CENTRAL NERVOUS SYSTEM
Brain
• The adult brain consists of four major parts:
brainstem, cerebellum, diencephalon, and
cerebrum
• The brainstem is continuous with the spinal
cord and consists of the medulla oblongata,
• pons, and midbrain
• Posterior to the brainstem is the cerebellum
• Superior to the brainstem is the diencephalon
• which consists of the thalamus, hypothalamus
• epithalamus.
•
• Supported on the diencephalon and brainstem
is the cerebrum, the largest part of
• the brain.
MENINGES
• The cranial meninges are continuous with the
spinal meninges, have the same basic
structure, and bear the same names:
• the outer dura mater
• the middle arachnoid mater
• inner pia mater
• The two dural layers are called the periosteal
layer (which is external) and the meningeal
layer (which is internal).
• The dural layers around the brain are fused
together except where they separate to
enclose the dural venous sinuses
• Three extensions of
• the dura mater separate parts of the brain:
• (1) The falx cerebri separates the two
hemispheres (sides) of the cerebrum.
• (2) The falx cerebelli separates the two
hemispheres of the cerebellum
• (3) The tentorium cerebelli
separates the cerebrum from the cerebellum.
• The blood–brain barrier (BBB) causes diff
erent substances to move between the blood
and the brain tissue at different rates and
prevents the movement of some substances
from blood into the brain.
Cerebrospinal Fluid
• Cerebrospinal fluid (CSF) is a clear, colorless
liquid composed primarily of water that
protects the brain and spinal cord from
chemical and physical injuries.
• CSF continuously circulates through cavities in
the brain and spinal cord and around the brain
and spinal cord in the subarachnoid space (the
space between the arachnoid mater and pia
mater).
• The total volume of CSF is 80 to 150 mL (3 to 5
oz) in an adult.
• CSF contains small amounts of glucose,
proteins, lactic acid, urea, cations
• (Na+, K+, Ca2+, Mg2+),
• anions (Cl− and HCO3
• it also contains some white blood cells.
• CSF filled cavities within the brain, which are
called ventricles.(4)
• There is one lateral ventricle in each
hemisphere of the cerebrum.
• Anteriorly, the lateral ventricles are separated
by a thin membrane, the septum pellucidum.
• The third ventricle is a narrow, slitlike cavity
along the midline superior to the
hypothalamus and between the right and left
halves of the thalamus.
• The fourth ventricle lies between the
brainstem and the cerebellum
Functions of CSF
• Mechanical protection :CSF serves as a
shock-absorbing medium that protects the
delicate tissues of the brain and spinal cord.
• Chemical protection:CSF provides an optimal
chemical environment for accurate neuronal
signaling.
• Circulation :CSF is a medium for minor
exchange of nutrients and waste products
between the blood and adjacent nervous
tissue.
BRAIN STEM
• The brainstem is the part of the brain
between the spinal cord and the
diencephalon.
• It consists of three structures:
• (1) medulla oblongata,
• (2) pons, and (3) midbrain.
Medulla Oblongata
• The medulla oblongata or more simply the
medulla, is continuous with the superior part
of the spinal cord contains both sensory tracts
and motor tracts.
• It contains a cardiovascular center, which
regulates heart rate and blood vessel
diameter (cardiovascular center)
• medullary respiratory center, which helps control
breathing.
• It also contains the gracile nucleus, cuneate
nucleus, gustatory nucleus, cochlear nuclei, and
vestibular nuclei, which are components of
sensory pathways to the brain
• Also present in the medulla is the inferior olivary
• nucleus, which provides instructions that the
cerebellum uses to adjust muscle activity when
you learn new motor skills
• Other nuclei of the medulla coordinate
vomiting, swallowing, sneezing, coughing, and
hiccupping.
• The medulla also contains nuclei associated
with the vestibulocochlear (VIII),
• glossopharyngeal (IX),
• vagus (X), accessory (XI),
• and hypoglossal (XII) nerves.
PONS
• The pons is superior to the medulla.
• It contains both sensory tracts and motor
tracts.
• Pontine nuclei relay nerve impulses related to
voluntary skeletal movements from the
cerebral cortex to the cerebellum.
• The pons also contains the pontine respiratory
group, which helps control breathing.
• Vestibular nuclei, which are present in the
pons and medulla, are part of the equilibrium
• pathway to the brain.
• Also present in the pons are nuclei associated
with the trigeminal (V), abducens (VI), and
facial (VII) nerves and the vestibular branch
• of the vestibulocochlear (VIII) nerve.
MIDBRAIN
• The midbrain connects the pons and
diencephalon and surrounds the cerebral
• Aqueduct.
• It contains both sensory tracts and motor
tracts.
• The superior colliculi coordinate movements
of the head, eye, and trunk in response to
• visual stimuli;
• the inferior colliculi coordinate movements of
the head, eyes,
• and trunk in response to auditory stimuli.
• The midbrain also contains nuclei associated
with the oculomotor (III) and trochlear (IV)
nerves.
