The middle ear is the cavity between the tympanic membrane on the outer side and the cochlea on the inner side (fig. 10.18). Within this cavity are three middle-ear ossicles—the malleus (hammer), incus (anvil), and stapes (stirrup). The malleus is attached to the tympanic membrane, so that vibrations of this membrane are transmitted via the malleus and incus to the stapes. The stapes, in turn, is attached to a membrane in the cochlea called the oval window, which thus vibrates in response to vibrations of the tympanic membrane.

esms gSy The auditory (eustachian) tube is a passageway ' leading from the middle ear to the nasopharynx (a ™ cavity positioned behind the nasal cavity and extending down to the soft palate). The auditory tube is usually collapsed, so that debris and infectious agents are prevented from traveling from the oral cavity to the middle ear. In order to open the auditory tube, the tensor tympani muscle, attaching to the auditory tube and the malleus (fig. 10.18), must contract. This occurs during swallowing, yawning, and sneezing. People sense a "popping" sensation in their ears as they swallow when driving up a mountain because the opening of the auditory canal permits air to move from the region of higher pressure in the middle ear to the region of lower pressure in the nasopharynx.

Clinical Investigation Clues

Remember that Ed experienced severe ear pain and reduced hearing immediately after disembarking from an international flight. Remember also that he had a bad head cold.

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