155 Anatomy-CNS-2013-14

CENTRAL
NERVOUS
SYSTEM
DR. T.C. MATHEW, Kuwait University

NEURONS AND
GLIAL CELLS.

Nervous Tissue

Neurons transmit
nerve messages.
Glial cells are
supporting cells that
surround the neurons
Each nerve cell consists
of a central portion
containing the nucleus,
known as the cell body,
and processes that arise
from the cell body, the
axons and dendrites.

Synapse
The junction between a nerve cell
and another cell is called a synapse.
Messages travel within the neuron as
an electrical action potential.
The space between two cells is
known as the synaptic cleft.
To cross the synaptic cleft requires
the actions of neurotransmitters.


NEUROGLIA

Neuroglia is non-excitable nervous
tissue that supports and insulates nerve
cells in the central and peripheral parts of
the nervous system.
Glial cells fill in the spaces not occupied
by neurons and blood vessels and provide
structural and metabolic support for the
nerves.
The myelin sheath surrounding
myelinated nerves is made from
neuroglia.

CNS
OLIGODENDROCYTES
ASTROCYTES
MICROGLIA
EPENDYMA


PNS
SCHWANN CELLS
SATELLITE CELLS

Nervous Tissue
Endoneurium – layer of
delicate connective tissue
surrounding the axon
Nerve fascicles – groups of
axons bound into bundles
Perineurium – connective
tissue wrapping surrounding
a nerve fascicle
Epineurium – whole nerve
is surrounded by tough
fibrous sheath

Basic Divisions of the
Nervous System
Central nervous system (CNS)



Brain and spinal cord
Integrating and command center

Peripheral nervous system (PNS)



Outside the CNS
Consists of nerves extending from
brain and spinal cord





Cranial nerves
Spinal nerves

Peripheral nerves link all regions of
the body to the CNS

Sensory Input and Motor Output



Sensory (afferent) signals picked up by sensory
receptors




Carried by nerve fibers of PNS to the CNS

Motor (efferent) signals are carried away from the
CNS


Innervate muscles and glands


Neurons Classified by Function

Most neuronal cell bodies are located within the CNS, protected by
bones of the skull and vertebral column
Ganglia – clusters of cell bodies, that lie along nerves in the PNS

Reflex arc
Reflex arcs – simple chains of neurons
Simple reflex arc- a two neuron pathway- elicits
contraction of muscles
Afferent- carries sensory impulse to the nervous
system
Efferent- carries motor impulse out of the central
nervous system


THE CENTRAL
NERVOUS SYTEM


Central nervous system
Central nervous system (CNS) consists of the brain and the
spinal cord.
The brain lies in the cranial cavity.
The average human brain weighs about 1,400 grams (3 lb).

The brain consists of:
CEREBRUM.
DIENCEPHALONS
BRAIN STEM AND
CEREBELLUM,

The cerebrum
The brain can be divided down the middle
lengthwise into two halves called the cerebral
hemispheres.
Outer rim of gray matter is the cerebral cortex.
Deep to it lies the cerebral white matter.

The right and left sides of the cerebral
cortex are connected by a thick band of
nerve fibers called the
"corpus callosum".

The Cerebral Hemispheres
Sulci – grooves on the surface of the cerebral
hemispheres
Gyri – twisted ridges between sulci
Prominent gyri and sulci are similar in all people



Fissures – deep grooves – separate major regions of
the brain
Transverse fissure – separates cerebrum and cerebellum
Longitudinal fissure – separates cerebral hemispheres

The Cerebral
Hemispheres

Deeper sulci divide cerebrum into
lobes
Lobes are named for the skull
bones overlying them
Central sulcus separates frontal
and parietal lobes
 Bordered by two gyri
Precentral gyrus
Postcentral gyrus
Parieto-occipital sulcus
 Separates the occipital from
the parietal lobe
Lateral sulcus
 Separates temporal lobe from
parietal and frontal lobes
Insula – deep within the lateral
sulcus


Lobes of cerebrum
Central sulcus- divides to frontal and parietal lobe. –
Precentral gyrus- primary motor area.
Post central gyrus- primary somatosensory area.


The cerebrum

Lateral cerebral sulcus separates the frontal lobe from
temporal lobe.
Parieto-occipital sulcus separates parietal lobe from the
occipital lobe.
Insula- lies in the lateral cerebral sulcus, deep to parietal
frontal and temporal lobes.


OCCIPITAL LOBE
Located at the back of the brain, behind the
parietal lobe and temporal lobe.
Concerned with many aspects of vision.


FRONTAL LOBE
Located in front of the central sulcus.
Concerned with reasoning, planning, parts of
speech and movement (motor cortex), emotions,
and problem-solving.


