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The Hard Stuff!All About BonesA Reading A–Z Level U Quick Reader

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The Hard Stuff!All About Bones Level U Quick Reader© 2004 Learning Page, Inc.Written by Lisa Trumbauer

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The Hard Stuff!All About Bones

www.readinga-z.com

Written by Lisa Trumbauer

CorrelationLEVEL U

Fountas & Pinnell QReading Recovery 24

DRA 40

Photo Credits:Front cover, back cover, title page, pages 3, 4, 5, 6, 7, 8, 9 (left), 11, 12, 13,14, 15, 16, 17, 18, 19 (in circles), 20 (left): © ArtToday; pages 9, 10: CraigFrederick/© LearningPage, Inc.; page 19: © Maxine Hall/CORBIS; page 20(right): © Lester V. Bergman/CORBIS; page 21: © Michal Heron/CORBIS

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Table of Contents

Body Shapers . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Heads Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Put Your Back Into It . . . . . . . . . . . . . . . . . . . . . .10

And Now the Appendages . . . . . . . . . . . . . . . . .14

Don’t Get Out of Joint . . . . . . . . . . . . . . . . . . . . .18

Inside Your Bones . . . . . . . . . . . . . . . . . . . . . . . . .20

Keeping Bones Healthy . . . . . . . . . . . . . . . . . . . .21

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

Explore More . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

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

Body Shapers

Lizards have one. Elephants have one. Evenfish in the ocean have one. You have one, too!What do you all have? You all have skeletons.

A skeleton is a collection of bones that is foundinside an animal’s body. The skeleton is like aframe that has muscles, blood vessels, and skinwrapped around it. Skeletons give manyanimals, called vertebrates, and all humans theirshape and form. In fact, you can identify manyanimals just by looking at their skeletons.

lion

elephant

cow

seal

monkey

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Heads Up

Press your hand against your forehead—thepart of your face above your eyebrows. Doesyour forehead feel soft, like a pillow, or does itfeel hard, like a desk? Your forehead feels hardbecause you can feel your skull, or cranium,under the skin. The cranium is one set of bonesin your body, and it protects your brain, which isvery important and very delicate. In some ways,the cranium is like a crash helmet, except it is not as strong. That is why when you ride a bike,in-line skate, or participate in some other sports,wearing a helmet provides extra protection.

The human skeleton is made up of 206 bones,starting at the top with the skull and ending atthe bottom with the toe bones. Many bones havemuscles attached to them by tendons, and thesebones help us to move. Some bones protectdelicate organs inside our bodies—for example,the heart and the brain. And many large boneshave a special core that produces blood cells. All the bones are connected to each other withspecial tissues called ligaments, which helpmake up the skeleton.

To fully appreciate the function of bones, let’stake a closer look at specific body areas. These racers wear helmets to protect their skulls.

These ligaments hold the hand and foot bones together.

ligaments

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In all, your skull has 29bones. The rest of the bonesin your skull are the bones inyour face, in your ears, and inyour jaw. Beneath the skin onyour cheek, you can probablyfeel your cheekbone, or thezygomatic bone. Your jaw ismade up of two bones—theupper jaw, or maxilla, and thelower jaw, or mandible. Thelower jaw is one of the onlybones in your skull that canmove on its own.

If you feel around your head, your skullappears to be all in one piece. Actually, though,the skull is made up of several different bones.The bones are held together at special jointscalled sutures. Unlike regular joints, which allowmovement, the suture joints are immovable.

Remember touching your forehead? This partof the skull is the frontal bone. A more technicalterm for your forehead is the supraorbital ridge.The largest part of your skull covers the top andback of your head. This bone is called the parietal(pa-RI-a-tul) bone. The part of your skull justabove your neck in the back is the occipital(awk-SIP-i-tul) bone, and the sides of the skull,above the ears, are the temporal bones.

cheekbone

upper jaw bone

A human skull

parietalbone

supraorbitalridge

occipitalbone temporal

bone

sutures

lower jaw bone

Bones BonusYour ears also

have bones—thehammer, the anvil, andthe stirrup, which areattached to theeardrum. These bonesare not only the tiniestbones in your body,but they also are theother skull bones thatcan move.

