Organ of Corti Micromachine Enables Hair Bundles to Deform the Stiff Basilar Membrane

Abstract

The organ of Corti (OC) is a highly organized structure in the mammalian cochlea that houses the sensory hair cells. It is believed that the OC functions to optimize force transmission from the outer hair cell (OHC) to the basilar membrane and the inner hair cell. Recent studies reveal that the OC cannot be considered as a rigid body and has a complex mode of deformation. We developed a 3-D finite element model of the OC to dissect its mechanics. Geometric and mechanical information was taken from the gerbil cochlea at 2 and 10 mm from the stapes, positions encoding high and low frequencies respectively, and in each case several hundred microns longitudinal extent was simulated. The model included all structurally significant components: OHCs, pillar cells, Deiters cells and reticular lamina. The model was validated by reproducing experimental results on point stiffness and longitudinal space constant measured at the basilar membrane and response to current steps through the OC. Deformation of the OC by two different active OHC forces (the OHC somatic force and the stereociliary-based force) was then simulated. A surprising result was that despite smaller magnitude, the stereociliary-based force (0.1and 0.7 nN at apex and base) was nearly as effective as the somatic force (10 nN) in displacing the basilar membrane. The results also suggested that for the active forces to work efficiently the radial stiffness of the tectorial membrane must be comparable to or greater than the hair bundle stiffness. Funded by NIH RO1 DC01362.