preganglionisilta

The term *preganglionic* refers to the first neuron in the autonomic nervous system, which transmits signals from the central nervous system (CNS) to an autonomic ganglion. In the context of autonomic innervation, these neurons originate in the brainstem or spinal cord and project to peripheral ganglia, where they synapse with postganglionic neurons. The term *preganglionic* is often paired with *sympathetic* or *parasympathetic* to specify the division of the autonomic nervous system involved.

In the sympathetic division, preganglionic neurons emerge from the thoracolumbar region of the spinal cord (T1–L2), sending axons via the white rami communicantes to sympathetic chain ganglia or prevertebral ganglia. These neurons release the neurotransmitter acetylcholine (ACh) at their synapses, acting on nicotinic acetylcholine receptors (nAChRs) on postganglionic neurons.

In contrast, the parasympathetic division features preganglionic neurons originating in the brainstem (cranial nerves III, VII, IX, X) or the sacral spinal cord (S2–S4). Their axons travel through cranial nerves or pelvic splanchnic nerves to terminate in terminal ganglia near or within target organs. Like their sympathetic counterparts, parasympathetic preganglionic fibers also release ACh, which stimulates postganglionic neurons via nicotinic receptors.

The length of preganglionic fibers varies between divisions: sympathetic preganglionic fibers are relatively short, while parasympathetic fibers tend to be longer, often extending from the CNS to ganglia located close to effector organs. This anatomical distinction influences the overall organization and functional dynamics of autonomic control. Dysfunction or damage to preganglionic pathways can disrupt autonomic regulation, leading to clinical conditions affecting cardiovascular, gastrointestinal, or other visceral functions.