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How does bone conduction allow sound to reach the inner ear?

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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.

Bone conduction is the process by which sound reaches the inner ear through vibrations of the skull bones, bypassing the outer and middle ear. This occurs through two primary mechanisms:21

Compressional Bone Conduction

Used for high-pitched sounds, this process involves the skull vibrating in segments. These vibrations directly compress the otic capsule—the bony case enclosing the inner ear—which transmits the energy to the cochlear fluids. Because the round window membrane is more mobile than the stapes footplate, these vibrations stimulate the organ of Corti.21

Inertial Bone Conduction

At lower frequencies (1,500 Hz and below), the skull moves as a rigid body. Due to their inertia and suspension within the middle-ear cavity, the ossicles move less freely than the cochlea. This creates relative motion between the oval window and the stapes footplate, effectively stimulating the inner ear as if the stapes were vibrating normally.21

These mechanisms are clinically significant for distinguishing between conductive and sensorineural hearing loss during audiology testing.13