The autonomic nervous system (ANS) controls involuntary body functions and is divided into the sympathetic and parasympathetic nervous systems. The sympathetic system mobilizes the body for fight or flight through widespread effects like increased heart rate and blood pressure. The parasympathetic system conserves energy resources and is active at rest, slowing the heart and contracting digestive organs. Both systems work in coordination to unconsciously adjust the body to its environment and maintain homeostasis.