Nervous System Overview

Dr. Hugo Bergen, Ph.D. Dept. Human Anatomy & Cell Science Faculty of Medicine E-mail: [email protected] Objectives:

1. Describe the basic organization of the central and peripheral nervous systems. 2. Describe the ventricular system within the brain 3. Describe meninges and the blood supply to the brain 4. Describe the structure and function of the spinal nerves and the cranial nerves Basic Organization of NS:

The nervous system consists of: 1. Central Nervous System (CNS): i. Brain carry out higher mental functions, ii. Spinal cord integrate & coordinate signals 2. Peripheral Nervous System (PNS): o Connects the CNS to tissues and organs in the periphery. Communication via nerves is both afferent/sensory and efferent/motor. i. Nerves connect CNS to peripheral targets a. Cranial Nerves (12 pairs) (Brain) b. Spinal Nerves (31 pairs) (Spinal cord) Spinal Cord

• Somatic Nervous System • Comprised of parts of both CNS & PNS that are under voluntary control • Uses 1 neuron connecting CNS to target tissue • Sensory: touch, pain, temperature, position • Motor: voluntary & reflexive movements • Autonomic Nervous System • Involuntary innervation to smooth & cardiac muscle, and glandular tissue • 2 neurons connecting CNS to target tissue (pre-ganglionic & post-ganglionic) • Divided into sympathetic & parasympathetic divisions

Sympathetic NS

Prevertebral ganglion Note: Pre-Ganglionics are blue & Post-Ganglionics are green Prevertebral ganglion

Prevertebral ganglion

Note: Pre-Ganglionics are purple & Post-Ganglionics are amber

o Constitutes ~ 2% of body weight o Contains approx. 100 billion neurons o Specialized for: • Reception of stimuli • Transduction of stimuli – electrical/chemical impulse • Conduction of impulse to various sites of CNS Central Nervous System (CNS)

CNS = Brain & Spinal Cord o Gray Matter = Cell bodies and dendrites of neurons. Nucleus/Nuclei = collections of nerve cell bodies and dendrites (sites of connections) o White Matter = Axons of neurons. Tracts = bundles of axons/nerve fibers that connect neighboring or distant nuclei o CNS is surrounded by membranous layers & fluid: provides structural support & protection o Recovers poorly from damage / trauma Mid-Sagittal Views Brain - divisions

1. Cerebrum • Telencephalon • Diencephalon 2. Brain stem • Midbrain • Pons • Medulla 3. Cerebellum Cerebrum / Cerebral Hemispheres

Telencephalon consists of: a. Cerebral Cortex (Gray matter) / Lobes b. White matter (axons) c. Ventricles (fluid-filled cavities) d. Basal Ganglia/Basal Nuclei (Gray; Motor) Diencephalon consists of: a. Thalamus b. Hypothalamus From: The Nervous System, B. Pentland, in Medical Sciences (2nd Ed.). © 2015, Figure 8.6 Elsevier Limited. Anatomical Divisions

Parietal

Frontal

Occipital

Temporal © Dept. HACS, U. of Manitoba Cerebral Cortex Functions

Coordination of complex activities: • Sensory perception • Voluntary movement • Language • Non verbal communication • Decision making processes / spatial relations • Memory • Emotions neurons These rely on white matter connections White Matter

• Constitutes the ‘wiring’ of the brain • Brain function depends on connectivity • 3 categories of connections: 1. Commissural fibres: connect the left and right cerebral hemispheres to each other 2. Association Fibres: connect cortical regions within a hemisphere (don’t cross midline) 3. Projection Fibres: connect cortex to sub- cortical regions: diencephalon, brainstem, spinal cord 1. Commissural Fibres (cross midline)

• Largest bundle (by far) is corpus callosum (CC) 2. Association Fibres (connect cortical areas within hemisphere)

Numerous connections connecting gyri within and between lobes 3. Projection Fibres: connect cortex to sub-cortical areas (to and from cortex)

• Includes corona radiata and internal capsule; projects to spinal cord, brainstem, etc. Diencephalon: Components and Functions

1. Thalamus – largest component, relay station for all sensory info. (except smell), transmits to all areas of the cortex. Also regulates consciousness and sleep 2. Hypothalamus – integrates behaviors & visceral function; controls Autonomic N.S. 3. Epithalamus – includes pineal gland: regulates circadian rhythms (releases melatonin) 4. Subthalamus – involved in the regulation of movements; part of basal nuclei Diencephalon: location

• Deep within brain on either side of midline rostral to midbrain Brainstem

Brainstem components are considered together: • 10 of the 12 cranial nerves attach to it (III – XII; form component of Peripheral NS) and cranial nerve nuclei (origin/termination) • Reticular formation: controls vegetative functions and consciousness/arousal; critical for life o Respiratory and cardiovascular centres; autonomic reflexes; pain modulation o Non-conscious adjustments in posture & locomotion o e.g., large lesions may result in coma Brainstem (cont.)

