The sympathetic nervous system is part of the autonomic nervous system. The sympathetic nervous system activates what is often termed the fight or flight response. The sympathetic nervous system directs the body's rapid involuntary response to dangerous or stressful situations. A flash flood of hormones boosts the body's alertness and heart rate, sending extra blood to the muscles. Breathing quickens, delivering fresh oxygen to the brain, and an infusion of glucose is shot into the bloodstream for a quick energy boost. The sympathetic nervous system allows animals to make quick internal adjustments and react without having to think about it.
