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How do the malleus, incus, and stapes transmit sound through the middle ear?
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sound reception
Auditory mechanisms in insects. (Left) A scolophore organ. (Top right) The mosquito ear. (Centre right) The ear of the cicada Magicicada septendecim. (Bottom right) The ear of the grasshopper.
The malleus, incus, and stapes—collectively known as the ossicular chain—function as a mechanical transformer that transmits sound vibrations from the tympanic membrane to the inner ear.123
Because sound must travel from air into the fluid-filled inner ear, the middle ear must overcome a significant impedance mismatch. The ossicles achieve this through two primary mechanisms:
- Area Concentration: The vibrations collected by the relatively large surface area of the tympanic membrane are concentrated onto the much smaller area of the stapes footplate, which increases pressure at least 13-fold.2
- Leverage: The malleus and incus act as a lever system. Because the handle of the malleus is longer than the projection of the incus, it provides a mechanical advantage of approximately 1.3.2
Together, these actions increase the pressure applied to the oval window at least 17-fold, allowing sound energy to effectively enter the cochlear fluids. The stapes rocks back and forth against the oval window, converting these mechanical vibrations into waves within the perilymph.24