[Stiffness gradient of the basilar membrane and tonotopia in the internal ear of mammals].

A comparison of calculated and experimental frequency-coordinate characteristics shows that the basilar membrane should be considered as a plate where the transverse stiffness exceeds considerably the longitudinal one. The change of density of fibril packing towards the apex must be taken into account for determination of stiffness in the middle and apical parts of cochlea. In the species investigated the frequency maps in the middle part of cochlea have a low-slope segment which midpoint coincides with the optimum hearing frequency of the given species.