Information from all over the body travels quickly to and from the central nervous system. This system consists of the brain and spinal cord, and information is sent with impulses via the nerves. Some of these impulses reach speeds from anywhere between 27 and 280 mph. The central nervous system is divided into two branches, the somatic [body] nervous system and the autonomic [self-governing] nervous system. In the somatic nervous system, information is picked up from the five senses and receptors that sense pain and temperature. This information is sent to the brain for interpretation and quickly assimilated according to previous experience. If necessary, signals are sent back from the brain, through the spinal cord and out to the peripheral nerves, where the muscles receive the command to react. In the case of a reflex, the reaction is necessarily quicker, and the signals return from the spinal cord, bypassing the brain. Because we have control over these movements, the somatic nervous system is called voluntary. The autonomic nervous system is beyond conscious control and therefore it is said to be involuntary. The autonomic nervous system ensures a stable inner environment that is held in balance by two opposing systems, both of which are always active. The sympathetic nervous system is responsible for situations of stress increasing heart rate and blood pressure, and increasing sensitivity and reaction to stimuli. The parasympathetic system is responsible for rest, relaxation and digestion.
