ANATOMY OF THE NERVOUS
SYSTEM
06:13
1
Functions of the nervous system
• 1. Initiate and/or regulate movement of body parts
• 2. Regulate secretions from glands
• 3. Gather information about the external environment and the
internal environment of the body
– using senses (sight, hearing, touch, balance, taste) and
mechanisms to detect pain, temperature, pressure, and
certain chemicals, such as carbon dioxide, hydrogen, and
oxygen
• 4. Maintain an appropriate state of consciousness
• 5. Stimulate thirst, hunger, fear, rage, and sexual behaviors
appropriate for survival
06:13
2
The nervous system
•
•
•
•
The nervous system consists:
Brain
Spinal cord
Peripheral nerves
– which connect the various parts of the
body to either the brain or spinal cord.
06:13
3
06:13
4
• 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
06:13
5
06:13
6
• In the PNS:
1- sensory (afferent) nerves
- gather information about the external and
internal environments and relay this information to
the CNS.
06:13
7
• CNS interprets information arriving via the
PNS, integrates that information, and
initiates
– appropriate movement of body parts
– glandular secretion
– behavior response.
2- Motor efferent
- Communication between the CNS and
muscles and accomplished via nerves of
the PNS
06:13
8
Microscopic Neuroanatomy
• The individual nerve cell is called a neuron.
Each neuronal cell body gives rise to one or
more nerve processes and cytoplasmic
extensions of the cell.
06:13
9
Microscopic Neuroanatomy
The nerve processes are called
dendrites if they transmit
electrical signals toward the
cell bodies
They are called axons if they
conduct electrical signals away
from the cell bodies.
06:13
10
• Neurons may be classified
morphologically according to their
number of nerve processes:
– Unipolar neurons have one process
– Bipolar neurons have one dendrite and one
axon
– Multipolar neurons have a number of
dendrites in addition to their single axon.
06:13
11
06:13
12
• Nervous tissue consists not only of neurons
but also of supportive cells.
– In the CNS, these supportive cells are the
neuroglia, comprising a variety of glial cells
– while most of the supporting tissue of the PNS is
ordinary white fibrous connective tissue.
• Groups of nerve cell bodies within the CNS
are generally called nuclei, while groups of
nerve cell bodies in the PNS are called
ganglia.
• In general terms:
– Aggregates of neuronal cell bodies form the gray
matter of the CNS
– Regions characterized primarily by tracts are
white matter.
06:13
13
Development of CNS
• Shortly after
gastrulation,
ectodermal cells on
the dorsum just
cranial to the primitive
streak begin to
proliferate and
differentiate into a
neural plate.
• The neural plate
proliferates faster
along its lateral
margins than on the
midline, creating the
neural groove
06:13
14
Development of CNS
• The edges of which
(the neural folds)
ultimately meet
dorsally to form the
neural tube.
• The entire CNS is
formed from the cells
of the neural tube.
• The lumen of the
neural tube persists in
the adult as the central
canal of the spinal
cord and as the
ventricles of the brain.
06:13
15
06:13
16
• Development of the spinal cord
continues by an increase in the
thickness of the wall of the neural
tube.
• As cells divide and differentiate, three
concentric layers of the neural tube
emerge:
– an inner (ventricular zone)
– a middle (intermediate zone)
– a superficial (marginal zone)
06:13
17
06:13
18
• The thin ventricular zone of cells (also
called ependymal zone) surrounds the
lumen of the neural tube
• The site of mitosis of neuronal and glial
precursors in the developing nervous
system.
– It will ultimately form the ependyma of the
central canal of the spinal cord and of the
ventricles of the brain.
06:13
19
• As cells are born in the germinal layer, they
migrate outward to form the intermediate
zone (also called mantle zone).
• The intermediate zone comprises neurons
and neuroglia and becomes the gray matter
near the center of the cord.
– The dorsal parts of the intermediate zone
develop into the dorsal horns.
- The ventral intermediate zone becomes
the ventral horns
06:13
20
06:13
21
• The marginal zone, which is most
superficial, consists of nerve processes that
make up the white matter of the spinal cord.
– The spinal cord white matter is divided into
dorsal, lateral, and ventral funiculi, which are
delimited by the dorsal and ventral horns of
gray matter.
06:13
22
06:13
23
• Development of the brain:
• The first gross subdivisions of the brain create the three-vesicle
stage.
• These subdivisions, which consist of three dilations of the
presumptive brain, are
– prosencephalon, or forebrain
– mesencephalon, or midbrain
– rhombencephalon, or hindbrain.
– In the five-vesicle stage of development
– the prosencephalon further subdivides to form the telencephalon (future
cerebrum) and the diencephalons ,
– the rhombencephalons divides into the Metencephalon (future pons and
cerebellum) and the myelencephalon (future medulla oblongata).
– The mesencephalon does not subdivide.
06:13
24
06:13
25
Central Nervous System
• Brain
• The gross subdivisions 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
06:13
26
06:13
27
• 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.
•
Deep to the cerebral cortex are aggregates of
subcortical gray matter called the basal nuclei
06:13
28
06:13
29
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
06:13
30
the hypophysis, or pituitary gland
06:13
31
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 crura cerebrii, 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).
06:13
32
06:13
33
06:13
34
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.
06:13
35
06:13
36
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.
06:13
37
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.
06:13
38
06:13
39
06:13
40
• 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.
• CSF is a modified transudate, formed
primarily through active secretion by
the ependymal cells, especially those
of the choroid plexuses.
06:13
41
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
06:13
42
the
CNS.
Meninges
• The 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.
• The space between the two layers is the
subarachnoid space.
– It is filled with CSF.
06:13
43
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.
06:13
44
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.
06:13
45
06:13
46
Cranial Nerves
• Twelve pairs:
– 2 attach to forebrain (Telen- &
Diencephalon)
– 10 attach to
brainstem
(Mes-, Met- and Myelencephalon)
• Names relate to
appearance or function
06:13
47
06:13
48
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)
06:13
49
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
XI - Accessory Nerve - An accessory part of the vagus
nerve
XII - Hypoglossal Nerves - Runs inferior to the tongue
Mixed nerve, innervates the tongue muscles
06:13
50