Anatomy of CNS and PNS

7/28/2019 Anatomy of CNS and PNS

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Anatomy of the Central

and Peripheral Nervous

System:An Introduction

Tony H, MD

Neurology Department

dr.Kariadi General Hospital


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ANATOMICAL ORGANIZATION of the NERVOUS

SYSTEM

Nervous

System

CNS PNS ANS

BRAIN

SPINAL

CORD

CRANIAL

NERVES

SPINAL

NERVES

SYMPATHETIC

PARA-

SYMPATHETIC


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Anatomy of Nervous System

CNS-central nervous system

Brain

Spinal Cord

PNS-peripheral nervous system

Cranial nerves IXII

Spinal nerves C1-S5

ANS-autonomic nervous system Sympathetic

Parasympathetic


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Central Nervous System (CNS)

Unpaired, bilaterally symmetrical structures

extending along the longitudinal axis of the

midsagittal plane of the body.

Structures arising directly from the neural

tube.

Includes:

Brain

Spinal cord


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CNS: Level of Functioning

Spinal Cord:

Lowest functioning level of CNS

Automatic motor responses and reflexes

Brain stem and subcortex (cerebellum anddiencephalon):

Second functional level

Blood pressure, respirations, equilibrium, and

primitive emotions Cortex:

Highest level

Cognition, memory, thinking, abstraction


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Peripheral Nervous System

(PNS)

Made up of transmission pathways carryinginformation between the CNS and

external/internal environments. Afferent (sensory) pathways:

Carry information to the CNS.

Efferent (motor) pathways:Carry information from the CNS.


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Peripheral Nervous System

Includes:

Cranial nerves (12 pairs)

Spinal nerves (31 pairs)

Also includes sensory receptors in skin andwall of gut tube as well as in tendons andskeletal muscles.

Also includes motor end plates betweenmotor neurons and skeletal muscle fibers.


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Autonomic Nervous System

May be considered a subdivision of the PNS.

Entirely motor.

Innervates smooth muscle and glands(viscera)


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ANS Subdivisions

Sympathetic system

(fight or flight)

Also called thoracolumbar

Parasympathetic system

(feed and breed)

Also called craniosacral


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Cells of Nervous System

Two cell types:

Neuroglia:

5-10 times more numerous than neurons

Provide support, nourishment, protection to neurons

Mitotic: CAN replicate if damaged

Neurons:

Primary functional unit of the nervous system Nonmitotic: cannot replicate


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BRAIN


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Brain

telencephalon (hemispheres)

diencephalon (thalamus etc)

mesencephalon (tegmentum, crus cerebri) metencephalon (pons, cerebellum)

myelencephalon (medulla oblongata)


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Cerebrum


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Dominance of a Cerebral Hemisphere

90% have left hemispheric dominance right handed

Some left handed people are left dominant

Each hemisphere receives sensory information from and controlsskeletal muscles of __________________ side of body

Hemispheres communicate with each other, but each hemispherespecializes in certain activities:

Left side:

language, analysis, problem solving, reading, writing,

verbal communication Right side:

perception of environment, music, art, nonverbalcommunication and perception of spiritual environment


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Frontal Lobe

Concentration, abstract thought

Affect, personality, inhibitions

Information storage, memory

Motor function Voluntary motor control

Betz cells/ pyramidal cells

Specific arrangement to body parts

Voluntary eye movement control Motor control of speech in dominant hemisphere

Motor control of involuntary activities

Respiration, BP, GI activity


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Parietal Lobe

General sensation

Primary sensory cortex: arranged in correlation to

motor strip

Perception of touch, position, pressure, vibration

Spatial perception and interrelationships

Interprets sensory perceptions and sends information

to thalamus and cortex


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Temporal Lobe Occipital Lobe

