Structure and Origin - The tympanic nerve contains sensory axons to the middle ear, including the internal surface of the tympanic membrane. - Cell bodies of these sensory axons are located in the superior ganglion of the glossopharyngeal nerve. - It also contains parasympathetic axons that continue as the lesser petrosal nerve to the otic ganglion. - The otic ganglion gives off postganglionic parasympathetic neurons. - The tympanic nerve arises from the inferior ganglion of the glossopharyngeal nerve (CN IX). - The origin is in the jugular fossa.

Course - The tympanic nerve passes through the petrous part of the temporal bone within the tympanic canaliculus. - The canaliculus is situated within the bony ridge separating the carotid canal and the jugular foramen. - It reaches the middle ear through this course. - In the tympanic cavity of the middle ear, it ramifies upon the promontory of the tympanic cavity. - This forms the tympanic plexus.

Sensory Distribution - The tympanic nerve provides sensation to the middle ear (tympanic cavity). - It also supplies the internal surface of the tympanic membrane, Eustachian tube, parotid gland, and mastoid air cells.

Parasympathetic Autonomic Distribution - The tympanic nerve is the parasympathetic root of the otic ganglion. - The otic ganglion provides secretomotor innervation of the parotid gland via the auriculotemporal nerve. - It is involved in the salivatory reflex to increase salivation during chewing.

Variation - The tympanic nerve usually arises from the inferior ganglion of the glossopharyngeal nerve. - Rarely, it may arise from a higher part. - Rarely, it may provide no parasympathetic fibers to the otic ganglion.