The brain is composed of two main types of tissue; one is called grey matter and the other white matter. The grey matter consists of nerve cells and the white matter of nerve fibres (lengths of nerve cells joined together). Unlike most other types of cells within the body, nerve cells do not regenerate or reproduce themselves. It is believed that each person is born with a full complement of these nerve cells to last the entire lifetime. They grow during childhood, but they do not multiply. If the cells die then the fibres will also die and vice versa. The nerve fibres connect the different cells together within the brain and also connect the brain to all parts of the body. They may be as long as fifty centimetres in length. It has been estimated that there are about two hundred million incoming and outgoing fibres linking the brain with the rest of the body.
The following is a brief description of the major functional areas of the brain.
The cerebellum is a fist-sized region located at the rear and lower part of the brain behind the top of the spine. It is concerned with maintaining muscular tone throughout the whole body. It supplies a continuous stream of nerve impulses to the motor nerves and thereby keeps the muscles in the appropriate state of partial contraction. The cerebellum also coordinates the movements of the muscles and harmonizes complex muscular actions. The entire process occurs automatically.
The thalamus is located at the top of the spine in the middle of the brain. It is the relay or transmitting station that sends information to the higher centres of the brain, having sorted out unwanted data. It is also the region where so-called protopathic sensations reach the threshold of conscious perception. The protopathic sensations are the instinctive signals which indicate pain, pleasure, etc. in different parts of the body without any discrimination regarding their importance, meaning, etc. Other more sensitive sensations are called epicritic; these are consciously perceived in the cerebral cortex, having passed through the thalamus.
The hypothalamus at the top of the spine is connected directly to the thalamus; it is part of the limbic system and is concerned with our emotional states and reactions. It is the centre that makes the emotional response of happiness, unhappiness, anger, etc. It is often inhibited by the higher brain centres, so that one suppresses emotional reactions. The reward (pleasure) and punishment (pain) areas of the brain are also located within the hypothalamus. It is interesting to note that the pleasure centre is appreciably larger than the pain centre. The hypothalamus is also the central control centre of the sympathetic and parasympathetic nervous outflows. These two systems are associated with control and activation of all the organs of the body, from the heart to the eyes, from the skin to respiration.
The hypothalamus also contains the centre of wakefulness, consisting of sympathetic nerves, and the centre of sleep, consisting of parasympathetic nerves. The hypothalamus is therefore a very important part of the brain.
Other parts of the brain include the fissure of Roland, parietal lobe and the occipital lobe, where most of the functions concerned with skin sensations such as touch, temperature and pressure, hearing, seeing, eye movements, sense of smell and taste, speech and so forth are received and interpreted.
The most well-known area of the brain is called the frontal lobe, located behind the forehead. It is this centre that most clearly differentiates man from animals. It is this area that is concerned with human traits such as truth, honesty, morality, justice, discretion, friendship and many other characteristic human attributes. This is the so-called silent area of the brain which determines the nature of an individual. Any injury or malfunction of this area can cause the individual to become careless, mentally deranged, depressed, anxious, or lose all sense of values. It is the centre of personality. It is also believed to be the instrument or centre which picks up the memory of the mind; this is demonstrated by the fact that electrical or nervous stimulation of this area brings about recall of past experiences, good and bad. This part of the brain acts as the switchboard of the mind.