These are the two branches of the autonomic nervous system, which we have no conscious control of. The sympathetic system is responsible for 'fight and flight' responses, preparing the body for exercise or stress, e.g. increasing heart rate, reducing gastric activity. It uses noradrenaline and adrenaline as its end terminal neurotransmittersThe parasympathetic system is responsible for 'rest and digest' responses. This system is dominant at rest, slowing heart rate and increasing gastric activity. It uses acetylcholine as its end terminal neurotransmitter.