The tympanic nerve is a branch of the glossopharyngeal nerve that contains general somatic sensory and general visceral motor fibers. The latter originate from the inferior salivatory nucleus of the medulla oblongata.
Innervation
The tympanic nerve supplies the middle ear, auditory tube, and mastoid air cells with sensory fibers. In addition, it provides secretory innervation to the parotid gland.
Anatomical course
The tympanic nerve arises from the inferior ganglion of the glossopharyngeal nerve without the parasympathetic fibers synapsing there. It then ascends through a small canal, the tympanic canaliculus, on the inferior surface of the petrous part of the temporal bone to the tympanic cavity. The tympanic 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 that, together with sympathetic fibers of the caroticotympanic nerves, form the tympanic plexus. The fibers of the plexus lie in fine sulci on the surface of the tympanic promontory.
The lesser petrosal nerve arises from the tympanic plexus. It consists of the parasympathetic components of the tympanic nerve that pass through the plexus. The lesser petrosal nerve travels as part of the Jacobson anastomosis through the sphenopetrosal fissure or the foramen lacerum to the otic ganglion. From there, the fibers travel to the parotid gland.