Figure 1.

Mechanical connectivity and the equivalent electric circuit of the system examined. The system is driven by changes in hair bundle conductance R_a. Unlike in vivo condition, movement of the cell body does not affect R_a. In the mechanical schematics (A), K is stiffness of the external mechanical load, m is the mass, and positive force F and positive displacement x of the cell are upward. The drag coefficient is η. The contribution of the motile element to cell length is anP, where P, a, and n respectively represent the fraction of the motile elements in the elongated state, unitary length change, and the number of such units, the unitary change of charge of which is q. The stiffness of the cell due to the material property alone is k. The broken line indicates the border of the OHC. In the equivalent circuit (B) of the hair cell, the membrane potential is V, the hair bundle resistance is R_a, the basolateral resistance is R_m, and the total membrane capacitance of the basolateral membrane is C_m, consisting of the structural capacitance C₀ and the contribution of charge movements in the motile element, which depends on the load (described in the section on nonlinear capacitance). The endocochlear potential is e_ec and the potential e_K is due to K⁺ permeability of the basolateral membrane. The apical capacitance is ignored in this model.