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).
Anatomy of the brain
The vertebrate brain can be subdivided as follows:
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.
Functions 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.
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.