The parasympathetic efferents have a cranio-sacral outflow from cranial nerves III, VII, IX and X and spinal roots S2-4 (Fig 1) .

The preganglionic cell bodies are in the cranial nerve nuclei or the lateral horns of the sacral spinal cord.

Parasympathetic ganglia from the vagus and sacral efferents are usually diffusely located in the walls of the viscera they supply (heart, lungs, gut).

Cranial nerves III, VII and IX that supply the head and neck synapse in four discrete intermediary ganglia: the ciliary, sphenopalatine, submaxillary or otic ganglion.