TEMPORAL LOBE
Located below the lateral fissure.
Concerned with perception and recognition of
auditory stimuli (hearing) and memory
(hippocampus).


PARIETAL LOBE
Located behind the central sulcus.
Concerned with perception of stimuli related to
touch, pressure, temperature and pain.


The Cerebral Hemispheres
Home of our conscious mind
Enables us to:
 Be aware of ourselves and our sensations
 Initiate and control voluntary movements
 Communicate, remember, and
understand


Basal Nuclei

A group of nuclei deep within the cerebral white
matter




Caudate nucleus – arches over the thalamus
Lentiform nucleus – “lens shaped”
Amygdala – sits on top of the caudate nucleu

Lentiform nucleus


Divided into two parts
Globus pallidus
Putamen


DIENCEPHALON


The Diencephalon
Diencephalon extends from cerebrum to brain stem.
Forms the center core of the
forebrain
Surrounded by the cerebral
hemispheres
Composed of three paired
structures:
 Thalamus, hypothalamus,
and epithalamus
Border the third ventricle
Primarily composed of gray
matter

Diencephalon
Thalamus
Thalamus makes up 80% of diencephalon.
Thalamus is involved in sensory and motor
integration.


Epithalamus
Epithalamus lies superior and posterior to thalamus.
It contains the pineal gland and habenular nuclei.
(Pineal gland: melatonin- biological clock;
Habenular nuclei: Olfaction- emotional response to odors).
Subthalamus
Subthalamus lies below the thalamus.
It is involved in the control of movements.

Functions of the Thalamus
Contains approximately a dozen major nuclei
Send axons to regions of the cerebral cortex
Nuclei act as relay stations for incoming sensory messages


Functions of the Hypothalamus









Control of the autonomic nervous system
Control of emotional responses
Regulation of body temperature
Regulation of hunger and thirst sensations
Control of behavior
Regulation of sleep-wake cycles
Control of the endocrine system
Formation of memory


The brain stem
It is the region
between the spinal
cord and diencephalon


The brain stem consists of
MIDBRAIN, PONS AND MEDULLA OBLONGATA
In addition to
these regions a
netlike region of
interspersed
gray and white
matter called
reticular
formation
extends through
the brain stem.


Midbrain (Mesencephalon)
The midbrain lies between pons and diencephalons.
It is about 2.5 cm.
The anterior part contains a pair of tracts called
cerebral peduncles containing axons of motor
neurons that relay impulses from the cerebrum to the
spinal cord, medulla and pons as well as sensory
neurons that extend from the medulla to the
thalamus.


The superior part contains four rounded elevations
called colliculi.
Superior colliculi are responsible for co-ordinating
movements of the eye balls in response to visual and
other stimuli.
Inferior colliculi co-ordinate movements of the head
and trunk in response to auditory stimuli and startle
reflex (sudden response of the head and body when
surprised by loud noises).

The nuclei of the midbrain are substantia nigra and red nuclei.
Substantia nigra means black substance.
Dopaminergic neurons from substantia nigra extend to basal ganglia and
help control subconscious muscle activities.
Loss of these neurons lead to Parkinson disease.


Red nuclei appear red coloured due to rich blood supply and an iron containing
pigment.
Together with cerebellum it coordinate muscular movements.
Axons from cerebellum and cerebral cortex synapse in the red nuclei.


Brain stem contains a broad region where the white
matter and grey matter show a netlike appearance.
This region is called reticular formation.


Neurons of the reticular formation have both
sensory and motor functions.
Reticular activating system (RAS), a part of
the reticular formation consists of sensory
axons that project to the cerebral cortex.
RAS helps to maintain consciousness.


Pons
Pons lies superior to the
medulla and anterior to the
cerebellum (~2.5 cm).
Pons contains tracts that
connect the right and left side
of the cerebellum as well as
ascending sensory and
descending motor tracts.


Pons lies superior to the medulla
and anterior to the cerebellum


Pons
It contains the pontine nuclei.
These nuclei are the sites at which signals for
voluntary movements that originate in the cerebral
cortex are relayed into the cerebellum.
Other nuclei present in the pons include apneustic
and pneumotaxic areas that are involved in the
control of breathing.

Nuclei present
in the pons
NUCLEI OF
CRANIAL NERVES
trigeminal (V),
abducens (VI),
fascial (VII) and
vestibulocochlear (VIII).


Medulla oblongata (Medulla)
The medulla oblongata begins
at foramen magnum and
extends to the inferior border
of the pons (~ 3cm).
The white matter of the
medulla consists of sensory
(ascending) and motor
(descending) tracts.

On the anterior aspect of the medulla, there are
protrusions of the white matter called pyramids.
The pyramids consist of largest motor tracts that
pass from the cerebrum to the spinal cord.

