Focus on California Life Science 7th Grade Unit 4 - Chapter 13 Bones and Muscles

Chapter 13 Bones and Muscles Standards Preview The anatomy and physiology of plants and animals illustrate the complementary nature of ture and function . As a basis for understanding this concept a . Students know plants and mals have levels of tion for structure and function , including cells , tissues . organs , organ systems , and the whole organism . Students know how bones and muscles work together to vide a structural framework for movement . Physical principles underlie biological structures and tions . As a basis for understanding this concept Students know how to pare joints in the body ( wrist , shoulder , thigh ) with used in machines and simple devices ( hinge , and sliding joints ) Students know how levers fer mechanical advantage and how the application of this principle applies to the system . No matter your age or ability level , playing sports is inn and healthful .

Preview SOON Ind Bones , Muscles , and Skin on the BIG Idea How do the physical principles of forces and machines relate to the functions of your muscles and skeleton ?

Check What You Know A cat sleeps on one end of a saw , while a mouse crouches on the other end . The cat wakes up and walks away . How will the forces acting on the ends change ?

How will the forces change if the cat runs across the board toward the mouse ?

Chapter 13 503 The images shown hare represent some of the Key Terms in this chapter . You can use this vocabulary skill to help you understand the meaning of some Key Terms in this chapter . Latin Word Origins Many English words come from Latin . In Chapter you learned that the Latin prefix means back or against . In this chapter you will learn the term resistance . Resistance comes from the Latin prefix re and the Latin word , which means to stand . So resistance means the act of standing against . The table below shows Latin words that are sources of some Key Terms in this chapter . Latin Word I Meaning of Latin Word I Key Term involuntary muscle Type of muscle that is not under a person conscious control ligament Connective tissue that holds bones together osteoporosis A condition in which bones lose minerals , develop larger openings than normal bones , and become weak to place against resistance force The force that a lever exerts against an object free will voluntary muscle Type of muscle that is under a person ( IOUS control cardiac muscle striated muscle smooth muscle

bone Chapter Vocabulary Section ( page 508 ) muscle tissue nephron nervous tissue urinary connective tissue pathogen epithelial antibody 509 immunity homeostasis digestion stress ( page 518 ) skeleton compact bone vertebrae spongy bone joint marrow ligament osteoporosis Section involuntary muscle voluntary muscle skeletal muscle tendon striated muscle smooth muscle cardiac muscle Section ( page 532 ) force resistance force machine resistance distance mechanical advantage effort arm resistance arm lever fulcrum effort force effort distance Build Science Vocabulary Online Visit web Code Chapter 13 505

! Take Notes When you take notes . you write important ideas in shortened form . Use a red or blue heading as the title of your notes . Create a organizer similar to the sample below . In the left column , write questions about the text that follows the heading . The questions should ask for important information . Write the answers in the right column . Write a summary statement that expresses the main idea . See the notes below on part of Section of this chapter . Questions Notes Cells What is a cell ?

The basic unit of structure and function in a living thing What is the See Figure structure Cali boundary of cell of , um cell activities contains DNA , which contains information determining structure and function inside cell except nucleus contains What are the Can ) on processes that let organisms live . grow , functions of calls ?

and reproduce Organisms are made of cells . Cells carry on important functions in organisms . Apply It ! Review the notes in the right column . what are two important ideas found in the notes ?

According to the summary , what is the main idea of this text ?

As you read Section , take notes on the rest of the section . When you read Section , take notes on the whole section .

fa . A Machine A prosthesis is an artificial device that replaces a human body part . Designing artificial replacements , such as prosthetic hands , can be a challenging task . This is because even a simple act , such as picking up a pen , involves a complex interaction of body parts . If you study the movements of your hand , you may see how some of its movements are like simple machines , such as levers and hinges . You can use the physical principles behind these and other simple machines to build a prosthetic hand . Your Goal To design , build , and test a replacement for a human hand Your prosthesis must grasp and lift a variety objects be activated by pulling a cord or string spring back when the cord is released be built following the safety guidelines in Appendix A Plan It ! Before you design your prosthetic hand , study the human hand . Watch how the fingers move to pick up objects . Make a list of tools , machines . or other devices that mimic the ability of the hand to pick up objects . Examples include tongs , tweezers , pliers , and chopsticks , Then , choose materials for your hand and sketch your design . When your teacher has approved your design , build and test your prosthetic hand .

' with your shoulders . Hold the books in this ' the huma performing this activity , note how your body What is homeostasis ?

Organ Systems and Homeostasis ?

Standards Focus Students know and animals have levels of How Does Your Body Respond ?

for structure and function , Stack one book on top of ing cells , tissues , organs , organ another one . the ' Lift the two stacked books in front of you so the lowest book is about level i the ?

position for 30 seconds . While you are body , and what are their functions , responds . For example , how do your arms feel at the beginning and toward the end of the 30 seconds ?

Balance one book on the top of your head . Walk a few steps with the book on your head . Key Terms Think It Over 236 Inferring List all the parts of your body that worked together as , tissue you performed the activities in Steps through . epithelial tissue i organ system . The bell ! You hurry down the noisy halls to nephron the cafeteria . The unmistakable aroma of hot pizza makes your urinary bladder mouth water . At last , you balance your tray of pizza and salad ' while you pay the cashier . You look around the cafeteria for your friends . Then , you walk to the table , sit down , and begin , to eat . Think about how many parts of your body were involved in the simple act of getting and eating your lunch . Every minute of the day , whether you are eating , studying , walking , or even sleeping , your body is busy . Each part of the body has a i function , or job . And all the different parts of your body ally work together so smoothly that you don even notice them . This smooth functioning is due partly to the way in which the body is organized . The levels of organization in the human body consist of cells , tissues , organs , and organ systems . The smallest unit of organization is the cell . The next largest unit is tissue then , organs . Finally , the organ system is the largest unit of organization 50 !

Cells From the cell theory , you know that a cell is the basic unit of structure and function in a living thing . Complex organisms Howls a Book are composed of many cells in the same way building is organized ?

composed of many bricks . The human body contains about In this you will 100 trillion analyze the levels of organization in a book . Structures of Cells Most animal cells , including those in Examine to the human body , have a structure similar to the cell in Figure see how it is . You may recall that the cell forms the outside boundary of , the cell . Inside the cell is a large structure called the nucleus , and so on . which directs the cell activities . The nucleus also contains . information that determines the cell form and Shows this function . When the cell divides . or reproduces , this ' tion is passed along to the newly formed cells . The material ) within a cell apart from the nucleus is the cytoplasm . The at plasm is made of a clear , jellylike substance containing many compare the levels of cell structures called . in this Functions of Cells Cells carry on processes that keep , the isms alive . Inside cells , for example . molecules from digested food undergo cellular respiration that releases energy for the body activities . Cells also grow and reproduce . And they get rid of waste products that result from these activities . Making Models Which level of organization in the textbook represents cells ?

Which represents tissues ?

Organs ?

Organ systems ?

Call from inner lining of check Cell membrane cytoplasm Nucleus FIGURE Cell Structure Your body is made of trillions of tiny structures called cells . Interpreting Photographs What structure forms the outside boundary of the cell ?

so ! Types of Tissues Your body contains four kinds of tissues muscle , nervous , connective , and epithelial . Comparing and Contrasting How is the function of nervous tissue different from that of epithelial tissue ?

