查看Ch15 Sensory Transduction的源代码

=== 听觉毛细胞的频率灵敏度取决于它们沿耳蜗基底膜的位置 ===

<b style=color:#0ae>The frequency sensitivity of auditory hair cells depends on their position along the basilar membrane of the cochlea</b>

The subjective experience of tonal discrimination is called pitch. Young humans can hear sounds with frequencies from ~20 to 20,000 Hz. N15-13 This range is modest by the standards of most mammals because many hear up to 50,000 Hz, and some, notably whales and bats, can hear sounds with frequencies >100,000 Hz.

声调辨别的主观体验称为音高。年轻人可以听到频率在 20 ~ 20,000 Hz 之间的声音[N15-13]。以大多数哺乳动物的标准来看，这个范围是适中的，因为许多哺乳动物听到的声音高达 50,000 Hz，而有些动物，特别是鲸鱼和蝙蝠，可以听到频率> 100,000 Hz 的声音。


A continuous pure tone (see p. 376) produces a wave that travels along the basilar membrane and has different amplitudes at different points along the base-apex axis (Fig. 15-24A). Increases in sound amplitude cause an increase in the rate of action potentials in auditory nerve axons—rate coding. N15-14 The frequency of the sound determines where along the cochlea the cochlear membranes vibrate most—high frequencies at one end and low at the other— and thus which hair cells are stimulated. This selectivity is the basis for place coding in the auditory system; that is, the frequency selectivity of a hair cell depends mainly on its longitudinal position along the cochlear membranes. The cochlea is essentially a spectral analyzer that evaluates a complex sound according to its pure tonal components, with each pure tone stimulating a specific region of the cochlea.

连续的纯音（见第 376 页）产生一个沿基底膜传播的波，并在沿基顶点轴的不同点具有不同的振幅（图 15-24A）。声音振幅的增加会导致听觉神经轴突中动作电位速率的增加——速率编码[N15-14]。声音的频率决定了耳蜗膜在耳蜗上振动最剧烈的位置（一端高频，另一端低频），从而决定了哪些毛细胞受到刺激。这种选择性是听觉系统中位置编码的基础;也就是说，毛细胞的频率选择性主要取决于其沿耳蜗膜的纵向位置。耳蜗本质上是一个频谱分析器，它根据其纯音调成分评估复杂的声音，每个纯音都刺激耳蜗的特定区域。

[[文件:Physiology-ch15-24.png]]

Using optical methods to study cadaver ears, Georg von Békésy found that sounds of a particular frequency generate relatively localized waves in the basilar membrane and that the envelope of these waves changes position according to the frequency of the sound (see Fig. 15-24B). Low frequencies generate their maximal amplitudes near the apex. As sound frequency increases, the envelope shifts progressively toward the basal end (i.e., near the oval and round windows). For his work, von Békésy N15-15 received the 1961 Nobel Prize in Physiology or Medicine.

使用光学方法研究死体的耳朵，Georg von Békésy 发现特定频率的声音在基底膜中产生相对局部的波，并且这些波的包络根据声音的频率改变位置（见图 15-24B）。<b style=color:#f80>低频</b>在<b style=color:#f80>顶点 (apex) </b>附近<b style=color:#0b0>产生最大振幅</b>。随着声音频率的增加，包络逐渐向基端移动（即靠近椭圆形和圆形窗口）。由于他的工作，von Békésy [N15-15] 获得了 <b>1961 年诺贝尔生理学或医学奖</b>。

