Acetylcholine acts on which receptors in the cholinergic system?

• A. Dopamine D1 and D2 receptors
• B. Nicotinic and muscarinic receptors
• C. Adrenergic alpha and beta receptors
• D. GABA-A receptors

Answer: (B)

Acetylcholine acts on two main receptor families in the cholinergic system: nicotinic and muscarinic receptors. Nicotinic receptors are ligand-gated ion channels that produce fast excitatory responses when acetylcholine binds, found at the neuromuscular junction and in certain CNS and autonomic ganglia. Muscarinic receptors are G protein–coupled receptors that mediate slower, modulatory parasympathetic effects such as decreased heart rate, increased glandular secretions, and smooth muscle actions in various organs. The other receptor types listed—dopamine D1/D2, adrenergic alpha/beta, and GABA-A—respond to different neurotransmitters (dopamine, norepinephrine/epinephrine, and GABA, respectively) and are not cholinergic receptors.