The brain is the supervisory center of the nervous system consisting of grey matter (superficial parts called cortex and deep brain nuclei) and white matter (deep parts except the brain nuclei). It controls and coordinates behavior, homeostasis (body functions such as heartbeat, blood pressure, fluid balance, and body temperature) and mental functions (such as cognition, emotion, memory and learning).

In most animals, the brain is located in the head. In vertebrates, the brain is protected by the bones of the skull. The meninges are the system of membranes that separate the skull from the brain.

Although the brain is usually referred to as the supervisory center of vertebrates, the same term can also be used for the invertebrate central nervous system.

Anatomy of the brain

The vertebrate brain can be subdivided as follows:

Sometimes a gross division into three major parts is used: hindbrain (medulla oblongata and myelencephalon), midbrain (metencephalon) and forebrain (diencephalon and telencephalon).

The cerebrum and the cerebellum consist each of two halves (hemispheres). The corpus callosum connects the two hemispheres of the cerebrum.

In most vertebrates the metencephalon is the highest integration center in the brain, whereas in mammals this role has been adopted by the telencephalon. Therefore the cerebrum is the largest section of the mammalian brain and its surface has many deep fissures (sulci) and convolutions (gyri), giving a wrinkled appearance to the brain.

See cephalic disorders for information on congenital development disorders relating to the brain.

The adult human brain usually weighs about 1 - 1.5 kilograms in an average volume of 1,600 cubic centimetres. The intelligence of the individual is not necessarily related with the weight of the brain, but with the efficiency and number of connections between cells.

The blood supply to the brain involves several arteries that enter the brain and communicate in a circle called the circle of Willis. Blood is then drained from the brain through a network of sinuses that drain into the right and left internal jugular veins.

The function of the brain

During many past millennia, the function of the brain was unknown. Ancient Egyptians threw the brain away prior to the process of mummification. Ancient thinkers such as Aristotle imagined that mental activity took place in the heart. The Alexandrian biologists Herophilus and Erasistratus were among the first to conclude that the brain was the seat of intelligence. Galen's theory that the brain's cavities, or ventricles, were the sites of thought and emotion prevailed until the work of the Renassiance anatomist Vesalius.

The brain is now studied in neurology and psychiatry, and known to be the organ responsible for the phenomena of consciousness, thought and emotion.

Studies of brain damage from accidents led to the identification of specialized areas of the brain devoted to functions such as the processing of seeing and hearing.

Brain imaging has allowed the function of the living brain to be studied without damaging the brain. For the first time, this has allowed the study of the neurophysiology of the brain to be studied in detail in a wide range of psychological tests.

A new discipline of cognitive science has started to fuse the results of these investigations with observations from psychology, philosophy and computer science.

Brain is also the name of a commune in the Côte-d'Or département in France.

The Brain is the think-tank part of an organization, where the ideas come from, or where problems are solved. Or it could describe the management of an organisation, wherever the actual ideas come from.

Brain is also the name of one of the lab mice on the cartoon Pinky and the Brain.