Chapter 14 *Lecture Powerpoint

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Chapter 14 *Lecture PowerPoint

The Brain and Cranial Nerves

*See separate FlexArt PowerPoint slides for all figures and tables preinserted into PowerPoint without notes.

• The human brain is complex • Brain function is associated with life • This chapter is a study of brain and cranial nerves directly connected to it • Will provide insight into brain circuitry and function

14-2 Introduction • Aristotle thought brain was “radiator” to cool blood

• Hippocrates was more accurate: “from the brain only, arises our pleasures, joys, laughter, and jests, as well as our sorrows, pains, griefs, and tears”

• Cessation of brain activity—clinical criterion of death

• Evolution of the central nervous system shows spinal cord has changed very little while brain has changed a great deal – Greatest growth in areas of vision, memory, and motor control of the prehensile hand

14-3 Overview of the Brain

• Expected Learning Outcomes – Describe the major subdivisions and anatomical landmarks of the brain. – Describe the locations of its gray and white matter. – Describe the embryonic development of the CNS and relate this to adult brain anatomy.

14-4 Major Landmarks

• Rostral—toward the Rostral Caudal forehead

Central sulcus

• Caudal—toward the spinal Gyri Cerebrum cord Lateral sulcus

Cerebellum • Brain weighs about 1,600 g Temporal lobe (3.5 lb) in men, and 1,450 g

in women Brainstem

Spinal cord

(b) Lateral view

Figure 14.1b

14-5 Major Landmarks

• Three major portions of the Rostral Caudal brain – Cerebrum is 83% of brain volume; cerebral hemispheres, Central sulcus

gyri and sulci, longitudinal Gyri Cerebrum fissure, corpus callosum Lateral sulcus

– Cerebellum contains 50% of the Temporal lobe Cerebellum neurons; second largest brain region, located in posterior

cranial fossa Brainstem

– Brainstem is the portion of the Spinal cord brain that remains if the (b) Lateral view cerebrum and cerebellum are Figure 14.1b removed; diencephalon, midbrain, pons, and medulla oblongata

14-6 Major Landmarks

• Gyri—thick folds Frontal lobe

Central sulcus • Sulci—shallow grooves

Parietal lobe • Corpus callosum—thick nerve bundle at bottom of Occipital lobe

longitudinal fissure that Longitudinal fissure connects hemispheres (a) Superior view Figure 14.1a

14-7 Major Landmarks

• Occupies posterior Rostral Caudal cranial fossa Central sulcus Gyri Cerebrum • Marked by gyri, Lateral sulcus sulci, and fissures Temporal lobe Cerebellum

• About 10% of brain Brainstem

volume Spinal cord (b) Lateral view Figure 14.1b • Contains over 50% of brain neurons

14-8 Major Landmarks

• Brainstem—what Rostral Caudal remains of the brain if the cerebrum and Central sulcus cerebellum are Gyri Cerebrum removed Lateral sulcus Temporal lobe Cerebellum • Major components Brainstem – Diencephalon Spinal cord

– Midbrain (b) Lateral view Figure 14.1b – Pons

– Medulla oblongata

Central sulcus

Parietal lobe Cingulate gyrus

Corpus callosum

Parieto–occipital sulcus Frontal lobe Occipital lobe Thalamus Habenula Anterior Epithalamus commissure Pineal gland Hypothalamus Optic chiasm Posterior commissure Mammillary body Cerebral aqueduct Pituitary gland Fourth ventricle Temporal lobe

Midbrain Cerebellum

Pons

Medulla oblongata

Cingulate gyrus

Corpus callosum Lateral ventricle

Parieto–occipital sulcus Choroid plexus Pineal gland Thalamus

Hypothalamus Occipital lobe

Midbrain Posterior commissure

Pons Fourth ventricle

Cerebellum Medulla oblongata

(b) b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer Figure 14.2b

14-11 Gray and White Matter

• Gray matter—the seat of neuron cell bodies, dendrites, and synapses – Dull white color when fresh, due to little myelin – Forms surface layer (cortex) over cerebrum and cerebellum – Forms nuclei deep within brain

• White matter—bundles of axons – Lies deep to cortical gray matter, opposite relationship in the spinal cord – Pearly white color from myelin around nerve fibers – Composed of tracts, or bundles of axons, that connect one part of the brain to another, and to the spinal cord

14-12 Embryonic Development • Nervous system develops from ectoderm – Outermost tissue layer of the embryo

• Early in third week of development – Neuroectoderm: dorsal streak appears along the length of embryo – Thickens to form neural plate • Destined to give rise to most neurons and all glial cells except microglia, which come from mesoderm

• As thickening progresses – Neural plate sinks and its edges thicken • Forming a neural groove with a raised neural fold on each side • Neural folds fuse along the midline – Beginning in the cervical region and progressing rostrally and caudally

14-13 Embryonic Development • By fourth week, creates a hollow channel—neural tube – Neural tube separates from overlying ectoderm – Sinks deeper – Grows lateral processes that later will form motor nerve fibers – Lumen of neural tube becomes fluid-filled space • Central canal in spinal cord • Ventricles of the brain

14-14 Embryonic Development Cont. • Neural crest—formed from ectodermal cells that lay along the margins of the groove and separate from the rest forming a longitudinal column on each side – Gives rise to the two inner meninges, most of the peripheral nervous system, and other structures of the skeletal, integumentary, and endocrine systems

• By fourth week, the neural tube exhibits three anterior dilations (primary vesicles) – Forebrain (prosencephalon) – Midbrain (mesencephalon) – Hindbrain (rhombencephalon) 14-15

Embryonic Development

• By fifth week, it subdivides into five secondary vesicles – Forebrain divides into two of them • Telencephalon—becomes cerebral hemispheres • Diencephalon—has optic vesicles that become retina of the eye

– Midbrain remains undivided • Mesencephalon

– Hindbrain divides into two vesicles • Metencephalon • Myelencephalon

14-16 Embryonic Development

Neural plate

Neural crest Neural crest Neural fold Ectoderm Neural groove

Notochord

(a) 19 days (b) 20 days

Neural crest

Neural tube Somites

Figure 14.3

14-17 Embryonic Development

Telencephalon

• Fourth week Prosencephalon Optic vesicle

Diencephalon

– Forebrain Mesencephalon Metencephalon Rhombencephalon – Midbrain Myelencephalon

– Hindbrain Spinal cord • Fifth week (a) 4 weeks (b) 5 weeks – Telencephalon

– Diencephalon Telencephalon Forebrain Diencephalon – Mesencephalon Mesencephalon Midbrain Pons Metencephalon Cerebellum – Metencephalon Hindbrain Myelencephalon (medulla oblongata)

– Myelencephalon Spinal cord

• Expected Learning Outcomes – Describe the meninges of the brain. – Describe the fluid-filled chambers within the brain. – Discuss the production, circulation, and function of the cerebrospinal fluid that fills these chambers. – Explain the significance of the brain barrier system.

