parts of central nervous system and its functions.

1. CENTRAL NERVOUS SYSTEM
BY
SONI KUMARI SHAH

2. CNS:
Consists of brain and spinal cord covered by meninges.
Brain
Brain is a highly specialized central organ of
nervous system encaged inside cranium.
It is the central controlling and coordinating center
of nervous system.it plays central role in control
of most bodily functions, including awareness,
movement, sensation, thought, speech and memory.

3. Parts Of Brain
1. Forebrain(Procencephalon): Cerebrum And Diencephalon
2. Midbrain(Mesencephalon): Midbrain
3. Hind Brain(Rhombencephalon): Cerebellum, Pons And Medulla
Brainstem: Midbrain, Pons And Medulla

4. Cerebrum:
Divided into two hemispheres by longitudinal fissure
Connected by corpus callosum
Cavity called lateral ventricle is present.
Outer grey matter(collection of cell bodies)
inner white matter(collection of neurites)
Numerous sulcus(depression) and
gyrus(elevation) present
Divided into four lobes: frontal, parietal,
temporal and occipital lobes.

5. Functions Of Cerebrum:
1. Mental activities involving memory, intelligence, sense of
responsibility, moral sense, thinking, reasoning, learning, etc.
2. Sensory perceptions including perception of pain, touch,
temperature, pressure, sight, hearing, taste, smell, etc.
3. Motor activities including initiation and control of voluntary
muscle contractions for the body movement.

6. Functional Areas Of Cerebrum
Motor Areas
Motor Area
Premotor Area
Motor Speech Area
Frontal Area
Sensory Areas
Sensory Area
Parietal Area
Sensory Speech Area
Auditory Area
Olfactory Area
Taste Area
Visual Area

7. Frontal lobe:
Also called motor cortex.
Lies in front of central sulcus.
Areas: motor area
premotor area
prefrontal cortex
motor speech area(Broca’s area)
Function: associated with reasoning, planning, parts of speech,
movement, emotions and problem solving.

8. Parietal lobe:
Lies behind the central sulcus.
Also called sensory cortex.
Areas: sensory area
sensory association area
Function: it is associated with movement, orientation, recognition,
perception of stimuli.

9. Temporal lobe:
Areas: olfactory area
olfactory association area
auditory area
auditory association area
sensory speech area
Function: it is associated with perception and recognition of auditory
stimuli, memory and speech.

10. Occipital lobe:
Located in the posterior region of cerebral cortex
Areas: primary visual area
visual association area
Function: it is associated with visual processing.

11. Diencephalon
Consists of thalamus and hypothalamus.
Thalamus
This consists of two masses of grey and white matter situated within the cerebral
hemispheres just below the corpus callosum, one on each side of the third ventricle.
Functions:
Relay center for all types of sensations.
Processing center of sensory information.
Center for determining the quality of sensation
Sexual sensation center
Arousal and alertness center
Center for reflex activities
Integration of motor activities.

12. Hypothalamus
It is situated below and in front of the thalamus, immediately above the pituitary
gland. The hypothalamus is linked to the posterior lobe of the pituitary gland by
nerve fibers and to the anterior lobe by a complex system of blood vessels. Through
these connections, the hypothalamus controls the output of hormones from both
lobes of the pituitary gland.
Functions:
Other functions of the hypothalamus include control of:
the autonomic nervous system
 appetite and satiety
 thirst and water balance
 body temperature
 emotional reactions, e.g. pleasure, fear, rage
 sexual behavior and child rearing
 sleeping and waking cycles.

13. Mid Brain
The midbrain is the area of the brain situated around the cerebral aqueduct
between the cerebrum above and the pons below. It consists of nuclei and
nerve fibres (tracts), which connect the cerebrum with lower parts of the brain
and with the spinal cord. It has two pair of colliculus( superior and inferior)
and two crura.
Functions:
1. Integration of different activities mainly visual(superior colliculi) and
auditory reflexes(inferior colliculi).
2. Acts as relay center to information from spinal cord and cerebellum
towards cerebrum and via crus cerebri.

