A model for the mechanics of the stereociliar bundle on acousticolateral hair cells

The stereociliar bundle on acousticolateral hair cells was modelled as a series of stiff rods (stereocilia), and springs (stereociliary links and rootlets). Predictions were made for the coupling of stimulus-induced deflections between the stereocilia on the hair bundle, and for the stretches of the different classes of link. Comparison of the results with the measured mechanical properties of hair bundles suggests that in the bullfrog sacculus the stiffness of a side link and a tip link are related to the rootlet's contribution to the stiffness of a stereocilium to deflection in approximately the ratio > or = 400:100:1. The results show that stretch of the tip links is closely related to the deflection of the hair bundle over a wide range of model parameters, while the stretch of the side links is more variable, and in some types of bundle the mean stretch of the side links may be zero or negative. The results are in accordance with the view that the tip links are in an appropriate position to detect the deflections, while the main role for the side links may be to couple the deflections between the stereocilia. The mechanical consequences of bundles of different configurations, as seen in different hair cell types, are investigated.