The answer is the sympathetic nervous system. The autonomic nervous system, which controls our body organs and systems, does so without our conscious awareness, and is therefore involuntary. The autonomic nervous system is divided into 2 systems: the sympathetic nervous system, and the parasympathetic nervous system. The sympathetic nervous system is activated in the fight or flight response, preparing the body to either fight or run from an external threat and danger. The parasympathetic nervous system is involved with activities such as digestion of food, reproduction, and resting.