Muscle Tissue Every movement you make depends on muscle tissue . The muscle tissue shown here allows your body to move . Nervous Tissue Nervous tissue , such as the brain cells shown here . enables you to see , hear , and think . Connective Tissue Connective tissue , such as the bone shown here , connects and supports parts of your body . Epithelial Tissue Epithelial tissue , such as the skin cells shown here , covers the surfaces of your body and lines your internal organs . 510 Tissues The next largest unit of in your body is a group of specialized cells that perform the same function The human body contains four basic types of tissue . Look at Figure as you read about each type . Like the muscle cells that form it , muscle tissue can contract , or shorten . By doing this , muscle tissue makes parts of your body move . While muscle tissue carries out movement , nervous tissue directs and controls the process . Nervous tissue carries electrical messages back and forth between the brain and other parts of the body . Another type of tissue , connective tissue , support for your body and connects all its parts . Bone tissue and fat are connective tissues . The surfaces of your body , inside and out , are ered by epithelial tissue ( ep uh THEE lee ul ) Some epithelial tissue . such as your skin , protects the delicate structures that lie beneath it . The lining of your tive system consists of epithelial tissue that allows you to digest and absorb the nutrients in your food . em Organs and Organ Systems The stomach , heart , brain , and lungs are all organs . Recall that an organ is a structure that is composed of different kinds of tissue and does jobs . For example , your heart pumps blood through your body . The heart contains all four kinds of , nervous , connective , and epithelial . Each tissue utes to the organs overall job of pumping blood . Each organ in your body is part of a system . An organ system is a group of organs that work together to perform a major function . OThe human body has 11 organ systems . The integumentary , skeletal , and muscular systems provide structure and allow movement . The circulatory , respiratory , digestive , excretory , immune , and reproductive systems carry out the processes of life . The nervous and endocrine systems provide control over body processes . The next pages describe the major functions of these systems . Remember that for each system to function , its organs and tissues must work together . And so must its cells . What is the job of muscle tissue ?

mis ( yer ) Dennis ( bottom layer ) Fat Sweat gland , Oil gland The Integumentary System Your skin , hair , and nails make up your body covering , or integumentary system . shows the structure of human skin . The cells and tissues of your skin work together to create a barrier that your body from injury and bacteria and . Skin also helps regulate your body temperature and keeps your cells from drying out . Your skin works with other systems , too . As part of your excretory system . skin helps remove waste when you perspire . Skin works with your vous system to give you information about your environment . The Skeletal System Your skeletal system is made up of all the bones in your body and other connective tissues . The etal system supports the body and gives it structure . It also your body organs . For example , hard rib bones shield your heart and lungs from damage . Your bones consist of hard , compact layers of tissue . Different kinds of specialized tissue provide structure , produce blood cells , and store important minerals , such as calcium . Connective tissue attaches one bone to another and forms joints that allow movement . The Muscular System Most of your muscles work to move your body by pulling on your skeleton . These muscles , called skeletal muscles , usually work only when you want them to . Other muscles work is , when you don think about them . Together , your muscles and bones are times called the musculoskeletal system . Each muscle cell mitochondria , which release energy for muscles to work . These muscle cells are combined into bundles of , which work together during movement . Fiber bundles are then into muscle groups that move your bones . For example , the biceps is a muscle group that helps move your arm . FIGURE The Skin In some ways , the skin is the largest organ . It accounts for about 15 percent of body weight . heavier than any internal organ . In an adult of average size , the skin covers a surface area of about or square meters . 13 511

FIGURE Circulatory System Blowing Bubbles The respiratory system moves air in and out of the lungs . 512 The Circulatory System Your circulatory system serves as a transportation network . It carries food and to all the cells of your body . It also collects the wastes that must be removed . vessels port these materials in the form of a mixture of cells and that is called blood . The circulatory system is powered by the pumping of your heart . Blood vessels that carry blood away from the heart are called arteries . Vessels that carry blood toward the heart are called veins . These vessels consist of epithelial tissue that lines their inner walls and tissue that covers their outer surfaces . muscle tissue within the vessel walls helps move the blood as it circulates . The smallest and thinnest blood the arteries and veins . Capillaries reach every cell , delivering and collecting the materials transported by the blood . The Respiratory System Take a deep breath . You can feel your lungs fill with air . The lungs are the main organs of your respiratory system , which takes in oxygen and disposes of carbon dioxide . Recall that your cells use oxygen for cellular respiration . Carbon dioxide is a waste product in this process . When you breathe . air moves into your lungs through a set of branching passageways . These passageways end in clusters of tissue that are surrounded by capillaries . There , oxygen crosses into the blood and is then distributed through the body by the circulatory system . Air moves in and out of your body as a result of the actions of muscles in your chest . You can sometimes control the action of these muscles . But not for long . Soon your respiratory system starts working on its own again . The Digestive System Have you had anything to eat today ?

Food provides your body with materials for growing and for repairing tissues . Food also provides energy for thing you do . Digestion is the breakdown of food into small molecules the body can use . The digestive system does this job .

Mouth Salivary Liver gland ' Esophagus Stomach Pancreas A Digestive System Figure shows most of the organs of the digestive system . Food enters the body through your mouth and gradually moves through the system . Epithelial tissues in the stomach and small intestine produce chemicals called enzymes that help digest the food . Involuntary muscle tissue churns the food and keeps it moving . Meanwhile , bile produced by the liver and enzymes from the pancreas help break down the food in the small intestine even more . Specialized cells in the lining of the small intestine then absorb the nutrients into the bloodstream . When the over material moves into the large intestine , water is removed and the solid waste material passes out of the body . The Excretory System Your body produces excess water and waste from the activities in cells and from the breakdown of some materials in the digestive system . The excretory system , shown in Figure , removes these wastes from your bloodstream . Your two kidneys are the major organs of the excretory system . Each kidney contains about million specialized structures called that act as tiny factories . These structures remove both wastes and needed materials from the blood . Then , the needed materials are returned to the bloodstream , and the wastes are combined with water to create urine . Urine flows from the kidneys to the urinary bladder , where it is stored until it leaves the body through the urethra . What is the function of the kidneys ?

A Excretory System FIGURE Materials in the Body The digestive system breaks down materials needed by the body . The excretory system removes wastes . Interpreting Diagrams What structure carries food from the mouth to the stomach ?

Break Up ! Model the breakup of fats in the small intestine . Fill two plastic jars half full of water . Add a few drops of oil to each jar . Add about spoonful of baking soda to one jar . Stir the contents of both jars . Record your observations . Observing In which jar did the oil begin to break up ?

what type of substance does the baking soda represent ?

Chapter 13 513 White blood , cell FIGURE Protection Against Disease The white blood cell in this colorized photo specializes in trapping and destroying bacteria . Predicting How would the body be affected if white blood cells failed to attack an invading pathogen ?

Which Pieces Fit Together ?

What does this activity tell you about how cells defend your body against pathogens ?

Your teacher will give you a piece of paper with a jagged edge . one student in the class has a piece of paper with a jagged edge that matches yours , like two pieces of a jigsaw puzzle . Find that student and the two edges together . Inferring Suppose one piece of paper is a pathogen , and the other is a cell in your body that fights invading pathogens . How many kinds of pathogens can each defender cell recognize ?

