Timing of the reticular lamina and basilar membrane vibration in living gerbil cochleae.
Timing of the reticular lamina and basilar membrane vibration in living gerbil cochleae.
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作者：
He W;Kemp D;Ren T
听觉感觉外毛细胞被认为通过反馈机制放大声音诱导的基底膜振动，以提高听力敏感度。为了获得最佳的放大效果，外毛细胞产生的力量必须在每个周期的适当时间作用于基底膜。然而，外毛细胞驱动的网状板振动和基底膜振动之间的时间关系尚不清楚。通过使用定制的外差低相干干涉仪直接测量外毛细胞的亚纳米振动，我们在活的沙土鼠耳蜗中证明了网状板振动发生在基底膜振动之后，而不是之前。单音和短声诱发的反应都表明，网状板和基底膜在耳蜗基底部以相反的方向振动，它们在最佳频率位置附近同步振荡。我们的结果表明，外毛细胞通过全局流体力学机制而不是通常认为的局部机械反馈来提高听力敏感度。耳朵能探测到的最安静的声音是什么？所有的声音都是从振动的空气分子开始的，空气分子进入耳朵并导致耳膜振动。我们可以探测到鼓膜移动不到一皮米的振动。这是千分之一纳米，或者说大约比一个氢原子小100倍。但耳朵如何达到这种程度的敏感度呢？鼓膜的振动会导致中耳内的三块小骨头振动。然后振动传播到内耳的一个充满液体的螺旋结构--耳蜗处。排列在耳蜗线上的微小毛细胞由于振动而移动。有两种类型的毛细胞：内毛细胞和外毛细胞。外毛细胞放大了这种振动。正是这种放大使我们能够检测到鼓膜的如此微小的运动。然后，内毛细胞将放大的振动转化为电信号，电信号通过听神经传递到大脑。外毛细胞的底部连接到一种称为基底膜的结构上，而它们的顶部固定在一种称为网状板的结构上。一般认为，外毛细胞通过局部正反馈机制放大基底膜的振动，该机制要求毛细胞首先振动。但通过比较沙土鼠网状板和基底膜振动的时间，他等人。证明事实并非如此。外毛细胞在基底膜之后振动，而不是在之前。这表明，外毛细胞使用一种不同于通常假设的局部反馈的机制来放大声音。他等人给出的结果。改变我们对耳蜗如何工作的理解，并可能帮助生物工程师设计更好的助听器和耳蜗植入物。全世界数百万遭受听力损失的患者最终可能会受益。
Auditory sensory outer hair cells are thought to amplify sound-induced basilar membrane vibration through a feedback mechanism to enhance hearing sensitivity. For optimal amplification, the outer hair cell-generated force must act on the basilar membrane at an appropriate time at every cycle. However, the temporal relationship between the outer hair cell-driven reticular lamina vibration and the basilar membrane vibration remains unclear. By measuring sub-nanometer vibrations directly from outer hair cells using a custom-built heterodyne low-coherence interferometer, we demonstrate in living gerbil cochleae that the reticular lamina vibration occurs after, not before, the basilar membrane vibration. Both tone- and click-induced responses indicate that the reticular lamina and basilar membrane vibrate in opposite directions at the cochlear base and they oscillate in phase near the best-frequency location. Our results suggest that outer hair cells enhance hearing sensitivity through a global hydromechanical mechanism, rather than through a local mechanical feedback as commonly supposed. What is the quietest sound the ear can detect? All sounds begin as vibrating air molecules, which enter the ear and cause the eardrum to vibrate. We can detect vibrations that move the eardrum by a distance of less than one picometer. That’s one thousandth of a nanometer, or about 100 times smaller than a hydrogen atom. But how does the ear achieve this level of sensitivity? Vibrations of the eardrum cause three small bones within the middle ear to vibrate. The vibrations then spread to the cochlea, a fluid-filled spiral structure in the inner ear. Tiny hair cells lining the cochlea move as a result of the vibrations. There are two types of hair cells: inner and outer. Outer hair cells amplify the vibrations. It is this amplification that enables us to detect such small movements of the eardrum. Inner hair cells then convert the amplified vibrations into electrical signals, which travel via the auditory nerve to the brain. The bases of outer hair cells are connected to a structure called the basilar membrane, while their tops are anchored to a structure called the reticular lamina. It was generally assumed that outer hair cells amplify vibrations of the basilar membrane via a local positive feedback mechanism that requires the hair cells to vibrate first. But by comparing the timing of reticular lamina and basilar membrane vibrations in gerbils, He et al. show that this is not the case. Outer hair cells vibrate after the basilar membrane, not before. This indicates that outer hair cells use a mechanism other than commonly assumed local feedback to amplify sounds. The results presented by He et al. change our understanding of how the cochlea works, and may help bioengineers to design better hearing aids and cochlea implants. Millions of patients worldwide who suffer from hearing loss may ultimately stand to benefit.