The inner ear of the human ear consists of cochlea and vestibular organ. The base of the cochlea borders on the middle ear with the auditory ossicles. The stapes is in contact with the so-called oval window (fenestra vestibuli or fenestra ovalis), behind which the scala vestibuli is located, which is connected to the scala tympani on the end (apex) of the cochlea via the helicotrema. The basis of the scala tympani borders on the round window which can vibrate freely. Therefore, pressure on the oval window, caused by vibration of the auditory ossicles, can be compensated by stretching of the round window. The scala media is separated from the scala vestibuli by Reissner`s membrane, and from the scala tympani by the basilar membrane. Scala vestibuli and scala tympani are filled with perilymph, which can be exchanged via the helicotrema. The scala media contains endolymph. These two fluids have a fundamentally different composition.