Abstract
The autonomic nervous system innervates and regulates nearly every major tissue and organ system in the body. This branch of the nervous system often acts without conscious control. The overall action of the autonomic nervous system is to maintain a normal internal environment to allow normal organ functions. The autonomic nervous system is classically defined as an efferent motor system with two divisions: sympathetic and parasympathetic. Each division includes preganglionic nerves that travel from the central nervous system to peripheral ganglia, where they synapse with postganglionic nerves that travel to regulate tissue and organ functions. The primary neurotransmitters released from these nerves are norepinephrine, acting on adrenergic receptors, and acetylcholine, acting on cholinergic receptors. Some autonomic drugs are designed to mimic the effects of these neurotransmitters by activating nicotinic or muscarinic cholinergic receptors or α or β adrenergic receptors. Various other autonomic drugs are designed to block nicotinic or muscarinic cholinergic receptors or α or β adrenergic receptors to inhibit autonomic effects. Still other drugs can modify the synthesis, storage, release, metabolism, or cellular uptake of these neurotransmitters. Thus understanding the function of the autonomic nervous system is critical for knowledge of the therapeutic use of autonomic drugs.