Body Movements S Table 8.1 How do animals move from place …ncert.nic.in/NCERTS/l/fesc108.pdf · 2010-09-27 · BODY MOVEMENTS 69 our head forward and backward and turn the head

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8 Body Movements

Sit absolutely still. Observe themovements taking place in yourbody. You must be blinking your

eyes, time to time. Observe themovements in your body as youbreathe. There are so many movementsthat happen in our bodies.

When you are writing in yournotebook which part of the body are youmoving? Or, when you turn and look atyour friend? Different parts of your bodymove while you remain at the sameplace, in these examples. You also movefrom one place to another — you get upand go to your teacher or to the schoolcompound, or go home after school. Youwalk, run, skip, jump and move fromplace to place.

Let us see how animals move fromplace to place by filling up Table 8.1,after discussing with our friends,teachers and parents.

Walk, run, fly, jump, creep, crawl,slither and swim – these are only a fewof the ways in which animals move fromone place to another. Why are there somany differences in the way thatanimals move from place to place? Whyis it that many animals walk while asnake slithers or crawls and a fishswims?

8.1 HUMAN BODY AND ITS MOVEMENTS

Let us look closely at some of our ownmovements to begin with, before lookingat all these varieties of movements inanimals.

Do you enjoy doing physical exerciseat school? How do you move your handsand legs while doing different exercises?

Table 8.1 How do animals movefrom place to place?

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Boojho wonders about movementsin plants. He knows they do notmove from place to place, but, dothey show any other kind ofmovements?

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Let us try some of the many movements,our body is capable of.

Bowl an imaginary ball at animaginary wicket. How did you moveyour arm? Did you rotate it at theshoulder in a circular movement? Didyour shoulder also move? Lie down androtate your leg at the hip. Bend yourarm at the elbow and the leg at the knee.Stretch your arm sideways. Bend yourarm to touch your shoulder with yourfingers. Which part of your arm did youbend? Straighten your arm and try tobend it downwards. Are you able to doit?

Try to move the various parts of yourbody and record their movements inTable 8.2.

Why is it that we are able to move afew parts of our body easily in variousdirections and some only in onedirection? Why are we unable to movesome parts at all?

Activity 1

Place a scale length-wise on your armso that your elbow is in the centre(Fig. 8.1).

Ask your friend to tie the scale andyour arm together. Now,try to bend your elbow.Are you able to do it?

Table 8.2 Movements in our body

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Fig. 8.1 Can you bend yourarm now?

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Did you notice that we are able tobend or rotate our body in places wheretwo parts of our body seem to be joinedtogether — like elbow, shoulder or neck?These places are called joints. Can youname more such joints? If our body hasno joints, do you think it would bepossible for us to move in any way atall?

What exactly is joined together atthese joints?

Press your fingers against the top ofyour head, face, neck, nose, ear, back ofthe shoulder, hands and legs includingthe fingers and toes.

Do you get a feel of something hardpressing against your fingers? The hardstructures are the bones. Repeat thisactivity on other parts of your body. Somany bones!

Bones cannot be bent. So, how dowe bend our elbow? It is not one longbone from the upper arm to our wrist. Itis different bones joined together at theelbow. Similarly, there are many bonespresent in each part of the body. Wecan bend or move our body only at thosepoints where bones meet.

There are different types of joints inour body to help us carry out differentmovements and activities. Let us learnabout some of them.

Ball and socket joints

Activity 2

Roll a strip of paper into a cylinder. Makea small hole in an old rubber or plasticball (under supervision) and push the

paper cylinder into it as in Fig. 8.2. Youcan also stick the cylinder on the ball.Put the ball in a small bowl. Is the ballrotating freely inside the bowl? Is thepaper cylinder also rotating?

Now, imagine that the paper cylinderis your arm and the ball is its end. Thebowl is like the part of the shoulder towhich your arm is joined. The roundedend of one bone fits into the cavity(hollow space) of the other bone(Fig.8.3). Such a joint allows movementsin all directions. Can you name anothersuch joint you can think of, recollectingthe body movements we tried at thebeginning of this section?

Fig. 8.2 Making a ball and socket joint

Fig. 8.3 A ball and socket joint

Pivotal JointThe joint where our neck joins the headis a pivotal joint. It allows us to bend

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our head forward and backward andturn the head to our right or left. Trythese movements. How are thesemovements different from those of ourarm that can rotate a complete circle inits ball and socket joint? In a pivotaljoint a cylindrical bone rotates in a ring.

Hinge jointsOpen and close a door a few times.Observe the hinges of the door carefully.They allow the door to move backand forth.

