Mechanical properties of the tectorial membrane in situ.

According to the classical model of cochlear hair-cell stimulation, the tectorial membrane moves in cross-section like a stiff beam, rotating around the lip of the spiral limbus. This produces a shearing motion against the reticular lamina and, as a result, a radial deflection of the hair-cell stereocilia. The deflection can be effectively produced by the tectorial membrane only if its stiffness in the radial direction is greater than that of the stereocilia. We were able to manipulate the tectorial membrane through a scala-media access in live Mongolian gerbils and to measure its transverse and radial stiffness. We found the membrane to behave like a rubber band and to be much less stiff than the stereocilia. This is incompatible with the classical model. The tectorial membrane must act on the stereocilia as a mass load rather than a stiff anchor.