Your brain has three main components: the cerebrum (which consists of the left and right cerebral hemispheres), the cerebellum and the brain stem. The cerebral hemispheres of the brain make up the largest part of your brain. The cerebellum is the structure located behind the brain stem, and the brain stem is the lowest section of the brain and is connected to the spinal cord.
The central structures of the brain are the thalamus, hypothalamus, and pituitary gland. The thalamus relays sensory information to the cerebrum; the hypothalamus helps regulate body functions such as thirst and appetite, as well as sleep, aggression, and sexual behavior; and the pituitary gland produces hormones that play a role in growth, development, and various other physiological variables. The pons, medulla, and midbrain are the three structures that compose the brain stem. The ventricles are natural cavities inside the brain filled with cerebrospinal fluid.
Source: AMA's Current Procedural Terminology, Revised 1998 Edition. CPT is a trademark of the American Medical Association.