The sympathetic nervous system (SNS) is a branch of the autonomic nervous system that controls the body’s response to stress or danger. The SNS activates the “fight or flight” reaction, which prepares the body to either confront or escape a threat. The SNS does this by increasing the heart rate, blood pressure, breathing rate, pupil size, and blood flow to the muscles. The SNS also inhibits some functions that are not essential in an emergency, such as digestion and urination. The SNS works in opposition to the parasympathetic nervous system (PNS), which promotes relaxation and recovery after a stressful situation.
