Amajor function of the division of the autonomic system is the fight-or-flight response in reaction to a threat

Autonomic nervous system (ANS) is the branch of the nervous system that provides unconscious control of basic body processes that is consists of two divisions; the sympathetic and parasympathetic. These two divisions have opposing effects on the internal organs they innervate. The Parasympathetic nervous system is the division that balances the actions of the sympathetic nervous system by slowing body processes, returning the body to homeostasis once a stressor has passed. The Sympathetic nervous system is the emergency system. Its major function is the fight-or-flight response in reaction to a threat. It speed-up key body processes to prepare the body for physical action.

Organism, organ system, organs, tissue, cells