ANATOMY OF THE NERVOUS
SYSTEM
• The entire nervous system can be
divided into two parts:
• 1- Central nervous system (CNS)
– includes the brain and spinal cord
• 2- Peripheral nervous system (PNS),
which consists of:
– Cranial nerves
– spinal nerves
Central Nervous System
• Brain
• The gross subdivisions of the adult brain
include the cerebrum, cerebellum, and
brainstem.
• The cerebrum develops from the embryonic
Telencephalon.
• The components of the brainstem are defined
in a number of ways
– include the diencephalon, midbrain, pons, medulla
oblongata
• Cerebrum comprises:
– the two cerebral hemispheres, including the
cerebral cortex, the basal nuclei
• The surface area of the cerebrum in domestic
mammals is increased by numerous foldings to
form convex ridges, called gyri (singular gyrus),
which are separated by furrows called fissures
or sulci.
• A particularly prominent fissure, the longitudinal
fissure, lies on the median plane and separates
the cerebrum into its right and left hemispheres.
•
Diencephalon
• Is a derivative of the prosencephalon.
– thalamus
– epithalamus
– hypothalamus
– the third ventricle are included in the diencephalon.
• The thalamus is an important relay center for nerve fibers
connecting the cerebral hemispheres to the brainstem
and spinal cord.
• The epithalamus, dorsal to the thalamus, includes a
number of structures, the pineal gland, which is an
endocrine organ in mammals.
• The hypothalamus, ventral to the thalamus, surrounds
the ventral part of the third ventricle and comprises
many nuclei that function in autonomic activities and
behavior.
– Attached to the ventral part of the hypothalamus is
the hypophysis, or pituitary gland
Mesencephalon
• The mesencephalon, or midbrain
• lies between the diencephalon rostrally and the pons caudally.
– The two cerebral peduncles
– four colliculi are the most prominent features of the midbrain.
• The cerebral peduncles, also called cruracerebrii, are large
bundles of nerve fibers connecting the spinal cord and
brainstem to the cerebral hemispheres.
– These peduncles consist of both sensory and motor fiber tracts.
• The colliculi are four small bumps (colliculus is Latin for little
hill) on the dorsal side of the midbrain.
• They consist of right and left rostral colliculi and right and
left caudal colliculi.
– The rostral colliculi coordinate certain visual reflexes,
– The caudal colliculi are relay nuclei for audition (hearing).
Metencephalon.
• The metencephalon includes
– the cerebellum dorsally and the pons ventrally.
• The cerebellum features two lateral hemispheres and a median
ridge called the vermis.
•
The surface of the cerebellum consists of many laminae called
folia. In the cerebellum, like the cerebrum, the white matter is
central, and the gray matter is peripheral in the cerebellar
cortex.
•
The cerebellum is critical to the accurate timing and execution
of movements; it acts to smooth and coordinate muscle
activity.
• The pons is ventral to the cerebellum, and its surface
possesses visible transverse fibers that form a bridge from one
hemisphere of the cerebellum to the other.
Myelencephalon
• The myelencephalon becomes the
medulla oblongata in the adult.
• It is the cranial continuation of the
spinal cord
• The medulla oblongata (often simply
called the medulla) contains a number
of important autonomic centers and
nuclei for cranial nerves.
Ventricular System.
• The ventricles of the brain are the remnants of the lumen of the
embryonic neural tube.
•
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.
•
The third ventricle connects with the fourth ventricle by way of the
mesencephalic aqueduct (cerebral aqueduct) passing through the
midbrain.
• 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.
• 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
ependyma lining the ventricles.
• CSF is a modified transudate, formed
primarily through active secretion by the
ependymal cells, especially those of the
choroid plexuses.
Meninges
• The coverings of the brain and spinal cord are
the meninges (singular meninx).
• They include, from deep to superficial
– the pia mater
– the arachnoid
– the dura mater.
• 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. The pia mater forms a
sheath around the blood vessels and follows
them into the substance of the CNS.
Meninges
• The middle meninx
– 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.
• 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.
– Another fold of dura mater, the tentorium cerebelli, runs
transversely between the cerebellum and the cerebrum.
• In some locations within the skull, the dura mater splits into
two layers divided by channels filled with blood. 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.
•
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.
• 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.