In general, the word choline refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin. It prevents fat deposits in the liver and facilitates the movement of fats into the cells. The richest sources of choline are liver, kidneys, brains, wheat germ, brewer's yeast, and egg yolk. Therefore, cholinergic typically refers to acetylcholine in the neurological sense. The parasympathetic nervous system, which uses acetylcholine almost exclusively to send its messages, is said to be almost entirely cholinergic. Neuromuscular junctions, preganglionic neurons of the sympathetic nervous system, the basal forebrain, and brain stem complexes are also cholinergic. In addition, the receptor for the merocrine sweat glands are also cholinergic, since acetylcholine is released from post-ganglionic sympathetic neurons.
In neuroscience and related fields, the term cholinergic is used in the following related contexts:
- A substance (or ligand) is cholinergic if it is capable of producing, altering, or releasing acetylcholine ("indirect-acting") or mimicking its behaviour at one or more of the body's acetylcholine receptor types ("direct-acting").
- A receptor is cholinergic if it uses acetylcholine as its neurotransmitter.
- A synapse is cholinergic if it uses acetylcholine as its neurotransmitter.