Download Skeletal Muscles— Move That Body!

Skeletal Muscles—Move That Body!
Skeletal Muscles—
Move That Body!
Your body is packed full of muscles. In fact, muscles make up
about half of your weight. Some muscles are large and thick, like
those that lift your legs. Others are small and thin, like those that
control your eyes. Some muscles work inside you day and night to
deliver materials around your body. But all muscles have one thing
in common—they move!
Muscle Contraction
All muscles are made of special cells that allow them to move.
Muscle cells can contract, or squeeze together, to become shorter
and thicker. When the cells contract, they can do work. If every
muscle cell in your body contracted at once, they could lift 25 tons!
Muscle cells are grouped into separate muscles. Each muscle is
responsible for specific movements. There are about 656 muscles in
your body, and more than 600 of them move your skeleton. These
are called skeletal muscles.
Skeletal muscles are the muscles you use to climb the stairs, wash
your hair, or chew your food. Most things you do during the day
require skeletal muscles. Let’s take a closer look at how these
muscles work.
When muscles contract, they get
shorter and thicker.
Muscle Connections
Skeletal muscles connect to your bones by tendons. Tendons are
strong, flexible cords. They often attach one end of a muscle to a
bone that is stable. The other end attaches to a part that can move—
when the muscle contracts, it pulls the movable part toward it.
You can feel some of your tendons. Let one arm hang down at your
side, palm forward. Bend your arm slightly and use your other hand
to press inside the bend in your elbow. Can you feel a tough cord?
This tendon connects your biceps muscle to bones in your lower
arm. Another tendon connects the upper end of the biceps to your
shoulder bone.
These arm muscles attach to bones
by tendons (shown in blue).
Muscles Working Together
Skeletal muscles often work in pairs. When one contracts, the other
relaxes. Muscles can only pull bones; they can’t push them. So
muscles on different sides of a bone pull it in different directions.
Discovery Education Science
© 2007 Discovery Communications, LLC
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Skeletal Muscles—Move That Body!
Now let’s check out how some muscles in your arm move. Place
your left hand on your right biceps and bend and straighten your
elbow. Can you feel your biceps contracting and relaxing?
Did you notice that when you contract, or flex, your biceps feels
shorter and thicker? This causes your lower arm bone to move up. A
muscle on the back of your arm (your triceps) contracts to
straighten it back out. Hold your arm very straight—can you feel
your triceps tightening?
Your muscles work hard to move your body, so it’s important to
keep them strong and healthy by exercising and eating right. Did
you know that your muscles are about 75 percent water? Most of
the remaining part is made of protein. Drinking plenty of water and
eating protein-rich foods, like nuts and meat, will help keep your
muscles in tip-top shape!
Discovery Education Science
Your biceps and triceps work
as a team to move your lower
arm.
© 2007 Discovery Communications, LLC
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