hippocampus projects to the mammillary – Th e entorhinal cortex projects through the nuclei. subiculum to the dentate gyrus. – Th e mammillary nuclei project to the anterior – Th e dentate gyrus projects to CA3. thalamic nuclei. – CA3 projects to CA1 via Schaff er collaterals. – Th e anterior thalamic nuclei project to the – CA1 projects to the subiculum. cingulate gyrus. – Th e subiculum projects along the alveus to the – Th e cingulate gyrus projects back to the entorhinal fi mbria, which passes posteriorly and becomes the cortex. crus of the fornix. ■ Th e Papez circuit is the cornerstone of memory – Th e subiculum also projects back to the entorhinal consolidation. c o r t e x .

Olfactory System

■ Th e olfactory neurons lie within the olfactory ■ Two principle classes of secondary olfactory neuron epithelium and project through the cribriform plate exist: tuft ed cells and mitral cells. to innervate the olfactory bulb. ■ Dendrites from secondary olfactory neurons ■ Th e olfactory bulb and tract are telencephalic communicate with the primary olfactory axons extensions of the cerebrum. within the glomerular layer of the olfactory bulb. ■ Th e medial olfactory stria innervates the medial ■ Th e olfactory system bypasses the thalamus in its olfactory area in the subcallosal region. projection to the cerebral cortex. ■ Th e lateral olfactory stria innervates the primary olfactory cortex in the basal frontal and anteromedial temporal lobes.

Olfactory Cortex & Basal Forebrain

■ Th e basal forebrain structures with the most notable ■ Th e medial olfactory cortex comprises, most notably, cholinergic properties are the medial septal nuclei, the subcallosal and paraterminal gyri. the diagonal band of Broca, and the basal nucleus of ■ Th e intermediate stria terminates in the olfactory Meynert. tubercle within the anterior perforated substance. ■ Th e medial, intermediate, and primary (aka lateral) ■ Th e primary olfactory cortex comprises the piriform olfactory cortices are innervated by the medial, cortex, periamygdaloid cortex, corticomedial intermediate, and lateral olfactory striae, amygdala, and a small portion of the entorhinal respectively. cortex, anteriorly. 360 Neuroanatomy: Draw It to Know It

2 3 9 17

28 27

19 10 26 20 4 8 16’ 21 16 a 18 11 7 23 5 1 25 14 15 24 a 22

12 11’ 6

FIGURE 21-1 Drawing showing a sagittal section, right hemisphere. Th e limbic lobe is separated from the isocortex by the limbic fi ssure and may be divided into two gyri: the limbic and intralimbic gyri. Th e line a-a indicates the plane of the section on Figure 21.1. Bar, 7.7 mm Limbic fi ssure: 1, anterior paraolfactory sulcus (subcallosal sulcus); 2, cingulate sulcus; 3, subparietal sulcus; 4, anterior calcarine sulcus; 5, collateral sulcus; 6, rhinal sulcus. Limbic gyrus; 7, subcallosal gyrus; 8, posterior paraolfactory sulcus; 9, cingulate gyrus; 10, isthmus; 11', parahippocampal gyrus, posterior part; 11, parahippocampal gyrus, anterior part (piriform lobe). Piriform lobe; 12, entorhinal area; 13, ambient gyrus; 14, semilunar gyrus; 15, prepiriform cortex. Intralimbic gyrus; 16, prehippocampal rudiment; 16', paraterminal gyrus; 17, indusium griseum. Hippocampus; 18, gyrus dentatus; 19, cornu Ammonis; 20, gyri of Andreas Retzius; 21, fi mbria (displaced upwards, arrows); 22, uncal apex; 23, band of Giacomini; 24, uncinate gyrus; 25, anterior perforated substance; 26, anterior commissure; 27, fornix; 28, corpus callosum. Used with permission from Duvernoy, Henri M. Th e Human Hippocampus: Functional Anatomy, Vascularization and Serial Sections with MRI, 3rd ed. Berlin; New York: Springer, 2005.

FIGURE 21-2 Dissection showing a sagittal section, right hemisphere. Th e limbic lobe is separated from the isocortex by the limbic fi ssure and may be divided into two gyri: the limbic and intralimbic gyri. Limbic fi ssure: 1, anterior paraolfactory sulcus (subcallosal sulcus); 2, cingulate sulcus; 3, subparietal sulcus; 4, anterior calcarine sulcus; 5, collateral sulcus; 6, rhinal sulcus. Limbic gyrus; 7, subcallosal gyrus; 8, posterior paraolfactory sulcus; 9, cingulate gyrus; 10, isthmus; 11', parahippocampal gyrus, posterior part; 11, parahippocampal gyrus, anterior part (piriform lobe). Piriform lobe; 12, entorhinal area; 13, ambient gyrus; 14, semilunar gyrus; 15, prepiriform cortex. Intralimbic gyrus; 16, prehippocampal rudiment; 16', paraterminal gyrus; 17, indusium griseum. Hippocampus; 18, gyrus dentatus; 19, cornu Ammonis; 20, gyri of Andreas Retzius; 21, fi mbria (displaced upwards, arrows); 22, uncal apex; 23, band of Giacomini; 24, uncinate gyrus; 25, anterior perforated substance; 26, anterior commissure; 27, fornix; 28, corpus callosum. Used with permission from Duvernoy, Henri M. Th e Human Hippocampus: Functional Anatomy, Vascularization and Serial Sections with MRI, 3rd ed. Berlin; New York: Springer, 2005. 21. Limbic and Olfactory Systems 361

Internal capsule

Tail of the caudate nucleus Putamen Optic tract Lateral geniculate Anterior commisure

Lateral ventricle Extreme capsule External capsule Claustrum Amygdala 10 mm Hippocampus Cerebellum

FIGURE 21-3 Oblique anatomic section through the limbic system to highlight the length of the hippocampus. Used with permission from the Michigan State University: Brain Biodiversity Bank. https://www.msu.edu/∼brains/

15 AB 17

14 16

1 4 2 18 13

3 20

5 6 12 7 8

19 10 9

21 22 11

FIGURE 21-4 Development of the gyrus dentatus (dotted area) and of the cornu Ammonis (hatched area) towards B their defi nitive desposition. Arrows indicate the hippocampal sulcus (superfi cial part). (Modifi ed aft er Williams 1995) 1, cornu Ammonis; 2, gyrus dentatus; 3, hippocampal sulcus (deep or vestigial part); 4, fi mbria; 5, prosubiculum, 6, subiculum proper; 7, presubiculum; 8, parasubiculum; 9, entorhinal area; 10, parahippocampal gyrus; 11, collateral sulcus; 12, collateral eminence; 13, temporal (inferior) horn of the lateral ventricle; 14, tail of caudate nucleus; 15, stria terminalis; 16, choroid fi ssure and choroid plexuses; 17, lateral geniculate body; 18, lateral part of the transverse fi ssure (wing of ambient cistern); 19, ambient cistern; 20, mesencephalon; 21, pons; 22, tentorium cerebelli. Used with permission from Williams, Peter. Gray’s Anatomy. 38th edition. New York: Churchill Livingstone, 1995. 362 Neuroanatomy: Draw It to Know It

Limbic System, Part 1

Here, we will draw the anatomy of the limbic system. parahippocampal gyrus, draw the hippocampus. Th e Generally, the limbic system is meant to encompass the hippocampus is the center for memory processing; we limbic lobe and functionally related structures, most draw it in detail in Drawing 21-3 . Next, just beneath the notably the cingulate and parahippocampal gyri, hip- splenium of the corpus callosum, draw the fasciolar pocampus, and amygdala. First, we will draw a sagittal gyrus, which is the transitional zone between the hip- view of the major gray matter structures of the limbic pocampus and the indusium griseum. system. Th e limbic system forms outer and inner rings Now, just anterior to the hippocampus, deep to the around the diencephalon. Draw the following important posterior aspect of the uncus, draw the almond-shaped anatomic landmarks: the corpus callosum, basal frontal amygdala (aka amygdaloid body). Th e simplest way to lobe, thalamus, and the septum pellucidum. Next, draw understand the amygdala is to divide it into corticome- the outer ring: the limbic gyrus. To do so, fi rst, above the dial and basolateral groups. Both groups connect to a corpus callosum, label the cingulate gyrus. Th e cingulate wide variety of brain regions, but the corticomedial gyrus is commonly divided into anterior and posterior group connects, most notably, to the olfactory system divisions. Th e anterior cingulate gyrus is part of the ante- and hypothalamus for autonomic function and the baso- rior network of motivation, attention, and behavior and lateral group connects, most notably, to the thalamus is associated with the amygdala, whereas the posterior and prefrontal cortex for more conscious-related pro- cingulate gyrus is part of the posterior network of learn- cesses such as sensory processing of visual, auditory, and ing and memory and is associated with the hippocam- somatosensory stimuli. 2 , 3 Bilateral amygdala destruction pus. Next, posterior to the rostrum of the corpus callosum results in Klüver Bucy syndrome, which involves, most and underneath the septum pellucidum, label the sub- prominently, social tameness and loss of avoidance man- callosal area; show that it extends anteriorly directly ifesting with hypermetamorphosis (the incessant explo- underneath the corpus callosum — we draw this region ration of objects within the environment), hyperorality, in detail at the end. Th en, show that the parahippocam- visual agnosia, and hypersexuality. Klüver Bucy syn- pal gyrus forms the inferior aspect of the limbic gyrus, drome was fi rst described from the eff ects of bilateral and label the gyral fold at its anterior tip as the uncus. amygdala and hippocampal destruction in monkeys, but Th e parahippocampal gyrus channels information to it is a rare complication of a variety of naturally occur- and from the hippocampus to help in memory consoli- ring illnesses in humans, including herpes simplex dation; an effi cient parahippocampal gyrus is required encephalitis, frontotemporal lobar dementia, and anoxic- for eff ective memory processing. Now, label the poste- ischemic lesions in the bilateral anterior medial tempo- rior transitional zone between the cingulate and para- ral lobes. 4 hippocampal gyri as the isthmus of the cingulate gyrus. Next, include the following diencephalic structures: Next, let’s draw the inner limbic ring: the intralimbic the anterior nuclei of the thalamus and the mammillary gyrus. Along the superior surface of the corpus callo- body of the hypothalamus, both of which are fundamen- sum, beneath the cingulate gyrus, draw the indusium tal to the Papez circuit. Th e mammillary bodies (along griseum (aka the supracallosal gyrus). Th e indusium gri- with other midline periventricular structures: the dorso- seum, along with the anatomically associated medial and medial thalamus, periaqueductal region, and fl oor of the longitudinal striae, are considered vestigial remnants of fourth ventricle) are aff ected in Wernicke-Korsakoff the hippocampal formation.1 Now, along the bulk of syndrome, which manifests with confusion, memory the anteroposterior length of the superior aspect of the loss, ophthalmoplegia, and ataxia.3 , 5 – 10 21. Limbic and Olfactory Systems 363

LIMBIC SYSTEM - GRAY MATTER - SAGITTAL VIEW Cingulate gyrus Indusium griseum Corpus callosum Fasciolar Septum gyrus pellucidum Ant. nuclei of thalamus Mammillary Isthmus, cingulate body Subcallosal gyrus area Hippocampus

Amygdala

Uncus Parahippocampal gyrus

DRAWING 21-1 Limbic System, Part 1 364 Neuroanatomy: Draw It to Know It

Limbic System, Part 2 (Advanced )

Now, let’s return to the subcallosal region and draw a commissure, and synapses, most notably, in the mammil- detailed view of its anatomy; include the anterior com- lary bodies. Note that postcommissural fornix connec- missure for reference. Indicate that the anterior paraol- tions to the anterior thalamic nuclei and midbrain also factory sulcus separates the subcallosal gyrus from the exist. Next, show that the mammillothalamic fasciculus frontal lobe, anteriorly, and show that the posterior connects the mammillary body to the anterior thalamic paraolfactory sulcus divides the subcallosal area into the nuclei. Note that the postcommissural fornix and the subcallosal gyrus, anteriorly, and the paraterminal gyrus, mammillothalamic fasciculus form key steps in the Papez posteriorly. Note that additional descriptors for this circuit. region include the terms the septal area and paraolfactory Now, show that via the stria terminalis, the amygdala (or parolfactory) area. Also note that the nomenclature projects along the dorsal aspect of the thalamus and ter- used to describe the subcallosal region displays extraordi- minates in the septal nuclei and bed nucleus of the stria nary intertextual inconsistency and contradiction. Next, terminalis and also in the hypothalamus. Finally, show show that the septal nuclei lie, most notably, within the that via the amygdalofugal tract, the amygdala projects fi brous septum pellucidum above the anterior commis- to diff use areas: most notably, the basal forebrain, pre- sure, beneath the corpus callosum, posterior to the sub- frontal, temporal, occipital, and insular cortices; thala- callosal area, and anterior to the fornix. Th en, show that mus; hypothalamus; septal nuclei; and the autonomic the bed nucleus of the stria terminalis sits just above the and neurobehavioral substrate of the brainstem.8 anterior commissure and below the septal nuclei. Finally, because the stria terminalis and fornix follow Next, let’s draw the limbic pathways in sagittal view. such similar paths, let’s draw a coronal view of the dien- Draw an outline of a sagittal view of the limbic system cephalon to distinguish their trajectories; in this dia- gray matter, corpus callosum, and thalamus. Th en, show gram, we will also show the position of the stria medullaris that the cingulum spans the cingulate and parahip- thalami, which is an important diencephalic pathway pocampal gyri. Indicate that it interconnects intracingu- that travels near the fornix and stria terminalis. As ana- late areas; synapses in the hippocampus (through the tomic landmarks, draw the corpus callosum, caudate, entorhinal cortex); and also projects to many additional thalamus, lateral ventricle, and third ventricle. Now, areas, including most cortical regions, including the pre- show the body of the fornix underneath the midline of frontal, temporal, parietal, and occipital cortices. Next, the corpus callosum; the fornix emerges from the hip- show that the fornix emerges from the hippocampus, pocampus, wraps around the thalamus, and passes ante- wraps around the thalamus, and passes anteriorly just riorly in midline just below the corpus callosum. Next, below the corpus callosum. At the interventricular fora- draw the stria terminalis along the inferomedial aspect men of Monro it divides and descends as bilateral col- of the caudate (lateral to the body of the fornix); the stria umns. Each column contains a small precommissural terminalis emerges from the amygdala and passes along bundle that descends anterior to the anterior commis- the inferomedial aspect of the caudate nucleus through- sure and projects to diff use areas, including the septal out most of its course along the lateral wall of the lateral nuclei, frontal lobes, hypothalamus, and ventral striatum; ventricular system. Finally, in midline, along the dorso- and each column also contains a large postcommissural medial aspect of the thalamus, draw the stria medullaris bundle, which originates solely within the subiculum of thalami, which spans from the habenula to the septal the hippocampus, projects posterior to the anterior nuclei.3 , 6 – 10 21. Limbic and Olfactory Systems 365

LIMBIC SYSTEM - GRAY MATTER - CORONAL VIEW - SELECT LIMBIC PATHWAYS SAGITTAL VIEW Corpus Lateral ventricle Cingulate gyrus callosum Indusium Caudate Body griseum Corpus callosum of fornix Fasciolar Stria terminalis Septum gyrus 3rd Stria medullaris pellucidum Ant. nuclei ventricle thalami of thalamus Thalamus Mammillary Isthmus, cingulate body LIMBIC PATHWAYS - SAGITTAL VIEW Subcallosal gyrus area Hippocampus Cingulum

Amygdala Stria terminalis Uncus Parahippocampal Fornix gyrus (Precomm.) SUBCALLOSAL Mamillo.- REGION thalam. Bed nucleus of Diffuse (Post- fascic. stria terminalis areas Septal nuclei comm.) Anterior commissure Anterior para- Posterior para- Ventral olfactory sulcus olfactory sulcus amygdalofugal Subcallosal gyrus Paraterminal tract gyrus

DRAWING 21-2 Limbic System, Part 2 366 Neuroanatomy: Draw It to Know It

Hippocampus: Anatomy

Here, we will draw a coronal view of the medial tempo- subicular complex as part of the hippocampus, whereas ral lobe (ie, the antero-inferior limbic lobe) to learn the other sources list the subiculum, only, as part of the hip- anatomy of the hippocampus and anterior parahip- pocampus and list the pre- and parasubiculum as part of pocampal gyrus. Before we begin our diagram, draw a the parahippocampal region. small coronal insert in the corner of the page of half of Next, label the inferior turn as the entorhinal cortex, the brain and upper brainstem. Include the temporal which forms the medial aspect of the anterior parahip- horn of the lateral ventricle and the tentorium cerebelli, pocampal gyrus. Now, draw the perirhinal cortex and and encircle the medial temporal lobe — this is the region show that the rhinal sulcus separates the perirhinal and we will draw. entorhinal cortices. Next, in the corner of the diagram, Next, begin our main diagram. Draw the pons and write out that the entorhinal and perirhinal cortices midbrain and extend our drawing along the basal fore- form the anterior parahippocampal gyrus. Th e posterior brain. Th en, include the temporal horn of the lateral parahippocampal gyrus is referred to as the parahip- ventricle. Next, use the choroid fi ssure to separate the pocampal cortex and corresponds to Von Economo areas temporal horn of the lateral ventricle from the neighbor- TF and TH.11 Next, for anatomic context, show that the ing subarachnoid space: the ambient cistern. collateral sulcus distinguishes the fusiform gyrus, later- To draw the hippocampus, fi rst draw a double-sided S. ally, from the parahippocampal gyrus, medially. Th en, divide the S into its superior turn, horizontal Now, let’s discuss the uncus, which, simply put, forms stretch, and inferior turn. As we will show, the cornu the anterior gyral thumb of the parahippocampal gyrus. ammonis, which is Latin for “horn of the ram,” and which Anteriorly, the uncus encompasses the amygdala, and is also known as Ammon’s horn or the hippocampus posteriorly, it forms the anterior portion of the hip- proper, comprises the superior turn; the subicular com- pocampus, which complicates the simple defi nition of plex forms the horizontal stretch; and the parahippocam- the uncus as listed, here. Th e term “uncal herniation” is pal gyrus comprises the inferior turn. Internal to the used to describe medial temporal lobe herniation over superior turn, draw the C-shaped dentate gyrus, which the tentorium cerebellum. During uncal herniation, the cups the cornu ammonis. Next, label the subdivisions of medial temporal lobe compresses the ipsilateral third the cornu ammonis: label CA4 adjacent to the dentate nerve as it exits the midbrain, causing an ipsilateral ocul- gyrus; label CA3 along the medial vertical; label CA2 omotor palsy. Also, the herniating temporal lobe can along the top of the turn; and fi nally, label CA1 along the compress the contralateral cerebral peduncle against its lateral vertical. CA1 forms the largest stretch of Ammon’s adjacent tentorium, forming a so-called Kernohan’s horn and is distinctively susceptible to anoxic injury. notch in that peduncle. Th e damaged cerebral peduncle Now, label the horizontal stretch of our diagram as results in motor weakness on the opposite side of the the subicular complex, and show that the hippocampal body— the side of the herniating temporal lobe and sulcus separates it from the dentate gyrus. From lateral to oculomotor palsy. medial (ie, from CA1 to the ambient cistern), the subic- Finally, internal to the perirhinal and entorhinal cor- ular complex comprises the subiculum, presubiculum, tices, label the parahippocampal white matter; and then and parasubiculum. Th e subiculum is the source of the label the white matter along the lateral border of the postcommissural fornix fi bers, which terminate in the cornu ammonis as the alveus; and show that along the mammillary nuclei and which form a key step in the Papez superomedial border of the cornu ammonis, the alveus circuit. Th e Terminologia Anatomica lists the complete becomes the fi mbria.3 , 6 – 9 , 12 21. Limbic and Olfactory Systems 367

Choroid fissure Temporal horn of Alveus Fimbria lateral CA 2 ventricle CA 3

Temporal CA 4 CA 1 Hippocampal sulcus horn of Dentate gyrus lateral ventricle Subicular complex Midbrain Tentorium Ambient cerebelli cistern Parahippocampal gyrus white matter Entorhinal cortex*

Perirhinal Pons cortex* Rhinal Fusiform sulcus gyrus Collateral sulcus Tentorium cerebelli *Entorhinal and perirhinal cortices form the anterior parahippocampal gyrus

DRAWING 21-3 Hippocampus: Anatomy 368 Neuroanatomy: Draw It to Know It

Hippocampus: Circuitry

Here, we will draw the fundamental extra- and intra- gyrus, which then projects to the perirhinal cortex, and hippocampal circuitry. We begin with the extra-hip- subsequently to the entorhinal cortex and on to the hippocampal circuitry, namely the Papez circuit. First, in pocampus. Note that although not shown as such, here, sagittal view draw the following structures: the corpus many areas skip synapsing in the posterior parahip- callosum, cingulate gyrus, basal forebrain, thalamus, and pocampal gyrus and directly synapse in the perirhinal or parahippocampal gryus with its anterior gyral fold— the entorhinal cortices or even directly in the hippocampus, uncus. Next, let’s show the steps in the Papez circuit. itself. First, indicate that the entorhinal cortex (in the anterior Now, let’s draw the intrahippocampal circuitry, parahippocampal gyrus) projects to the hippocampus, namely the perforant pathway. First, in coronal view, which projects via the fornix to the mammillary nuclei. redraw the medial temporal lobe. Include the dentate Divide the fornix as follows: the crus of the fornix is its gyrus, cornu ammonis, subiculum, entorhinal cortex, vertical ascent; the body of the fornix is its anterior pro- alveus, and fi mbria. Th en, add the posterior length of jection underneath the corpus callosum; and the column the hippocampus. Show that the fi mbria becomes the of the fornix is its descent. Note that the fornix descends crus of the fornix, which makes its vertical ascent at the both anterior and posterior to the anterior commissure. splenium of the corpus callosum. Th e intrahippocampal Th e anterior projection is called the precommissural circuitry is distinct in that it follows a very specifi c unidi- fornix and the posterior projection through the hypo- rectional progression — unlike most cortical projections, thalamus (shown here) is called the postcommissural which are generally bidirectional. Show that the entorhi- fornix. Next, indicate that the mammillary nuclei proj- nal cortex projects through the subiculum (it perforates ect to the anterior thalamic nuclei via the mammillotha- it) to synapse in the dentate gyrus. Th en, indicate that lamic fasciculus (aka the Vicq d’Azyr bundle), and then the dentate gyrus projects to CA3, which projects to show that the anterior thalamic nuclei project to the cin- CA1 via Schaff er collaterals. CA1 then projects to the gulate gyrus. Finally, show that the cingulate gyrus proj- subiculum, which projects along the alveus to the fi m- ects back to the entorhinal cortex via the cingulum to bria, which passes posteriorly and becomes the crus of close the Papez circuit loop. When James Papez intro- the fornix. Th e fornix ultimately projects, most notably, duced this circuit in 1937, he believed it played a funda- to the mammillary nuclei (as shown in the Papez circuit mental role in emotional processing; however, now the portion of the diagram). Finally, show that the subicu- Papez circuit is understood to be the cornerstone of lum also projects back to the entorhinal cortex. Note memory consolidation, instead. that CA3 and CA1 also send direct projections to the Neuronal input reaches the hippocampus through fi mbria that skip the intervening steps in this pathway, widespread neocortical, limbic, diencephalic, and brain- and also note that many other intrahippocampal projec- stem neurobehavioral areas. Here, we will show two tions also exist, including subiculum projections to the examples of how these areas reach the hippocampus. other components of the subicular complex (ie, the pre- First, simply show that the cingulate gyrus has reciprocal subiculum and parasubiculum). 13 Lastly, consider that connections with the neocortex that project via the cin- because of the anatomic relationship between the ento- gulum to the entorhinal cortex, which then projects to rhinal cortex, dentate gyrus, cornu ammonis, and subic- the hippocampus. Second, indicate that widespread neo- ulum, these structures are oft en collectively referred to as cortical areas project to the posterior parahippocampal the hippocampal formation.3 , 6 – 9 , 12 21. Limbic and Olfactory Systems 369

EXTRA-HIPPOCAMPAL CIRCUITRY INTRA-HIPPOCAMPAL CIRCUITRY & THE PAPEZ CIRCUIT & THE PERFORANT PATHWAY Neocortex Neocortex Cingulum

Fornix(body) Fornix Crus (crus) Mm-thlm. of fornix Splenium fasc. Alveus of corpus Fornix (colmn) callosum Fimbria Hippocampus CA 2 CA 3 Entorhinal cortex CA 4 CA 1 Perirhinal Posterior Dentate gyrus cortex parahippocampal gyrus Subiculum

Entorhinal cortex

DRAWING 21-4 Hippocampus: Circuitry 370 Neuroanatomy: Draw It to Know It

Olfactory System, Part 1

Here, we will draw the olfactory system; we will focus on Next, let’s draw an expanded view of the olfactory the olfactory nerve, bulb, tract, and striae, here, and learn nerve and bulb. Draw the olfactory epithelium, cribri- the olfactory cortex in Drawings 21-7 and 21-8 . Begin form plate, olfactory bulb, and the anterior segment of with a sagittal view of the midline nasal cavity; include the connected olfactory tract. Next, draw a representa- the following anatomic landmarks: the cribriform plate, tive primary olfactory neuron (aka olfactory receptor which separates the cranial vault from the nasal cavity; cell), which is bipolar. Show that at one end, it projects the medial anterior frontal lobe and temporal lobe; and an apical dendrite to the epithelial surface. Indicate that the anterior corpus callosum. Note that fracture to the cilia from the apical dendrite interact with the mucus cribriform plate (or more commonly to the ethmoid air layer of the olfactory epithelial surface. Next, indicate cells posterolateral to the cribriform plate) is a common that an unmyelinated nerve bundle, which is the olfac- cause of rhinorrhea— a cerebrospinal fl uid leak from the tory nerve, itself, projects from the other end of the pri- nasal cavity. Now, along the upper nasal cavity, draw the mary olfactory neuron through the cribriform plate to olfactory epithelium. Next, just above the cribriform the olfactory bulb. As we will soon show, it interacts with plate, draw an olfactory bulb, and underneath the fron- dendrites from the secondary olfactory neuron at the tal lobe, draw the olfactory tract. Th en, within the olfac- glomerular layer of the olfactory bulb. Other constitu- tory epithelium, draw a bipolar primary olfactory neuron ents of the olfactory epithelium include the sustentacular and show that its centrally mediated axon, the olfactory cells, which are olfactory supporting cells; the basal cells, nerve, extends through the cribriform plate to innervate which renew the primary olfactory neurons and susten- the olfactory bulb. Note that this is the extent of cranial tacular cells; and the Bowman’s glands, which secrete a nerve 1, the olfactory nerve. Th e olfactory bulb and tract serous, watery fl uid that serves as an odor dissolvent.18 are telencephalic extensions of the cerebrum, itself. Next, Now, within the olfactory bulb, draw a representative within the olfactory bulb, draw a bipolar secondary bipolar secondary olfactory neuron. Two principal forms olfactory cell, and show that it connects with the olfac- of secondary olfactory neuron exist: tuft ed cells and mitral tory nerve in the inferior olfactory bulb and also sends cells; less notable interneurons (eg, periglomerular and an axon down the olfactory tract. Th en, at the posterior granule cells) also exist within the olfactory bulb. Indicate end of the olfactory tract, at the olfactory trigone, show that dendrites from the secondary olfactory neurons com- that the olfactory tract divides into a medial olfactory municate with the primary olfactory axons within the stria, which innervates the medial olfactory area in the inferior olfactory bulb. Th ese nerve processes intermingle subcallosal (aka septal) region, and a lateral olfactory within spherical glomeruli— thus, this layer is called the stria, which innervates the primary olfactory cortex in glomerular layer. Lastly, show that the secondary olfac- the basal frontal and anteromedial temporal lobes. Note tory neurons project axons that travel either directly down that (as we will draw later) olfactory impulses also extend the olfactory tract to synapse in the olfactory cortex or across the anterior commissure to the opposite side of fi rst to the anterior olfactory nucleus, which then projects the cerebrum.14 – 17 down the olfactory tract to the olfactory cortex.10 , 14 , 17 , 18 21. Limbic and Olfactory Systems 371

OLFACTORY SYSTEM SAGITTAL VIEW Secondary Medial olfactory olfactory cell area Olfactory Olfactory bulb tract Olfactory Cribriform trigone plate Olfactory Lateral olfactory Primary epithelium Primary olfactory stria olfactory neuron cortex

Secondary olfactory cell (tufted & mitral cells) EXPANDED VIEW Glomerulus Cribriform plate Anterior olfactory nucleus Primary olfactory Mucus layer neuron

DRAWING 21-5 Olfactory System, Part 1 372 Neuroanatomy: Draw It to Know It

Olfactory System, Part 2 (Advanced )

Next, let’s show the fl ow of olfactory information from innervated by a third, not yet introduced, olfactory stria: the olfactory bulb to the olfactory cortex. Note that this the intermediate olfactory stria. Th e existence and sig- fl ow of information is actually bidirectional, although nifi cance of the intermediate stria in humans is contro- we show it one direction, only, here. Also, note that the versial. Next, return to the olfactory tract and show that olfactory system bypasses the thalamus in its projection the anterior olfactory nucleus lies along its anteroposte- to the cerebral cortex, which is unique. Consider that rior length. Th e anterior olfactory nucleus has cortical auditory, visual, somatosensory, and gustatory sensory cytoarchitecture and, thus, is oft en referred to as the pathways all relay within the thalamus prior to synapsing anterior olfactory cortex, and it is commonly considered in the cerebral cortex. Draw an inferior view of the fron- to be part of the primary olfactory cortex (see Drawing tal and anterior-temporal lobes and, for anatomic refer- 21-8 ). 8 , 21 , 22 ence, include the optic chiasm, pituitary stalk, and Finally, we’re ready to show the fl ow of information mammillary bodies. Also, in front of the optic chiasm, from the olfactory bulb to the primary olfactory cortex. draw the diagonal band of Broca, which is a prominent First, show an impulse pass from the olfactory bulb cholinergic gray and white matter structure (see Drawing down the olfactory tract into the lateral olfactory stria 21-7 ). Next, in the frontal lobes, draw the bilateral olfac- to the primary olfactory cortex. Note that we defi ne the tory bulbs and tracts, which lie within the olfactory sulci. structures of the primary olfactory cortex in Drawing Note that the olfactory bulb is oft en distinguished as the 21-8 . From the primary olfactory cortex, information main olfactory bulb because the majority of vertebrates projects to secondary olfactory regions, which include also have an accessory olfactory system. 19 , 20 H o w e v e r , t h e the orbitofrontal cortex, lateral hypothalamus, insula, role and existence of the accessory olfactory system (aka anterior hippocampus, and indusium griseum. Next, vomeronasal system) in humans is disputed. show an impulse pass from the anterior olfactory nucleus Now, show that at the olfactory trigone the olfactory down the ipsilateral olfactory tract to the ipsilateral tract splits into lateral and medial striae. Th e bilateral medial stria. Show that it decussates in the anterior medial striae communicate at the anterior commissure. commissure to the contralateral medial stria and that it In between the olfactory trigone and the diagonal band then passes anteriorly along the contralateral olfactory of Broca, label the anterior perforated substance; the tract to the olfactory bulb. Again, note that olfactory perforated appearance of this gross anatomic area gives it sensory impulses are bidirectional, which means that the its name. Next, indicate that behind the olfactory trig- olfactory cortex also communicates with the olfactory one, overlying the anterior perforated substance, is a gray bulb in a reciprocal manner to what we have drawn, matter structure called the olfactory tubercle, which is here. 16 , 17 21. Limbic and Olfactory Systems 373