514 ' The Immune System Your immune system protects your body from bacteria and viruses , or pathogens . Specialized white blood cells target and destroy these gens . An example of one kind of white blood cell is shown in Figure . Its captures and destroys bacteria that could cause infection Other white blood cells specialize in identifying types of viruses . These white blood cells recognize ent marker molecules on the surface of the viruses . In some cases , the white blood cells attack and destroy these viruses . In other cases , white blood cells activate different cells that make that help destroy pathogens . The bodies bind to the marker molecules on the pathogens , causing them to clump together . These clumps are then destroyed by white blood cells like the one in the . After an infection , your immune system remembers the pathogen and can produce antibodies more quickly if you are exposed again . This ability to destroy pathogens before they can cause disease is called immunity . The Reproductive System The reproductive systems of males and females contain organs that produce sex cells . Recall that sex cells carry in the form of DNA . When these cells combine . the DNA can direct the development of a new individual . The organs of the reproductive system also produce chemicals that regulate the physical development of maturing bodies . In mature females , for example , these chemicals make pregnancy and the delivery of a baby possible . ad ! i What is the function of the immune system ?

Sight Touch Hearing The Nervous System You can think . move , hear music , and do much more because of your nervous system . The vous system takes in information from your environment and from within your body . It processes this information and mands the body to respond . For example , you might sense that it is too warm and decide to take off your coat . In this case , you actually think about what to do . But in many other ways , your nervous system functions automatically . The nervous system includes the brain and spinal cord . Specialized nerve cells make up these two organs . These nerve cells also reach from the spinal cord to all parts of your body . Nerve cells transmit information between the parts of your body and the spinal cord and brain . The Endocrine System The systems in your body constantly make adjustments to maintain the internal conditions you need to live and function . Your endocrine system helps regulate the activities of the organs and organ systems by releasing hormones . are chemicals that change the activity in your body cells . Each hormone affects a group of cells or an organ in a particular way . The endocrine system consists of a lection of specialized tissues that produce and release hormones . Your crine glands are located in different places throughout your body . These glands release their hormones into your bloodstream , where the circulatory system carries them to the targeted tissues . Complex processes regulate the amount of every hormone in your body . The levels can go up or down , depending on signals from other glands or from your brain . Thyroid gland Pancreas FIGURE in the throat ?

Parathyroid glands Taste Smell Senses of Your Nervous System Your eyes , ears , skin , mouth , and nose contain nerve cells that transmit information to your brain about the world around you . Hypothalamus Pituitary gland Adrenal glands some Glands of the Endocrine System The endocrine glands produce hormones , which are then released into the bloodstream . Interpreting Diagrams Which glands are located Chapter 13 515

, For Links on body systems Visit Web Code FIGURE Maintaining Homeostasis Regardless of the surrounding temperature , your body temperature remains fairly constant at about . Sweating ( left ) and shivering ( right ) help regulate your body temperature . Applying Concepts What is the term for the body tendency to maintain a stable internal environment ?

516 Homeostasis The different organ systems work together and depend on one another . When you ride a bike , you use your muscular and skeletal systems to steer and push the pedals . But you also need your nervous system to direct your arms and legs to move . Your respiratory . digestive , and circulatory systems work together to fuel your muscles with the energy they need . And your , respiratory , and excretory systems remove the wastes produced while your muscles are hard at work . All the systems of the body work together to maintain homeostasis ( hob mee oh STAY sis ) the body tendency to keep an internal balance . Homeostasis is the process by which an organism internal environment is kept stable in spite of changes in the external environment . Homeostasis in Action To see homeostasis in action , all you have to do is take your temperature when the air is cold . Then , take it again in an overheated room . No matter what the temperature of the air around you , your internal body will be close to . Of course , if you become sick , your body temperature may rise . But when you are well again , it returns to . Maintaining Homeostasis Your body has various ways of maintaining homeostasis . For example , when you are too warm , you sweat . Sweating helps to cool your body . On the other hand , when you are cold , you shiver . Shivering occurs when your muscles rapidly contract and relax . This action produces heat that helps keep you warm . Both of these processes help your body regulate your temperature and maintain homeostasis .

Stress and Homeostasis Sometimes , things can pen to disrupt homeostasis . As a result , your heart may beat more rapidly or your breathing may increase . These tions of your circulatory and respiratory system are signs of stress . Stress is the reaction of your body to potentially threatening , challenging , or disturbing events . Think about what happens when you leave the starting line in a bike race . As you pedal , your heart beats faster and your breathing increases . What is happening in your body ?

First , your endocrine system releases a chemical called adrenaline into your bloodstream . Adrenaline gives you a burst of energy and prepares your body to take action . As you pedal , your muscles work harder and require more oxygen . Oxygen is carried by the circulatory system , so your heart beats even faster to move more blood to your muscles . Your breath comes faster and faster , too , so that more oxygen can get into your body . Your body is stress . If stress is over quickly , your body soon returns to its normal state . Think about the bike race again . After you cross the finish line . you continue to breathe hard for the next few minutes . Soon , however , your breathing and heart rate return to normal . The level of adrenaline in your blood returns to normal . Thus , homeostasis is restored 10 after just a few minutes of rest . 51 , Your body reacts to stress , such as the start , What Is stress ?

of a bike race , by releasing adrenaline and carrying more oxygen to body cells . section Assessment Target Reading Skill Take Notes Review your . Defining What is homeostasis ?

notes for this section . What are two important . Explaining How does stress affect homeostasis ?

med Under OVENS and Organ Relating Cause and Effect Describe what ) happens inside your body as you give an oral Reviewing Key concepts report in front of your class . Identifying List the four levels of organization ' in the human body from smallest to largest . In I ( Give an example of each . and Contrasting What is the difference between tissues and organs ?

I I a . the I main systems of the uh ' sentences supporting . Describing Next to the name of each system , write a phrase that describes its . Chapter 13 517 Standards Focus Students know how bones and muscles work together to provide a structural framework for movement . Students know how to compare joints in the body ( wrist . shoulder , thigh ) with structures used in machines and simple devices ( hinge , and sliding joints ) 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 vertebrae joint ligament cartilage compact bone I spongy bone marrow osteoporosis 518 Hard as a Rock ?

Your teacher will give you a rock and a leg bone from a cooked turkey or chicken . Use a hand lens to examine both the rock and the bone . Gently tap both the rock and the bone on a hard surface . Pick up each object to feel how heavy it is . Wash your hands . Then make notes of your observations . It Over Observing Based on your observations , why do you think bones are sometimes compared to 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 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 . however , the building framework will no longer be visible . Like a building , you also have an inner framework , but it isn 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 . Functions of the Skeletal System Just as a budding 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 .

Shape and Support Your skeleton determines the shape of your body , much as a steel frame determines the shape of a building . The backbone , also called the vertebral or spinal column , is the center of the skeleton . Locate the backbone in Figure 11 . Notice that the bones in the skeleton are in some way connected to this column . If you move your down the center of your back . you can feel the 26 small bones , or vertebrae ( tuh bray ) singular vertebra ) that make up your backbone . Bend forward at the waist and feel the bones adjust as you move . Each individual vertebra is like a bead on a string . Iust as a beaded necklace is and able to bend , so too i is your vertebral column . If your backbone were just one bone , you would not be able to bend or twist . Why is the vertebral column ' considered the center of the Metatarsals . Phalanges I , in FIGURE 11 The Skeleton The skeleton provides a framework that supports and protects many other body parts . Comparing and Contrasting In is the skeleton like the steel framework of a building ?

