The Skeletal System ~~-~ Although you may not be aware of all your bones, your body actually contains about 206 bones of different shapes and sizes. All of these bones are arranged in a very orderly way. They are fastened together by stringy connective tissues called ligaments. Together, your bones and the ligaments that hold them in place help make up most of your skeletal system. The skeletal system has five impor tant functions: it provides shape, allows movement, protects organs, produces blood cells, and stores certain materials. Functions of the Skeleton Without your skeletal system, your body would look like little more than a mass of jelly. Besides giv ing the body shape and support, the skeletal system also serves four other important function s. One of Scapula Sternum Ribs y Vertebra Pelvis In -t---Femur Metacarpals K"l-I'---- Patella ft--- In Fibula I-+!----Tibia h Phalanges Section Objective To describe the structure and function of the skeletal system Figure 12-4 You r body contains about 206 bones. Working together, the bones and the muscles to which most of the bones are attached allow you to' do many things, including play basketball like Magic Johnson. What is the name of the connective tissue that connects bone to bone? these is movement. Almost all of your bones are tached to muscles. Working together, bones and muscles allow you to walk, sit, stand, and even Bones also protect the organs of your body. Your brain is surrounded by a bony skull that it from being injured. If you move your fingers along the center of your back, you can feel your backbone, or vertebral column. Your backbone teets your spinal cord , which contains nerve tissue. The spinal cord is the main message "cable" be tween the brain and other parts of the body. What other organs are protected by bones? Bones store important minerals. For example, calcium and phosphorus are constantly deposited bones for future use. The long bones in your also produce many of the blood cells necessary for healthy blood. Figure 12-5 This X-ray shows how the 19 bones in each of your hands allow you to unscrew a batt/e . What are the five functions of the skeletal system? Parts of the Skeleton Su ppose you were asked to make a life-sized model of a skeleton. Where would you start? You may begin by thinking of the human skeleton as HELP WANTED: ATHLETIC TRAINER Knowledge of diving required. Must know first aid. Previous instructional experience and surface-diving ability desi red. Back ground study in anatomy and physiology a plus . You are enjoying the diving competition on television. Divers twist and turn thei r bodies as they glide through the air to the delight of their audience. For trained athletes diving is safe, but for beginners it requires instruction and equipment. Serious injury can occur to those beginners who have not learned proper techniques, including the best way to warm up before the com peti tion. The people who help prepare athletes for the Olympics or for other athletic competitions are called athletic trainers. Their job is to be sure athletes keep physically fit for participation in athletic competition. Trainers instruct ath letes on how to strengthen muscles by doing special exercises and suggest special diets keep athletes in the best of health . T must also know when an injury or problem pears serious and a doctor should be If you are interested in sports and enjoy helping athletes do w ell. you can f'n rl""t1,'>t; a career as an athletic trainer. To receive information. write to the National AS~50clatl()n' for Sport and Physical Education , 1900 ASl:iOCIIJ tion Drive, Reston, VA 22091. lones are at )nes and \d even smile. ur body . .un that keeps elr fingers 1 feel your backbone pronerve tissue. "cable" be \e body. What ) For example, . Illy deposited In ~s in your body Is necessary for ke a life-sized t) You l you star. i\an skeleton as I' special diets to ot health , TraIners . . rv or problem ap InlUshould be ca\~e~~ in sports and m~g you can consIder To receive ~~re Na~ional Assoclatl~n , 1900 Assocla being divided into two major parts. The two major parts of the human skeleton are the axial (AK-see uhl) skeleton and the appendicular (ap-uhn-DIHK yuh-luhr) skeleton. AXIAL SKElETON The axial skeleton covers the area that runs from the top of your head down your body in a straight line to your hips. This part includes the skull, the chest with its ribs and other bones, and the vertebral column . The vertebral col umn consists of 33 separate bones. Each of these bones is called a vertebra (vER-tuh-bruh; plural: vertebrae) . The appendicular skeleton includes the bones that branch out from the axial skeleton. These bones include the pelvis, or hip bones, the bones of the arms and legs, the clavicle (KLAv-uh-kuhl), or collar bone, and the scapula (sKAP-yoo-luh), or shoulder blade. APPENDICULAR SKELETON "''A---Vertebra Figure 12-6 The vertebral column consists of 33 vertebrae, or small bones, stacked one on top of the other. These bones not only protect the spinal cord, but they also form a strong support for the body. Is the vertebral column part of the axial or appendicular skeleton? Formation of Bones Of all our body parts, bones are the strongest and the hardest. Perhaps this is the reason why many people tend to think of bone as permanent and unchanging. Actually, bone is made up partly of living tissue. Your bones grow and change just as your skin does. During childhood, bones are shaped reshaped as the shape and weight of the body Figure 12-7 X-rays of the hands of a two year old (top left) and a three year old (bottom left) show that bone has not yet replaced the cartilage in the wrist. In the X-ray of the 14-year-old hand (center), bone formation is almost as complete as it is in the X-ray of a 60-year-old's hand (right). What process changes cartilage to bone? 279 Sharpen Your Skills Bones as Levers Using reference materials in the library, find out about le vers. Distinguish between first-class and second-class levers. How do bones act as levers? On posterboard, draw an example of a first-class and second-class lever. Below each drawing, draw an example of the bones that act like that type of lever. In each of the drawings, label the effort, load, and fulcrum. At the bot tom of the posterboard, define each of these terms. changes through growth. Even in adulthood, bone' being continually made and removed, especially where it is under pressure. With your index