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Power Efficiency of Outer Hair Cell Somatic Electromotility

Figure 7

Power conversion efficiency.

A) The taxonomy of electrical to mechanical power conversion efficiency delineating regions where input electrical power is lost to series-elastic piezoelectric coupling, OHC stiffness, fluid viscosity, entrained mass, and OHC intracellular axial electrical resistance for a 28 µm long cell. Results are shown under control conditions when the base of the OHC has a high impedance (solid red, cross-hatch, high Z_b), and under conditions of low basal impedance associated with the action of efferent neurotransmitter on the base of the OHC (dashed green, diagonal hatch, low Z_b). The peak efficiency occurs at a best frequency , and shifts down in magnitude and up in frequency with opening of conductive ion channels in the basal cell membrane (, ). Hence, shunting of the basal impedance by efferent action on OHCs is predicted to attenuate their power output at best frequency , by well over an order of magnitude. B) The most efficient frequency depends upon cell length. Shorter cells show peak efficiencies at higher frequencies (10 µm) while longer cells show peak efficiencies at lower frequencies (80 µm). These predictions were computed by adjusting the load to be impedance matched at each frequency (peak efficiency load in Fig. 6 denoted by *).

doi: https://doi.org/10.1371/journal.pcbi.1000444.g007