Nerve cells of the brain are indeed organized in modules- clusters of nerve cells that communicate with each other. The brain has three major functions: controlling behavior; processing and retaining the information we receive from the environment; regulating the body"s physiological processes. Central nervous system is consists of the brain and the spinal cord. Spinal cord: a long, thin collection of nerve cells attached to the base of the brain and running the length of the spinal column (it contains circuits of nerve cells that control some simple reflexes) The central nervous system communicated with the rest of the body through nerves. Nerve: a bundle of fibers that transmits information between the central nervous system and the body"s sense organs, muscles, and glands. Peripheral nervous system: the cranial and spinal nerves; that part of the nervous system peripheral to the brain and spinal cord.