14-19 Meninges

• Meninges—three connective tissue membranes that envelop the brain – Lies between the nervous tissue and bone – As in spinal cord, they are the dura mater, arachnoid mater, and the pia mater – Protect the brain and provide structural framework for its arteries and veins

14-20 Meninges

• Dura mater – In cranial cavity; has two layers • Outer periosteal—equivalent to periosteum of cranial bones • Inner meningeal—continues into vertebral canal and forms dural sac around spinal cord

– Cranial dura mater is pressed closely against cranial bones • No epidural space • Not attached to bone except: around foramen magnum, sella turcica, the crista galli, and sutures of the skull • Layers separated by dural sinuses—collect blood circulating through brain

14-21 Meninges

Cont. – Folds inward to extend between parts of the brain • Falx cerebri separates the two cerebral hemispheres • Tentorium cerebelli separates cerebrum from cerebellum • Falx cerebelli separates the right and left halves of cerebellum

14-22 Meninges

• Arachnoid mater and pia mater are similar to those in the spinal cord

• Arachnoid mater – Transparent membrane over brain surface – Subarachnoid space separates it from pia mater below – Subdural space separates it from dura mater above in some places

• Pia mater – Very thin membrane that follows contours of brain, even dipping into sulci – Not usually visible without a microscope

Skull

Dura mater: Periosteal layer Subdural space Meningeal layer Subarachnoid Arachnoid granulation space

Arachnoid mater Superior sagittal sinus Blood vessel

Falx cerebri Pia mater (in longitudinal fissure only)

Brain: Gray matter

White matter

Figure 14.5 14-24 Meningitis • Meningitis—inflammation of the meninges – Serious disease of infancy and childhood – Especially between 3 months and 2 years of age

• Caused by bacterial and virus invasion of the CNS by way of the nose and throat

• Pia mater and arachnoid are most often affected

• Bacterial meningitis can cause swelling of the brain, enlargment of the ventricles, and hemorrhage

• Signs include high fever, stiff neck, drowsiness, and intense headache; may progress to coma then death within hours of onset

• Diagnosed by examining the CSF for bacteria – Lumbar puncture (spinal tap) draws fluid from subarachnoid space between two lumbar vertebrae

14-25 Ventricles and Cerebrospinal Fluid

Caudal Rostral

Lateral ventricles Cerebrum

Interventricular Lateral ventricle foramen Interventricular Third ventricle foramen Cerebral Third ventricle aqueduct Cerebral Fourth ventricle aqueduct Lateral aperture Fourth ventricle Median aperture Lateral aperture Median aperture Central canal

(a) Lateral view (b) Anterior view

Figure 14.6a,b

Longitudinal fissure

Frontal lobe

Gray matter (cortex)

White matter Corpus callosum (anterior part) Lateral ventricle Caudate nucleus Septum emporalT lobe pellucidum Third ventricle Sulcus Lateral sulcus Gyrus Insula

Thalamus Lateral ventricle Choroid plexus

Corpus callosum Occipital lobe (posterior part) Longitudinal fissure

Figure 14.6c

(c) Caudal (posterior) c: © The McGraw-Hill Companies, Inc./Rebecca Gray,photographer/Don Kincaid, dissections 14-27 Ventricles and Cerebrospinal Fluid

• Ventricles—four internal chambers within the brain

– Two lateral ventricles: one in each cerebral hemisphere • Interventricular foramen—a tiny pore that connects to third ventricle

– Third ventricle: single narrow medial space beneath corpus callosum • Cerebral aqueduct runs through midbrain and connects third to fourth ventricle

– Fourth ventricle: small triangular chamber between pons and cerebellum • Connects to central canal, runs down through spinal cord

14-28 Ventricles and Cerebrospinal Fluid Cont.

• Choroid plexus—spongy mass of blood capillaries on the floor of each ventricle

• Ependyma—neuroglia that lines the ventricles and covers choroid plexus – Produces cerebrospinal fluid

14-29 Ventricles and Cerebrospinal Fluid

• Cerebrospinal fluid (CSF)—clear, colorless liquid that fills the ventricles and canals of CNS – Bathes its external surface

• Brain produces and absorbs 500 mL/day – 100 to 160 mL normally present at one time – 40% formed in subarachnoid space external to brain – 30% by the general ependymal lining of the brain ventricles – 30% by the choroid plexuses

• Production begins with the filtration of blood plasma through the capillaries of the brain – Ependymal cells modify the filtrate, so CSF has more sodium and chloride than plasma, but less potassium, calcium, glucose, and very little protein

14-30 Ventricles and Cerebrospinal Fluid

• CSF continually flows through and around the CNS – Driven by its own pressure, beating of ependymal cilia, and pulsations of the brain produced by each heartbeat

• CSF secreted in lateral ventricles flows through intervertebral foramina into third ventricle

• Then down the cerebral aqueduct into the fourth ventricle

• Third and fourth ventricles add more CSF along the way 14-31

Ventricles and Cerebrospinal Fluid

• Small amount of CSF fills the central canal of the spinal cord – All escapes through three pores • Median aperture and two lateral apertures • Leads into subarachnoid space of brain and spinal cord surface

• CSF is reabsorbed by arachnoid villi – Cauliflower-shaped extension of the arachnoid meninx – Protrudes through dura mater – Into superior sagittal sinus – CSF penetrates the walls of the villi and mixes with the

blood in the sinus 14-32 Ventricles and Cerebrospinal Fluid

• Functions of CSF – Buoyancy • Allows brain to attain considerable size without being impaired by its own weight • If it rested heavily on floor of cranium, the pressure would kill the nervous tissue – Protection • Protects the brain from striking the cranium when the head is jolted • Shaken child syndrome and concussions do occur from severe jolting – Chemical stability • Flow of CSF rinses away metabolic wastes from nervous tissue and homeostatically regulates its chemical environment

14-33 Ventricles and Cerebrospinal Fluid

Arachnoid villus 8 Superior sagittal sinus

Arachnoid mater

1 CSF is secreted by choroid plexus in Subarachnoid each lateral ventricle. space Dura mater 1 2 CSF flows through interventricular foramina into third ventricle. 2 Choroid plexus

3 Third ventricle 3 Choroid plexus in third ventricle adds more CSF. 7 4 Cerebral 4 CSF flows down cerebral aqueduct aqueduct to fourth ventricle. Lateral aperture 5 Choroid plexus in fourth ventricle adds more CSF. Fourth ventricle

6 5 6 CSF flows out two lateral apertures and one median aperture.

7 CSF fills subarachnoid space and Median aperture bathes external surfaces of brain and spinal cord. 7

8 At arachnoid villi, CSF is reabsorbed into venous blood of dural Central canal venous sinuses. of spinal cord

Subarachnoid space of spinal cord

Figure 14.7 14-34 Blood Supply and the Brain Barrier System • Brain is only 2% of the adult body weight, and receives 15% of the blood – 750 mL/min.

• Neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical to the nervous system

– A 10-second interruption of blood flow may cause loss of consciousness – A 1- to 2-minute interruption can cause significant impairment of neural function – Going 4 minutes without blood causes irreversible brain damage

14-35 Blood Supply and the Brain Barrier System • Blood is also a source of antibodies, macrophages, bacterial toxins, and other harmful agents

• Brain barrier system—strictly regulates what substances can get from the bloodstream into the tissue fluid of the brain

• Two points of entry must be guarded – Blood capillaries throughout the brain tissue – Capillaries of the choroid plexus

14-36 Blood Supply and the Brain Barrier System

• Blood–brain barrier—protects blood capillaries throughout brain tissue – Consists of tight junctions between endothelial cells that form the capillary walls – Astrocytes reach out and contact capillaries with their perivascular feet – Induce the endothelial cells to form tight junctions that completely seal off gaps between them – Anything leaving the blood must pass through the cells, and not between them – Endothelial cells can exclude harmful substances from passing to the brain tissue while allowing necessary ones to pass 14-37 Blood Supply and the Brain Barrier System • Blood–CSF barrier—protects the brain at the choroid plexus – Forms tight junctions between the ependymal cells – Tight junctions are absent from ependymal cells elsewhere • Important to allow exchange between brain tissue and CSF

• Blood barrier system is highly permeable to water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics

• Slightly permeable to sodium, potassium, chloride, and the waste products urea and creatinine 14-38 Blood Supply and the Brain Barrier System

• Obstacle for delivering medications such as antibiotics and cancer drugs

• Trauma and inflammation can damage BBS and allow pathogens to enter brain tissue – Circumventricular organs (CVOs)—places in the third and fourth ventricles where the barrier is absent • Blood has direct access to the brain • Enables the brain to monitor and respond to fluctuations in blood glucose, pH, osmolarity, and other variables • CVOs afford a route for invasion by the human immunodeficiency virus (HIV)

14-39 The Hindbrain and Midbrain

• Expected Learning Outcomes – List the components of the hindbrain and midbrain and their functions. – Describe the location and functions of the reticular formation.