Primary auditory receptive

area

Interpretive area: At

junction of temporal,parietal and frontal lobes

Visual, auditory and

olfactory perception and

memory, learning,emotional affect

Visual perception

Visual association

Some visual reflexes

and involuntary eyemovements (smooth

tracking of objects)


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Basal Ganglia (basal nuclei)

Several masses of subcortical nuclei located

deep in cerebral hemispheres, just above

thalamus

Like brakes in a car control of movement

Controls and facilitates learned and automatic

movements

Fine motor control, particularly of hands and lowerextremities


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Diencephalon: Thalamus

Egg shaped masses of gray matter lying ventromedially in hemispheres

Major relay center for sensory and otherafferent input to cortex

Divided into groups of nuclei responsible forvarious functions

Plays a role in conscious pain awareness,consciousness, focusing attention, emotions,among other vital functions

Helps control primitive responses


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Diencephalon: Hypothalamus Located below thalamus

Regulates autonomic functions

Controls:

Temperature: monitors blood temp and sends afferentimpulses to sweat glands, muscles, etc

Water metabolism

Hypophyseal secretion

Visceral and somatic activities: BP, HR, peristalsis, etc Visible physical emotional expression (blushing, clammy

hands)


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Internal Capsule

Part of white matter ofcerebrum

The point at which

fibers coming fromvarious portions of thecortex converge at brainstem and enter

thalamus-hypothalamusregion

Crucial anatomical area


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Limbic System

Located lateral to hypothalamus;

forms border around brain stem

Made up of several structures:Hippocampus, fornix, mammillary body,

amigdala

Controls biological rhythms, sexual behavior,emotions of fear and rage

Helps balance extremes in emotion

Essential for normal memory (hippocampus)


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Reticular Formation

Nuclei from brainstem and portions of

diencephalon

Motor and sensory neurons providing

information about muscle activity

Continuous input to support body against

gravity

Vasomotor and respiratory control


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Reticular Activating System: RAS

Nuclei in spinal cord, brain stem,

thalamus and hypothalamus

Control sleep-wakefulness cycle,consciousness, focused attention

Stimulation of brain stem portion will

cause wakefulness Stimulation of thalamic portion adds

cognition and cerebral cortical activity


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Brainstem

Midbrain: nuclei for pupillary reflexes, eyemovements; auditory reflexes

Pons: Respiratory center, 4th ventricle, reticular

formation, nuclei of several cranial nerves Medulla: rate and strength of heartbeat; rate and

strength of respirations; sneezing, sucking,coughing, gagging, swallowing, vomiting, bloodvessel diameter


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Cerebellum, Brain Stem

C71.2C71.7 C71.6


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Cerebellum

Located in posterior cranial fossa

Coordinates muscular activity so movements

are fluid Position sense

Coordinates agonist and antagonist muscles

Maintains muscle tone and equilibrium Fine movement

Balance


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Protective Structures

Cranium: portion of skullcovering brain

Composed of 8 bones

Lobes named for bonesthey lie under

Meninges

Three layers of tissue

Provide protection,support, andnourishment to brainand spinal cord


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Dura Mater (Hard mother)

Outermost layer

2 layers of inelastic membrane space between

bone and dura is potential space calledepidural SPACE

Falx cerebri: between the two hemispheres

Tentorium cerebelli: between cerebrum and

cerebellum Falx cerebelli: between lobes of cerebellum

Diaphragm sella: over the sella tursica (pituitary)


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Arachnoid Mater

Thin, delicate, elastic layer, covers entire brain

Houses blood vessels of different sizes

Space between dura and arachnoid called subdural

SPACE

Pia Mater______________________________________________________________________________________________________________________________________________________________

Covers entire surface of brain, follows surface folds

Space that separates arachnoid and pia calledsubarachnoid SPACE CSF flow


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Ventricular System

4 fluid filled cavities within brain; connect with each

other and cord

2 lateral ventricles

Cerebral hemispheres

Third ventricle

Walls made up of thalamus and hypothalamus

Fourth ventricle Lies between cerebellum and

medulla and pons


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Ventricular System


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Cerebrospinal Fluid (CSF)