In what ways is it different ?

Clavicle ( collar bone ) Scapula ( shoulder blade ) skeleton ?

Phalanges Metacarpals Humerus Radius Ulna Vertebral column ( backbone ) A Skull Pelvic girdle ' Chapter 13 519 Go For Movable Joints activity Visit Web Code FIGURE 12 Movable Joints without movable joints , your body would be as stiff as a board . The different kinds 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 socket join ( 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 . Movement and Protection Your skeleton allows you to move . Most of the body 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 a 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 . allow bones to move in different ways . There are two kinds of joints and movable joints . Joint joints allow the greatest range of motion . The joint in your shoulder allows you to swing your arm freely in a circle . Your hips also have joints .

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 . 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 . Movable Joints Most joints in the body are movable joints . Movable joints allow the body to make a wide range of ments . Look at Figure 12 to see the variety of movements that these joints make possible . Notice how some joints move much like a simple machine . For example , your knee makes the same motion as a door hinge . 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 ( tuh ) which is more 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 lubricates the ends of the bones , allowing them to move smoothly over each other . How are movable joints held together ?

Sliding Joint A sliding joint allows one bone to slide over another . The sliding joint in your wrist or ankle enables you to bend and flex as well as make limited motions . 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 . Al ' 6521

Boone 13 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 ?

and Living When you think of a skeleton , you may think of the paper outs 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 The bones of your skeleton , however , are not dead at all . Bones are complex living structures that undergo growth and development . Activity ' Bone Structure Figure 13 shows the structure of the femur , or thighbone . The femur , which is the body longest bone , Soft Bones ?

in mi , activity , you connects the pelvic bones to the lower leg bones . Notice that a explore the role that calcium thin , tough membrane covers all of the bone except the ends . Plays in bones . Blood vessels and nerves enter and leave the bone through the . Put on protective membrane . Beneath the bone outer membrane is a layer of Soak one clean chicken compact bone , which is hard and dense , but not solid . As you 313 ?

with can see in Figure 13 , small canals run through the compact bone . These canals carry blood vessels and nerves from the bone a Med bone surface to the livin cells ' th with vinegar . Vinegar me causes calcium to dissolve lust the femur 130119 13 ) out of ham ) bone . Like a sponge , spongy bone has many small spaces After one week , put on within it This structure makes spongy bone tissue lightweight protective gloves and but strong . Spongy bone is also found at the ends of the bone . remove the bones from The spaces in many bones contain a soft , connective tissue the Jars . called marrow . There are two types of and yellow . Compare how the two Red bone marrow produces most of the body blood cells . As a bones look and feel . Note child , most of your bones contained red bone marrow . As a ' what are the two types of bone marrow ?

5226 tax bemeen teenager , only the ends of your femurs , skull , hip bones , and . Drawing Based sternum ( breastbone ) contain red marrow . Your other bones on you , mugs , why contain yellow marrow . This marrow stores fat that can Serve it is important to consume a as an energy reserve . diet that is high in calcium .

compact Bone Canal Blood vessels spongy bone Bone marrow membrane Bone Strength The structure of bone makes it both strong and lightweight . 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 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 phosphorus and calcium . Bone Growth Bones are 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 . 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 A You can jump up and down . or turn cartwheels without Sometimes , new bone tissue forms after an accident . lfyou ho . nes . break a bone , for example , new bone tissue to the gap between the broken ends of the bone . In fact , the healed region of new bone may be stronger than the original bone ! Chapter 13 523

524 Bones . Muscle , and Skin Bone Development Try this Move the tip of your nose from side to side with your . 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 by the time you stop growing . You ve seen , however , that not all of your body 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 tions . 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 balanced diet . A 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 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 14 Caring for Your Bones Exercising regularly and eating a balanced diet help to keep your bones strong and healthy .

FIGURE 15 Osteoporosis Without enough calcium in the diet , a person 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 ?

Healthy Spine I Spine with Osteoporosis 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 bones become weak and break easily . You can see the effect of osteoporosis in Figure . Evidence indicates that exercise throughout life and a diet with enough calcium can help prevent osteoporosis . If you eat enough I foods now , you may help prevent osteoporosis later in life . Section . Reading . Relating Cause and Effect How does the Assessment Vocabulary Skill Latin Word Origins The Greek word means What does the Latin word poms mean ?

How do these two word parts combine to produce the meaning of osteoporosis ?

Reviewing Key Concepts a . Listing What are functions of the skeleton ?

Explaining How does the skeleton protect the body ?

Predicting How would your life be different if your backbone were just one long bone ?

a . Naming What are four types of movable joints ?

Comparing and Contrasting Compare immovable joints with movable joints . Classifying Which of your movable joints are joints ?

Identifying What are three layers within the femur ?

structure of bones make them both strong and lightweight ?

Applying Concepts How do a diet and exercise help keep bones strong ?

Model Joints Choose two examples of movable joints from Figure 12 . 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 13 525

Section The Muscular System Standards Students know how bones and muscles work together to provide a structural framework for movement . What types of muscles are found in the body ?

Why do skeletal muscles work in pairs ?

Key Terms involuntary muscle voluntary muscle skeletal muscle tendon striated muscle smooth muscle ' cardiac muscle Go For . More on types Visit Web Code 526 How Do Muscles Work ?

Grip a clothespin with the thumb and index finger of your writing hand . Squeeze the clothespin open and shut as quickly as possible for two minutes . Count how many times you can squeeze the clothespin before your muscles tire . Rest for one minute . Then , repeat Step . Think It Over Predicting What do you think would happen if you repeated Steps and with your other hand ?

Give a reason for your prediction . Then , test your prediction . A rabbit becomes still when it senses danger . The rabbit sits so still that it does seem to move a muscle . Could you sit out moving any muscles ?

Saliva builds up in your mouth . You swallow . You need to breathe . Your chest expands to let air in . All of these actions involve muscles . It is impossible to sit lutely still without muscle movement . There are about 600 muscles in your body . Muscles have many functions . For example , they keep your heart beating , pull your mouth into a smile , and move the bones of your skeleton . The girl doing karate on the next page uses many of her muscles to move her arms , legs , hands , feet , and head . Other muscles expand and contract her chest and allow her to breathe . Types of Muscle Some of your body movements , such as smiling , are easy to control . Other movements , such as the beating of your heart , are impossible to control completely . That is because some of your muscles are not under your conscious control . Those muscles are called involuntary muscles . Involuntary muscles are responsible for such essential activities as moving food along the digestive tract and controlling the size of an eye pupil .

