Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Compr Physiol. 2017 Sep 12;7(4):1197-1227. doi: 10.1002/cphy.c160049.
Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via submicrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower end of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell's characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses. © 2017 American Physiological Society. Compr Physiol 7:1197-1227, 2017.
冲击耳朵的声压波动被传递到耳蜗，在那里它们使基底膜振动，而基底膜上则排列着毛细胞，这是内耳的机械感受器。毛细胞电反应的记录表明，它们通过毛细胞束的亚微米级偏转而将声音转换，毛细胞束是由相互连接的静纤毛组成的阵列，其中包含机械电换能器（MET）通道。MET 通道被桥接相邻静纤毛的细胞外尖端连接的张力激活，它们可以在几微秒内对束的纳米级位移做出反应，这得益于 Ca2+依赖的适应的多个过程。对小鼠突变体的研究提供了大量关于静纤毛、尖端连接及其附着位点的分子组织的详细信息，以及定位于每个尖端连接下端的 MET 通道。哺乳动物耳蜗包含两类毛细胞。内毛细胞通过多个传递快速而无衰减的带状突触传递声信息。外毛细胞对于放大声音引起的振动很重要。放大机制主要涉及外毛细胞的收缩，这是由膜电位的变化驱动的，并由外毛细胞侧向膜中的运动蛋白 prestin 介导。不同的声音频率沿着耳蜗分离，每个毛细胞都调谐到一个狭窄的频率范围；放大作用提高了频率分辨率，并在外毛细胞特征频率周围将灵敏度提高了 100 倍。遗传突变和环境因素（如声音过度刺激）会通过对毛细胞的不可逆损伤或内毛细胞突触的退化而导致听力损失。© 2017 美国生理学会。综合生理学 7:1197-1227,2017。
