Suzanne de Bruijn

22 Chapter 1.1 lead to deformation of the cochlear duct. 25 The traveling sound wave propagates from the base towards the apex of the cochlea, until maximum displacement is reached. The site of maximum displacement depends on the sound frequency; higher frequencies only reach the stiffer base of the cochlea while low frequency sounds are perceived in the apex. This is called the tonotopy of the cochlea and serves as amechanical frequency analyzer. 25 A Outer ear Middle ear Inner ear B Pinna External ear canal Tympanic membrane Oval window Auditory ossicles Auditory nerve Cochlea Vestibular system Scala tympani Scala vestibuli Scala media Stria vascularis Inner hair cell Outer hair cell Stereocilia Reissner’s membrane Tectorial membrane Basilar membrane Round window C Pillar cell Deiter cell Hensen cell Nerve fibres Figure 3. Schematic representation of the human ear. (A) An overview of the three anatomical compartments of the ear: the outer, middle and inner. (B) Intersection of the cochlea that contains three fluid-filled chambers: the scala media, the scala tympani and the scala vestibuli. The scala media is filled with potassium-rich endolymph fluid, the scala tympani and vestibuli are filled with sodium-rich perilymph fluid. The scala media houses the sensory epithelium of the inner ear: the organ of Corti. (C) The cellular structures of the organ of Corti. The epithelium contains one row of inner hair cells and three rows of outer hair cells. The hair cells are separated and flanked by different types of supporting cells (Deiter’s, pillar, Hensen’s, inner phalangeal and border cells). The figures are adapted and published with permission from Adobe Stock and Servier Medical Art.