www.readinga-z.com

Get Moving!All About Muscles

A Reading A–Z Level U Quick Reader

Word Count: 2,002

QQ UU II CC KK RR EE AA DD EE RR •• UU

Visit www.readinga-z.com for thousands of books and materials.

Written by Lisa Trumbauer

Get Moving! All About MusclesLevel U Quick Reader© 2004 Learning Page, Inc.Written by Lisa Trumbauer

ReadingA–ZTM

© Learning Page, Inc.

All rights reserved.

Learning Page1630 E. River Road #121Tucson, AZ 85718

www.readinga-z.comwww.readinga-z.com

Written by Lisa Trumbauer

CorrelationLEVEL U

Fountas & Pinnell QReading Recovery 24

DRA 40

Photo Credits:Front cover, back cover, pages 3, 5 (stop watch), 6 (art), 7, 8, 10, 11, 12, 14 (art), 15, 19, 20, 24 : © ArtToday; Title page: © Neal Preston/CORBIS;page 4: © Royalty-Free/CORBIS; page 5, 9: Craig Frederick/© LearningPage,Inc.; page 13: © PICIMPACT/CORBIS; page 16: © Bettmann/CORBIS; page18: David Gates/© LearningPage, Inc.; page 21: © Royalty-Free/CORBIS

43

Table of Contents

A Moving Machine . . . . . . . . . . . . . . . . . . . . . . . . . .4

Muscle Monster . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Make a Muscle—the Skeletal Muscles . . . . . . . . . . .8

Mirror, Mirror . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Don’t Think About It—the Smooth Muscles . . . . .14

One More—the Cardiac Muscle . . . . . . . . . . . . . . .16

A Closer Look . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Muscle Building . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

A Moving Machine

Have you ever walked by a gym and watchedpeople lifting weights? Maybe you even haveweight training in school. Running, bending,twisting—these are all forms of training your bodyand “shaping up.” But what, exactly, are you

training? What areyou shaping? What isall this lifting andgrunting andstraining about? It’sabout your muscles.

Muscles are thepart of the body thatallows you to move.If you didn’t havemuscles, youwouldn’t be able tolift or jump or walk,or even write or smileor chew. Yourmuscles make yourbody a moving

machine. Shaping up, or getting into shape, meansshaping your muscles so they are strong andpowerful. Strong, powerful muscles make yourbody move more efficiently.

This woman lifts weights to keepher arm muscles in shape.

65

Muscle Monster

This scary creature isn’tthe latest creepy moviemonster, or even an oddballsuperhero. Actually, thiscreature is you. It’swhat you look like,under your skin, withall your skeletalmuscles in place. The dark, stringy-looking things arethe muscles, andthe whitish partsare the tendons.Tendons are fibersthat attach musclesto bones.

You can’t see any bones in this diagram,can you? That’s becausemuscles cover the bonesand are attached to them.The muscles literally pickup the bones, like those inyour arms and legs, andmake them move.

The human body is loaded with muscles of manydifferent sizes—more than 600 muscles in all.Although all muscles help your body move, musclesare divided into three main types: the skeletalmuscles, the smooth muscles, and the cardiacmuscle. Two of these muscle types—the smoothmuscles and the cardiac muscle—are involuntarymuscles. That means that they move on their own,without us telling them to move. Skeletal muscles,on the other hand, are voluntary, which means theymove because we want them to. Most of the musclesin your body are skeletal muscles.

So let’s get moving, and see what the skeletalmuscles are all about.

A Muscle MinuteYou’re getting ready to turn the page,aren’t you? As you do, think of all themuscles you use just to do this one, smalltask. Muscles liftyour arm, andmuscles move yourhand and fingers,which enable youto flip the page.You could say that muscles madeyou do it!

This iswhat yourbody lookslike underyour skin.

87

Make a Muscle—the Skeletal Muscles

Have you ever asked anyone to “feel yourmuscle”? What did you do? You probably made a fist, lifted your forearm toward your shoulder,and pointed to the bulge that formed on yourupper arm. Good job! You’ve just provided a goodexample of how muscles work.

When youpulled your armupward, themuscle in yourupper arm, the biceps,contracted. Itpulled on thebone, causing

your forearmto lift. Youcan feel the

contractedbiceps muscle

bulging underyour skin.

Although muscles allow us to do all kinds ofmovements, pulling is the only movement thatmuscles themselves can do.

Here’s how these muscles work. If you want to move, you form the thought in your brain. Your brain then sends a signal to the musclesneeded to make themovement you arethinking about. Youmight wiggle yourtoes, or snap yourfingers, or even liftyour eyebrows.

