What are the primary neurotransmitters used by the autonomic nervous system (ANS), and which divisions and fibers release them?
The ANS uses three primary neurotransmitters: acetylcholine, norepinephrine, and epinephrine. Acetylcholine is released by all preganglionic fibers in both sympathetic and parasympathetic divisions, as well as by postganglionic fibers in the parasympathetic division. Norepinephrine (and to a lesser extent, epinephrine) is mainly released by sympathetic postganglionic fibers.