Activity 3

Let us look at the kind of movementallowed by a hinge. Make a cylinder withcardboard or thick chart paper, asshown in Fig. 8.4. Attach a small pencilto the cylinder by piercing the cylinderat the centre, as shown. Make a hollowhalf cylinder from cardboard such thatthe rolled up cylinder can fit inside iteasily. The hollow half cylinder with therolled up cylinder sitting inside it, allowsmovement like a hinge. Try to move therolled up cylinder. How does it move?How is this movement different fromwhat we saw with our constructed ball

and socket joint? We saw this kind ofmovement at the elbow in Activity 1.What we have constructed in Fig. 8.4 isdifferent from a hinge, of course. But, itillustrates the direction in which a hingeallows movement. The elbow has a hingejoint that allows only a back and forthmovement (Fig. 8.5). Can you think ofmore examples of such joints?

Fixed jointsThere are some bones in our head thatare joined together at some joints. Thebones cannot move at these joints. Suchjoints are called fixed joints. When youopen your mouth wide, you can moveyour lower jaw away from your head,isn’t it? Try to move your upper jaw,now. Are you able to move it? There is ajoint between the upper jaw and the restof the head which is a fixed joint.

We discussed only some of the jointsthat connect parts of our body.

What gives the different parts of thebody their different shapes?

If you wanted to make a doll, whatwill you make first? Perhaps aframework to give the doll shape beforemaking its outer structure, isn’t it? All

Fig. 8.4 Directions of movement allowed by a hingelike joint

Fig. 8.5 Hinge joints of the knee

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Bend your fingers. Are you able tobend them at every joint? How manybones does your middle finger have?Feel the back of your palm. It seems tohave many bones, isn’t it (Fig. 8.8)? Isyour wrist flexible? It is made up ofseveral small bones. What will happenif it has only one bone?

Fig 8.7 X-ray images of ankle and knee joints

the bones in our body also form aframework to give a shape to our body.This framework is called the skeleton(Fig. 8.6.)

How do we know that this is theshape of a human skeleton? How do weknow the shapes of the different bonesin our body? We can have some ideaabout the shape and number of bonesin some parts of our body by feelingthem. One way we could know thisshape better would be to look at X-rayimages of the human body.

Did you or anyone in your familyever have an X-ray of any part of yourbody taken? Sometimes when we arehurt, or have an accident, doctors usethese X-ray images to find out aboutany possible injuries that mighthave happened to the bones. The X-rays show the shapes of the bones inour bodies.

Feel the bones in your forearm,upper arm, lower leg and upper leg. Tryto find the number of bones in each part.Similarly, feel the bones of your ankleand knee joints and compare these withthe X-ray images (Fig. 8.7).

Fig. 8.8 Bones of the hand

Activity 4

Take a deep breathe and hold it for alittle while. Feel your chest bones and theback bone by gently pressing the middle

Fig. 8.6 The Human skeleton

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of the chest and back at the same time.Count as many ribs (bones of the chest)as possible. Observe Fig. 8.9 carefullyand compare with what you feel of thechest bones. We see that the ribs arecuriously bent. They join the chest boneand the backbone together to form abox. This is called the rib cage. Someimportant internal parts of our body lieprotected inside this cage.

Ask a friend to touch his toes withoutbending his knees. Putyour fingers at the centreof his back. Can you feelsome long and hardstructure? Starting fromthe neck, move yourfingers downwards on theback of your friend. Whatyou feel is his backbone.It is made of many smallbones (Fig. 8.10). The ribcage is joined to thesebones.

If his backbone weremade up of only one longbone will your friend beable to bend?

Fig. 8.11 Shoulder bones

Fig. 8.12 Pelvic bones.

Fig. 8.13 The skullFig. 8.10 The

backbone

Fig. 8.9 The rib cage

The skull is made of many bonesjoined together (Fig. 8.13). It enclosesand protects a very important part ofthe body, the brain.

We discussed the many bones andthe joints of our skeleton. There are

Make your friend stand with hishands pressed to a wall. Ask him to andtry to push the wall. Do you see two bonesstanding where his shoulders are? Theyare called shoulder bones (Fig 8.11).

Observe Fig. 8.12 carefully. Thisstructure is made of pelvic bones. Theyenclose the portion of your bodybelow the stomach. This is the partyou sit on.

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some additional parts of the skeletonthat are not as hard as the bones andwhich can be bent. These are calledcartilage.

Feel your ear. Do you find any hardbony parts that can be bent(Fig. 8.14)? There do not seem to be anybones here, isn’t it? Do you noticeanything different between the ear lobeand the portions above it (Fig. 8.15), asyou press them between your fingers?