OLFACTORY SYSTEM SAGITTAL VIEW Secondary Medial olfactory OLFACTORY SYSTEM olfactory cell area INFERIOR VIEW Medial Olfactory Olfactory olfactory stria bulb tract Olfactory Olfactory Cribriform trigone bulb plate Olfactory Olfactory Lateral tract olfactory Primary epithelium Primary olfactory stria olfactory Ant. olfactory neuron cortex nucleus Medial Olfactory olf. stria tubercle Secondary olfactory Lateral Ant. comm. cell (tufted & mitral cells) olf. stria EXPANDED VIEW Glomerulus Primary olfactory cortex Cribriform Diagonal plate Anterior band of Broca olfactory nucleus Anterior perforated substance Primary olfactory Mucus layer neuron

DRAWING 21-6 Olfactory System, Part 2 374 Neuroanatomy: Draw It to Know It

Olfactory Cortex & Basal Forebrain, Part 1

Here, we will draw two coronal sections through the Next, let’s complete the more posterior diagram: the basal frontal and medial temporal lobes to learn the one through the optic tract. In the middle of the dia- anatomy of the olfactory cortex and basal forebrain. gram, inferiorly, label the hypothalamus. Superiorly, in First, let’s establish the anteroposterior positions of our midline, label the septal nuclei and the bed nucleus of two coronal sections: indicate that one section lies along the stria terminalis below them. Next, in the basal fron- the plane of the optic chiasm, which is the more anterior tal lobe, lateral to the hypothalamus and beneath the diagram, and the other lies along the plane of the optic basal ganglia, label the substantia innominata. Above tract, just posterior to the plane of the optic chiasm. In the substantia innominata and below the basal ganglia, the optic chiasm diagram, draw the putamen, caudate, label the anterior commissure. Within the substantia and their ventral connection: the nucleus accumbens. innominata, label the basal nucleus of Meynert. Note Th en, label the intervening internal capsule. Also, for that the basal nucleus of Meynert is variably considered reference, include the frontal horn of the lateral ventricle to be either synonymous with the substantia innominata and the corpus callosum. In the optic tract diagram, or to reside within this “unnamed substance” as it is again draw the caudate and putamen, but here show that drawn, here. Th en, just below the anterior commissure, they are completely separated by the internal capsule label the ventral pallidum. Now, in the medial temporal (the nucleus accumbens lies anterior to this plane). Next, lobe, draw the amygdala, but show that in this more pos- medial to the putamen, draw the globus pallidus. Now, terior section, the amygdala extends to the surface of the again include the frontal horn of the lateral ventricle and temporal lobe. Again, divide the amygdala into cortico- the corpus callosum. Next, in each diagram, draw the medial and basolateral divisions. Finally, along the border of the basal frontal and medial temporal lobes medial rim of the temporal lobe, medial to the amygdala, and draw the inferior border of the insula. label the entorhinal cortex. Now, let’s complete the diagram through the optic Certain basal forebrain structures share important chiasm. First, for further reference, show that the medial cholinergic properties that are understood to play a sub- hypothalamus connects the optic chiasm to the basal stantive role in memory. Of the listed structures, those frontal lobe. Next, along the basal perimeter, from medial with the most notable cholinergic properties are the to lateral, label the subcallosal gyrus, olfactory tubercle, medial septal nuclei, the diagonal band of Broca, and the and piriform cortex. Th en, draw the periamygdaloid basal nucleus of Meynert. As a clinical corollary, acetyl- cortex in between the piriform cortex, laterally, and the cholinesterase inhibitors, which prevent the breakdown entorhinal cortex, medially. Now, in the center of the of acetylcholine, were developed to promote cholinergic medial temporal lobe, draw the amygdala; separate it health in the basal forebrain with the hope of slowing into corticomedial and basolateral divisions. Finally, in the progression of Alzheimer’s disease. 23 Unfortunately, between the subcallosal gyrus and the nucleus accum- although these medications are widely used, they have bens, label the diagonal band of Broca. limited clinical effi cacy.6 , 9 , 10 , 24 21. Limbic and Olfactory Systems 375

Internal Corpus callosum ANTERIORCorpus callosum POSTERIOR capsule Caudate Septal (head) Internal Caudate nuclei Frontal capsule (head) horn Putamen Bed nucleus Putamen Globus of stria Nucleus Diagonal band pallidus terminalis of Broca Piriform accumbens Basal nucleus Anterior commissureVentral pallidum cortex Subcallosal (of Meynert) Hypo- Periamygdaloid gyrus Substantia thalamus cortex Optic innominata chiasm Optic (Corticomedial) Medial (Corticomedial) Olfactory tract Amygdala hypothalamus Amygdala (Basolateral) tubercle (Basolateral) Entorhinal cortex Entorhinal cortex

DRAWING 21-7 Olfactory Cortex & Basal Forebrain, Part 1 376 Neuroanatomy: Draw It to Know It

Olfactory Cortex & Basal Forebrain, Part 2 (Advanced )

Now, let’s group the anatomic structures we have drawn Finally, let’s address the basal forebrain. Th e list of into olfactory and basal forebrain listings. Begin with structures that constitute the basal forebrain is inconsis- the olfactory cortex. Divide it into medial, intermediate, tently defi ned throughout the literature; therefore, and primary (or lateral) cortices, which are innervated here we will focus only on those structures that are nearly by the medial, intermediate, and lateral striae, respec- universally grouped within the basal forebrain and tively. Indicate that the medial olfactory cortex com- will disregard the less commonly affi liated structures. prises, most notably, the subcallosal and paraterminal Indicate that the following structures are commonly gyri, which are collectively referred to (in this context) considered part of the basal forebrain: the septal nuclei, as the medial olfactory area. Next, show that the inter- diagonal band of Broca, ventral pallidum, basal nucleus mediate stria terminates in the olfactory tubercle within of Meynert, substantia innominata, the corticomedial the anterior perforated substance, which makes the amygdala, and the extended amygdala, which refers to olfactory tubercle part of the intermediate olfactory those areas of the basal forebrain with prominent con- cortex. However, note that the olfactory tubercle is vari- nections to the corticomedial amygdala: most notably, ably considered part of the primary olfactory cortex, as the bed nucleus of the stria terminalis and the nucleus well. Now, show that the primary olfactory cortex com- accumbens. Note that the ventral pallidum and nucleus prises the piriform cortex, periamygdaloid cortex, corti- accumbens are alternatively (or additionally) categorized comedial amygdala, and a small portion of the entorhinal as part of the basal ganglia. Also note that the cortico- cortex, anteriorly. Note that as we discussed previously, medial amygdala is commonly organized along with the anterior olfactory nucleus is also variably listed as both the olfactory cortex and basal forebrain. And as a part of the primary olfactory cortex. Also, note that the fi nal note, consider that the piriform cortex in rats, the distinction between the primary and secondary olfac- animal model for olfaction, is extensive and functionally tory cortices is highly variable; as an example, certain important, but its size and signifi cance in humans texts include the entorhinal cortex as secondary olfac- remains to be determined.6 , 9 , 10 , 24 , 26 , 27 tory cortex rather than as primary cortex — many other discrepancies can also be found.8 , 14 , 25 21. Limbic and Olfactory Systems 377

OLFACTORY CORTEX BASAL FOREBRAIN MEDIAL PRIMARY (or LATERAL) septal nuclei subcallosal gyrus piriform cortex diagonal band of Broca paraterminal gyrus periamygdaloid cortex ventral pallidum corticomedial amygdala basal nucleus (of Meynert) INTERMEDIATE entorhinal cortex substantia innominata olfactory tubercle anterior olfactory nucleus (not shown) corticomedial amygdala extended amygdala bed nucleus stria terminalis nucleus accumbens

DRAWING 21-8 Olfactory Cortex & Basal Forebrain, Part 2 378 Neuroanatomy: Draw It to Know It

References 1 . Psarros , T. G. & Moore , S. P. Intensive neurosurgery board review: 14 . Binder , D. K. , Sonne , D. C. & Fischbein , N. J. Cranial nerves: neurological surgery Q & A, p. 37 (Lippincott Williams & Wilkins, anatomy, pathology, imaging, Chapter 1 ( Th ieme, 2010 ). 2006 ). 15 . Brazis , P. W. , Masdeu , J. C. & Biller , J. Localization in clinical 2 . R a m a m u r t i, R . Textbooks of operative neurosurgery, Vol. 1 , p. 635 neurology, 6th ed., p. 163 (Wolters Kluwer Health/Lippincott (BI Publications Pvt. Ltd., 2005 ). Williams & Wilkins , 2011 ). 3 . B r o d a l, P. Th e central nervous system: structure and function, 4th ed., 1 6. M i l l e r, J . H . Eighty Years Behind the Masts, p. 106 (AuthorHouse , Chapter 31 ( Oxford University Press , 2010 ). 2011 ). 4 . To n k o n o g ii , I . M . & P u e n t e, A . E . Localization of clinical syndromes 17 . Wilson-Pauwels , L. Cranial nerves: function and dysfunction, in neuropsychology and neuroscience, p. 592 (Springer Pub., 2009 ). 3rd ed., Chapter 1 (People’s Medical Pub. House, 2010 ). 5 . Ts o k o s, M . Forensic pathology reviews, Vol. 5 (Humana Press, 2008 ). 18 . Young , B. & Wheater , P. R. Wheater’s functional histology: a text 6 . Mai , J. K., Voss , T. & Paxinos , G. Atlas of the human brain, 3rd ed. and colour atlas, 5th ed., p. 401 (Churchill Livingstone Elsevier, ( Elsevier/Academic Press , 2008 ). 2006 ). 7 . D u v e r n o y, H . M . & C a t t i n, F. Th e human hippocampus: functional 19 . Davis , S. F. & Buskist , W. 21st century psychology: a reference anatomy, vascularization and serial sections with MRI, 3rd ed. handbook, p. 222 (SAGE Publications, 2008 ). (Springer , 2005 ). 2 0. Å g m o, A . Functional and dysfunctional sexual behavior: a synthesis of 8 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and neuroscience and comparative psychology. 1st ed., pp. 105 – 108 atlas, 2nd ed., Chapter 21 ( Lange Medical Books/McGraw-Hill , ( Elsevier/Academic Press , 2007 ). 2005 ). 21 . Shepherd , G. M. Th e synaptic organization of the brain, 5th ed., 9 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human p. 416 ( Oxford University Press , 2004 ). brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal 22 . Gazzaniga , M. S. Th e cognitive neurosciences, 3rd ed., p. 263 structure, vascularization and 3D sectional anatomy (S p r i n g e r, (MIT Press, 2004 ). 2009 ). 23 . Papanicolaou , A. C. & Billingsley-Marshall , R. Th e amnesias: a 1 0. N i e u w e n h u y s, R ., Vo o g d, J . & H u i j z e n, C . V. Th e human central clinical textbook of memory disorders, pp. 45 – 47 ( Oxford University nervous system, 4th ed. (Springer , 2008 ). Press, 2006 ). 1 1. S a l e e m, K . S . A combined MRI and histology atlas of the rhesus 24 . Federative Committee on Anatomical Terminology . Terminologia monkey brain in stereotaxic coordinates, pp. 13 – 16 (Elsevier Ltd., anatomica: international anatomical terminology (Th ieme, 1998 ). 2007 ). 2 5. A n d r e w J o h n Ta y l o r, D . D . R . Flavor perception, pp. 212 – 214 12 . Andersen , P. Th e hippocampus book, Chapter 2 (Oxford University (Blackwell Publishing Ltd., 2004 ). Press, 2007 ). 26 . Heilman , K. M. & Valenstein , E. Clinical neuropsychology, 4th ed., 13 . Burwell , R. D. & Agster , K. L. Anatomy of the hippocampus and the p. 533 ( Oxford University Press , 2003 ). declarative memory system . Chapter 10 in Concise learning and 2 7. B r u n i, J . E . & M o n t e m u r r o, D . G . Human neuroanatomy: a text, memory: the editor’s selection ( e d J o h n H . B y r n e) (E l s e v i e r L t d ., brain atlas, and laboratory dissection guide ( Oxford University Press , 2009 ). 2009 ). 2 2 Vision

The Eye

The Retina ( Advanced )

Visual Pathways: Axial View

Visual Pathways: Sagittal View

Visual Field Deﬁ cits

Cortical Visual Processing (Advanced) 380 Neuroanatomy: Draw It to Know It

Know-It Points

The Eye

■ Th e outer layer comprises the cornea and the sclera. ■ Th e vitreous chamber contains vitreous humor, ■ Th e middle layer comprises the iris, choroid, and which helps maintain the eye’s shape. ciliary body. ■ Th e retina transitions into optic nerve where it exits ■ Th e inner layer is the retina and, from inner to outer, the eye, posteriorly, at the lamina cribrosa. lies the nerve fi ber layer, the synaptic and cell body ■ In the center of the optic nerve head sits the optic layers, and the photoreceptor cell segment layer (the cup: a white-appearing hole through which the rods and cones). central retinal vessels (artery and vein) emanate. ■ Th e lens is transparent and focuses a target on the ■ Th e optic disc is the pink-colored ring of nerve tissue retina. that surrounds the optic cup. ■ During near accommodation, the ciliary bodies ■ Impaired axoplasmic transport at the lamina cribrosa contract (ie, shorten), which relaxes the zonule and results in optic disc swelling (disc edema). rounds the lens (ie, thickens it), and the near object is ■ Th e fovea lies in the center of the retina and is the brought into focus. area of highest visual acuity. ■ Ciliary epithelia actively secrete aqueous humor, ■ Th e optic nerve head corresponds to the blind spot. which is reabsorbed at the iridocorneal fi ltration angle into the canal of Schlemm.

Visual Pathways: Axial View

■ Th e right visual fi eld projects to the temporal left ■ Th e left lateral geniculate nucleus sends optic hemiretina and the nasal right hemiretina. radiations to the left occipital cortex. ■ Th e left temporal hemiretina projects ipsilaterally to ■ Th e optic projections between the retina and the the left lateral geniculate nucleus. optic chiasm are the optic nerve. ■ Th e right nasal hemiretina sends crossing fi bers ■ Th e projections between the optic chiasm and the through the optic chiasm to the contralateral lateral lateral geniculate nucleus are the optic tract. geniculate nucleus (the left lateral geniculate nucleus).

Visual Pathways: Sagittal View

■ Th e superior visual world projects to the inferior ■ Th e inferior optic radiation bundle projects to the portion of the retina. inferior primary visual cortex. ■ Th e inferior visual world projects to the superior ■ Injury to an optic radiation disrupts visual perception portion of the retina. of a single visual quadrant, called quadrantanopia. ■ Central vision comprises the majority of the lateral ■ Cortical representation of central (or macular) vision geniculate body and lies posterior. lies in the posterior calcarine sulcus and occupies a ■ Peripheral vision comprises the minority of the lateral large cortical area relative to its small retinal expanse. geniculate body and lies anterior. ■ Cortical representation of peripheral vision lies in the ■ Th e superior optic radiation bundle projects to the anterior calcarine sulcus and encompasses a small superior primary visual cortex. cortical area relative to its broad retinal expanse. 22. Vision 381

Cortical Visual Processing

■ Th e ventral stream comprises the “what,” object ■ Th e lateral occipital complex responds recognition pathway (or P pathway). disproportionately strongly for object recognition ■ Th e dorsal stream comprises the “where,” spatial and displays perceptual constancy. localization (or M pathway). ■ Th e fusiform face area is the most well-studied area ■ Th e cone photoreceptors are responsible for color for facial processing. detection and excite parvocellular ganglion cells of ■ Non-face body parts are processed separate from the “what” pathway. faces: most notably, in the extrastriate body area in ■ Th e rod photoreceptors are responsible for motion the lateral occipitotemporal cortex. detection and excite magnocellular ganglion cells of ■ Th e parahippocampal place area processes places: the “where” pathway. environmental scenes and buildings. ■ Th e primary visual cortex in each hemisphere ■ Th e motion-processing center lies at the occipital- encodes the visual fi eld from the opposite half of the temporal-parietal junction. world. ■ Th e parietal lobes contain numerous visual cortical ■ Th e secondary visual cortex processes illusory areas dedicated to the processing of spatial awareness, boundaries: contours that cannot actually be collectively called the “parietal dorsal stream area,” visualized but that are implied by the context of a which comprises the “where” pathway. larger scene. ■ High-level processing of vision allows for the ■ Area V4 is the color processing area; it demonstrates preservation of depth perception in the setting of color constancy. monocular (one-eye) vision. 382 Neuroanatomy: Draw It to Know It

The Eye

Here, we will draw the eye. First, we will draw the outer sphincter muscles contract and constrict pupil size; and middle layers of the eye and then we will draw the whereas, in darkness, sympathetically innervated, radi- inner layer of the eye — the retina. Begin with the cornea, ally arranged, pupillary dilator muscles activate and which is the anterior portion of the eye’s outer layer. Th e widen pupil size (also, see Drawing 23-6). cornea is avascular and transparent to optimize the pas- Lateral to the iris, draw the ciliary body, and posterior sage of light. Its contour, smoothness, transparency, and to it, draw the choroid. Indicate that these three struc- refractive index all play an important role in focusing tures form the middle layer of the eye, called the uvea. light on the retina, and they all demand a healthy Th e choroid is a thin, brown, highly vascular layer sand- endothelium and epithelium. wiched between the sclera and retina; it nourishes the Next, show that where the cornea ends, the outer layer retina and removes heat produced during phototrans- becomes the sclera. In contrast to the cornea, the sclera is duction, which is the process wherein the photorecep- opaque and blocks the transmission of light. We refer to tors transform light into neural signal. the portion of the sclera we can see as the “white of the Th e functions of the ciliary body are twofold. First, eye”; conjunctiva covers it. Posterior to the conjunctiva, show that it anchors suspensory ligaments, collectively the six extraocular muscles insert into the sclera. Note called zonule, which stretch the lens and alter its refrac- that both the cornea and sclera comprise a fi brous histol- tive power. As mentioned, the refraction of light adjusts ogy that gives the outer eye a semi-elasticity and high where a visual object falls on the retina, and the adjust- tensile strength to allow it to endure the extraocular ment for near or far objects is called accommodation. muscle forces placed upon it and to protect the eye from Accommodation for near objects occurs from relaxation physical harm. of the zonule. During far vision, the ciliary bodies are Now, draw the biconvex lens. Like the cornea, the lens relaxed, the zonule are stretched, and the lens is fl at- is transparent and serves to focus a target on the retina. tened. During near accommodation, the ciliary bodies Th e cornea and lens bend the target’s light rays so that contract (ie, shorten), which relaxes the zonule and they strike the retinal area of maximal visual acuity: the rounds the lens (ie, thickens it), and the near object is fovea. Th is light ray manipulation is called optic refrac- brought into focus. tion. Unfortunately, opacities, called cataracts, commonly To demonstrate this principle for yourself, do the fol- develop in the lens and produce hazy vision, reduced color lowing. Extend your right index fi nger to represent a intensity, increased glare, and worsened visual acuity. relaxed ciliary body. Th en make a V with your left hand’s In front of the lens, draw the iris, and show it in coro- thumb and index fi nger and touch their tips to the ends nal view, as well. Indicate that the open region within the of the relaxed ciliary body. Th e V represents the taut center of the iris is the pupil. Th e pigmented epithelium zonular fi bers. Imagine that your left hand is the lens; of the iris blocks light transmission and funnels light feel the pull of the zonule on your left hand and imagine through the pupil. Th e iris forms an adjustable dia- the lens being fl attened. Th en, contract the ciliary body phragm that opens and closes based on the illumination (ie, collapse your stretched right index fi nger); the zonule demands of the eye. In bright light, show that parasym- fold in on themselves, which causes your left hand to pathetically innervated, circumferentially arranged, iris relax, and you can imagine the lens rounding. 22. Vision 383

Coronal view Dilator m. Outer layer Iris Cornea (transparent) Pupil Cornea Sclera (opaque) Iris Ciliary body Sclera Middle layer (uvea) Sphincter m. Pupil Zonule Choroid Iris Ciliary body Lens Choroid

DRAWING 22-1 Th e Eye— Partial 384 Neuroanatomy: Draw It to Know It

The Eye (Cont.)

In addition to being an anchor for the zonule, the ciliary reduce aqueous humor production or promote aqueous bodies also produce aqueous humor, which is a low- humor reabsorption. protein, aqueous (ie, watery) fl uid. Show that the ciliary Next, draw the vitreous chamber, which contains vit- epithelia actively secrete aqueous humor into the poste- reous humor. Like aqueous humor, vitreous humor is rior chamber (the space between the lens and iris) and primarily water, but the presence of glycosaminoglycans show that the aqueous humor then fl ows through the and collagen within this substance gives it its gel-like pupil into the anterior chamber (the space between the composition, which helps maintain the eye’s shape. 1 – 3 iris and cornea), and fi nally show that the aqueous humor Now, draw the retina internal to the choroid. We will is then reabsorbed at the iridocorneal fi ltration angle parse the retina into its specifi c layers later, but fi rst let’s through the trabecular meshwork into the canal of draw the optic nerve. Indicate that the retina transitions Schlemm. Th e trabecular meshwork and canal of Schlemm into optic nerve where it exits the eye, posteriorly, at the (along with the scleral spur) lie within the internal scleral lamina cribrosa, which is an opening in the sclera. Next, sulcus, which sits at the inner surface of the sclera–corneal indicate that in the center of the optic nerve lie the cen- junction, called the limbus. Th e trabecular meshwork tral retinal artery and vein. Now, label the optic nerve gates the reabsorption of aqueous humor through the head and draw a coronal view of it. Indicate that in the canal of Schlemm, which drains directly into the venous center of the optic nerve head sits the optic cup, a white- system. Note that an alternative reabsorption pathway appearing hole through which the central retinal vessels also exists in which aqueous humor is directly reabsorbed emanate. Next, label the optic disc, the pink-colored through the ciliary body into the uveal vessels. ring of nerve tissue that surrounds the optic cup. Th en, Pathology in the aqueous system produces increased back in our main diagram show that the subarachnoid intraocular pressure, called glaucoma. Although there space and dura mater, which is an extension of the are many causes of glaucoma, glaucoma is commonly sclera, extend along the optic nerve. Th e presence of the divided into two forms: open-angle (i.e., wide-angle) subarachnoid space, here, allows increased intracranial and angle-closure (i.e., narrow-angle) glaucoma. In open- pressure to translate along the optic nerve and impair angle glaucoma, the more common form, there is failure its axoplasmic transport. Impaired axoplasmic transport of adequate aqueous reabsorption through the canal of at the lamina cribrosa results in optic disc swelling, Schlemm, most commonly due to aberrancy in the tra- which is called disc edema or, rather, papilledema when becular meshwork, itself. In angle-closure glaucoma, the it occurs in the setting of increased intracranial pressure. rarer form, there is apposition of key anterior structures, Papilledema causes disc margin blurring (i.e., blurring of which trap the fl ow of aqueous humor. For instance, the nerve layer around the disc), venous congestion, and there is abutment of the iris and cornea or lens and iris. optic disc hyperemia from capillary dilatation secondary Common pharmacologic therapies for glaucoma either to reduced venous return. 22. Vision 385

Coronal view Dilator m. Trabecular meshwork & Outer layer Iris Canal of Schlemm Cornea (transparent) Pupil Cornea Anterior Sclera (opaque) chamber Iris Ciliary body Sclera Middle layer (uvea) Sphincter m. Pupil Zonule Choroid Iris Ciliary body Posterior Retina Lens Choroid chamber

Vitreous chamber

Coronal view Cup optic n. head Disc Optic n. head Dura mater Sub. arach.

Optic nerve at lamina Central retinal cribrosa artery and vein

DRAWING 22-2 Th e Eye— Partial 386 Neuroanatomy: Draw It to Know It

The Eye (Cont.)

Now, we will address the specifi c layers of the retina, dis- of light: the nerve fi bers become myelinated only aft er cuss the passage of light through the retina, and discuss they exit the eye as the optic nerve. Note that the pig- the transformation of light into neural signal, called mented epithelium captures light not picked up by the phototransduction. By convention, the retina contains photoreceptors and that the photoreceptor cell seg- ten distinct layers, which are reviewed in detail in ments are metabolically dependent upon the pigmented Drawing 22-4 ; here, we will simply group the retinal epithelium for photoreceptor regeneration and waste layers into four diff erent functional layers and skip the disposal. retinal membranes. First, let’s orient ourselves: indicate Finally, show that the fovea lies in the center of the that internal to the retina lies the vitreous chamber, and retina. Draw the center of the fovea as a pin-sized depres- external to it lies the choroid. Next, label the innermost sion; in this central pit, the ganglion and bipolar cells are retinal layer as the nerve fi ber layer; then, label the pushed aside so as not to impede the path of light rays to surrounding layers as the synaptic and cell body layers; the photoreceptor layer. Th is unimpeded path, in com- then, label the surrounding layer as the photoreceptor bination with the pure cone composition of the central cell segment layer (the rods and cones); and fi nally, label foveal photoreceptor layer, makes the center of the fovea the outermost layer as the retinal pigmented epithelium. the area of highest visual acuity. Note that in contrast, Indicate that light passes through the retina and is the optic nerve head is devoid of photoreceptors and we captured by the photoreceptor cell segments. Show do not perceive the visual region that corresponds to the that the phototransduction cascade occurs, here, which optic nerve: it forms the blind spot. As a corollary, when transforms light into neural signal, and indicate that disc edema occurs (ie, when the optic nerve head swells), the signal is passed back through the retina and passed the blind spot enlarges. Enlarged blind spots are com- out of the eye through the optic nerve. Th e nerve fi ber monly observed in the clinical syndrome of idiopathic layer is unmyelinated to avoid blocking the passage intracranial hypertension (aka pseudotumor cerebri). 22. Vision 387

Vitreous chamber

Coronal view Cup optic n. head Disc Light Optic n. perception Signal exit Inner (Vitreous) head Dura mater Retina layers: Sub. arach. Nerve fiber layer Synapses and cell bodies Signal Photoreceptor cell segments transduction Fovea Optic nerve Pigmented epithelium at lamina Central retinal cribrosa Outer (Choroid) artery and vein

DRAWING 22-3 Th e Eye— Complete 388 Neuroanatomy: Draw It to Know It

The Retina (Advanced )

Here, let’s address the organization of the ten distinct Next, show that the ganglion cell layer contains ganglion layers of the retina in further detail. Label the top of the cell bodies, the axons of which form the nerve fi ber layer. page as internal to the retina (the vitreous chamber) and Th en, indicate that the plexiform layers are synaptic zones: the bottom of the page as external to it (the choroid). the inner plexiform layer is relatively thick whereas the From inner to outer, the retinal layers are the inner limit- outer plexiform layer is much thinner. Now, show that the ing membrane; nerve fi ber layer; ganglion cell layer; nuclear layers contain cell bodies: the inner nuclear layer inner plexiform layer; inner nuclear layer; outer plexi- comprises retinal interneuronal cell bodies and the outer form layer; outer nuclear layer; outer limiting mem- nuclear layer comprises photoreceptor cell bodies. brane; photoreceptor cell segment layer; and retinal Lastly, let’s further defi ne the fi ve neuronal cell types pigmented epithelium. that exist within the retina. Th e outermost cells are the Once again, indicate that light passes through the rods and cones, which are the photoreceptor cells, and retina and is captured by the photoreceptor cell seg- the innermost cells are the ganglion cells, whose unmy- ments. Show that the phototransduction cascade occurs elinated axons form the nerve fi ber layer. Sandwiched in here, which transforms light into neural signal, and indi- between the photoreceptor cells and ganglion cells are cate that the signal is passed back through the retina and the bipolar cells, which pass forward visual information passed out of the eye through the optic nerve. Note that from the photoreceptor cells to the ganglion cells, and the photoreceptor cell segments are metabolically depen- also the horizontal and amacrine cells, which enhance dent upon the pigmented epithelium. visual contrast. It is well recognized that the visual system Indicate that the inner limiting membrane is a thin, relies more on visual contrast than the overall level of basal lamina that separates the nerve fi ber layer from the illumination for visual perception: Th e visual system vitreous chamber and that the outer limiting membrane attends to the borders between light and dark areas or is a row of intercellular junctions that separates the pho- color diff erences more so than light intensity. As long as toreceptor cell segments from the outer nuclear layer. we can read the page of a book comfortably, we perceive Müller glial cells extend across the retina: their proximal the words on it just the same in varying levels of illumi- endings oppose the inner limiting membrane and their nation; it is the contrast of the ink from the page that distal processes help form the outer limiting membrane. makes the largest impression in our mind. 22. Vision 389

Inner (Vitreous) Light perception Retinal layers: Structure/function: Signal exit Inner limiting membrane Thin, basal lamina through the optic nerve Nerve fiber layer Axons of ganglion cells

Ganglion cell layer Ganglion cell bodies

Inner plexiform layer Thick synaptic zone

Inner nuclear layer Retinal interneuronal cell bodies

Outer plexiform layer Thin synaptic zone

Outer nuclear layer Photoreceptor cell bodies

Outer limiting membrane Row of intercellular junctions

Photoreceptor cell segment layer Light capture & phototransduction

Retinal pigmented epithelium Photoreceptor metabolism

Outer (Choroid)

DRAWING 22-4 Th e R e t i n a 390 Neuroanatomy: Draw It to Know It

Visual Pathways: Axial View

Here, we will draw an axial view of the visual pathways the left visual cortex receives the right visual fi eld and from the retinae to the occipital cortices. We will show that the right visual cortex receives the left visual fi eld. only the right visual fi eld projection to the left visual Now, show that the left temporal hemiretina projects cortex for simplicity— the left visual fi eld projects to the ipsilaterally to the left lateral geniculate nucleus, and right visual cortex in mirror-image fashion. First, let’s then, show that the right nasal hemiretina sends crossing address the visual fi elds: the visual fi elds represent the fi bers through the optic chiasm to the contralateral lat- person’s view of the world. Draw axial sections through eral geniculate nucleus (the left lateral geniculate the left and right eyes and draw projections from central nucleus). Finally, show that the left lateral geniculate vision to the fovea of each eye. Using the fovea as the nucleus sends optic radiations to the left occipital cortex. midpoint of the retina, subdivide the retinae into nasal We have now completed the path from the right visual and temporal hemiretinae. Now, we are ready to march fi eld to the left visual cortex. through the optic projections from the right visual fi eld Next, let’s defi ne the optic nerve and optic tract. to the left visual cortex. Encircle the optic projection between the retina and First, show that the right visual fi eld projects to the the chiasm and label it as the optic nerve, and encircle temporal left hemiretina and the nasal right hemiretina. the projection between the optic chiasm and the lateral Next, let’s establish the key structures along the path of geniculate nucleus and label it as the optic tract. Optic the optic projections. Draw the optic chiasm, the lateral nerve injuries are prechiasmatic and optic tract injuries geniculate nuclei, and the visual cortices. Indicate that are postchiasmatic.

