preganglionik

Preganglionik, or preganglionic, refers to neurons of the autonomic nervous system that have their cell bodies in the central nervous system and project their axons to autonomic ganglia where they synapse on postganglionic neurons. These neurons are part of the two main divisions of the autonomic system: sympathetic and parasympathetic. At the synapse with the postganglionic neuron, preganglionic fibers release acetylcholine onto nicotinic receptors.

In the sympathetic division, the cell bodies of preganglionic neurons reside in the intermediolateral cell column of the spinal cord, typically from T1 to L2. Their axons may synapse in the sympathetic chain ganglia or in prevertebral (collateral) ganglia. In the parasympathetic division, preganglionic neurons are located in the brainstem nuclei associated with cranial nerves III, VII, IX, and X, as well as in spinal segments S2–S4. Their axons travel longer distances to ganglia located near or within target organs.

The typical pattern of innervation includes differences in axon length: sympathetic preganglionic fibers are relatively short, while parasympathetic preganglionic fibers are relatively long. Postganglionic neurons, in contrast, are usually unmyelinated and release various neurotransmitters depending on the division and target; most sympathetic postganglionic neurons release norepinephrine, though sweat glands receive acetylcholine, and parasympathetic postganglionic neurons release acetylcholine onto muscarinic receptors.

Etymology derives from pre- “before” and ganglion, reflecting the location of these neurons before they form synapses in autonomic ganglia.