How the Human Cochlea Moves: Biomechanical Modeling of a Wide, Layered Osseous Spiral Lamina

The human cochlear partition (CP) at the high-frequency region features a radially wide, layered osseous spiral lamina (OSL) and a soft-tissue bridge connecting it to the basilar membrane (BM). The OSL consists of two thin bony plates separated by a cavernous space that serves as a conduit for auditory nerve fibers. We used a finite element model with two fluid chambers, incorporating novel implementations of the CP features, to study the human cochlea. Model results were compared with experimental measurements of CP motion.

Model geometrical and material properties either came from the literature or were tuned to produce a frequency-place map for the passive human cochlea and measurements of the CP velocity normalized to the stapes velocity in human cadaver temporal bones. The best frequency (BF) for the experimental measurements' seven specimens ranged from 9.5 to 14.4 kHz.

The model motion results of the basal CP had similar trends to the experimentally measured results in both magnitude and phase. Sensitivity analysis studies changing material-property parameters of the nerve-fiber layer between the OSL plates produced small changes and showed negligible stress along a neutral axis compared to the outer OSL plates.

Our model, which incorporated human cochlear structures like the wide OSL with a layer sandwiched between the plates for auditory nerve fibers, successfully simulated CP motion, exhibiting trends that closely resembled experimental data. The relatively wide three-layered OSL structure's neutral axis may serve as a stress-free conduit for the passage of auditory nerve fibers.