Optic nerve (CN II)

Temporal pole Olfactory tract Anterior commissure

Optic chiasma Optic tract

Crus cerebri Lateral geniculate nucleus

Medial geniculate nucleus

Optic radiations

Primary visual area (occipital lobe)

FIGURE 22-1 Axial view of optic pathway. Used with permission from Bruni, J. E. & Montemurro, D. G. Human Neuroanatomy: A Text, Brain Atlas, and Laboratory Dissection Guide. New York: Oxford University Press, 2009. 22. Vision 391

Left visual field Central vision Right visual field

Temporal hemiretina Temporal hemiretina

Left eye’s fovea Nasal hemiretina Nasal hemiretina Right eye’s fovea Optic nerve Optic nerve

Optic chiasm

Optic tract

Left lateral Right lateral geniculate geniculate nucleus nucleus

Optic Left primary Right primary radiations visual cortex visual cortex (right visual field) (left visual field)

DRAWING 22-5 Visual Pathways: Axial View 392 Neuroanatomy: Draw It to Know It

Visual Pathways: Sagittal View

Here, we will draw the visual pathways in sagittal view. Lastly, draw an enlarged retinotopic map of the pri- First, draw a sagittal view of a cerebral hemisphere and mary visual cortex. Indicate that the cortical representa- include an eye. Indicate that the superior visual world tion of central (or macular) vision lies in the posterior projects to the inferior portion of the retina and that the calcarine sulcus and occupies a large cortical area relative inferior visual world projects to the superior portion of to its small retinal expanse, whereas representation of the retina. Next, show that the retina projects to the lateral peripheral vision lies in the anterior calcarine sulcus and geniculate nucleus. Th en, indicate that the stretch of the encompasses a small cortical area relative to its broad pathway anterior to the optic chiasm is optic nerve, and retinal expanse. Visual cortex is also called “calcarine the stretch posterior to the optic chiasm is optic tract. cortex” because it lies within the dorsal and ventral banks Now, draw an enlarged retinotopic map of the lateral of the calcarine sulcus, which separates the cuneus from geniculate body. Indicate that central vision comprises the lingual gyrus. Th e upper bank of the calcarine sulcus the majority of the lateral geniculate body and lies encodes the lower half of the visual fi elds whereas the posterior, whereas peripheral vision localizes within the lower bank encodes the upper half of the visual fi elds. most anterior portion of the lateral geniculate body. Now, let’s address the neuroscience of the lateral Next, let’s draw the optic radiations. First, defi ne the geniculate body. Th e lateral geniculate body has both occipital horn of the lateral ventricle and show that the parvocellular and magnocellular components and also superior optic radiation bundle, which carries superior koniocellular components; we will address only the par- retinal input (from the inferior visual world), projects vocellular and magnocellular components, here, because along the occipital horn through the superior temporal the koniocellular components are less well understood. and inferior parietal lobes and terminates in the superior Layers 3 through 6, the most posterior layers, are parvo- primary visual cortex. Th en, defi ne the temporal horn cellular, whereas layers 1 and 2, the most anterior layers, of the lateral ventricle and show that the inferior optic are magnocellular. Th e parvocellular layers receive input radiation bundle, which carries inferior retinal input from the cone layers of the retina and the magnocellular (from the superior visual world), fans out in Meyer’s layers receive input from the rod layers. Cones lie within loop over the temporal horn and projects back the central retina (the macula) and communicate with X through the inferior temporal lobe to the inferior pri- retinal ganglion cells called midget cells, which have mary visual cortex. Injury to the inferior bundle is small fi elds and are responsible for visual acuity and color more common than to the superior bundle, so superior vision. Rods lie in the periphery of the retina and com- visual fi eld defects are more common than inferior fi eld municate with Y retinal ganglion cells called parasol defects. Injury to one optic radiation or the other is cells, which have large fi elds and are sensitive to motion. called quadrantanopia because it results in injury to a Th us, because the X and Y division of the retinal gan- single visual quadrant with preservation of the other glion output cells is preserved within the lateral genicu- three quadrants. For instance, a lesion to the left infe- late nucleus as parvocellular and magnocellular regions, rior radiation will aff ect vision from the right, superior respectively, the X and Y ganglion cells are synonymously visual quadrant, only. Th e anterior extent of the inferior referred to as P (for parvocellular) and M (for magnocel- optic radiation is important because surgeons must be lular) cells, respectively. Note, however, that the X-Y mindful of the optic radiations during anterior temporal and P-M comparison is imperfect—the diff erences are lobe resection. 4 beyond our scope, here. 4 – 11 22. Vision 393

Retinotopic organization of the lateral geniculate nucleus Magnocellular Parvocellular Layers1, 2 Layers 3 - 6 (Peripheral) (Central) Rods Cones Y (parasol) cells X (midget) cells Superior radiation (superior retinal image) Occipital horn Optic Lateral geniculate Optic tract nucleus Superior chiasm Superior Optic retina Inferior radiation primary visual cortex visual nerve (inferior retinal image) world Meyer’s Temporal Inferior loop visual horn world Inferior retina Retinotopic organization of the primary visual cortex Peripheral Central

DRAWING 22-6 Visual Pathways: Sagittal View 394 Neuroanatomy: Draw It to Know It

Visual Field Deﬁ cits

Here, we will learn the diff erent visual fi eld defi cits. and the primary visual cortices. Next add the path- First, let’s set up our axial diagram of the visual pathways. On the right-hand side of the page, for each case, ways. Label the left and right visual fi elds, then draw we will draw a pair of eyes with their left and right visual the eyes, the optic chiasm, the lateral geniculate nuclei, fi elds.

Case I Patient presents with loss of vision in the left eye. Exam lesion, either in the optic nerve or in the retina, itself. We reveals absent vision in the left eye, only. Th e right eye is learn how to distinguish retinal and optic nerve lesions normal. later. Note that a relative aff erent pupillary defect would Our diagnosis is a left optic nerve lesion. Th e unilater- almost certainly accompany this optic nerve injury (see ality of the injury localizes the defi cit to a prechiasmatic Drawing 23-6).

Case II Patient presents with right eye loss of vision. Exam that the temporal retinal fi bers are selectively aff ected. reveals left visual fi eld loss in the right eye, only. Th e left Note that this pattern of injury could also occur along eye is normal. the optic nerve, but it is in the optic chiasm that the nasal Our diagnosis is a right lateral optic chiasm lesion. and temporal retinal fi bers split apart: this case high- Again, the defi cit is limited to one eye; therefore, the lights the separation of the nasal and temporal retinal injury is anterior to the optic tract. Th e defi cit is in the fi bers within the optic chiasm. visual fi eld contralateral to the aff ected eye, which means

Case III Patient presents with bilateral loss of vision. Exam reveals important exam fi nding because it oft en suggests the bitemporal hemianopia. presence of a sellar mass, such as a pituitary adenoma or Our diagnosis is an optic chiasm lesion. Th e optic craniopharyngioma. Oft en it is stated that this lesion chiasm contains crossing fi bers from the bilateral nasal produces a constriction of vision and a sensation of hemiretinae. Th e nasal hemiretinae receive the temporal “wearing horse blinders”; however, more accurately, visual fi elds, which means that the left nasal retina per- bitemporal hemianopia produces a loss of binocular ceives the left visual fi eld and the right nasal retina perfusion, which results in “hemifi eld slide.”12 ceives the right visual fi eld. Bitemporal hemianopia is an 22. Vision 395

Lateral geniculate Meyer’s nucleus loop

DRAWING 22-7 Visual Field Defi cits— Partial 396 Neuroanatomy: Draw It to Know It

Visual Field Deﬁ cits (Cont.)

Case IV Patient presents with diffi culty seeing the right half of right homonymous hemianopia. Th ese retinal fi bers the world, which is bilateral (both eyes aff ected). Exam fi rst bundle posterior to the optic chiasm within the reveals a right homonymous hemianopia: right visual optic tract; however, a lesion anywhere along the postfi eld blindness in both eyes. chiasmatic pathway— in the left optic tract, left lateral Our diagnosis is a lesion of the left postchiasmatic geniculate nucleus, left optic radiations, or left visual pathway. Disruption of fi bers from both the nasal right cortex — will produce the described right homonymous hemiretina and temporal left hemiretina produces a hemianopia.

Case V Patient presents with diffi culty seeing the right half of Th ese radiations maintain the same superior–inferior the world, which is bilateral (both eyes aff ected). Exam retinotopic organization found in the retina; therefore, reveals a right homonymous inferior quadrantanopia. a superior optic radiation lesion produces an inferior Our diagnosis is a left superior optic radiation lesion. fi eld defect. Th e hemianopia lateralizes to the right Th e lateral geniculate nucleus projects through supe- side, which means that the lesion is postchiasmatic on rior and inferior optic radiations to the visual cortex. the left .

Case VI Patient presents with diffi culty seeing the right half of the same superior–inferior retinotopic organization as the world, which is bilateral (both eyes aff ected). Exam found in the retina; therefore, an inferior radiation lesion reveals a right homonymous superior quadrantanopia. produces a superior fi eld defect. Also, as described previ- Our diagnosis is a left inferior optic radiation lesion. ously, the hemianopia lateralizes to the right side, so the As described in the previous case, projections from the lesion is postchiasmatic on the left . lateral geniculate nucleus to the visual cortex maintain

Case VII (Advanced ) Patient presents with diffi culty seeing the right half of which the middle cerebral artery supplies. Th erefore, in the world, which is bilateral (both eyes aff ected). Exam the setting of posterior cerebral artery infarction, the reveals a right homonymous hemianopia with preserved middle cerebral artery maintains perfusion of the occipi- central vision, called macular sparing. tal pole, which spares macular cortical representation. Our diagnosis is a left occipital lobe lesion. Our cur- Additionally, or alternatively, macular sparing is rent patient has a right homonymous hemianopia with argued to occur from redundant macular representation preserved central vision through sparing of left macular in both occipital cortices in much the same way that cortical representation. According to the vascular model auditory information is redundantly localized to both for macular sparing, the posterior cerebral artery sup- transverse temporal gyri (of Heschl).13 plies the occipital cortex except for the occipital pole, 22. Vision 397

Left visual field Right visual field LEFT EYE RIGHT EYE VISUAL FIELDS Left eye Central vision Right eye Left Right Left Right Tmprl Nsl Nsl Tmprl Optic 1. nerve Lateral 2. Optic nerve chiasm (1) Optic Optic chiasm (3) 3. Lateral chiasm chiasm (2) Post 4. Post- chiasm chiasm(4) Superior Lateral 5. geniculate radiation Meyer’s nucleus Inferior 6. loop Superior radiation (5) radiation Primary 7. visual Primary cortex Inferior visual radiation (6) cortex (7)

DRAWING 22-8 Visual Field Defi cits— Partial 398 Neuroanatomy: Draw It to Know It

Visual Field Deﬁ cits (Cont.)

Case VIII (Advanced ) Patient presents with blurry vision in the right eye. Exam following categories: central or cecocentral scotomas reveals a central scotoma in the right eye, only. from injury to the papillomacular bundle; arcuate fi eld Our diagnosis is a right-side retinal lesion, specifi - defects, which obey the horizontal meridian; and tem- cally a lesion within the macula. Th e restriction of poral wedge defects from nasal retinal wedge fi ber injury. the defi cit to one eye makes this a prechiasmatic lesion, We must appreciate, however, that a partial optic nerve localizing to either the retina or optic nerve. However, injury can potentially assume the same defi cit pattern as the limited pattern of visual fi eld defect allows us to any retinal layer injury, and we must go beyond visual further localize this as a retinal lesion (with the caveat fi eld testing to distinguish the localization of a prechias- noted at the end). Retinal lesions typically parse into the matic lesion.14

Case IX (Advanced ) Patient presents with bilateral visual loss. Exam reveals scotoma (aka anterior junction syndrome) and junc- a central scotoma on the right and a left superior tional scotoma of Traquair. Both forms of anterior junc- quadrantanopia. tional defect involve the ipsilateral optic nerve. Junctional Our diagnosis is a junctional scotoma. To understand scotoma results in an ipsilateral central scotoma (from the pathogenesis of junctional scotoma, show a fi ber subtotal involvement of the ipsilateral optic nerve) and project from the left nasal hemiretina through the optic contralateral superior temporal quadrantanopia from chiasm, and then bend anteriorly into the contralateral injury to the crossed inferonasal fi bers from the opposite optic nerve (the nerve on the right) before projecting eye. Whereas, junctional scotoma of Traquair is an ante- posteriorly into the right optic tract. Indicate that this rior junction injury with isolated ipsilateral optic nerve bend is called Wilbrand’s knee, and show that it carries defi cit and results in an ipsilateral temporal hemifi eld inferonasal fi bers. Wilbrand’s knee has actually been defect, only. 15 , 17 , 18 proven to be an artifact of pathologic processing and not Let’s not let the diff erences of the junctional scotoma a true anatomic entity; however, it is still commonly dis- and junctional scotoma of Traquair distract us from a cussed and still teaches us about the separation of the key similarity between the two. Both syndromes are inferior and superior nasal projections. Although the perichiasmatic, and yet they both can easily be mistaken bend into the optic nerve does not exist, the inferonasal for optic nerve lesions. Distinguishing perichiasmatic fi bers do collect in the anterior optic chiasm and the supe- from optic nerve lesions is important because perichias- ronasal fi bers do collect in the posterior optic chiasm. 15 , 16 matic lesions are almost universally secondary to para- Junctional scotoma is a lesion at the junction between sellar tumors or aneurysms, whereas optic nerve lesions the optic nerve and optic chiasm. Two forms of anterior occur from both compressive and also noncompressive junctional defect are commonly recognized: junctional causes. 15 , 17 , 18 22. Vision 399

Left visual field Right visual field LEFT EYE RIGHT EYE VISUAL FIELDS Left eye Central vision Right eye Left Right Left Right Tmprl Nsl Nsl Tmprl Optic 1. nerve Retina (8) Lateral 2. Optic nerve Anterior chiasm (1) junction (9) Optic Optic chiasm (3) 3. Lateral chiasm chiasm (2) Post 4. Post- Wilbrand’s knee chiasm chiasm(4) (inferonasal Lateral Superior fibers) 5. geniculate radiation Meyer’s nucleus Inferior 6. loop Superior radiation (5) radiation Primary 7. visual Primary cortex Inferior visual radiation (6) 8. Retina cortex (7) Anterior 9. junction

DRAWING 22-9 Visual Field Defi cits— Complete 400 Neuroanatomy: Draw It to Know It

Cortical Visual Processing (Advanced )

Here, we will create a diagram for the organization of the parahippocampal gyrus, medially, from the fusiform visual cortex. To create an overview of cortical visual gyrus, laterally); then, within the lateral hemisphere, processing, draw a lateral cerebral hemisphere. First, label the Sylvian fi ssure and the temporo-parietal- label the posterior, occipital region as the occipital area. occipital junction. Now, show that V1 (the primary In this region, initial cortical visual processing occurs. visual cortex) lies along the calcarine sulcus of the medial For our purposes, here, consider this region to encom- face of the occipital lobe, and also show that it lies at the pass the primary visual cortex (aka striate cortex) and very tip of the lateral occipital pole. Th e primary visual the secondary and tertiary visual cortices. Next, label cortex is known as V1 because visual cortical stimuli fi rst the inferior temporal lobe as the ventral stream and the collect in this area. V1 is oft en referred to by its Brodmann parietal lobe as the dorsal stream. Th e ventral stream designation — Brodmann area 17. Also, it is commonly comprises the “what,” object recognition pathway (or referred to as the striate cortex because of the heavy P pathway), and the dorsal stream comprises the “where,” myelination of its fourth cytoarchitectural layer, which spatial localization (or M pathway). Note that the divi- produces a white stripe called the stria of Gennari. sion between these pathways begins within the photore- Within layer 4, sublayer 4Ca is the primary recipient of ceptors of the retinae: the cone photoreceptors are magnocellular input and sublayer 4Cb is the primary responsible for color detection and excite parvocellular recipient of parvocellular input. Th e primary visual ganglion cells of the “what” pathway, and the rod photo- cortex processes the most basic visual properties: for receptors are responsible for motion detection and excite example, line orientation, motion direction, luminance magnocellular ganglion cells of the “where” pathway. orientation, and color. Th e primary visual cortex in each As visual information is fed forward within the cortex, hemisphere encodes the visual fi eld from the opposite the “what” and “where” properties of vision separate half of the world: right V1 encodes the left visual fi eld topographically into ventral and dorsal visual streams. and left V1 encodes the right visual fi eld. Th e cortical Within the ventral stream, components of objects are representation of central, or macular, vision lies in the integrated to allow for cohesive object identifi cation, posterior calcarine sulcus and occupies a large cortical and within the dorsal stream, numerous diff erent visu- area relative to its small retinal expanse, whereas repre- ospatial processing centers exist. To complete this over- sentation of the peripheral retina lies in the anterior view diagram, draw the frontal eye fi elds, which are calcarine sulcus and encompasses a small cortical area responsible for the cortical initiation of many diff erent relative to its broad retinal expanse. Th e upper bank of classes of eye movements. the calcarine sulcus encodes the lower half of the visual Next, let’s label the most well-studied cortical visual fi eld and the lower bank encodes the upper half of the areas. Draw the posterior aspect of the medial and lateral visual fi eld. Interestingly, patients with injury to area V1 hemispheres. Th en, draw the following anatomic land- oft en report having blindsight — an unconscious utiliza- marks. Within the medial hemisphere, draw the calcarine tion of visual information from the visual fi eld in which sulcus and then the collateral sulcus (which separates the they are blind. 19 – 24 22. Vision 401

Occipital area - V1 Primary visual cortex initial cortical processing (Primary processing) Frontal Dorsal Dorsal stream - eye fields stream “where” pathway Ventral stream Occipital Ventral stream - area “what” pathway Frontal eye fields - eye movements

Medial Lateral hemisphere hemisphere

Temporo-parieto- occipital junction

Sylvian Calcarine V1 fissure sulcus V1

Collateral V1 sulcus

DRAWING 22-10 Cortical Visual Processing— Partial 402 Neuroanatomy: Draw It to Know It

Cortical Visual Processing (Advanced ) (Cont.)

Next, let’s draw the secondary and tertiary visual corti- designating V4 as part of the ventral stream — the ventral ces. Secondary visual cortex is called V2 and corresponds stream is commonly considered to begin anterior to V4. to Brodmann area 18; tertiary visual cortex is called V3 On the medial and lateral surfaces of the cerebral hemi- and corresponds to Brodmann area 19. Indicate that on sphere, in the ventral-occipital lobe, label the region the medial face of the cerebral hemisphere, V2 lies above inferior to V3 as V4. Note that debate exists regarding and below V1, and V3 lies above and below V2. Note the anatomy of V4, and also note that an additional that the ventral part of V3 is commonly referred to as VP visual area separate from V4, called V8, has also been instead of V3 because controversy exists as to whether introduced into the literature; for this reason, the ven- the ventral part of V3 is a unique visual cortical area or tro-occipital region is oft en referred to as the V4/V8 whether the dorsal and ventral parts of V3 are both part region. Also, note that a similar term for V8 has been of a common visual cortical area. Also note that the introduced called VO, which stands for the “ventral dorsal and ventral parts of the visual cortices are oft en occipital” cluster. 19 – 24 denoted by the abbreviations “d” for dorsal and “v” for One important aspect of color processing found ventral; for instance, the ventral part of V2 is oft en within area V4 is that of color constancy, which is the denoted as “V2v.” Next, on the lateral surface of the property of color vision wherein regardless of the illumi- hemisphere, indicate that V2 comprises a small strip of nation cast on an object, the object maintains its per- the posterior occipital lobe, just anterior to V1; and then ceived color. It has been shown that a red patch will show that V3 lies in front of V2 — leave a small space maintain its perceived red color and a white patch will inferior to V3 for V4 (drawn next). Th e secondary and maintain its perceived white color even when the level tertiary visual cortices process simple visual properties illumination cast on the two diff erent colors is adjusted akin to those processed in V1; notably, however, V2 pro- so that they should be perceived as the same color. To cesses illusory boundaries, contours that cannot actually demonstrate this for yourself, consider the color of your be visualized but that are implied by the context of a pants. Now, look closely at them and see that your pants larger scene. Stand in the doorway with one half of are not a single color or even a discrete combination of your body in the room and the other half outside of view; colors but, instead, they comprise a vast array of colors no one will misperceive that only half of you exists. from the diff erent levels of illumination cast onto them— Th rough grouping principles of proximity, continuity, yet we are able to retain a uniform impression of our and similarity, we naturally incorporate the hidden half clothing color due to the high-level color vision process- of your body into our Gestalt— our general makeup of ing that occurs within area V4. As a clinical corollary for the world. We generate an illusory boundary of your color processing, before functional MRI studies could body based on the characteristics of you that we are able identify the ventral occipital cortical response to color to visualize.19 – 24 patterns, clinical-pathologic case studies demonstrated Now, let’s label the color-processing area V4, which, that ventral occipito-temporal injury caused abnormali- for practical purposes, can be considered a transitional ties in color processing, called achromatopsia, which zone in the visual pathway wherein the ventral stream results in the visual world appearing gray or drained of (the “what” pathway) begins to topographically sepa- color; note, however, that injury to area V4, alone, may rate from the dorsal stream; note that we take liberty in or may not be suffi cient to cause achromatopsia.25 22. Vision 403

Medial Lateral hemisphere hemisphere

Temporo-parieto- occipital junction V3 V2 Sylvian Calcarine V1 fissure sulcus V1 V2 V3 V3 V4 V2 V4 Collateral V1 sulcus

DRAWING 22-11 Cortical Visual Processing— Partial 404 Neuroanatomy: Draw It to Know It

Cortical Visual Processing (Advanced ) (Cont.)

Now, in the lateral hemisphere diagram, in the lateral perceived in the visual world, and they maintain this occipital cortex, anterior to V4, label the lateral occipital contiguous relationship when they are projected to the complex. Th is area responds disproportionately strongly primary visual cortex and, presumably, as they step for object recognition. It displays perceptual constancy, through the secondary and tertiary visual cortices. But meaning an object can be recognized equally well regard- for higher-level visual processing, at least in part, the less of such properties as object viewpoint, size, or illu- body is separated from the face and is processed near the mination; it also displays form-cue invariance, meaning, V5 motion-sensitive area (discussed next), presumably for example, that an object is equally identifi able whether because of the relationship between body parts and move- it is viewed in the form of a drawing or a photograph.26 ment. Note, however, that just as multiple centers for Next, label the fusiform face area within the right, lat- facial processing exist, so, too, multiple body part analysis eral posterior fusiform gyrus; the fusiform face area is centers also exist, such as the fusiform body area.22 , 28 the most well-studied area for facial processing, but Next, show that the processing of places lies within additional facial processing centers for diff erent attri- the parahippocampal place area, which lies within the butes of facial recognition do exist — they include the posterior parahippocampal and anterior lingual cortices. occipital face area as well as a region of the superior tem- Th e parahippocampal place area responds to environ- poral sulcus. Also, note that a longstanding debate is mental scenes and buildings. Injury to the parahip- whether the fusiform face area is specifi c for the recogni- pocampal place area can potentially cause landmark tion of human faces or whether it responds to any over- agnosia, which is the inability to recognize fundamental trained visual stimulus (eg, cars in car salesmen or birds navigation landmarks: for example, one’s own house. in bird-watchers). As a clinical corollary, injury to the Landmark agnosia is oft en categorized under the more fusiform face area can result in prosopagnosia: a defi cit broad clinical phenomenon of topographic disorienta- for the recognition of familiar faces (ie, friends and tion, which is the inability to fi nd one’s way through an family).27 environment, because patients with landmark agnosia Now, show that non-face body parts are processed naturally have substantial navigational disorientation. separate from faces, most notably, in the extrastriate Note, also, that the parahippocampal place area is body area in the lateral occipitotemporal cortex. When separate from the parietal dorsal stream area, which is we view a human fi gure, the person’s face and body responsible for encoding orientation of the body in are projected onto the retina contiguously, as they are space. 26 , 29 – 32 22. Vision 405

Occipital area - V1 Primary visual cortex initial cortical processing (Primary processing) Frontal Dorsal Dorsal stream - V2 Secondary visual cortex (Illusory boundary processing) eye fields stream “where” pathway Ventral V3 Tertiary visual cortex stream Occipital Ventral stream - area “what” pathway Frontal eye fields - V4 Color processing (eg, color constancy) eye movements LOC Lateral occipital complex Medial Lateral (Object recognition) hemisphere hemisphere FFA Fusiform face area (Face analysis) Temporo-parieto- occipital junction EBA Extrastriate body area (Body analysis) V3 V2 Sylvian PPA Parahippocampal place area Calcarine V1 fissure (Environment analysis) sulcus V1 EBA V2 PPA V3 LOC V3 V4 V2 FFA V4 Collateral V1 sulcus

DRAWING 22-12 Cortical Visual Processing— Partial 406 Neuroanatomy: Draw It to Know It

Cortical Visual Processing (Advanced ) (Cont.)

Now, at the occipital-temporal-parietal junction, label “where” pathway. Some of the specifi c visual areas that area V5, which is the motion-processing center and are identifi ed within the parietal dorsal stream area are which is oft en referred to as hMT because it represents the parietal reach region in the intraparietal sulcus, the human correlate to the macaque middle temporal which activates during reach and pointing movements; visual area. Visual perception of motion is processed in the anterior parietal area in the anterior parietal sulcus, this region; this visual area is part of our model for the which activates during fi ne motor movements; the ven- circuitry of smooth pursuit eye movements (see Drawing tral parietal area in the depths of the intraparietal sulcus, 23-5)— it plays a fundamental role in the tracking of a which activates during multimodal motion detection of moving target. Note that motion processing also involves moving stimuli; the lateral intraparietal area in the pos- other brain regions, including area V5a, the human cor- terior intraparietal sulcus, which activates during visually ollary for the macaque medial superior temporal visual guided saccadic eye movements; and the superior and area, which lies adjacent (just superior) to V5. Note, as inferior parietal lobules, which function in attention well, that for practical purposes, just as we consider V4 control and spatial awareness. We can think of the pari- to be the fi rst step in the topographic separation of the etal dorsal stream area as the “show me the way” area; it ventral stream from the dorsal stream, so, too, here, we instructs the motor cortex where to move.22 take the practical liberty of considering V5 to be the fi rst As a fi nal point, consider that an important aspect of step in the separation of the dorsal stream from the ven- visual processing is depth perception, which, as it turns tral stream— even though the dorsal stream, itself, is out, is more than simply a product of stereoscopic vision commonly limited to the parietal visual areas (discussed (the reconciliation of binocular disparity); it also involves next). Finally, as a clinical corollary, patients with injury high-level processing of numerous visual cues. Th is visual to V5 demonstrate akinetopsia, which is an inability to processing allows for the preservation of depth percep- visualize moving objects despite a preserved ability to tion in the setting of monocular (one-eye) vision. As a accurately visualize stationary objects. prominent example of the capability of monocular vision Next, label the lateral parietal lobe as P-DSA, which to provide depth perception, consider that Wiley Post stands for “parietal dorsal stream area.” Th e parietal lobes was a highly regarded pilot who won the 1930 Los contain numerous visual cortical areas dedicated to the Angeles to Chicago Air Derby with the use of only one processing of spatial awareness, and they comprise the eye. 33 – 35 22. Vision 407

Occipital area - V1 Primary visual cortex initial cortical processing (Primary processing) Frontal Dorsal Dorsal stream - V2 Secondary visual cortex (Illusory boundary processing) eye fields stream “where” pathway Ventral V3 Tertiary visual cortex stream Occipital Ventral stream - area “what” pathway Frontal eye fields - V4 Color processing (eg, color constancy) eye movements LOC Lateral occipital complex Medial Lateral (Object recognition) hemisphere hemisphere FFA Fusiform face area (Face analysis) Temporo-parieto- occipital junction EBA Extrastriate body area (Body analysis) V3 V2 Sylvian P-DSA PPA Parahippocampal place area Calcarine V1 fissure V5 (Environment analysis) sulcus V1 EBA V2 V5 Motion-processing PPA V3 LOC V3 V4 V2 FFA V4 Collateral V1 P-DSA Parietal dorsal stream area (Spatial awareness) sulcus

DRAWING 22-13 Cortical Visual Processing— Complete 408 Neuroanatomy: Draw It to Know It

