How do our ears hear?

1. When a bell rings, it shakes back and forth. It pushes and pulls the air around it, and those wiggles spread out in every direction. That is sound!
2. The curvy outer ear catches sound like a funnel and sends it down the ear canal, a short tunnel into your head.
3. At the end of the ear canal is the eardrum, a thin skin stretched tight like a drum. Sound makes it vibrate back and forth.
4. Three tiny bones called the hammer, the anvil and the stirrup pass the vibration along. The stirrup is the smallest bone in your whole body!
5. The stirrup pushes on the cochlea, a snail shell full of fluid. A wave runs along a ribbon inside it. High sounds shake it near the start, and low sounds shake it near the tip.
6. Hair cells in the cochlea bend and send electrical messages along the hearing nerve to your brain. Your brain puts it all together: that's a bell!

Tap each part of the ear. Watch it move when you find it!

• Outer ear. The outer ear, or pinna, is made of bendy cartilage. Its curves catch sound and steer it into the ear canal.
• Ear canal. The ear canal is a short tunnel that carries sound to the eardrum. It makes earwax, which traps dust and keeps the canal clean.
• Eardrum. The eardrum is a very thin skin stretched across the end of the ear canal. It vibrates when sound waves hit it, fast for high sounds and slower for low sounds.
• Three tiny bones. The hammer, anvil and stirrup are the three smallest bones in your body. They pass the eardrum's vibration to the inner ear and make it stronger.
• Cochlea. The cochlea is shaped like a snail shell and filled with fluid. Inside it, a long ribbon vibrates in different places for different pitches: high sounds near the start, low sounds near the tip.
• Hair cells. Thousands of hair cells sit on the ribbon in the cochlea. When the ribbon shakes, their tiny hairs bend, and they send a message to the nerve.
• Hearing nerve. The hearing nerve (auditory nerve) carries the messages from the hair cells to your brain, where they become the sounds you hear.
• Balance loops. Next to the cochlea are three loops filled with fluid. They aren't for hearing: they sense when your head turns, which helps you balance. Spin around and the fluid keeps swirling, which is why you feel dizzy!
• Ear-to-throat tube. The Eustachian tube connects the middle ear to the back of your throat. When you yawn or swallow, it opens and lets air in or out, so the pressure on both sides of your eardrum stays the same. Pop!

Slide the pitch from low to high. Watch the waves, the eardrum and the unrolled cochlea. Press Play sound to hear a gentle tone.

Experiment: Where in the cochlea do high-pitched sounds make the biggest wiggle?

1. Slide the pitch all the way to low. Where does the ribbon wiggle most?
2. Now slide it all the way to high. Where is the wiggle now?
3. Watch the waves too: are they close together or far apart?

What we found: High sounds make the ribbon wiggle most near the start of the cochlea, where it is narrow and stiff. Low sounds travel all the way to the tip, where it is wide and floppy. High sounds also have waves packed close together; low sounds have waves spread far apart.

Turn on JavaScript to try it yourself.

Each sound shakes one part of the cochlea's ribbon the most. Tap the right part for 5 sounds.

Every sound starts with something vibrating: a guitar string, a drum or the vocal cords in your throat. The vibration pushes and pulls on the air, making waves of squeezed and stretched air that spread out. When those waves reach you, your outer ear catches them and sends them down the ear canal.

At the end of the canal, the waves make your eardrum vibrate. Three tiny bones, the hammer, the anvil and the stirrup, pass the vibration along and make it stronger. The stirrup pushes on a little window into the cochlea, a snail-shaped tube filled with fluid.

Inside the cochlea is a long ribbon covered with hair cells. The ribbon is narrow and stiff at the start and wide and floppy at the tip. High sounds shake the start the most, and low sounds shake the tip. The hair cells that bend send messages along the hearing nerve, and your brain works out what the sound is.

Pitch is how many vibrations happen each second. A high whistle vibrates thousands of times a second, while a low drum might vibrate less than a hundred times. Very loud sounds can hurt your hair cells, and they don't grow back, so protect your ears from loud noise.

Key words

Pitch

How high or low a sound is. It depends on how fast the vibration is.

Frequency

The number of vibrations per second, measured in hertz (Hz).

Eardrum

A thin skin at the end of the ear canal that vibrates when sound hits it.

Cochlea

The snail-shaped, fluid-filled part of the inner ear that turns vibrations into nerve messages.

Hair cells

Tiny cells with hairs on top that bend when the cochlea vibrates and send messages to the brain.

Decibel

A unit for how loud a sound is.

Check your thinking

1. What has to happen to make a sound?

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   Something vibrates. Every sound starts with a vibration that shakes the air.

2. Which part of the ear vibrates first when sound arrives?

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   The eardrum. The eardrum vibrates first, then passes the vibration to the three tiny bones.

3. Where in the cochlea do high sounds make the biggest wiggle?

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   Near the start (the base). The start of the ribbon is narrow and stiff, so it shakes best for fast, high vibrations.

4. A big drum makes a low sound. What does that tell you about its vibration?

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   It vibrates slowly. Low sounds come from slow vibrations, with fewer wiggles each second.

5. Why should you protect your ears from very loud sounds?

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   Loud sounds can damage hair cells, and they don't grow back. Hair cells bent too hard can be damaged for good, so cover your ears near very loud noises.

6. Why do you feel dizzy after spinning around?

   Show the answer

   Fluid in the balance loops keeps swirling after you stop. The fluid keeps moving for a moment, so your brain thinks you are still spinning.