Effects of spiral geometry of cochlea in hearing sensitivity and audible frequency band inferred from motions of basilar membrane

There exists a controversy whether the spiral geometry of cochlea enhances the hearing sensitivity and extends the audible frequency band in mammal compared to straight cochlea. In order to investigate this issue, two finite element (FE) models based on human cochlea were developed with consideration of fluid-structure interaction. Two FE models differ only in geometry: straight and spiral scalae. Using the developed FE model, the motion of the basilar membranes and flow directions of the scala fluid were computed and compared. The spiral effects were investigated in terms of cochlea input impedance, the velocities of the basilar membranes, the pressure differences between scalae and the particle velocities of scala fluid. In the comparison, some advantages of spiral cochlea were found in hearing sensitivity and audible frequency range especially at lower frequencies.