14-40 The Medulla Oblongata

• Embryonic myelencephalon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. becomes medulla oblongata Central sulcus Parietal lobe Cingulate gyrus Corpus callosum Parieto–occipital sulcus Frontal lobe Occipital lobe • Begins at foramen magnum of Thalamus Habenula Anterior Epithalamus commissure Pineal gland the skull Hypothalamus Optic chiasm Posterior commissure Mammillary body Cerebral aqueduct Pituitary gland Fourth ventricle Temporal lobe • Extends for about 3 cm rostrally Midbrain Cerebellum Pons

and ends at a groove between Medulla oblongata the medulla and pons (a)

Figure 14.2a • Slightly wider than spinal cord

• Pyramids—pair of external ridges on anterior surface – Resembles side-by-side baseball bats

14-41 The Medulla Oblongata

• Olive—a prominent bulge Central sulcus Parietal lobe lateral to each pyramid Cingulate gyrus Corpus callosum Parieto–occipital sulcus Frontal lobe Occipital lobe Thalamus Anterior Habenula Epithalamus • Posteriorly, gracile and commissure Pineal gland Hypothalamus Optic chiasm Posterior commissure cuneate fasciculi of the Mammillary body Cerebral aqueduct Pituitary gland spinal cord continue as two Temporal lobe Fourth ventricle Midbrain Cerebellum pair of ridges on the medulla Pons Medulla oblongata (a) • All nerve fibers connecting the brain to the spinal cord Figure 14.2a pass through the medulla

• Four pairs of cranial nerves begin or end in medulla—IX, X, XI, XII

14-42 The Medulla Oblongata

• Cardiac center – Adjusts rate and force of heart • Vasomotor center – Adjusts blood vessel diameter • Respiratory centers – Control rate and depth of breathing • Reflex centers – For coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head

(a) Midbrain

(b) Pons

Nucleus of Cuneate nucleus vagus nerve

Dorsal spinocerebellar Trigeminal nerve: tract Nucleus Tract Reticular formation Tectospinal tract Medial lemniscus

Inferior olivary nucleus Olive Hypoglossal nerve

Corticospinal tract Pyramids of medulla (c) Medulla oblongata Figure 14.9c • Pyramids contain descending fibers called corticospinal tracts – Carry motor signals to skeletal muscles • Inferior olivary nucleus—relay center for signals to cerebellum • Reticular formation—loose network of nuclei extending throughout the medulla, pons, and midbrain

Diencephalon: Thalamus Infundibulum Mammillary body Optic tract Cranial nerves: Midbrain: Optic nerve (II) Cerebral peduncle Oculomotor nerve (III)

Trochlear nerve (IV)

Trigeminal nerve (V)

Abducens nerve (VI) Pons Facial nerve (VII)

Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX) Vagus nerve (X)

Accessory nerve (XI) Medulla oblongata: Regions of the brainstem Pyramid Hypoglossal nerve (XII) Diencephalon Anterior median fissure Midbrain Pyramidal decussation Spinal nerves Pons Spinal cord Medulla oblongata (a) Ventral view Figure 14.8a 14-45 The Pons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Regions of the brainstem Diencephalon

Midbrain

Pons

Medulla oblongata

Diencephalon: Thalamus Lateral geniculate body Pineal gland Medial geniculate body Optic tract Midbrain: Superior colliculus Inferior colliculus Cerebral peduncle

Pons Superior cerebellar peduncle

Fourth ventricle Middle cerebellar peduncle

Inferior cerebellar peduncle Medulla oblongata Olive Cuneate fasciculus

Gracile fasciculus

Spinal cord

(b) Dorsolateral view Figure 14.8b 14-46 The Pons

Central sulcus

Parietal lobe Cingulate gyrus Corpus callosum

Parieto–occipital sulcus Frontal lobe Occipital lobe Thalamus Anterior Habenula Epithalamus commissure Pineal gland Hypothalamus Optic chiasm Posterior commissure Mammillary body Cerebral aqueduct Pituitary gland Temporal lobe Fourth ventricle

Midbrain Cerebellum Pons

Medulla oblongata Figure 14.2a (a)

• Metencephalon—develops into the pons and cerebellum • Pons—anterior bulge in brainstem, rostral to medulla • Cerebral peduncles—connect cerebellum to pons and midbrain

14-47 The Pons • Ascending sensory tracts

• Descending motor tracts

• Pathways in and out of cerebellum

• Cranial nerves V, VI, VII, and VIII – Sensory roles: hearing, equilibrium, taste, facial sensations – Motor roles: eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears

• Reticular formation in pons contains additional nuclei concerned with sleep, respiration, posture

14-48 The Pons

(a) Midbrain

(b) Pons

Superior cerebellar peduncle Middle cerebellar Ventral peduncle spinocerebellar tract Tectospinal tract Trigeminal nerve nuclei Anterolateral system Sensory root of trigeminal nerve

Trigeminal nerve

Reticular formation Transverse fascicles

Medial lemniscus Longitudinal fascicles

(b) Pons Figure 14.9b

14-49 The Midbrain

• Mesencephalon becomes one mature brain structure, the midbrain – Short segment of brainstem that connects the hindbrain to the forebrain – Contains cerebral aqueduct – Contains continuations of the medial lemniscus and reticular formation – Contains the motor nuclei of two cranial nerves that control eye movements: CN III (oculomotor) and CN IV (trochlear)

14-50 The Midbrain • Mesencephalon (cont.) – Tectum: rooflike part of the midbrain posterior to cerebral aqueduct • Exhibits four bulges, the corpora quadrigemina • Upper pair, the superior colliculi, function in visual attention, tracking moving objects, and some reflexes • Lower pair, the inferior colliculi, receives signals from the inner ear – Relays them to other parts of the brain, especially the thalamus

14-51 The Midbrain Cont. – Cerebral peduncles: two stalks that anchor the cerebrum to the brainstem anterior to the cerebral aqueduct

• Cerebral peduncles—three main components – Tegmentum • Dominated by the red nucleus • Pink color due to high density of blood vessels • Connections go to and from cerebellum • Collaborates with cerebellum for fine motor control

14-52 The Midbrain

– Substantia nigra • Dark gray to black nucleus pigmented with melanin • Motor center that relays inhibitory signals to thalamus and basal nuclei preventing unwanted body movement • Degeneration of neurons leads to tremors of Parkinson disease

– Cerebral crus • Bundle of nerve fibers that connect the cerebrum to the pons • Carries corticospinal tracts

Posterior

Superior colliculus Tectum Cerebral aqueduct

Medial geniculate nucleus

Reticular formation Central gray matter

Cerebral peduncle: Oculomotor nucleus Tegmentum Medial lemniscus Red nucleus

Substantia nigra

(a) Midbrain

Cerebral crus

(b) Pons Oculomotor nerve (III)

Anterior (c) Medulla (a) Midbrain Figure 14.9a

14-54 The Reticular Formation

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Radiations to cerebral cortex • Loosely organized web of Thalamus gray matter that runs vertically through all levels of the brainstem • Clusters of gray matter scattered throughout pons, midbrain, and medulla • Occupies space between white fiber tracts and brainstem nuclei Auditory input Visual input • Has connections with many Reticular formation areas of cerebrum Ascending general sensory fibers Descending motor – More than 100 small neural fibers to spinal cord networks without distinct boundaries