Once the signalreaches the muscles,your muscles beginto move. Eachmuscle pulls on thebone to which it isattached, and thispulling puts yourbody in motion.Because your brainmust tell thesemuscles to move,these movementsare voluntary. Thevoluntary musclesare your skeletalmuscles. Your brain tells your leg muscles

to kick a ball.

The biceps muscle contracts to pull up the forearm.

➡biceps muscle

109

Muscles in your legs move your legs in a similarway as the muscles in your arms. Try this: sitdown, stretch out your leg, and feel the top of yourthigh. The muscle you feel here is the quadriceps(KWAD-ri-seps), which enables you to lift your leg.If you bend your knee toward you, you might feela muscle on the back of your thigh. This is thehamstring, which makes your knee bend.

A big muscle bulges on your lower leg, at theback. You might call this your calf muscle, but itsmore scientific name is the gastrocnemius (gas-trahk-NE-mee-us). Stand up, and lift your footbehind you. This is the function of the calfmuscle—to pull up the heel of your foot.

In order for you to lower your arm, anothermuscle must get into action. This muscle is thetriceps muscle, and it lies on the underside of yourupper arm. When you lower your arm, the bicepsmuscle relaxes, and the triceps muscle contracts—itpulls your forearm down.

In most cases, therefore, your muscles mustwork as a team. One muscle pulls, or contracts, sothat you can move in one way, then another musclemust pull, or contract, so your body can move inthe opposite way.

quadricepshamstring

calfmuscle

sartorius

Achillestendon

gluteusmaximus

Muscles work as a team so this man can lift the box.

A Muscle MinuteThe deltoid muscles in

the shoulders lift the arms.The trapezius (treh-PE-zee-us)muscles are near the neck,and they lift theshoulders. The bicepsand triceps movethe lower arm.deltoids

triceps

trapezius

Runners use their leg muscles.

biceps

Mirror, Mirror

Take a look at yourself in the mirror, and makea bunch of funny faces. Wiggle your eyebrows,move your lips, blink your eyes. How is your faceable to make all these expressions? Once again,your skeletal muscles made you do it.

In fact, the muscles of your eye are the mostactive muscles in your body. Scientists think thatthese muscles move more than 100,000 times a day.

The skull is the bone that makes up most ofyour head, and it is largely covered with muscles.Only one bone on your face actually moves—yourjaw, or the mandible (MAN-deh-behl). Only twomuscles on your face are needed to raise and loweryour jaw. The temporalis is connected to yourtemple, and the masseter (ma-SEET-her) isconnected to your cheekbone.

Run your hand down from the back of your calfto the top of your heel. Do you feel that flexible part,just above your ankle? This is actually a tendon,called the Achilles (eh-KIL-eez) tendon. It is yourbody’s longest and strongest tendon, connectingyour calf muscle to the bone in your heel.

A few other important muscles are found in yourlegs, such as the sartorius (sahr-TO-reeus). It isyour body’s longest muscle, and it is responsiblefor allowing your leg to twist and bend at the

knee. Then there’s thebiggest muscle of all—thegluteus maximus

(GLEWT-ee-usMAK-seh-mus). This is the musclethat you feel in

your butt.

12

A Muscle MinuteAchilles was a warrior

in Greek myth whose onlyweak spot was his heel.The tendon that connectsthe calf muscle to the heel bone is called theAchilles tendon after him.

11

Your jaw muscles help you bite and chew food.

The sartorius muscle allows this runner’s knee to bend so she canstretch her leg muscles.

Don’t Think About It—the Smooth Muscles

Every time you eat, you set a variety of musclesinto motion. A few of those muscles are skeletal,because they move your jaw up and down. Other

muscles move insideyour body to helpmove food throughyour system. Thesemuscles movewithout anyinstructions fromyou. Moving all ontheir own, orinvoluntarily, thesemuscles are calledsmooth muscles.

Smooth musclesare generallysmaller and thinnerthan skeletalmuscles. They areresponsible for the

small ways in which the organs inside your bodymove. Smooth muscles push food to your stomach,then smooth muscles push food from your stomachinto your intestines. Eventually, smooth musclespush the unused food out of your body.

So what do theother muscles on yourface move? They moveother muscles, whichare attached to theskull. As the musclesmove under your skin,your face showsdifferent expressions.

For example, somemuscles of your facehelp you to smile andfrown. Muscles thathelp you smile areattached to yourcheekbone on one end and to your lips on theother. When the muscles contract, your lipsmove up. Other muscles are attached to the chinand the lips. These muscles pull your lips downinto a frown.

