ANATOMY OF THE NERVOUS SYSTEM�

Ventricular System.

• The ventricles of the brain are the remnants of the lumen of the embryonic neural tube.

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• Right and left lateral ventricles lie within the respective cerebral hemispheres.
• They communicate with the midline third ventricle by way of the interventricular foramina.
• Most of the third ventricle is surrounded by the diencephalon.

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• The third ventricle connects with the fourth ventricle by way of the mesencephalic aqueduct (cerebral aqueduct) passing through the midbrain.

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• The fourth ventricle, between the cerebellum above and pons and medulla below, communicates with the subarachnoid space surrounding the CNS through two lateral apertures.

• Each ventricle features a choroid plexus
• a tuft of blood capillaries that protrudes into the lumen of the ventricle.
• The plexus of capillaries is covered by a layer of ependymal cells that are continuous with the lining membrane of the ventricles.

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• Cerebrospinal fluid (CSF), filling the ventricular system and surrounding the CNS, is formed primarily by the choroid plexuses, with a smaller contribution made by the ependymal lining the ventricles.

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• CSF is a modified transudate, formed primarily through active secretion by the ependymal cells, especially those of the choroid plexuses.

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• In some locations within the skull, the dura mater splits into two layers divided by channels filled with blood.

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• These dural sinuses receive blood from the veins of the brain and empty into the jugular veins.
• They are also the site of reabsorption of CSF back into the circulation.

Meninges�

• The coverings of the brain and spinal cord are the meninges (singular meninx).

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• They include, from deep to superficial
• the pia mater
• the arachnoid
• the dura mater.

Meninges�

• The pia mater:
• the deepest of the meninges
• is a delicate membrane that invests the brain and spinal cord
• following the grooves and depressions closely.

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• The pia mater forms a sheath around the blood vessels and follows them into the substance of the CNS.

Meninges�

• The middle meninx (arachnoid):
• arises embryologically from the same layer as the pia mater but separates from it during development so that a space forms between them.
• Because of the weblike appearance of these filaments, this middle layer is called the arachnoid (arachnoidea, arachnoid mater).
• Together, the pia mater and arachnoid constitute the Ieptomeninges (from the Latin word lepto, delicate), reflecting their fine, delicate nature.

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• The space between the two layers is the subarachnoid space.
• It is filled with CSF.

Meninges�

• The dura mater is the tough fibrous outer covering of the CNS.
• Within the cranial cavity the dura mater is intimately attached to the inside of the cranial bones and so fulfills the role of periosteum.

It also forms the falx cerebri, a median sickle-shaped fold that lies in the longitudinal fissure and partially separates the cerebral hemispheres.

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Another fold of dura mater, the tentorium cerebelli, runs transversely between the cerebellum and the cerebrum.

Meninges�

• In some locations within the skull, the dura mater splits into two layers divided by channels filled with blood.

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• These dural sinuses receive blood from the veins of the brain and empty into the jugular veins.
• They are also the site of reabsorption of CSF back into the circulation.

Spinal Cord�

• The spinal cord is the caudal continuation of the medulla oblongata.

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• Unlike that of the cerebrum, the spinal cord’s gray matter is found at the center of the cord, forming a butterfly shape on cross-section.
• Myelinated fiber tracts, the white matter, surround this core of gray matter.

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• A spinal cord segment is defined by the presence of a pair of spinal nerves.
• Spinal nerves are formed by the conjoining of dorsal and ventral roots.

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�Spinal Cord�

• Sensory neurons of neural crest origin are present in aggregates, called dorsal root ganglia, lateral to the spinal cord.
• The neurons within these ganglia are pseudounipolar
• they give rise to axons that enter the dorsal horn of the spinal cord and other fibers that join with motor fibers from the ventral horn neurons to become a spinal nerve extending into the periphery.

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• The ventral root of the spinal nerve consists largely of motor fibers that arise from the nerve cells in the ventral horn of the spinal cord.

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• The dorsal and ventral roots unite to form the spinal nerve close to the intervertebral foramen between adjacent vertebrae.

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Conus Medullaris:  is the tapered, lower end of the spinal cord.

Filum terminale: the fibrous cord derived from the pia meter,

extending from the conus to caudal vertebrae

Cauda equina: the structure formed by nervous roots leaving the

caudal part of the spinal cord, traveling caudally to reach their exit

from the vertebral canal

Cranial Nerves

Cranial Nerves

• Twelve pairs:
• 2 attach to forebrain (Telen- & Diencephalon)
• 10 attach to brainstem (Mes-, Met- and Myelencephalon)
• Names relate to appearance or function
• Classification ?

The 12 Pairs of Cranial Nerves

I - Olfactory Nerves - Sensory - sense of smell

II - Optic Nerves - Sensory - nerve of vision. Transmits visual impulses from retina to thalamus

III - Oculomotor Nerves - Mixed nerve, Primary motor

Innervates four of the extrinsic eye muscles

IV - Trochlear Nerves - Mixed nerves, innervates an extrinsic eye muscle

V - Trigeminal Nerves - Provides sensory innervation to the face and motor innervation to chewing muscles

VI -Abducens Nerve - Mixed nerve, Abducts the eyeball (lateral movement)

The 12 Pairs of Cranial Nerves

VII - Facial Nerves - Mixed nerves, innervates muscles of facial expression, sensory nerve from taste buds and outer 1/3 of tongue

VIII - Vestibulocochlear Nerves -Sensory nerve of hearing and equilibrium

IX - Glossopharyngeal Nerves - Mixed nerves, innervates structures of the tongue and pharynx

X - Vagus Nerves - A mixed sensory and motor nerve

“Wanders” into thorax and abdomen

The 12 Pairs of Cranial Nerves

XI - Accessory Nerve - An accessory part of the vagus nerve

• The dorsal branch passes between the brachiocephalic and the splenius muscle to innervate the covering brachiocephalic (except the cleidobrachial muscle), the omotransverse and the trapezius muscles.

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• The ventral branch innervates the sternocephalic muscle.

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XII - Hypoglossal Nerves - Runs inferior to the tongue

Mixed nerve, innervates the tongue muscles

Blood supply of the brain