Final answer:
Preganglionic sympathetic fibers release acetylcholine (ACh) while postganglionic sympathetic fibers release norepinephrine (NE), except for certain fibers. Preganglionic fibers of both sympathetic and parasympathetic neurons release ACh, which binds to nicotinic receptors in ganglionic neurons.
Step-by-step explanation:
All preganglionic fibers, both sympathetic and parasympathetic, release acetylcholine (ACh). All ganglionic neurons, the targets of these preganglionic fibers, have nicotinic receptors in their cell membranes. The nicotinic receptor is a ligand-gated cation channel that results in depolarization of the postsynaptic membrane. Postganglionic sympathetic fibers release norepinephrine (NE), except for fibers that project to sweat glands and to blood vessels associated with skeletal muscles, which release ACh.