The brain and nervous system

All our thinking processes physical activities and sensations, are initiated, controlled, and co-ordinated by the brain and nervous system. If you accidentally put your hand into some hot water, you will pull it away immediately. This response (called a reflex) is brought about by messages that are sent at high speed through the nervous system. The brain is like an extremely complicated computer, with thousands of electrical messages traveling from place to place. But it is much more than a computer because it makes us conscious persons with feelings and emotions.

The skull encloses the brain. The spinal cord comes down from it and goes down the spine (vertebral column). The human brain is of a soft consistency. It has a soft material on the outside called the grey matter which contains the basic cell units of the brain. These cells are called neurons; there are about 100 billion neurons in the brain. In the deeper parts of the brain there is a whitish firm material, called the while matter, which contains the connecting tracts, which carry the messages from the neurons. The brain is divided into the - cerebrum, cerebellum, and brain stem. Surrounding the soft brain tissue on the outside are two membranes (the meninges) with a thin layer of fluid (cerebro-spinal fluid, CSF) between them. The CSF nourishes the brain and also serves as a shock absorber, so that the brain is cushioned from damage when a person jumps around or bangs the head. There is a cavity in the inside of the brain, which is filled with CSF. This cavity continues as a canal inside me spinal cord. Doctors put in a needle at the back of the spine and get a small amount of CSF (Present between the two coverings of the meninges) for examination, to diagnose diseases such as meningitis and encephalitis.

The functions of the brain and nervous system may be broadly divided into; Higher functions such as thinking, speaking; remembering things (memory), emotions, appreciation of music; motor functions such as movements of the different parts of the body, sensory functions like appreciation of sensations such as pain, touch, seeing, hearing, taste, and smell, balance and coordination of movement in the different parts of the body and involuntary (unintentional) functions. Involuntary functions are two types, regular functions such as breathing and the beating of the heart and certain involuntary reactions with are referred to as reflexes which are usually take place at the level of the spinal cord.

The cerebrum controls the higher functions as well as motor and sensory functions. It is divided into 2 halves (left and right) which are called cerebral hemispheres. The left hemisphere controls the right side of the body, and the right hemisphere the left side of the body. The left hemisphere is said to be dominant in right handed people, and the right hemisphere in left handed people. The cerebellum is situated at the back of the brain. Its main function is to co-ordinate movements of the skeletal muscles and help maintain balance, a function which it shares with the inner ear. The cerebrum and cerebellum lead to the brain stem, which continues downwards as the spinal cord. The Spinal cord is a cylindrical structure that comes down through the vertebral column (spine) to the lower part of the back of the body. Nerves proceed from the brain stem and spinal cord to all parts of the body. In this way every part of the body is connected to the brain which ultimately controls all its activities.