查看Ch15 Sensory Transduction的源代码

=== 外耳和中耳收集和调节气压波，以便在内耳内进行转导 ===

<b style=color:#0ae>The outer and middle ears collect and condition air pressure waves for transduction within the inner ear</b>

Sound is a perceptual phenomenon that is produced by periodic longitudinal waves of low pressure (rarefactions) and high pressure (compressions) that propagate through air at a speed of 330 to 340 m/s. Absolute sound depends on the amplitude of the longitudinal wave, measured in pascals (Pa). Intensities of audible sounds are commonly expressed in decibel sound pressure level (dB SPL), which relates the absolute sound intensity (PT) to a reference pressure (Pref) of 20 μPa, close to the average human threshold at 2000 Hz.

声音是一种感知现象，由低压（稀疏）和高压（压缩）的周期性纵波产生，这些纵波以 330 至 340 m/s 的速度在空气中传播。绝对声音取决于纵波的振幅，以帕斯卡 (Pa) 为单位。可听声音的强度通常以分贝声压级 (dB SPL) 表示，它将绝对声强 (PT) 与 20 μPa 的参考压力 （Pref） 联系起来，接近 2000Hz 时的平均人类阈值。


The logarithmic scale compresses the wide extent of sound pressures into a convenient range. An increase of 6 dB SPL corresponds to a doubling of the absolute sound pressure level; an increase of 20 dB SPL corresponds to a 10-fold increase.

对数刻度将较宽的声压范围压缩到一个方便的范围内。增加 6 dB SPL 对应于绝对声压级的两倍;增加 20 dB SPL 相当于增加 10 倍。


Sound can be a pure tone of a single frequency, measured in hertz (Hz). Sounds produced by musical instruments or the human voice consist of a perceived fundamental frequency (pitch) and overtones. Sound that is noise contains no recognizable periodic elements. N15-8 Pure tones are used clinically for the determination of hearing thresholds (pure-tone audiogram). Humans do not perceive sounds that have the same sound pressure level but different frequencies as equally loud. The psychoacoustic phon scale accounts for these differences in perception. N15-9

声音可以是单个频率的纯音调，以赫兹 (Hz) 为单位。乐器或人声产生的声音由感知到的基频（音高）和泛音组成。声音，即噪声，不包含可识别的周期性元素[N15-8]。纯音在临床上用于确定听力阈值（纯音听力图）。人类不会将具有相同声压级但不同频率的声音感知为同样响亮的声音。心理声学语音量表解释了这些感知差异[N15-9]。


Sound waves vary in frequency, amplitude, and direction; our auditory systems are specialized to discriminate all three. We can also interpret the rapid and intricate temporal patterns of sound frequency and amplitude that constitute words and music. Encoding of sound frequency and amplitude begins with mechanisms in the cochlea, followed by further analysis in the CNS. To distinguish the direction of a sound along the horizontal plane, the brain compares signals from the two ears.

声波的频率、振幅和方向各不相同;我们的听觉系统专门用于区分这三者。我们还可以解释构成文字和音乐的声音频率和振幅的快速而复杂的时间模式。声音频率和振幅的编码从耳蜗中的机制开始，然后在 CNS 中进一步分析。为了区分声音沿水平面的方向，大脑会比较来自两只耳朵的信号。


All mammalian ears are strikingly similar in structure. The ear is traditionally divided into outer, middle, and inner components (see Fig. 15-17A). We discuss the outer and middle ear here. The inner ear consists of the membranous labyrinth, with both its vestibular and auditory components.

所有哺乳动物的耳朵在结构上都惊人地相似。耳朵传统上分为外部、中部和内部组件（见图 15-17A）。我们在这里讨论外耳和中耳。内耳由膜迷路组成，包括前庭和听觉成分。


Outer Ear Proceeding from outside to inside, the most visible part of the ear is the pinna, a skin-covered flap of cartilage, and its small extension, the tragus. Together, they funnel sound waves into the external auditory canal. These structures, which compose the outer ear, focus sound waves on the tympanic membrane. Many animals (e.g., cats) can turn each pinna independently to facilitate hearing without changing head position. The shapes of the pinna and tragus tend to emphasize certain sound frequencies over others, depending on their angle of incidence. The external ear parts in humans are essential for localization of sounds in the vertical plane. Sound enters the auditory canal both directly and after being reflected; the sound that we hear is a combination of the two. Depending on a sound’s angle of elevation, it is reflected differently off the pinna and tragus. Thus, we hear a sound coming from above our head slightly differently than a sound coming from straight in front of us. The external auditory canal is lined with skin and penetrates ~2.5 cm into the temporal bone, where it ends blindly at the eardrum (or tympanic membrane). Sound causes the tympanic membrane to vibrate, much like the head of a drum.