Figure 14.10 14-55 The Reticular Formation • Networks – Somatic motor control • Adjust muscle tension to maintain tone, balance, and posture • Especially during body movements • Relays signals from eyes and ears to the cerebellum • Integrates visual, auditory, and balance and motion stimuli into motor coordination • Gaze center—allows eyes to track and fixate on objects • Central pattern generators—neural pools that produce rhythmic signals to the muscles of breathing and swallowing

14-56 The Reticular Formation Cont. – Cardiovascular control • Includes cardiac and vasomotor centers of medulla oblongata

– Pain modulation • One route by which pain signals from the lower body reach the cerebral cortex • Origin of descending analgesic pathways—fibers act in the spinal cord to block transmission of pain signals to the brain

14-57 The Reticular Formation

– Sleep and consciousness • Plays central role in states of consciousness, such as alertness and sleep • Injury to reticular formation can result in irreversible coma

– Habituation • Process in which the brain learns to ignore repetitive, inconsequential stimuli while remaining sensitive to others

Anterior lobe

Posterior lobe

Folia Cerebellar Posterior hemisphere Figure 14.11b (b) Superior view • The largest part of the hindbrain and the second largest part of the brain as a whole

• Consists of right and left cerebellar hemispheres connected by vermis

• Cortex of gray matter with folds (folia) and four deep nuclei in each hemisphere

• Contains more than half of all brain neurons—about 100 billion – Granule cells and Purkinje cells synapse on deep nuclei

• White matter branching pattern is called arbor vitae 14-59

The Cerebellum

Superior colliculus

Inferior colliculus Pineal gland Posterior commissure

Cerebral aqueduct

Mammillary body Midbrain White matter (arbor vitae) Oculomotor nerve Gray matter Fourth ventricle

Pons

Medulla oblongata Figure 14.11a (a) Median section

• Cerebellar peduncles—three pairs of stalks that connect the cerebellum to the brainstem – Inferior peduncles: connected to medulla oblongata • Most spinal input enters the cerebellum through inferior peduncle – Middle peduncles: connected to the pons • Most input from the rest of the brain enters by way of middle peduncle – Superior peduncles: connected to the midbrain • Carries cerebellar output • Consist of thick bundles of nerve fibers that carry signals to and from the cerebellum 14-60 The Cerebellum

• Monitors muscle contractions and aids in motor coordination

• Evaluation of sensory input – Comparing textures without looking at them – Spatial perception and comprehension of different views of three- dimensional objects belonging to the same object

• Timekeeping center – Predicting movement of objects – Helps predict how much the eyes must move in order to compensate for head movements and remain fixed on an object

14-61 The Cerebellum

Cont. • Hearing – Distinguish pitch and similar-sounding words

• Planning and scheduling tasks

• Lesions may result in emotional overreactions and trouble with impulse control

14-62 The Forebrain • Expected Learning Outcomes – Name the three major components of the diencephalon and describe their locations and functions. – Identify the five lobes of the cerebrum and their functions. – Identify the three types of tracts in the cerebral white matter. – Describe the distinctive cell types and histological arrangement of the cerebral cortex. – Describe the location and functions of the basal nuclei and limbic system.

14-63 The Forebrain

• Forebrain consists of two parts

– Diencephalon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Encloses the third ventricle Telencephalon Forebrain • Most rostral part of the Diencephalon Mesencephalon Midbrain brainstem Pons Metencephalon Cerebellum Hindbrain Myelencephalon • Has three major (medulla oblongata)

embryonic derivatives Spinal cord

– Thalamus (c) Fully developed – Hypothalamus – Epithalamus Figure 14.4c – Telencephalon • Develops chiefly into the cerebrum 14-64 The Diencephalon: Thalamus

Thalamic Nuclei

Anterior group Part of limbic system; memory and emotion

Medial group Emotional output to prefrontal cortex; awareness of emotions

Ventral group Somesthetic output to postcentral gyrus; signals from cerebellum and basal nuclei to motor areas of cortex Figure 14.12a

Lateral group Somesthetic output to association areas of cortex; contributes to emotional function Lateral geniculate nucleus of limbic system

Medial geniculate nucleus Posterior group Relay of visual signals to occipital lobe (via lateral (a) Thalamus geniculate nucleus) and auditory signals to temporal lobe (via medial geniculate nucleus)

• Thalamus—ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres – Constitutes about four-fifths of the diencephalon – Two thalami are joined medially by a narrow intermediate mass – Composed of at least 23 nuclei; to consider five major functional groups

14-65 The Diencephalon: Thalamus

Cont. – “Gateway to the cerebral cortex”: nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex

– Plays key role in motor control by relaying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and the basal nuclei

– Involved in the memory and emotional functions of the limbic system: a complex of structures that include some cerebral cortex of the temporal and frontal lobes and some of the anterior thalamic nuclei

14-66 The Diencephalon: Hypothalamus

Central sulcus

• Hypothalamus—forms part Parietal lobe Cingulate gyrus of the walls and floor of the Corpus callosum Parieto–occipital sulcus Frontal lobe Occipital lobe third ventricle Thalamus Anterior Habenula Epithalamus commissure Pineal gland Hypothalamus Optic chiasm Posterior commissure Mammillary body Cerebral aqueduct Pituitary gland • Extends anteriorly to optic Temporal lobe Fourth ventricle Midbrain Cerebellum chiasm and posteriorly to Pons Medulla the paired mammillary oblongata bodies (a) Figure 14.2a • Each mammillary body contains three or four mammillary nuclei – Relay signals from the limbic system to the thalamus

14-67 The Diencephalon: Hypothalamus

• Infundibulum—a stalk that attaches the pituitary gland to the hypothalamus

• Major control center of autonomic nervous system and endocrine system – Plays essential role in homeostatic regulation of all body systems

• Functions of hypothalamic nuclei – Hormone secretion • Controls anterior pituitary • Regulates growth, metabolism, reproduction, and stress responses

14-68 The Diencephalon: Hypothalamus

Cont. – Hormone secretion • Controls anterior pituitary • Regulates growth, metabolism, reproduction, and stress responses

– Autonomic effects • Major integrating center for autonomic nervous system • Influences heart rate, blood pressure, gastrointestinal secretions, motility, etc.

– Thermoregulation • Hypothalamic thermostat monitors body temperature • Activates heat-loss center when temp is too high • Activates heat-promoting center when temp is too low 14-69 The Diencephalon: Hypothalamus

Cont. – Food and water intake • Hunger and satiety centers monitor blood glucose and amino acid levels – Produce sensations of hunger and satiety • Thirst center monitors osmolarity of the blood – Rhythm of sleep and waking • Controls 24-hour (circadian) rhythm of activity – Memory • Mammillary nuclei receive signals from hippocampus – Emotional behavior • Anger, aggression, fear, pleasure, and contentment

14-70 The Diencephalon: Epithalamus

Central sulcus

Parietal lobe Cingulate gyrus Corpus callosum

Midbrain Cerebellum Pons

Medulla oblongata Figure 14.2a (a) • Epithalamus—very small mass of tissue composed of: – Pineal gland: endocrine gland – Habenula: relay from the limbic system to the midbrain – Thin roof over the third ventricle

Central sulcus

Parietal lobe Cingulate gyrus Corpus callosum

Midbrain Cerebellum Pons

Medulla oblongata Figure 14.2a (a) • Cerebrum—largest and most conspicuous part of the human brain – Seat of sensory perception, memory, thought, judgment, and voluntary motor actions 14-72 The Cerebrum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cerebral hemispheres Rostral Caudal