Two properties of the basilar membrane underlie the low-apical to high-basal gradient of resonance: taper and stiffness (see Fig. 15-24C). If we could unwind the cochlea and stretch it straight, we would see that it tapers from base to apex. The basilar membrane tapers in the opposite direction—wider at the apex, narrower at the base. More important, the narrow basal end is ~100-fold stiffer than its wide and floppy apical end. Thus, the basilar membrane resembles a harp. At one end—the base, near the oval and round windows—it has short, taut strings that vibrate at high frequencies. At the other end—the apex—it has longer, looser strings that vibrate at low frequencies. Although von Békésy’s experiments were illuminating, they were also paradoxical. A variety of experimental data suggested that the tuning of living hair cells is considerably sharper than the broad envelopes of von Békésy’s traveling waves on the basilar membrane could possibly produce. N15-16 Recordings from primary auditory nerve cells are also very sharp, implying that this tuning must occur within the cochlea, not in the CNS. Some enhancement of tuning comes from the structure of the inner hair cells themselves. Those near the base have shorter, stiffer stereovilli, which makes them resonate to higher frequencies than possible with the longer, floppier stereovilli on cells near the apex. The blue curve in Figure 15-25 approximates von Békésy’s envelope of traveling waves for a passive basilar membrane from cadavers. It is important to note that von Békésy used unnaturally loud sounds. With reasonable sound levels, the maximum passive displacement of the basilar membrane would be slightly more than 0.1 nm. This distance is less than the pore diameter of an ion channel and also less than the threshold (0.3 to 0.4 nm) for an electrical response from a hair cell. However, measurements from the basilar membrane in living animals (the orange curve in Fig. 15-25) by very sensitive methods show that movements of the basilar membrane are much more localized and much larger than predicted by von Békésy. The maximal physiological displacement is ~20-fold greater than threshold and ~40-fold greater than that predicted by the passive von Békésy model. Moreover, the physiological displacement decays sharply on either side of the peak, >100-fold within ~0.5 mm (recall that the human basilar membrane has a total length of >30 mm).

基底膜的两个特性是共振的低顶端到高基底梯度的基础：锥度和刚度（见图 15-24C）。如果我们能解开<b style=color:#f80>耳蜗</b>并将其伸直，我们会看到它<b style=color:#0b0>从基部到顶端逐渐变细</b>。<b style=color:#f80>基底膜</b>向相<b style=color:#0b0>反方向逐渐变细</b> --- 顶端较宽，基部较窄。更重要的是，<b style=color:#f80>狭窄的基端</b>比其宽而松软的<b>顶端</b><b style=color:#0b0>硬约 100 倍</b>。因此，<b style=color:#f80>基底膜</b>类似于竖琴。在一端 --- <b style=color:#f80>底座</b>，靠近椭圆形和圆形窗口 --- 它有<b style=color:#0b0>短而紧</b>的琴弦，在高频下振动。在另一端 --- <b style=color:#f80>顶点 (apex)</b> --- 它有<b style=color:#0b0>更长更松散的琴弦，在低频下振动</b>。尽管 von Békésy 的实验具有启发性，但它们也是自相矛盾的。各种实验数据表明，活毛细胞的调谐比基底膜上 von Békésy 行波的宽包络可能产生的要尖锐得多[N15-16]。来自初级听觉神经细胞的记录也非常清晰，这意味着这种调整必须发生在耳蜗内，而不是在 CNS 中。调音的一些增强来自<b style=color:#f80>内毛细胞</b>本身的结构。那些<b style=color:#f80>靠近基部的</b><b style=color:#0b0>具有</b><b style=color:#e00>更短、更硬的立体绒毛</b>，这使它们比靠近顶点单元上较长、更松软的立体绒毛<b style=color:#0b0>能产生更高的频率共振</b>。图 15-25 中的蓝色曲线近似于尸体被动基底膜的 von Békésy 行波包络。值得注意的是，von Békésy 使用了不自然的响亮声音。在合理的声级下，基底膜的最大被动位移将略大于 0.1nm。该距离小于离子通道的孔径，也小于毛细胞电响应的阈值（0.3 ~ 0.4nm）。然而，通过非常敏感的方法对活体动物的基底膜（图 15-25 中的橙色曲线）进行的测量表明，基底膜的运动比 von Békésy 预测的要局限得多，也大得多。最大生理位移比阈值约大 20 倍，比被动 von Békésy 模型预测的约大 40 倍。此外，生理位移在峰的两侧急剧衰减，在约 0.5mm 内 > 100 倍（回想一下，人耳基底膜的总长度为 >30 mm）。


Both the extremely large physiological excursions of the basilar membrane and the exquisitely sharp tuning of the cochlea depend on the cochlear amplifier (see p. 380). Indeed, selectively damaging outer hair cells—with large doses of certain antibiotics, for example—considerably dulls the sharpness of cochlear tuning and dramatically reduces the amplification.

