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== 前庭和听觉转导：毛细胞 ==

VESTIBULAR AND AUDITORY TRANSDUCTION: HAIR CELLS

Balancing on one foot and listening to music both involve sensory systems that have similar transduction mechanisms. Sensation in both the vestibular and auditory systems begins with the inner ear, and both use a highly specialized kind of receptor called the hair cell. Common structure and function often suggest a common origin, and indeed, the organs of mammalian hearing and balance both evolved from the lateral line organs present in all aquatic vertebrates. The lateral line consists of a series of pits or tubes along the flanks of an animal. Within each indentation are clusters of sensory cells that are similar to hair cells. These cells have microvilli-like structures that project into a gelatinous material that in turn is in contact with the water in which the animal swims. The lateral line is exquisitely sensitive to vibrations or pressure changes in the water in many animals, although it is also sensitive to temperature or electrical fields in some species. Reptiles abandoned the lateral line during their evolution, but they retained the hair cell– centered sensory structures of the inner ear that evolved from the lateral line.

单脚平衡和听音乐都涉及具有相似转导机制的感觉系统。前庭和听觉系统的感觉都从内耳开始，两者都使用一种称为毛细胞的高度专业化的受体。共同的结构和功能通常表明一个共同的起源，事实上，哺乳动物的听觉和平衡器官都是从所有水生脊椎动物中存在的侧线器官进化而来的。侧线由沿动物侧面的一系列凹坑或管子组成。每个凹痕内都有类似于毛细胞的感觉细胞簇。这些细胞具有微绒毛状结构，这些结构投射到凝胶状材料中，而凝胶状材料又与动物游泳的水接触。在许多动物中，侧线对水中的振动或压力变化非常敏感，尽管在某些物种中它也对温度或电场敏感。爬行动物在进化过程中放弃了侧线，但它们保留了从侧线进化而来的以毛细胞为中心的内耳感觉结构。


The vestibular system generates our sense of balance and the auditory system provides our sense of hearing. Vestibular sensation operates constantly while we are awake and communicates to the brain the head’s orientation and changes in the head’s motion. Such information is essential for generating muscle contractions that will put our body where we want it to be, reorienting the body when something pushes us aside (vestibulospinal reflexes), and moving our eyes continually so that the visual world stays fixed on our retinas even though our head may be nodding about (vestibuloocular reflexes). N15-4 Vestibular dysfunction can make it impossible to stabilize an image on our moving retinas, and it causes the disconcerting feeling that the world is uncontrollably moving around—vertigo. Walking and standing can be difficult or impossible. With time, compensatory adjustments are made as the brain learns to substitute more visual and proprioceptive cues to help guide smooth and accurate movements.

前庭系统产生我们的平衡感，听觉系统提供我们的听觉。当我们清醒时，前庭感觉不断运作，并将头部的方向和头部运动的变化传达给大脑。这些信息对于产生肌肉收缩至关重要，这将使我们的身体处于我们想要的位置，当有东西将我们推到一边时重新定位身体（前庭脊髓反射），以及不断移动我们的眼睛，以便视觉世界保持在我们的视网膜上，即使我们的头可能在点头（前庭脑膜反射）。N15-4 前庭功能障碍会导致我们无法稳定我们移动的视网膜上的图像，并导致世界不受控制地移动的令人不安的感觉——眩晕。行走和站立可能很困难或不可能。随着时间的推移，随着大脑学会用更多的视觉和本体感觉线索来代替，以帮助指导平稳和准确的运动，就会进行代偿性调整。


Auditory sensation is often at the forefront of our conscious experience, unlike vestibular information, which we rarely notice unless something goes wrong. Hearing is an exceptionally versatile process that allows us to detect things in our environment, to precisely identify their nature, to localize them well at a distance, and, through language, to communicate with speed, complexity, nuance, and emotion.