Central sulcus Frontal lobe Gyri Cerebrum

Lateral sulcus

Central sulcus

Temporal lobe Cerebellum

Parietal lobe

Brainstem Occipital lobe

Longitudinal fissure Figure 14.1a,b Spinal cord (b) Lateral view (a) Superior view • Two cerebral hemispheres divided by longitudinal fissure – Connected by white fibrous tract, the corpus callosum – Gyri and sulci: increase amount of cortex in the cranial cavity – Gyri increases surface area for information-processing capability – Some sulci divide each hemisphere into five lobes named for the cranial bones overlying them 14-73 The Cerebrum • Frontal lobe – Voluntary motor functions – Motivation, foresight, planning, memory, mood,

– Receives and integrates Frontal lobe Parietal lobe general sensory information,

taste, and some visual Precentral processing gyrus • Occipital lobe Postcentral gyrus Central – Primary visual center of sulcus brain • Temporal lobe Insula Occipital lobe – Areas for hearing, smell, learning, memory, and Lateral sulcus some aspects of vision and emotion • Insula (hidden by other Temporal lobe regions) – Understanding spoken language, taste and sensory information from visceral receptors 14-74 Tracts of Cerebral White Matter Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Association tracts Projection tracts

Frontal lobe

Corpus callosum Parietal lobe

Temporal lobe Occipital lobe

(a) Sagittal section

Longitudinal fissure

Corpus callosum Commissural tracts

Lateral ventricle

Basal nuclei Thalamus Third ventricle

Mammillary body Cerebral peduncle

Pons Projection tracts Pyramid Decussation in pyramids Medulla oblongata

(b) Frontal section

Figure 14.14 14-75 The Cerebral White Matter

• Most of the volume of cerebrum is white matter – Glia and myelinated nerve fibers transmitting signals from one region of the cerebrum to another and between cerebrum and lower brain centers

14-76 The Cerebral White Matter

• Three types of tracts – Projection tracts • Extends vertically between higher and lower brain and spinal cord centers • Carries information between cerebrum and rest of the body

– Commissural tracts • Cross from one cerebral hemisphere through bridges called commissures – Most pass through corpus callosum – Anterior and posterior commissures – Enables the two sides of the cerebrum to communicate with each other

14-77 The Cerebral White Matter

Cont. – Association tracts • Connect different regions within the same cerebral hemisphere

• Long association fibers—connect different lobes of a hemisphere to each other

• Short association fibers—connect different gyri within a single lobe

14-78 The Cerebral Cortex

I • Cerebral gray matter Small pyramidal cells found in three places II – Cerebral cortex III – Basal nuclei Stellate cells – Limbic system IV

Large pyramidal V cells

White matter 14-79 The Cerebral Cortex

• Cerebral cortex—layer covering the surface of Figure 14.15 the hemispheres Cortical surface

– Only 2 to 3 mm thick I Small pyramidal – Cortex constitutes about cells 40% of brain mass II

– Contains 14 to 16 billion III

neurons Stellate cells

Large pyramidal V cells

White matter 14-80 The Cerebral Cortex

• Contains two principal types of neurons – Stellate cells • Have spheroid somas with dendrites projecting in all directions • Receive sensory input and process information on a local level

– Pyramidal cells • Tall, and conical, with apex toward the brain surface • A thick dendrite with many branches with small, knobby dendritic spines • Include the output neurons of the cerebrum • Only neurons that leave the cortex and connect with other parts of the CNS.

14-81 The Cerebral Cortex

• Neocortex—six-layered tissue that constitutes about 90% of the human cerebral cortex – Relatively recent in evolutionary origin

14-82 The Basal Nuclei

Cerebrum

Corpus callosum Lateral ventricle

Thalamus Internal capsule Caudate nucleus Putamen Insula Corpus Lentiform striatum Third ventricle Globus pallidus nucleus Hypothalamus Subthalamic nucleus Optic tract Pituitary gland Figure 14.16

• Basal nuclei—masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus – Receives input from the substantia nigra of the midbrain and the motor areas of the cortex – Send signals back to both these locations – Involved in motor control 14-83 The Basal Nuclei

• At least three brain centers form basal nuclei – Caudate nucleus – Putamen – Globus pallidus • Lentiform nucleus—putamen and globus pallidus collectively

• Corpus striatum—putamen and caudate nucleus collectively

14-84 The Limbic System

• Limbic system—important

Medial prefrontal • Most anatomically prominent cortex Corpus Fornix callosum components are: Cingulate gyrus Thalamic – Cingulate gyrus: arches nuclei Orbitofrontal Mammillary over the top of the corpus cortex body callosum in the frontal and Basal nuclei Hippocampus Amygdala

parietal lobes Temporal lobe – Hippocampus: in the medial temporal lobe; memory – Amygdala: immediately Figure 14.17 rostral to the hippocampus; emotion

14-85 The Limbic System

• Limbic system components are connected through a Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. complex loop of fiber tracts Medial allowing for somewhat prefrontal cortex circular patterns of Corpus Fornix callosum Cingulate feedback gyrus Thalamic nuclei Orbitofrontal Mammillary cortex body Basal nuclei Hippocampus

• Limbic system structures Amygdala have centers for both Temporal lobe gratification and aversion – Gratification: sensations of pleasure or reward Figure 14.17 – Aversion: sensations of fear or sorrow

14-86 Integrative Functions of the Brain

• Expected Learning Outcomes – List the types of brain waves and discuss their relationship to mental states. – Describe the stages of sleep, their relationship to the brain waves, and the neural mechanisms of sleep. – Identify the brain regions concerned with consciousness and thought, memory, emotion, sensation, motor control, and language. – Discuss the functional differences between the right and left cerebral hemispheres.

14-87 Integrative Functions of the Brain

• Higher brain functions—sleep, memory, cognition, emotion, sensation, motor control, and language

• Involve interactions between cerebral cortex and basal nuclei, brainstem, and cerebellum

• Functions of the brain do not have easily defined anatomical boundaries

• Integrative functions of the brain focus mainly on the cerebrum, but involve combined action of multiple brain levels

14-88 The Electroencephalogram

• Alpha waves 8 to 13 Hz – Awake and resting with eyes closed and mind wandering – Suppressed when eyes open or performing a mental task

• Beta waves 14 to 30 Hz – Eyes open and performing mental tasks – Accentuated during mental activity and sensory stimulation

• Theta waves 4 to 7 Hz – Drowsy or sleeping adults – If awake and under emotional stress

• Delta waves (high amplitude) <3.5 Hz – Deep sleep in adults

14-89 The Electroencephalogram

Alpha ()

Beta ()

Theta ()

Delta (δ) Figure 14.18a

1 second Figure 14.18b (b) • Electroencephalogram (EEG)—monitors surface electrical activity of the brain waves – Useful for studying normal brain functions as sleep and consciousness – In diagnosis of degenerative brain diseases, metabolic abnormalities, brain tumors, etc.

