Corpus: Tympanic nerve

The tympanic nerve is a branch of the glossopharyngeal nerve (IX nerve) that contains general somatosensory and general visceromotor (parasympathetic) fibres. The latter originate from the inferior salivatory nucleus of the medulla oblongata.

The tympanic nerve emerges from the inferior ganglion of the glossopharyngeal nerve (petrosal ganglion) without the parasympathetic fibres being connected there. It then ascends through a small canal, the canaliculus tympanicus, on the underside of the petrous bone to the tympanic cavity (cavum tympani). The nerve is located in a bony ridge that separates the carotid canal from the jugular fossa.

On the medial wall of the tympanic cavity, the tympanic nerve divides into fine branches which, together with sympathetic fibres of the carotid tympanic nerves (from the internal carotid plexus), form the tympanic plexus. The fibres of the plexus lie in fine sulci on the surface of the promontorium tympani.

The petrosal nerve in turn emerges from the tympanic plexus. It consists of the parasympathetic parts of the tympanic nerve that run through the plexus. As part of the Jacobson's anastomosis, the lesser petrosal nerve runs through the sphenopetrous fissure or the foramen lacerum to the otic ganglion. From there, the fibres run to the parotid gland.

The tympanic nerve supplies the middle ear, the auditory tube and the mastoid cells with sensory fibres. It also provides the secretory innervation of the parotid gland.