Clear, colorless fluid found within brain

Surrounds brain and spinal cord

Functions:

Cushions brain

Allows fluid shifts from cranial cavity to spinal cavity

Carries nutrients

Produced by choroid plexus: specialized structure in ventricles

Approximately 400500 ml/day

Reabsorbed at same rate by arachnoid villi

Approximately 150 ml in ventricular / subarachnoid system

Provides valuable diagnostic information


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Flow of CSF

Low pressure system: 9-14 mmHG

Choroid plexus lateral ventricles Foramen of

Monro Third VentricleAqueduct of Sylvius

Fourth Ventricle several foramen subarachnoid

space circulates around brain and spinal cord

reabsorbed into venous circulation through the

arachnoid villi

protrusions of arachnoid primarilyin the sagittal sinus


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Cerebral Blood Flow

Anteriorly: internal carotid arteries

Divide into anterior and middle cerebral arteries

Anterior 3/5 cerebrum

Posteriorly: vertebral arteries join to form BASILAR artery

Divides at midbrain to form posterior cerebral arteries

Posterior 2/5 of cerebrum; cerebellum and brainstem


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Cerebral Arteries

Anterior Cerebral Artery

Supplies anterior portion of brain; frontal lobes

Areas affected control thought, personality, motor

movement especially of leg Middle Cerebral Artery

Largest branch off internal carotid

Areas affected: sensory and motor for face, throat,

hand and arm Dominant hemisphere: motor speech; receptive

speech

Most often occluded in stroke! !


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Circle of Willis

Internal carotids branch

2 anterior cerebral arteries

joined to each other byanterior communicating

artery

2 posterior

communicating arteries 2 posterior cerebral

arteries


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Cerebral Venous Drainage

Does NOT parallel its arterial supply

Cerebellar and brain stem venous drainage

DOES parallel Cerebral veins drain into dural sinuses: formed

between dural layers (superior sagittal sinus;

transverse sinus) drain into internal jugular veins

Decreased venous outflow can INCREASEintracranial pressure


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Blood Brain Barrier

Structure of CNS capillaries different

Junctions between endothelial cells very tight

Solutes and water must pass through endothelial cells, NOTjunctions

Astrocytes form transport system

Oxygen, glucose, other nutrients allowed to enter, wasteproducts removed

Excludes water soluble and ionized; large molecules (mostantibiotics)

Affects penetration of pharmaceutical substances

Altered by trauma, cerebral edema, cerebral hypoxemia


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Pineal and Pituitary Glands


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Cranial Nerves


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R th h th t b l l


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Spinal Cord Runs through the vertebral canal

Extends from foramen magnum to secondlumbar vertebra

Regions

Cervical

Thoracic

Lumbar

Sacral

Coccygeal

Gives rise to 31 pairs of spinal nerves

All are mixednerves

Not uniform in diameter

Cervical enlargement: supplies upper limbs

Lumbar enlargement: supplies lower limbs

Conus medullaris- tapered inferior end

Ends between L1 and L2

Cauda equina - origin of spinal nervesextending inferiorly from conus medullaris.

C i i b


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Meninges Connective tissue membranes

Dura mater: outermost layer; continuous with

epineurium of the spinal nerves

Arachnoid mater: thin and wispy

Pia mater: bound tightly to surface

Forms the filum terminale

anchors spinal cord to coccyx

Forms the denticulate ligaments that attach the

spinal cord to the dura

Spaces

Epidural: external to the dura

Anesthestics injected here

Fat-fill

Subdural space: serous fluid

Subarachnoid: between pia and arachnoid

Filled with CSF


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Cross Section

of Spinal Cord

Anterior median fissure and posteriormedian sulcus

deep clefts partially separating left andright halves

Gray matter: neuron cell bodies,dendrites, axons

Divided into horns

Posterior (dorsal) horn

Anterior (ventral) horn

Lateral horn

White matter Myelinated axons

Divided into three columns (funiculi)