The muscles that are under your conscious control are called voluntary muscles . Smiling , turning a page in a book , and getting out of your chair when the bell rings are all actions controlled by voluntary muscles . Your body has three types of muscle muscle , smooth muscle , and cardiac muscle . Only skeletal muscle is voluntary . Smooth muscle and cardiac muscle are involuntary . In Figure 16 , you see a view of each type of muscle in the body . Both skeletal and smooth muscles are found in many places in the body . Cardiac muscle is found only in the heart . Each muscle type performs functions in the body . Skeletal muscle 16 Types of Muscle Your body has three types of muscle tissue skeletal muscle , smooth muscle , and cardiac muscle . Classifying Which type of muscle is found only in the heart ?

Smooth muscle chapter 13 527 Are skeletal muscles at work when you not moving ?

Hold a stirrer in front of you , parallel to a table top . Do not touch the table . Have a partner place a hairpin on the stirrer . Raise the stirrer until the legs of the hairpin just touch the table . The head of the should rest on the stirrer . Hold the stirrer steady for 20 seconds . Observe what happens to the hairpin . Grip the stirrer tighter and repeat Step . Observe . Are the skeletal muscles in your hand at work when you hold your hand still ?

Explain . 5280 Skeletal Muscle Every time you type on a computer keyboard , shoot a basketball , or walk across a room , you are using skeletal muscles . As their name suggests , skeletal muscles are attached to the bones of your skeleton . These muscles provide the force that moves your bones . At each end of a skeletal muscle is a tendon . A tendon is a strong connective tissue that attaches muscle to bone . Skeletal muscle cells appear banded , or striated . For this reason , skeletal muscle tissue is sometimes called striated ( ay tid ) muscle . Because you have conscious control of skeletal muscles . they are as voluntary muscles . One characteristic of skeletal muscles is that they react very quickly . Think about what happens during a swim meet . Immediately after the ing gun sounds , a swimmers leg muscles push the swimmer off the block into the pool . However , another characteristic of skeletal muscles is that they tire quickly . By the end of the race , the swimmer muscles are tired and need a rest . If you did the Standards at the start of this section , you felt the of tired muscles in your . Smooth Muscle The inside of many internal organs , such as the stomach and blood vessels , contain smooth muscles . Smooth muscles are involuntary muscles They work to control certain movements inside your body , such as those involved in digestion . For example , as the smooth of your stomach contract , they produce a churning action . The churning mixes the food with chemicals . and helps to digest the food . Unlike skeletal muscles , smooth muscle cells are not ated Smooth muscles behave differently than skeletal muscles , too . Smooth muscles react more slowly and tire more slowly . Cardiac Muscle The tissue called cardiac muscle is found only in your heart . Cardiac muscle has some characteristics in common with both smooth muscle and skeletal muscle . Like smooth muscle , cardiac muscle is involuntary . Like skeletal muscle , cardiac muscle cells are striated . However , unlike etal muscle , cardiac muscle does not get tired . It can contract repeatedly . A specialized group of nerve cells within the heart sends out signals that cause the cardiac muscle to contract . You call those repeated contractions heartbeats . Where Is smooth muscle found ?

when You Flex Your Ann i Biceps contracts amp relaxes Triceps relaxes Muscles at Work Has anyone ever asked you to make a muscle ?

If so , you ably tightened your , bent your arm at the elbow , and made the muscles in your upper arm bulge . Like other skeletal muscles , the muscles in your arm do their by contracting , becoming shorter and thicker . Muscles work in coordination with the tal system and the nervous system First , messages from the nervous system cause a muscle to contract . Then the shortened muscle pulls on the attached bone , causing it to move . Because muscle cells can only move bones by contracting , skeletal muscles must work in pairs . While one muscle contracts . the other the pair relaxes to its original length . Muscles Work In Pairs The coordinated contraction and relaxation of different muscles allows you , for instance , to bend your arm . Figure 17 shows this action . The biceps muscle on the upper arm contracts . This motion bends , or , your arm at the elbow . The angle between the bones in your forearm ( the radius and ulna ) and the bone in your upper arm ( the humerus ) then decreases . Your biceps muscle bulges as it shortens . You make a As the biceps contracts , the triceps on the back of the upper arm relaxes and extends . To move the weight down , the biceps and triceps also work together . This time , the triceps muscle contracts . The action causes the angle between your upper arm bone and lower arm bone to increase . In other words , our arm straightens . At the same time , the biceps relaxes and extends to its original length . When you lift a weight . the biceps moves your arm . But the triceps is important , too . It helps keep the motion smooth and controlled , protecting the elbow joint from a sudden , strong contraction . When you extend your arm , the biceps smoothes the motion . The and extending of your arm is a good example of how muscles work in coordinated pairs . FIGURE 17 Muscle Pairs Because muscles can only contract . or shorten , they must work in pairs To bend the arm at the elbow , the biceps contracts while the triceps returns to its original length . Interpreting Diagrams What happens to each muscle to straighten the arm ?

Chapter 13 529 Muscular Strength and Flexibility Regular cise is important for maintaining both muscular strength and . Exercise makes individual cle cells grow in size . As a result , the whole muscle becomes thicker . The thicker a muscle is , the stronger the muscle is . When you warm up thoroughly before exercising , the blood to your muscles increases and they become more . Stretching after you warm up helps prepare your muscles for the more Vigorous exercise or play ahead . Sometimes , despite taking proper precautions , muscles can become injured . A muscle strain , or pulled muscle , can occur when muscles are overworked or stretched . Tendons can also be overstretched or partially torn . After a long period of exercise , a skeletal muscle can cramp . When a muscle cramps , the entire muscle tracts strongly and stays contracted . If you injure a muscle or tendon , it is important to follow medical FIGURE 13 instructions and to rest the injured area so it can heal . Preventing Muscle Injuries when you warm up before exercising you What are two ways to prepare the muscles increase the flexibility of your muscles . Reading section Assessment Target Reading Skill Take Notes Review your notes for this section . What are two important ideas that you noted under Muscles at Work ?

in Science ( Reviewing Key Concepts Identifying What are the three types of muscle tissue ?

Write a . Comparing and Contrasting How do voluntary and paragraph comparing smooth involuntary muscles differ ?

Give an example of each muscle tissue and skeletal muscle type of muscle . tissue . Include whether these Predicting The muscles that move your are muscle tissues are voluntary or attached to the bones in your by tendons . involuntary , where they are found Suppose one of the tendons in a person index and what their functions are . In were cut . How would it affect movement in the finger ?

addition . describe what you might Identifying Where might you muscle pairs ?

lfyou looked . Describing Describe how the muscles in your upper arm work together to bend and straighten your arm . Applying Concepts When exercising to build muscular strength , why is it important to exercise both muscles in a muscle pair equally ?

530 Skills Lab , A Look Beneath the Skin , Problem What are some characteristics of skeletal muscles ?

How do skeletal muscles work ?

Skills Focus observing , inferring , classifying Materials water uncooked thicken paper towels wing , treated with scissors bleach dissecting tray Procedure . Put on goggles , an apron , and protective gloves . CAUTION Wear gloves whenever you handle the chicken . Your teacher will give you a chicken wing . Rinse it well with water . dry it with paper towels , and place it in a dissecting tray . Carefully extend the wing to find out how many major parts it has . Draw a diagram of the external structure . Label the upper arm . elbow , lower arm , and hand ( wing tip ) Use scissors to remove the skin . Cut only through the skin . CAUTION Cut away from your body and your classmates . Examine the muscles , which are the bundles of pink tissue around the bones . Find the two groups of muscles in the upper arm . Hold the arm down at the shoulder , and alternately pull on each muscle group . Observe what happens . Find the two groups of muscles in the lower arm . Hold down the arm at the elbow , and alternately pull on each muscle group . Then , make a diagram of the muscles . Find the white tissue at the ends of the muscles . Notice what parts the tendons connect . Add the tendons to your diagram . Remove the muscles and tendons . Find the ligaments , which are the whitish shaped structures between bones . Add them to your diagram . Dispose of the chicken parts according to your teacher instructions . Wash your hands . Analyze and conclude . Observing How does a chicken wing move at the elbow ?

