In the sympathetic nervous system, which of the following describes sweat gland innervation?

• A. Sweat glands use norepinephrine on alpha receptors.
• B. Sweat glands use acetylcholine released by postganglionic neurons acting on muscarinic receptors.
• C. Sweat glands use acetylcholine released by postganglionic neurons acting on nicotinic receptors.
• D. Sweat glands respond to epinephrine on beta receptors.

Answer: (B)

Sweat glands are controlled by sympathetic nerves that release acetylcholine onto muscarinic receptors, not by norepinephrine on adrenergic receptors. This cholinergic sympathetic innervation is what stimulates sweat secretion, typically via muscarinic receptors (M3) on the gland. While most sympathetic targets use norepinephrine, eccrine sweat glands are an exception, relying on acetylcholine from postganglionic neurons acting on muscarinic receptors. The other descriptions don’t fit: norepinephrine on alpha receptors is a common sympathetic pathway but not for sweat glands; nicotinic receptors are in autonomic ganglia, not the gland itself; epinephrine acting on beta receptors reflects circulating hormone effects rather than direct postganglionic innervation of the gland.