The brain weighs about 3 pounds and is composed of bundles of neurons that process information. It requires a constant supply of oxygen and glucose to function properly. There are four major divisions of the brain: the brain stem, diencephalon, cerebellum, and cerebrum. The cerebrum is the largest part and is responsible for higher level functions such as thought, language, and reasoning. It is divided into four lobes - frontal, parietal, occipital, and temporal - each of which controls different functions.