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Nervous System Overview
Dr. Hugo Bergen, Ph.D.
Dept. Human Anatomy & Cell Science
Faculty of Medicine
E-mail: [email protected]
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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
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Basic Organization of NS:
The nervous system consists of:
1. Central Nervous System (CNS): i. Brain
ii. Spinal cord
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 targetsa. Cranial Nerves (12 pairs) (Brain)
b. Spinal Nerves (31 pairs) (Spinal cord)
carry out higher mental functions, integrate & coordinate signals
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From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 1.3 and 1.4
Spinal Cord
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Functional Organization
• 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
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Sympathetic NS
From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 4.2
Note:Pre-Ganglionics are blue&Post-Ganglionics are green
Prevertebralganglion
Prevertebralganglion
Prevertebralganglion
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Parasympathetic NS
From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 4.4
Note:Pre-Ganglionics are purple&Post-Ganglionics are amber
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Brain
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
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Central Nervous System (CNS)
CNS = Brain & Spinal Cordo 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
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Brain - divisions
1. Cerebrum
• Telencephalon
• Diencephalon
2. Brain stem
• Midbrain
• Pons
• Medulla
3. Cerebellum
Mid-Sagittal Views
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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
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From: The Nervous System, B. Pentland, in Medical Sciences (2nd
Ed.). © 2015, Figure 8.6 Elsevier Limited.
Frontal
Temporal
Occipital
Parietal
© Dept. HACS, U. of Manitoba
Anatomical Divisions
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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
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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
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1. Commissural Fibres (cross midline)
• Largest bundle (by far) is corpus callosum (CC)
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2. Association Fibres (connect cortical
areas within hemisphere)
Numerous connections connecting gyri within and between lobes
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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.
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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
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Diencephalon: location
• Deep within brain on either side of midline rostral to midbrain
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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
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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
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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
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Brainstem & Cerebellum
Medulla
Midbrain
Pons
Midbrain
C. Callosum
Medulla
Pons
© Dept. HACS, U. of Manitoba
C. Callosum
Cerebellum
Cerebellum
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Cranial Nerves
Ascending and DescendingTracts
Nuclei(e.g. CNs & RF)
© H. Bergen, University of Manitoba
Cerebellum
Thalamus
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Cerebellum: Inputs and Outputs
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
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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
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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
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From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure
1.19
From: The Nervous System, B. Pentland, in Medical Sciences (2nd Ed.). © 2015, Figure 8.15 Elsevier Limited.
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Medulla
Midbrain
Pons
Spinal Cord
Cerebellum
© Dept. HACS, U. of Manitoba
Brainstem &Spinal Cord
Vertebrae
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Spinal Cord
• 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
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AMIRSYS | Reference Centers
Dorsal RootVertebra
Dorsal RootGanglion
Ventral RootSpinal Nerve Gray Matter White Matter
Dorsal
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Spinal Reflexes
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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
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From: The Nervous System, B. Pentland, in Medical Sciences (2nd
Ed.). © 2015, Figure 8.19 Elsevier Limited.
From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Limited. Figure 6.7
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Cerebrospinal Fluid
• 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
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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
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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)
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Cerebrospinal System - Meninges
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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
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Anterior Circulation
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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
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Middle Cerebral
Internal Carotid
PosteriorCommunicating
Vertebral
AnteriorCerebral
Anterior Communicating
Basilar
PosteriorCerebral
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Dural Venous Sinuses
• A sinus is a channel formed within the dura that carries venous blood from the brain to the internal jugular vein.
Internal Carotid
Sinuses
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From: Neuroanatomy: An Illustrated Colour Text (5th Ed.) by Crossman & Neary. © 2015, Elsevier Ltd.. Figure 7.9
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Peripheral Nervous System
• 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.
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From: The Nervous System, B. Pentland, in Medical Sciences (2nd
Ed.). © 2015, Figure 8.19 Elsevier Limited.
Dorsal Root
Ventral Root
© Amirsys Reference Centers
Spinal Nerve
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Terminal Nerves
– Receive contributions from several levels
– Contain both motor & sensory components
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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)
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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
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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)
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Cranial Nerves
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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)
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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
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CN I: Olfactory Nerve
CN I = Smell
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CN II: Optic Nerve
CN II = Vision
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CN III, IV & VI: Occulomotor, Trochlear,
and Abducens Nerves
CN III, IV, and VI = Eye movements
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CN V: Trigeminal Nerve
Motor Fibres
Somatosensory FibresCN V = Somatosensory for face and chewing
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CN VII: Facial Nerve
Taste
&
Salivary Glands
Facial Expression
CN VII = Facial expression, taste, and glands
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CN VIII: Vestibulocochlear Nerve
Semi-circular Canals (n=3)
Cochlea
CN VIII = Hearing and Balance
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CN IX: Glossopharyngeal Nerve
CN IX = Parotid gland, taste, sensory (pharynx) and viscerosensory
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CN X: Vagus Nerve
CN IX = Swallowing, speech, viscerosensory, and visceromotor
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CN XI: (Spinal) Accessory Nerve
CN XI = Shrugging shoulders (trapezius) and turning head (sternocleidomastoid)
Trapezius
Sternocleidomastoid
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CN X: Hypoglossal Nerve
CN XII = Tongue movements
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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