Figure 1. Morphological organization of the inner ear. (a) Different sensory structures of the inner ear. P.C., perilymphatic compartment and E.C., endolymphatic compartment. (b)–(d) Sensory neuroepithelia and accessory structures present in the semicircular canals (b), otolith organs (c) and the cochlea (d). Type I and II hair cells are found in the cristae and maculae; inner (IHCs) and outer (OHCs) hair cells are found in the organ of Corti. In the semicircular canals, the stereocilia are embedded in a gelatinous material called the cupula (b). Movement of the cupula, as a consequence of head rotation (white arrow), results in stereociliar deflection. In the saccule and utricle, the tips of the stereocilia are embedded in the otolith membrane (c), note the presence of several small pebbles called otoliths made of calcium carbonate and proteins. Otolith movement produced by vertical or horizontal head accelerations (white arrows) displaces the otolith membrane, which deflects the stereocilia. In the cochlea (d), sound-induced vibration of the basilar membrane causes a shear force between the tectorial membrane and the inner and outer hair cells, resulting in hair bundle displacement. For clarity, only one afferent or efferent fibre is shown to contact an IHC and OHC. This composite figure has been partially redrawn and reprinted with permission from Hennig Arzneimittel GmbH & Co. KG, Wiesbaden, Germany (www.hennig-arzneimittel.de).