13OVERVIEW OF CNS-II

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. 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 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. 28

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. 29

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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 31