1413

A Muscle MinuteHow many muscles are needed to make

you smile? 17! That’s nothing, though, compared tohow many muscles are needed to form a frown—40!That’s more than double the amount needed to smile. So it really does take less effort to smile than to frown.

Involuntary muscles keep your food moving through your body.

This man is a champion ofmaking his face muscles movein unusual ways.

stomach

inte

stine

s

esophagus

One More—the Cardiac Muscle

Your body has one more type of muscle, and itis the only one of its kind. It is the cardiac muscle,or your heart. Like the smooth muscles, your heartmuscle is always in motion, even though you

haven’t asked it to doanything. It is aninvoluntary muscle,pumping and pushingblood through your body,every minute, everysecond, of every day.

Your heart keeps yourbody running smoothlyby pumping bloodthroughout your body.The heart has openings

that control the flow of blood moving through it.These openings, called valves, are controlled bysmooth muscles, which open and close the valves.In fact, the shutting of the valves is the sound ofyour heart beating. When smooth muscles insideyour heart contract, blood moves from one sectionof the heart to the other.

Your heart might not be the biggest muscle inyour body, but it is definitely the most important.

Blood vessels also have smooth muscles, andthese muscles are found inside the vessels’ walls.These smooth muscles help push blood through thevessels and ultimately through your body.

Smooth muscles are also important forbreathing. Once the air enters your body, smoothmuscles push the air downward and into yourlungs. Without smooth muscles, you wouldn’t beable to breathe, your blood would not be able toflow, and your food would not pass into yourstomach and out again.

1615

The Eyes Have ItAnother important smooth muscle is in

your eye. The black part of your eye is calledthe pupil. It gets bigger when you are in the dark to

let in more light, and it gets smaller when you are in thelight to limit the light. How does the pupil get bigger andsmaller? Muscles pull the pupil open and closed.

What you need: A flashlight, mirror, and dark room.

1. Put your face close to the mirror. Look into the mirrorwith the flashlight off. See how large your pupils are.

2. Turn on the flashlight. Shine the light toward youreyes, but notdirectly in them,and watch yourpupils get smaller.

Try Th

is

Doctors hold a human heartduring surgery.

A Closer Look

You’ve probably noticed that skeletal musclesappear to be dark and rather stringy. Muscles aremade up of special cells called fibers, and the fibersare, indeed, very long. In addition, each musclefiber is made up of smaller fibers, called myofibril.Long muscle fibers are bound together in groupscalled fascicles. All the fascicles are held togetherby tissues, and the fascicles and tissues make upone strand of muscle. So one muscle can haveseveral thousand fibers, and many more myofibrils.

1817

Protein PowerYour skeletal muscles

are also made up ofprotein. Eating proteinreplenishes the proteinin your muscles,keeping your musclesstrong. So where doyou get protein? You getit from meat, such asfish or chicken, or fromplants, such as spinach,bean products, seeds,pasta, and seaweed. Eating protein helps your muscles.

How the Cardiac Muscle WorksWhen doctors listen to your heart they hear your cardiacmuscle contracting. The sound it makes is lub-dub. Thelub is the cardiac muscle contracting the upperchambers of the heart. The dub is the cardiac musclecontracting the lower chambers of the heart.

1 The lub, or firstcontraction, pushes bloodfrom the upper chambers ofthe heart to the lowerchambers.

2 The dub, or secondcontraction, pushes the bloodfrom the lower chambers out

to the lungs and therest of your body.

3 Then thecardiac musclerests, which allows

the upper chambersto fill with blood again.

4 The next lub-dub, or pair of contractions,happens withoutyou having tothink about it.

upperchamber

upperchamber

lowerchamber

lowerchamber

to lungs

tobody

bloodfrombody

blood fromlungs

3

1

3

1

2

2

The average adult heart beats72 times per minute. One beatis one lub-dub. That means eachlub-dub and rest happens in lessthan one second!

Muscle Building

Your smooth muscles and your cardiac muscleare constantly moving, so you don’t need toexercise them. Your skeletal muscles, however,need you to take care of them. Your muscles adjustto the way your body uses them. If you use yourmuscles a lot, your muscles remain strong and mayeven become stronger. Health experts tell us toexercise to keep our muscles working properly.

Muscles also become tired. Unlike your smoothand cardiac muscles, which never rest, yourskeletal muscles do need to rest. It takes a lot ofoxygen to keep these muscles moving. Rest helpsthe muscles regain their strength.

