The autonomic nervous system consists of two divisions: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic division is often called the “fight or flight” system because it usually stimulates tissue metabolism, increases alertness, and generally prepares the body to deal with emergencies. The parasympathetic division is considered the “rest and repose” division because it conserves energy and promotes sedentary activities, such as digestion. In general, both the sympathetic and parasympathetic divisions innervate the target cells.