Autonomic Nervous System

Innervates all effector organs and tissues except for skeletal muscles. It is autonomic because it functions subconsciously and involuntarily.
Dual Innervation
There are two branches or divisions of the autonomic nervous system (ANS): the sympathetic and parasympathetic. Both branches innervate most organs in an arrangement called dual innervation. The parasympathetic division is most active during rest and stimulates digestive activities. The sympathetic division is most active during times of excitement and physical activity. Animation Comparing Sympathetic and Parasympathetic Nervous Systems

The two divisions of the ANS work together to finely control the functions of the various organs so that they operate appropriately in different situations. The two systems often perform this control by working at cross purposes. So, for example, to precisely control the heart rate the sympathetic division will increase it while the parasympathetic decreases it