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. .