What are the roles of the parasympathetic and sympathetic nervous systems?

The sympathetic nervous system and parasympathetic nervous systems are both part of the autonomic nervous system. They work together to achieve homeostasis. The sympathetic nervous system primarily activates the 'fight or flight response' it increases heart rate, respiratory rate and sweating. The parasympathetic nervous system balances these actions and acts to reduce heart rate, respiratory rate whilst promoting digestion and urine production which are functions best achieved in the absence of potential stressors or threats.