References 1 . Atchison , D. A. & Smith , G. Optics of the human eye, pp. 11 – 12 syndrome . Graefes Arch Clin Exp Ophthalmol 242 , 468 – 477 ( Butterworth-Heinemann , 2000 ). (2004 ). 2 . K r a c h m e r, J . H ., M a n n i s, M . J . & H o l l a n d, E . J . Cornea, 2nd ed., 18 . Karanjia , N. & Jacobson , D. M. Compression of the prechiasmatic pp. 3 – 27 ( Elsevier Mosby , 2005 ). optic nerve produces a junctional scotoma . Am J Ophthalmol 128 , 3 . J e n k i n s, A . J . Drug testing in alternate biological specimens, p. 118 256 – 258 (1999 ). (Humana Press, 2008 ). 19 . Brown , J. M. Visual streams and shift ing attention. Prog Brain Res 4 . Sherbondy , A. J. , Dougherty , R. F. , Napel , S. & Wandell , B. A. 176 , 47 – 63 (2009 ). Identifying the human optic radiation using diff usion imaging and 20 . Grill-Spector , K. & Malach , R. Th e human visual cortex . Annu Rev fi ber tractography. J Vis 8 , 12.1 – 11 (2008 ). Neurosci 27 , 649 – 677 (2004 ). 5 . Alonso , J. M. , Yeh , C. I. , Weng , C. & Stoelzel , C. Retinogeniculate 21 . Wandell , B. A., Dumoulin , S. O. & Brewer , A. A. Visual fi eld maps connections: A balancing act between connection specifi city and in human cortex. Neuron 56 , 366 – 383 (2007 ). receptive fi eld diversity. Prog Brain Res 154 , 3 – 13 (2006 ). 22 . Rajimehr , R. & Tootell , R. Organization of human visual cortex . 6 . F i t z p a t r i c k, D ., I t o h, K . & D i a m o n d, I . T. Th e laminar organization In Th e senses: a comprehensive reference ( e d A . I . B a s b a u m) of the lateral geniculate body and the striate cortex in the squirrel (Elsevier Inc., 2008 ). monkey (Saimiri sciureus) . J Neurosci 3 , 673 – 702 (1983 ). 2 3. F u k u s h i m a, T. , K a s a h a r a, H ., K a m i g a k i, T. & M i y a s h i t a , Y . 7 . Glees , P. & le Gros Clark , W. E. Th e termination of optic fi bres in High-level visual processing. In Th e senses: a comprehensive reference. the lateral geniculate body of the monkey . J Anat 75 , 295 – 308 (ed A.I. Basbaum ) ( Elsevier Inc. , 2008 ). (1941 ). 24 . Downing , P. E. , Chan , A. W. , Peelen , M. V. , Dodds , C. M. & 8 . Guido , W. Refi nement of the retinogeniculate pathway . J Physiol Kanwisher , N. Domain specifi city in visual cortex. Cereb Cortex 1 6, 586 , 4357 – 4362 (2008 ). 1453 – 1461 (2006 ). 9 . Kaplan , E. & Shapley , R. M. X and Y cells in the lateral geniculate 25 . Walsh , V. & Kulikowski , J. J. Perceptual constancy: why things look as nucleus of macaque monkeys. J Physiol 330 , 125 – 143 (1982 ). they do, pp. 359 – 362 ( Cambridge University Press , 1998 ). 10 . Murray , K. D., Rubin , C. M., Jones , E. G. & Chalupa , L. M. 26 . Banich , M. T. Cognitive neuroscience, 10th ed., pp. 190 – 191 , 225 Molecular correlates of laminar diff erences in the macaque dorsal (Wadsworth/Cengage Learning, 2010 ). lateral geniculate nucleus. J Neurosci 28 , 12010 – 12022 (2008 ). 2 7. C a l d e r, A . Oxford handbook of face perception, new book ed., 11 . Schiller , P. H. & Malpeli , J. G. Functional specifi city of lateral pp. 115 – 117 ( Oxford University Press , 2011 ). geniculate nucleus laminae of the rhesus monkey . J Neurophysiol 4 1, 28 . Astafi ev , S. V. , Stanley , C. M. , Shulman , G. L. & Corbetta , M. 788 – 797 (1978 ). Extrastriate body area in human occipital cortex responds to the 12 . Schiefer , U. , Wilhelm , H. & Hart , W. M. Clinical neuro- performance of motor actions . Nat Neurosci 7 , 542 – 548 (2004 ). ophthalmology: a practical guide , p. 8 ( Springer , 2007 ). 29 . Dudchenko , P. A. Why people get lost: the psychology and 1 3. L e ff , A. A historical review of the representation of the visual fi eld neuroscience of spatial cognition, pp. 221 – 249 ( Oxford University in primary visual cortex with special reference to the neural Press, 2010 ). mechanisms underlying macular sparing . Brain Lang 88 , 268 – 278 30 . D’Esposito , M. Neurological foundations of cognitive neuroscience, (2004 ). pp. 89 – 90 (Th e MIT Press, 2002 ). 14 . Walsh , F. B., Hoyt , W. F. & Miller , N. R. Walsh and Hoyt’s clinical 31 . Devinsky , O. & D’Esposito , M. Neurology of cognitive and neuro-ophthalmology: the essentials, 2nd ed., Chapter 2 (Lippincott behavioral disorders, pp. 248 – 249 ( Oxford University Press , 2004 ). Williams & Wilkins , 2008 ). 32 . Aguirre , G. K. & D’Esposito , M. Topographical disorientation: a 15 . Horton , J. C. Wilbrand’s knee of the primate optic chiasm is an synthesis and taxonomy. Brain 122 (Pt 9), 1613 – 1628 (1999 ). artefact of monocular enucleation . Trans Am Ophthalmol Soc 9 5, 3 3. D a v i s, J . R . Fundamentals of aerospace medicine, 4th ed., p. 16 579 – 609 (1997 ). ( Lippincott Williams & Wilkins , 2008 ). 16 . Lee , J. H. , Tobias , S. , Kwon , J. T. , Sade , B. & Kosmorsky , G. 3 4. G i b b, R ., G r a y, R . & S c h a r ff , L . Aviation visual perception: research, Wilbrand’s knee: does it exist? Surg Neurol 66 , 11 – 17 (2006 ). misperception and mishaps, pp. 80 – 81 (Ashgate , 2010 ). 17 . Schiefer , U. , et al. Distribution of scotoma pattern related to 35 . Vickers , J. N. Perception, cognition, and decision training: the quiet chiasmal lesions with special reference to anterior junction eye in action, pp. 22 – 23 ( Human Kinetics , 2007 ). 2 3 Eye Movements

Final Common Pathway

Horizontal Saccade Circuitry

Horizontal Saccade Details ( Advanced )

Vertical Saccades ( Advanced )

Smooth Pursuit

Pupillary Light Reﬂ e x 410 Neuroanatomy: Draw It to Know It

Know-It Points

Final Common Pathway

■ Th e abducens nucleus of cranial nerve 6 comprises ■ Th rough the fi nal common pathway, the abducens pools of motoneurons and interneurons. nucleus and the contralateral oculomotor nucleus act ■ Th e motoneurons innervate the ipsilateral lateral in tandem. rectus muscle, which drives the attached eye laterally. ■ In a complete abducens nuclear injury, there is loss of ■ Th e interneurons project fi bers across midline that gaze to the side of the lesion. ascend the medial longitudinal fasciculus and synapse ■ In an internuclear ophthalmoplegia (or MLF in the oculomotor nucleus. syndrome), the ipsilateral eye is unable to adduct and ■ Th e oculomotor nucleus innervates the ipsilateral the opposite eye has horizontal nystagmus when it medial rectus muscle, which drives the attached eye a b d u c t s . medially.

Horizontal Saccade Circuitry

■ Th e superior colliculus is commonly divided into a ■ Th e excitatory burst neurons also excite the ipsilateral dorsal, “visuosensory” division and a ventral, “motor” inhibitory burst neurons (of the medullary reticular division. formation), which inhibit the contralateral abducens ■ Th e frontal eye fi elds directly excite contralateral nucleus. excitatory burst neurons. ■ Th e omnipause cells tonically inhibit the excitatory ■ Th e frontal eye fi elds also send an indirect excitatory burst neurons and also the inhibitory burst neurons. pathway through the superior colliculus, which ■ Th e excitatory burst neurons inhibit the omnipause also excites the contralateral excitatory burst neurons and inactivate their tonic suppression of the neurons. burst neurons. ■ Th e excitatory burst neurons (of the paramedian ■ Th e neural integrator receives fi bers from and projects pontine reticular formation) excite the ipsilateral fi bers to a wide array of nuclei, including the excitatory abducens nucleus. and inhibitory burst neurons, to sustain gaze.

Vertical Saccades (Advanced )

■ Th e rostral interstitial nuclei of the medial ■ Th e riMLF produces bilateral projections for upward longitudinal fasciculus (riMLF) comprise the gaze but only ipsilateral projections for downward gaze. excitatory burst neurons for vertical and torsional ■ From the subject’s point of view, the right riMLF saccades. produces clockwise torsional rotation of the eyes, and ■ Th e interstitial nuclei of Cajal (INC) are the neural the left riMLF produces counterclockwise torsional integrator for vertical and torsional saccades. rotation of the eyes. 23. Eye Movements 411

Smooth Pursuit

■ Each hemisphere is responsible for ipsilateral smooth ■ Th e frontal eye fi elds (and other cortical visual pursuit eye movements; for instance, the right areas, as well) project to the ipsilateral pontine hemisphere detects and tracks images as they move to nuclei. the right. ■ Th e pontine nuclei project across midline to the ■ M retinal ganglion cells receive rod photoreceptor opposite side of the cerebellum, most notably to the detection of the target’s movement. vestibulocerebellum. ■ Th e primary visual cortex projects to visual area V5 ■ Th e cerebellum projects to the ipsilateral medial (the human homologue to the macaque middle vestibular nucleus in the medulla. temporal [MT] area). ■ Th e medial vestibular nucleus projects to the ■ Area V5 projects to visual area V5a (the human contralateral abducens nucleus (on the side of the homologue to the macaque medial superior temporal brain that detected the movement), which excites the [MST] area). fi nal common pathway for horizontal eye ■ Area V5a projects to the posterior parietal cortex, m o v e m e n t s . which projects to the frontal eye fi elds.

Pupillary Light Reﬂ ex

■ O p t i c fi bers of the pupillary light refl ex synapse in ■ Each Edinger–Westphal nucleus projects to its the pretectal olivary nucleus of the pretectal area ipsilateral ciliary ganglion. rather than the lateral geniculate nucleus. ■ Th e ciliary ganglion sends short ciliary nerves to ■ Th e prectectal olivary nucleus projects directly to the innervate the sphincter pupillae muscles to produce ipsilateral Edinger–Westphal nucleus and to the pupillary constriction. contralateral Edinger–Westphal nucleus via the posterior commissure. 412 Neuroanatomy: Draw It to Know It

Final Common Pathway

Here, we will draw the anatomy of the fi nal common of gaze to the side of the lesion: for example, in a left pathway for conjugate horizontal eye movements. Note abducens nuclear injury, the eyes are unable to deviate to that our diagram is a simplifi ed schematic: the topo- the left . graphic anatomy of the oculomotor and abducens nuclei Now, again, redraw our diagram. Show that when the is more accurately depicted in Chapters 11 & 12. First, medial longitudinal fasciculus is injured, the ipsilateral draw a coronal view of the brainstem and label the mid- eye is unable to adduct. Th is is called an internuclear brain, pons, and medulla. Th en, draw axial sections ophthalmoplegia (or MLF syndrome)— the ipsilateral through the eyes. Now, label the left side of the page as eye is unable to adduct and the opposite eye has horizon- left and the right side as right, and also denote the mid- tal nystagmus when it abducts. line of the diagram. Next, attach a lateral rectus muscle to Next, redraw our diagram, again, but here include the the left eye and a medial rectus muscle to the right eye. bilateral eye movement circuitry: draw the bilateral Now, let’s draw the cranial nerve nuclei involved in medial and lateral recti muscles and draw eye movements the fi nal common pathway for horizontal eye move- for both horizontal directions of gaze. Th en, show that ments. In the pons, on the left side, draw the abducens when both medial longitudinal fasciculus tracts are nucleus of cranial nerve 6. Show that it comprises pools injured, neither eye can adduct: the right eye can’t turn of motoneurons and interneurons. Indicate that the horizontally to the left and the left eye can’t turn hori- motoneurons innervate the left eye’s lateral rectus muscle, zontally to the right. Th is is called bilateral internuclear which drives the left eye to the left (laterally). Next, draw ophthalmoplegia. Pathologic processes that cross mid- the right oculomotor nucleus of cranial nerve 3 in the line, such as demyelinating plaques, hemorrhages, or midbrain. Now, let’s show the internuclear connection tumors, can cause this form of injury because the medial between these two nuclei: the right medial longitudinal longitudinal fasciculus tracts run close together in the fasciculus. Th en, show that the left abducens interneu- midline of the brainstem. rons project fi bers across midline that ascend the right For the last diagram, redraw the bilateral fi nal medial longitudinal fasciculus and synapse in the right common pathway arrangement. Show that when the left oculomotor nucleus. Finally, show that the right oculo- abducens nucleus is injured, there is loss of gaze toward motor nucleus innervates the right eye’s medial rectus the side of the lesion (left gaze palsy), and then show that muscle and drives the right eye to the left (medially). when the adjacent medial longitudinal fasciculus is Next, to enhance our understanding of this pathway, injured, the ipsilateral eye (the left eye) can’t adduct. let’s address the common lesions that disrupt it. First, Th us, when both the abducens nucleus and the adjacent redraw our diagram. Th en, show that injury to the medial longitudinal fasciculus are injured, the only intact abducens motoneurons causes loss of ipsilateral eye movement is right eye abduction (and it has nystagmus abduction. Next, show that injury to the abducens from the left medial longitudinal fasciculus injury); thus, interneurons causes loss of contralateral eye adduction. one-and-a-half of the two complete eye movements are Finally, encircle the entire abducens nucleus to indicate impaired, so the injury pattern is called one-and-a-half that in a complete abducens nuclear injury, there is loss syndrome.1 , 2 23. Eye Movements 413

Left Right

Lateral Medial rectus Midline rectus Abducens nuclear Internuclear Midbrain injury ophthalmoplegia Oculomotor nucleus Motor Inter- neurons neurons Pons Medial Abducens longitudinal nucleus fasciculus

Medulla

Bilat. internuclear One-and-a-half ophthalmoplegia syndrome

DRAWING 23-1 Final Common Pathway 414 Neuroanatomy: Draw It to Know It

Horizontal Saccade Circuitry

Here, we will draw the supra-ocular circuitry for hori- excitatory pathway that synapses within the superior col- zontal saccadic eye movements (aka horizontal sacca- liculus, which, in turn, excites the contralateral excit- des). First, draw a brainstem in coronal view and divide atory burst neurons. Note that the indirect pathway is it into its midbrain, pons, and medulla, and then label its actually more robust than the direct pathway. Now, draw anatomic left and right sides. Next, above the brainstem, excitatory projection fi bers from the excitatory burst draw a right cerebral hemisphere and label the frontal neurons to the ipsilateral abducens nucleus. Th is excita- eye fi elds. Now, in the upper midbrain, draw the right tion stimulates the fi nal common pathway for horizontal superior colliculus. For a long time, the importance of saccades (see Drawing 23-1 ). the superior colliculus went unrecognized because iso- Next, let’s interrupt our diagram to demonstrate lated lesions of the superior colliculus are rare, but exper- with our fi sts that the right hemisphere drives the eyes imental inactivation of the superior colliculus has proven to the left and that the left hemisphere drives the eyes to its signifi cance. Th e superior colliculus is commonly the right. Hold your fi sts in front of you; they represent divided into a dorsal, “visuosensory” division and a ven- the frontal eye fi elds. Point your index fi ngers inward in tral, “motor” division. Th e dorsal division receives an a V shape to show that each cerebral hemisphere drives organized retinotopic map of the contralateral visual the eyes in the opposite direction. Next, drop your right hemifi eld from retinal ganglion cells and also receives fi st to show that a destructive lesion, such as a stroke, aff erent input from visual cortical regions, as well, includ- causes a loss of innervation from the right frontal eye ing the striate, extrastriate, and frontal cortices. Th e ven- fi elds, and as a result, the left frontal eye fi elds drive the tral division projects to the contralateral abducens eyes to the right. Th en, shake your right hand to show nucleus (as drawn next). that an excitatory event, such as a seizure, causes over- Now, draw the bilateral abducens nuclei, which span stimulation of the right frontal eye fi elds, and so the right from the mid-pons to the low pons. For the remainder of frontal eye fi elds overpower the left and drive the eyes to the diagram, we will draw the left brainstem ocular the left . nuclei, only. Next, in the mid-pons, draw the excitatory Now, let’s continue with our diagram. Show that in burst neurons of the paramedian pontine reticular for- addition to exciting the abducens nucleus, the excitatory mation; they lie anterior to the superior aspect of burst neurons also excite the ipsilateral inhibitory burst the abducens nucleus. Th en, draw the inhibitory burst neurons, which inhibit the contralateral abducens neurons of the medullary reticular formation; they lie nucleus. Th us, when the left abducens nucleus is stimu- within the rostral medulla anterior to the plane of the lated, the right abducens nucleus is inactivated, which abducens nucleus. Now, show that the neural integrator prevents both nuclei from fi ring at the same time. lies along the dorsal tegmentum of the upper medulla; Next, show that the omnipause cells tonically inhibit it lies just anterior to the fourth ventricle. Finally, draw the excitatory burst neurons and also the inhibitory the omnipause neurons in midline, which lie in between burst neurons. Th en, indicate that the excitatory burst the rootlets of the abducens nerves in the pontine neurons inhibit the omnipause neurons and inactivate tegmentum. their tonic suppression of the burst neurons. Finally, Next, let’s add the functional circuitry for horizontal indicate that the neural integrator receives fi bers from saccades. First, show that the frontal eye fi elds directly and projects fi bers to a wide array of nuclei, including excite contralateral excitatory burst neurons, and then the excitatory and inhibitory burst neurons, to sustain show that the frontal eye fi elds also send an indirect gaze, as detailed further in Drawing 23-3 .1 – 3 23. Eye Movements 415

Frontal eye fields

LEFT RIGHT

Superior colliculus

MIDBRAIN

*EBN - Excitatory PONS EBN* Omnipause neurons burst neurons

VI VI

*IBN - Inhibitory IBN* MEDULLA Diffuse nuclei burst neurons Neural integrator

DRAWING 23-2 Horizontal Saccade Circuitry 416 Neuroanatomy: Draw It to Know It

Horizontal Saccade Details (Advanced )

Here, we will review and elaborate on our discussion of Now, let’s address the inhibitory burst neurons; show the anatomy and control of horizontal saccades. Across that they lie within the nucleus paragigantocellularis the top of the diagram, write the following headings: dorsalis of the medullary reticular formation — the center, anatomy, action, and defi cit. First, list the supra- nucleus paragigantocellularis dorsalis lies within the ocular command centers for horizontal saccades. Begin rostral medulla anterior to the plane of the abducens with the frontal eye fi elds, which comprise the frontal nucleus. Indicate that the inhibitory burst neurons, most eye fi e l d , a discrete region in the anterior precentral notably, suppress the contralateral abducens nucleus sulcus near the superior frontal sulcus that is homolo- from fi ring, which prevents antagonist forces on the gous to the location of the frontal eye fi eld of the macaque intended horizontal saccade movement. Injury to the monkey; and then show that the frontal eye fi elds also inhibitory burst neurons is hypothesized to produce comprise, most notably, the supplementary eye fi eld and ocular fl utter, high-frequency conjugate horizontal sac- dorsolateral prefrontal cortex. Other important supra- cades without an intersaccadic interval. 1 ocular command centers include the superior colliculus Next, let’s address the neural integrator; show that it and cerebellum, and also the anterior cingulate cortex lies within the medial vestibular nucleus and the nucleus and basal ganglia. Now, in regards to their action, indi- prepositus hypoglossi of the perihypoglossal complex, cate that the frontal eye fi elds and superior colliculus which lie along the dorsal tegmentum of the upper drive the eyes to the contralateral side, and then show medulla just anterior to the fourth ventricle. Indicate that that injury to these structures produces contralateral the neural integrator produces gaze holding. Show that volitional horizontal gaze palsy.4 , 5 Note that horizontal injury to the neural integrator causes a leaky integrator, saccades via the vestibulo-ocular refl ex are spared in the which means that the eyes do not remain in the intended setting of frontal eye fi eld or superior colliculus injury. direction of gaze but instead drift back to center, prompt- Next, let’s address the excitatory burst neurons; indi- ing a corrective saccade. cate that they lie within the nucleus reticularis pontis Finally, let’s address the omnipause neurons; show that caudalis of the paramedian pontine reticular formation they lie within the nucleus raphe interpositus, which sits (PPRF)— the nucleus reticularis pontis caudalis lies in midline in between the rootlets of the abducens nerves within the mid-pons, anterior to the superior aspect of in the pontine tegmentum. Indicate that omnipause cells the abducens nucleus. Indicate that the excitatory burst tonically suppress the excitatory and inhibitory burst neurons activate the ipsilateral abducens nucleus, and neurons except immediately before and during saccadic also show that they activate the ipsilateral inhibitory eye movements. Th e predicted defi cit in omnipause cell burst neurons, which inhibit the contralateral abducens injury is opsoclonus: multidirectional saccadic oscilla- nucleus. Th en, show that the excitatory burst neurons tions without an intersaccadic interval, but what is actu- also inhibit the omnipause neurons and innervate the ally observed, instead, is a slowing of saccades. Opsoclonus neural integrator, as well. Next, show that injury to the is oft en ascribed to cerebellar injury; the cerebellum PPRF produces ipsilateral horizontal gaze palsy. When receives projections from the frontal eye fi elds and supe- the PPRF is selectively injured, the fi nal common path- rior colliculus, which fi rst relay, most notably, within the way will be spared; however, due to its proximity to the nucleus reticularis tegmenti pontis, which lies within the abducens nucleus, PPRF injury is most oft en associated mid- to upper antero-central pontine tegmentum.1 – 3 with abducens nucleus injury, which disrupts the fi nal common pathway. 23. Eye Movements 417

CENTER ANATOMY ACTION DEFICIT Supraocular Frontal eye fields: frontal eye field, Frontal eye fields & superior Contralateral command supplementary eye field, dorsolateral colliculus produce contra- volitional horizontal centers prefrontal cortex. Superior colliculus, lateral horizontal saccades gaze palsy cerebellum, anterior cingulate cortex, & basal ganglia.

Excitatory Nucleus reticularis pontis caudalis Activate ipsilateral abducens Ipsilateral horizontal burst (of the paramedian pontine nucleus & ipsilateral inhibitory gaze palsy neurons (EBN) reticular formation) burst neurons, inhibit omnipause neurons, & innervate neural integrator

Inhibitory Nucleus paragigantocellularis Inhibit the contralateral Ocular flutter burst dorsalis (of the medullary reticular abducens nucleus neurons (IBN) formation)

Neural Medial vestibular nucleus & Gaze holding Leaky integrator integrator nucleus prepositus hypoglossi (of the perihypoglossal complex)

Omnipause Nucleus raphe interpositus Tonic inhibition of excitatory Saccade slowing neurons & inhibitory burst neurons

DRAWING 23-3 Horizontal Saccade Details 418 Neuroanatomy: Draw It to Know It

Vertical Saccades (Advanced )

Here, we will draw the anatomic substrate for vertical nucleus raphe interpositus contains the omnipause neu- and torsional saccades. First, draw a coronal section rons for vertical and torsional saccades just as it does for through the midbrain and pons. Label the left and right horizontal saccades. Lastly, note that certain texts sides of the brainstem. At the top of the diagram, at the describe the INC as containing the inhibitory burst neu- midbrain–diencephalic junction, in the plane of the rons for vertical and torsional saccades whereas others mammillary bodies, near the midline of the diagram, describe the riMLF as containing them; as a reminder, draw the bilateral rostral interstitial nuclei of the medial for comparison, the nucleus paragigantocellularis dorsa- longitudinal fasciculus (riMLF). Next, just beneath the lis of the medullary reticular formation contains the bilateral riMLF, still in the midbrain–diencephalic junc- inhibitory burst neurons for horizontal saccades. tion, near midline in the dorsal tegmentum, draw the Next, we will list the high points of vertical and tor- bilateral interstitial nuclei of Cajal (INC). Now, beneath sional saccade circuitry. First, indicate that the riMLF the bilateral INCs, show that the oculomotor complex produces bilateral projections for upward gaze but only straddles the midline of the mid- to upper midbrain; it ipsilateral projections for downward gaze. Th us, a unilat- lies within the dorsal tegmentum just anterior to the eral riMLF lesion will cause isolated downward gaze periaqueductal gray area. Note that although we oft en palsy (observed as slowing of downward gaze), but represent the oculomotor nuclei as comprising two dis- redundant innervation for upward gaze preserves the crete nuclei, it actually forms a single oculomotor com- function and speed of upward gaze. Next, indicate the plex consisting of many subnuclei (see Drawing 12-5). laterality of riMLF innervation for torsional saccades. Next, beneath the oculomotor complex, in the lower Show that from the subject’s point of view, the right midbrain (in the plane of the inferior colliculi), draw the riMLF produces clockwise torsional rotation of the eyes, bilateral trochlear nuclei, which also lie within the dorsal whereas the left riMLF produces counterclockwise tor- tegmentum, near midline. Lastly, draw the nucleus raphe sional rotation of the eyes. Stated diff erently, from the interpositus in midline in the pontine tegmentum; it lies subject’s perspective, the top poles of the eyes rotate in between the rootlets of the abducens nerves. toward the riMLF that is activated. To demonstrate this, Now that we have completed an anatomic view of the hold your fi sts in front of you and point your index fi n- relevant ocular nuclei for vertical and torsional saccades, gers straight up. Now, activate the right riMLF and rotate let’s describe their supranuclear control. Write out the your fi ngers to the right; then, activate the left riMLF headings: nucleus and function. Th en, indicate that the and rotate your fi ngers to the left . Note that the torsional riMLF comprises the excitatory burst neurons for verti- defi cits observed in unilateral riMLF lesions are more cal and torsional saccades; it acts in similar fashion to the substantial than the vertical defi cits. nucleus reticularis pontis caudalis of the PPRF for hori- Finally, consider that whereas the frontal eye fi elds zontal saccades. Now, show that the INC is the neural and superior colliculus project to the contralateral PPRF integrator for vertical and torsional saccades, similar to excitatory burst neurons for horizontal saccades, they the medial vestibular nucleus and nucleus prepositus project to the ipsilateral riMLF for vertical and torsional hypoglossi for horizontal saccades. Next, show that the saccades. 1 – 3 , 6 23. Eye Movements 419

LEFT RIGHT NUCLEUS FUNCTION riMLF* riMLF* - rostral Excitatory INC* interstitial nucleus burst of medial longitudinal neurons fasciculus Oculomotor complex INC* - interstitial Neural MIDBRAIN nucleus of Cajal integrator Trochlear Nucleus raphe Omnipause nucleus interpositus neurons (INC* or riMLF*) Inhibitory burst neurons VERTICAL SACCADES riMLF projects bilaterally for upgaze riMLF projects ipsilaterally for downgaze TORSIONAL SACCADES From subject’s point of view, the right riMLF produces clockwise saccades; the left riMLF produces counterclockwise saccades PONS Nucleus raphe SUPRA-OCULAR PROJECTIONS interpositus riMLF receives ipsilateral projections from the frontal eye fields and superior colliculus

DRAWING 23-4 Vertical Saccades 420 Neuroanatomy: Draw It to Know It

Smooth Pursuit

Here, we will draw a model for smooth pursuit eye move- the frontal eye fi elds without projecting through any of ments. Smooth pursuit eye movements allow us to keep the intervening connections; also, reciprocal connec- a moving target in our fovea and clearly visualize it. To tions between visual areas exist— for instance, the poste- begin our diagram, show a target object move from left rior parietal cortex both receives projections from and to right. Each hemisphere is responsible for ipsilateral sends projections to visual area V5a. smooth pursuit eye movements, meaning the right Now, show that the frontal eye fi elds (and other corti- hemisphere detects and tracks images as they move to cal visual areas, as well) project to the ipsilateral dorso- the right and the left hemisphere detects and tracks lateral pontine nuclei (DLPN) in the high pons and the images as they move to the left . 6 – 8 Within the circuitry ipsilateral nucleus reticularis tegmenti pontis (NRTP) for smooth pursuit, the contralateral cerebellum and in the upper pons. Next, show that the right DLPN medulla and the ipsilateral pons are incorporated via a and right NRTP project across midline to the left side of double decussating pathway. the cerebellum, specifi cally to the fl occulus and parafl oc- Now, divide the remainder of the page into left and culus of the vestibulocerebellum and also to the dorsal right sides, making the right side larger than the left . vermis. Th en, show that the vestibulocerebellum and Next, indicate that M retinal ganglion cells receive rod dorsal vermis project to the ipsilateral medial vestibular photoreceptor detection of the target’s movement. nucleus in the medulla. Finally, show that the left medial Note that the visual system is generally divided into the vestibular nucleus projects to the contralateral abducens pathway for detection of movement (the magnocellular nucleus in the right mid- to low pons, which completes [or M] pathway, which receives rod photoreceptor the double decussation. Th e right abducens nucleus then stimulation) and the pathway for detection of color (the initiates horizontal pursuit eye movements to the right. parvocellar [or P] pathway, which receives cone photo- Note that y-group vestibular nuclear connections to the receptor stimulation). Show that visual detection of the oculomotor and trochlear nuclei also exist, which are target’s movement from left to right is projected from involved in vertical pursuit movements.9 the retinae to the right lateral geniculate nucleus and Lastly, let’s use axial pontine sections to draw the top- then to the right primary visual cortex (V1). Next, let’s ographic anatomy of the DLPN, NRTP, and abducens show the notable cortical visual processing steps for nucleus. First, draw the posterior–anterior and right– motion detection. Show that the primary visual cortex left planes of orientation for an anatomic, axial view of projects to visual area V5 (the human homologue to the the pons. Th en, draw an outline of the pons and remind macaque middle temporal [MT] area), which then proj- ourselves of the territories of the pontine basis and teg- ects to visual area V5a (the human homologue to the mentum. In each section of the following pontine dia- macaque medial superior temporal [MST] area)— in grams, we will include the anatomy of the fourth ventricle humans, both V5 and V5a lie at the temporo-occipito- for reference. Now, show that the abducens nucleus of parietal junction. Th en, indicate that visual area V5a cranial nerve 6 lies near midline within the posterior projects to the posterior parietal cortex, which projects to tegmentum of the mid- to low pons. Next, show that the frontal eye fi elds. Note that although we have shown the NRTP lies in the anterior, midline tegmentum of the this projection pathway as being sequential and unidirec- upper pons. Lastly, show that the DLPN lies within the tional, many non-sequential, bidirectional connections posterior lateral aspect of the high pontine basis.3 exist. For instance, visual area V5 also projects directly to 23. Eye Movements 421

TARGET movement from: Left Right (detection) M ganglion retinal cells Lateral geniculate Primary visual LEFT RIGHT nucleus cortex (V1)

Frontal eye Posterior parietal Visual area V5a Visual area V5 fields cortex

4th Dorsolateral pontine nucleus (DLPN) HIGH PONS Vestibulocerebellum & DLPN PONS AXIAL VIEW dorsal vermis Posterior 4th Right Left Nucleus reticularis NRTP tegmenti pontis (NRTP) UPPER Anterior PONS TEGMENTUM 4th BASIS CrN6 Abducens nucleus (CrN 6) MID TO LOW PONS Medial vestibular nucleus (medulla)

