Abstract
As the ear's sensory receptors, hair cells detect sound vibrations via their hair bundles. A recent experimental report shows that efferent nerve activation can reduce hair bundle sensitivity, potentially protecting hair cells from loud sounds. In mammals, hair cells do not regenerate, making this protective mechanism crucial. However, the intrinsic dynamic mechanisms remain unknown. This paper integrates a model of the hair bundle, hair cell, and efferent nerve to reproduce the experimental observations initially. Then, the complex nonlinear mechanism for the reduced response is obtained with bifurcation analysis. The inhibitory synaptic current from the efferent nerve, when activated, causes a reduction in the membrane potential of the hair cell. This reduction further induces a decrease in the amplitude and an increase in the frequency of the mechanical oscillations of the hair bundle. Activation of the efferent nerve induces the appearance of weakened response or reduced sensitivity. Finally, feasible indicators to characterize sensitivity and measures to reduce sensitivity to enhance protection ability are obtained. The sensitivity is affected by oscillation patterns. Modulations of calcium concentration, conductance of electromechanical coupling current, or activation to efferent nerve are proposed to reduce sensitivity. The results present theoretical explanations to the protection function of the efferent nerve, potential measures to enhance the hearing protection ability, and a candidate coupling model to study these complex dynamics. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11571-025-10349-4.