BIOLOGY [5 Mark Question Answer]

Brain consists of main three parts and lies in the cranial cavity of the skull.

1. The cerebrum
2. The cerebellum
3. The medulla oblongata
   Cerebrum: It is very large and forms 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 have a 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.

Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it, a very long process is given out. It is called axon or nerve fiber.
The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contract or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called a synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes? It is like this:
Organ → Message goes to dendrites →Cell body → Axon → Muscles or glands

The brain is the main control centre of the nervous system.
It is enclosed within the bony shell of the cranium.
It consists of three main part:
1.Cerebrum: It is the uppermost and largest part with many ridges and grooves. It is divided into right and left halves called cerebral hemispheres. It controls our thinking, reasoning, intelligence, memory, and perception of pain, sound, touch, taste, and smell.
2.Cerebellum: It is located under the cerebrum at the back of the head. It maintains the balance of the body and coordinates muscular activity.
3.Brain stem (medulla oblongata): It joins the brain to the spinal cord. It controls the activity of internal organs like heartbeat and breathing.