Which receptor type is activated at the neuromuscular junction?

• A. Dopaminergic
• B. Nicotinic
• C. Adrenergic
• D. Muscarinic

Answer: (B)

At the neuromuscular junction, acetylcholine binds to nicotinic acetylcholine receptors on the motor end plate. These receptors are ligand-gated ion channels, so their opening lets sodium (and some potassium) to flow, quickly depolarizing the muscle membrane and producing an end-plate potential. If that depolarization is strong enough, it triggers a muscle action potential and contraction. This fast, direct excitation is the hallmark of nicotinic receptors at the NMJ. In contrast, muscarinic receptors are slower, G protein–coupled receptors found in parasympathetic targets; adrenergic receptors respond to norepinephrine/epinephrine; dopaminergic receptors respond to dopamine. The NMJ uses nicotinic receptors specifically for rapid signaling leading to muscle contraction.