middleear

The middle ear is an air-filled cavity in the temporal bone that lies between the tympanic membrane (eardrum) and the inner ear. It contains the auditory ossicles—the malleus (hammer), incus (anvil), and stapes (stirrup)—the tympanic cavity, and the tympanic membrane’s handle projecting into it. The cavity communicates with the nasopharynx through the pharyngotympanic (Eustachian) tube, which helps equalize pressure and ventilate the space.

The ossicles form an impedance-matching system that transmits sound vibrations from the tympanic membrane to the oval window of the inner ear. The lever action of the ossicles, their surface area differences, and pressure changes at the oval window amplify vibrations and transfer them efficiently. Two small muscles, the tensor tympani and the stapedius, tense in response to loud sounds, reducing movement of the ossicles and protecting the inner ear. The stapedius is innervated by the facial nerve (CN VII), and the tensor tympani by the mandibular branch of the trigeminal nerve (CN V3).

Developmentally, the middle ear cavity arises in conjunction with the first pharyngeal pouch and is connected to the mastoid air cell system via the aditus ad antrum.

Common pathologies include otitis media (acute or chronic) with effusion, which can cause conductive hearing loss; otosclerosis, where fixation of the stapes reduces transmission; cholesteatoma; and tympanic membrane perforation. Diagnosis often involves otoscopy and tympanometry.