DRAWING 23-5 Smooth Pursuit 422 Neuroanatomy: Draw It to Know It

Pupillary Light Reﬂ ex

Here, we will draw a diagram of the pupillary light refl ex. pupillary light refl ex, instead, synapse in the pretectal First, in axial view, draw the eyes and the midbrain, and, olivary nucleus of the pretectal area. Th en, indicate that then, lateral to the posterior midbrain tegmentum, draw the prectectal olivary nucleus projects directly to the the lateral geniculate nucleus. Th en, within the eyes, ipsilateral Edinger–Westphal nucleus and to the contral- draw the lenses, and within the midbrain, draw the red ateral Edinger–Westphal nucleus via the posterior com- nuclei and label the superior colliculi, for reference. missure. Now, show that each Edinger–Westphal nucleus Next, draw a sagittal view of the midbrain and dienceph- projects to the ipsilateral ciliary ganglion. Th en, using alon and indicate that our axial section lies at the level of the left side of the diagram, only, show that the ciliary the midbrain–diencephalic junction. Now, draw the fol- ganglion sends short ciliary nerves to innervate the lowing pupillary light refl ex landmarks: the pretectal oli- sphincter pupillae muscles to produce pupillary constric- vary nucleus of the pretectal area, which lies anterolateral tion. Th e short ciliary nerves pass initially within the to the superior pole of the superior colliculus; the poste- sclera and then within the suprachoroidal space as they rior commissure, which forms the roof of the cerebral wrap around the globe to innervate the sphincter pupil- aqueduct (of Sylvius); the paired Edinger–Westphal lae. Note that the majority of short ciliary nerves actu- nuclei of the oculomotor complex; the bilateral ciliary ally innervate the ciliary muscle of the ciliary body (see ganglia in the posterior orbit, each of which lies in Drawing 22-3), which assists in the accommodation between the related optic nerve and lateral rectus muscle; refl ex, rather than the sphincter pupillae muscles for the and the sphincter pupillae of the iris, which are small cir- pupillary light refl ex (drawn here). 5 , 10 , 11 cumferential rings of smooth muscle in the pupillary As a clinical corollary, in an Adie’s tonic pupil, pathol- margin of each eye. Next, to better illustrate the anat- ogy within the ciliary ganglion or the short ciliary nerves omy of the sphincter pupillae muscle, draw a coronal prevents the pupil from constricting in reaction to light. view of the iris and pupil. Show that the parasympathetic- On evaluation, cholinergic supersensitivity is present: a innervated sphincter pupillae muscle fi bers are circum- dose of pilocarpine (a cholinergic agonist) that would ferentially arranged to constrict pupil size, whereas the not aff ect a normal eye is able to produce pupillary con- sympathetic-innervated pupillary dilator muscle fi bers striction because the denervated sphincter pupillae in the are radially arranged to widen pupil size. Adie’s pupil is supersensitive to acetylcholine. Finally, Now, let’s draw the pupillary light refl ex pathway. consider that unlike saccadic eye movement circuitry, First, show that light activates the retinae. Th en, show which involves brainstem projections that pass inferior to that the optic nerve fi bers combine to form the optic the midbrain to enter the lower pons and upper medulla, tracts, which pass toward the lateral geniculate nucleus— the circuitry for the pupillary light refl ex does not descend we show the left optic tract, only, here, for simplicity. below the upper midbrain. Th us, impaired pupillary con- Next, show that whereas the majority of optic fi bers syn- striction is extremely important to detect because it can apse within the lateral geniculate nucleus, fi bers of the be an early warning sign of brainstem herniation. 23. Eye Movements 423

Sphincter pupillae AXIAL VIEW muscle CORONAL VIEW Dilator muscle Iris Pupil

Sphincter pupillae Short ciliary nerve CrN III, para- Ciliary ganglion sympathetic fiber

DIENCEPHALON & MIDBRAIN - SAGITTAL VIEW

Optic tract Red nucleus Lateral Edinger-Westphal geniculate nucleus nucleus Superior colliculus Pretectal olivary nucleus Posterior commissure of the pretectal area

DRAWING 23-6 Pupillary Light Refl e x 424 Neuroanatomy: Draw It to Know It

References 1 . Leigh , R. J. & Zee , D. S. Th e neurology of eye movements (Oxford 7 . Wr i g h t, K . W., S p i e g e l, P. H . & Th ompson, L. S. Handbook of University Press, 2006 ). pediatric strabismus and amblyopia, pp. 29 – 30 (Springer , 2006 ). 2 . Wo n g, A . M . F. Eye movement disorders ( Oxford University Press , 8 . Ya n o ff , M ., D u k e r, J . S . & A u g s b u r g e r, J . J . Ophthalmology, 3rd ed., 2008 ). p. 1004 ( Mosby Elsevier , 2009 ). 3 . Naidich , T. P. & Duvernoy , H. M. Duvernoy’s atlas of the human 9 . B e n a r r o c h, E . E . Basic neurosciences with clinical applications, p. 503 brain stem and cerebellum: high-fi eld MRI: surface anatomy, internal ( Butterworth Heinemann Elsevier , 2006 ). structure, vascularization and 3D sectional anatomy (Springer , 2009 ). 1 0. J a n k o v i c, D . & H a r r o p - G r i ffi t h s, W. Regional nerve blocks and 4 . Hall , W. C. & Moschovakis , A. Th e superior colliculus: new approaches infi ltration therapy: textbook and color atlas, 3rd ed., p. 20 (Blackwell for studying sensorimotor integration , pp. 36 – 37 ( CRC Press , 2004 ). Pub., 2004 ). 5 . A fi fi , A . K . & B e r g m a n, R . A . Functional neuroanatomy: text and atlas, 1 1. F o r r e s t e r, J . V. Th e eye: basic sciences in practice, 2nd ed., p. 28 2nd ed., pp. 136 – 137 , 143 ( Lange Medical Books/McGraw-Hill , ( W.B. Saunders , 2002 ). 2005 ). 6 . Brazis , P. W. , Masdeu , J. C. & Biller , J. Localization in clinical neurology, 6th ed., pp. 221 – 228 (Wolters Kluwer Health/Lippincott Williams & Wilkins , 2011 ). 2 4 Cognition

Language Disorders

Memory: Classes

Memory: Capacity & Consolidation

Apraxia & Neglect ( Advanced ) 426 Neuroanatomy: Draw It to Know It

Know-It Points

Language Disorders

■ I n 9 0% of individuals, the language centers lie within gyrus and the surrounding temporal and parietal the left hemisphere. lobes and insula. ■ Broca’s aphasia is a non-fl uent aphasia with preserved ■ Global aphasia, which is most easily thought of as a comprehension and impaired repetition. combined Broca’s and Wernicke’s aphasia, is due to ■ Broca’s aphasia localizes to Broca’s area and also extensive injury to the left middle cerebral artery involves the precentral gyrus, basal ganglia, insula, territory. and related white matter pathways. ■ In transcortical aphasia, the perisylvian region is spared, ■ Wernicke’s aphasia is a fl uent aphasia with poor which is presumably why repetition is unaff ected. comprehension and impaired repetition. ■ Conduction aphasia is a fl uent aphasia with normal ■ Wernicke’s aphasia localizes to Wernicke’s area and comprehension but impaired repetition; it classically the neighboring supramarginal gyrus and angular localizes to the arcuate fasciculus.

Memory: Classes

■ Sensory memory is the transitory retention of a ■ Episodic memory refers to the recollection of primary sensory stimulus. episodes, typically autobiographical episodes, which ■ Short-term memory lasts for roughly 3 to 30 seconds. have a strong contextual stamp. ■ Long-term memory refers to memories that are ■ Semantic memory refers to our knowledge stores: anywhere from older than 30 seconds to the most our collection of facts or information, which have no remote memories. contextual stamp. ■ Declarative (aka explicit) memories are those that ■ Procedural memory refers to skills learning, such as are consciously recalled (eg, reciting a country’s riding a bicycle. capitals). ■ Priming refers to the improved ability to identify ■ Nondeclarative (aka implicit) memories are those recently perceived stimuli in comparison to new that are unconsciously retrieved (eg, riding a bicycle). s t i m u l i .

Memory: Capacity & Consolidation

■ Short-term memory is able to hold seven bits of ■ According to multiple memory trace theory, every information (plus or minus two) at any given time. time an episodic memory is retrieved, the ■ Chunking is the process wherein we organize hippocampal–neocortical ensemble of that memory information into fewer chunks or bits. is strengthened. ■ Encoding is the process in which information is ■ Anterograde amnesia is the inability to form new transformed into a format that can be stored and memories aft er the development of amnesia. retrieved. ■ Retrograde amnesia is the inability to retrieve ■ Storage is the stockpiling of memory into its stored memories that occurred prior to the development of state. the amnesia. ■ Retrieval is the accessing of stored memories. 24. Cognition 427

Apraxia & Neglect (Advanced )

■ Overall, apraxias are more common with left brain ■ Balint syndrome (optic ataxia, gaze apraxia, injuries and neglect is more common with right brain simultagnosia) is due to bilateral occipitoparietal injuries. lesions. ■ Broadly, the frontally based executive apraxias aff ect ■ Gerstmann syndrome is a four-part syndrome of movement and the posterior apraxias aff ect sensory left –right disorientation, fi nger agnosia, dyscalculia, skills and sensorimotor planning. and dysgraphia. ■ Ideational apraxia is an inability to correctly ■ Gerstmann syndrome localizes to the left hemispheric conceptualize an action; for instance, patients might inferior parietal lobule with specifi c involvement of seal an envelope and then try to stuff a letter into it. the angular gyrus. ■ Ideational apraxia localizes to the left hemispheric ■ Hemispatial neglect involves a lack of regard for temporoparietal junction. objects in the contralateral hemisphere. ■ Ideomotor apraxia is a failure to know how to ■ Right parietal lobe injuries can cause anosognosia, perform a complex motor movement — for instance, which is a lack of awareness of the presence of a patients might have trouble waving goodbye. defi cit. ■ Ideomotor apraxia localizes to the left inferior parietal lobule. 428 Neuroanatomy: Draw It to Know It

Language Disorders

Here, we will learn the major language disorders as a and sentences. 4 Show that transcortical motor aphasia window into the neuroanatomy of language. First, draw is commonly due to anterior and middle cerebral artery an outline of a left lateral cerebral hemisphere and then watershed injury with resultant injury to the dorsolat- list the following headings: aphasia, fl uency, comprehen- eral prefrontal cortex and with sparing of the perisyl- sion, and repetition. Note that in regards to the laterality vian region— the presumptive reason for the preserved of language, in 90% of individuals, the language centers repetition. 5 – 7 lie within the left hemisphere, which is why we draw a Next, list transcortical sensory aphasia, which, like left hemisphere, here.1 Wernicke’s aphasia, is a fl uent aphasia with poor single- Begin with Broca’s aphasia, which is a nonfl uent apha- word comprehension. However, in transcortical sen- sia with preserved comprehension and impaired repeti- sory aphasia, unlike in Wernicke’s aphasia, repetition is tion. Broca’s aphasia is agrammatic, has a monotonous intact. Indicate that transcortical sensory aphasia is (or fl at) melody, and is dysarthric, eff ortful, and hesitant. due to middle and posterior cerebral artery watershed Show that Broca’s aphasia localizes to the inferior frontal distribution injury with involvement of the temporo- gyrus, which is the site of Broca’s area, and also involves parieto-occipital junction and with sparing of the peri- the precentral gyrus, basal ganglia, insula, and related sylvian region.5 – 7 white matter pathways.2 Now, list mixed transcortical aphasia, which, like Now, list Wernicke’s aphasia, which is a fl uent aphasia global aphasia, is a nonfl uent aphasia with poor compre- with poor comprehension and impaired repetition. In hension. However, in mixed transcortical aphasia, unlike Wernicke’s aphasia, there is preserved melody and in global aphasia, repetition is intact. Indicate that mixed rhythm but the speech content is empty or meaningless, transcortical aphasia can occur with combined anterior producing a word salad (a high-frequency, unintelligible and middle cerebral artery and middle and posterior jumble of words), and there are paragrammatic and para- cerebral artery watershed distribution strokes that spare phasic substitution errors, and even the production of the perisylvian region.5 – 7 new, meaningless words, called neologisms. Indicate that Finally, list conduction aphasia, which is essentially the site of injury in Wernicke’s aphasia is the posterior the opposite of mixed transcortical aphasia; it is a fl uent superior temporal gyrus (Wernicke’s area) and the neigh- aphasia with normal comprehension but impaired repe- boring supramarginal gyrus and angular gyrus and the tition. In conduction aphasia, speech is hesitant and surrounding temporal and parietal lobes and insula.2 paraphasic, presumably from an inability to accurately Next, list global aphasia, which is most easily thought transmit the intended word choice from the comprehen- of as a combined Broca’s and Wernicke’s aphasia; it is a sion center to the speech production center. Indicate nonfl uent aphasia with poor comprehension and impaired that conduction aphasia classically localizes to the arcu- repetition. Indicate that global aphasia is due to extensive ate fasciculus, most notably, and also to the associated injury to the left middle cerebral artery territory.3 supramarginal gyrus and insula.2 Note, however, that Now, list transcortical motor aphasia, which, like although historically and still commonly we consider Broca’s aphasia, is a nonfl uent aphasia with preserved the arcuate fasciculus to be the tract that carries language comprehension. However, in transcortical motor apha- from the comprehension center to the production center sia, unlike in Broca’s aphasia, repetition is intact. In fact, (as we have shown, here), this process may actually occur make a notation that repetition is such a prominent through the superior longitudinal fasciculus, middle aspect of the transcortical aphasias that they all can cause longitudinal fasciculus, and the extreme capsule (see echolalia — the parrot-like tendency to repeat words Drawing 17-2).8 24. Cognition 429

C APHASIA FLUENCY COMPREHENSION REPETITION TM B W TS Broca’s Non-fluent Preserved Impaired

Wernicke’s Fluent Poor Impaired Broca’s (B): Inferior frontal gyrus, precentral Global Non-fluent Poor Impaired gyrus, basal ganglia, insula, & white matter

Wernicke’s (W): Posterior superior temporal Transcortical Non-fluent Preserved Intact gyrus, & supramarginal & angular gyri, & motor neighboring parietal and temporal lobes, & insula Transcortical Fluent Poor single- Intact Global: Extensive left middle cerebral sensory word artery territory Mixed Non-fluent Poor Intact Transcortical motor (TM): Dorsolateral transcortical prefrontal cortex with perisylvian sparing Conduction Fluent Preserved Impaired Transcortical sensory (TS): Temporo-parietal- occipital junction with perisylvian sparing

Mixed transcortical: Ant./middle & middle/post. *Echolalia can occur in all cerebral artery watersheds; perisylvian sparing transcortical aphasias Conduction (C): Arcuate fasciculus *In 90% of individuals, language (& supramarginal gyrus & insula) lateralizes to the left hemisphere

DRAWING 24-1 Language Disorders 430 Neuroanatomy: Draw It to Know It

Memory: Classes

Here, we will create a diagram to categorize memory leave out of our discussion, here, for simplicity, the con- types based on their duration. Note that the terms used, cepts of the central executive and episodic buff er. 10 here, demonstrate intertextual inconsistency because Next, show that long-term memory refers to memo- they are derived from multiple memory theories gener- ries that are anywhere from older than 30 seconds to our ated over many decades. To begin, let’s divide memory most remote memories. Indicate that long-term memory into three diff erent time spans: sensory, short-term, and is parsed based on the presentation type of the memory, long-term. Sensory memory is the transitory retention basically its sensory form (ie, verbal, visual, olfactory, of a primary sensory stimulus; it is assumed that each etc.), and whether or not there is awareness of the sensation has its own time duration, but show that sen- memory. Show that declarative (aka explicit) memories sory memory as a class lasts from a fraction of a second to are those that are consciously recalled (eg, reciting a a few seconds. Visual sensory memory is retained for an country’s capitals) and that nondeclarative (aka implicit) exceedingly short period of time: a third of a second, memories are those that are unconsciously retrieved (eg, meaning every fraction of a second, our snapshot of the riding a bicycle). world is refreshed. Th is explains why when we view a fan, Indicate that declarative memory is most commonly the blades appear continuous — the rapidly moving stim- subdivided into episodic and semantic memory. Episodic uli (the blades) overlap in our visual memory and conse- memory refers to our recollection of episodes, typically quently blur. However, at slow enough fan speeds, if we autobiographical episodes, which have a strong contex- blink, we can visualize the individual blades. Auditory tual stamp, whereas semantic memory refers to our sensory memory (aka echoic memory) retention is longer: knowledge stores: our collection of facts or information, a few seconds. Just as we ask people what they were saying which have no contextual stamp. Th e memories of times we oft en “hear” them using our echoic memory.9 spent with family are part of our episodic memory, Now, show that short-term memory lasts for roughly whereas the dates of family members’ birthdays and 3 to 30 seconds. Note, however, that the decay of short- anniversaries are part of our semantic memory. term memory begins within a few seconds; thus, we must Nondeclarative memory encompasses several diff er- rehearse what’s available in our short-term memory in ent unconscious forms of memory; indicate that three order to preserve it (eg, a newly learned telephone prominent forms of them are procedural memory, prim- number). Th erefore, indicate that we need to divide ing, and classical conditioning. Procedural memory short-term memory into automatic processing, in which refers to our skills learning, such as riding a bicycle. a memory is not consciously manipulated, and eff ortful Priming refers to our improved ability to identify recently processing (or as it is more commonly referred to, work- perceived stimuli in comparison to new stimuli; for ing memory), in which a memory is actively maintained instance, our processing speed for words recently read is through various processes, such as subvocal rehearsal. faster than that of our processing speed for more unfa- Indicate that working memory relies on at least two dif- miliar words. Classical conditioning refers to the trans- ferent storage mechanisms: the phonological loop, formation of a neutral stimulus into a conditioned which stores acoustic information through subvocal stimulus with a conditioned response; for instance, rehearsal of words or sounds, and the visuospatial sketch- Pavlov observed that his laboratory dogs so strongly pad, which stores visual and spatial information about associated his laboratory workers with meat powder that object characteristics and localization. Note that we the dogs would salivate at the site of them.11 24. Cognition 431

Sensory memory (fraction of a second to 3 seconds)

Automatic processing

Short-term memory Phonological loop (3 to 30 seconds) Effortful processing (aka working memory) Visuospatial sketchpad

Presentation of memory Episodic memory Long-term memory Declarative memory (aka explicit memory) (>30 seconds to remote) Awareness of memory Semantic memory

Nondeclarative memory Procedural memory (aka implicit memory) Priming Classical conditioning

DRAWING 24-2 Memory: Classes 432 Neuroanatomy: Draw It to Know It

Memory: Capacity & Consolidation

Here, we will address the concept of memory capacity In regards to the neuroanatomic circuitry for memory and we will create a workfl ow for the consolidation of processing, draw a medial face of a cerebral hemisphere, memory. First, in regards to short-term memory capac- and show that memories pass from the sensory associa- ity, indicate that short-term memory is able to hold seven tion cortices to the limbic lobe where they are encoded bits of information (plus or minus two) at any given (most notably, in the Papez and amygdaloid circuits), time. However, these bits of information are routinely and then pass to the neocortex, where they are stored manipulated to ease their memory burden. Show that and from where they are retrieved. However, this model the most commonly discussed example of information predicts noninvolvement of the limbic lobe (more spe- manipulation is the process of chunking, wherein we cifi cally, the hippocampus) in the storage process, but take a large amount of information and organize it into multiple memory trace theory has shown that the hip- fewer chunks or bits. For instance, we can represent the pocampal–neocortical bond for episodic memory does string of digits in a telephone number as seven separate not decay but, instead, persists as part of a memory scaf- digits, which we may struggle to remember and have to fold. Th us, indicate that every time an episodic memory frequently rehearse to avoid their decay, or we can use is retrieved, an additional memory trace is formed, and the principles of chunking to combine digits into larger the hippocampal–neocortical ensemble of that memory chunks and reduce their memory burden. For example, is strengthened.15 , 16 even the 11-digit number 18005551212 can easily be Lastly, let’s learn about the clinical corollary of amne- memorized when we chunk it into just three bits of sia (ie, loss of memory), through the oft en-written-about information: 1-800, 555, 1212. patient Henry Gustav Molaison, universally referred to Chunking can also occur through more abstract means, by the initials H.M., who in 1953 underwent bilateral as well. As a remarkable example, albeit rare, through syn- medial temporal lobe resection for intractable epilepsy. esthesia, certain individuals unconsciously perceive infor- Th e primary dysfunction in H.M. was the encoding of mation in sensorial rather than semantic fashion, which new memories; for example, people who came daily to can have disastrous eff ects on comprehension but can visit H.M. were strangers anew every day. On the con- allow for an astonishing ability to chunk extremely large trary, H.M.’s sensory memory was unaff ected and his quantities of information and dramatically boost memory short-term memory was only partially aff ected. Indicate capacity. 12 , 13 For the autistic savant Daniel Tammet, num- that anterograde amnesia is the inability to form new bers appear to him as colors and sounds and carry person- memories aft er the development of amnesia, whereas alities; he unconsciously creates landscape-like projections retrograde amnesia is the inability to retrieve memories of numbers in his mind that allow him to remember stag- that occurred prior to the development of the amnesia. gering amounts of information.14 H.M. had complete anterograde amnesia and also partial Now, let’s shift our focus to the consolidation of retrograde amnesia, which demonstrated a temporal gra- memory. Show that memory consolidation relies upon dient as follows: the degree of his retrograde amnesia encoding (the process in which information is transformed was at its maximum for memories just prior to the opera- into a format in which it can be stored and retrieved), stor- tion and at its minimum for memories 11 years prior to age (the stockpiling of memory into its stored state), and the operation — note that the true duration of H.M.'s retrieval (the accessing of stored memories). temporal gradient is debated.17 24. Cognition 433

Short-term memory capacity: 7+/- 2 bits of information

Neocortex Association Chunking: the process of reducing large amounts of information Retrieval cortex into fewer chunks/bits Storage Encoding Encoding: the transformation of memory into a storagable state Limbic lobe

Storage: the storing of memory

Retrieval: the accessing of stored memories

Multiple memory trace theory: episodic memory retrieval creates memory traces that strenghthen the hippocampal–neocortical ensemble

Anterograde amnesia: the inability to form new memories post development of amnesia

Retrograde amnesia: the inability to retrieve memories from prior to development of amnesia

DRAWING 24-3 Memory: Capacity & Consolidation 434 Neuroanatomy: Draw It to Know It

Apraxia & Neglect (Advanced )

Here, we will learn about the anatomy of the apraxias anterior corpus callosum. Variations in the defi nitions and the phenomenon of neglect. Overall, apraxias are of ideational and ideomotor apraxia exist, but by at least more common with left brain injuries and neglect is one accepted defi nition, ideational apraxia is an inabil- more common with right brain injuries; therefore, we ity to correctly conceptualize an action. For instance, will use a sagittal view of the left lateral hemisphere to patients with ideational apraxia might brush their teeth draw the anatomy of the apraxias and a sagittal view of with a spoon or may be unable to sequence a complex the right lateral hemisphere to draw the anatomy of action, meaning, for instance, rather than putting a letter neglect. However, we need to accept that apraxias can into an envelope and sealing it, they might seal the enve- occur from right brain injury and neglect can occur from lope and then try to stuff the letter into it. Ideomotor left brain injury, and we need to accept, as well, that apraxia is a failure to know how to perform a complex although the laterality of the aff ected limb in the aprax- motor movement; gestures, such as waving goodbye, are ias is oft en contralesional, it is variable. In simple terms, more severely aff ected than concrete movements, such as an apraxia is an inability to perform a purposeful action using an actual tool. 18 – 21 in the setting of preserved overall neurologic function. Now, let’s show an example of a more restricted poste- Broadly, the apraxias can be divided into the frontally rior apraxia. Indicate that injury to the superior parietal based executive apraxias, which aff ect movement, and lobule has traditionally been considered the site of optic the posterior apraxias, which aff ect sensory skills and ataxia (aka visuomotor ataxia); note, however, that the sensorimotor planning.10 actual lesion site for optic ataxia may lie more infero- First, in the left hemisphere, draw the following ana- posterior at the parieto-occipital junction. Optic ataxia tomic landmarks: the precentral sulcus, central sulcus, manifests with an inability to accurately reach for objects and intraparietal sulcus. Now, in regards to the executive due to visual guidance impairment. Optic ataxia is apraxias, fi rst, show that limb-kinetic apraxia occurs one of three important features of Balint syndrome, from injury to the premotor area. In limb-kinetic apraxia, which is due to bilateral occipitoparietal lesions. Th e there is impairment in fi nely graded fi nger movements other two features of Balint syndrome are gaze apraxia and awkwardness of the arm and hand, manifesting with (aka oculomotor apraxia or optic apraxia), which is an an inability to rhythmically open and close the aff ected inability to direct the eyes toward the intended target hand. In speech apraxia, which is a slowing and incoordi- (instead the eyes fi xate on random objects or wander nation of speech in the presence of otherwise normal aimlessly), and simultagnosia, which is the visual fi xa- language and sound vocalization, there is injury to what tion on a part of an object and an inability to see the is referred to in this context as the left precentral gyrus of object for its whole. 7 , 22 , 23 the insula (not shown).10 Gerstmann syndrome occurs from injury to the In regards to the posterior apraxias, fi rst, show that left hemispheric inferior parietal lobule with specifi c injury to the left hemispheric temporoparietal junction involvement of the angular gyrus. It is a four-part syn- produces ideational apraxia and then that left inferior drome of left –right disorientation; fi nger agnosia, which parietal lobule injury produces ideomotor apraxia. Note is a fi nger naming disorder; dyscalculia, which is a that ideomotor apraxia also occurs through disconnec- calculation disorder; and dysgraphia, which is a writing tion phenomena from injury to the premotor cortex and disorder.24 24. Cognition 435

Central Ideomotor Precentral Optic Limb-kinetic sulcus apraxia sulcus ataxia apraxia Intra- parietal sulcus

Ideational apraxia

APRAXIA NEGLECT Left lateral hemisphere Right lateral hemisphere

DRAWING 24-4 Apraxia & Neglect — Partial 436 Neuroanatomy: Draw It to Know It

Apraxia & Neglect (Advanced ) (Cont.)

Now, in regards to neglect, in the right cerebral hemi- presence of a defi cit. When anosognosia accompanies sphere, draw the intraparietal sulcus and label the infe- occipital lobe injury, which results in a visual fi eld defi - rior parietal lobule as the site for hemispatial neglect. cit, patients may display a denial of their own blindness, Hemispatial neglect involves a lack of regard for objects called Anton syndrome. In a separate form of lack of in the contralateral hemisphere. It may be as mild as to awareness, patients may demonstrate autotopagnosia, cause extinction to double simultaneous stimulation, which manifests with an unawareness of one’s own body meaning that patients will perceive a sensory stimulus on parts; for instance, in right hemispheric strokes with the left side when it is presented only to that side and hemispatial neglect, patients with autotopagnosia may neglect the stimulus when it is presented to both sides. insist that their left hand is not their own but is instead Or it may be as severe as to cause failure to attend to the the examiner’s hand. Note that autotopagnosia can occur left half of the world, entirely.21 as a more restricted clinical phenomenon (separate from Finally, show that large right parietal lobe injuries can a broad neglect injury). 25 , 26 cause anosognosia, which is a lack of awareness of the 24. Cognition 437

Central Ideomotor Precentral Optic Limb-kinetic sulcus apraxia sulcus ataxia Anosognosia apraxia Intra- parietal sulcus

Hemispatial Ideational apraxia neglect

APRAXIA NEGLECT Left lateral hemisphere Right lateral hemisphere

DRAWING 24-5 Apraxia & Neglect — Complete 438 Neuroanatomy: Draw It to Know It

References 1 . Wilson , R. A. & Keil , F. C. Th e MIT encyclopedia of the cognitive 15 . Nadel , L. & Moscovitch , M. Hippocampal contributions to cortical sciences , p. 369 ( MIT Press , 2001 ). plasticity. Neuropharmacology 37 , 431 – 439 (1998 ). 2 . M u r d o c h, B . E . Acquired speech and language disorders: a 16 . Nadel , L. , Samsonovich , A. , Ryan , L. & Moscovitch , M. Multiple neuroanatomical and functional neurological approach, 2nd ed., trace theory of human memory: computational, neuroimaging, and pp. 58 – 61 (Wiley-Blackwell , 2010 ). neuropsychological results. Hippocampus 10 , 352 – 368 (2000 ). 3 . Kent , R. D. & Massachusetts Institute of Technology . Th e MIT 17 . Spielberger , C. Encyclopedia of applied psychology, Vol. 3 (Elsevier , encyclopedia of communication disorders , pp. 243 , 250 ( MIT Press , 2003 ). 2004 ). 1 8. M o h r, J . P. Stroke: pathophysiology, diagnosis, and management, 4 . B e r t h i e r, M . L . Transcortical aphasias , pp. 154 – 155 ( Psychology 4th ed., pp. 152 – 154 ( Churchill Livingstone , 2004 ). Press, 1999 ). 1 9. B o c k, G . & G o o d e, J . Sensory guidance of movement, p. 310 (John 5 . F e s t a, J . R . & L a z a r, R . M . Neurovascular neuropsychology, Wiley, 1998 ). pp. 27 – 29 ( Springer , 2009 ). 20 . Banich , M. T. Cognitive neuroscience, 10th ed., p. 141 (Wadsworth/ 6 . S c h a l l e r, B . State-of-the-art imaging in stroke, Vol. 2 , p. 144 Cengage Learning, 2010 ). (Nova Sciences Publishers, Inc., 2008 ). 2 1. C a m p b e l l, W. W., D e J o n g, R . N . & H a e r e r, A . F. DeJong’s the 7 . Devinsky , O. & D’Esposito , M. Neurology of cognitive and behavioral neurologic examination: incorporating the fundamentals of disorders , pp. 147 , 188 – 192 ( Oxford University Press , 2004 ). neuroanatomy and neurophysiology , 6th ed., pp. 93 – 95 ( Lippincott 8 . S c h m a h m a n n, J . D . & P a n d y a, D . N . Fiber pathways of the brain Williams & Wilkins , 2005 ). ( Oxford University Press , 2006 ). 22 . Clark , D. L. , Boutros , N. N. & Mendez , M. F. Th e brain and 9 . Hockenbury , D. H. & Hockenbury , S. E. Psychology , 4th ed., behavior: an introduction to behavioral neuroanatomy , 3rd ed., p. 50 pp. 242 – 246 (Worth Publishers, 2006 ). ( Cambridge University Press , 2010 ). 1 0. C a p p a, S . F. Cognitive neurology: a clinical textbook (Oxford 2 3. G o l d e n b e r g, G . & M i l l e r, B . L . Neuropsychology and behavioral University Press, 2008 ). neurology , p. 400 ( Elsevier , 2008 ). 11 . Byrne , J. H. Concise learning and memory: the editor’s selection, 24 . Mitchell , A. J. Neuropsychiatry and behavioural neurology explained, pp. 22 – 25 ( Elsevier , 2008 ). p. 84 ( W.B. Saunders , 2004 ). 1 2. C y t o w i c, R . E . Synesthesia: a union of the senses, 2nd ed., 25 . Brazis , P. W. , Masdeu , J. C. & Biller , J. Localization in clinical pp. 103 – 104 ( MIT Press , 2002 ). neurology , 5th ed., p. 154 ( Lippincott Williams & Wilkins , 2007 ). 13 . Mills , C. B. , Innis , J. , Westendorf , T. , Owsianiecki , L. & McDonald , 26 . Itti , L. , Rees , G. & Tsotsos , J. K. Neurobiology of attention, p. 345 A . E ff ect of a synesthete’s photisms on name recall . Cortex 4 2, (Elsevier Academic Press, 2005 ). 155 – 163 (2006 ). 14 . Tammet , D. Born on a blue day: inside the extraordinary mind of an autistic savant , p. 3 ( Free Press: a Division of Simon & Schuster, Inc., 2006 ). 2 5 Sleep and Wakefulness

Sleep Neurocircuitry ( Advanced )

Suprachiasmatic Circuitry

Wakefulness Circuitry

Flip-Flop Switch ( Advanced ) 440 Neuroanatomy: Draw It to Know It

Know-It Points

Sleep Neurocircuitry (Advanced )

■ Th e area for non-REM sleep induction lies within the ■ Th rough the phenomenon of sensory gating, sensory anterior hypothalamus, specifi cally in the ventrolateral stimuli that might otherwise wake us from sleep fail preoptic area and the median preoptic nucleus. to reach our cerebral cortex. ■ Th e thalamocortical networks generate sleep ■ Th e putative primary REM-promoting region lies electroencephalographic (EEG) patterns: sleep within the pons in what is called the sublaterodorsal spindles and slow-wave sleep. nucleus in the rat and the peri-locus coeruleus in the ■ Th e reticular thalamic nuclei gate the fl ow of cat. information between the thalamus and cortex. ■ Th e supra-olivary medulla is responsible for muscle ■ When the thalamocortical membrane hyperpolarizes atonia during REM sleep. more negatively than –65 mV, T-type calcium channels open, which generates a low-threshold spike.

