2 The Skeletal System

Transcription

1 Section 2 The Skeletal System 2 The Skeletal System Objectives After this lesson, students will be able to D Identify the functions of the skeleton. D Explain the role that joints play in the body. D Describe the characteristics of bone and how to keep bones strong and healthy. Target Reading Skill Asking Questions Explain that changing a head into a question helps students anticipate the ideas, facts, and events they are going to read about. Sample answers: What does the skeleton do? (The skeleton provides shape and support, helps you to move, protects organs, produces blood cells, and stores minerals and other materials.) How do joints move? (Joints can move forward or backward, in a circle, in a rotating motion, and in a gliding motion.) How strong are bones? (Bones can absorb more force without breaking than granite or concrete.) What can I do to care for my bones? (Eat a wellbalanced diet and get plenty of exercise.) Transparency D2 Reading Preview Key Concepts What are the functions of the skeleton? What role do joints play in the body? What are the characteristics of bone, and how can you keep your bones strong and healthy? Key Terms skeleton vertebra joint ligament cartilage compact bone spongy bone marrow osteoporosis Target Reading Skill Asking Questions Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, answer your questions. Question What does the skeleton do? The Skeletal System Answer The skeletal system provides shape... Hard as a Rock? 1. Your teacher will give you a rock and a leg bone from a cooked turkey or chicken. 2. Use a hand lens to examine both the rock and the bone. 3. Gently tap both the rock and the bone on a hard surface. 4. Pick up each object to feel how heavy it is. 5. Wash your hands. Then make notes of your observations. Think It Over Observing Based on your observations, why do you think bones are sometimes compared to rocks? List some ways in which bones and rocks are similar and different. A high rise construction site is a busy place. After workers have prepared the building s foundation, they begin to assemble thousands of steel pieces into a frame for the building. People watch as the steel pieces are joined to create a rigid frame that climbs toward the sky. By the time the building is finished, however, the building s framework will no longer be visible. Like a building, you also have an inner framework, but it isn t made up of steel. Your framework, or skeleton, is made up of all the bones in your body. The number of bones in your skeleton, or skeletal system, depends on your age. A newborn has about 275 bones. An adult, however, has about 206 bones. As a baby grows, some of the bones in the body fuse together. For example, as you grew, some of the bones in your skull fused together. Preteach Build Background Knowledge What Bones Look Like Ask students to feel the bones beneath the skin in one of their hands, then draw a picture of what they think the bones look like. Have students brainstorm what they know or think they know about bones. List these on a piece of poster paper, and address misconceptions as you teach the section. 310 Skills Focus Observing Materials leg bone from a cooked chicken or turkey, rock of similar size, hand lens Time 10 minutes Tips Remind students to observe as many characteristics as possible, such as size, shape, color, texture, composition, and What the Skeletal System Does Just as a building could not stand without its frame, you would collapse without your skeleton. Your skeleton has five major functions. It provides shape and support, enables you to move, protects your organs, produces blood cells, and stores minerals and other materials until your body needs them. strength. Make sure the chicken or turkey bone has been thoroughly cooked and washed. Think It Over Possible answer: They are both hard; bone is not as dense as rock and has a definite structure. Bone is living, while rock is not. 310

2 Shape and Support Your skeleton determines the shape of your body, much as a steel frame determines the shape of a building. The backbone, or vertebral column, is the center of the skeleton. Locate the backbone in Figure 6. Notice that the bones in the skeleton are in some way connected to this column. If you move your fingers down the center of your back, you can feel the 26 small bones, or vertebrae (VUR tuh bray) (singular: vertebra), that make up your backbone. Bend forward at the waist and feel the bones adjust as you move. You can think of each individual vertebra as a bead on a string. Just as a beaded necklace is flexible and able to bend, so too is your vertebral column. If your backbone were just one bone, you would not be able to bend or twist. FIGURE 6 The Skeleton The skeleton provides a framework that supports and protects many other body parts. Comparing and Contrasting In what ways is the skeleton like the steel framework of a building? In what ways is it different? Why is the vertebral column considered the center