Ventral

Dorsal

lateral

Each of these divided into sensory ormotor tracts


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Organization of Spinal Cord Gray

Matter

Recall, it is divided into horns

Dorsal, lateral (only in thoracic region), and ventral

Dorsal half sensory roots and ganglia

Ventral half

motor roots

Based on the type of neurons/cell bodies located in eachhorn, it is specialized further into 4 regions

Somatic sensory (SS) - axons of somatic sensory neurons

Visceral sensory (VS) - neurons of visceral sensory neur.

Visceral motor (VM) - cell bodies of visceral motor neurons

Somatic motor (SM) - cell bodies of somatic motor neurons


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Gray Matter: Organization

Figure 12.31


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White Matter in the Spinal Cord

Divided into three funiculi (columns) posterior, lateral, and

anterior

Columns contain 3 different types of fibers (Ascend., Descend., Trans.)

Fibers run in three directions

Ascending fibers - compose the sensory tracts

Descending fibers - compose the motor tracts

Commissural (transverse) fibers - connect opposite sides of cord


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White Matter

Fiber Tract Generalizations Pathways decussate (most)

Most consist of a chain of two or three

neurons

Most exhibit somatotopy (precise spatial

relationships)

All pathways are paired

one on each side of the spinal cord

Whit M tt P th


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White Matter: Pathway

Generalizations


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Descending (Motor) Pathways

Descending tracts deliver motorinstructions from the brain to the spinalcord

Divided into two groups

Pyramidal, or corticospinal, tracts

Indirect pathways, essentially all others

Motor pathways involve two neurons

Upper motor neuron (UMN) Lower motor neuron (LMN)

aka anterior horn motor neuron (also,finalcommon pathway)

P id l (C ti i l) T t


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Pyramidal (Corticospinal) Tracts

Originate in theprecentral gyrus of brain (aka, primary motor area)

I.e., cell body of the UMN located in precentral gyrus Pyramidal neuron is the UMN

Its axon forms the corticospinal tract

UMN synapses in the anterior horn with LMN

Some UMN decussate in pyramids = Lateral corticospinal tracts

Others decussate at other levels of s.c. = Anterior corticospinal tracts

LMN (anterior horn motor neurons)

Exits spinal cord via anterior root

Activates skeletal muscles

Regulates fast and fine (skilled) movements


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Corticospinal

tracts

1. Location of UMN cellbody in cerebral cortex

2. Decussation of UMNaxon in pyramids or atlevel of exit of LMN

3. Synapse of UMN andLMN occurs in anterior

horn of s.c.4. LMN axon exits viaanterior root

E t id l M t T t


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Extrapyramidal Motor Tracts

Includes all motor pathways not part of the pyramidal system

Upper motor neuron (UMN) originates in nuclei deep in cerebrum (notincerebral cortex)

UMN does notpass through the pyramids!

LMN is an anterior horn motor neuron

This system includes

Rubrospinal

Vestibulospinal

Reticulospinal

Tectospinal tracts

Regulate:

Axial muscles that maintain balance and posture

Muscles controlling coarse movements of the proximal portions of limbs

Head, neck, and eye movement


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Extrapyramidal

Tract

Note:1. UMN cell body location

2. UMN axon decussates in pons3. Synapse between UMN and LMN

occurs in anterior horn of sc3. LMN exits via ventral root4. LMN axon stimulates skeletal

muscle

E t id l (M lti l)


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Extrapyramidal (Multineuronal)

Pathways

Reticulospinal tracts originates at reticular formation of brain;

maintain balance

Rubrospinal tracts originate in red nucleus of midbrain;

control flexor muscles

Tectospinal tracts - originate in superior colliculi and mediate

head and eye movements towards visual targets (flash of light)


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Main Ascending Pathways

The central processes of first-order neurons branch diffusely

as they enter the spinal cord and medulla

Some branches take part in spinal cord reflexes

Others synapse with second-order neurons in the cord and

medullary nuclei


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Three Ascending Pathways

The nonspecific and specific ascending pathwayssend impulses to the sensory cortex

These pathways are responsible for discriminativetouch

(2 pt. discrimination) and consciousproprioception (bodyposition sense).