Touch it with the other hand. Do youfeel a swollen region inside your upperarm? This is a muscle. The musclebulged due to contraction (it becamesmaller in length). Now bring your armback to its normal position. Whathappened to the muscle? Is it stillcontracted? You can observe similarcontraction of muscles in your leg whenyou walk or run.

When contracted, the musclebecomes shorter, stiffer and thicker. Itpulls the bone.

Muscles work in pairs. When one ofthem contracts, the bone is pulled inthat direction. The other muscle of thepair relaxes. To move the bone in theopposite direction, the relaxed muslecontracts to pull the bone towards itsoriginal postion, while the first relaxes.A muscle can only pull. It cannot push.Thus, two muscles have to work togetherto move a bone (Fig. 8.16).

Are muscles and bones alwaysrequired for movement? How do otheranimals move? Do all animals have

Fig. 8.15 The ear lobeFig. 8.14 Upper part of

ear has cartilage

You do feel something in the upper partsof the ear that is not as soft as the earlobe but, not as hard as a bone, isn’t it?This is cartilage. Cartilage is also foundin the joints of the body.

We have seen that our skeleton ismade up of many bones, joints andcartilage. You could see, bend and movemany of them. Draw a neat figure of theskeleton in your notebook.

We have learnt about the bones in ourbody and about joints that help us movein different ways. What makes the bonesmove the way they do? Let us find out.

Make a fist with one hand, bend yourarm at the elbow and touch yourshoulder with the thumb (Fig. 8.16). Doyou see any change in your upper arm?

Fig. 8.16 Two muscles work together to movea bone

(a)

(b)

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bones? What about an earthworm or asnail? Let us study the manner ofmovement, that is, the gait of someanimals.

8.2 “GAIT OF ANIMALS”

Earthworm

Activity 5

Observe an earthworm moving on soilin a garden. Gently lift it and place iton a piece of blotting or filter paper.Observe its movement (Fig. 8.17). Thenplace it on a smooth glass plate or anyslippery surface. Observe its movementnow. Is it different from that on paper?Do you find that the earthworm is ableto move easily on a hard slipperysurface?

The body of an earthworm is madeup of many rings joined end to end. An

This is called the shell and it is theouter skeleton of the snail, but is notmade of bones. The shell is a single unitand does not help in moving from placeto place. It has to be dragged along.

Place the snail on a glass plate andwatch it. When it starts moving,carefully lift the glass plate along withthe snail over your head. Observe itsmovements from beneath.

A thick structure and the head of thesnail may come out of an opening in

Fig. 8.17 Movement of earthworm

earthworm does not have bones. It hasmuscles which help to extend andshorten the body. During movement,the earthworm first extends the frontpart of the body, keeping the rearportion fixed to the ground. Then it fixesthe front end and releases the rear end.It then shortens the body and pulls therear end forward. This makes it moveforward by a small distance. Repeatingsuch muscle expansions and

contractions, the earthworm can movethrough soil. The body secretes a slimysubstance to help the movement.

How does it fix parts of its body tothe ground? Under its body, it has alarge number of tiny bristles (hair likestructures) projecting out. The bristlesare connected with muscles. The bristleshelp to get a good grip on the ground.

The earthworm, actually, eats its waythrough the soil! Its body then throwsaway the undigested part of the materialthat it eats. This activity of an earthwormmakes the soil more useful for plants.

Snail

Activity 6

Collect a snail from a garden. Have youseen the rounded structure it carries onits back (Fig. 8.18)?

Fig. 8.18 A snail

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units joined together and that permitsmovement.

There are two pairs of wings attachedto the breast. The cockroaches havedistinct muscles — those near the legsmove the legs for walking. The breastmuscles move the wings when thecockroach flies.

BirdsBirds fly in the air and walk on theground. Some birds like ducks andswans also swim in water. The birds canfly because their bodies are well suitedfor flying. Their bones are hallow andlight. The bones of the hind limbs aretypical for walking and perching. The

Fig. 8.19 A cockroach

the shell. The thick structure is its foot,made of strong muscles. Now, carefullytilt the glass plate. The wavy motion ofthe foot can be seen. Is the movement ofa snail slow or fast as compared to anearthworm?

Cockroach

Activity 7

Observe a cockroach (Fig. 8.19).Cockroaches walk and climb as well

as fly in the air. They have three pairsof legs. These help in walking. The bodyis covered with a hard outer skeleton.This outer skeleton is made of different

Fig. 8.20 Skeleton of a bird

bony parts of the forelimbs are modifiedas wings. The shoulder bones are strong.The breastbones are modified to holdmuscles of flight which are used to movethe wings up and down (Fig. 8.20).