of the skeleton? Skull Humerus Radius Ulna Femur Patella Clavicle (collar bone) Scapula (shoulder blade) Sternum (breastbone) Ribs Vertebral column (backbone) Pelvic girdle Phalanges Metacarpals Carpals Instruct What the Skeletal System Does Teach Key Concepts Functions of the Skeleton Focus Ask: What would your body be like if you did not have a skeleton? (Sample answers: You would not have a shape; you would not be able to stand or perform any other movements.) Teach Ask students to identify as many functions of the skeletal system as they can by examining Figure 6. (Helps you to move, provides shape, provides support, protects organs) Ask: Why are vertebrae important? (They are the bones that make up your backbone, and all other bones are connected to the backbone.) What other functions does the skeletal system perform? (It produces certain blood cells and stores minerals.) Apply Explain that a bone s structure relates to its function. Ask students to locate these bones in Figure 6 and identify their primary function: Sternum (Protection), Carpals (Movement), Femur (Support and movement), Ribs (Protection), Vertebral column (Protection, support, and movement) learning modality: visual Transparency D3 Tibia Tarsals Metatarsals Phalanges Fibula Independent Practice Guided Reading and Study Worksheet: The Skeletal System Student Edition on Audio CD Chapter Differentiated Instruction English Learners/Beginning Comprehension: Key Concept On the board, rewrite the boldface sentence about the five major functions of the skeleton as individual sentences. Explain each function. Then have students construct a concept circle with Functions of the Skeletal System in the center and the five functions connected to the center by lines. learning modality: visual English Learners/Intermediate Vocabulary: Science Glossary Have students write the definition of each Key Term in this section in their own words, and then write a sentence that uses each of these words. learning modality: verbal Monitor Progress Writing Ask students to list the five main functions of the skeletal system. Figure 6 Like the steel framework, the skeleton shapes and supports the body. Unlike the framework, the skeleton is living, produces necessary materials, and is flexible. The bones in the skeleton are in some way connected to the backbone. 311

3 Joints of the Skeleton Teach Key Concepts The Role of Joints Focus Ask students to bend their right elbows. Ask: What is the point where your elbow bends? (Most students will know that it is a joint.) Teach Explain that joints hold bones together. Not all joints are movable; two bones can come together and not move for example, in the skull. Have volunteers read aloud the captions in Figure 7. Ask a question about each type of movable joint, such as: What types of movements does the ball-and-socket joint in the shoulder allow the arm to make? (Up and down, backward and forward, shrugging, in a circle) Then ask: What do ligaments do? (They hold together the bones in movable joints.) What substance keeps bones from rubbing against each other? (Cartilage) Apply Instruct students to move one ear back and forth, then the tip of their nose. Explain that the flexible part is cartilage, the same material that covers the ends of bones. Extend The Active Art will show students how joints move. learning modality: visual Transparency D4 Help Students Read Comparing and Contrasting As students read the section, have them create a table that compares and contrasts the types of joint. For: Movable Joints activity Visit: PHSchool.com Web Code: cep-4012 FIGURE 7 Movable Joints Without movable joints, your body would be as stiff as a board. The different kinds of joints allow your body to move in a variety of ways. Comparing and Contrasting How is the movement of a hinge joint different from that of a ball-andsocket joint? Movement and Protection Your skeleton allows you to move. Most of the body s bones are associated with muscles. The muscles pull on the bones to make the body move. Bones also protect many of the organs in your body. For example, your skull protects your brain, and your breastbone and ribs form a protective cage around your heart and lungs. Production and Storage of Substances Some of your bones produce substances that your body needs. You can think of the long bones of your arms and legs as factories that make certain blood cells. Bones also store minerals such as calcium and phosphorus. When the body needs these minerals, the bones release small amounts of them into the blood. Joints of the Skeleton Suppose that a single long bone ran the length of your leg. How would you get out of bed or run for the school bus? Luckily, your body contains many small bones rather than fewer large ones. A joint is a place in the body where two bones come together. Joints allow bones to move in different ways. There are two kinds of joints immovable joints and movable joints. Hinge Joint A hinge joint allows forward or backward motion. Your knee is a hinge joint that allows you to bend and straighten your leg. Your elbow is also a hinge joint. Ball-and-Socket Joint Ball-and-socket joints allow the greatest range of motion. The ball-and-socket joint in your shoulder allows you to swing your arm freely in a circle. Your hips also have ball-and-socket joints

