In the sympathetic nervous system, postganglionic neurons typically release norepinephrine to activate target organs. However, there is a notable exception: some sympathetic postganglionic neurons are cholinergic, meaning they release acetylcholine as their neurotransmitter. Understanding which tissues are innervated by these cholinergic sympathetic neurons reveals unique aspects of autonomic control.

Key Targets of Sympathetic Cholinergic Postganglionic Neurons

The primary and classic target of cholinergic sympathetic postganglionic neurons is the sweat glands (eccrine glands). These neurons innervate sweat glands to regulate thermoregulatory sweating, an important physiological response that helps maintain body temperature. Unlike most other sympathetic postganglionic neurons, which release norepinephrine, those going to sweat glands release acetylcholine.

Other Targets

• Sweat glands (1): These are exclusively innervated by cholinergic sympathetic postganglionic neurons. This cholinergic transmission triggers sweat secretion.

• Hair follicles (3): Sympathetic postganglionic neurons can influence hair follicle muscles (arrector pili muscles), causing piloerection (goosebumps). These sympathetic fibers typically release norepinephrine, not acetylcholine.

• Parotid glands (2) and Pancreas (4): These are primarily innervated by parasympathetic postganglionic neurons, which are cholinergic but are part of a different autonomic division. Their sympathetic innervation is mostly adrenergic (norepinephrine releasing), not cholinergic.

Scientific Insights

Evidence from neurochemical and developmental studies confirms that the cholinergic phenotype of sympathetic postganglionic neurons innervating sweat glands emerges during early development and is maintained throughout life. These cholinergic neurons express markers like choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT), distinguishing them from the overwhelmingly noradrenergic population in the sympathetic nervous system. Understanding this distinction helps explain unique physiological mechanisms like thermoregulation.pmc.ncbi.nlm.nih+2

Summary

To answer the question accurately:

Sympathetic postganglionic neurons that are cholinergic innervate: (1) sweat glands