OVER VIEW OF CENTRAL NERVOUS SYSTEM (CNS)

Dr.Mohammed Sharique Ahmed QuadriAssistant prof. Physiology

Al Maarefa College

بسم الله الرحمن الرحيم

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.8

Brain Stem• 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.

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 SystemHuman 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 pre-

central 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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