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152 How Ears Work THE OUTER EAR—the part you see—catches sound waves. It’s shaped like a funnel, catching noise and q Crickets use organs in their knees to listen. sending it down the ear canal Fish respond to sound through ridges on their to the eardrum. Sound waves bodies, and snakes use their cause the eardrum to vibrate. tongues. Humans, Three small bones in the of course, have middle ear then pass these ears. vibrations on to the cochlea, a fluid-filled structure of the inner ear. The cochlea contains liquid that moves like a wave in response to sounds. The cochlea is also lined with microscopic hairs that move, creating nerve signals that are sent to the brain, which makes sense of the sounds we hear. FACTSWAX The skin cells of the outer ear contain tiny glands that produce wax that protects the ears by trapping dirt and other things in the ear. The wax slowly works its way out of the ear. 152_09Kids_Ears 4/28/09 11:22 AM Page 153

153 ANATOMY OF THE EAR HEALTH INNER MIDDLE OUTER EAR

G B I

ND H SOU

F E C D A

A external auditory canal F eustachian tube B eardrum G semicircular canals that house the C hammer receptors for equilibrium D anvil H cochlea (houses the receptors for hearing) E stapes (stirrup) I nerve that transmits impulses to the brain The hammer, anvil, and stirrup pass along vibrations. q Did You Know? approx. actual size The smallest bone in the human body is the stapes, or stirrup. It’s 0.10 to 0.13 inch long and weighs 1.9 to 4.3 milligrams.

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154 Take Care of Y

You have two, but one will never work as well as the pair.

q Never play your headset volume too loud.

In a Dizzy Daze Have you ever felt dizzy after spinning? Three small loops in your inner ear called semicircular canals are filled with fluid and covered with microscopic hairs, just like the cochlea. Whenever you move your head, the fluid in these canals moves, too. Spinning makes you dizzy because the fluid in the canals continues to spin after you stop. You feel dizzy until the fluid stops moving.

the Pop Can’t Stop Whenever you change altitude (fly in an airplane or travel a mountain road), the air pressure inside your ear changes. This pressure is regulated by the eustachian tube, which connects the middle ear with the back of the nose. This tube helps to equalize pressure on both sides of the eardrum. Whenever it opens, you hear a pop. 152_09Kids_Ears 4/29/09 9:10 AM Page 155

155 off Your Ears HEALTH

Heard Any Good e Earworms Lately? e

Don’t be alarmed! An earworm is not an insect; it’s a song such as “Who Let the Dogs Out?,” “YMCA,” or “It’s a Small World After All” that you can’t get out of your head once you hear it. The term comes from the German word for the problem, Ohrwurm.

Shore It Is . . . The next time you’re at the ocean, hold a large seashell to your ear. People say that you’ll hear ocean waves or the blood traveling in your ears. Wrong! You hear the sounds around you bouncing off the inside of the shell.

q Wear earplugs or special earmuffs when you’re around loud noises.

q Never put anything—a cotton swab, pen, or pencil, for instance—in your ear. You could puncture your eardrum.

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