When the eardrumpicks up sounds andvibrates, the eardrummoves the hammer.The hammer thenvibrates, which makesthe anvil vibrate, whichin turn pushes thestirrup bone! The brainreceives the vibrationsand interprets them aswords, music, or othersounds.

anvil

eardrum

hammer

stirrup

Put Your Back Into It

The skull connects to a major system ofbones—the spinal column, also called thebackbone. You can feel the first few parts of thespinal column at the back of your neck. Theseridges continue down your back, all the way toyour hips. These ridges are the individual bonesof your backbone, and they are called vertebrae(VER-te-bray).

The backbone has 33 vertebrae in all. Sevenvertebrae are found in the neck, and they arecalled the cervical vertebrae. Twelve vertebrae run from the top of your back to about themiddle of your back, and they are called thethoracic (the-RA-sik) or dorsal vertebrae. Fivelumbar vertebrae are found at the small of yourback, followed by five sacral vertebrae, which sitbetween your hips. The remaining vertebraeform the coccyx (KOK-sicks) bone at the bottomof your spinal column.

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If you look at a skeleton, you might seesomething missing from the skeleton’s face—anose. Your nose is not made out of bone, but outof a tissue called cartilage (CAR-ti-lidg).Cartilage is more flexible than bone. Try it—touch your nose and move it around. It canbend, whereas your bones cannot. Cartilage isalso found at the ends of bones to keep one hardbone from rubbing against another hard bone.

Skeletons also have teeth, but teeth are notbones. In fact, teeth are harder than bones. Theoutside of a tooth is made of a substance calledenamel. It is the hardest substance in the body.

Teeth are harder than bones. Cartilage is softer than bones.

Bones BonusThe top two

vertebrae are calledthe atlas and the axis.These two vertebraeallow you to nod andshake your head.

Your spinal column has two very importantfunctions. First, the spinal column protects thedelicate spinal cord, which runs through thevertebrae. The spinal cord is the place where allthe nerves in your body meet to transmit information to your brain.

The second function is that the spinal columnallows you to bend and twist, roll and flip.Because the backbone is a chain of bones, not onesolid bone, it is very flexible.

The skull is not the only bone attached to thebackbone; the shoulder bones, ribs, and pelvicbones are attached to it, too.

Along with giving shape to your torso, the ribsserve a very important purpose—to protect thelungs and heart. The lungs and heart lie inside theribs, which form the rib cage. So if you bang yourtorso, your lungs and heart don’t get squashedbecause the ribs provide a sturdy wall aroundthem. Your rib cage has 12 bones on each side,and each of those bones is connected to one of the12 dorsal vertebrae.

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Spinalcolumn

spinalcolumn

ribs

clavicle

pelvis

scapula

thoracic

lumbar

sacrum

cervical

coccyx

And Now the Appendages

Your hands and arms, feet and legs, are yourappendages, and they enable you to do manydifferent activities. Your hands and arms enableyou to lift and hold things, while your feet andlegs help you to move. Being able to do theseactions is partially possible because of the bonesinside your appendages.

Your arms are made upof three bones each—thehumerus, the ulna, and theradius. The humerus is theupper arm bone, and it isattached at the top to theshoulder. The ulna and theradius make up the lowerpart of the arm, betweenthe wrist and the elbow.

1413

These kids use their arms to helphold themselves up.

At the top end of the spinal column, you willalso find the scapula and the clavicle. Scapula isthe technical term for the shoulder blade, andclavicle is the technical term for the collarbone.The scapula and the clavicle make up theshoulder.