Suprachiasmatic Circuitry

■ Our internal clock allows us to maintain a 24-hour ᭺ Th e cervical spinal cord excites the superior cycle of behavioral activities even when we are placed cervical ganglion in non-24-hour environments. ᭺ Th e superior cervical ganglion activates the ■ Th e timing of our internal clock is aff ected by certain production of melatonin in the pineal body environmental cues, called zeitgebers, of which light – Light phase: is commonly considered the most potent. ᭺ Th e suprachiasmatic nucleus inhibits the ■ Th e retinohypothalamic pathway: paraventricular nucleus, thus inactivating the rest – Dark phase: of the pathway ᭺ Descending hypothalamospinal projections from ■ Tumor necrosis factor-alpha and interleukin-1 are the paraventricular nucleus excite the cervical two well-studied substances with sleep-promoting spinal cord p r o p e r t i e s .

Wakefulness Circuitry

■ Th e laterodorsal tegmental and pedunculopontine ■ Th e tuberomammillary nucleus lies within the nuclei lie within the lower midbrain and upper pons hypothalamus and is the sole source of histamine in and are cholinergic. the brain. ■ Th e locus coeruleus lies, most notably, within the ■ Cholinergic basal forebrain nuclei lie within the posterior pons and is noradrenergic. ventral surface of the frontal lobe. ■ Th e substantia nigra and ventral tegmental area lie ■ Th e intralaminar thalamic nuclei play an important within the anterior midbrain and are dopaminergic. role in the ascending arousal system. ■ Th e dorsal group of raphe nuclei lie within the central upper pons and midbrain and are serotinergic. 25. Sleep and Wakefulness 441

Flip-Flop Switch (Advanced )

■ Th e arousal center inhibits the sleep center. ■ Orexins are produced by a discrete neuronal ■ Th e orexigenic cells stabilize the arousal center. population within the lateral hypothalamus. ■ Th e sleep center inhibits the arousal center and also ■ Loss of orexin results in the clinical condition of the orexigenic cells. n a r c o l e p s y w i t h c a t a p l e x y .

a Aq

D Hy

N. oculamet V4

FIGURE 25-1 Von Economo’s clinical–pathologic correlation for the sleep and wakefulness centers. Th e center for sleep is designated by horizontal lines and the center for wakefulness is designated by vertical (diagonal) lines. Used with permission from Economo, Constantin von. “Sleep as a Problem of Localization.” Th e Journal of Nervous and Mental Disease 71, no. 3 (1930). 442 Neuroanatomy: Draw It to Know It

Sleep Neurocircuitry (Advanced )

Here, we will learn the neurocircuitry of sleep: we will negatively than –65 mV, which causes the T-type calcium learn the anatomic location of the sleep center, the phys- channels to open, which generates a low-threshold spike: iology of the thalamocortical circuits, and the pathway a burst of action potentials. In our drawing, show that for the generation of REM sleep. Indicate that the area the thalamocortical burst acts both on the reticular thal- for non-REM sleep induction lies within the anterior amic cells to facilitate their rhythmic oscillation and also hypothalamus, specifi cally in the ventrolateral preoptic on the cortical pyramidal neurons, which generate the area and the median preoptic nucleus. Baron Constantin EEG patterns observed during sleep. Lastly, show that von Economo fi rst hypothesized that this area was the aft er the low-threshold spike, there is a refractory period sleep induction center when in 1916–17 he studied the for the thalamocortical neurons. Indicate that as a clinical–pathologic correlations of patients who had byproduct of the refractory period, there is cessation of died from encephalitis lethargica (aka von Economo’s the excitatory thalamocortical inputs to such relay neu- encephalitis). Th e parkinsonian and oculomotor mani- rons as the lateral geniculate nucleus, which results in festations found in patients with that disorder led him the phenomenon of sensory gating: the process wherein to postulate that the sleep induction center lies within sensory stimuli that might otherwise wake us from sleep the anterior hypothalamus and the area for wakefulness fail to reach our cerebral cortex.2 – 6 lies, roughly, within the posterior hypothalamus/upper Now, let’s turn our attention to REM sleep. Note brainstem, and over the next several decades, he was that no defi nitive model for REM sleep has been con- proven, to a large extent, correct (see Figure 25-1 ).1 fi rmed and our fl ow diagram, here, represents only a Now, let’s shift our discussion to the physiology of best hypothesis. First, indicate that the putative primary sleep: specifi cally, we will show how the thalamocortical REM-promoting region lies within the pons, in what is networks generate sleep electroencephalographic (EEG) called the sublaterodorsal nucleus in the rat and the peri- patterns— sleep spindles and slow-wave sleep. First, let’s locus coeruleus in the cat. Indicate that this region excites draw the major cell populations responsible for this net- the cortex to produce the characteristic EEG pattern of work; draw the thalamus and label the GABAergic retic- REM sleep, and also excites a constellation of nuclei ular thalamic neurons, and then draw the T-type calcium called the supra-olivary medulla to produce muscle channel thalamocortical neurons. Next, draw the corti- atonia during REM sleep. Now, indicate that during cal pyramidal cells. Th e reticular thalamic nuclei gate the wakefulness and non-REM sleep, the ventrolateral peri- fl ow of information between the thalamus and cortex, aqueductal gray area and the dorsal deep mesencephalic and the thalamocortical neurons drive cortical EEG pat- reticular nucleus tonically inhibit the sublaterodorsal terns through, at least in part, the low-threshold spike. nucleus/peri-locus coeruleus. Lastly, show that during To illustrate the physiology of the low-threshold REM sleep, the dorsal paragigantocellular nucleus (in spike, include in our diagram a graph of the membrane the medulla) and the lateral hypothalamic melanin- potential of the thalamocortical neurons. Label voltage concentrating hormone nuclei suppress the ventrolateral on the Y-axis and time on the X-axis. Th en, demarcate periaqueductal gray area and dorsal deep mesencephalic the –65 mV point. Now, show that excitation of the reticular nuclei, which disinhibits the sublaterodorsal reticular thalamic nuclei causes GABAergic inhibition nucleus/peri-locus coeruleus, freeing them to act on the of thalamocortical cells. Th en, indicate that eventually supra-olivary medulla and cerebral cortex to produce the thalamocortical membrane hyperpolarizes more REM sleep as previously described. 7 – 10 25. Sleep and Wakefulness 443

NON-REM SLEEP CIRCUITRY Cortical pyramidal Low-threshold neurons spike

Refractory Voltage period *Non-REM sleep induction center lies within the -65mV Thalamocortical anterior hypothalamus T-type calcium neurons (ventrolateral preoptic area Reticular channels open & median preoptic nucleus) Nuclei Time Lateral Thalamocortical neuronal geniculate membrane potetnial Sensory gating

REM SLEEP CIRCUITRY Lateral hypothalamic REM EEG melanin-concentrating Ventrolateral peri- Cortex hormone nuclei aqueductal grey area Sublaterodorsal nucleus/peri-locus dorsal deep mesen- coeruleus Dorsal paragiganto- cephalic reticular nucleus Supraolivary cellular reticular nucleus medulla Muscle atonia

DRAWING 25-1 Sleep Neurocircuitry 444 Neuroanatomy: Draw It to Know It

Suprachiasmatic Circuitry

Here, we will draw the circuitry for the suprachiasmatic Now, show that during the light phase, light passes control of melatonin production and release. As a along the retinohypothalamic pathway to excite the byproduct of 3.5 billion years of the Earth’s daily rota- suprachiasmatic nucleus. Th en, indicate that the supra- tion around its axis, all of us have a circadian rhythm of chiasmatic nucleus inhibits the paraventricular nucleus, approximately 24 hours. Because of this internal clock, which causes inhibition of the production and release of we maintain a 24-hour cycle of behavioral activities even melatonin, thus promoting wakefulness.11 when we are placed in non-24-hour environments. In addition to melatonin, several other substances Importantly, the timing of our internal clock is aff ected have been shown to play an important role in sleep by certain environmental cues, called zeitgebers, of which induction. At the beginning of the 20th century, light is commonly considered the most potent. In this Kuniomi Ishimori in Japan and Henri Piéron in France, diagram, we will see how through the retinohypotha- independently but concurrently, performed experiments lamic pathway, light acts on the suprachiasmatic nucleus wherein they transferred brain matter (cerebrospinal (the master timekeeper) to adjust the production and fl uid or brain tissue) from sleep-deprived dogs to well- release of melatonin and, in turn, the timing of our inter- rested dogs and observed that the well-rested dogs went nal clock. to sleep. From this evidence, they both concluded that First, draw an outline of the hypothalamus — include certain agents within the body must accumulate to pro- the pituitary gland and mammillary bodies. Next, add mote sleep. Experiments over the past 30 years have the optic chiasm. Th en, label the suprachiasmatic nucleus identifi ed several sleep-promoting substances. Tumor just above the optic chiasm in the anterior hypothalamus. necrosis factor-alpha and interleukin-1 are two well- Next, label the paraventricular nucleus. Now, add a cross- studied substances with sleep-promoting properties. section through the cervical spinal cord. Th en, show the Th ey have been shown to cause sleepiness and fatigue as superior cervical ganglion and the pineal gland. well as other somatic symptoms commonly associated Next, show that during the dark phase, descending with sleepiness: cognitive dysfunction, sensitivity to hypothalamospinal projections from the paraventricular pain, impaired glucose tolerance, and chronic infl amma- nucleus excite the cervical spinal cord, which, in turn, tion. Another sleep-promoting substance of particular excites the superior cervical ganglion, which activates interest is adenosine because caff eine, which is second the production of melatonin from within the pineal only to oil in its importance as a global commodity, is body, causing its release into circulation, which helps believed to produce its wake-promoting eff ects through promote sleep. its actions on adenosine receptors.12 25. Sleep and Wakefulness 445

Pineal gland

Paraventricular Melatonin Postsympathetic nucleus production fibers & release

Suprachiasmatic nucleus

Optic Descending Chiasm hypothalamo- Superior spinal cervical Retino- pathway ganglion hypothalamic pathway Presympathetic fibers

DRAWING 25-2 Suprachiasmatic Circuitry 446 Neuroanatomy: Draw It to Know It

Wakefulness Circuitry

Before the center for sleep was proven, the center for locus coeruleus and label it as noradrenergic (the largest wakefulness was discovered. In the 1940s and 1950s concentration of locus coeruleus neurons lies within neurophysiologists Giuseppe Moruzzi and H. W. the pons); in the anterior midbrain, group the substantia Magoun performed a series of EEG studies to prove the nigra and ventral tegmental area together and show that existence of the wakefulness center. Th ey described an they are dopaminergic; and fi nally, in the central upper active arousal generator in the brainstem reticular for- pons and midbrain, draw the dorsal group of raphe mation, coined the ascending reticular activating system, nuclei and indicate that they are serotinergic. Note that which was shown to directly and indirectly activate the the locus coeruleus, substantia nigra, and raphe nuclei cerebral cortex by way of diff use projection fi bers that are drawn in greater detail in Chapter 9. Next, move to projected directly to the cortex and also indirectly to the the hypothalamus. Draw the tuberomammillary nucleus cortex through the thalamus. Over the past several in the hypothalamus; it is the sole source of histamine in decades, discovery of the specifi c brainstem, hypotha- the brain and it is important for wakefulness. Now, lamic, thalamic, and basal forebrain cell populations include the cholinergic basal forebrain nuclei in the responsible for the arousal system has elaborated and ventral surface of the frontal lobe; they are important to shaped our understanding of wakefulness anatomy. wakefulness. Finally, consider that in Drawings 20-3 and Numerous neurotransmitters and neuronal populations 20-4, we showed that the intralaminar thalamic nuclei within the brainstem, hypothalamus, thalamus, and basal also play an important role in the arousal system. forebrain have been discovered, some of which we will As a pharmacologic corollary to the list of neuro- specifi cally indicate here. transmitters involved in wakefulness, consider that In the corner of the diagram, for reference, draw a amphetamines are adrenergic reuptake inhibitors and mid-sagittal view of a brain. Next, in the center of the are stimulatory — they increase the amount of circulat- page, draw an expanded view of the basal forebrain, ing monoamines; consider that antihistamines, such as hypothalamus, and brainstem. To begin our process of diphenhydramine (Benadryl), cause drowsiness, as do labeling the wake-promoting cells, indicate the latero- anti cholinergic agents; and consider that tricyclic anti- dorsal tegmental and pedunculopontine nuclei in the depressants can be especially sedating because they lower midbrain and upper pons and show that they are oft en have both anti cholinergic and anti histaminergic cholinergic. Next, we will draw the upper brainstem properties. 13 monoaminergic nuclei. In the posterior pons, draw the 25. Sleep and Wakefulness 447

Basal forebrain Lateral dorsal (cholinergic) Tuberomammillary Substantia tegmental / nucleus nigra & ventral pedunculopontine (histaminergic) tegmental area nuclei (cholinergic) (dopaminergic)

Locus coeruleus (noradrenergic) Dorsal raphe nuclear group (serotinergic)

DRAWING 25-3 Wakefulness Circuitry 448 Neuroanatomy: Draw It to Know It

Flip-Flop Switch (Advanced )

Here, we will draw the fl ip-fl op switch, which is the cir- sleep center inhibits the arousal center and also the orex- cuit for the transition between sleep and wakefulness. igenic cells. 14 A fl ip-fl op circuit is an electrical engineering term for a Th e story of the discovery of orexin is both interest- switch that avoids transitional states; the circuit is in ing and illuminating. In 1998, two diff erent research either one of two states but not a blend of both. If you groups concurrently but independently identifi ed a pair are tired when you lie down, you quickly fall asleep, of hypothalamic neuropeptides, named orexins by and when you’re ready to rise, you suddenly wake up. Sakurai et al. and hypocretins by de Lecea et al. (we refer To begin, indicate the sleep and wake states and then to them here as orexins). Orexins are produced by a dis- draw the fl ip-fl op switch, which transitions between crete neuronal population within the lateral hypothala- them. In our fi rst diagram, we will show the circuit in a mus, and their functional role in the nervous system state of wakefulness. Indicate the following important came as a surprise. A decade and a half prior to the iden- hypothalamic areas: the ventrolateral preoptic area and tifi cation of the orexins, in 1982, Baker et al. identifi ed a the median preoptic nucleus, which constitute the sleep candidate gene, designated canarc-1, for the clinical dis- center; the wake-promoting cells; and the perifornical- order of narcolepsy in a colony of Doberman Pinschers lateral hypothalamic orexigenic cells, which form the wake- with canine narcolepsy. Despite extensive study of this fulness stabilizer— discussed in detail at the end. Show that gene, however, the protein responsible for narcolepsy during wakefulness, the wake-promoting cells inhibit the was unable to be identifi ed. In 1999, when researchers sleep center and that the perifornical-lateral hypothalamic began studying the fi rst orexin knockout mouse, they orexigenic cells excite the wake-promoting cells. were not expecting to fi nd any manifestations of narco- Next, let’s show the fl ip-fl op circuitry in the sleep lepsy; instead, they hypothesized that orexin would be state. Re-draw the sleep and wake states and the fl ip-fl op shown to aff ect energy metabolism, given the already switch, and then again include the previously listed proven role of the lateral hypothalamus in energy homeo- structures. Now, show that in the sleep state, the sleep stasis. However, study of homozygote orexin knockout center inhibits the wake-promoting cells and also inhib- mice, instead, demonstrated that the mice expressed a its their stabilizer: the perifornical-lateral hypothalamic phenotype consistent with narcolepsy with cataplexy: orexigenic cells. they displayed cataplexy and abnormal wake-REM sleep In short, when we consider the sleep and wake states transitions. Th us, orexin was discovered to play an unan- as a whole, the arousal center inhibits the sleep center; ticipated yet highly important role in the stabilization of the orexigenic cells stabilize the arousal center; and the wakefulness.15 25. Sleep and Wakefulness 449

Sleep Wake

Ventrolateral preoptic Perifornical & median preoptic lateral hypothalamus hypothalamic (Sleep center) area (orexigenic)

Wake-promoting cells

Sleep Wake

Ventrolateral preoptic Perifornical & median preoptic lateral hypothalamus hypothalamic (Sleep center) area (orexigenic)

Wake-promoting cells

DRAWING 25-4 Flip-Flop Switch 450 Neuroanatomy: Draw It to Know It

References 1 . W i n k e l m a n, J . W. & P l a n t e, D . T. Foundations of psychiatric sleep 8 . Hassani , O. K., Lee , M. G. & Jones , B. E. Melanin-concentrating medicine , Chapter 2 ( Cambridge University Press , 2010 ). hormone neurons discharge in a reciprocal manner to orexin 2 . B r a z i e r, M . A . Th e history of the electrical activity of the brain as a neurons across the sleep-wake cycle . Proc Natl Acad Sci USA 106 , method for localizing sensory function . Med Hist 7 , 199 – 211 2418 – 2422 (2009 ). (1963 ). 9 . Ve t r i v e l a n, R ., F u l l e r, P. M ., To n g, Q . & L u, J . M e d u l l a r y c i r c u i t r y 3 . Crunelli , V. , Cope , D. W. & Hughes , S. W. Th alamic T-type Ca2 + regulating rapid eye movement sleep and motor atonia . J Neurosci channels and NREM sleep . Cell Calcium 40 , 175 – 190 (2006 ). 29 , 9361 – 9369 (2009 ). 4 . Steriade , M. , McCormick , D. A. & Sejnowski , T. J. Th alamocortical 10 . Mallick , B. N. Rapid eye movement sleep: regulation and function oscillations in the sleeping and aroused brain . Science 262 , 679 – 685 ( Cambridge University Press , 2011 ). (1993 ). 11 . Benarroch , E. E. Suprachiasmatic nucleus and melatonin: reciprocal 5 . Livingstone , M. S. & Hubel , D. H. Eff ects of sleep and arousal on the interactions and clinical correlations. Neurology 71 , 594 – 598 (2008 ). processing of visual information in the cat. Nature 291 , 554 – 561 12 . Basics of sleep guide , 2nd ed. ( Sleep Research Society , 2009 ). (1981 ). 13 . Moruzzi , G. & Magoun , H. W. Brain stem reticular formation and 6 . Anderson , M. P. , et al . Th alamic Cav3.1 T-type Ca2 + channel plays activation of the EEG. 1949 . J Neuropsychiatry Clin Neurosci 7 , a crucial role in stabilizing sleep. Proc Natl Acad Sci USA 102 , 251 – 267 (1995 ). 1743 – 1748 (2005 ). 1 4. S a p e r, C . B ., S c a m m e l l, T. E . & L u, J . H y p o t h a l a m i c r e g u l a t i o n o f 7 . F o r t, P. , B a s s e t t i, C . L . & L u p p i, P. H . A l t e r n a t i n g v i g i l a n c e s t a t e s : sleep and circadian rhythms . Nature 437 , 1257 – 1263 (2005 ). new insights regarding neuronal networks and mechanisms. Eur J 15 . Chemelli , R. M., et al. Narcolepsy in orexin knockout mice: Neurosci 29 , 1741 – 1753 (2009 ). molecular genetics of sleep regulation . Cell 98 , 437 – 451 (1999 ). Index

abdomen, cutaneous nerves , 86 , 87 annulus of Zinn, 196 , 198 , 204 abducens nerve anosognosia , 427 , 436 , 437 cranial nerve nuclei , 182 , 183 , 185 ansa cervicalis, cervical plexus, 50 , 51 skull foramina , 190 , 191 ansa lenticularis abducens nucleus, eye movements, 412 , 413 basal ganglia , 310 , 311 abductor digiti minimi, ulnar nerve , 44 , 45 pathway , 312 , 313 abductor pollicis, ulnar nerve , 44 , 45 anteriomedian nucleus, oculomotor nuclei, 206 , 207 abductor pollicis brevis, median nerve, 40 , 41 anterior (chiasmatic) group, hypothalamus , 352 , 353 abductor pollicis longus, radial nerve, 48 , 49 anterior cellebellum , 249 f accessory nerve anterior cerebral artery cranial nerve nuclei , 182 , 183 , 185 arterial borderzones , 328 , 329 skull foramina , 190 , 191 circle of Willis, 322 , 323 acetylcholine, parasympathetic nervous system, 94 , 95 deep cerebral arteries, 326 , 327 Achilles refl ex, muscle stretch refl ex, 132 leptomeningeal cerebral arteries, 324 , 325 Adamkiewicz, artery of , 319 , 334 anterior choroidal artery adductor muscles, thigh , 66 , 67 deep cerebral arteries, 326 , 327 adenohypophysis leptomeningeal cerebral arteries, 324 , 325 diencephalon , 344 , 345 anterior cingulate gyrus, limbic system, 362 , 363 hypothalamus , 354 , 355 anterior cranial fossa, skull base, 188 , 189 adenosine, sleep, 444 anterior funiculus, spinal cord , 110 , 111 Adie's tonic pupil , 422 anterior group nuclei, thalamus, 346 , 347 , 350 , 351 adrenocorticotropic hormone, hypothalamus, 354 , 355 anterior inferior cerebellar artery (AICA) Aicardi syndrome , 300 cerebellum , 332 , 333 alar plates, spinal and cranial nerve, 174 , 178 , 179 cranial nerves, 198 , 199 alexia without agraphia anterior interosseous group, median nerve , 39 , 41 axial view, 299 , 301 anterior junction, visual fi eld defi cits, 398 , 399 disconnection syndrome , 298 , 300 anterior junction syndrome , 398 alien hand syndrome , 298 , 300 , 301 anterior parahippocampal gyrus, hippocampus , allocortex, cerebral cytoarchitecture, 269 , 282 , 283 366 , 367 Ammon's horn, 366 anterior peripheral nerve map , 74 f amygdale, limbic system , 362 , 363 anterior semicircular canal, ear, 238 , 239 amyotrophic lateral sclerosis (ALS) anterior spinal artery gag refl ex, 228 , 229 circle of Willis, 322 , 323 spinal cord disorder , 124 , 125 spinal cord arteries, 334 , 335 anatomic axial images, terminology, 8 , 9 anterior spinal artery ischemia, disorder , 120 , 121 , anatomy 123, 125 basal ganglia, 304 , 308 , 309 anterior spinocerebellar tract, spinal cord , 107 , cranial nerve 7 , 222–225 118, 119 cranial nerves 3, 4, and 6 , 198 , 199 anterograde amnesia, memory, 432 , 433 deep cerebral arteries, 326 , 327 anterolateral group, brainstem arteries , 330 , 331 direct and indirect pathways of basal ganglia , 312 , 313 anterolateral system hippocampus , 358 , 366 , 367 medulla , 156 , 157 nervous system, 6 , 7 spinal cord, 106 , 112 , 113 ventricular system, 15 f anterolateral system fi bers, spinal cord, 107 , 116 , 117 anconeus, radial nerve , 46 , 47 anteromedial group, brainstem arteries, 330 , 331 angiography anteromedial hypothalamus , 352 , 353 internal carotid system , 320f anticholinergic agents , 446 vertebrobasilar system, 320 f antihistamines , 446 452 Index

Anton syndrome, 436 pupillary light refl ex, 422 , 423 segmental organization of peripheral aortic bodies, cardiac refl ex, 102 , 103 spinal cord arteries, 334 , 335 nerves, 129 f aphasia, language disorder, 428 , 429 upper medulla/pontomedullary junction, serratus anterior, 30 f appendix, referred pain , 88 , 89 242 , 243 brachioradialis, radial nerve, 46 , 47 , 49 apraxias , 434 , 435 , 437 visual pathways, 380 , 390 , 391 brain arachnoid mater, meninges, 16 , 17 axillary artery, brachial plexus and, 29f , 30 arteries of base of , 332 f archicortex, allocortex, 282 , 283 axillary nerve, 32 , 33 injury , 10 , 11 arcuate fasciculus, long association fi bers, orientational terminology, 4 , 8 , 9 294, 295 plate 4 and plate 8 from 1810 atlas , 5f arcuate nucleus, hypothalamus, 354 Babinski sign, 4 , 10 brainstem , 6 , 7 , 140 , 160–161 arm, cutaneous nerves , 82 , 83 back, cutaneous nerves, 86 , 87 anterior aspect, 141 f arm fi bers Balint syndrome, 427 , 434 arteries , 319 , 330 , 331 motor projections , 164 , 165 basal forebrain , 359 , 374–377 , 446 , 447 central nervous system, 10 , 11 sensory projections, 162 , 163 basal ganglia, 6 , 7 , 304 , 305 composite-axial view, 140 , 148 , 149 Arnold–Chiari syndrome , 300 anatomy , 308 , 309 cranial nerve 6 , 198 , 199 arterial borderzones, 318 , 328 , 329 anatomy of direct and indirect pathways, major motor projections , 164–165 arterial supply, 318 , 319 312 , 313 major sensory projections, 162–163 angiography of internal carotid system , 320f circuitry of direct and indirect pathways , medulla , 156–157 angiography of vertebrobasilar system , 320 f 314 , 315 medullary syndromes, 170–171 arterial borderzones , 328 , 329 coronal view through anterior region , 305f midbrain , 150–153 base of brain , 332f coronal view through middle region , 306f midbrain syndromes, 166–167 brainstem arteries , 330 , 331 coronal view through posterior region , 307f pons , 154–155 cerebellar arteries, 332 , 333 nomenclature , 310 , 311 pontine syndromes , 168–169 cerebellum , 258 , 259 thalamus , 350 , 351 posterior aspect , 142f circle of Willis, 322 , 323 white matter connections , 310 , 311 sagittal view, 227 deep cerebral arteries, 326 , 327 basal nucleus of Meynert, 374 , 375 , 376 , 377 spinal and cranial nuclear classifi cation, leptomeningeal cerebral arteries, 324 , 325 basal plates, spinal and cranial nerve, 174 , 180, 181 spinal cord arteries, 334 , 335 178, 179 Broca's aphasia, language disorder, 428 , 429 thalamic arteries , 336 , 337 basal veins of Rosenthal, 14 , 22 , 23 Broca's area artery of Adamkiewicz , 319 , 334 basilar artery Brodmann areas , 284 , 285 ascending arousal system, thalamus , 350 , 351 brainstem , 330 , 331 diagonal band of Broca, 372 , 373 ascending pathways, spinal cord , 106 , 112 , 113 circle of Willis, 322 , 323 Brodmann areas , 284 , 285 association fi bers, cerebral white matter, basis cortical visual areas, 400 , 402 292, 293 brainstem , 180 , 181 diagram , 272 f auditory physiology, 233 , 244 , 245 brainstem composite, 148 , 149 Brown-Séquard syndrome, 120 , 121 , 123 , 125 auditory processes. See also ear midbrain , 151 , 153 central pathways, 242 , 243 pons , 154 , 155 physiology , 244 , 245 Bell's palsy, cranial nerve 7 , 220 , 221 calcarine cortex , 392 , 393 auditory system, medial geniculate nucleus , bend, internal capsule, 296 , 297 calcarine sulcus, Brodmann areas, 284 , 285 348 , 349 , 350 , 351 Benedikt's syndrome, midbrain syndrome , 160 , canal of Schlemm, iridocorneal fi ltration , autonomic fi ber arrangements, 92 , 94 , 95 166 , 167 384, 385 parasympathetic nervous system , 96–97 benign paroxysmal positional vertigo, ear , 238 capacity, memory , 432 , 433 sympathetic nervous system, 98–99 Betz cell, cerebral cytoarchitecture, 282 , 283 cardiac pain, referred pain, 88 , 89 autotopagnosia , 427 , 436 , 437 biceps brachii, 30 , 31 cardiac refl ex, 93 , 102 , 103 axial, terminology, 4 biceps refl ex, muscle stretch refl ex, 132 cardiorespiratory region, cranial nerves 9 & 10 , axial section biconvex lens, eye, 382 , 383 226 , 227 brain , 8 , 9 bilateral amygdale, limbic system, 362 , 363 carotid arteries, sympathetic nervous system , developing embryo , 176 f bilateral eye movement circuitry, 412 , 413 98 , 99 medulla , 145f , 147 f bilateral internuclear ophthalmoplegia, 412 , 413 carotid body, cardiac refl ex, 102 , 103 midbrain , 143 f , 146 f binaural sound localization , 244 , 245 carpal tunnel, median nerve , 38 , 39 neural tube, 176 f bitemporal hemianopia, 394 carpal tunnel syndrome , 38 pons , 144 f , 146 f bladder, urinary system , 100 , 101 cataplexy , 448 skull base , 177f , 189 , 191 blind spot, eye , 386 cataracts, eye, 382 axial view body analysis, extrastriate body area, 404 , 405 cauda equine, spinal canal, 130 , 131 alexia without agraphia , 299 , 301 borderzones, arterial, 318 , 328 , 329 cauda equina syndrome, 130 basal ganglia , 308 , 309 Bouthillier, classifi cation scheme, 192 caudal, terminology, 4 , 8 , 9 brainstem arteries , 330 , 331 Bowman's gland, 370 caudate commissural fi bers, 298 , 299 , 301 brachial plexus , 28 , 29f , 30–35 basal ganglia , 308 , 309 internal capsule, 296 , 297 biceps brachii, 30 f limbic system, 364 , 365 leptomeningeal cerebral arteries, 324 , 325 complete drawing, 35 nomenclature , 310 , 311 optic pathway, 390 f , 391 partial drawing, 31 , 33 cavernous sinus , 175 , 192 , 193 , 198 , 199 pons , 420 , 421 rhomboids , 30 f cell bodies, retina, 386 , 387 Index 453

