1.47. Hearing and Balance http://www.ck12.org
No doubt you’ve been warned that listening to loud music or other loud sounds can damage your hearing. It’s true.
In fact, repeated exposure to loud sounds is the most common cause of hearing loss. The reason? Very loud sounds
can kill the tiny hair cells lining the cochlea. The hair cells do not generally grow back once they are destroyed, so
this type of hearing loss is permanent. You can protect your hearing by avoiding loud sounds or wearing earplugs or
other ear protectors.
Balance
Did you ever try to stand on one foot with your eyes closed? Try it and see what happens, but be careful! It’s
harder to keep your balance when you can’t see. Your eyes obviously play a role in balance. But your ears play
an even bigger role. The gymnast pictured below (Figure1.93) may not realize it, but her ears—along with her
cerebellum—are mostly responsible for her ability to perform on the balance beam.
FIGURE 1.93
This gymnast is using the semicircular canals in her ears, along with the
cerebellum in her brain, to help keep her balance on the balance beam.The parts of the ears involved in balance are thesemicircular canals. Above, the semicircular canals are colored
purple (Figure1.92). The canals contain liquid and are like the bottle of water pictured below (Figure1.94). When
the bottle tips, the water surface moves up and down the sides of the bottle. When the body tips, the liquid in the
semicircular canals moves up and down the sides of the canals.
Tiny hair cells line the semicircular canals. Movement of the liquid inside the canals causes the hair cells to
send nerve impulses. The nerve impulses travel to the cerebellum in the brain. In response, the cerebellum sends
commands to muscles to contract or relax so that the body stays balanced.
Vocabulary
- anvil: Second of three tiny bones that pass vibrations through the ear.
- cochlea: Coiled tube filled with liquid inside the inner ear and lined with hairs that detect vibrations.
- ear canal: Tube-shaped opening in the ear.
- eardrum: Thin membrane that vibrates like the head of a drum when sound waves hit it.
- hammer: First of three tiny bones that pass vibrations through the ear.
- hearing: Ability to sense sound.
- oval window: Thin membrane that passes vibrations from the stirrup to the cochlea.
- semicircular canals: Canals inside the ear that are filled with fluid that moves when the head changes position;
helps to maintain the body’s balance. - stirrup: Last of three tiny bones that pass vibrations through the ear.