Figure 4.

Modeled responses of a hair bundle to stimulation with a 5-kHz sinusoidal force 0.2 pN in amplitude (Bottom trace). (A) In the active-channel model, the bundle displays oscillations of roughly threshold amplitude upon stimulation. The system’s high Q is revealed by the gradual rise and decline of the response. (B) The response of a similar model without Ca²⁺-induced channel reclosure shows far less amplification and no resonance after stimulation. (C) For a passive model without channel gating, the displacement is roughly the driving force divided by the bundle’s stiffness. In each instance, M_HB = 60 pg, ξ_HB = 100 nN⋅s⋅m⁻¹, K_SP = 9,000 μN⋅m⁻¹, κ_GS = 1,200 μN⋅m⁻¹, N_S = 210, N_T = 184, γ = 0.50, b = 4.5 nm, δ₁₂ = 0.9, δ₃₆ = 0.1, δ₄₅ = 0.1, k_F = 93,500 s⁻¹, k_R = 10,300 s⁻¹, and k₃₆ = 0.88 s⁻¹. The response in B displays an offset of −2.9 nm; the system’s bistability around a resting position at which p_O,REST = 0.5 emerges from fixed-point analysis.