Antriorinferior
view


Decussation of pyramids
90% of the axons of the right pyramid cross
to the left side and 90% of axons from left
side cross to the right side just superior to
the junction of the medulla with the spinal
cord.
This crossing is called decussation of
pyramids.

It is well-known that the right side of the brain
controls muscles on the left side of the body and the
left side of the brain controls muscles on the right
side of the body.
Similarly, sensory information from the left side of
the body crosses over to the right side of the brain
and information from the right side of the body
crosses over to the left side of the brain.
Therefore, brain damage to one side of the brain
will affect the opposite side of the body.


Nuclei present in the medulla
The medulla contains various nuclei that
control various vital activities of the body.
They are the cardiovascular center
(regulates the rate and force of the heart
beat and diameter of blood vessels) and
medullary rhythamicity area (adjusts the
basic rhytham of breathing) of the
respiratory center.

Medulla- OLIVE
Another structure of the
medulla is the olive.
It is an oval shaped
swelling that lies lateral
to each pyramid.
The olive contains the
inferior olivary nucleus.

Medulla- OLIVE
The inferior olivary nucleus relays impulses
from proprioceptors that monitor joint and
muscle position to the cerebellum.
Prorioception is the awareness of the precise
positions of the body part.


Nuclei present in the medulla
Other nuclei in the medulla control
reflexes for vomiting,
coughing and
sneezing.
The major nuclei present in the medulla are the
gracile (=slender) and cuneate (wedge shaped) nuclei.
These nuclei are associated with sensations of touch,
conscious proprioception, pressure and vibration.

Nuclei present in
the medulla
NUCLEI OF CRANIAL
NERVES
VIII (vestibulocochlear),
IX (glossopharyngeal),
X (vagus),
XI (accessory), and
XII (hypoglossal).


Cerebellum
The word "cerebellum" comes from the Latin word
for "little brain".
The cerebellum is located behind the brain stem.
It has a butterfly like appearance.
Although it is about a tenth of the brain in size, it
contains nearly half of the neurons in the brain.


Cerebellum
The central constricted area of the cerebellum is
called vermis (means worm).
The wings like structures are the cerebellar
hemispheres.
The cerebellar hemisphere is divided into anterior
and posterior lobes by distinct fissure.
These lobes are concerned with the subconscious
aspects of skeletal muscle movements.

Cerebellum

Cerebellar cortex consists of grey matter that
appears as parallel ridges called folia.
Deep to folia are tracts called arbour vitae (=
tree of life).
Deep within the white matter are nuclei that
give rise to axons that carry impulses from the
cerebellum to other brain centers and to the
spinal cord.

Cerebellum
Three paired cerebellar peduncles attach cerebellum to the brain
stem.
They are:
Inferior cerebellar peduncle :
Middle cerebellar peduncles:
Superior cerebellar peduncle:


Cerebellum
Cerebellum is the main brain region that
regulate posture and balance.
It is responsible for all skilled muscular
activities.
Cerebellum may also have a role in cognition
and language processing.


Ventricles of the Brain
Expansions of the brain’s
central cavity
Filled with cerebrospinal fluid
Lined with ependymal cells
Continuous with each other
Continuous with the central
canal of the spinal cord

Lateral ventricles – located in cerebral hemispheres
Horseshoe-shaped from bending of the cerebral
hemispheres
Third ventricle – lies in diencephalon
Connected with lateral ventricles by interventricular
foramen
Cerebral aqueduct – connects 3rd and 4th ventricles
Fourth ventricle – lies in hindbrain
Connects to the central canal of the spinal cord


The 12 Pairs of Cranial Nerves


Cranial Nerves
Number

Name

Function

I

Olfactory Nerve

Smell

II

Optic Nerve

Vision

III

Oculomotor
Nerve

Eye movement; Pupil dilation

IV

Trochlear Nerve

Eye movement

Trigeminal
Nerve

Somatosensory information (touch,
pain) from the face and head; muscles
for chewing.

V


VI

VII

Abducens Nerve

Eye Movement

Facial Nerve

Taste (anterior 2/3 of tongue);
Somatosensory information from
ear; Controls muscles used in
facial expression.

Vestibulocochlear
VIII
Nerve

IX

Glossopharyngeal
Nerve

Hearing; Balance
Taste (posterior 1/3 of tongue);
Somatosensory information from
tongue, tonsil, pharynx; Controls
some muscles used in swallowing.

Vagus Nerve

Sensory, motor and autonomic
functions of viscera (glands,
digestion, heart rate)

Spinal Accessory
XI
Nerve

Controls muscles used in head
movement.

Hypoglossal
XII
Nerve

Controls muscles of tongue

X


Thank you


155 Anatomy-CNS-2013-14

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