Hearing | 听觉

📚 Hearing | 听觉

Hearing is one of the five main senses and allows us to detect sound waves in the environment. Sound is produced by vibrating objects and travels as longitudinal waves through a medium such as air. The human ear converts these vibrations into electrical signals that the brain interprets as sound. Understanding how hearing works helps us protect our ears and explains why different animals hear different ranges of sound.

听觉是五种主要感觉之一，使我们能够探测环境中的声波。声音由振动的物体产生，并以纵波的形式通过空气等介质传播。人耳将这些振动转化为电信号，由大脑解读为声音。了解听觉的工作原理有助于保护耳朵，也解释了为什么不同动物能听到不同范围的声音。

1. What Is Sound? | 什么是声音？

Sound is a form of energy produced when an object vibrates. These vibrations disturb nearby air particles, creating regions of high pressure called compressions and low pressure called rarefactions. The disturbance travels away from the source as a longitudinal wave.

声音是物体振动时产生的一种能量形式。这些振动扰动附近的空气粒子，形成高压区（压缩）和低压区（稀疏）。扰动以纵波的形式从声源向外传播。

In a longitudinal wave, particles vibrate in the same direction as the wave travels. Sound cannot travel through a vacuum because there are no particles to pass on the vibration.

在纵波中，粒子沿波传播的方向振动。声音不能在真空中传播，因为没有粒子来传递振动。

The speed of sound depends on the medium. In air at room temperature, sound travels at about 343 metres per second. It travels faster in liquids and even faster in solids because particles are closer together.

声音的速度取决于介质。在室温空气中，声音传播速度约为343米每秒。在液体中传播更快，在固体中更快，因为粒子之间的距离更近。

v = f × λ

The relationship between speed (v), frequency (f) and wavelength (λ) is shown above. Frequency is measured in hertz (Hz), wavelength in metres (m), and speed in metres per second (m/s).

声速（v）、频率（f）与波长（λ）之间的关系如上所示。频率以赫兹（Hz）为单位，波长以米（m）为单位，速度以米每秒（m/s）为单位。

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2. The Human Ear: An Overview | 人耳概览

The human ear has three main parts: the outer ear, the middle ear and the inner ear. Each part plays a different role in collecting, transmitting and detecting sound vibrations.

人耳由三个主要部分组成：外耳、中耳和内耳。每个部分在收集、传递和探测声音振动方面发挥着不同的作用。

The outer ear collects sound waves and directs them to the eardrum. The middle ear amplifies the vibrations. The inner ear changes vibrations into nerve impulses that travel to the brain.

外耳收集声波并将其引导至鼓膜。中耳放大振动。内耳将振动转化为神经冲动，传向大脑。

The key structures can be grouped as follows. The outer ear includes the pinna and ear canal. The middle ear includes the eardrum and ossicles. The inner ear includes the cochlea and auditory nerve.

关键结构可分类如下：外耳包括耳廓和耳道；中耳包括鼓膜和听小骨；内耳包括耳蜗和听神经。

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3. The Outer Ear | 外耳

The outer ear consists of the visible part called the pinna or auricle, and the ear canal. The pinna is shaped to collect sound waves from a wide area and funnel them into the ear canal.

外耳包括可见部分（称为耳廓或耳壳）和耳道。耳廓的形状有助于从较大范围收集声波，并将其导入耳道。

The ear canal is a tube about 2.5 centimetres long in adults. It carries sound waves to the eardrum and also produces earwax, which traps dust and protects the ear from infection.

成人耳道约2.5厘米长。它将声波传至鼓膜，同时产生耳垢，耳垢能粘住灰尘并保护耳朵免受感染。

The eardrum, also called the tympanic membrane, is a thin, tightly stretched sheet of tissue at the end of the ear canal. When sound waves reach it, it vibrates back and forth at the same frequency as the sound.

鼓膜又称耳膜，是耳道末端一层薄而紧绷的组织。当声波到达鼓膜时，它会以与声音相同的频率前后振动。

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4. The Middle Ear | 中耳

The middle ear is an air-filled cavity behind the eardrum. It contains three tiny bones called ossicles: the malleus (hammer), incus (anvil) and stapes (stirrup). They are the smallest bones in the human body.

中耳是鼓膜后方充满空气的空腔。它包含三块叫作听小骨的小骨：锤骨、砧骨和镫骨。它们是人体中最小的骨头。

The ossicles form a chain that links the eardrum to the oval window of the inner ear. When the eardrum vibrates, the malleus moves first, then the incus, then the stapes.

听小骨形成一条链条，将鼓膜与内耳的卵圆窗连接起来。当鼓膜振动时，锤骨先动，然后砧骨，最后镫骨。

This chain of bones acts as a lever system that amplifies the force of the vibration by about 1.5 to 2 times. The oval window has a much smaller area than the eardrum, which further increases the pressure, by about 20 times overall.

这条骨链起到杠杆系统的作用，将振动力放大约1.5至2倍。卵圆窗的面积比鼓膜小得多，进一步增加了压力，总体约增加20倍。

The middle ear is connected to the throat by the Eustachian tube. This tube equalises air pressure on both sides of the eardrum, which is why swallowing or yawning can make your ears pop.

中耳通过咽鼓管与咽喉相连。该管平衡鼓膜两侧的气压，这就是为什么吞咽或打哈欠会让耳朵发出砰的一声。

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5. The Inner Ear and Cochlea | 内耳与耳蜗

The inner ear contains the cochlea, a coiled, fluid-filled tube shaped like a snail shell. It is the part of the ear where mechanical vibrations are converted into electrical nerve signals.

内耳包含耳蜗，它是一个充满液体、像蜗牛壳一样盘旋的管道。耳蜗是将机械振动转化为电神经信号的部位。

When the stapes pushes on the oval window, it creates pressure waves in the fluid inside the cochlea. These waves travel through the fluid and make the basilar membrane vibrate.

当镫骨推动卵圆窗时，会在耳蜗内的液体中产生压力波。这些波在液体中传播并使基底膜振动。

Along the basilar membrane are thousands of hair cells. Different parts of the basilar membrane respond best to different frequencies. High-frequency sounds cause vibrations near the base of the cochlea, while low-frequency sounds affect the apex.

基底膜上排列着数千个毛细胞。基底膜的不同部位对不同频率的反应最佳。高频声音在耳蜗底部附近引起振动，而低频声音影响蜗顶。

The hair cells have tiny hair-like projections called stereoc

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