• Ascending tracts destined for cortex pass through the brainstem o All somatosensory information (pain, temp. touch, vibration, & proprioception) from the periphery (ascending from the spinal cord) passes through the brainstem • Descending tracts pass through brainstem o Responsible for controlling motor activity of the body • These tracts are essential for maintaining normal motor and somatosensory function Cerebellum (lat.: ‘little brain’)

• Gray matter surrounds core of white matter • Attached to midbrain, pons, and medulla • Critical for coordinating motor activity and is important for precision and timing of movements • Motor learning • Important for maintaining posture • Cerebellar lesions can result in incoordination of movements Brainstem & Cerebellum C. Callosum

Midbrain

Pons

Medulla Cerebellum

C. Callosum

Midbrain Cerebellum Pons

Medulla

Nuclei (e.g. CNs & RF)

Cranial Nerves Cerebellum Ascending and Descending Tracts

Inputs: • Motor-related input from cerebral cortex • Proprioceptive input from spinal cord • Vestibular input from vestibular apparatus Integrates sensory info. with motor info. to produce normal movement patterns Acts like a comparator; it adjusts motor activity in response to proprioceptive feedback Cerebellum (cont.)

Outputs: • Projects to higher centres (cortex via thalamus) to adjust activity of descending motor pathways (from cortex to spinal cord) • Projects to brainstem circuits to adjust posture and balance; automatic adjustments in posture and locomotion Spinal Cord

• Rostrally it is continuous with the medulla • Contained within spinal canal of vert. column • 31 pairs of spinal nerves (component of PNS) are attached to cord White matter surrounds core of gray matter White Matter: o Ascending tracts carry somatosensory information from the periphery to higher centres o Descending tracts carry fibres that control the motor neurons that innervate voluntary muscle From: The Nervous System, B. Pentland, in Medical From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) Sciences (2nd Ed.). © 2015, Figure 8.15 Elsevier Limited. by Crossman & Neary. © 2015, Elsevier Limited. Figure 1.19 Brainstem & Cerebellum Spinal Cord Midbrain Pons Medulla

Spinal Cord

Vertebrae

• Spinal nerves are the source of the segmental innervation of the body • Each spinal nerve is formed from a dorsal root (sensory fibres) and a ventral root (motor fibres) • Dorsal root contains the cell bodies of the sensory neurons that convey pain, temp., touch, etc. (cell bodies are in dorsal root ganglion) • Ventral root contains motor axons

Dorsal Vertebra Dorsal Root Dorsal Root Ganglion

Spinal Nerve Ventral Root Gray Matter White Matter

AMIRSYS | Reference Centers Spinal Reflexes Ventricular System & Cerebrospinal Fluid

• Within the cerebral hemispheres are the large bilateral C-shaped lateral ventricles (n=2) filled with cerebrospinal fluid (csf) • These drain into the midline 3rd ventricle via the interventricular foramen (foramen of Monro) • The 3rd ventricle drains into midline 4th ventricle via the cerebral aqueduct • Total of 4 fluid-filled ventricles

• CSF is a clear fluid derived from plasma of the highly vascularized choroid plexus • Choroid plexus (CP) appears as tufts of material in all 4 ventricles • Regulates extracellular environment of CNS • Absorbed into venous circulation Meninges

• Brain & spinal cord are covered with 3 membranous layers: 1. Dura Mater: tough, dense layer tightly attached to inner surface of skull 2. Arachnoid Mater: thinner layer attached to dura; extensions from arachnoid to pia (‘spider- web’ like) 3. Pia Mater: very thin translucent layer attached to cortical surface; follows contours of the gyri Meninges - Functions

1. Protection (together with CSF, skull, vertebral column) 2. Compartmentalization of cranial cavity which provides structural support and suspends spinal cord within the dural sleeve 3. Conduit for cerebrospinal fluid (subarachnoid space) and venous blood (venous sinuses)

Cerebrospinal System - Meninges Arterial Supply to the Brain

Brain consumes ~ 20% of oxygen and is supplied by 2 major pairs of arteries: 1. Internal carotids (anterior circulation): give rise to Anterior cerebral art. (ACA) & Middle cerebral art. (MCA) to supply most of telencephalon (ant., med., & lat.) and diencephalon 2. Vertebrals (posterior circulation): give rise to basilar and Posterior cerebral art. (PCA) supply occipital lobe and inferior part of temporal lobe, brainstem, cerebellum, and cervical spinal cord

Anterior Circulation Vertebral Artery (Posterior Circ.)

