The parasympathetic pathway can be thought of as a two neuron chain. A long pre ganglionic nerve leaves the brainstem or the sacral spinal cord and travels most of the way toward the target organ. This first neuron releases acetylcholine onto nicotinic receptors in a tiny ganglion located either in or very near the organ. Then a very short post ganglionic neuron continues the signal the last few millimetres into the actual target tissue and releases acetylcholine again, but this time onto muscar

Fluoroscopic Guided Stellate Ganglion Block - Technique and Overview - The Procedure Guide