The brain is composed of more than a thousand billion neurons. Specific groups of them, working in concert, provide us with the capacity to reason, to experience feelings, and to understand the world. They also give us the capacity to remember numerous pieces of information.
The 3 major components of the brain are the cerebrum, cerebellum, and brain stem.
The cerebrum is divided into left and right hemispheres, each composed of a frontal, temporal, parietal, and occipital lobe. The cerebral cortex (gray matter) is the outside portion of the cerebrum and provides us with functions associated with conscious thought. The grooves and folds increase the cerebrum’s surface area, allowing us to have a tremendous amount of gray matter inside of the skull. Deep to the gray matter is the cerebral "white matter." The white matter provides for the communication between the cortex and lower central nervous system centers.
The cerebellum is located near the base of the head. It creates automatic programs so we can make complex movements without thinking.
The brain stem connects the brain with the spinal cord and is composed of 3 structures: the midbrain, pons, and medulla oblongata. The brain stem provides us with automatic functions that are necessary for survival.
Update Date 4/18/2013
Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.