The cholinergic system includes which neurotransmitter and receptor types?

• A. Dopamine on adrenergic receptors
• B. Acetylcholine on nicotinic and muscarinic receptors
• C. Norepinephrine on beta receptors
• D. Serotonin on GABA receptors

Answer: (B)

The cholinergic system is defined by acetylcholine as the transmitter and two receptor families that respond to it: nicotinic and muscarinic receptors. Nicotinic receptors are ligand-gated ion channels that produce fast excitation, found at the neuromuscular junction and in autonomic ganglia. Muscarinic receptors are G-protein–coupled receptors that mediate slower, modulatory effects on parasympathetic target organs. So, acetylcholine on nicotinic and muscarinic receptors best describes the cholinergic system. Other options pair different neurotransmitters with receptor types not part of the cholinergic system (for example, dopamine with adrenergic receptors, norepinephrine with beta receptors, or serotonin with GABA receptors), which belong to other signaling systems.