Fig. 4.

Comparison of the extended model with experimental results. (A) Power spectra portray the responses of an actual hair bundle in a control preparation (red) and after the tip links have been severed by BAPTA (blue). (B) The power spectra predicted for the series viscoelastic model accord with the experimental results. The parameter values used to fit this experimental power spectrum are listed in the caption of Fig. 2. (C) The complex viscoelastic modulus can be determined from measurements of a hair bundle’s thermal fluctuations and provides a valuable alternative view of the rheological properties. Because we set the geometric factor to identity, the resulting quantity, a proxy for the modulus and a visualization of the linear response function, is a complex spring constant with units of newtons per meter. The real part of the modulus (continuous lines), which represents the hair bundle’s elasticity, is shown under control conditions (red) and after scission of the tip links by BAPTA (blue). The corresponding imaginary part of the modulus (dotted lines) reflects the hair bundle’s viscosity. The shaded areas represent 95% confidence intervals obtained by bootstrapping. (D) The complex modulus predicted for an extended model with series viscoelasticity resembles the observations under both experimental conditions.