The purpose of the perilymph-filled scala tympani and scala vestibuli is to transduce the movement of air that causes the tympanic membrane and the ossicles to vibrate, to movement of liquid and the basilar membrane. This movement is conveyed to the organ of Corti inside the scala media, composed of hair cells attached to the basilar membrane and their stereocilia embedded in the tectorial membrane. The movement of the basilar membrane compared to the tectorial membrane causes the sterocilia to bend. They then depolarise and send impulses to the brain via the cochlear nerve. This produces the sensation of sound.