听觉感觉通常处于我们意识体验的最前沿，这与前庭信息不同，除非出现问题，否则我们很少注意到它。听觉是一个非常通用的过程，它使我们能够检测环境中的事物，精确识别它们的性质，在远处很好地定位它们，并通过语言以速度、复杂性、细微差别和情感进行交流。


'''Bending the stereovilli of hair cells along one axis causes cation channels to open or to close'''

沿一个轴弯曲毛细胞的立体绒毛会导致阳离子通道打开或关闭

Hair cells are mechanoreceptors that are specialized to detect minuscule movement along one particular axis. The hair cell is an epithelial cell (see pp. 43–45); the hair bundles project from the apical end, whereas synaptic contacts occur at the basal end. Hair cells are somewhat different in the vestibular and auditory systems. In this section, we illustrate concepts mainly with the vestibular hair cell (Fig. 15-15A), which comes in two subtypes. Vestibular type I cells have a bulbous basal area, surrounded by a calyx-shaped afferent nerve terminal (see Fig. 15-15B, left). Vestibular type II hair cells are more cylindrical and have several simple, boutonshaped afferent nerve terminals (see Fig. 15-15B, right). Auditory hair cells also come in two varieties, inner hair cells and outer hair cells (see pp. 378–380). However, all hair cells sense movement in basically the same way.

毛细胞是专门用于检测沿一个特定轴的微小运动的机械感受器。毛细胞是上皮细胞（见第 43-45 页）;发束从顶端伸出，而突触接触发生在基底端。前庭和听觉系统中的毛细胞略有不同。在本节中，我们主要用前庭毛细胞（图 15-15A）来说明概念，它有两种亚型。前庭 I 型细胞具有球状基部区域，周围环绕着花萼状传入神经末梢（见图 15-15B，左）。前庭 II 型毛细胞更圆柱形，有几个简单的钮扣形传入神经末梢（见图 15-15B，右）。听觉毛细胞也有两种类型，内毛细胞和外毛细胞（见第 378-380 页）。然而，所有毛细胞都以基本相同的方式感知运动。


As part of their hair bundles, vestibular hair cells (see Fig. 15-15B) have one large kinocilium, which is a true cilium with the characteristic 9 + 2 pattern of microtubules (see Fig. 2-11C). The role of the kinocilium is unknown. In mammals, auditory hair cells lose their kinocilium with maturity.

作为毛束的一部分，前庭毛细胞（见图 15-15B）有一个大的肌纤毛，它是一个真正的纤毛，具有微管的特征性 9 + 2 模式（见图 2-11C）。肌基纤毛的作用尚不清楚。在哺乳动物中，听觉毛细胞会随着成熟而失去纤毛。


Both vestibular and auditory hair cells have 50 to 150 stereovilli, which are filled with actin and are more akin to microvilli. The stereovilli—often called stereocilia, although they lack the typical 9 + 2 pattern of true cilia—are 0.2 to 0.8 μm in diameter and are generally 4 to 10 μm in height. These “hairs” are arranged in a neat array. In the vestibular system, the kinocilium stands tallest along one side of the bundle and the stereovilli fall away in height to the opposite side (see Fig. 15-15B). Stereovilli are narrower at their base and insert into the apical membrane of the hair cell, where they make a sort of hinge before connecting to a cuticular plate. Within the bundle, stereovilli are connected one to the next, but they can slide with respect to each other as the bundle is deflected side to side. The ends of the stereovilli are interconnected with very fine strands called tip links, which are visible by electron microscopy.

前庭和听觉毛细胞都有 50 到 150 个立体绒毛，它们充满了肌动蛋白，更类似于微绒毛。立体绒毛（通常称为立体纤毛，尽管它们缺乏真纤毛的典型 9 + 2 模式）直径为 0.2 至 0.8 μm，高度通常为 4 至 10 μm。这些 “头发” 排列整齐。在前庭系统中，肌束一侧的纤毛最高，而立体绒毛的高度下降到另一侧（见图 15-15B）。立体绒毛的基部较窄，并插入毛细胞的顶膜，在连接到表皮板之前，它们在那里形成一种铰链。在线束内，立体绒毛彼此相连，但当线束左右偏转时，它们可能会相互滑动。立体绒毛的末端与称为尖端链节的非常细的链相互连接，这些链可以通过电子显微镜看到。

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