Power dissipation in the sub-tectorial space of the mammalian cochlea modulated by inner hair cell stereocilia
Friday, September 26, 2014
The stereocilia bundle is the mechano-transduction apparatus of the inner ear. In the mammalian cochlea, the stereocilia bundles are situated in the subtectorial space (STS) – a micrometer-thick space between two flat surfaces vibrating relative to each other. Because microstructures vibrating in fluid are subject to high viscous friction, previous studies considered the STS as the primary place of energy dissipation in the cochlea. While there have been extensive studies on how metabolic energy is used to compensate the dissipation (amplifying the vibrations of the cochlear epithelium), much less attention has been paid to the mechanism of energy dissipation. Using a computational model, we investigated the power dissipation in the STS. The model simulates fluid flow around the inner hair cell (IHC) stereocilia bundle. The results show that the presence of the IHC stereocilia in the STS increases the power dissipation. The power dissipation in the STS due to the presence IHC stereocilia decreased as the stimulating frequency increased. Along the axis of the stimulating frequency, there were two asymptotic values of power dissipation. At low stimulating frequencies, the power dissipation was dominated by the viscous friction around the IHC stereocilia bundle. At high stimulating frequencies, the power dissipation was determined by the shear friction between the two flat surfaces of the STS. There exists a characteristic frequency for STS power dissipation that defines the transition between these two extremes. The IHC stereocilia stiffness and the gap size between the IHC stereocilia and the tectorial membrane determine the characteristic frequency. In addition to the generally assumed shear flow, non-shear STS flow patterns were simulated. Different flow patterns have little effect on the CFSTS. When the mechano-transduction of the IHC was tuned near the vibrating frequency, the active motility of the IHC stereocilia bundle reduced the power dissipation in the STS.