The autonomic nervous system is a division of the peripheral nervous system that controls involuntary bodily functions, such as heart rate, digestion, and respiratory rate. It is further divided into the sympathetic and parasympathetic nervous systems, which work together to maintain homeostasis in the body. The sympathetic nervous system is responsible for the "fight or flight" response, while the parasympathetic nervous system is responsible for the "rest and digest" response. These two systems work in opposition to each other to regulate various bodily functions and maintain overall balance in the body.