<P> The name cochlea derives from Ancient Greek κοχλίας (kōhlias), meaning' spiral, snail shell' . </P> <P> The cochlea (plural is cochleae) is a spiralled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the oval window) to the apex (the top or center of the spiral). The spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30 mm long and makes 23⁄4 turns about the modiolus . The cochlear structures include: </P> <Ul> <Li> Three scalae or chambers: <Ul> <Li> the vestibular duct or scala vestibuli (containing perilymph), which lies superior to the cochlear duct and abuts the oval window </Li> <Li> the tympanic duct or scala tympani (containing perilymph), which lies inferior to the cochlear duct and terminates at the round window </Li> <Li> the cochlear duct or scala media (containing endolymph) a region of high potassium ion concentration that the stereocilia of the hair cells project into </Li> </Ul> </Li> <Li> The helicotrema, the location where the tympanic duct and the vestibular duct merge, at the apex of the cochlea </Li> <Li> Reissner's membrane, which separates the vestibular duct from the cochlear duct </Li> <Li> The basilar membrane, a main structural element that separates the cochlear duct from the tympanic duct and determines the mechanical wave propagation properties of the cochlear partition </Li> <Li> The Organ of Corti, the sensory epithelium, a cellular layer on the basilar membrane, in which sensory hair cells are powered by the potential difference between the perilymph and the endolymph </Li> <Li> hair cells, sensory cells in the Organ of Corti, topped with hair - like structures called stereocilia . </Li> </Ul> <Li> Three scalae or chambers: <Ul> <Li> the vestibular duct or scala vestibuli (containing perilymph), which lies superior to the cochlear duct and abuts the oval window </Li> <Li> the tympanic duct or scala tympani (containing perilymph), which lies inferior to the cochlear duct and terminates at the round window </Li> <Li> the cochlear duct or scala media (containing endolymph) a region of high potassium ion concentration that the stereocilia of the hair cells project into </Li> </Ul> </Li>

What two things does the cochlea have inside it
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