A radial gradient of fibril density in the gerbil tectorial membrane.

The tectorial membrane plays a key role in the transduction of mechanical to neural energy in the inner ear. To better understand the transduction process the composition of the tectorial membrane needs to be elucidated. This study was done to determine if Type A collagen fibrils are distributed homogeneously in the tectorial membrane or if there are longitudinal or radial gradients of fibril concentrations. Our results suggest that while there is no longitudinal gradient, there is a radial gradient of fibril concentration. The concentration of fibrils in the limbal (inner) zone of the tectorial membrane exceeds that in the marginal (outer) zone in all cochlear locations examined. This gradient is most marked in the basal, high frequency coding region of the cochlea. While fibril gradients in the tectorial membrane have not been the focus of previous investigations, several findings by other authors support the proposition that the marginal zone of the tectorial membrane is more compliant than the limbal zone. This radial gradient of tectorial membrane stiffness is likely to contribute to the characteristics of movement of the cochlear partition.