14-90 The Electroencephalogram

Cont. • Brain waves—rhythmic voltage changes resulting from synchronized postsynaptic potentials at the superficial layer of the cerebral cortex – Four types distinguished by amplitude (mV) and frequency (Hz)

• Persistent absence of brain waves is common clinical and legal criterion of brain death

14-91 Sleep

• Sleep occurs in cycles called circadian rhythms – Events that reoccur at intervals of about 24 hours

• Sleep—temporary state of unconsciousness from which one can awaken when stimulated – Characterized by stereotyped posture • Lying down with eyes closed – Sleep paralysis: inhibition of muscular activity – Resembles unconsciousness but can be aroused by sensory stimulation – Coma or hibernation: states of prolonged unconsciousness where individuals cannot be aroused by sensory stimulation

14-92 Sleep Cont. • Restorative effect – Brain glycogen and ATP levels increase in non-REM sleep – Memories strengthened in REM sleep • Synaptic connections reinforced

• Four stages of sleep – Stage 1 • Feel drowsy, close eyes, begin to relax • Often feel drifting sensation, easily awakened if stimulated • Alpha waves dominate EEG

14-93 Sleep Cont. – Stage 2 • Pass into light sleep • EEG declines in frequency but increases in amplitude • Exhibits sleep spindles—high spikes resulting from interactions between neurons of the thalamus and cerebral cortex

– Stage 3 • Moderate to deep sleep • About 20 minutes after stage 1 • Theta and delta waves appear • Muscles relax and vital signs fall (body temperature, blood pressure, heart and respiratory rates)

14-94 Sleep Cont. – Stage 4 • Called slow-wave sleep (SWS)—EEG dominated by low- frequency, high-amplitude delta waves • Muscles now very relaxed, vital signs at their lowest, and more difficult to awaken

• About five times a night, a sleeper backtracks from stage 3 or 4 to stage 2 – Exhibits bouts of rapid eye movement (REM) sleep, eyes oscillate back and forth – Also called paradoxical sleep, because EEG resembles the waking state, but sleeper is harder to arouse than any other stage

14-95 Sleep

Cont. – Vital signs increase, brain uses more oxygen than when awake – Sleep paralysis stronger to prevent sleeper from acting out dreams

• Dreams occur in both REM and non-REM sleep – REM tends to be longer and more vivid • Parasympathetic nervous system active during REM sleep – Causing constriction of the pupils – Erection of the penis and clitoris

14-96 Sleep

• Rhythm of sleep is controlled by a complex interaction between the cerebral cortex, thalamus, hypothalamus, and reticular formation – Arousal induced in the upper reticular formation, near junction of pons and midbrain – Sleep induced by nuclei below pons, and in ventrolateral preoptic nucleus in the hypothalamus

14-97 Sleep

• Suprachiasmatic nucleus (SCN)—another important control center for sleep – Above optic chiasma in anterior hypothalamus – Input from eye allows SCN to synchronize multiple body rhythms with external rhythms of night and day • Sleep, body temperature, urine production, secretion, and other functions

14-98 Sleep

• Sleep has a restorative effect, and sleep deprivation can be fatal to experimental animals – Bed rest alone does not have the restorative effect of sleep— why must we lose consciousness? – Sleep may be the time to replenish such energy sources as glycogen and ATP – REM sleep may consolidate and strengthen memories by reinforcing some synapses, and eliminating others

A wake Sleep spindles

Stage 1 REM Drowsy sleep

Stage Stage 2 Light sleep

Stage 3 Moderate to deep sleep Stage 4 Deepest sleep

0 10 20 30 40 50 60 70 Time (min.) (a) One sleep cycle

Awake REM REM REM REM REM

Stage 1

Stage 2 EEG stages EEG Stage 3

Stage 4

0 1 2 3 4 5 6 7 8

(b) Typical 8-hour sleep period Time (hours) Figure 14.19 14-100 Cognition

• Cognition—the range of mental processes by which we acquire and use knowledge – Such as sensory perception, thought, reasoning, judgment, memory, imagination, and intuition

• Association areas of cerebral cortex have above functions – Constitute about 75% of all brain tissue

14-101 Cognition

• Studies of patients with brain lesions, cancer, stroke, and trauma yield information on cognition – Parietal lobe association area: perceiving stimuli • Contralateral neglect syndrome—unaware of objects on opposite side of the body

– Temporal lobe association area: identifying stimuli • Agnosia—inability to recognize, identify, and name familiar objects • Prosopagnosia—person cannot remember familiar faces

– Frontal lobe association area: planning our responses and personality; inability to execute appropriate behavior

14-102 Memory

• Information management entails: – Learning: acquiring new information – Memory: information storage and retrieval – Forgetting: eliminating trivial information; as important as remembering

• Amnesia—defects in declarative memory: inability to describe past events

• Procedural memory—ability to tie one’s shoes – Anterograde amnesia: unable to store new information – Retrograde amnesia: person cannot recall things known before the injury

14-103 Memory

• Hippocampus—important memory-forming center – Does not store memories

– Organizes sensory and cognitive information into a unified long-term memory

– Memory consolidation: the process of “teaching the cerebral cortex” until a long-term memory is established

– Long-term memories are stored in various areas of the cerebral cortex

14-104 Memory

Cont. – Vocabulary and memory of familiar faces stored in superior temporal lobe

– Memories of one’s plans and social roles stored in the prefrontal cortex

• Cerebellum—helps learn motor skills

• Amygdala—emotional memory

14-105 Accidental Lobotomy

• Phineas Gage—railroad construction worker; severe injury with metal rod

• Injury to the ventromedial region of both frontal lobes

• Extreme personality change – Fitful, irreverent, grossly profane – Opposite of previous personality

• Prefrontal cortex functions – Planning, moral judgment, and emotional control

Figure 14.20 14-106 Emotion

• Emotional feelings and memories are interactions between prefrontal cortex and diencephalon

• Prefrontal cortex—seat of judgment, intent, and control over expression of emotions

• Feelings come from hypothalamus and amygdala – Nuclei generate feelings of fear or love

14-107 Emotion • Amygdala receives input from sensory systems – Role in food intake, sexual behavior, and drawing attention to novel stimuli – One output goes to hypothalamus influencing somatic and visceral motor systems • Heart races, raises blood pressure, makes hair stand on end, induces vomiting

– Other output to prefrontal cortex important in controlling expression of emotions • Ability to express love, control anger, or overcome fear

• Behavior shaped by learned associations between stimuli, our responses to them, and the reward or punishment that results 14-108 Sensation

• Primary sensory cortex—sites Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. where sensory input is first Anterior received and one becomes conscious of the stimulus Precentral Frontal • Association areas nearby to gyrus lobe sensory areas that process and interpret that sensory information Central sulcus – Primary visual cortex is bordered by visual association Parietal lobe area: interprets and makes cognitive sense of visual stimuli Postcentral gyrus Occipital lobe

– Multimodal association areas: Posterior receive input from multiple (a) senses and integrate this into an overall perception of our Figure 14.22a surroundings 14-109 The Special Senses

• Special senses—limited to the head and employ relatively complex sense organs • Primary cortices and association areas listed below • Vision – Visual primary cortex in far posterior region of occipital lobe

– Visual association area: anterior, and occupies all the remaining occipital lobe • Much of inferior temporal lobe deals with facial recognition and other familiar objects

• Hearing – Primary auditory cortex in the superior region of the temporal lobe and insula – Auditory association area: temporal lobe deep and inferior to primary auditory cortex • Recognizes spoken words, a familiar piece of music, or a voice on the phone

14-110 The Special Senses

• Equilibrium – Signals for balance and sense of motion project mainly to the cerebellum and several brainstem nuclei concerned with head and eye movements and visceral functions – Association cortex in the roof of the lateral sulcus near the lower end of the central sulcus • Seat of consciousness of our body movements and orientation in space • Taste and smell – Gustatory (taste) signals received by primary gustatory cortex in inferior end of the postcentral gyrus of the parietal lobe and anterior region of insula – Olfactory (smell) signals received by the primary olfactory cortex in the medial surface of the temporal lobe and inferior surface of the frontal lobe 14-111 The General Senses

• General (somesthetic, somatosensory, or somatic) senses—distributed over the entire body and employ relatively simple receptors – Senses of touch, pressure, stretch, movement, heat, cold, and pain • Several cranial nerves carry general sensations from head • Ascending tracts bring general sensory information from the rest of the body – Thalamus processes the input – Selectively relays signals to the postcentral gyrus • Fold of the cerebrum that lies immediately caudal to the central sulcus and forms the rostral border of the parietal lobe – Primary somesthetic cortex is the cortex of the postcentral gyrus – Somesthetic association area: caudal to the gyrus and in the roof of the lateral sulcus

