Acetylcholine: a chemical neurotransmitter found widely in the body. It triggers the stimulation of post-synaptic nerves, muscles, and exocrine glands.
Acetylcholinesterase (generally referred to as cholinesterase): an enzyme that rapidly breaks down the neurotransmitter, acetylcholine, so that it does not over-stimulate post-synaptic nerves, muscles, and exocrine glands.
Acetylcholinesterase inhibitor (generally referred to as cholinesterase inhibitor): a chemical that binds to the enzyme, cholinesterase, and prevents it from breaking down the neurotransmitter, acetylcholine. With toxic doses, the result is that excessive levels of the acetylcholine build up in the synapses and neuromuscular junctions and glands.