4 Immovable Joints Some joints in the body connect bones in a way that allows little or no movement. These joints are called immovable joints. The bones of the skull are held together by immovable joints. Movable Joints Most of the joints in the body are movable joints. Movable joints allow the body to make a wide range of movements. Look at Figure 7 to see the variety of movements that these joints make possible. The bones in movable joints are held together by strong connective tissues called ligaments. Most joints have a second type of connective tissue, called cartilage (KAHR tuh lij), which is more flexible than bone. Cartilage covers the ends of the bones and keeps them from rubbing against each other. For example, in the knee, cartilage acts as a cushion that keeps your femur (thighbone) from rubbing against the bones of your lower leg. In addition, a fluid lubricates the ends of the bones, allowing them to move smoothly over each other. Pivot Joint A pivot joint allows one bone to rotate around another. The pivot joint in your neck allows you to turn your head from side to side. How are movable joints held together? Gliding Joint A gliding joint allows one bone to slide over another. The gliding joint in your wrist or ankle enables you to bend and flex as well as make limited side-to-side motions. Classifying Perform these activities. Move your arm in a circle. Push open a door. Lift a book from a desk. Kneel down. Wave your hand. Twist your head from side to side. Determine which type of movable joint or joints is involved in performing each activity. Give a reason to support your classifications. For: Movable Joints activity Visit: PHSchool.com Web Code: cep-4012 Students explore the skeletal and muscular systems. Observing Joints Materials model of a human skeleton Time 5 minutes whole class; 5 minutes per pair or small group of students Focus Show students the model and ask: How does the human skeleton enable you to move? (Bones are connected at joints and can rotate, pivot, and bend back and forth.) Teach Move one joint of each type on the model, and state the type of joint as you move it. Instruct students to take turns examining the model in pairs, spending no more than 5 minutes manipulating the bones to see how the joints of the skeleton move. Tell them to write down their observations. You might schedule this activity while students are working on their Chapter Projects or doing independent seat work. Apply Make copies of a human skeleton, and have students indicate each joint they felt on the model and the name of the type of joint. learning modality: kinesthetic Skills Focus Classifying Materials none Time 15 minutes Tips Students can work in pairs. One student can perform the activity while the other student observes the movement; then partners can switch roles. Expected Outcome Arm ball and socket joint (shoulder); door hinge joint Chapter (elbow), gliding joint (wrist); book hinge joint (elbow), gliding joint (wrist); kneeling hinge joint (knee); hand gliding joint (wrist); head pivot joint (neck) Extend Challenge students to demonstrate the movement of other joints and classify their types. learning modality: kinesthetic Monitor Progress Skills Check Ask students to identify the different types of movable joints in addition to the ball-and-socket joints in the picture of the batter. (Neck pivot joint; hands gliding; knees hinge) Ask students to give an example of a joint that is immovable. (Sample answer: The bones of the skull) Figure 7 A hinge joint allows only one type of movement forward or backward motion. A ball-and-socket joint permits movement in many directions. By strong connective tissues called ligaments 313

5 Bones Strong and Living Teach Key Concepts Characteristics of Bone Focus Ask: Which function of the skeletal system gives you a clue that bones are not dead or solid? (Bones make certain blood cells and release small amounts of minerals into the blood when needed.) Teach Refer students to Figure 8. Have them locate and examine each part of the femur. Ask: What covers the bone except for the ends? (A thin, tough membrane) What is just beneath this membrane? (Compact bone) How do blood and other materials get to the living cells inside the bone? (Blood vessels run through canals in the compact bone.) How does the structure of spongy bone relate to its function? (Spongy bone has many small spaces that make it lightweight but strong.) Where is marrow produced? (In the spaces in bone) What is marrow? (Two types of soft, connective tissue; one type produces some types of blood cells, the other type stores fat.) Does new bone tissue stop forming after you stop growing? (No; bones make new tissue