What does the autonomic nervous system regulate?

The autonomic nervous system is responsible for the body’s automatic functions (digestion, heart rate, sweating, etc.). It consists of two systems: the sympathetic and parasympathetic nervous systems. These two systems control the activity of internal organs, counteracting actions. Their fibers bind to smooth muscle cells (found in the mucous membranes of many organs), heart muscle, glands and cells of the immune system. The sympathetic system reacts to stress in preparation for action, while the parasympathetic system causes a general slowdown in body functions.