The autonomic nervous system (ANS) controls the activities of organs, glands, and various involuntary muscles such as cardiac and smooth muscles.

The ANS consists of two divisions:

• The sympathetic nervous system is involved in the stimulation of activities that prepare the body for action, such as increasing the heart rate, increasing the release of sugar from the liver into the blood, and other generally considered as fight-or-flight responses (responses that serve to fight off or retreat from danger).
• The parasympathetic nervous system activates tranquil functions, such as stimulating the secretion of saliva or digestive enzymes into the stomach.