The Cerebrum
• The cerebrum is the “seat of intelligence.” It
provides us with the ability to read, write, and
speak; to make calculations and compose
• music; and to remember the past, plan for the
future, and imagine things that have never
existed before.
• The cerebrum consists of an outer cerebral
cortex, an internal region of cerebral white
matter, and gray matter nuclei deep within
the white matter.
• The cerebrum is the largest part of the brain.
Its cortex contains gyri (convolutions),
fissures, and sulci.
• The cerebral hemispheres are divided into
four lobes: frontal, parietal, temporal, and
occipital
Cerebral Cortex
The Cerebellum
• The cerebellum, second only to the cerebrum
in size, occupies the inferior and posterior
aspects of the cranial cavity.
• In superior or inferior views, the shape of the
cerebellum resembles a butterfly
• The central constricted area is the vermis
• . or lobes are the cerebellar hemispheres
• The anterior lobe and posterior lobe govern
subconscious aspects of skeletal muscle
• movements.
• The superficial layer of the cerebellum, called
the cerebellar cortex, consists of gray matter
in a series of slender, parallel folds called
folia
• The cerebellum smooths and coordinates the
contractions of skeletal muscles. It also
maintains posture and balance.
SPINAL CORD
ANATOMY OF SPINAL CORD
• 1. The spinal cord is protected by the vertebral
column, the meninges, cerebrospinal fluid, and
denticulate ligaments.
• 2. The three meninges are coverings that run
continuously around the spinal cord and brain.
They are the dura mater, arachnoid mater, and
pia mater.
• 3. The spinal cord begins as a continuation of the
medulla oblongata and ends at about the second
lumbar vertebra in an adult.
• The spinal cord contains cervical and lumbar
enlargements that serve as points of origin for
nerves to the limbs.
• 5. The tapered inferior portion of the spinal
cord is the conus medullaris, from which arise
the filum terminale and cauda equina.
• 6. Spinal nerves connect to each segment of
the spinal cord by two roots.
• The posterior or dorsal root contains sensory
axons, and the anterior or ventral root
contains motor neuron axons.
• The anterior median fissure and the posterior
median sulcus partially divide the spinal cord
into right and left sides.
• The gray matter in the spinal cord is divided into
horns, and the white matter into columns. In the
center of the spinal cord is the central canal, which
runs the length of the spinal cord.
• Parts of the spinal cord observed in transverse section
are the gray commissure; central canal; anterior,
posterior, and lateral gray horns; and anterior,
• posterior, and lateral white columns, which contain
ascending and descending tracts
• .
• The spinal cord conveys sensory and motor
information by way of ascending
• and descending tracts, respectively
Spinal Nerves
• The 31 pairs of spinal nerves are named and
numbered according to the region and level of
the spinal cord from which they emerge.
• There are 8 pairs of cervical,
• 12 pairs of thoracic,
• 5 pairs of lumbar, 5 pairs of sacral, and
• 1 pair of coccygeal nerves.
• Spinal nerves typically are connected with the
spinal cord by a posterior root and an anterior
root.
• All spinal nerves contain both sensory and
motor axons (they are mixed nerves).
• Three connective tissue coverings associated
with spinal nerves are the endoneurium,
perineurium, and epineurium.
• Branches of a spinal nerve include the
posterior ramus, anterior ramus, meningeal
branch, and rami communicantes.
• The anterior rami of spinal nerves, except for
T2–T12, form networks of nerves called
plexuses.
• Anterior rami of nerves T2–T12 do not form
plexuses and are called intercostal
• (thoracic) nerves. They are distributed directly
to the structures they supply in intercostal
spaces.
Cervical Plexus
• The cervical plexus is formed by the roots
(anterior rami) of the first four cervical nerves
(C1–C4), with contributions from C5.
Nerves of the cervical plexus supply the skin
and muscles of the head, neck,
• and upper part of the shoulders; they connect
with some cranial nerves and innervate the
diaphragm.
Brachial Plexus
• The roots (anterior rami) of spinal nerves
C5–C8 and T1 form the brachial plexus.
• Nerves of the brachial plexus supply the
upper limbs and several neck and shoulder
muscles.
Lumbar Plexus
• The roots (anterior rami) of spinal nerves
L1–L4 form the lumbar plexus.
• Nerves of the lumbar plexus supply the
anterolateral abdominal wall, external
• genitals, and part of the lower limbs.
Sacral and Coccygeal Plexuses
• The roots (anterior rami) of spinal nerves L1–L5 and
S1–S4 form the sacral plexus.
• Nerves of the sacral plexus supply the buttocks,
perineum, and part of the lower limbs.
• The roots (anterior rami) of the spinal nerves S4–S5
and the coccygeal nerves form the coccygeal plexus.
• Nerves of the coccygeal plexus supply the skin of the
coccygeal region.
Spinal Cord Physiology
• The spinal cord has two principal functions in
maintaining homeostasis: nerve impulse
propagation and integration of information.
