In the sympathetic nervous system, what neurotransmitters are released by preganglionic and postganglionic neurons, and what receptors do they activate?

• A. Preganglionic acetylcholine onto nicotinic receptors; postganglionic norepinephrine onto adrenergic receptors (alpha/beta); sweat glands use acetylcholine on muscarinic receptors.
• B. Preganglionic norepinephrine; postganglionic acetylcholine on nicotinic receptors.
• C. Both preganglionic and postganglionic neurons release acetylcholine onto nicotinic receptors.
• D. Preganglionic acetylcholine onto nicotinic receptors; postganglionic epinephrine onto adrenergic receptors; sweat glands use acetylcholine on muscarinic receptors.

Answer: (A)

In the sympathetic system, the signal chain starts with preganglionic neurons releasing acetylcholine that binds to nicotinic receptors on the postganglionic neuron. The postganglionic neuron then releases norepinephrine onto adrenergic receptors (alpha and beta) on the target organs. A key exception is the sweat glands, which are innervated by sympathetic fibers that release acetylcholine onto muscarinic receptors on the sweat glands.

This pattern fits the classic sympathetic pathway: acetylcholine at the ganglion (nicotinic receptors) followed by norepinephrine on the target (adrenergic receptors), with the sweat glands as a notable cholinergic exception.