when they absorb the force of your weight and when a bone has broken.) Apply Have students write a paragraph describing how the structure of bones allows the bones to grow and makes them strong. (Sample answer: The membrane allows blood vessels to run through canals in the compact bone to deliver materials the bone needs to function. Spongy bone has spaces within it that allow it to absorb large amounts of force.) learning modality: visual Transparency D5 FIGURE 8 Bone Structure The most obvious feature of a long bone, such as the femur, is its long shaft. Running through the compact bone tissue within the shaft is a system of canals. The canals bring materials to the living bone cells. Interpreting Diagrams What different tissues make up the femur? Soft Bones? In this activity, you will explore the role that calcium plays in bones. 1. Put on protective gloves. Soak one clean chicken bone in a jar filled with water. Soak a second clean chicken bone in a jar filled with vinegar. (Vinegar causes calcium to dissolve out of bone.) 2. After one week, put on protective gloves and remove the bones from the jars. 3. Compare how the two bones look and feel. Note any differences between the two bones. Drawing Conclusions Based on your results, explain why it is important to consume a diet that is high in calcium. Femur Bones Strong and Living When you think of a skeleton, you may think of the paper cutouts that are used as decorations at Halloween. Many people connect skeletons with death. The ancient Greeks did, too. The word skeleton actually comes from a Greek word meaning a dried body. The bones of your skeleton, however, are not dead at all. Bones are complex living structures that undergo growth and development. Bone Structure Figure 8 shows the structure of the femur, or thighbone. The femur, which is the body s longest bone, connects the pelvic bones to the lower leg bones. Notice that a thin, tough membrane covers all of the bone except the ends. Blood vessels and nerves enter and leave the bone through the membrane. Beneath the bone s outer membrane is a layer of compact bone, which is hard and dense, but not solid. As you can see in Figure 8, small canals run through the compact bone. These canals carry blood vessels and nerves from the bone s surface to the living cells within the bone. Just inside the femur s compact bone is a layer of spongy bone. Like a sponge, spongy bone has many small spaces within it. This structure makes spongy bone tissue lightweight but strong. Spongy bone is also found at the ends of the bone. The spaces in many bones contain a soft, connective tissue called marrow. There are two types of marrow red and yellow. Red bone marrow produces most of the body s blood cells. As a child, most of your bones contained red bone marrow. As a teenager, only the ends of your femurs, skull, hip bones, and sternum (breastbone) contain red marrow. Your other bones contain yellow marrow. This marrow stores fat that can serve as an energy reserve. What are the two types of bone marrow? Skills Focus Drawing conclusions Materials 2 plastic jars, vinegar, water, 2 clean chicken bones, gloves Time 15 minutes for setup; 15 minutes for observation Tips CAUTION: After students examine the chicken bones, make sure they wash their hands after removing the gloves. Expected Outcome Bones soaked in vinegar lose their calcium and become rubbery; a diet high in calcium helps keep bones hard. Extend Ask students to examine food labels at home to find food sources rich in calcium, and then report their findings to the class. learning modality: kinesthetic

6 Compact Bone Canal Outer membrane Bone marrow Compact bone Spongy bone Differentiated Instruction Gifted and Talented L3 Investigating the Effects of Microgravity Tell students that weightbearing exercise promotes bone growth and prevents bone loss. Exercises performed against the force of gravity stimulate osteoblasts, the cells that make bone. Ask students to find out the effects of microgravity on the bones of astronauts and how scientists are using this Blood vessels Bone Strength The structure of bone makes it both strong and lightweight. In fact, bones are so strong that they can absorb more force without breaking than can concrete or granite rock. Yet, bones are much lighter than these materials. In fact, only about 20 percent of an average adult s body weight is bone. Have you ever heard the phrase as hard as a rock? Most rock is hard because it is made up of minerals that are packed tightly together. In a similar way, bones are hard because they contain minerals primarily phosphorus and calcium. Bone Growth Bones are alive they contain cells and tissues, such as blood and nerves. Because they are alive, bones also form new bone tissue as you grow. Even after you are grown, however, bone tissue continues to form within your bones. For example, every time you play soccer or basketball, some of your bones absorb the force of your weight. They respond by making new bone tissue. Sometimes, new