The inner hair cell stereocilia bundle performs the role of transducer in mammalian hearing. Acoustic stimuli deflect the hair bundle to open ion channels, resulting in cation influx and the subsequent release of a neurotransmitter at the base of the cell. Hypotheses for this transduction include fluid shear-driven motion between the tectorial membrane and the reticular lamina to deflect the bundle. It is presumed that 'molecular gates' sense tension in tip-links that connect adjacent stepped rows of stereocilia to open the channels. However, almost nothing is known about the endolymphatic flow in the micron-sized gap surrounding the bundle and the nanoscale sized gaps between individual stereocilia rows and between individual bundles. Here we show with nanometer resolution, how each row of stereocilia, their associated tip links and gates and the corresponding flow patterns move in response to acoustical input.
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