central auditory pathways, 232 , 242 , 243 cervical spinal cord, 110 , 111 cornu ammonis, hippocampus , 366 , 367 central canal, spinal cord , 106 , 110 , 111 axial section , 108f coronal, terminology, 4 central caudal nucleus, oculomotor nuclei , cranial nerve nuclei , 183 , 185 coronal view 206, 207 cervico-medullary junction, motor projections, arterial borderzones , 328 , 329 central cord syndrome , 122 , 123 , 125 164 , 165 basal ganglia , 305f , 306 f, 307 f, 308 , 309 central nervous system, divisions and signs , Chiari malformation, syndrome, 258 brain , 8 , 9 10, 11 chiasmatic group, hypothalamus , 352 , 353 cavernous sinus , 192 , 193 central sulcus, insula , 280 , 281 choroids, eye, 382 , 383 , 384 , 385 central auditory pathways, 242 , 243 central tegmental tract, midbrain , 152 , 153 choroid plexus, 14 , 18 , 19 cerebral white matter , 292 , 293 central vision, cortical representation, 392 , 393 chunking, memory , 432 , 433 diencephalon , 342f , 344 , 345 centrum semiovale, cerebral white matter , ciliary body, eye , 382 , 383 eye , 382 , 383 , 385 , 387 292 , 293 ciliary ganglion, pupillary light refl ex, 422 , 423 hippocampus , 366 , 367 cerebellar cortex, corticopontocerebellar cingulate gyrus, limbic system, 362 , 363 hypothalamus , 352 , 353 pathway , 264 , 265 cingulate sulcus, medial face of cerebrum , limbic pathways , 364 , 365 cerebellar tonsils, midline structure , 258 , 259 276, 277 pupillary light refl ex, 422 , 423 cerebellum , 6 , 7 , 248–249 cingulum spinal cord arteries, 334 , 335 anterior , 249 f limbic system, 364 , 365 corona radiate, cerebral white matter , 292 , 293 arterial supply, 257 , 258 , 259 long association fi bers, 294 , 295 corpus callosum arteries , 332 , 333 circle of Willis, 318 , 322 , 323 commissure , 298 central nervous system, 10 , 11 circuitry limbic system, 362 , 363 , 364 , 365 cerebellar somatotopy , 251f basal ganglia pathways , 305 , 314 , 315 sagittal view, 299 , 301 corticopontocerebellar pathway, 264–265 cerebellum , 260–263 corpus cerebelli , 252 , 253 lobes, zones and modules , 252 , 253 fl ip-fl op switch, 441 , 448 , 449 corpus striatum, term , 304 , 310 , 311 midline structures , 257 , 258 , 259 hippocampus , 359 , 368 , 369 cortex modules , 250 f horizontal saccade , 410 , 414 , 415 circuitry of basal ganglia, 314 , 315 nuclei and circuitry , 260–263 sleep neurocircuitry, 440 , 442 , 443 insular , 280 f peduncles , 256 , 257 , 259 suprachiasmatic , 440 , 444 , 445 cortical cell layers, cerebellum, 260–263 somatotopy and lobules, 254 , 255 wakefulness , 440 , 446 , 447 corticobasal degeneration, 300 cerebral aqueduct of Sylvius , 20 circular sulcus, insula, 280 , 281 corticopontocerebellary pathway, 249 , 264 , 265 cerebral arteries , 319 , 332 , 333 cisternal segment, cranial nerve 7 , 222 , corticospinal tract fi bers, pons, 154 , 155 cerebral cortex, cytoarchitecture , 269 , 282 , 283 223, 225 corticospinal tracts, medulla, 156 , 157 cerebral cortical pyramidal cells, 4 cisterns , 14 , 22 , 23 cranial nerve 3 , 196 , 198 , 199 cerebral grey matter, 268–269 classical conditioning, memory, 430 , 431 extraocular movements, 200 , 201 Brodmann areas, 272 f, 284 , 285 Claude's syndrome, midbrain, 160 , 166 , 167 sagittal view, 197 f cerebral cytoarchitecture, 282 , 283 climbing fi bers, nuclei and circuitry , 248 , cranial nerve 4 , 198 , 199 inferior cerebral surface , 271f 260–263 extraocular movements , 200 , 201 inferior face of cerebral hemisphere , cochlea sagittal view, 197 f 278 , 279 auditory physiology, 244 , 245 cranial nerve 5 , 212 insula , 280 , 281 ear , 236 , 237 , 239 nuclei , 216 , 217 lateral cerebral surface , 270 f cochlear nuclei, auditory physiology, 244 , 245 peripheral innervation , 214 , 215 lateral face of cerebral hemisphere, 274 , 275 cognition , 426 , 427 tracts , 218 , 219 medial cerebral surface, 270 f apraxia and neglect, 434–437 cranial nerve 6 , 198 , 199 medial face of cerebral hemisphere, 276 , 277 language disorders, 428 , 429 extraocular movements , 200 , 201 cerebral infarction, arterial borderzones, 328 memory capacity and consolidation , 432 , 433 sagittal view, 197 f cerebral opercula, insula, 280 , 281 memory classes , 430 , 431 cranial nerve 7 , 212 , 213 cerebral ventricles , 14 , 20 , 21 collateral sulcus, medial face of cerebrum , anatomy , 222–225 cerebrospinal fl uid fl ow, 18 , 19 276 , 277 complete drawing, 225 cerebral white matter , 288 , 292 , 293 color detection, cone photoreceptors, 400 innervation , 220 , 221 Achille–Louis Foville's illustrations, 290 f color processing, visual area , 402 , 403 partial drawing, 223 commissures and disconnections , 298–301 commissures & disconnections , 289 , 298–301 cranial nerve 9 , 213 , 226 , 227 internal capsule, 296 , 297 complete drawing, 301 cranial nerve 10 , 213 , 226 , 227 long association fi bers, 294 , 295 partial drawing, 299 cranial nerve 12 , 197 , 208 , 209 organization , 291f comprehension, language disorder, 428 , 429 cranial nerve nuclei , 4 , 174 , 182–187 c e r e b r o - s p i n a l fl uid, 6 , 7 conduction aphasia, language disorder, 428 , 429 complete drawing, 185 fl ow, 14 , 18 , 19 cone photoreceptors, 400 partial drawing, 183 fl ow pattern , 15f consolidation, memory , 432 , 433 simplifi ed, 186 , 187 pons , 154 , 155 contralateral volitional horizontal gaze palsy , cranial nerves, 196–197 cervical plexus , 29 , 50–53 416 , 417 cavernous sinus , 192 , 193 complete drawing, 53 conus medullaris, spinal canal, 130 , 131 nuclei of cranial nerve 5 , 216 partial drawing, 51 coracobrachialis, brachial plexus , 34 , 35 origins , 174 , 178–179 segmental organization of peripheral c o r d fi bers, cerebral white matter , 292 , 293 parasympathetic nervous system , 96 , 97 nerves, 129 f cornea, eye, 382 , 383 peripheral innervation of nerve 5 , 214 , 215 454 Index

cribriform plate, olfactory system , 370 , dorsal motor nucleus of vagus, cranial nerve , excitatory burst neurons 371, 373 96 , 97 anatomy and control , 416 , 417 cuneate fasciculus, spinal cord , 106 , 112 , 113 dorsal nucleus, oculomotor nuclei , 206 , 207 horizontal saccade, 414 , 415 cuneocerebellar tract, spinal cord , 107 , dorsal nucleus of Clark, spinal cord , 110 vertical saccades , 418 , 419 118, 119 dorsal pallidum, nomenclature, 310 , 311 explicit memory, 430 , 431 cuneus, medial face of cerebrum, 276 , 277 dorsal rami, nerve roots and rami, 136 , 137 extensor carpi radialis, radial nerve, 46 , 47 , 49 cutaneous nerves – lower limb, 72 , 84–85 dorsal raphe nuclei, wakefulness circuitry, extensor digitorum brevis, leg and foot , 62 , cutaneous nerves – trunk, 73 , 86–87 446, 447 63, 65 cutaneous nerves – upper limb, 72 , 82–83 dorsal striatum, nomenclature, 310 , 311 extensor digitorum communis, radial nerve , cytoarchitecture, cerebral, 269 , 282 , 283 dorsal vermis, eye movement , 420 , 421 48, 49 dorsolateral nucleus, thalamus , 346 , 347 external ear canal, ear, 236 , 237 , 239 dorsolateral pontine nucleus (DLPN), 420 , 421 external granular layer, neocortical Dandy–Walker syndrome , 300 dural sinuses and veins, 22 , 23 cytoarchitecture , 282 , 283 dark phase, suprachiasmatic circuitry , 444 , 445 dura mater, meninges, 16 , 17 external pyramidal layer, neocortical declarative memory, 430 , 431 dysarthria-clumsy hand syndrome, 160 , cytoarchitecture , 282 , 283 deep cerebellar nuclei, cerebellum, 260 , 261 , 263 168, 169 extracranial segment, cranial nerve 7 , 222 , deep cerebral arteries, 318 , 326 , 327 dyscalculia , 434 223, 225 Deiter's nucleus , 240 , 241 dysgraphia , 434 extra-hippocampal circuitry, 368 , 369 Dejerine's syndrome , 161 , 170 , 171 extraocular movements deltoid, brachial plexus , 32 , 33 cranial nerves 3, 4, and 6 , 196 , 200 , 201 dendrites, olfactory system, 370 ear, 232, 236–239. See also auditory processes oblique muscles, 204 , 205 dentate nucleus, corticopontocerebellar complete drawing, 239 recti muscles, 202 , 203 pathway , 264 , 265 inner ear , 234f extrastriate body area, visual processing , depth perception, visual processing , 406 , 407 oculomotor eff ects of semicircular canal 404, 405 dermatomal maps stimulation , 234f extreme capsule, long association fi bers, anterior , 80 , 81 outer, middle and inner , 233f 294, 295 Keegan & Garrett's work , 74f partial drawing, 237 eye , 380 , 382–387 O. Foerster's work, 73 f vestibule-ocular refl ex pathways , 235f complete drawing, 387 posterior , 80 , 81 Economo's encephalitis , 442 partial drawing , 383 , 385 dermatomes , 72 , 80–81 ectoderm, spinal and cranial nerve , 174 , retina , 388 , 389 spinal and cranial nerve, 174 , 178 , 179 178, 179 eye movements, 410 , 411 developing embryo Edinger–Westphal nucleus fi nal common pathway, 412 , 413 axial section , 176f cranial nerve, 96 , 97 horizontal saccade circuitry , 414 , 415 ectoderm, mesoderm and endoderm, 174 , cranial nerve nuclei , 182 , 183 , 185 , 206 , 207 horizontal saccade details , 416 , 417 178 , 179 pupillary light refl ex, 422 , 423 pupillary light refl ex, 422 , 423 diagonal band of Broca , 372 , 373 , 374 , 375 , e ff ector tissue, sympathetic nervous system, semicircular canals, 232 , 238 376 , 377 98 , 99 smooth pursuit, 420 , 421 diaphragm, referred pain , 88 , 89 elbow group, radial nerve , 46 , 47 , 49 vertical saccades , 418 , 419 diencephalons , 340 , 341 , 342 , 345 electroencephalographic (EEG) patterns, sleep , eye muscle, extraocular movements , 200 , 201 anatomy and function of thalamus , 350 , 351 442 , 443 coronal section through, 343 f embryo, developing hypothalamus , 352 , 353 axial section , 176f face analysis, fusiform face area , 404 , 405 hypothalamus tracts, 354 , 355 ectoderm, mesoderm and endoderm, 174 , facial expression, cranial nerve 7 , 222 , 224 limbic system, 362 , 363 178 , 179 facial fi bers sagittal section through, 344 f embryogenesis , 20 motor projections , 164 , 165 thalamus , 346–349 encoding, memory capacity, 432 , 433 sensory projections, 162 , 163 digestive tract, 94 endoderm, spinal and cranial nerve , 174, facial nerve direct pathway, basal ganglia , 314 , 315 178 , 179 cranial nerve 7 , 220 , 221 disc edema, optic swelling , 384 end-zone infarct, borderzones, 328 , 329 skull foramina , 190 , 191 distal basilar artery, brainstem, 330 , 331 enteric nervous system, 94 femoral nerve divisions , 4 entorhinal cortex , 366 , 367 , 368 , 369 cutaneous nerves, 84 , 85 dopamine environment analysis, parahippocampal place sensory map of foot , 78 , 79 circuitry of basal ganglia, 314 , 315 area, 404 , 405 thigh , 56 , 66–69 release-inhibiting hormone, 354 epidermal hematoma, 15 fi ber bundles Dorello's canal, cranial nerves, 198 , 199 epidural hematoma , 16 , 24 internal capsule, 296 , 297 dorsal, terminology, 4 , 8 , 9 epidural space, spinal canal, 130 , 131 Fiber Pathways of the Brain, textbook, 292 dorsal cochlear nucleus, auditory pathways , episodic memory , 430 , 431 fi elds of Forel, direct and indirect pathways , 242 , 243 epithalamus, diencephalon, 344 , 345 312 , 313 dorsal foot, sensory map , 78 , 79 ethmoid bone fi ght-or-fl ight response, 6 , 94 dorsal hand, sensory map , 76 , 77 skull base , 188 , 189 fi nger agnosia, 434 dorsal motor nucleus, cranial nerves 9 & 10 , skull foramina , 190 , 191 fi nger and thumb extensors, radial nerve , 48 , 49 226 , 227 excitatory, circuitry of basal ganglia, 314 , 315 fi rst dosal interosseous, ulnar nerve , 44 , 45 Index 455

fl exor carpi radialis, median nerve , 36 , 37 gastrocnemius, leg and foot, 64 , 65 heart fl exor carpi ulnaris, ulnar nerve, 42 , 43 gaze, cardinal positions of, 200 , 201 cardiac refl ex, 102 , 103 fl exor digitorum longus, leg and foot , 64 , 65 general sensory aff erent fi bers, cranial nerve 7 , referred pain , 88 , 89 fl exor digitorum profundus 222 , 223 , 224 , 225 hemianopia, visual fi eld defi cit, 394 , 396 median nerve , 38 , 39 general somatic aff erent column hemifi eld slide, 394 ulnar nerve, 42 , 43 brainstem , 174 , 180 , 181 hemispatial neglect, 427 , 436 , 437 fl exor digitorum superfi cialis, median nerve, spinal cord, 174 , 180 , 181 hemispheric lobules, cerebellum , 254 , 255 36 , 37 general somatic eff erent column hemorrhages , 15 , 24 , 25f fl exor hallucis longus, leg and foot , 64 , 65 brainstem , 174 , 180 , 181 Herrick, Charles Judson, 184 fl exor pollicis brevis, median nerve , 40 , 41 cranial nerve nuclei , 182 , 183 Heschl's gyri fl exor pollicis longus, median nerve , 38 , 39 spinal cord, 174 , 180 , 181 auditory physiology, 244 , 245 fl ip-fl op switch general visceral aff erent column Brodmann areas , 284 , 285 circuitry , 441 , 448 , 449 brainstem , 174 , 180 , 181 central auditory pathways, 242 , 243 sleep-wake , 441 , 448 , 449 spinal cord, 174 , 180 , 181 insula , 280 , 281 fl occulonodular lobe general visceral eff erent cells, cranial nerve 7 , medial geniculate nucleus, 348 cerebellum , 252 , 253 222 , 223 , 224 , 225 hippocampal commissure, pathway , 298 midline structure , 258 general visceral eff erent column hippocampus somatotopy and lobules, 254 , 255 brainstem , 174 , 180 , 181 anatomy , 358 , 366 , 367 fl ow pattern, cerebrospinal fl uid, 15 f cranial nerve nuclei , 182 , 183 circuitry , 359 , 368 , 369 fl uency, language disorder, 428 , 429 spinal cord, 174 , 180 , 181 illustration , 361 f Foerster, O., dermatomal maps, 73f genioglossus, cranial nerve 12 , 208 , 209 limbic system, 362 , 363 follicle-stimulating hormone, hypothalamus, genitofemoral nerve, 86 , 87 histaminergic nuclei, wakefulness , 446 , 447 354 , 355 Gerstmann syndrome, 427 , 434 horizontal canal projections, vestibular system , foot. See sensory map of foot glaucoma, causes, 384 240 , 241 foramen magnum global aphasia, language disorder , 428 , 429 horizontal saccade skull foramina , 190 , 191 globus pallidus anatomy and control , 416 , 417 spinal canal, 130 , 131 basal ganglia , 308 , 309 circuitry , 410 , 414 , 415 foramen of Magendie, cerebrospinal fl uid fl ow , circuitry of basal ganglia , 314 , 315 horizontal semicircular canal, ear, 238 , 239 18 , 19 direct and indirect pathways, 312 , 313 hormones, hypothalamus, 354 , 355 foramina of Luschka, cerebrospinal fl uid fl ow , nomenclature , 310 , 311 hyoglossus, cranial nerve 12 , 208 , 209 18 , 19 glomerular layer, olfactory system, 370 , hypogastric nerve, urinary system, 100 , 101 foramina of Monro 371, 373 hypogastric plexus, urinary system , 100 , 101 cerebral ventricles , 20 , 21 glossopharyngeal nerve hypoglossal nerve cerebrospinal fl uid fl ow, 18 , 19 cardiac refl ex, 102 , 103 cervical plexus , 50 , 51 forearm, cutaneous nerves , 82 , 83 cranial nerves 9 & 10 , 226 , 227 cranial nerve 12 , 208 , 209 forearm muscle group, ulnar nerve , 42 , 43 gag refl ex, 228 , 229 cranial nerve nuclei, 182 , 183 , 185 fovea, eye, 386 , 387 skull foramina , 190 , 191 skull foramina , 190 , 191 Foville, Achille Louis, illustration of white gluteus maximus, lumbosacral plexus, 58 , 59 , 61 hypothalamospinal tract, spinal cord, 106 , matter, 290 f gluteus medius, lumbosacral plexus , 58 , 59 , 61 114, 115 Friedreich's ataxia, 122 , 123 , 125 Golgi tendon organs, muscle stretch refl ex , hypothalamus , 6 , 7 frontal bone, skull base, 188 , 189 132 , 133 diencephalon , 344 , 345 frontal eye fi elds gracile fasciculus, spinal cord , 106 , 112 , 113 sympathetic nervous system, 98 , 99 eye movement, 420 , 421 granule layer, cerebellum , 260 , 261 , 262f , 263 hypothenar group, ulnar nerve , 45 horizontal saccade , 414 , 415 gray matter. See also cerebral gray matter frontal horn, cerebral ventricles, 20 , 21 limbic system, 362 , 363 frontal lobe spinal cord, 110 , 111 ideational apraxia, 434 , 435 , 437 Brodmann areas , 284 , 285 gray matter horns, spinal cord , 109f ideomotor apraxia , 434 , 435 , 437 inferior face of cerebrum, 278 , 279 growth hormone, hypothalamus, 354 , 355 iliohypogastric nerve, cutaneous nerves, 86 , 87 lateral face of cerebrum, 274 , 275 Guillain–Mollaret ilioinguinal nerve, cutaneous nerves, 86 , 87 medial face of cerebrum, 276 , 277 medulla , 156 iliopsoas, thigh, 66 , 67 frontal operculum, insula, 280 , 281 midbrain , 140 , 150 , 152 implicit memory, 430 , 431 fusiform face area, face analysis , 404 , 405 gustatory region, cranial nerves 9 & 10 , 226 , 227 indirect pathway, circuitry of basal ganglia , fusiform gyrus, medial face of cerebrum , Guyon's canal, ulnar nerve, 42 , 43 , 45 314 , 315 276, 277 Guyon's tunnel, 42 inferior cerebellar peduncle (ICP) , 256 , g y r i 257, 259 inferior face of cerebrum, 278 , 279 inferior cerebellum, arteries, 332 , 333 gag refl ex, 213 , 228 , 229 lateral face of cerebrum, 274 , 275 inferior colliculi Gall, Franz Joseph, brain, 5 f medial face of cerebrum, 276 , 277 central auditory pathways, 242 , 243 ganglion, sympathetic nervous system , 98 , 99 midbrain , 152 , 153 ganglion cell layer, retina , 388 , 389 inferior face of cerebrum, 268 , 271 f , 278 , 279 Gasser scheme, muscle-nerve physiology , hamstrings, thigh, 66 , 67 inferior longitudinal fasciculus, long 134, 135 hand. See sensory map of hand association fi bers, 294 , 295 456 Index

inferior oblique, extraocular muscle , 204 , 205 intralateral nuclear group, thalamus , leg fi bers inferior olive, medulla, 156 , 157 348 , 349 motor projections , 164 , 165 inferior optic radiation bundle, visual pathway , intralimbic gyrus, limbic system, 362 , 363 sensory projections, 162 , 163 392 , 393 intratemporal segment, cranial nerve 7 , 222 , lenticular fasciculus inferior radiation, visual fi eld defi cit, 396 , 397 223 , 225 basal ganglia , 310 , 311 inferior rectus intrinsic arterial territories, 334 , 335 pathway , 312 , 313 extraocular movement , 200 , 201 intrinsic hand group, ulnar nerve, 45 lenticulostriate arteries, 326 , 327 extraocular muscle , 202 , 203 ipsilateral horizontal gaze palsy, 416 , 417 lentiform nucleus inferior salivatory nucleus, cranial nerves 9 & ipsilateral inferior cerebellar peduncle, spinal basal ganglia , 308 , 309 10 , 226 , 227 cord, 107 , 118 , 119 nomenclature , 310 , 311 inferior visual world, visual pathway, 392 , 393 iridocorneal fi ltration, canal of Schlemm , leptomeningeal cerebral arteries, 318 , 324 , 325 infrahyoid muscles, cervical plexus, 50 , 51 384, 385 levator scapulae, cervical plexus , 52 , 53 infraspinatus, brachial plexus , 32 , 33 iris, eye, 382 , 383 ligament of Struthers, median nerve , 38 , 39 , 41 inhibitory, circuitry of basal ganglia, 314 , 315 Ishimori, Kuniomi, 444 light phase, suprachiasmatic circuitry, 444 , 445 inhibitory burst neurons island of Reil, insula, 280 , 281 limbic lobe anatomy and control , 416 , 417 inferior face of cerebrum, 278 , 279 horizontal saccade, 414 , 415 medial face of cerebrum, 276 , 277 vertical saccades , 418 , 419 jugum sphenoidale, skull base, 188 , 189 limbic system, 358 , 362–365 inner ear canal, 236 , 237 , 239 junctional scotoma, 398 dorsolateral nucleus, 346 , 347 inner limiting membrane, retina , 388 , 389 illustration , 360 f inner nuclear layer, retina , 388 , 389 oblique anatomic section , 361f inner plexiform layer, retina, 388 , 389 Keegan & Garrett's work, dermatomal thalamus , 350 , 351 innervation , 15 maps, 74 f limb-kinetic apraxia , 434 , 435 , 437 bladder and urethra , 100 Klüver Bucy syndrome , 362 Lissauer's tract, spinal cord, 112 , 113 corticonuclear , 228 , 229 Kubrick, Stanley, Dr. Strangelove, 300 Lloyd class, muscle-nerve physiology , 134 , 135 cranial nerve 7 , 212 , 220 , 221 lobes, cerebellum , 248 , 252 , 253 hemorrhages and , 24 , 25f lobules, cerebellum , 254 , 255 peripheral, of cranial nerve 5 , 212 , 214 , 215 lamina cribrosa, optic nerve, 384 , 385 locked-in syndrome, pontine , 160 , 168 , 169 referred pain , 73 , 88 , 89 language disorders, 426 , 428 , 429 locus coeruleus, wakefulness circuitry, 446 , 447 sympathetic nervous system, 98 , 99 lateral, terminology , 4 locus coeruleus nuclei, pons, 154 , 155 insula , 268 , 280 , 281 lateral chiasm, visual fi eld defi cit, 394 , 395 long association fi bers, 288 , 294 , 295 insular cortex, 280 f lateral corticospinal tract , 106 , 114 , 115 cerebral white matter , 292 , 293 intercostal nerve, nerve roots and rami, 136 , 137 lateral corticospinal tract fi bers, 107 , 116 , 117 white matter organization, 291 f interior oblique, extraocular movement , 200 , 201 lateral face, Sylvian fi ssure, 278 , 279 long-term memory, 430 , 431 interleukin- 1 , 444 lateral face of cerebrum, 268 , 274 , 275 Lou Gehrig's disease, spinal cord disorder , intermediate nucleus, oculomotor nuclei , Brodmann areas , 284 , 285 124, 125 206, 207 drawing , 270 f lower motor neuron (LMN) , 4 , 10 , 11 intermediate olfactory cortex , 376 , 377 lateral funiculus, spinal cord, 110 , 111 lumbar plexus, segmental organization of internal capsule, 288 , 296 , 297 lateral geniculate nucleus peripheral nerves , 129 f internal carotid artery (ICA) retinotopic organization, 392 , 393 lumbosacral plexus , 56 , 58–61 cerebral angiography, 320 f visual pathway, 390 , 391 , 392 , 393 complete drawing, 61 circle of Willis, 322 , 323 visual system, 348 , 349 , 350 , 351 lumbar plexus , 57 f cranial nerves, 198 , 199 lateral group, brainstem arteries , 330 , 331 partial drawing, 59 deep cerebral arteries, 326 , 327 lateral group nuclei, thalamus , 350 , 351 sacral plexus , 57 f internal granular layer, neocortical lateral lemniscus tracts, central auditory lumbosacral spinal cord, 108 f, 110 , 111 cytoarchitecture , 282 , 283 pathways , 242 , 243 lumbricals, median nerve, 40 , 41 internal medullary lamina, thalamus , 346 , 347 lateral nuclear group, thalamus , 346 , 347 , luteinizing hormone, hypothalamus, 354 , 355 internal pyramidal layer, neocortical 350, 351 cytoarchitecture , 282 , 283 lateral occipital cortex, object recognition , interneurons, eye movements , 412 , 413 404, 405 macular sparing, visual fi eld defi cit, 396 internuclear ophthalmoplegia, eye movements , lateral olfactory cortex , 376 , 377 magnetic resonance angiography, cerebral 412 , 413 lateral olfactory stria, 370 , 371 , 372 , 373 arterial system , 322f interstitial nuclei of Cajal , 418 , 419 lateral posterior choroidal artery, posterior magnocellular layers, visual pathway, 392 , 393 intervertebral foramen, nerve roots and rami , thalamus, 336 , 337 Magoun, H. W., 446 136 , 137 lateral pterygoids, cranial nerve 5 , 214 , 215 major motor projections, 160 , 164 , 165 intra-axial segment, cranial nerve 7 , 222 , lateral rectus, 200 , 201 , 202 , 203 major sensory projects, 160 , 162 , 163 223, 225 lateral vestibulospinal tract, vestibular system , mammillary bodies, limbic system , 362 , 363 intracranial herniation syndromes, 16 240 , 241 mammillary group, hypothalamus, 352 , 353 intra-hippocampal circuitry, 368 , 369 latissimus dorsi, brachial plexus, 32 , 33 mandibular division, cranial nerve 5 , 214 , 215 , intralaminar thalamic nuclei, wakefulness leaky integrator , 416 , 417 216 , 217 circuitry, 446 , 447 leg and foot, 56 , 62–65 "man in a barrel" syndrome , 328 Index 457

