The complexity of the mammalian auditory system and the process of mechanotransduction reflects the underlying genetic complexity of hearing. (a) A cross-section through a mammalian cochlea, illustrating the fluid-filled scalae that transmit sound impulses to the organ of Corti, the neuroepithelium where the process of mechanotransduction takes place and sound is converted into neural signals. The organ of Corti consists of one row of inner hair cells and three rows of outer hair cells (illustrated in pink) that are overlaid by the tectorial membrane (yellow). (b) A scanning electron micrograph (courtesy of Charlotte Rhodes) illustrating the regular arrays of stereocilia that project from the surface of outer and inner hair cells in the organ of Corti. (c) As sound impulses travel down the cochlea, movement of the organ of Corti causes deflection of the stereocilia. Tip links connect adjacent stereocilia and are believed to link ion channels in one stereocilium to the tip of the adjacent stereocilium. Movement of the stereocilia results in an increase in tension on the tip-links and the gating of the ion channels, leading to cation influx from the endolymph of the scala media, hair-cell depolarization, and the transmission of a neural impulse to the brain via the spiral ganglion - the process of mechanotransduction.