Humans hear primarily by detecting sound waves, which enters the pinna and are and magnified by the auditory canal. Sound waves are then directed towards the tympanic membrane. The pressure of the air molecules cause the tympanic to vibrate. This causes the malleus on the other side of the membrane to move. The handle of the malleus strikes the incus causing it to vibrate. The vibrating incus moves the stapes in and out and vibrates the oval window.
The sound wave is transferred to the oval window and given support from the ossicles. They are particularly helpful because the fluid in the inner ear is more difficult to move than air; therefore the sound must be amplified. As the vibrations pass from the large area of the eardrum through the osscicles, which have a smaller area, their force is much more concentrated and causes the sound to become amplified. Once the sound wave reaches the inner ear from the oval window it sets up pressure changes that vibrates the vestibule. To relieve this pressure, the membrane of the oval window bulges in and out. The basilar membrane moves because of the alternating changes of pressure in the fluid of the canals. The organ of Corti also moves causing the hairlike projections to bend. As the hairlike projections bend, they stimulate the sensory cells to transmit impulses along the auditory nerve to the brain.
