OVER VIEW OF CENTRAL NERVOUS
SYSTEM (CNS)
Dr.Mohammed Sharique Ahmed Quadri
Assistant prof. Physiology
Al Maarefa College
Central Nervous System
• CNS consists of brain and spinal cord
– 100 billion neurons in brain
• Enables you to:
– Subconsciously regulate your internal environment by
neural means
– Experience emotions
– Voluntarily control your movements
– Be consciously aware of your own body and your
surroundings
– Engage in other higher cognitive processes such as
thought and memory
Brain Anatomy
• Brain components
• Forebrain
a) Cerebrum
i) Cerebral cortex
ii) Basal nuclei
b) Diencephalon
i) Thalamus
ii) Hypothalamus
• Brain stem
- Mid brain
- Pons
- Medulla
• Cerebellum
CEREBRUM
• Cerebrum constitutes 80% of total brain weight.
• Outer layer, i.e. cerebral cortex of cerebrum is
highly convoluted.
• It has gyri [ridges] and sulci [depression].
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Basal Nuclei
• Basal Nuclei are present deep in the cerebrum.
• Functions:
- Co-ordination of movements
- Muscle tone regulation
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Diencephalon
• Diencephalon is present in the interior of
cerebrum.
• It has 2 components:
- Thalamus
- Hypothalamus
 Thalamus
• All sensory information passes.
• Crude awareness of sensation.
 Hypothalamus
• Regulates body temperature, has thirst and food
intake center.
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Brain Stem
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•

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Brain Stem [mid brain, Pons, Medulla].
Brain Stem is continuous below with spinal cord.
Functions:
Majority of cranial nerves originate from brain
stem.
• Control Center for cardiovascular, respiratory
system.
• Regulation of postural reflexes.
• Role in sleep – wake cycle.
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Cerebellum
• Cerebellum is attached at the back portion of
brain stem.
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•
•
•
Functions:
Balance of body.
Muscle tone.
Co-ordination and planning of skilled
movements e.g. dance.
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CEREBRUM
• Cerebrum is the largest portion human brain.
• It is divided into TWO halves, Right and Left
cerebral hemispheres. They are connected by
CORPUS CALLOSUM which consists of about
300 million axons connecting two cerebral
hemispheres.
• Cerebral cortex– It is the outer shell of Gray
matter covering the inner white matter.
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Chapter 5 The Central Nervous System
Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning
CEREBRUM (cont)
 Q—What is the GRAY Matter ?
• A– It is the Cerebral cortex , which consists of
cell bodies and their dendrites, as well as
connective tissue glial cells.
•
 Q– What is the WHITE Matter ?
• A– It is the myelinated nerve fibers (Axons) . Its
white appearance is due to Myelin sheath (lipid
layer).
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CEREBRAL CORTEX
 NOTE – Gray matter of cerebral cortex is like
computers of CNS.
• White matter is like wires that connect the
computers to each other.
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CEREBRAL HEMISPHERE
• Each cerebral hemisphere is divided into FOUR
LOBES.
• 1) Frontal lobe
• 2) Parietal lobe
• 3) Temporal lobe
• 4) Occipital lobe
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LOBES OF BRAIN
• Central Sulcus separates the Frontal and
Parietal lobe .
 Frontal Lobe
• It is located at the front and at the top.
• It has MOTOR CORTEX area in the PRE CENTRAL GYRUS- which controls the motor
activity.
• Motor speech area.
• Elaboration of Thought.
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LOBES OF BRAIN
 Parietal lobe
• It is located posterior to the central sulcus.
• It has sensory cortex at post central gyrus.
 Temporal Lobe
• Located laterally [on the sides of head].
• It has auditory cortex.
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LOBES OF BRAIN
 Occipital Lobe
• Located posteriorly [back of head].
• It has visual cortex ( center).
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Primary Motor Cortex
• Primary Motor Cortex is located in the precentral gyrus in the frontal lobe.
• Motor Cortex controls the moments of opposite
side of the body.
• Motor tracts originating from the right motor
cortex cross to the opposite side at medulla and
then go down to spinal cord to terminate on
efferent motor neuron.
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Primary Motor Cortex
• In motor cortex, presentation is not equal but
some parts e.g. fingers, thumbs, muscles of
speech [lips, tongue have more presentation
due to fine degree of motor work].
• Trunk, arms, lower limbs have less presentation
than their size as they do not perform complex
movements.
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Primary Motor Cortex
 Applied clinical aspect
• Damage to the right motor cortex will produce
paralysis [loss of power] on the left side of the
body.
• Damage to the left motor cortex will produce
paralysis on the right side of the body.
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Somato Sensory Cortex
• Somato Sensory Cortex is present in the post
central gyrus in the parietal lobe.
• All body parts are not represented equally, but
some areas have more representation due to
their degree of fine work and have more
receptors e.g. fingers [hand], face, tongue.
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Somato Sensory Cortex
• Right side sensory cortex gets sensory input
[information] from left side of the body.
• Left side sensory cortex gets sensory input from
the right side of the body.
 Why?
• Because sensory pathways carrying the
information cross to the opposite side of the
body before they terminate in the sensory
cortex.
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Somato Sensory Cortex
 Applied clinical Aspect
• Damage to the sensory cortex in the left
hemisphere [left side] produces sensory deficit
on the right side of the body.
• Damage to the sensory cortex in right
hemisphere produces sensory deficit on the left
side of the body.
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References
• Human physiology by Lauralee Sherwood,
seventh edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition
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