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CNS Gross Anatomy

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Spinal Cord

• Same Meningeal Layers as the Brain

• About 45cm long

• Diameter of 1 cm.

Root filamentsDorsalVentral

Mixed spinal nerve

Dura mater

Arachnoid mater

Pia mater

Spinal Nerve Components

• Dorsal Division: sensory part of nerve, sensory information enters spinal cord through dorsal root fibers

• Ganglion: cell bodies of these nerves come together to create the dorsal root ganglion

• Dorsal Horn or Column: information enters the spinal column at the dorsal horn

Spinal Nerve Components• Ventral Division: motor commands, leave the

ventral root and go to muscles

• Ventral Horn or Column: information passed from brain to spinal cord then from the ventral root to the extremities

Transverse view of spinal cord

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Segmental Spinal Reflex Arc

• A stimulus/response system that maintains a constant state of muscular tone

• Works by:– muscles spindles sense stretching and send information through

gamma nerves to dorsal root of spinal cord– a signal is sent back from the ventral root for the muscle to contract

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Spinal Cord

• Dorsal root fibers form ganglion

• Connect to ventral fibers to form peripheral spinal nerves.

• Attached by Filum Terminale

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Internal Spinal Cord

• Gray Matter

• Two Dorsal Horns (Sensory Info)

• Two Ventral Horns (Motor Info)

• White Matter

• Three Myelinated Fasciculi

• Dorsal, Lateral and Ventral

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Spinal Cord Segments & Nerves

Lumbar5

Coccygeal1

31 Spinal Segments and Nerves

Cervical8

Thoracic12

Sacral5

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Ventricles

• Lateral Ventricles• Connected by

interventricular foramen• Collateral trigone area• Posterior and inferior horns• Connects to Third Ventricle

through Monro’s foramen

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Ventricles

• Birds Eye View– Usually symmetrical in healthy people

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Other ventricles…

• Third Ventricle• Ventral to the corpora

quadrigemina• Surrounded by central gray

area• Connects to fourth ventricle

through Cerebral Aqueduct• Fourth ventricle

– Near Pons / Medulla

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Ventricles

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Ventricles in clinical setting

• Hydrocephalus– E.G. cyst

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White matter fibers from the cortex

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Medullary Centers

• Interhemispheric (between) Connections

• Intrahemispheric (within) Connections

• Three types of fibers– Projection: Project through internal capsule– Association: Within a hemisphere

i.e. Arcuate fasciculus– Commissural: Between hemispheres i.e. Corpus

callosum

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Meninges

• Three Basic Levels

• Extensions of Dura mater

• Falx Cerebri: Vertical partition dipping into cranial space (Refection)

• Tentorium Cerebri: Houses the cerebellum

• Falx Cerebelli: Separates two cerebellar hemispheres

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Meninges

• Arachnoid Trabeculae– Connects Pia and Arachnoid– Inside subarachnoid space

• Arachnoid Villi– Specialized protrusions through

which Cerebrospinal Fluid (CSF) leaves the brain

Peripheral Nervous System (PNS)• 12 pairs of cranial nerves-

– Sensory, motor, or mixed

“On Old Olympus Towering Top A Famous Vocal German Viewed Some Hops.”

• 31 pairs of spinal nerves

Cranial Nerves (12 pair)

I. Olfactory: sensory for smell

II. Optic: sensory for vision

III. Oculomotor: motor for vision

IV. Trochlear: motor for vision

V. Trigeminal: sensory to eyes, nose, face and meningies; motor to muscles of mastication and tongue

Cranial Nerves

I. Abducen: motor to lateral eye musclesII. Facial: sensory to tongue and soft palate,

motor to muscles of the face and stapesIII. Vestibulocochlear: sensory for hearing and

balance (aka Acoustic)IV. Glossopharyngeal: sensory to tongue,

pharynx, and soft palate; motor to muscles of the the pharynx and stylopharyngeus

Cranial Nerves

I. Vagus Nerve: sensory to ear, pharynx, larynx, and viscera; motor to pharynx, larynx, tongue, and smooth muscles of the viscera, 2 parts: superior laryngeal branch and recurrent laryngeal branch

II. Spinal Accessory Nerve: motor to pharynx, larynx, soft palate and neck

III. Hypoglossal Nerve: motor to strap muscles of the neck, intrinsic and extrinsic muscles of the tongue