Marchiafava–Bignami disorder, 300 mesoderm, spinal and cranial nerve , 174, musculocutaneous nerve, brachial plexus , 31 , maxillary division, cranial nerve 5 , 214 , 215 , 178 , 179 33 , 35 216 , 217 metathalamus myelin, nodes of Ranvier, 134 Meckel's cave diencephalon , 344 , 345 myotome, spinal and cranial nerve , 174 , cavernous sinus , 192 , 193 lateral geniculate nuclei , 348 , 349 178, 179 cranial nerve 5 , 216 medial geniculate nuclei , 348 , 349 medial, terminology, 4 Meyer's loop , 392 , 393 , 395 medial face of cerebrum, 268 , 276 , 277 midbrain , 6 , 7 , 149 , 150–153 narcolepsy , 448 Brodmann areas , 284 , 285 axial section , 143f , 146 f nasal hemiretina, visual pathway, 390 , 391 drawing , 270 f complete drawing, 153 navigational disorientation, 404 medial geniculate nucleus cranial nerve nuclei , 183 , 185 neighborhood association fi bers, white matter , auditory system, 350 , 351 inferior face of cerebrum, 278 , 279 292 , 293 central auditory pathways, 242 , 243 midbrain syndromes, 160 , 166–167 neocortex, cerebral cytoarchitecture , 269 , metathalamus , 348 , 349 parasympathetic nervous system , 96 , 97 282, 283 medial group nuclei, thalamus , 346 , 347 , partial drawing, 151 nerve fi ber layer, retina , 386 , 387 , 388 , 389 350 , 351 midbrain syndromes, 160 , 166 , 167 nerve maps, 74 f , 75 f medial longitudinal fasciculus, medulla , middle (tuberal) group, hypothalamus, nerve roots and rami, 129 , 136 , 137 156, 157 352, 353 nervous system medial nucleus, oculomotor nuclei , 206 , 207 middle cerebellar peduncle (MCP) , 256 , anatomy , 6 , 7 medial olfactory area, 370 , 371 , 372 , 373 257 , 259 divisions and signs , 10 , 11 medial olfactory cortex, 374 , 376 , 377 middle cerebellum, arteries , 332 , 333 orientational planes, 8 , 9 medial posterior choroidal artery, medial middle cerebral artery parasympathetic , 96 , 97 thalamus, 336 , 337 arterial borderzones , 328 , 329 sympathetic , 98 , 99 medial rectus , 200 , 201 , 202 , 203 circle of Willis, 322 , 323 neural crests, spinal and cranial nerve , 174 , medial vestibular nucleus, eye movement , deep cerebral arteries, 326 , 327 178 , 179 420, 421 leptomeningeal cerebral arteries, 324 , 325 neural integrator medial vestibulospinal tract, vestibular system , middle cranial fossa, skull base , 188 , 189 anatomy and control , 416 , 417 240 , 241 middle ear canal, ear, 236 , 237 , 239 horizontal saccade, 414 , 415 median digital sensory branches, hand, 76 , 77 middle longitudinal fasciculus, long association vertical saccades , 418 , 419 median nerve , 28 , 29f , 36–42 fi bers, 294 , 295 neural tube, axial section , 176f brachial plexus , 31 , 33 , 35 midline nuclear group, thalamus, 348 , 349 neuroanatomy , 6 , 7 , 428 , 429 complete drawing, 41 midline structures, cerebellum, 257 , 258 , 259 neurocircuitry, sleep, 440 , 442 , 443 partial drawings , 37 , 39 MLF syndrome , 412 neurohypophysis, hypothalamus , 354 , 355 medulla , 6 , 7 , 140 , 156 , 157 modules, cerebellum, 248 , 252 , 253 neuronal cell types, retina, 388 axial section , 145f , 147 f molecular layer, neocortical cytoarchitecture, neurotransmitters, autonomic fi ber axial view, 227 282 , 283 arrangements, 94 , 95 cardiac refl ex, 102 , 103 monaural localization of sound, auditory , nodes of Ranvier, myelin, 134 cranial nerve 12 , 197 , 208 , 209 244, 245 nomenclature cranial nerve nuclei , 183 , 185 monocular vision, 406 , 407 basal ganglia, 304 , 310 , 311 medullary syndromes, 170–171 Moruzzi, Giuseppe , 446 cerebral white matter , 292 , 293 parasympathetic nervous system , 96 , 97 mossy fi bers, cerebellum, 260 , 261 , 262 f , 263 nondeclarative memory, 430 , 431 medullary arteries motion detection, rod photoreceptors, 400 non-REM (rapid eye movement), sleep arterial borderzones , 328 motion processing, occipital-temporal-parietal circuitry, 442 , 443 brainstem , 330 , 331 junction , 406 , 407 nuclei, cerebellum , 260–263 medullary syndromes, 161 , 170 , 171 motoneurons, eye movements , 412 , 413 nuclei and circuitry medulloblastoma tumors , 20 motor laminae, spinal cord, 106 , 110 , 111 cerebellar histological architecture, 262 f melanocyte stimulating hormone, motor loop, gag refl ex, 228 , 229 cerebellum , 248 , 260–263 hypothalamus, 354 , 355 motor nerves complete drawing, 263 melatonin, sleep induction, 444 cervical plexus , 50 , 51 partial drawing, 261 memory muscle stretch refl ex, 132 , 133 nucleus, sympathetic nervous system, 98 , 99 capacity and consolidation , 426 , 432 , 433 M retinal ganglion cells, 420 , 421 nucleus ambiguus classes , 426 , 430 , 431 Müller glial cells, 388 cranial nerves 9 & 10 , 226 , 227 hippocampus , 362 multiform layer, neocortical cytoarchitecture , gag refl ex, 228 , 229 meningeal layers, cerebrospinal fl uid fl ow , 282 , 283 nucleus of Perlia, oculomotor nuclei , 206 , 207 18, 19 multiple memory trace theory , 432 , 433 nucleus reticularis tegmenti pontis (NRTP) , meninges , 14 , 16 , 17 muscle-nerve physiology , 128 , 134 , 135 420 , 421 meningiomas , 18 muscle spindle mesencephalic nucleus, cranial nerve 5 , muscle-nerve physiology , 134 , 135 216 , 217 muscle stretch refl ex, 132 , 133 object recognition pathway mesocortex, cerebral cytoarchitecture, 269 , muscle stretch refl ex, 128 , 132 , 133 lateral occipital complex, 404 , 405 282 , 283 muscle tone, muscle-nerve physiology, 134 , 135 ventral stream , 400 , 401 458 Index

oblique muscles, extraocular , 204 , 205 paleocortex, allocortex , 282 , 283 lumbosacral plexus, 57 f, 58–61 oblique view, cavernous sinus, 192 , 193 palmar hand, sensory map , 76 , 77 median nerve , 36–41 obturator nerve, thigh, 56 , 66–69 palmar interossei, ulnar nerve , 44 , 45 parasympathetic , 96–97 occipital bone, skull base, 188 , 189 palmaris brevis, ulnar nerve , 42 , 43 radial nerve , 46–49 occipital horn, cerebral ventricles , 20 , 21 palmaris longus, median nerve , 36 , 37 referred pain , 88–89 occipital lobe Papez circuit, 354 , 362 , 366 , 368 , 369 sensory map of foot , 78–79 Brodmann areas , 284 , 285 papilledema, disc edema , 384 sensory map of hand , 76–77 inferior face of cerebrum, 278 , 279 parahippocampal gyrus sympathetic , 98–99 lateral face of cerebrum, 274 , 275 limbic system, 362 , 363 thigh , 66–69 medial face of cerebrum, 276 , 277 medial face of cerebrum, 276 , 277 ulnar nerve, 42–45 occipital-temporal-parietal junction, motion white matter, 366 , 367 urinary system, 100–101 processing, 406 , 407 parahippocampal place area, environment peripheral vision, cortical representation , ocular fl utter , 416 , 417 analysis , 404 , 405 392 , 393 oculomotor eff ects, semicircular canal parasympathetic fi bers, urinary system, perirhinal cortex stimulation , 234f 100, 101 hippocampus , 366 , 367 oculomotor nerve parasympathetic nervous system , 92 , 94 , 95 , hippocampus circuitry, 368 , 369 cranial nerve nuclei , 182 , 183 , 185 96 , 97 peroneal nerve skull foramina , 190 , 191 paraventricular and supraoptic nuclei, leg and foot, 56 oculomotor nucleus, eye movements , 412 , 413 hypothalamus, 354 , 355 lumbosacral plexus , 58 , 59 , 61 olfactory bulb , 370 , 371 , 372 , 373 parietal dorsal stream area, spatial awareness , sensory map of foot, 78 , 79 olfactory cortex, 359 , 374–377 406 , 407 peroneus longus, leg and foot , 62 , 63 , 65 olfactory nerve bundles, skull foramina, 190 , 191 parietal lobe pharyngeal arch derivatives, cranial nerve olfactory system, 359 , 370–373 lateral face of cerebrum, 274 , 275 nuclei, 182 , 184 , 185 inferior view , 373 medial face of cerebrum, 276 , 277 photoreceptor cell segments, retina , 386 , 387 , sagittal view, 371 , 373 parietal operculum, insula, 280 , 281 388 , 389 olfactory trigone , 370 , 371 , 372 , 373 parieto-occipital sulcus, medial face of physiology olivary nuclei, medulla , 156 , 157 cerebrum, 276 , 277 auditory , 233 , 244 , 245 omnipause neurons Parkinson's disease , 314 muscle-nerve , 128 , 134 , 135 anatomy and control , 416 , 417 parvocellular layers, visual pathway , 392 , 393 pial network, spinal cord arteries , 334 , 335 horizontal saccade, 414 , 415 patellar refl ex, muscle stretch refl ex, 132 pia mater vertical saccades , 418 , 419 pectoralis major, brachial plexus, 32 , 33 meninges , 16 , 17 one-and-a-half syndrome , 412 , 413 pectoral nerves, brachial plexus, 32 , 33 spinal canal, 130 , 131 one-eye vision, visual processing , 406 , 407 peduncles, cerebellar , 256 , 257 , 259 Piéron, Henri , 444 ophthalmic division, cranial nerve 5 , 214 , 215 , pelvic plexus, urinary system , 100 , 101 pigmented epithelium, retina , 386 , 387 216 , 217 perforant pathway, hippocampus circuitry , plantar foot, sensory map, 78 , 79 opponens pollicis, median nerve, 40 , 41 368, 369 polio syndrome, spinal cord disorder , 124 , 125 optic ataxia , 434 , 435 , 437 perforating arterial territories, 326 , 327 , pons , 6 , 7 , 140 , 154 , 155 optic chiasm , 374 , 375 , 377 328, 329 axial section , 144f , 146 f suprachiasmatic circuitry , 444 , 445 periallocortex, mesocortex , 282 , 283 axial view, 420 , 421 v i s u a l fi eld defi cit, 394 , 395 periaqueductal gray area, midbrain , 150 , cranial nerve nuclei , 183 , 185 visual pathway , 390 , 391 151 , 153 parasympathetic nervous system , 96 , 97 optic disc, eye , 384 , 385 periarchicortex, mesocortex, 282 , 283 pontine syndromes , 168–169 optic nerve perioculomotor cell group, oculomotor nuclei , pontine arterial supply, brainstem , 330 , 331 skull foramina , 190 , 191 206 , 207 pontine nuclei v i s u a l fi eld defi cit, 394 , 395 peripaleocortex, mesocortex , 282 , 283 corticopontocerebellar pathway, 264 , 265 optic radiation, quadrantanopia , 392 peripheral autonomic nervous system, 6 , 7 pons , 154 , 155 optic refraction, light ray manipulation, 382 peripheral innervation, cranial nerve 5 , 212 , pontine syndromes ,, 160 , 168 , 169 optic tract, visual pathway, 390 , 391 214 , 215 pontocerebellar tracts, pons , 154 , 155 orbital operculum, insula, 280 , 281 peripheral nerves, segmental pontocerebellum , 250 f, 252 , 253 orexigenic cells, fl ip-fl op switch, 441 , 448 , 449 organization of , 129f popliteal fossa, leg and foot, 62 , 63 , 65 orexin, fl ip-fl op switch, 441 , 448 , 449 peripheral nervous system , 6 , 7 , 28–29 , 56 , Post, Wiley, one-eyed pilot, 406 orientational planes, 8 , 9 72–73 , 92–93 postcentral gyrus, lateral face of cerebrum , orientational terminology , 4 autonomic fi ber arrangements, 94–95 274 , 275 outer limiting membrane, retina, 388 , 389 brachial plexus , 30–35 post chiasm, visual fi eld defi cit, 396 , 397 outer nuclear layer, retina, 388 , 389 cardiac refl ex, 102–103 posterior (mammillary) group, hypothalamus , outer plexiform layer, retina, 388 , 389 cervical plexus , 50–53 352 , 353 oxytocin, hypothalamus, 354 , 355 cutaneous nerves - lower limb , 84–85 posterior cerebral arteries cutaneous nerves - trunk, 86–87 arterial borderzones , 328 , 329 cutaneous nerves - upper limb , 82–83 brainstem , 330 , 331 pain, referred, 73 , 88 , 89 dermatomes , 80–81 circle of Willis, 322 , 323 palate, supranuclear innervation, 228 , 229 divisions and signs , 10 , 11 cranial nerves, 198 , 199 palatoglossus , 197 leg and foot, 62–65 leptomeningeal cerebral arteries, 324 , 325 Index 459

posterior column fi bers, spinal cord , 107 , rami, nerve roots and, 129 , 136 , 137 olfactory system, 370–373 116, 117 raphe nuclei skull base , 189 posterior cranial fossa, skull base , 188 , 189 medulla , 156 , 157 spinal canal, 130 , 131 posterior funiculus, spinal cord , 110 , 111 midbrain , 152 , 153 terminology , 4 posterior group, brainstem arteries, 330 , 331 Rathke's pouch, 342 visual pathways, 380 , 392 , 393 posterior inferior cerebellar artery, cerebellum , recti muscles, extraocular muscles , 202 , 203 salivatory nucleus, cranial nerves, 96 , 97 332 , 333 red nucleus, corticopontocerebellar pathway , saphenous nerve, thigh, 68 , 69 posterior nuclear group, thalamus, 346 , 347 264 , 265 S c h a ff er collaterals, 368 posterior parahippocampal gyrus, referred pain , 73 , 88–89 sciatic nerve hippocampus , 366 , 367 Reissner's membrane, ear, 232 , 236 lumbosacral plexus , 58 , 59 , 61 posterior peripheral nerve map , 75 f REM (rapid eye movement), sleep circuitry , thigh , 56 , 66–69 posterior semicircular canal, ear, 238 , 239 442 , 443 sclera, eye , 382 , 383 posterior spinal arteries, 334 , 335 Renshaw cells, muscle stretch refl ex, 132 , 133 sclerotome, spinal and cranial nerve , 174 , posterior spinocerebellar tract, spinal cord , repetition, language disorder, 428 , 429 178 , 179 107 , 118 , 119 reticular formation secondary olfactory cells , 370 , 371 , 372 , 373 posterolateral hypothalamus , 352 , 353 medulla , 156 , 157 secondary visual cortex, cortical visual precentral gyrus, lateral face of cerebrum, midbrain , 152 , 153 processing, 402 , 403 274, 275 reticular projections, vestibular system, 240 , 241 segmental arteries, spinal cord , 334 , 335 prefrontal cortex, thalamus , 350 , 351 reticular thalamic nuclei, sleep circuitry, sella turcica, 22 , 23 , 188 , 189 pretectal olivary nucleus , 422 , 423 442 , 443 semantic memory , 430 , 431 primary lateral sclerosis, disorder, 124 , 125 reticulospinal tracts, spinal cord, 106 , 114 , 115 semicircular canals, ear, 238 , 239 primary motor area, 274 , 275 , 284 , 285 retina , 382 , 383 , 388 , 389 sensory fi bers primary olfactory cortex, 370 , 371 , 372 , 373 , layers , 386 , 387 , 388 , 389 nerve roots and rami, 136 , 137 374–377 v i s u a l fi eld defi cits, 398 , 399 spinal cord, 106 , 112 , 113 primary sensory area, 274 , 275 , 284 , 285 retinal pigmented epithelium , 388 , 389 sensory gating, sleep circuitry , 442 , 443 primary visual cortex retinohypothalamic pathway, suprachiasmatic sensory information, thalamus, 346 , 348 cortical visual processing , 400 , 401 circuitry, 444 , 445 sensory laminae, spinal cord, 106 , 110 , 111 eye movement, 420 , 421 retrieval, memory , 432 , 433 sensory loop, gag refl ex, 228 , 229 v i s u a l fi eld defi cit, 396 , 397 retrograde amnesia, memory, 432 , 433 sensory map of foot , 72 , 78–79 priming, memory, 430 , 431 Rexed laminae, spinal cord, 110 sensory map of hand , 72 , 76–77 principal sensory nucleus, cranial nerve 5 , rhesus monkey frontal eye fi elds, Brodmann sensory memory, 430 , 431 216 , 217 areas , 284 , 285 sensory nerves procedural memory, 430 , 431 rhomboids, brachial plexus, 30 , 31 cervical plexus , 50 , 51 proisocortex, mesocortex , 282 , 283 rod photoreceptors, 400 muscle stretch refl ex, 132 , 133 prolactin, hypothalamus, 354 , 355 rostral, terminology, 4 , 8 , 9 septum pellucidum, limbic system , 362 , 363 pronator quadratus, median nerve , 38 , 39 rostral interstitial nuclei of medial longitudinal serratus anterior, brachial plexus, 30 , 31 pronator teres, median nerve , 36 , 37 fasciculus (riMLF) , 418 , 419 short association fi bers, cerebral white matter , proprius fasciculus, spinal cord, 110 , 111 rostral spinocerebellar tract, spinal cord , 107 , 292 , 293 pulvinar 118 , 119 short-term memory , 430 , 431 , 432 , 433 thalamus , 350 , 351 rubrospinal tract, spinal cord, 106 , 114 , 115 signs , 4 visual attention, 346 , 347 sinuses , 14 , 22 , 23 pupillary light refl ex, 411 , 422 , 423 skull base, 175 , 188 , 189 Purkinje layer , 260 , 261 , 262f , 263 saccade slowing , 416 , 417 axial view, 177 f , 189 , 191 putamen sacral component, parasympathetic nervous sagittal view, 189 basal ganglia , 308 , 309 system, 96 , 97 skull foramina , 175 , 190 , 191 direct and indirect pathways, 312 , 313 sacral plexus, segmental organization of sleep nomenclature , 310 , 311 peripheral nerves , 129 f fl ip-fl op switch, 441 , 448 , 449 sagittal view neurocircuitry , 440 , 442 , 443 basal ganglia , 308 , 309 Von Economo's correlation for, and quadrantanopia, optic radiation, 392 , 396 , 398 brainstem , 8 , 9 , 227 wakefulness, 441 f quadriceps femoris, thigh , 66 , 67 corpus callosum , 298 , 299 , 301 smooth pursuit, eye movement, 411 , 420 , 421 cranial nerves 3, 4, and 6 , 197 f solely special sensory set, cranial nerve nuclei , diencephalon , 343f , 344 , 345 174 , 182 , 183 , 185 radial nerve , 28 , 29f , 46–49 diencephalon & midbrain, 423 solitary tract nucleus, cranial nerves 9 & 10 , brachial plexus , 31 , 33 , 35 hypothalamus , 352 , 353 , 354 , 355 226 , 227 complete drawing, 49 internal capsule, 296 , 297 somatomotor fi bers, urinary system , 100 , 101 partial drawing, 47 leptomeningeal cerebral arteries, 324 , 325 somatomotor set, cranial nerve nuclei , 174, sensory map of hand , 76 , 77 limbic pathways , 364 , 365 182 , 183 upper limb cutaneous, 82 , 83 limbic system, 362 , 363 , 364 , 365 somatosensory cortex, thalamus , 350 , 351 radiculomedullary artery, spinal cord arteries, long association fi ber bundles, 294 , 295 somatotopy , 251 f , 254 , 255 334 , 335 midbrain syndrome, 160 , 166 , 167 spatial awareness, parietal dorsal stream area , radiographic axial images, terminology , 8 , 9 oculomotor complex , 206 , 207 406 , 407 460 Index

spatial localization, dorsal stream, 400 , 401 subarachnoid cisterns , 22 , 23 supratentorial herniation , 16 special somatic aff erent column, brainstem , subarachnoid hemorrhage , 24 , 25f sural nerve , 56 , 84 , 85 174 , 180 , 181 subcallosal region, limbic pathways, 364 , 365 Sylvian fi ssure special visceral aff erent column subcortical cord bundles, white matter , cortical visual areas , 400 , 401 brainstem , 174 , 180 , 181 292, 293 insula , 280 , 281 cranial nerve 7 , 184 , 185 subcortical white matter , 6 , 7 lateral face , 278 , 279 special visceral aff erent fi bers, cranial nerve 7 , subdural hematoma, 15 , 24 lateral face of cerebrum, 274 , 275 222 , 223 , 224 , 225 sublaterodorsal nucleus, sleep circuitry , leptomeningeal cerebral arteries, 324 , 325 special visceral eff erent cells, cranial nerve 7, 442, 443 sympathetic fi bers, urinary system , 100 , 101 222 , 223 , 225 subparietal sulcus, medial face of cerebrum , sympathetic ganglion, nerve roots and rami , special visceral eff erent column, cranial nerve 276 , 277 136 , 137 nuclei, 184 , 185 subscapularis, brachial plexus, 34 , 35 sympathetic nervous system, 92 , 94 , 95 , 98 , 99 speech apraxia , 434 , 435 , 437 substantia nigra synapses, retina, 386 , 387 sphenoid bone, skull base , 188 , 189 circuitry of basal ganglia, 314 , 315 syphilitic myelopathy, 120 , 121 , 123 , 125 sphincter pupillae , 422 , 423 direct and indirect pathways, 312 , 313 syringomyelia spinal and cranial nerve, 174 , 178 , 179 midbrain , 150 , 151 , 153 Chiari malformation , 258 spinal and cranial nuclear classifi cation , 174 , wakefulness circuitry, 446 , 447 spinal cord disorder , 122 , 123 , 125 180 , 181 subthalamic fasciculus spinal canal, 128 , 130 , 131 basal ganglia , 310 , 311 spinal cord, 6 , 7 , 106–107 , 110 , 111 pathway , 312 , 313 tabes dorsalis , 120 , 121 , 123 , 125 arteries , 319 , 334 , 335 subthalamic nucleus, direct and indirect taste, cranial nerve 7 , 184 , 185 ascending pathways , 106 , 112 , 113 pathways , 312 , 313 tectospinal tract, spinal cord , 106 , 114 , 115 axial sections through cervical, thoracic and subthalamus, diencephalon, 342 , 345 tectum lumbosacral , 108 f sulci brainstem , 180 , 181 cardiac refl ex, 102 , 103 inferior face of cerebrum, 278 , 279 brainstem composite, 148 , 149 cranial nerve nuclei , 183 , 185 insula , 280 , 281 midbrain , 151 , 153 descending pathways , 106 , 114 , 115 lateral face of cerebrum , 274 , 275 tegmentum disorders , 120–125 medial face of cerebrum, 276 , 277 brainstem , 180 , 181 divisions and signs , 10 , 11 sulcus limitans brainstem composite, 148 , 149 gray matter horns , 109f brainstem , 180 , 181 medulla , 156 , 157 injury , 10 , 11 spinal and cranial nerve, 174 , 178 , 179 midbrain , 151 , 153 major ascending and descending tracts , 107 , s u p e r fi cial forearm group, median nerve, 37 , pons , 154 , 155 116 , 117 39 , 41 tela choroidea, cerebrospinal fl uid fl ow, 18 , 19 spinal and cranial nuclear classifi cation, superior cerebellar artery temporal bone, skull base , 188 , 189 180 , 181 cerebellum , 332 , 333 temporal hemiretina, visual pathway , 390 , 391 spinocerebellar pathways, 107 , 118 , 119 cranial nerves, 198 , 199 temporal horn, cerebral ventricles, 20 , 21 sympathetic nervous system, 98 , 99 superior cerebellar peduncle temporal lobe spinal motor neurons, 4 corticopontocerebellar pathway, 264 , 265 inferior face of cerebrum, 278 , 279 spinal muscular atrophy, 124 , 125 midbrain , 150 , 151 , 153 lateral face of cerebrum, 274 , 275 spinal trigeminal nucleus spinal cord, 107 , 118 , 119 medial face of cerebrum, 276 , 277 cranial nerve 5 , 216 , 217 superior cerebellar peduncle , 256 , 257 , 259 temporal operculum, insula , 280 , 281 cranial nerve 5 tracts , 218 , 219 superior cerebellum, arteries, 332 , 333 temporo-parietal-occipital junction, cortical cranial nerves 9 & 10 , 226 , 227 superior colliculus, horizontal saccade, 414 , 415 visual areas , 400 , 401 spinocerebellar pathways, spinal cord, 107 , superior longitudinal fasciculus, long teres major, brachial plexus, 34 , 35 118 , 119 association fi bers, 294 , 295 teres minor, brachial plexus, 34 , 35 spinocerebellar tracts, spinal cord, 106 , 112 , 113 superior oblique, 200 , 201 , 204 , 205 terminal group, median nerve, 41 spinocerebellum , 250 f, 252 , 253 superior olivary complex, auditory pathways , tertiary visual cortex, cortical visual processing , spinothalamic fi bers, medulla , 156 242 , 243 402 , 403 Spurzheim, Johann Kaspar, brain, 5f superior optic radiation bundle, visual pathway , thalamic arteries, 319 , 326 , 327 , 336 , 337 sternocleidomastoid, cervical plexus, 52 , 53 392 , 393 thalamic bundle, white matter , 292 , 293 storage, memory capacity, 432 , 433 superior radiation, visual fi eld defi cit, 396 , 397 thalamic fasciculus strap muscles, cervical plexus, 50 , 51 superior rectus , 200 , 201 , 202 , 203 , 206 basal ganglia , 310 , 311 stria of Gennari, 400 superior visual world, visual pathway, 392 , 393 pathway , 312 , 313 s t r i a t a l fi bers, cerebral white matter , 292 , 293 supinator, radial nerve , 48 , 49 thalamic projections, vestibular system , stria terminalis, limbic system , 364 , 365 suprachiasmatic circuitry , 440 , 444 , 445 240, 241 striatum , 310 , 311 suprachiasmatic nucleus, circuitry , 444 , 445 thalamic reticular nucleus, 350 , 351 anterior aspect, 141 f supraocular command centers, horizontal thalamocortical networks, sleep circuitry , circuitry of basal ganglia, 314 , 315 saccade, 416 , 417 442, 443 posterior aspect , 142f supra-ocular projections, eye movements , thalamogeniculate arteries, lateral thalamus, styloglossus, cranial nerve 12 , 208 , 209 418, 419 336 , 337 subacute combined degeneration, spinal cord supra-olivary medulla, sleep circuitry, 442 , 443 thalamoperforating arteries, medial thalamus , disorder , 122 , 123 , 125 suprasellar cistern, 22 , 23 336 , 337 Index 461 thalamotuberal artery, anterior thalamus , hand , 76 , 77 vestibulospinal tracts, spinal cord, 106 , 336 , 337 partial drawing, 43 114 , 115 thalamus , 6 , 7 , 340 , 346–349 uncal herniation, term , 366 visceral nuclei, oculomotor nuclei, 206 , 207 anatomy and function, 340 , 350 , 351 uncinate fasciculus, long association fi bers, vision, 380, 381. See also eye anterior aspect, 141 f 294, 295 axial view of visual pathways, 390 , 391 basal ganglia , 308 , 309 upper motor neuron , 4 , 10 , 11 cortical visual processing, 400–407 circuitry of basal ganglia , 314 , 315 urethra, urinary system , 100 , 101 eye , 382–387 diencephalon , 344 , 345 urethral sphincter, urinary system, 100 , 101 sagittal view of visual pathways , 392 , 393 direct and indirect pathways, 312 , 313 urinary system , 93 , 100 , 101 v i s u a l fi eld defi cits, 394–399 posterior aspect , 142f visual attention thenar group , 41 , 45 pulvinar , 346 , 347 thigh , 56 , 66–69 vagus nerve thalamus , 350 , 351 complete drawing, 69 cardiac refl ex, 102 , 103 visual cortex, visual pathways, 392 , 393 cutaneous nerves, 84 , 85 cranial nerves 9 & 10 , 226 , 227 visual pathways partial drawing, 67 gag refl ex, 228 , 229 axial view, 380 , 390 , 391 thoracic branches, cutaneous nerves , 86 , 87 skull foramina , 190 , 191 sagittal view , 380 , 392 , 393 thoracic spinal cord, 108 f , 110 , 111 vasopressin, hypothalamus, 354 , 355 v i s u a l fi eld defi cits, 394–399 thorax, cutaneous nerves , 86 , 87 vein of Galen, 14 , 22 , 23 visual system, lateral geniculate nucleus , 348 , thyroid stimulating hormone, hypothalamus , veins , 14 , 22 , 23 349 , 350 , 351 354 , 355 ventral, terminology, 4 , 8 , 9 vitamin B12 defi ciency, spinal cord disorder , tibialis anterior, leg and foot, 62 , 63 , 65 ventral cochlear nucleus, central auditory 122 , 123 , 125 tibialis posterior, leg and foot, 64 , 65 pathways , 242 , 243 vitreous chamber, eye , 384 , 385 , 386 , 387 tibial nerve, lumbosacral plexus , 58 , 59 , 61 ventral nucleus, oculomotor nuclei, 206 , 207 Von Economo areas , 366 , 441f tongue muscles, cranial nerve 12 , 208 , 209 ventral pallidum, nomenclature, 310 , 311 tonotopy, auditory physiology, 244 , 245 ventral rami, nerve roots and rami, 136 , 137 "top of the basilar" syndrome, 330 ventral striatum, nomenclature, 310 , 311 wakefulness topographic disorientation , 404 ventral tegmental area, wakefulness circuitry , circuitry , 440 , 446 , 447 torsional saccades, eye movements , 418 , 419 446 , 447 fl ip-fl op switch, 441 , 448 , 449 transcortical aphasia, language disorder , ventricular system, anatomy, 15 f Von Economo's correlation for sleep 428, 429 ventroanterior nucleus, thalamus , 346 , 347 , and, 441 f transverse temporal gyri, auditory physiology , 350 , 351 Wallenberg's syndrome, medullary syndrome , 244 , 245 ventrolateral nucleus, thalamus , 346 , 347 , 161 , 170 , 171 trapezius, cervical plexus, 52 , 53 350 , 351 Warwick's model, oculomotor complex , 206 Traquair, junctional scotoma of, 398 ventrolateral nucleus of thalamus, watershed infarct, arterial borderzones , triceps, radial nerve, 46 , 47 , 49 corticopontocerebellar pathway , 328, 329 triceps refl ex, muscle stretch refl ex, 132 264, 265 Weber's syndrome , 160 , 166 , 167 trigeminal ganglion ventroposterior lateral nucleus, thalamus , Wernicke–Korsakoff syndrome , 362 cavernous sinus , 192 , 193 346, 347 Wernicke's aphasia, language disorder, 428 , 429 cranial nerve 5 , 216 , 217 ventroposterior medial nucleus, thalamus , Wernicke's area, Brodmann areas, 284 , 285 trigeminal motor nerve, cranial nerve 5 , 346, 347 "what" pathway 216 , 217 vermian lobules, cerebellum, 254 , 255 long association fi bers, 294 , 295 trigeminal motor system, cranial nerve 5 , vertebral arteries, circle of Willis, 322 , 323 ventral stream, 400 , 401 214 , 215 vertebral-basilar arterial system , 322 , 323 "where" pathway trigeminal nerve, skull foramina , 190 , 191 vertebral column, spinal canal, 130 , 131 dorsal stream , 400 , 401 trigeminothalamic projections, cranial nerve 5 vertebrobasilar system, cerebral long association fi bers, 294 , 295 tracts, 218 , 219 angiography, 320 f white matter. See also cerebral white matter trochlear nerve vertical saccades, eye movements , 418 , 419 diencephalon , 344 , 345 cranial nerve nuclei, 182 , 183 , 185 vestibular nuclear complex , 240 , 241 Foville's illustration, 290 f skull foramina , 190 , 191 vestibular system , 232 , 240 , 241 organization , 291f trunk, cutaneous nerves, 86 , 87 ear , 236–239 parahippocampal gyrus, 366 , 367 tuberal group, hypothalamus , 352 , 353 vestibule-ocular refl ex pathways , 235f spinal cord, 110 , 111 tuberomammillary nucleus, wakefulness vestibulocerebellum , 252 , 253 Willis, Th omas , 322 circuitry, 446 , 447 cerebellar module , 250f Woltman's sign, muscle stretch refl ex, 132 tumor necrosis factor-alpha , 444 eye movement, 420 , 421 vestibulocochlear nucleus cranial nerve nuclei , 182 , 183 zona incerta, direct and indirect pathways , ulnar nerve, 28 , 29 f , 42–45 skull foramina , 190 , 191 312 , 313 brachial plexus , 31 , 33 , 35 vestibulocolic refl ex, vestibular system , zones, cerebellum, 248 , 252 , 253 complete drawing, 45 240, 241 zonule, eye , 382 , 383