Brain:

The centre piece of  the nervous system is the brain which  IS possibly the most organised form of matter known. It  is unlike any other organ of  the body, as ~t alone can recelve, handle and analyse information and issue necessary commands. The human brain containing billions of neurons with their axons and dendrites, is soft matter whlch has a folded appearance. Since the brain  is a delicate organ, it is extremely well L  protected by  three tough membranes and floats In  a special fluid which helps to absorb shocks. The whole organ  is then enclosed In  a bony skull. (Flg.). The brain  is very well supplied with oxygen, whtch is carried by  blood. In fact, 75% of  the body  requirement of oxygen is used by  the brain.  

Four inter-connected  arteries carry blood  to the brain so that even if  two are blocked there are still two alternate passages. These four arteries are connected to mill~ons  of blood vessels called capillhries whlch reach every part of the brain. If  the flow of  blood is  interrupted for even  10 seconds, we become unconscious and an interruption of a few minutes may cause permanent damage to the brain cells. These damaged brain cells cannot be  replaced as the number of  neurons in  the brain does not increase after the age of  five years. In fact, some neurons die every day. But, fortunately, we have them in such large numbers that it does not make too much of  a difference.

This slow but permanent loss of neurons is thought to be  responsible for the loss of mental ability in old age. Becausefhe loss of  neurons is irreplaceable, diseases like poliomyelitis that destroy neurons,  lead to muscular disability, called paralysis as muscles connected to the destroyed neurons do not receive any messages. Even though the total number of neurons deerease, as ane grows older, the number of connections  amongst them  in the brain increase. It  is thought that learning involves the establishment  of  new connections or circuits  in the brain and once they are established,  they are relatively permanent. Persons with larger heads are not necessarily more intelligent,  but persons with more and complex interconnections are. Let us now have a brief overview of  the major regions and structures  of  the brain. It would be best to read this section without trying to memonse all the new terms. You could refer back  to them as needed. The major regions of  the brain are showo in Fig. These are forebrain, midbrain &d  hindbrain. The forebrain itself has many parts which we will now describe.  .