• Vertebrals enter the cranium (foramen magnum) and form the single basilar artery which ascends along the pons before before splitting into posterior cerebral arteries (left and right) • The anastomosing network of arteries at base of brain is the ‘Circle of Willis’ • The posterior communicating artery connects the anterior circulation with the posterior circulation Anterior Communicating Anterior Cerebral Internal Carotid

Middle Posterior Cerebral Communicating

Posterior Cerebral Basilar

Vertebral Dural Venous Sinuses

• A sinus is a channel formed within the dura that carries venous blood from the brain to the internal jugular vein.

Sinuses

• Consists of nervous system outside of brain and spinal cord 1. Spinal Nerves (31 pairs attached to spinal cord): each nerve has sensory fibres (enter cord through dorsal root) and motor fibres (exit cord through ventral root) 2. Cranial Nerves (12 pairs attached to brain): innervation of head, neck, and viscera. May have sensory fibres only, motor fibres only, or both. Have specialized sensory functions. © Amirsys Reference Centers

Dorsal Root

Spinal Nerve

Ventral Root

From: The Nervous System, B. Pentland, in Medical Sciences (2nd Ed.). © 2015, Figure 8.19 Elsevier Limited. Terminal Nerves – Receive contributions from several levels – Contain both motor & sensory components Sensory Endings

Sensory system is capable of detecting • Mechanical stimuli (mechanoreceptors) • Pain (nociceptors) and • Temperature (thermoreceptors) Mechanoreceptors (many types) include • Neuromuscular spindles - receptors for stretch, respond to change in length (basis for stretch reflex i.e. Knee jerk) • Golgi Tendon organs - stimulated by tension in tendons (protection against damage from excessive stretch) Spinal Nerves & Roots (cont.)

• Anterior Root = Ventral Root = Motor Root contains efferent fibres; action potentials are leaving the cord • Motor neurons (cell bodies in the ventral horn of the cord) innervate skeletal muscle (via motor fibres) cause contractions of the muscle (LMNs) • Descending fibres from the cerebral cortex and brainstem activate these motor neurons to produce voluntary (and reflexive) movement

Cranial Nerves

2 of the 12 attached to cerebrum (CN I and CN II) 10 of the 12 arise from brainstem: • Midbrain: CNs III (Occulomotor) & IV (Trochlear) • Pons: CNs V (Trigeminal), VI (Abducens), VII (Facial), and VIII (Vestibulocochlear) • Medulla: CNs IX (Glossopharyngeal), X (Vagus), XI (Spinal Accessory), & XII (Hypoglossal) Cranial Nerves Cranial Nerves (cont.)

Some CNs are entirely motor, some entirely sensory, and some are mixed (motor and sensory fibres) (different than spinal nerves) and also contain visceromotor Efferents: carry motor fibres and visceromotor (i.e., parasympathetics) 1. Motor fibres: facial expression, eye movement, chewing, swallowing, speech, and 2 neck muscles (trapezius, & sternocleidomastoid) Cranial Nerves (cont.)

2. Parasympathetics: regulates heart, blood pressure, involuntary muscles, glands, gut 3. Afferents: carry sensory fibres (Somatosensory Special sensory, and Visceral sensations) Somatosensory: skin and muscles of face Special sensory: smell, vision, taste, hearing, and balance Visceral sensations: includes blood pressure, blood oxygen and CO2, various visceral sensations of the thoracic and abdominal viscera CN I: Olfactory Nerve

CN I = Smell CN II: Optic Nerve

CN II = Vision CN III, IV & VI: Occulomotor, Trochlear, and Abducens Nerves

CN III, IV, and VI = Eye movements CN V: Trigeminal Nerve

CN V = Somatosensory Somatosensory Fibres for face and chewing

Motor Fibres Facial Expression CN VII: Facial Nerve

CN VII = Facial expression, taste, and glands

Taste

Salivary Glands CN VIII: Vestibulocochlear Nerve

CN VIII = Hearing and Balance

Semi-circular Canals (n=3)

Cochlea CN IX: Glossopharyngeal Nerve

CN IX = Parotid gland, taste, sensory (pharynx) and viscerosensory CN X: Vagus Nerve

CN IX = Swallowing, speech, viscerosensory, and visceromotor CN XI: (Spinal) Accessory Nerve

CN XI = Shrugging shoulders (trapezius) and turning head (sternocleidomastoid)

Sternocleidomastoid

Trapezius CN X: Hypoglossal Nerve

CN XII = Tongue movements Lesions Involving Cranial Nerves

• Deficits may be evident in motor and/or sensory function • Most commonly involving a specific area of the face and/or neck • Deficits in cranial nerve function are commonly associated with brainstem lesions • Assessment Website: www.neuroexam.com