The parasympathetic nervous system (PNS or PSNS) is part of the autonomic nervous system. It does the opposite things of the sympathetic nervous system, the other part of the autonomic nervous system. This way, the parasympathetic and sympathetic nervous systems balance each other's effects. The sympathetic nervous system helps a person "fight or flight" when they are in danger. When the danger is gone, the parasympathetic nervous system lets the person "rest and digest," "feed and breed."