How does the motion compare to how your elbow moves ?

What type of joint is involved ?

Inferring what happened when you pulled on one of the arm muscles ?

What muscle action does the pulling represent ?

Categorize the muscles you observed as smooth , cardiac , or skeletal . Communicating Why is it valuable to record your observations with accurate diagrams ?

Write a paragraph in which you describe what your diagrams show . More to Explore Use the procedures from this lab to examine an uncooked thigh and leg . Compare how the chicken leg and a human leg move . Obtain your teacher permission before carrying out your investigation . Chapter 13 531

00 . Students know how to compare joints in the body ( wrist , shoulder , thigh ) with structures used in machines and simple devices ( hinge , and sliding joints ) Students know how levers confer mechanical advantage and how the application of this ple applies to the musculoskeletal system . How are force and work related ?

How does a lever make work easier ?

How no bones and muscles function as levers in the body ?

Key Terms force work machine lever I fulcrum ' effort force effort distance resistance force resistance distance ' mechanical advantage effort arm ' resistance arm FIGURE 19 Using Machines Shovels and rakes make the work of these students easier . 532 Machines and the Body , Standards Focus , Standards Are You an Eating Machine ?

Using your front teeth , bite off a piece of a cracker . Now chew the cracker . Pay attention to how your lower jaw moves . Touch your jaw just in front of your ear , as shown in the photo . As you chew , push in slightly on your jaw so that you can feel how it moves . If the movement is still not clear , try opening your mouth wide while you feel the back of the jaw . Think It Over Inferring when you bite and chew , the back of your jaw moves less than your teeth . Why is that ?

A fresh load of soil for your school garden has been dumped too far from the garden . To move the soil , you migh use ple machines such as a lever , shovel , or wheelbarrow to make the job easier . As you work in the garden , you may also lift handfuls of soil by bending your arm and using your hand just like a shovel . Many bones and muscles of the human body act like the simple machine known as a lever .

Force and Work To understand how parts of your body act like machines . you first need to know about two concepts force and work . Force A force is a push or a pull on an object . A force is described by its strength , or magnitude , and the direction in which it acts . If you push on a door , you exert a force in a ferent direction than if you pull on the door . The standard unit for the magnitude of a force is the newton ( An arrow can represent the direction and strength of a force . The arrow points in the direction of the force . The longer the arrow is drawn . the greater the force strength . Work You do work when you exert a force on an object that causes the object to move some distance in the same direction as the force . You can calculate the amount of work done on an object by multiplying force times distance . work Force Distance You can use this formula to calculate the amount of work you do to lift a plant . When you lift an object , the upward force must be at least equal to the object weight . 80 , to lift a plant that weighs 50 newtons by a distance of meter requires 25 ( of work . The symbol means that the units are multiplied . Work But what can you do if an object weighs more than the amount of force you can exert ?

For example , what if you wanted to lift a piano up a of stairs ?

You would need to use a machine . A machine is a device that allows you to do work in a way that is easier or more effective . How can you calculate work ?

Smaller force Greater force 20 Representing Forces Arrows tell you how the strengths of different forces compare . A force arrow points in the direction of a force . 21 Amount of work When you lift a plant , you do work . You do more work when you lift a heavier plant the same distance . Relating Cause and Effect Why does it take more work to lift the heavier plant ?

Chapter 13 533 The girl pushes down with a small force over a long distance . the lever changes the small force to a larger force , and the crate moves up a I Resistance force Effort distance ' Resistance distance 22 noun A Simple Machine A lever is a simple machine that makes lifting heavy objects easier . Applying Concepts Why does the girl place the fulcrum close to the crate ?

Levers Have you ever played sticks ?

If so , you are already familiar with a simple machine called a lever . A lever is a rigid rod that is free to rotate around a pivot point . The point that a lever rotates around is called the fulcrum . You can use a lever to turn a small force into a large force so you can lift a piano . Levers were probably used in prehistoric times . But the first person to explain how levers work was Archimedes . a of ancient Greece . Force and Work in Levers To understand levers , look at Figure 22 . The girl is using a lever to lift a crate that weighs 100 newtons . She places the fulcrum close to the crate and stands far away from the fulcrum , on the other side . She applies a force out a Na on the lever of 10 newtons over a distance of meter . In this A hammer am as a you way , she can lift the crate meter . The work done on use is to pun a nan from boa each side of the lever IS equal , but the girl has to apply less force The hammer changes the direction than she would need without a lever . A lever makes work a . easier by changing the amount of force exerted , the distance he ' over which the force is exerted . or the direction of the force . The force that you exert on a lever is called the force . The distance you push down is the effort distance . In , the force that a lever exerts on an object is called the resistance force , and the distance the lever pushes up on an object is the resistance distance . In Figure 22 , the girl applies a small effort force on the lever , which becomes a larger resistance force on the crate . A small force that is applied over a long distance can create a larger force over a short distance . When you apply an effort force over an effort distance , you are doing work on the lever . In turn , the lever applies a force over a resistance distance and does work on an object . The work you do on the lever equals the work the lever does on the object . FIGURE 23 Effort force Resistance force 5340

The relationship between the work done on a lever and the work that the lever does on an object can be written as this formula . Effort force distance ' Resistance distance Resistance force If you know any three values in the formula , you can late the fourth value , as shown in the Sample Problem below . Math Measurement and Geometry ample ) Calculating Effort Distance Suppose you need to move a boulder . Using a wooden plank as a lever and a log for the fulcrum . you plan to lift the boulder and then let it roll away . The boulder weighs 240 and you can exert 80 of force . How far will you have to push down on your end of the lever to lift the boulder ?

Read and Understand What information are you given ?

Resistance force 240 Resistance distance Effort force 80 Plan and Solve at quantity are you trying to calculate ?

Effort distance I What formula contains the given quantities and the unknown quantity ?

Effort Effort Resistance force distance force distance Perform the calculation . Effort 80 distance 240 In so 12 Mom Effort 12 ' distance WI Back and Check Does your answer make sense ?

An effort distance of is more than the resistance distance of This answer makes sense because . your effort force is less than the resistance force . Calculating Effort Force A friend who weighs 400 is sitting on the end of a seesaw . You push down a distance of on the opposite end , which lifts your friend a distance of in . How much effort force did you apply ?

Calculating Resistance Force In order to lift a box , you push down on a lever with an effort force of 100 if the box moves up , how much does the box weigh ?