14. Pons Varoli
The pons is situated in front of the cerebellum, below the midbrain and above
the medulla oblongata. It consists mainly of nerve fibres (white matter) that
form a bridge between the two hemispheres of the cerebellum, and of fibres
passing between the higher levels of the brain and the spinal cord.
Functions:
1. There are nuclei within the pons that act as
relay stations and some of these are associated
with the cranial nerves.
1. Form the pneumotaxic and apnoustic centers
that operate in conjunction with the respiratory
center in the medulla oblongata to control respiration.

15. Medulla Oblongata
The medulla oblongata, or simply the medulla, is the most interior region of the brain
stem. Extending from the pons above, it is continuous with the spinal cord below.
The vital centers, consisting of groups of cell bodies (nuclei) associated with autonomic
reflex activity, lie in its deeper structure. These are the:
• cardiovascular center
• respiratory center
• reflex centers of vomiting, coughing, sneezing and swallowing.
Functions:
1. Cardiac center regulates heart beat.
2. Vasomotor centers regulates the diameter of blood
vessels and thereby blood pressure.
3. Respiratory center regulates breathing.
4. Reflex centers of vomiting, coughing, sneezing
and swallowing.

16. Cerebellum
The cerebellum is situated behind the pons and immediately below the
posterior portion of the cerebrum occupying the posterior cranial fossa. It is
ovoid in shape and has two hemispheres, separated by a narrow median strip
called the vermis. Grey matter forms the surface of the cerebellum, and the
white matter lies deeply.
Functions:
1. Coordination and regulation of muscle tone.
2. Appropriate trajectory and endpoint of
movements.
3. Maintenance of posture and equilibrium.
4. Cerebellar activity is not under voluntary control.

17. Spinal Cord
Long cylindrical lower part of nervous system
Occupies Upper 2/3 of vertebral canal
Enclosed in three meninges
Gives rise to 31 pairs of spinal nerves
45 cm in adult male; 42 cm in adult female
Extends from upper border of atlas vertebra to
lower of L1 vertebra(L3 vertebra in case of children)
Continuous with medulla oblongata superiorly
Terminates as conus medullaris inferiorly

18. Vertebral Spine Is Lower Than Corresponding Spinal Segment
Vertebral Levels Spinal Segments
C1-C7 C1-C8
C8 -T6 T1-T8
T7-T9 T9-T12
T10-T11 L1-L5
T12-L1 S1-S5 & Co1

19. Enlargements:
1. Cervical Enlargement
C4-T1; max C6
2. Lumbar Enlargement
L2-S3; max S1

20. External Features of Spinal Cord
Divided into two halves by:
Anterior median fissure
posterior median sulcus
Each half divided into 3 parts
(anterior, lateral & posterior) by:
anterolateral sulci
posterolateral sulci

21. Internal Structure of Spinal Cord:
Outer white matter
Inner grey matter:
H shaped
anterior horn
posterior horn
Lateral horn in T1-L2 and S2-S4.
Central canal

22. Variation In Shape And Size Of Horn In Different Segments
Segments of
spinal cord
Posterior
horn
Lateral horn Anterior Horn
Cervical, oval Slender Absent Narrow in C1-C3;
Broad in C4-C8;
Supply upper
limb
Thoracic,
circular
Slender Present;
thoracolumbar
flow
Broad in T1;
Slender in T2-T12
Lumbar,
circular
Bulbous Present
(only in L1 )
Bulbous;
Supply lower
limbs
Sacral,
circular but
smaller
Thick Present
(S2-S4);
Sacral outflow
Bulbous;
Supply lower
limbs

23. Functions Of Spinal Cord
1. To transmit impulses to and from the brain and to house spinal reflex.
2. Tracts carrying sensory information to brain are ascending tracts.
3. Tracts carrying motor information from brain are descending tracts.
4. Many spinal reflexes also passes through the spinal cord.

