Final answer:
The neurotransmitter released by all parasympathetic neurons is acetylcholine (ACh), which binds to muscarinic receptors on the target cells, inducing rest-and-digest responses.
Step-by-step explanation:
The neurotransmitter released by all parasympathetic neurons is acetylcholine (ACh). It is important to note that all preganglionic fibers in the autonomic nervous system, whether sympathetic or parasympathetic, release ACh onto their nicotinic receptors. Afterward, the postganglionic parasympathetic fibers also release ACh which then bind to muscarinic receptors on the target cells to provoke rest-and-digest responses. On the other hand, postganglionic sympathetic fibers generally release norepinephrine with some exceptions.