If you compare the three types of muscles under a microscope, you can see other ways inwhich skeletal, smooth, and cardiac muscles differ.The cells of the skeletal muscles appear separateand straight. Smooth-muscle cells are also straight,but they are more firmly connected. The cells of the cardiac muscle, or the heart, are more wavyand branching.

2019

Different ways to exercise your skeletal muscles

Cardiacmuscle cells

A Muscle MinuteThe smallest muscle in your body is a

smooth muscle, and it is in your ear. It is calledthe stapedius, and it controls the movement of abone in your ear. You would need a microscope to seethis muscle—it is only 0.01 inches (0.0254 cm) long.

Smoothmuscle cells

Skeletalmuscle cells

Sometimes people can actually stretch theirmuscles too far. When this happens, a doctor willsay they have “pulled a muscle.” Often when amuscle has been pulled, some muscle fibers havetorn. The muscle usually hurts, and it might evenfeel a little tight. Rest will help the muscle to healand rebuild its broken fibers.

Muscles also weaken if you break a bone. Broken bones are healed by preventing the bonesfrom moving. If the bones don’t move, then themuscles don’t move either. When a cast comes off,the broken bone will be stronger, but the muscleswill be weak. Doing slow, moderate exercise willstrengthen the weakened muscles.

Conclusion

Your body is a muscle machine. To keep yourmuscles working, the muscles need to remainactive. Doctors stress the importance of exercise forkeeping muscles strong, and they’re right. Exercisenot only strengthens your skeletal muscles, but itkeeps your heart pumping and your blood flowing.

Your muscles react to the messages you send toyour brain. Tell your muscles to move, and theywill. Exercise your muscles daily, and they’ll workmore efficiently.

So go on—get moving, and mind your muscles!

However, when you are not very active, yourmuscles are not active. Slowly, they adjust to beinginactive, becoming weaker and weaker. Weakmuscles don’t allow you to do as many activities;for example, you won’t be able to run very far or for very long, and you won’t be able to lift heavy objects.

That’s where “bodybuilding” comes in.Bodybuilding is really muscle building. People“build” their bodies by making their musclesbigger and stronger. As they lift weights, theirmuscles adjust to the activity and become morepowerful, so moreand more weightcan be lifted eachtime. At first, themuscles will not beable to lift veryheavy loads. Overtime and withconstant training,the muscles buildand become strong.

2221

Bodybuilders.lift weights to.build muscles.

Index

Achilles tendon, 10, 11arm(s), 5, 6, 8, 9

biceps, 8, 9triceps, 9

blood vessels, 15bodybuilding, 21bone(s), 6, 8, 22brain, 7, 22contract(s), 8, 9, 13, 17ear, 19exercise, 20, 22eye, 12, 15face, 12, 13fibers, 6, 18, 22

fascicles, 18myofibril, 18

heart, 16, 17, 22jaw, 12, 14

masseter, 12temporalis, 12

Glossary

Achilles a tendon that connects the calf tendon muscle to the heel bone (p. 11)

deltoid shoulder muscle that lifts arm (p. 9)

fascicles groups of long muscle fibers (p. 18)

gastrocnemius calf muscle that lifts the heel (p. 10)

gluteus muscle in butt and upper thigh thatmaximus helps move legs forward (p. 11)

hamstring muscle on back of thigh that makesthe knee bend (p. 10)

involuntary muscles that move without you muscles having to tell them to (p. 5)

masseter muscle connected to cheekbone thathelps raise and lower the jaw (p. 12)

myofibril small fibers that make up musclefibers (p. 18)

quadriceps muscle on top of thigh that lifts theleg (p. 10)

sartorius muscle that allows leg to twist andbend at knee (p. 11)

stapedius muscle that controls the bones inthe ear (p. 19)

temporalis muscle connected to temple thathelps raise and lower the jaw (p. 12)

trapezius neck muscle that lifts the shoulder(p. 9)

voluntary muscles that move when you tellmuscles them to (p. 7)

2423

leg(s), 6, 10, 11gastrocnemius, 10gluteus maximus, 10, 11hamstring, 10 quadriceps, 10 sartorius, 10, 11

lungs, 15oxygen, 20protein, 18pulled, 22relax(es), 9shaping up, 4shoulder, 9

deltoid, 9trapezius, 9

stomach, 14tendon(s), 6, 11types of muscle

cardiac, 5, 16, 19, 20involuntary, 5, 14, 16skeletal, 5-8, 12, 14, 18-20smooth, 5, 14-16, 19, 20voluntary, 5, 7