same frequency as the waves of air hitting it. The vibrations of the tympanum cause the three tiny bones of the middle ear to move. Their transmission of the vibrations from the tympanum to the oval window enhances the pressure applied to the oval window to over twenty times the pressure of the original air waves. This enhancement allows the ear to detect even faint sounds. The movement of the stapes, the third small bone, causes the oval window membrane to vibrate which, in turn, causes the fluids of the vestibular and tympanic canals to move. As the fluids of the canals move, still at the same frequency of the original air waves, the round window membrane functions as an expansion valve, being pushed outward or being sucked inward as the oval window membrane is pushed in or sucked out, respectively, by the stapes. The movement of the fluid in the vestibular and tympanic canals causes the basilar membrane of the cochlear canal to move up and down in a frequency-dependent way, which causes the hairs of some receptor cells to be pushed against the less-mobile tectorial membrane. The deformation of the hairs causes the receptor cells to stimulate the sensor neurons which carry the impulses to the brain's auditory centers.
