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Unit 19: Biology Part 2 Page 74 of 137
organs that control hearing, which
is the ability to detect sound. Ears
also sense the position of the body
and help maintain balance when
you walk a balance beam or ride a
bike.
Imagine a pebble being dropped
into a lake. Waves of water go off
in all directions. A similar thing
happens when a car driving down
Figure 59 – Although modern the street honks its own. Waves
bifocals look more stylish than go off from the car in all direction.
these Benjamin Franklin-style The difference is that these are not
glasses, they still use the same waves of water, but instead are
basic idea. sound waves, which travel through
the air. If you are nearby, some of
Today, some people with vision those sound waves make it to your
problems choose to have surgery ear.
called LASIK. In this surgery, a
laser changes the shape of the The pinna, or outer ear, which is
cornea correcting the vision the part of your ear that you can
problem. As a result, the person see, gathers up some of the sound
usually no longer needs to wear waves, sends them down the ear
glasses or contacts. canal, and eventually they strike
the eardrum. The eardrum is a
Hearing and Balance thin membrane that vibrates like a
drum when the waves hit it. The
It may seem like walking across a vibrations pass three tiny bones,
balance beam and listening to your called the hammer, anvil, and
favorite song are very different stirrup, as well as a membrane
activities, but they both depend on called the oval window, causing
your ears. Ears are the sense them all to vibrate.
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