The Path of Sound in the Inner Ear
Sound waves which enter the inner ear travel from the oval window to the base of the cochlea, then up the vestibular canal, winding along the spiral toward the tip. At the apex, the wave motion changes direction, descending downward through the tympanic canal to the base of the cochlea, where it travels a short distance, then terminates at the round window.
When sound first enters the base of the cochlea at the vestibular canal, it presses against the middle duct, causing the basilar membrane to vibrate. The sympathetic motions of the basilar membrane create a slower wave, known as a traveling wave. This second wave, which travels along the basilar membrane, stimulates the hair cells on the organ of Corti, which in turn conduct sound messages to the brain.
By the time the initial sound wave in the vestibular canal has reached the tip of the spiral, it is nearly dissipated, and what little motion remains travels down the tympanic canal, and is absorbed by the round window.