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Figure 8. Sound transmission. Three-dimensional VR CT image demonstrates the anatomic structures involved in the transmission of sound. Sound vibrations transmitted through the tympanic membrane (TM) are amplified multifold across the middle ear cavity by the lever mechanism of the ossicles. In addition, the disproportionately larger size of the tympanic membrane allows sound waves to be concentrated onto the smaller oval window (OW), further contributing to sound augmentation. Inward deflection of the oval window by the footplate of the stapes (St) compresses the fluid in the scala vestibuli (wavy yellow line). This compression wave travels along the coils of the cochlea in the scala vestibuli to the helicotrema (He). It then spirals back through the scala tympani (wavy green line) to the round window (RW), which serves as a pressure-relief diaphragm. The vibrations in the scala vestibuli also stimulate the cochlear duct (lying adjacent to the osseous spiral lamina [SL]), where mechanical energy is converted into electrical impulses and transmitted via the cochlear nerve to the brainstem (not shown). In = incus, M = malleus.