The spinocerebellar tracts send impulses to thecerebellum and do not contribute to sensory

perception

Nonspecific Ascending Pathway


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Nonspecific Ascending Pathway

Include the lateral and anterior

spinothalamic tracts Lateral: transmits impulses

concerned with pain and temp.to opposite side of brain

Anterior: transmits impulsesconcerned with crude touch andpressure to opposite side of brain

1st order neuron: sensory neuron 2nd order neuron: interneurons

of dorsal horn; synapse with 3rdorder neuron in thalamus

3rd order neuron: carry impulsefrom thalamus to postcentral

gyrus

Specific and Posterior Spinocerebellar Tracts


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Specific and Posterior Spinocerebellar Tracts

Dorsal Column Tract1. AKA Medial lemniscal pathway2. Fibers run only in dorsal column

3. Transmit impulses from receptors inskin and joints

4. Detect discriminative touch andbody position sense =proprioception

1st O.N.- a sensory neuron synapses with 2nd O.N. in nucleus

gracilis and nucleus cuneatus ofmedulla

2nd O.N.- an interneuron decussate and ascend to thalamuswhere it synapses with 3rd O.N.

3rd-order (thalamic neurons)transmits impulse to somato-sensory cortex (postcentral gyrus)

Spinocerebellar Tract Transmit info. about trunk and lowerlimb muscles and tendons to cerebellum No conscious sensation

Spinal Cord Trauma and Disorders


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Severe damage to ventral root results inflaccid paralysis (limp and unresponsive)

Skeletal muscles cannot move either voluntarily or involuntarily Without stimulation, muscles atrophy.

When only UMN of primary motor cortex is damaged spastic paralysis occurs - muscles affected by persistent spasms and

exaggerated tendon reflexes Muscles remain healthy longer but their movements are no longer

subject to voluntary control. Muscles commonly become permanently shortened.

Transection (cross sectioning) at any level results in total motor andsensory loss in body regions inferior to site of damage.

If injury in cervical region, all four limbs affected (quadriplegia) If injury between T1 and L1, only lower limbs affected (paraplegia)



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Spinal shock - transient period of functional loss that follows the injuryResults in immediate depression of all reflex activity caudal to lesion. Bowel and bladder reflexes stop, blood pressure falls, and all muscles

(somatic and visceral) below the injury are paralyzed and insensitive. Neural function usually returns within a few hours following injury If function does not resume within 48 hrs, paralysis is permanent.

Amyotrophic Lateral Sclerosis (aka, Lou Gehrigs disease)

Progressive destruction of anterior horn motor neurons and fibers of the

pyramidal tracts Lose ability to speak, swallow, breathe. Death within 5 yrs Cause unknown (90%); others have high glutamate levels

Poliomyelitis

Virus destroys anterior horn motor neurons Victims die from paralysis of respiratory muscles Virus enters body in feces-contaminated water (public swimming pools)

CNS Anatomy


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CNS Anatomy

Cerebrum


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Cerebrum

Cerebellum Brain Stem


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Cerebellum, Brain Stem

C71.2C71.7 C71.6

Ventricular System


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Ventricular System

Pi l d Pit it Gl d


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Pineal and Pituitary Glands

Cranial Nerves


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Cranial Nerves

Meninges


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Tentorium


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Tentorium

Image source: A Primer of Brain Tumors, ABTA

Spinal Cord C72 0


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Spinal Cord C72.0

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Anatomy of CNS and PNS