**1. Introduction**

The whole inner ear or the cochlea, responsible for hearing perception, can be described as unique sense organ, including the organ of Corti and the inner ear endo- and perilymph. The fluid homeostasis of the lymph spaces with its parameters volume, concentration, osmolarity and pressure corresponds to the specific necessities for adequate response to continuous stimulation and the outstanding discrimination capacity of the hearing system. Discrimination of loudness is regulated mainly by discharge intensity of stimulus transmission, rhythm by discharge duration and discrimination of frequency and tone colour timbre by harmonized fine regulation of the geometrically and functionally aligned hearing structures along the cochlear duct. Surrounded by endolymph, the inner and outer hair cells with their distinct

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

geometrically arranged finger-like processes, the stereocilia, are the mechanoelectrical transducers of the mechanoreceptor organ ear. The complex afferent and efferent innervation of the hair cells respond to further fine processing of the hearing stimulus. In this context, the efferent innervation supplies further qualities, in particular noise protection, mediation of selective attention and improvement of signal-to-noise ratio. It also supports adaptation and frequency selectivity by modification of the micromechanical properties of the outer hair cells. The past five decades of molecular biological research involved immense achievements in understanding of the physiological and biochemical mechanisms leading to current geneticbased, nanotechnology-based and stem cell research [1, 2].