基底膜的极大生理偏移和耳蜗的精致尖锐的调谐都取决于耳蜗放大器（见第 380 页）。事实上，选择性地破坏外毛细胞（例如，使用大剂量的某些抗生素，比如奎宁 quinine）会大大减弱人工耳蜗调谐的清晰度，并显着降低放大功能。

[[文件:Physiology-ch15-25.png]]

The brain can control the tuning of hair cells. Axons that arise in the superior olivary complex in the brainstem synapse mainly on the outer hair cells and, sparsely, on the afferent axons that innervate the inner hair cells. N15-17 Stimulation of these olivocochlear efferent fibers suppresses the responsiveness of the cochlea to sound and is thought to provide auditory focus by suppressing responsiveness to unwanted sounds—allowing us to hear better in noisy environments (Box 15-2). The main efferent neurotransmitter is acetylcholine (ACh), which activates ionotropic ACh receptors (see pp. 206–207)—nonselective cation channels—and triggers an entry of Ca2+. The influx of Ca2+ activates Ca2+-activated K+ channels, causing a hyperpolarization—effectively an inhibitory postsynaptic potential—that suppresses the electromotility of outer hair cells and action potentials in afferent dendrites. Thus, the efferent axons allow the brain to control the gain of the inner ear.

大脑可以控制毛细胞的调整。出现在脑干突触上橄榄复合体中的轴突主要在外毛细胞上，稀疏地出现在支配内毛细胞的传入轴突上[N15-17]。刺激这些橄榄耳蜗传出纤维会抑制耳蜗对声音的反应，并被认为通过抑制对不需要的声音的反应来提供听觉焦点 —— 让我们在嘈杂的环境中听得更清楚（框 15-2）。主要的传出神经递质是乙酰胆碱 （ACh），它激活离子型 ACh 受体（参见第 206-207 页）—— 非选择性阳离子通道 —— 并触发 Ca2+ 的进入。Ca2+ 的流入激活了 Ca2+ 激活的 K+ 通道，导致超极化 —— 实际上是一种抑制性突触后电位 —— 从而抑制了外毛细胞的电动性和传入树突中的动作电位。因此，传出轴突允许大脑控制内耳的增益。


<b style=color:#f80>N15-18</b>
Conductive Hearing Loss  传导性听力损失, Contributed by Philine Wangemann

Conductive hearing losses are disorders that compromise the conduction of sound through the external ear, tympanic membrane, or middle ear. Pressure differences across the tympanic membrane (eardrum) can rupture it. Accumulations of fluid in the middle ear can lead to conductive hearing losses that are seen particularly often in children with middle ear infections (otitis media). With proper treatment, the hearing loss due to otitis media is usually self-limited. Otosclerosis, which stiffens the ossicular chain, is another common cause of conductive hearing loss.

传导性听力损失是影响声音通过外耳、鼓膜或中耳传导的疾病。鼓膜（鼓膜）的压力差可能导致鼓膜破裂。中耳积液会导致传导性听力损失，这在中耳感染（中耳炎）的儿童中尤其常见。通过适当的治疗，中耳炎引起的听力损失通常是自限性的。耳硬化症使听骨链变硬，是传导性听力损失的另一个常见原因。

Treatments for conductive hearing loss encompass a palette of devices including hearing aids and middle ear implants. Hearing aids amplify the sound in the external ear canal. Prosthetic devices can replace the tympanic membrane and the ossicular chain. Middle ear implants are clamped onto the incus and enhance the vibrations of the ossicular chain.

传导性听力损失的治疗包括各种设备，包括助听器和中耳植入物。助听器放大外耳道中的声音。假体装置可以替代鼓膜和听骨链。中耳植入物夹在砧骨上并增强听骨链的振动。

<br>