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How does the basilar membrane respond to sound vibrations?

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Diagram showing auditory mechanisms in insects, including labeled illustrations of a scolophore organ, the mosquito ear with antenna shaft and scolophores, the cicada ear with auditory capsule and tympanic membrane, and the grasshopper ear with sensory body and tympanic membrane. — 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 basilar membrane plays a critical role in the human ear by acting as a frequency analyzer for sound vibrations. When sound waves reach the cochlea, they create pressure waves in the cochlear fluids, which cause the basilar membrane to vibrate.1

The membrane is structured to respond differently to various sound frequencies due to its physical properties: it increases in width and mass while decreasing in stiffness from its base to its apex. Consequently, different regions of the membrane are tuned to specific frequencies:12
* High-frequency sounds cause the stiffer basal end of the membrane to vibrate.12
* Low-frequency sounds cause the more flexible apical end to vibrate.12

As vibrations travel along the membrane, they form waves that reach a peak amplitude at a location corresponding to the sound's frequency. This movement causes the organ of Corti, which rests on the membrane, to move against the tectorial membrane. This shearing force bends the stereocilia of the hair cells, triggering the electrical impulses that the brain interprets as sound. Additionally, the amplitude of these vibrations determines the perceived loudness of the sound.13