Permeability of fluid flow through hair cell cilia

Models (∠400×) were constructed of the one row of inner hair cell cilia bundles and the three row array of ’’w’’ shaped outer hair cell cilia bundles found in the mammalian cochlea. These were placed between parallel plates simulating the under surface of the tectorial membrane and the upper surface of the reticular lamina. The pressure required to produce a given volume of flow through the obstacles was measured. For low flow rate, the behavior is linear, i.e., the ratio of flow rate to pressure drop (permeability) is independent of flow rate. For higher flow rates (Reynold’s number Λ?0.08) the behavior is nonlinear, characterized by an increase in the effective permeability to a maximum at Λ∠10 and an asymmetry in the flow through the OHC cilia bundles. Interpretation in terms of cochlear function is beyond the scope of the present work. A very tentative estimate places the onset of nonlinearity at around 80 dB SPL, so the flow around the cilia bundles in the cochlea is linear for normal intensity levels.