The main function of the Autonomic Nervous System comes in the way of involuntary muscle control. It effectively regulates the function of your internal organs such as the heart, stomach and intestines. It is further divided up into the Parasympathetic and Sympathetic division.
The parasympathetic nervous system controls sexual arousal, salivation, lacrimation, urination, digestion and defecation. While the sympathetic nervous system constricts blood vessels, dilates pupils, speeds up heart rate, raises blood pressure, and perspiration. It’s also involved in the fight-or-flight response, which is an automatic reaction to potential danger that typically results in accelerated heart rate and increase in metabolic rate.