bone tissue forms after an accident. If you break a bone, for example, new bone tissue forms to fill the gap between the broken ends of the bone. In fact, the healed region of new bone may be stronger than the original bone! FIGURE 9 Bone Strength You can jump up and down or turn cartwheels without breaking bones. Chapter information to help people with spinal cord injuries and people with osteoporosis. (Students may discover some interesting facts, for example, that some astronauts on the space station Mir lost 13% of their bone mass, mostly from the legs.) Ask students to present a report to the class. learning modality: verbal Observing Bone Structure Materials leg bones from thoroughly cooked chickens or turkeys, dissecting trays, gloves, hand lens; before class, use a small kitchen saw to slice one leg bone crosswise and one lengthwise for each group. Place the bones in the trays. Time 15 minutes setup; 15 minutes class Focus Remind students that bones are organs that are composed of different types of tissue. Teach Have groups of students use Figure 8 to identify the various parts of the bones. Ask them to write down and sketch their observations. CAUTION: After students examine the chicken bones, make sure they wash their hands after removing the gloves. Apply Ask: Where did you find the largest concentration of compact bone and spongy bone? (Compact in the shaft, spongy at the ends) Explain that short bones, such as those in the fingers, are mostly spongy bone. Ask students to infer why long bones have more compact bone. (Long bones, such as those in the legs, must have harder, denser compact bone to support the body.) learning modality: visual Monitor Progress Skills Check Have students draw concept maps showing the structure of bone. Suggest that students draw concentric circles indicating the layers of tissue and draw arrows where blood vessels and nerves flow through. Students can save their concept maps in their portfolios. Figure 8 Compact bone, bone marrow, spongy bone, outer membrane Red blood marrow produces some of the body s blood cells. Yellow marrow stores fat that can serve as an energy reserve. 315

7 Address Misconceptions Bones Are Living Focus Some students might think that bone is dead. Teach Explain that some people think of bones as lifeless because they see skeletons in movies or skeletons of dead animals. Bone does contain nonliving material, such as calcium. However, it is composed of living tissue. Ask: What are the levels of organization before bones? (Cells, then tissues) What kinds of functions do these perform? (Cells grow, reproduce, and take in energy. Tissues perform a specific function.) Point out that bones are living because they are made of cells and tissues, which compose all living things. Apply Ask: Would a bone bleed if it were cut? (Yes, because bones have blood vessels) Would it hurt? (Yes, because bones have nerves) learning modality: verbal Taking Care of Your Bones Teach Key Concepts Habits for Strong, Healthy Bones Focus Remind students that calcium is a mineral that helps bones to be hard. Teach Ask: How can you get enough calcium? (Eat a well-balanced diet that includes good sources of calcium.) What kind of exercise helps your bones grow stronger and denser? (Activities in which your bones support the weight of your body) How can you reduce your risk of osteoporosis? (Eat calcium-rich foods and get plenty of exercise) Tell students that osteoporosis can be largely prevented by building bone mass during adolescence and young adulthood. Apply Encourage students to create a list of activities that are weight-bearing and a list of those that are not. (Weight-bearing activities include jogging, aerobics, walking, jumping rope, weight lifting, skating, dancing, soccer, and basketball. Non-weight-bearing activities include cycling and swimming.) learning modality: verbal 316 Bones, Muscle, and Skin Video Preview Video Field Trip Video Assessment Bone Development Try this activity: Move the tip of your nose from side to side with your fingers. Notice that the tip of your nose is not stiff. That is because it contains cartilage. As an infant, much of your skeleton was cartilage. Over time, most of the cartilage was replaced with hard bone tissue. The replacement of cartilage by bone tissue usually is complete by the time you stop growing. You ve seen, however, that not all of your body s cartilage is replaced by bone. Even in adults, many joints contain cartilage that protects the ends of the bones. Taking Care of Your Bones Because your skeleton performs so many necessary functions, it is important to keep it healthy. A combination of a balanced diet and regular exercise are important for a lifetime of healthy bones. Diet One way to help ensure healthy bones is to eat a wellbalanced diet. A well-balanced diet includes enough calcium and phosphorus to keep your bones strong while they are growing. Meats, whole grains, and leafy green vegetables are all good sources of both calcium and