This document discusses the autonomic nervous system (ANS) and how drugs can influence it. The ANS is divided into the sympathetic and parasympathetic systems. The parasympathetic system uses acetylcholine at ganglionic and organ synapses. The sympathetic system uses acetylcholine at ganglionic synapses and norepinephrine at organ synapses. Drugs can mimic or block the neurotransmitters acetylcholine and norepinephrine, acting as agonists or antagonists respectively to influence the ANS.