Figure 4.

The real and imaginary components of the effective model BM impedance during sound stimulation to the stapes (30 kHz), for three values of OHC motility. (a) Imaginary component, no OHC motility. In basal regions, the imaginary component is stiffness-dominated (negative value), becoming mass-dominated (positive value) apical to the peak, indicating that true resonance occurs apical to the peak (because of the relatively large resistance). At each position from the base, the BM stiffness increases symmetrically to either side of a central minimum, consistent with simple stretching of the BM fibers because of a uniform hydrodynamic load. (b) Imaginary component, normal OHC motility. Small reduction in stiffness basal to the peak, and significant radial asymmetry. (c) Imaginary component, enhanced OHC motility. Further reduction in stiffness beneath the OHCs and pillar cells. Beneath the pillar cells, the position of resonance has moved significantly toward the base. (d) Real component, no OHC motility. The (positive) resistance value is approximately constant along the length of the model. (e) Real component, normal OHC motility. Dramatic changes in value basal to the peak, with a large increase beneath the pillar cells and negative values beneath the OHCs. (f) Real component, enhanced OHC motility. There is a further increase in resistance beneath the pillar cells, and the negative values beneath the OHCs are now smaller than those with normal motility.