Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA, USA.
Department of Physics & Astronomy, University of Southern California, Los Angeles, CA, USA.
J Assoc Res Otolaryngol. 2023 Apr;24(2):129-145. doi: 10.1007/s10162-022-00884-w. Epub 2023 Feb 1.
The cochlea of the mammalian inner ear includes an active, hydromechanical amplifier thought to arise via the piezoelectric action of the outer hair cells (OHCs). A classic problem of cochlear biophysics is that the RC (resistance-capacitance) time constant of the hair-cell membrane appears inconveniently long, producing an effective cut-off frequency much lower than that of most audible sounds. The long RC time constant implies that the OHC receptor potential-and hence its electromotile response-decreases by roughly two orders of magnitude over the frequency range of mammalian hearing, casting doubt on the hypothesized role of cycle-by-cycle OHC-based amplification in mammalian hearing. Here, we review published data and basic physics to show that the "RC problem" has been magnified by viewing it through the wrong lens. Our analysis finds no appreciable mismatch between the expected magnitude of high-frequency electromotility and the sound-evoked displacements of the organ of Corti. Rather than precluding significant OHC-based boosts to auditory sensitivity, the long RC time constant appears beneficial for hearing, reducing the effects of internal noise and distortion while increasing the fidelity of cochlear amplification.
哺乳动物内耳的耳蜗包括一个活跃的、液力机械放大器，据认为它是通过外毛细胞（OHC）的压电作用产生的。耳蜗生物物理学的一个经典问题是，毛细胞膜的 RC（电阻-电容）时间常数显得很不方便长，产生的有效截止频率远低于大多数可听声音的频率。长的 RC 时间常数意味着 OHC 感受器电位，因此它的电动响应，在哺乳动物听觉的频率范围内大约降低了两个数量级，这使得基于 OHC 的循环放大在哺乳动物听觉中的假设作用受到质疑。在这里，我们回顾了已发表的数据和基础物理知识，以表明通过错误的视角来看待“RC 问题”已经被夸大了。我们的分析发现，高频电动性的预期幅度与 Corti 器官的声诱发位移之间没有明显的不匹配。长的 RC 时间常数并没有排除对听觉灵敏度的显著 OHC 增强，而是有助于听觉，减少了内部噪声和失真的影响，同时提高了耳蜗放大的保真度。