Chapter 13 535 force force I Gun Effort The law of the arm arm A levers effort arm is the distance from the fulcrum to the effort on A am is Mechanical Advantage If you compare the effort force to the distance from the fulcrum the resistance force , you can the advantage of using a lever . A lever mechanical advantage is the number of times a lever increases a force exerted on it . The mechanical advantage of a lever is equal to the ratio of resistance force to the force . Mechanical advantage In the sample problem on the previous page . an effort force of 80 newtons was exerted to move a boulder . The lever mechanical advantage is 240 newtons divided by 80 tons , or . The lever tripled the effort force . The Law of the Lever Have you ever balanced a metal spoon on your ?

If so , you have experience with the law of the lever . The spoon is a lever , and your acts as the crum . To make the spoon balance , your has to be closer to the heavier , bowl end of the spoon than to the other end . Figure 24 shows how a lever may be balanced when the effort force and resistance force are different . Notice that the fulcrum is not in the middle . The distance from the fulcrum to the effort force is called the effort arm . The distance from the fulcrum to the resistance force is the resistance arm . The law of the lever states , that for a lever to be balanced , force times the effort arm must be equal to the resistance force times the arm . Classes of Levers There are three classes of levers . These are by the location of the fulcrum relative to the effort force and the resistance force . In a lever , the fulcrum is between the effort force and the resistance force . In a lever , the resistance force is between the effort force and the fulcrum . In a lever , the effort force is between the resistance force and the fulcrum . Figure 25 shows 50 , Mad , examples of all three classes of levers . How many different classes of levers are there ?

5360 25 Three Classes of Levers The three classes of levers differ in the positions of the fulcrum , effort force , and resistance force . Applying Concepts Which type of level always has a mechanical advantage less than ?

Resistance force Levers levers always change the direction of the effort force . If the fulcrum is closer to the resistance force , these levers also increase force if the fulcrum is closer to the effort force . these levers also increase distance . Other examples , Effort include scissors , pliers , ram and seesaws . Fulcrum Levers Resistance These levers increase force , but do not change force the direction of the effort force . Other examples include doors , nutcrackers , and bottle openers . some Resistance force Fulcrum Levers These levers increase distance , but do not ' change the direction of the effort force . other examples include fishing poles , shovels , and baseball bats . Resistance 5970 ?

force Resistance force ?

Chapter 13 531 , Mechanical Advantage the horizontal axis ?

advantage of Lever lin For Links on work Visit Web Code 5380 Data The effort force and resistance force for three different levers are shown in the graph . Reading Graphs What variable is plotted on . Interpreting Date If an effort force is exerted on Lever what is the resistance force ?

Calculating Calculate the mechanical . Drawing Conclusions Which lever produces the greatest resistance force when an effort force of 20 is exerted ?

Of 40 ?

Which lever has the greatest mechanical advantage ?

Math Algebra and Functions , Mechanical Advantages of Levers Machines in the Body Now that you know how levers work , you can see how parts of your body act like levers . When you move your legs , hips . hands , or head , you are using a lever system to perform the movement . Most of the machines in your body are levers that consist of bones and muscles . Joints as Machine structures In Section , you learned about the joints of the human skeleton . of the movable joints are actually . The joints in the body act as pivot points for the bones . The bones act as levers , and muscles provide the force . The thigh joint , the wrist joint , the shoulder joint , the knee joint , and the elbow joint are examples of for levers in the body . The thigh joint , also known as the hip joint , is an example of a et joint . Your thigh bone , or femur , has a rounded end that fits into a hole of the bone that is your pelvic girdle . Another example of a joint is your shoulder . Your wrist is an example of a sliding joint , where one bone slides over another bone . Your elbow and your knee are examples of hinge joints . These joints function like the hinges on a door . What of joint is the wrist ?

Lever The joint at the top of your neck is the fulcrum of a lever . The muscles In the back of your neck provide the effort force . The resistance force is used to tilt your head back . Bones and Muscles as Lever Systems The most common type of lever in your body is the lever . But your body also has and levers . You can see examples of all three classes of levers in Figure 26 . In each case , the effort force is applied at the point where a muscle attaches to a bone . Lever The ball of your foot is the fulcrum of a lever . The muscle in the calf of your leg provides the effort force . The resistance force is used to raise your body . Lever Your elbow is the fulcrum of a lever . Your biceps muscle provides the effort force . The resistance force is used to lift your arm . 26 Levers in the Body You do need to look further than your own body to find machines . Three different types of levers are responsible for many of , i The bone serves as the lever , and the resistance force is the force Your exerted by the bone . This force may be used for many things , such as chewing , running . or lifting a glass of water . Section Vocabulary Skill Latin Word Origins Remember that the Latin word means to place How does this meaning help you understand the key term resistance force ?

Reviewing Key Concepts ' a . Defining What is a force ?

Comparing and Contrasting How is work different from force ?

Measuring How is the value for a distance measurement important in calculating work done on an object ?

Reviewing What is a lever , and how is a A . lever useful ?

Explaining What is the mechanical advantage of a lever ?

Comparing and Contrasting How does a lever differ from a lever ?

Assessment . leading a . Listing Name three joints that act as for levers in the body . Applying Concepts For one of the joints you listed above , explain how the joint functions as a fulcrum when you move . a . Calculating With an effort force of 50 , Archimedes pushes a lever down . On the other side of the fulcrum , a statue that weighs rises How far down did Archimedes push the lever ?

Calculating A lever has an effort force of 40 and a resistance force of 80 What is its mechanical advantage ?

539 Using Your Leverage Problem is the law of the lever accurate ?

Skills Focus calculating , predicting , interpreting data Materials meter stick I set of weight holders spring scales ( plastic fulcrum or other pivoted support Procedure PART set of hooked weights Lever . Copy the data table onto a separate piece of paper . Label the data table Lever . Place the meter stick with its center resting on the fulcrum so that it is balanced evenly . Make sure the left end is above the table and the right end hangs over the edge . Choose a position on the meter stick to the left of the fulcrum . Record the distance from the fulcrum to that position as the resistance arm . Hang the lightest hooked weight at that position . The meter stick should tilt until that side is resting on the table . Record the value of the hooked weight in newtons as the resistance force . Hint A mass of gram weighs tons , so you can convert grams to newtons by multiplying the mass by . 5400 ' Choose a position on the meter stick to the right of the fulcrum . Record the distance from the fulcrum to that position as the effort arm Using the spring scale at that position , pull down on the meter stick until it is horizontal with the table . Record the ing on the spring scale in newtons as the effort force . Repeat the experiment four more times with four different hooked weights . Record your data in the table . if necessary , use a larger spring scale for heavier weights . PART Lever . Draw a new data table on a separate piece of paper . Label the table Lever . Balance the meter stick from by hanging it on the spring scale . Record the weight of the meter stick in newtons . You will need this value because the weight of the meter stick adds to the resistance force . Place the meter stick with one end resting on the fulcrum and the other end resting on the table . Choose the mark as the resistance arm . Hang the lightest hooked weight at that position . Record the resistance force in newtons as the sum of the weights of the meter stick ( from Step ) and the hooked weight . Recall that you can convert grams to newtons by multiplying the mass by . Part !