Near the bottom of the backbone is the hipbone, or pelvic bone. Oneach side, the pelvic bonelooks like a shallow dish orbowl. That’s because in thisarea of the body lie yourintestines and other lower-body organs.

humerus

radius

wrist

fingersandthumb

palm

ulna

Boning UpThe skeleton of a newborn baby is not the same as an

adult’s skeleton. An unborn baby has cartilage instead ofbones. As the unborn baby grows and develops, thecartilage hardens and turns to bone. By the time the baby isborn, most of the cartilage has hardened and turned to bone.

As babies become children and childrenbecome adults, their bones continue to

harden or even join together. One of the last sets of bones to jointogether is the group that makes upthe pelvis. These bones become onesolid structure when a person is inhis or her late teens or early 20s.

pelvicbones

The structure of the legs and feet is comparableto the structure of the arms and hands. The topportion of the leg is one solid bone, called thethighbone, or femur. The bottom part of the legcomes in two parts—the shinbone, or tibia, and thefibula. Between the upper and lower parts of theleg is one more bone—the kneecap, or patella. The kneecap lies over the knee joint and protectsthe tendons beneath that allow the leg to bend.

Your hand, including your wrist, is full ofbones. In fact, your hand and wrist together havemore bones than any other part of your body—27! That’s 54 bones total for both hands. Becausehands and wrists have so many bones, they arevery flexible and dexterous, and we can do small,precise activities, such as writing and drawing,playing the piano, and tying shoelaces.

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Many for Manipulating Your fingers may be smaller than your arms, but

they have more bones. Here’s how the numbers ofbones in each part of your hands and armscompare.

Bones BonusThe longest, strongest, and largest bone in your body is

in your leg. It’s the thighbone, or femur. It extends from thepelvis to the knee. To break the femur requires a lot of force.For example, you would have to fall from a great height orhave a high-speed collision while skiing or skating.

Arm: 3Wrist (carpus): 8Palm (metacarpus): 5Each finger: 3

Each thumb: 2Fingers and thumbs

(phalanges): 14

Leg bones help us move in many ways.

Don’t Get Out of Joint

Along with over 206 bones, the human bodyhas over 100 joints. Joints are the places wherebones meet. Bones are hard and unbending, butbecause bones are connected at joints, our bodiescan bend and twist.

Like a hand, the foot is a complex system ofmany bones. Each foot has only one less bonethan a hand—26—for a total of 52 bones for bothfeet. The heel of a foot has seven tarsal bones, andthe ball of a foot has five metatarsal bones. Likethe hand, the foot has 14 phalange bones—two forthe big toe and three each for the remaining toes.Skin and tissue on the bottoms, or soles, of thefeet protect the bones from the impact of jumpingand running.

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Bones BonusSometimes we say that people are double-jointed,

but this doesn’t mean that they have two jointsinstead of one. Double-jointed people are moreflexible than the average person because theligaments between the joints are looser. These looseligaments enable them to bend in unusual ways.

Foot bones are cushioned by the skin andtissue around them so they don’t breakwhen you run, jump, and hop.

femur

fibula

heel

toes

ball

tibia

patella

Inside Your Bones

It might seem as if a bone is nothing morethan a hard, solid object, like a rock, but thatcouldn’t be further from the truth. Bones aredefinitely alive with thousands of bone cells thatneed oxygen and food to survive, just like othertypes of cells.

On the outside, a bone is hard and solid. Thisouter layer is called the compact bone. Below thecompact bone is the spongy bone, which hasholes to keep the bones light in weight so ourmuscles can lift them.

Below the spongy bone and also within it isthe bone marrow. The bone marrow is importantbecause it is where the body makes blood cells.

About half a pound of bonemarrow makes about 5 billionred blood cells every day!

Not all joints are the same.The joints where the upper armbone is connected to the shoulder bone andwhere the upper leg bone is connected to thehipbone are ball-and-socket joints. The top endsof the humerus and the femur have a ball shape.These balls fit snugly into a round socket in theshoulder and hipbone respectively.

