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Exploration: Make a muscle model.

Cut the index card in half. Drawarm bones and label them. Punchthree holes in each half, as shown.

Fasten the cards together withthe paper fastener. Tie a ribbon toeach hole on the lower arm bone,and then thread them through theholes on the upper arm bone.

Pull on the loose end of oneribbon at a time. Observe what happens.

Now design your own model of an arm muscle. Forexample, how could you use empty paper towel tubes?What else would you need?

Try your model out and make any alterations youthink might improve it.

I n t e r p ret your re s u l t s .• What happened to the “bones” when you pulled the

“muscles” in your model?

• Do arm muscles push or pull? Do they both work at thesame time?

• How would your arm work if it had only one muscle?

• Did your model teach you anything else about your muscles?

Communicate your re s u l t s .• Write up your exploration and invite a family

member to try it.

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What Makes Your Body Move?Your skeleton allows your body to move, but what makes

it move? Your muscles. Some muscles are “voluntary.” Theyare the ones you control, the ones that let you exercise—orrelax. Some muscles are “involuntary.” They just do theirjob with no effort on your part—like your heart muscles.How do you think muscles make your body move?

Tendons

Muscles

You have no musclesin your fingers andtoes. Look at thispicture and see ifyou can tell whatmoves your toes.

Biceps musclecontracted

▲

Biceps musclerelaxed

Biceps

Biceps

Triceps

Triceps

Exploration Connection:Your muscles

What muscles immediately come to mindwhen you think of your own body? Your bodyhas muscles wherever your bones can move.

Some muscles are near the surface, likethose that move your arms and legs. You canfeel them tense and bulge as you move. Somea re deep inside you, like the diaphragm and ribmuscles that help you breathe, or the stomachand intestinal muscles that push food along asit is digested.

Muscles are unusual tissues that can changethe energy in their cells to pulling power. Mostmuscles are attached to bones by strong whitecords called tendons. One end of the tendon isattached to the muscle, the other end to the bone. Muscles move bones by pulling on tendons.

Muscle movement is controlled by nerves which, in turn, are controlled by signals from the brain. At the right signal, the long, thin cells inside the muscle become shorter and thicker. As themuscle shortens, it pulls the bone it is attachedto forward.