[3 marks Question Answer]

Question 13 Marks

Describe three kinds of nerves, giving the example of each.

Answer

A nerve is formed by a group of nerve fibres $($axons$)$ encased by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons $($nerve fibres$)$ We have three kinds of nerves:
$1.$ Sensory nerve: It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
$2.$ Motor nerves: These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eye ball.
$3.$ Mixed nerve: It has both sensory and motors fibres as nerve going to the tongue.

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Question 23 Marks

Briefly describe the structure of the cerebrum in human brain and mention its functions.

Answer

Brain consists of main three parts and lies in the cranial cavity of skull.
$1.$ The cerebrum
$2.$ The cerebellum
$3.$ The medulla oblongata
Cerebrum: It is very large and form two third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.
Functions:
$1.$ It controls all the voluntary activities.
$2.$ It is the seat of intelligence, consciousness and will power.

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BIOLOGY [3 marks Question Answer]

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