Acetylcholine is described as which of the following?

• A. Hormone released by adrenal glands; increases glucose.
• B. Neurotransmitter released by parasympathetic neurons; binds to muscarinic receptors.
• C. Neurotransmitter released by sympathetic neurons. Binds with nicotinic and muscarinic receptor proteins in the parasympathetic nervous system.
• D. Neurotransmitter released by motor neurons; binds to NMDA receptors.

Answer: (D)

Acetylcholine is a neurotransmitter used in the peripheral nervous system. In the parasympathetic pathways, postganglionic neurons release acetylcholine that binds to muscarinic receptors on target organs, mediating the classic rest-and-digest effects. It also functions at the skeletal neuromuscular junction, where motor neurons release acetylcholine to bind nicotinic receptors on muscle fibers and trigger contraction. It is not a hormone produced by the adrenal glands (that would be adrenaline/epinephrine), and it does not bind NMDA receptors (NMDA receptors are glutamate receptors in the CNS). Therefore, the description that acetylcholine is a neurotransmitter released by parasympathetic neurons and binds to muscarinic receptors best captures its role.