Acetylcholine binds to which receptors in the parasympathetic nervous system?

• A. Dopamine receptors.
• B. Adrenergic receptors.
• C. GABA receptors.
• D. Nicotinic and muscarinic receptors.

Answer: (D)

Acetylcholine mediates parasympathetic signaling by acting on two receptor types: nicotinic receptors at autonomic ganglia and muscarinic receptors at the target organs. Preganglionic parasympathetic fibers release ACh that binds nicotinic receptors on the postganglionic neuron, triggering propagation of the signal. The postganglionic fiber then releases ACh onto muscarinic receptors on the heart, smooth muscle, and glands, producing the characteristic parasympathetic effects. Dopamine, adrenergic, and GABA receptors respond to their respective neurotransmitters (dopamine, norepinephrine/epinephrine, and GABA) and are not activated by acetylcholine in this pathway.