'''外耳''' 从外到内，耳朵最明显的部分是耳廓，一种覆盖着皮肤的软骨瓣，以及它的小延伸部分，耳屏。它们一起将声波汇入外耳道。这些结构构成外耳，将声波聚焦在鼓膜上。许多动物（例如猫）可以独立转动每个耳廓以促进听力，而无需改变头部位置。耳廓和耳屏的形状往往强调某些声音频率而不是其他声音频率，具体取决于它们的入射角。人类的外耳部件对于声音在垂直平面上的定位至关重要。声音直接进入耳道，并在被反射后进入耳道;我们听到的声音是两者的结合。根据声音的仰角，它在耳廓和耳屏上的反射方式不同。因此，我们听到的声音从头顶传来的声音与从我们正前方传来的声音略有不同。外耳道内衬皮肤，穿透颞骨约 2.5 cm，在鼓膜（或鼓膜）处盲目结束。声音会导致鼓膜振动，很像鼓头。


Middle Ear The air-filled chamber between the tympanic membrane on one side and the oval window on the other is the middle ear (see Fig. 15-17A). The eustachian tube connects the middle ear to the nasopharynx and makes it possible to equalize the air pressure on opposite sides of the tympanic membrane. The eustachian tube can also provide a path for throat infections and epithelial inflammation to invade the middle ear and lead to otitis media. The primary function of the middle ear is to transfer vibrations of the tympanic membrane to the oval window (Fig. 15-19). The key to accomplishing this task is a chain of three delicate bones called ossicles: the malleus (or hammer), incus (anvil), and stapes (stirrup). The ossicles are the smallest bones in the body.

'''中耳''' 一侧鼓膜和另一侧椭圆形窗口之间的充气腔室是中耳（见图 15-17A）。咽鼓管将中耳连接到鼻咽部，可以平衡鼓膜相对两侧的气压。咽鼓管还可以为咽喉感染和上皮炎症提供侵入中耳并导致中耳炎的途径。中耳的主要功能是将鼓膜的振动传递到椭圆形窗口（图 15-19）。完成这项任务的关键是一连串的三块称为听小骨的精致骨头：锤骨、砧骨和镫骨（马镫）。听小骨是体内最小的骨骼。

[[文件:Physiology-ch15-19.png]]

Vibration transfer is not as simple as it might seem because sound starts as a set of pressure waves in the air (within the ear canal) and ends up as pressure waves in a watery cochlear fluid within the inner ear. Air and water have very different acoustic impedances, which is the tendency of each medium to oppose movement brought about by a pressure wave. N15-10 This impedance mismatch means that sound traveling directly from air to water has insufficient pressure to move the dense water molecules. Instead, without some system of compensation, >97% of a sound’s energy would be reflected when it met a surface of water. The middle ear serves as an impedance-matching device that saves most of the aforementioned energy by two primary methods. First, the tympanic membrane has an area that is ~20-fold larger than that of the oval window, so a given pressure at the air side (the tympanic membrane) is amplified as it is transferred to the water side (the footplate of the stapes). Second, the malleus and incus act as a lever system, which again amplifies the pressure of the wave. Rather than being reflected, most of the energy is successfully transferred to the liquids of the inner ear.

振动传递并不像看起来那么简单，因为声音从空气中（耳道内）中的一组压力波开始，到内耳内水样耳蜗液中的压力波结束。空气和水具有非常不同的声阻抗，这是每种介质与压力波带来的运动相反的趋势。N15-10 这种阻抗失配意味着直接从空气传播到水中的声音没有足够的压力来移动致密的水分子。相反，如果没有某种补偿系统，当声音遇到水面时，>97% 的能量会被反射。中耳作为阻抗匹配设备，通过两种主要方法节省大部分上述能量。首先，鼓膜的面积比椭圆窗的面积约大 20 倍，因此空气侧（鼓膜）的给定压力在转移到水侧（镫骨的脚板）时被放大。其次，锤骨和砧骨充当杠杆系统，再次放的压力。大部分能量没有被反射，而是成功地转移到内耳的液体中。


Two tiny muscles of the middle ear, the tensor tympani and the stapedius, insert onto the malleus and the stapes, respectively. These muscles exert some control over the stiffness of the ossicular chain, and their contraction serves to dampen the transfer of sound to the inner ear. They are reflexively activated when ambient sound levels become high. These reflexes are probably protective and may be particularly important for suppression of self-produced sounds, such as the roar you produce in your head when you speak or chew.

中耳的两块微小肌肉，鼓膜张肌和镫骨肌，分别插入到锤骨和镫骨上。这些肌肉对听骨链的刚度施加了一些控制，它们的收缩有助于抑制声音向内耳的传递。当环境声级变高时，它们会反射性地激活。这些反射可能具有保护作用，对于抑制自身产生的声音可能特别重要，例如您说话或咀嚼时在脑海中发出的咆哮。

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