The brain is the most vital part of the human body. It is the control centre of the body. This is the main part of the central nervous system. The human nervous system has about 13 billion nerve cells, of which 10 billion are in the brain. It weighs about 1.4 kilograms. The brain controls all the activities of the body such as, movement, sleep, digestion, breathing, etc. It needs a lot of energy to keep us working efficiently, hence, the brain uses one-fifth of the total energy produced in our body alone. The brain is connected with every other part of the body by nerves, and messages to and from the brain pass along these nerves. The human brain is divided into three main parts: cerebrum, cerebellum and medulla oblongata. The largest part of the human brain is the cerebrum, which consists of two cerebral hemispheres. The outer layer of each hemisphere is known as the cerebral cortex. This consists of a much-folded mass, of grey matter containing about 2,500 million nerve cells. Many activities are controlled by this part of the brain, which includes voluntary movements, conscious feelings, speech, hearing, sight, smell, thought and memory. It is also responsible for our intelligence and learning. Each activity is controlled by a particular part of the cortex. The cerebellum is the second largest part of the brain which helps coordinate the movements and control balance. The thalamus is a relay station. It processes all sensory nerve impulses before passing them on to the cortex. The hypothalamus controls body temperature, blood pressure and the pituitary gland. The hindbrain, which consists of medulla oblongata, the pons, and the cerebellum, controls the heart, lungs and the digestive system. The left portion of the brain controls the right parts of the body and vice-versa. A thick bone covering called the ‘skull’ protects the brain. However, the brain can be injured by sharp blows on the skull or if oxygen supply to its cells is cut off. If there is not enough blood reaching the brain the person may faint. After about five minutes without oxygen, brain cells die. They can never be replaced. The normal functioning of the brain can also be affected by certain diseases such as, brain tumour and by certain drugs such as, morphine.