phosphorus. Dairy products, including yogurt, are good sources of calcium. Exercise Another way to build and maintain strong bones is to get plenty of exercise. During activities such as running, skating, or dancing, your bones support the weight of your entire body. These weight-bearing activities help your bones grow stronger and denser. To prevent injuries while exercising, be sure to wear appropriate safety equipment, such as a helmet and pads. What are two ways to keep your bones healthy? FIGURE 10 Caring for Your Bones Exercising regularly and eating a balanced diet help to keep your bones strong and healthy. Show the Video Field Trip to let students experience a trip through a bone and understand the structure and function of bones. Discussion question: What happens to the cartilage that makes up much of an infant s skeleton? (It is replaced by bone tissue as the child grows.) 316

8 Healthy Spine Osteoporosis As people become older, their bones begin to lose some of the minerals they contain. Mineral loss can lead to osteoporosis (ahs tee oh puh ROH sis), a condition in which the body s bones become weak and break easily. You can see the effect of osteoporosis in Figure 11. Osteoporosis is more common in women than in men. Evidence indicates that regular exercise throughout life can help prevent osteoporosis. A diet with enough calcium can also help prevent osteoporosis. If you eat enough calcium-rich foods now, during your teenage years, you may help prevent osteoporosis later in life. 2 Section 2 Assessment Spine with Osteoporosis Target Reading Skill Asking Questions Work with a partner to check the answers in your graphic organizer. Reviewing Key Concepts 1. a. Listing What are five functions of the skeleton? b. Explaining How does the skeleton protect the body? c. Predicting How would your life be different if your backbone consisted of just one long bone? 2. a. Naming What are four types of movable joints? b. Comparing and Contrasting Compare immovable joints with movable joints. c. Classifying Which of your movable joints are ball-andsocket joints? 3. a. Describing Describe the structure of the femur. b. Relating Cause and Effect How does the structure of bones make them both strong and lightweight? c. Applying Concepts How do a well-balanced diet and weight-bearing exercise help keep bones strong? FIGURE 11 Osteoporosis Without enough calcium in the diet, a person s bones weaken. These photos show how the shape and structure of vertebrae in a healthy spine compare with those in a person with osteoporosis. Relating Cause and Effect What can you do to prevent osteoporosis? Model Joints Choose two examples of movable joints from Figure 7. Ask a family member to perform separate movements that involve one joint and then the other. Make drawings to represent the joints and bones involved in each movement. Use the drawings to explain to your family how the motions of the two joints differ. Chapter Monitor Progress Figure 11 Exercise regularly and eat a diet with enough calcium. Eat a well-balanced diet and get plenty of exercise. Assess Reviewing Key Concepts 1. a. Provide shape and support, enable you to move, protect your organs, produce blood cells, and store minerals and other materials b. The skull protects the brain, and the breastbone and ribs protect the heart and lungs. c. Sample answer: You could not bend at the waist or twist. You would not be able to do some activities you do now, such as certain sports, twisting to get something behind you, or getting out of bed the same way. 2. a. Hinge, ball-and-socket, pivot, and gliding b. Both immovable and movable joints join two bones. Immovable joints allow little or no movement. Movable joints allow the body to make a wide range of movements. c. Shoulders and hips 3. a. Compact bone, spongy bone, and marrow b. Compact bone is hard and dense. Spongy bone has many small spaces within it that make it strong but lightweight. c. A well-balanced diet contains calcium and phosphorus, which bones need to keep them strong. Weight-bearing exercises help bones grow stronger and denser. Reteach Call on students to define the Key Terms in this section and relate each to the Key Concepts. Performance Assessment Writing Ask students to describe one of the major functions of the human skeleton and explain how the skeleton carries out that function. Keep Students on Track Check that students have completed their designs and sketches of the model hands, and have begun building their models. Approve all designs, and help students locate materials. Remind students that they can use parts from other devices, such as discarded or broken toys. Model Joints As a class, review the different types of joints and their movements. Suggest that students closely note the direction of the movement when a family member performs it. Advise them to keep their drawings simple to emphasize the movement. Section Summary: The Skeletal System Review and Reinforce: The Skeletal System Enrich: The Skeletal System 317