哺乳动物低频听觉放大的棘轮机制
A ratchet mechanism for amplification in low-frequency mammalian hearing
摘要：
听觉的灵敏度和频率选择性来自机械感受毛细胞中的主动过程的调谐放大。在大多数脊椎动物中，主动过程源于毛束的主动运动。哺乳动物耳蜗表现出另一种形式的机械活动，称为电运动：其外毛细胞（OHC）在电刺激时改变长度。这两种机制对哺乳动物内耳活动过程的相对贡献是当前激烈辩论的主题。在这里，我们表明，积极的毛束运动性和电运动性可以一起实现一个有效的放大机制，功能就像一个棘轮：声音诱发的力量作用于基底膜被传输到毛束，而电运动性的主动毛束力从基底膜。这种单向耦合可以将听力范围扩展到远低于基底膜的共振频率。因此，它提供了一个低频听力的概念，占各种无法解释的实验观察从耳蜗顶点，包括顶端调谐曲线的形状和相位行为，他们缺乏显着的非线性，以及形状变化的阈值调谐曲线的听觉神经纤维沿耳蜗。棘轮机构构成了在工程应用中实现机械放大的一般设计原理。
英文摘要：
The sensitivity and frequency selectivity of hearing result from tuned amplification by an active process in the mechanoreceptive hair cells. In most vertebrates the active process stems from the active motility of hair bundles. The mammalian cochlea exhibits an additional form of mechanical activity termed electromotility: its outer hair cells (OHCs) change length upon electrical stimulation. The relative contributions of these two mechanisms to the active process in the mammalian inner ear is the subject of intense current debate. Here we show that active hair-bundle motility and electromotility can together implement an efficient mechanism for amplification that functions like a ratchet: sound-evoked forces acting on the basilar membrane are transmitted to the hair bundles whereas electromotility decouples active hair-bundle forces from the basilar membrane. This unidirectional coupling can extend the hearing range well below the resonant frequency of the basilar membrane. It thereby provides a concept for low-frequency hearing that accounts for a variety of unexplained experimental observations from the cochlear apex, including the shape and phase behavior of apical tuning curves, their lack of significant nonlinearities, and the shape changes of threshold tuning curves of auditory nerve fibers along the cochlea. The ratchet mechanism constitutes a general design principle for implementing mechanical amplification in engineering applications.
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