Central Nervous System

Central Nervous System
The central nervous system is composed of two principal structures: the
brain and the spinal cord. The brain is one of the largest organs in the human
body, weighing on average about three pounds and consisting of one
trillion neurons by early adulthood.
The brain is subdivided into four major functional areas. The cerebrum,
the largest portion of the brain, regulates sensory and motor functions. The
convolutions characteristic of the human brain represent the physical appearance
of the cerebrum. The brain stem connects the brain with the spinal
cord, carrying out both sensory and motor functions. The diencephalon
consists of the thalamus, the relay center for sensory functions entering the
cerebrum, and the hypothalamus, which controls much of the peripheral
nervous system activity and regulates endocrine processes. The fourth portion
of the brain is the cerebellum, the rear of the brain where voluntary
muscle activity is controlled.