Named after the Latin word for snail shell, the cochlea is a coiled, tapered tube inside the inner ear, responsible for transmitting sound to the auditory nerve. It consists of three fluid-filled chambers - scala tympani and scala vestibuli (both of which contain perilymph), and scala media (which contains endolymph). The stapes transmits vibrations to the fenestra ovalis (oval window) on the outside of the cochlea, which vibrates the perilymph in scala vestibuli. This in turn vibrates the endolymph in scala media, which causes movement of the basilar membrane between scala media and scala tympani. When the basilar membrane moves, it stimulates hair cells in the organ of Corti, which are connected to the auditory nerve; the auditory nerve transmits sound data to the brain.

See also: Cochlear implant