Nervous System Organization

The nervous system is composed of the central nervous system and the peripheral nervous system. The central nervous system which includes the brain and spinal cord, processes and coordinates all incoming sensory information and outgoing motor commands, and it is also the seat of complex brain functions such as memory, intelligence, learning, and emotion.
The peripheral nervous system includes all neural tissue outside of the central nervous system. It is responsible for providing sensory, or afferent, information to the central nervous system and carrying motor, or efferent, commands out to the body’s tissues. Voluntary motor commands, such as moving muscles to walk or talk, are controlled by the somatic nervous system, while involuntary motor commands, such as digestion and heart beat, are controlled by the autonomic nervous system. The autonomic nervous system is further divided into two systems. The sympathetic nervous system, sometimes called the “fight or flight” system, increases alertness, stimulates tissue, and prepares the body for quick responses to unusual situations. In contrast, the parasympathetic nervous system, sometimes called the “rest and repose” system, conserves energy and controls sedentary activities, such as digestion.
source: wiki/encarta encyclopedia