24. Tracts Of Spinal Cord
Ascending Tracts:
1. Spinocerebellar Tract
2. Spinothalamic Tract
3. Spino Tectal Tract
4. Spinoreticular Tract
5. Spinorubral Tract
6. Spinovestibular Tract
7. Fasciculus Gracillis
8. Fasciculus Cuneatus
Descending Tracts:
Pyramidal Tract
1. Anterior Corticospinal Tract
2. Lateral Corticospinal Tract
Extrapyramidal Tract
1. Anterior Vestibular Tract
2. Lateral Vestibular Tract
3. Reticulospinal Tract
4. Tectospinal Tract
5. Rubrospinal Tract
6. Olivospinal Tract

25. Meninges
The connective tissue membrane that covers the brain and spinal cord are
called meninges.
Three Layers:
Dura Mater
Arachnoid Mater
Pia Mater

26. Dura Mater
Outermost tough and fibrous layer.
Attached to bony surface of skull and vertebral canal.
Covers whole of brain and extends through foramen magnum to lower
border of S2 vertebrae, covers filum terminale and gets fused with
periosteum of coccyx.
Supports and protects soft and delicate nervous tissue of brain and spinal
cord from mechanical forces.

27. Arachnoid Mater
Middle, thin, transparent web like strands of connective tissue which covers
brain and spinal cord.
Extends down to S2 vertebrae
Pia Mater
Inner and very thin membrane on the surface of brain and spinal cord.
It dips in all sulci and fissures.
Extends to lower border of L1 (up to L3 in children)

28. Spaces In Between The Meninges
Epidural/Extradural Space: Small space below the bone and above the dura mater
Subdural Space: Small space below the dura mater and above arachnoid mater
Subarachnoid Space: Space below the arachnoid mater and above pia mater.
It consists CSF.

29. Ventricles Of Brain
Communicating network of cavities filled with CSF which is located within
brain parenchyma. It contains capillary network called choroid plexus.
Types Of Ventricle:
Lateral Ventricle: these are cavities within cerebral hemisphere. there are two
lateral ventricles. Each lateral ventricle is separated from each other by septum
pellucidum.it communicates with third ventricle through interventricular
foramen.
Third Ventricle: it is space situated below the lateral ventricle and in between
thalamus.it communicates with fourth ventricle through cerebral aqueduct.
Fourth Ventricle: it is diamond shaped space below and behind third ventricle
between cerebellum and pons. It is continuous below with central canal of
spinal cord.

30. Ventricles Of Brain

31. Cerebro Spinal Fluid (CSF)
CSF is clear, colorless fluid which is composed mainly of water and amino acids
and ions. Formed by choroid plexus in ventricles and circulates in subarachnoid
space. It is about 80-150 ml in adult.
Functions of CSF:
1. It serves as cushion between CNS and supporting bones.
2. It acts as shock absorber.
3. It supports brain and spinal cord and maintains uniform pressure upon them.
4. It nourishes CNS.
5. It removes metabolites( waste products).
6. It serves as pathway for pineal secretion to reach pituitary gland.

32. Formation of CSF
About two third or more of this fluid originates as secretion from choroid
plexus in the four ventricles, mainly lateral ventricle. Additional small amount
are secreted by ependymal surface of all ventricles and arachnoid
membranes; and a small amount comes from brain itself through the
perivascular spaces that surrounds the blood vessels passing through the
brain.
Composition of CSF
Water, inorganic salts(Na, K, Cl, Mg), protein, glucose, urea, uric acid,
creatinine, few lymphocytes.

33. Circulation of CSF
1. The fluid secreted by lateral ventricle passes to third ventricle through
inter ventricular foramen.
2. Small amount of fluid is added in the third ventricle, it flows downwards
along cerebral aqueduct to the fourth ventricle.
3. In fourth ventricle another small amount of fluid is added. Finally the
fluid passes out of fourth ventricle through three openings: two lateral
foramen of Lushka and a midline foramen of Magendie, entering the
cisterna magna, a fluid filled space that lies behind medulla and beneath
cerebellum.
4. The cisterna magna is continuous with the subarachnoid space that
surrounds the entire brain and spinal cord.
Absorption of CSF
CSF is absorbed by arachnoid villi that projects into the large sagittal venous
sinus and other venous sinuses of cerebrum.

34. Circulation of CSF

35. CSF is secreted from
I. Choroid plexus
II. Arachnoid villi
III. Pia mater
IV. Corpus callosum
CSF is present in
I. Subrachnoid space
II. Subdural space
III. Blood
IV. All of above
CSF
I. afloat the brain
II. Is blood filtrate
III. Acts as shock absorber
IV. All of above
The immediate covering of brain is
I. Dura mater
II. Arachnoid mater
III. Pia mater
IV. None of above