Sympathetic / Parasympathetic
The central nervous system consists of the brain, spinal cord, and all of the nerves within the body. The autonomic nervous system is the part of the central nervous system that regulates involuntary body functions.
The parasympathetic nervous system controls “rest and digest” functions and is the opposite of the sympathetic nervous system’s “fight or flight” response.
Both systems control the same parts of the body (heart rate, blood pressure, respiratory rate) but with opposing effects.
The fight or flight is based on survival while rest and digest, allows the body to relax and repair itself.