The knee joint and the elbow joint areexamples of hinge joints. Here, the joints canonly bend in one direction. The joints betweenthe vertebrae of your spine are called swiveljoints, which enable the body to tilt and turn.And the last type of joint is a suture joint, likethose found on the skull. These joints connectbones but do not allow any movement.

19 20

compactbone

spongybone

bone marrow

X-ray of the shoulder joint, whichconnects the scapula and humerus(right) ball-and-socket joint

ball

socket

ball

hingejoint

hip

socket

Bones need to remain healthy in order forthem to remain strong. Eating a well-balanceddiet ensures not only that the bones willcontinue to be strong, but also that they willcontinue to produce healthy blood cells in thebone marrow. Foods rich in calcium phosphateare especially important. Dairy products like milkhave calcium, which is why doctors oftensuggest that people drink milk. Exercise alsokeeps your bones in good working order.

Your bones give your body its shape, but theyalso give you much more. They give you theability to move, to sit, to stand, and to write. Youwouldn’t be you without your bones!

Keeping Bones Healthy

Even though bones are very strong, they canbreak if they are struck with enough force.Broken bones can be fixed with a little help froma doctor and a lot ofhelp from bone cells.

In order for a bone to healproperly, the bonemust be put backtogether exactly the way it wasbefore the break.Depending on howsevere the break is,doctors may need tomove around thebroken bones to putthem back together.A cast is then placedaround the bodypart where the bone was broken. The castprevents the body part from moving so the bonehas time to heal. As soon as the bone broke, thebone cells immediately began repairing it.Holding the broken bone in place with a cast letsthe bone cells do their job.

2221

Bones helpyou do all

kinds of funactivities.

A cast helps hold broken bones inplace so they can heal.

Index

arm, 14, 15humerus, 14, 19radius, 14ulna, 14

bone cells, 20, 21

bone marrow, 20, 22

brain, 6, 8, 11

broken bones, 21

cartilage, 9, 13

clavicle (collarbone), 12, 13

cranium (skull), 5-8, 10, 12,19

occipital bone, 7parietal bone, 7supraorbital ridge, 7temporal bones, 7

ear, 8anvil, 8hammer, 8 stirrup, 8

fingers, 14, 15

foot, 17hand, 15

jaw, 8mandible, 8maxilla, 8zygomatic bone, 8

Glossary

appendages arms and legs (p. 14)

ball-and- joints that fit together like a ball fits intosocket a glove (p. 19)

bone material in large bones that creates redmarrow blood cells (p. 20)

calcium a mineral that helps keep bones strongphosphate (p. 22)

cartilage a tough, rubbery substance found at the end of bones or in the nose (p. 9)

dexterous able to make precise movements (p. 15)

hinge joints that open like a door (p. 19)

ligaments tissues that connect one bone to anotherbone (p. 5)

spinal cord collection of nerves protected by vertebrae(p. 11)

sutures joints or seams between skull bones (p. 7)

swivel tilt or turn (p. 19)

tendons tissue that attaches muscles to bones (p. 5)

vertebrates animals with an interior skeleton (p. 4)

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Explore More

On the Internet, use www.google.com to find out moreabout topics presented in this book. Use terms fromthe text, or try searching for glossary or index words.

Some searches to try: skeletal system, bone marrow, orspinal column.

joint, 7, 16, 18ball-and-socket, 19hinge, 19suture, 7, 19swivel, 19

legs, 16 femur, 16-19fibula, 16, 17 patella (knee), 16tibia, 16, 17

nerves, 11

nose, 9

pelvic bone (hip), 12, 13,18, 19

pelvis, 12, 13, 16

red blood cells, 20, 22

rib cage, 12

scapula (shoulder), 12, 18

spinal column (backbone),10-12, 19

vertebrae, 10, 19atlas, 10 axis, 10cervical, 10coccyx, 10lumbar, 10sacral, 10thoracic (dorsal), 10, 12

wrist, 14, 15

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