Figure 1.

Schematic diagram of the active-channel model. Each transduction channel is posited to exist in either a closed form, C, or an open one, O. Application of a positive stimulus force to the hair bundle promotes channel opening, whereas binding of Ca²⁺ favors closure. The rate constants for reactions in the counterclockwise direction are designated k_F, those pertaining to the clockwise direction k_R, and those for the two central transitions k₃₆. During sinusoidal stimulation or limit-cycle oscillation, the occupancy of the channel’s six states cycles in the counterclockwise direction.