14-112 The General Senses

• Awareness of stimulation occurs in primary somesthetic cortex

• Making cognitive sense of the stimulation occurs in the somesthetic association area

• Because of decussation, the right postcentral gyrus receives input from the left side of the body and vice versa

• Sensory homunculus—upside-down sensory map of the contralateral side of the body

• Somatotopy—point-for-point correspondence between an area of the body and an area of the CNS

14-113 The General Senses

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Sensory homunculus— diagram of the primary Figure 14.22b somesthetic cortex which II III IV V V resembles an upside-down IV I III II sensory map of the Toes contralateral side of the body Genitalia

• Shows receptors in the lower limbs projecting to the superior Teeth, gums and medial parts of the gyrus Tongue Abdominal viscera Viscerosensory area • Shows receptors from the face Lateral sulcus projecting to the inferior and Insula lateral parts

Lateral Medial

• Somatotopy—point-to-point (b) correspondence between an area of the body and an area of the CNS 14-114 Functional Regions of the Cerebral Cortex

Motor association Primary gustatory area cortex Wernicke area Broca area Prefrontal Visual association cortex area Primary visual cortex

Olfactory Primary association auditory cortex area Auditory association area

Figure 14.21 14-115 Motor Control

• The intention to contract a muscle begins in motor association (premotor) area of frontal lobes – Where we plan our behavior – Where neurons compile a program for degree and sequence of muscle contraction required for an action – Program transmitted to neurons of the precentral gyrus (primary motor area) • Most posterior gyrus of the frontal lobe

14-116 Motor Control • Premotor area (cont.) – Neurons send signals to the brainstem and spinal cord – Ultimately resulting in muscle contraction – Precentral gyrus also exhibits somatotopy • Neurons for toe movement are deep in the longitudinal fissure of the medial side of the gyrus • The summit of the gyrus controls the trunk, shoulder, and arm • The inferolateral region controls the facial muscles – Motor homunculus has a distorted look because the amount of cortex devoted to a given body region is proportional to the number of muscles and motor units in that body region

14-117 Motor Control

• Pyramidal cells of the precentral gyrus are called upper motor neurons – Their fibers project caudally – About 19 million fibers ending in nuclei of the brainstem – About 1 million forming the corticospinal tracts – Most fibers decussate in lower medulla oblongata – Form lateral corticospinal tracts on each side of the spinal cord

• In the brainstem or spinal cord, the fibers from upper motor neurons synapse with lower motor neurons whose axons innervate the skeletal muscles

• Basal nuclei and cerebellum are also important in muscle control 14-118 Motor Control • Basal nuclei – Determines the onset and cessation of intentional movements • Repetitive hip and shoulder movements in walking – Highly practiced, learned behaviors that one carries out with little thought • Writing, typing, driving a car – Lies in a feedback circuit from the cerebrum, to the basal nuclei, to the thalamus, and back to the cerebrum – Dyskinesias: movement disorders caused by lesions in the basal nuclei

• Cerebellum – Highly important in motor coordination – Aids in learning motor skills – Maintains muscle tone and posture – Smoothes muscle contraction – Coordinates eye and body movements – Coordinates the motions of different joints with each other – Ataxia: clumsy, awkward gait 14-119 Motor Homunculus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

V IV III II

I Toes

Vocalization Salivation Mastication Swallowing

Lateral Medial Figure 14.23b (b)

14-120 Motor Pathways Involving the Cerebellum

(a) Input to cerebellum (b) Output from cerebellum

Motor cortex Cerebrum

Cerebrum

Cerebellum Reticular formation Brainstem Cerebellum

Brainstem Eye

Inner ear

Reticulospinal and vestibulospinal Spinocerebellar tracts of spinal cord tracts of spinal cord Figure 14.24

Limb and postural Muscle and joint proprioceptors muscles 14-121 Language • Language include several abilities: reading, writing, speaking, and understanding words assigned to different regions of the cerebral cortex • Wernicke area – Permits recognition of spoken and written language and creates plan of speech – When we intend to speak, Wernicke area formulates phrases according to learned rules of grammar – Transmits plan of speech to Broca area • Broca area – Generates motor program for the muscles of the larynx, tongue, cheeks, and lips – Transmits program to primary motor cortex for commands to the lower motor neurons that supply relevant muscles • Affective language area lesions produce aprosody—flat emotionless speech 14-122 Language Centers of the Left Hemisphere

Precentral gyrus Postcentral gyrus Speech center of primary motor cortex Angular Primary gyrus auditory cortex (in lateral sulcus) Primary visual cortex Broca area Wernicke area

Figure 14.25

14-123 Aphasia • Aphasia—any language deficit from lesions in same hemisphere (usually left) containing the Wernicke and Broca areas • Nonfluent (Broca) aphasia – Lesion in Broca area – Slow speech, difficulty in choosing words, using words that only approximate the correct word • Fluent (Wernicke) aphasia – Lesion in Wernicke area – Speech normal and excessive, but uses senseless jargon – Cannot comprehend written and spoken words • Anomic aphasia – Can speak normally and understand speech, but cannot identify written words or pictures

14-124 Cerebral Lateralization

Left hemisphere Right hemisphere

Olfaction, right nasal cavity Olfaction, left nasal cavity Anterior

Verbal memory Memory for shapes

(Limited language Speech comprehension, mute)

Left hand motor control Right hand motor control Feeling shapes with left hand Feeling shapes with right hand Hearing nonvocal sounds Hearing vocal sounds (left ear advantage) (right ear advantage) Musical ability Rational, symbolic thought Intuitive, nonverbal thought

Superior recognition of Superior language faces and spatial comprehension relationships

Vision, right field Posterior Vision, left field

Figure 14.26 14-125 Cerebral Lateralization

• Cerebral lateralization—the difference in the structure and function of the cerebral hemispheres • Left hemisphere—categorical hemisphere – Specialized for spoken and written language – Sequential and analytical reasoning (math and science) – Breaks information into fragments and analyzes it in a linear way • Right hemisphere—representational hemisphere – Perceives information in a more integrated holistic way – Seat of imagination and insight – Musical and artistic skill – Perception of patterns and spatial relationships – Comparison of sights, sounds, smells, and taste

14-126 Cerebral Lateralization

• Highly correlated with handedness – Left hemisphere is the categorical one in 96% of right-handed people • Right hemisphere in 4% – Left-handed people: right hemisphere is categorical in 15% and left in 70% • Lateralization develops with age – Males exhibit more lateralization than females and suffer more functional loss when one hemisphere is damaged

14-127 The Cranial Nerves

• Expected Learning Outcomes – List the 12 cranial nerves by name and number. – Identify where each cranial nerve originates and terminates. – State the functions of each cranial nerve.