Fish

Activity 8

Make a paper boat. Put it in water andpush it with one narrow end pointingforward [Fig. 8.21 (a)]. Did it go into thewater easily? Now hold the boatsideways and push it into the waterfrom the broad side [Fig. 8.21 (b)]. Areyou able to make the boat move in waterwhen you push it from this side?

(a)

(b)

Fig. 8.21 Playing with boats

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Have you noticed that the shape of aboat is somewhat like a fish (Fig 8.22)?The head and tail of the fish are smallerthan the middle portion of the body –the body tapers at both ends. This bodyshape is called streamlined.

The shape is such that water can flowaround it easily and allow the fish tomove in water.The skeleton of the fishis covered with strong muscles. Duringswimming, muscles make the front partof the body curve to one side and thetail part swings towards the oppositeside. The fish forms a curve as shownin Fig. 8.23. Then, quickly, the body andtail curve to the other side. This makesa jerk and pushes the body forward. Aseries of such jerks make the fish swimahead. This is helped by the fins ofthe tail.

Fish also have other fins on theirbody which mainly help to keep thebalance of the body and to keepdirection, while swimming. Did you evernotice that under water divers wear finlike flippers on their feet, to help themmove easily in water?

How do snakes move?Have you seen a snake slither? Does itmove straight(Fig. 8.24)?

Snakes have a long backbone. Theyhave many thin muscles. They areconnected to each other even though theyare far from one another. They alsointerconnect the backbone, ribs and skin.

The snake’s body curves into manyloops. Each loop of the snake gives it aforward push by pressing against theground. Since its long body makesmany loops and each loop gives it thispush, the snake moves forward very fastand not in a straightline.

We have learned about the use ofbones and muscles for the movementsof different animals. Paheli and Boojhohave many questions in their sacksabout the different movements inanimals. So must you be having manyunanswered questions buzzing in your

Fig. 8.22 Fish

Fig. 8.23 Movement in Fish Fig. 8.24 Movement in a snake

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minds? The ancient Greek philosopherAristotle, in his book Gait of Animals,asked himself these questions. Why dodifferent animals have the body partsthat they do have and how do thesebody parts help animals to move theway they do? What are the similaritiesand differences in these body partsbetween different animals? How manybody parts are needed by differentanimals for moving from place to

place? Why two legs for humans andfour for cows and buffaloes? Manyanimals seem to be having an evennumber of legs, why? Why is thebending of our legs different from thatof our arms?

So many questions and perhapswe have looked for some answersthrough our activities in this chapterand we need to look for manymore answers.

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Bones and cartilage form the skeleton of the human body. It gives theframe and shape to the body and helps in movement. It protects theinner organs.

The skeleton comprises the skull, the back bone, ribs and the breastbone, shoulder and hipbones, and the bones of hands and legs.

The bones are moved by alternate contractions and relaxations of twosets of muscles.

The bone joints are of various kinds depending on the nature of jointsand direction of movement they allow.

Strong muscles and light bones work together to help the birds fly. Theyfly by flapping their wings.

Fish swim by forming loops alternately on two sides of the body.

Snakes slither on the ground by looping sideways. A large number ofbones and associated muscles push the body forward.

The body and legs of cockroaches have hard coverings forming an outerskeleton. The muscles of the breast connected with three pairs of legsand two pairs of wings help the cockroach to walk and fly.

Earthworms move by alternate extension and contraction of the bodyusing muscles. Tiny bristles on the underside of the body help in grippingthe ground.

Snails move with the help of a muscular foot.

1. Fill in the blanks:

(a) Joints of the bones help in the ——————— of the body.

(b) A combination of bones and cartilages forms the _______ of the body.

(c) The bones at the elbow are joined by a ______________________ joint.

(d) The contraction of the _____________ pulls the bones during movement.

2. Indicate true (T) and false (F) among the following sentences.

(a) The movement and locomotion of all animals is exactly the same. ( )

(b) The cartilages are harder than bones. ( )

(c) The finger bones do not have joints. ( )

(d) The fore arm has two bones. ( )

(e) Cockroaches have an outer skeleton. ( )

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3. Match the items in Column I with one or more items of Column II.

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4. Answer the following:

(a) What is a ball and socket joint?

(b) Which of the skull bones are movable?

(c) Why can our elbow not move backwards?

THINGS TO THINK ABOUT

We discussed the many movements our bodies are capable of. Healthy bones,muscles, joints and cartilages are needed by the body for all these movements.Some of us suffer from conditions that could make these movements not so easy. Ina whole class activity, try to find ways that one would manage everyday activities, ifany one of our body movements was not possible. In Activity 1, for instance, youtied a scale on your arm and disabled the elbow movement. Think of other ways ofrestricting normal body movements and find ways that everyday activities couldthen be managed.

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