Trial Am ( lo . Choose the mark at the free end of the meter stick as the effort arm . Using the spring scale at that position , lift the meter stick until it is horizontal with the table . Record the reading on the spring scale in newtons as the effort force . 11 . Repeat the experiment four more times with four different hooked weights . Record all your data . If necessary , use a larger spring scale for heavier weights . Analyze and conclude . Calculating In each data table . calculate the value of the resistance arm times the force and the value of the effort arm times the effort force . Record the results in the appropriate place on each data table . Interpreting Data How do your calculations in Question compare to the law of the lever as it is stated on page 536 ?

Calculating Calculate and record the mechanical advantage of the lever for each trial . Interpreting Data Did the two classes of levers have the same mechanical advantage ?

if so , why ?

if not , which type of lever had the greater mechanical advantage ?

Why ?

Predicting How can you balance a lever using a hooked weight and a hooked weight ?

Explain . with your teachers permission , test your prediction . Communicating Many sports such as tennis and baseball use equipment that extends the arm . The racquet or bat is made of material that is strong , but lightweight . Suppose you work for a company that produces racquets or bats . Write an advertisement describing your product . In the advertisement , explain how the racquet or bat acts as a lever to make the work of hitting the ball easier . More to Explore Repeat the experiment with a lever . Hang the weight at the end of the meter stick . and pull up with the spring scale at the center of the meter stick . Remember to take into account the weight of the meter stick as you did for the lever . This time , however , the weight of the stick opposes your effort force and must be subtracted from the value on the spring scale . Does the lever give you the same results as the lever ?

Explain . chapter 13 541 Chapter 13 Study Guide The I a when muscles contract . they exert a force that pulls on bone and makes it move . Many bones act as levers by rotating around a joint that acts as a fulcrum . Organ Systems and Homeostasis ( Key Concepts The levels of organization in the body consist of cells , tissues , organs . and organ systems . The human body has 11 organ systems . The integumentary , skeletal , and muscular systems provide structure and allow movement . The circulatory , respiratory , digestive , excretory , immune , and reproductive systems carry out the processes of life . The nervous and endocrine systems provide control over body processes . Homeostasis is the process by which an organism internal environment is kept stable in spite of changes in the external environment . Key Terms muscle tissue nephron nervous tissue urinary bladder connective tissue pathogen epithelial tissue antibody organ system immunity digestion homeostasis kidney stress The Skeletal System Key Concepts . Your skeleton 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 . Joints allow bones to move in different ways . Bones are complex living structures that undergo growth and development . A balanced diet and regular exercise are important for a lifetime of healthy bones . Key Terms skeleton compact bone vertebrae spongy bone joint marrow ligament osteoporosis cartilage 5420 The Muscular System Key Concepts Your body has three types of muscle skeletal , smooth , and cardiac . Skeletal muscles work in pairs . While one muscle contracts , the other muscle in the pair relaxes to its original length . Key Terms striated muscle smooth muscle cardiac muscle involuntary muscle voluntary muscle skeletal muscle tendon Machines and the Body Key Concepts . How are force and work related ?

How does a lever make work easier ?

How do bones and muscles function as levers in the body ?

Key Terms force effort distance work resistance force machine resistance distance lever mechanical advantage fulcrum effort arm effort force resistance arm Review and Assessment For Web Code ' Target Reading Skill Take Notes To help you review part of Section , take notes on the text following the heading Joints of the Skeleton A in up mo ( pages ) The notes have been together started for you at the right . is Reviewing Key Terms ' choose the letter of the best answer . Complete the following sentences so that . Which type of body tissue covers the surfaces your dewy the Key Terms of the body ?

The mouth , Stomach , and small intestine are muscle tissue organs that function in digestion , which I ) nervous tissue involves ' i tissue . Strong connective tissue found at the ends of tissue bones is called cartilage , which is important . A soft , connective tissue found inside some because ?

bones ' Smooth muscles are also called involuntary . muscles because I ) marrow . a type of machine , which is useful osteoporosis . go ' Muscles that help the bones move are 10 ' A . can increase advantage . which is cardiac muscles . smooth muscles . muscles Writing in Science ( involuntary muscles . The force you apply to a lever is called the effort force . resistance force . Write I tow effort distance . 953751599 ' resistance distance . wan . The distance from the fulcrum to the resistance force in a lever is called the effort distance . resistance distance . effort arm . resistance arm . Bones , Muscles , and Skin , Chapter 13 543

Review and Assessment Checking Concepts 11 . Explain the relationship among cells , tissues , organs , and organ systems . 12 . List the four kinds of movable joints . Describe the type of movement each joint allows . 13 . How does eating a diet and exercising regularly contribute to health ) bones ?

14 . Explain how skeletal muscles work in pairs . What three things can a lever do to make work easier ?

16 . Describe a lever in your body . Locate the effort force , the resistance force , and the fulcrum . Thinking Critically 17 . Inferring In addition to bone , cartilage , and fat . Scientists classify blood as a connective tissue . Explain why . 18 . Making Generalizations How is homeostasis important to survival ?

19 . Comparing and Contrasting Explain how the structure of compact bone and spongy bone relate to the function of a bone , such as your femur . 20 . Predicting If smooth muscle had to be controlled consciously , what problems could you foresee in living ?

21 . Making Judgments Suppose a member of your running team suggests eliminating time because it takes too much time away from practice . Do you think this suggestion is a good idea ?

Why or why not ?

22 . Applying Concepts does the law of the lever explain why the seesaw pictured below stays balanced ?

5440 Math Practice 23 . Calculating You use a lever to lift a box onto a shelf . If you push down an effort distance of using an effort force of 60 , how high will the box rise ?

Him In this problem , the box weight is equal to the resistance force . Applying Skills Use the diagram to answer Questions . 24 . Classifying Which structure in the diagram is the triceps ?

Which is the biceps ?

25 . Predicting How will the shape of each muscle change if the arm in the diagram is extended ?

26 . Interpreting Diagrams Which structure in the diagram serves as the fulcrum for extending the arm ?

Standards investigation Performance Assessment Before testing your prosthetic hand , explain to your classmates how and why you designed the hand the way you did . When you test the hand , observe how it picks up objects . How does it compare with a real human hand ?

How could you improve the function of your prosthetic hand ?

Standards Practice Choose the letter of the best answer . Which of the following represents the smallest level of organization in the body ?

A cardiac muscle tissue the heart a muscle cell the circulatory system . The muscles that you use to lift a book are A cardiac muscles . smooth muscles . involuntary muscles . skeletal muscles . Use the graph to answer Question . Age and Bone Density in Men and Women . Which of the following statements is true according to the graph shown above ?

A The bones of women are more dense than the bones of men . I The bones of men contain less calcium than do the bones of women . The bone density of both men and women decreases as they age . An average woman has stronger bones than an average man . Success Trucker at . Which skeletal joint functions most like the machine shown below ?

A neck knee wrist shoulder . Which statement describes what happens when you bend your arm at the elbow ?

A The biceps contracts and the triceps relaxes . The triceps contracts and the biceps relaxes . Both the biceps and the triceps contract . Only the triceps functions . To open a door , you push on the part of the door that is farthest from the hinges . Why would it be harder to open the door if you pushed on its center ?

A You would have to apply a larger effort force . You would have to apply a larger resistance force . The door is a lever . You would be increasing the effort arm . A shovel is a type of lever that has a greater effort force than resistance force . Explain why a shovel is still useful . What class of lever is the shovel ?

Identify an example of how this class of lever is used in the body . 545