14-128 The Cranial Nerves

• Brain must communicate with rest of body

– Most of the input and output travels by way of the spinal cord

– 12 pairs of cranial nerves arise from the base of the brain

– Exit the cranium through foramina

– Lead to muscles and sense organs located mainly in the head and neck

14-129 Cranial Nerve Pathways

• Most motor fibers of the cranial nerves begin in nuclei of brainstem and lead to glands and muscles

• Sensory fibers begin in receptors located mainly in head and neck and lead mainly to the brainstem – Sensory fibers for proprioception may travel to brain in a different nerve from motor nerve

14-130 Cranial Nerve Pathways

• Most cranial nerves carry fibers between brainstem and ipsilateral receptors and effectors – Lesion in left brainstem causes sensory or motor deficit on same side • Exceptions: optic nerve where half the fibers decussate, and trochlear nerve where all efferent fibers lead to a muscle of the contralateral eye

14-131 Cranial Nerve Classification

• Some cranial nerves are classified as motor, some sensory, others mixed

– Sensory (I, II, and VIII)

– Motor (III, IV, VI, XI, and XII) • Stimulate muscle but also contain fibers of proprioception

– Mixed (V, VII, IX, X) • Sensory functions may be quite unrelated to their motor function – Facial nerve (VII) has sensory role in taste and motor role in facial expression

14-132 The Cranial Nerves

Frontal lobe Frontal lobe Longitudinal Cranial nerves: fissure Olfactory bulb (from olfactory nerve, I) Olfactory tract Olfactory tract Optic chiasm Optic nerve (II) Temporal lobe T emporal lobe Oculomotor nerve (III)

Trochlear nerve (IV) Infundibulum

Trigeminal nerve (V) Optic chiasm

Pons Abducens nerve (VI)

Facial nerve (VII)

Pons Medulla Vestibulocochlear nerve (VIII)

Glossopharyngeal nerve (IX)

Vagus nerve (X) Cerebellum Medulla Hypoglossal nerve (XII) oblongata

Accessory nerve (XI) Cerebellum

Spinal cord Spinal cord

(a) (b) b: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer/DonKincaid, dissections 14-133 The Olfactory Nerve (I)

Olfactory bulb Olfactory tract Cribriform plate of ethmoid bone Fascicles of olfactory nerve (I) Nasal mucosa

Figure 14.28 • Sense of smell • Damage causes impaired sense of smell

14-134 The Optic Nerve (II)

Eyeball

Optic nerve (II)

Optic chiasm Optic tract

Pituitary gland

Figure 14.29 • Provides vision

• Damage causes blindness in part or all of visual field

Oculomotor nerve (III): Superior branch Inferior branch Ciliary ganglion Superior orbital fissure

Figure 14.30

• Controls muscles that turn the eyeball up, down, and medially, as well as controlling the iris, lens, and upper eyelid • Damage causes drooping eyelid, dilated pupil, double vision, difficulty focusing, and inability to move eye in certain directions 14-136 The Trochlear Nerve (IV)

Superior oblique muscle

Superior orbital fissure

Trochlear nerve (IV)

Figure 14.31 • Eye movement (superior oblique muscle) • Damage causes double vision and inability to rotate eye inferolaterally 14-137 The Trigeminal Nerve (V)

• Largest of the cranial Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. nerves Superior orbital fissure Ophthalmic division (V1) Trigeminal ganglion Trigeminal nerve (V) • Most important sensory Infraorbital Maxillary division (V ) 2 nerve Foramen ovale

Superior Mandibular division (V3) nerve of the face alveolar nerves Foramen rotundum Lingual nerve

Anterior trunk of V3 to chewing muscles • Forks into three divisions Inferior alveolar nerve

– Ophthalmic division Temporalis muscle Lateral pterygoid muscle (V1): sensory Medial pterygoid muscle

V1 V Masseter muscle – Maxillary division 2 V3 Anterior belly of digastric muscle (V2): sensory Motor branches of the mandibular division (V3) Distribution of sensory – Mandibular division fibers of each division (V ): mixed 3 Figure 14.32

14-138 The Abducens Nerve (VI)

Lateral rectus muscle

Superior orbital fissure

Abducens nerve (VI)

Figure 14.33 • Provides eye movement (lateral rectus m.) • Damage results in inability to rotate eye laterally and at rest eye rotates medially 14-139 The Facial Nerve (VII)

Facial nerve (VII) Internal acoustic meatus Geniculate ganglion Pterygopalatine ganglion Lacrimal (tear) gland

Chorda tympani branch (taste and salivation)

Submandibular ganglion Motor branch Sublingual gland to muscles of Parasympathetic fibers facial expression

Submandibular gland

Stylomastoid foramen Figure 14.34a

(a) • Motor—major motor nerve of facial muscles: facial expressions; salivary glands and tear, nasal, and palatine glands • Sensory—taste on anterior two-thirds of tongue • Damage produces sagging facial muscles and disturbed sense of taste (no sweet and salty) 14-140 Five Branches of Facial Nerve

Temporal

Zygomatic

Buccal

Buccal Mandibular

Cervical

(b)

(c) c: © The McGraw-Hill Companies, Inc./Joe DeGrandis, photographer Figure 14.34b,c Clinical test: test anterior two-thirds of tongue with substances such as sugar, salt, vinegar, and quinine; test response of tear glands to ammonia fumes; test motor functions by asking subject to close eyes, smile, whistle, frown, raise eyebrows, etc. 14-141 The Vestibulocochlear Nerve (VIII)

Internal acoustic meatus Cochlea Vestibule

Figure 14.35 • Nerve of hearing and equilibrium • Damage produces deafness, dizziness, nausea, loss of balance, and nystagmus (involuntary rhythmic oscillation of the eyes from side to side) 14-142 The Glossopharyngeal Nerve (IX)

control of BP and Glossopharyngeal nerve (IX) Jugular foramen respiration Superior ganglion Inferior ganglion Otic ganglion • Sensations from Parotid salivary gland posterior one-third of tongue Carotid sinus Pharyngeal muscles • Damage results in loss of bitter and sour taste and impaired Figure 14.36 swallowing

14-143 The Vagus Nerve (X)

• Major role in the control of cardiac, pulmonary, digestive, Jugular foramen Pharyngeal nerve and urinary function Laryngeal nerve Carotid sinus

Vagus nerve (X) • Swallowing, speech, regulation of viscera Lung

Heart • Damage causes hoarseness Spleen or loss of voice, impaired Liver swallowing, and fatal if both Kidney Stomach are cut Colon (proximal portion) Small intestine

Figure 14.37 14-144 The Accessory Nerve (XI)

Jugular foramen Vagus nerve

Accessory nerve (XI) Foramen magnum

Sternocleidomastoid Spinal nerves muscle C3 and C4

Trapezius muscle

Posterior view

Figure 14.38 • Swallowing; head, neck, and shoulder movement – Damage causes impaired head, neck, shoulder movement; head turns toward injured side 14-145 The Hypoglossal Nerve (XII)

Hypoglossal canal Intrinsic muscles of the tongue Extrinsic muscles of the tongue Hypoglossal nerve (XII)

Figure 14.39 • Tongue movements for speech, food manipulation, and swallowing – If both are damaged: cannot protrude tongue – If one side is damaged: tongue deviates toward injured side; see ipsilateral atrophy 14-146 Cranial Nerve Disorders

• Trigeminal neuralgia (tic douloureux) – Recurring episodes of intense stabbing pain in trigeminal nerve area (near mouth or nose) – Pain triggered by touch, drinking, washing face – Treatment may require cutting nerve

• Bell palsy – Degenerative disorder of facial nerve causes paralysis of facial muscles on one side – May appear abruptly with full recovery within 3 to 5 weeks

14-147 Images of the Mind

• Positron emission tomography (PET) and MRI visualize increases in blood flow when brain areas are active – Injection of radioactively labeled glucose • Busy areas of brain “light up”

• Functional magnetic resonance imaging (fMRI) looks at increase in blood flow to an area (additional glucose is needed in active area)—magnetic properties of hemoglobin depend on how much oxygen is bound to it (additional oxygen is there due to additional blood flow) – Quick, safe, and accurate method to see brain function

14-148 Images of the Mind

Rostral Caudal Primary auditory cortex Premotor area Primary motor cortex

Visual cortex Wernicke area Broca area

1 The word car is seen in 2 Wernicke area conceives 3 Broca area compiles a 4 The primary motor cortex the visual cortex. of the verb drive to go with it. motor program to speak executes the program and the word drive. the word is spoken.

Figure 14.40

14-149