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How do the three middle-ear bones of mammals transmit sound?
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Vertebrate
The major groups of vertebrates include fishes, amphibians, reptiles, birds, and mammals.
The three middle-ear bonesāthe malleus (hammer), incus (anvil), and stapes (stirrup)āform an ossicular chain that transmits sound vibrations from the tympanic membrane to the inner ear.1
Because sound travels through air but must eventually vibrate the fluid within the cochlea, the middle ear acts as an impedance-matching transformer to overcome the significant energy loss that would otherwise occur at the air-fluid interface. This transmission is achieved through two primary mechanical mechanisms:2
- Area Reduction: Sound energy collected across the relatively large surface area of the tympanic membrane is concentrated onto the much smaller area of the stapes footplate, which fits into the oval window. This significantly increases the pressure of the vibrations.2
- Lever Action: The malleus and incus function as a lever system. Because the handle of the malleus is longer than the projection of the incus, it provides a mechanical advantage that further amplifies the force applied to the stapes.2
Together, these mechanisms increase the pressure of sound waves reaching the inner ear, ensuring efficient hearing.23