The division of the autonomic nervous system whose activation broadly causes arousal and prepares the body for ‘fight or flight’. It thus antagonizes the effects of the parasympathetic nervous system. Preganglionic sympathetic neurons arise on either side of the body from the thoracic and lumbar regions of the spinal cord, connect with ganglia arranged in chains alongside the spinal cord, and release acetylcholine. Some preganglionic neurons connect with visceral ganglia, such as the coeliac ganglion or inferior mesenteric ganglion. The postganglionic sympathetic neurons release mainly noradrenaline as a neurotransmitter (smaller amounts of adrenaline are also released). The actions of the sympathetic nervous system tend to antagonize those of the parasympathetic nervous system, thus achieving a balance in the organs they serve. For example, the sympathetic nervous system decreases salivary gland secretion, increases heart rate, and constricts blood vessels, while the parasympathetic nervous system has opposite effects.