Preganglionic

Preganglionic refers to neurons of the autonomic nervous system whose cell bodies reside in the central nervous system and whose axons project to autonomic ganglia where they synapse with postganglionic neurons. These fibers are myelinated and conduct impulses relatively quickly. The term contrasts with postganglionic neurons, whose cell bodies lie in autonomic ganglia and whose unmyelinated axons extend to effector organs.

In the sympathetic division, preganglionic neurons are located in the intermediolateral cell column of the spinal cord from T1 to L2. Their axons exit via the ventral roots, join sympathetic trunks, and may synapse in paravertebral ganglia, prevertebral ganglia, or pass through to collateral ganglia via splanchnic nerves. All sympathetic preganglionic terminals release acetylcholine onto nicotinic receptors on postganglionic neurons. Postganglionic neurons then typically release norepinephrine to many targets, or acetylcholine to a few, such as sweat glands.

In the parasympathetic division, preganglionic neurons originate in the brainstem nuclei of cranial nerves III, VII, IX, X and from spinal segments S2–S4. Their long preganglionic fibers extend to ganglia located near or within the effector organs (terminal or intramural ganglia). They also release acetylcholine onto nicotinic receptors in the ganglia, and the postganglionic neurons release acetylcholine onto muscarinic receptors of the target tissue.

Anatomically, sympathetic preganglionic fibers are typically short, whereas parasympathetic preganglionic fibers are long. This arrangement reflects distinct wiring patterns and target organization, enabling autonomic commands to modulate heart rate, digestion, glandular secretion, and other involuntary functions.