finger, touch the tip of your nose. Now gently move the tip of your nose from side to side. You are able to move the tip of your nose because it contains cartilage (KAHRT-uhl-ihj). Cartilage is a type of flexible connective tissue. It supports such structures as the nose and ears. lage also connects the ribs to the sternum, or breast bone, and acts as a cushion between the bones of the vertebral column. This connective tissue also covers the ends of bones to keep them from rub bing against one another where they meet. Most bone is made from cartilage. In the early stages before birth, the skeleton is composed a entirely of this flexible tissue. Then, over several months, a great deal of cartilage disappears and is replaced by bone . This process is called ossitlc;atJ(Jln. (ahs-uh-fuh-KAy-shuhn) . Most of the bones in the skeleton are formed this way. Structure of Bones Figure 12-8 The femur, which is the longest bone in the body, has two enlarged ends with a long shaft connecting them. The ends of the femur are made up of softer spongy bone, while the shaft is made up of compact bone. What is the tough membrane that surrounds the shaft called? Periosteum Bones are made up of living tissue. Yet in some ways they are similar to such nonliving things as rocks. Two obvious similarities are hardness and strength. Both bones and rocks owe their hardness and strength to chemical substances called min Although rocks contain a wide variety of minerals, bones are made up mainly of mineral compounds that contain the elements calcium and phosphorus. Marrow Shaft 280 Spongy bone Solid bone Blood vessels Dairy products are rich in calcium and phosphorus. Next time someone suggests that you drink milk "to keep your bones strong and healthy ," you will know why this suggestion makes sense. ) of your Let's take a close look at the longest bone in the nose from body to see what it, and other bones, are made of. ip of your This bone, called the femur, links your hip to your tT-uhl-ihj). knee. Perhaps the most obvious part of this bone is e tissue. It . its long shaft, or column , which is shaped something ld ears. Cartl like a hollow cylinder. The shaft contains solid bone um , or breast and is surrounded by the periosteum (pehr-ih-AHs le bones of tee-uhm). The periosteum is a tough membrane that . tissue also contains bone-forming cells and blood vessels. The n from rub bone-forming cells aid in repairing injuries to the meet. bone. The blood vessels su pply food and oxygen to 1n the early the bone's living tissue. Muscles are attached to the ;mposed almost periosteum's surface. At each end of the shaft is an over several. enlarged knob. These knobs are made of a softer appears and ~s type of bone called spongy bone. llled ossificatlon Running through the middle of the thick bone is e bones in the a system of pipelike passageways called the Haversian (huh-vER-shuhn) canals. They contain blood vessels, which bring food and oxygen to the living bone cells. These canals also contain nerves. The nerves send messages through the canals to livparts of the bone. Yet in some ssue. If you have ever broken a chicken bone in half, .iving things as hardness and may have noticed that it contains a hollow cav "'e their hardness or space. Inside the cavity of every bone is a soft ~~ ' ll d minerals. or yellow material called marrow. Red marrow :e.s ~(t o~' rnineral s , . ,·f\rhuops most of the body's blood cells , and yellow tne Y d . contains fat and blood vessels. nera, 1 cornpoun s hosphorus. :) an d P )od, bone peciaHy IS > _ """"'::lI You walk slowly to the edge of the diving board gaze nervously into the water. Then you raise arms high and lower your head between them. . slightly at the knees, you leap into the air kick your legs out behind you , meeting the sur of the water with your fingertips. None of movements would be possible if your body was equipped with structures called joints. A joint is place where two bones meet. There are several types of joints. Some joints, as the gliding, ball-and-socket, hinge, and pivot Figure 12-9 Th e tiny openings in this photograph of thick, compa c t bone are the Haversian canals. What do these canals contain? Sharpen Your Skills What's in a Bone? Because bones are made up of living tissue, they need structures that will protect and nourish them. 1. Obtain a large bone from a turkey or chicken drumstick. 2. Remove all of the meat from the bone. 3. Using a knife, cut off one end of the bone. CAUTION: Be careful when using a knife. 4. Examine the bone care fully and identify as many parts as you can. Draw a diagram of the bone and label its parts. In the human skeleton, what is this bone called? 281 Sharpen Your Skills First-Aid Techniques Contact the local chapter of the American National Red Cross that gives first-aid in struction. Visit a class to ob serve the first-aid techniques for fractures, dislocations, and sprains that may occur due to accidents. Present your find ings to the class in an oral report. Be sure to mention the meaning of the term first aid. Also explain the first-aid treat ment for each of these inju ries. Explain how each occurs. Figure 12-10 The actions involved in diving require the use of many types of joints. What movement does the ball-and socket joint allow you to do? joints, are called movable joints. Movable joints the bones they connect to move. Others, such as joints in the skull do not permit movement. These joints are called immovable joints. In the diving example, a gliding joint allows you to lower your head as you ready yourself for your dive into the water. The gliding joint allows the tebrae in the neck to slide over one another. 'When you raise your arms high, the ball-and socket joints of your shoulders make the possible. The ball-and-socket joints allow you to swing your arms in a circle. These joints are made of a bone with a rounded head that fits into the cuplike pocket of another bone. Can you name an other example of a ball-and-socket joint in the . As you swing your arms forward, you turn them palm side down . This movement is made possible the pivot joint. The pivot joint permits a turning motion in which one bone rotates on a ring-shaped bone. As you get ready to leap off the diving board, you bend your knees. The knee is another type of Neck vertebrae Humerus joint, the ment SECTI 1. Wh syst 2. Wh 3. Lisl fo u 4. Wh 5. COl ble 6. Su ~ steI PIVOT JOINT GLIDING JOINT 12 ~--Femur Humerus BALL-AND-SOCKET JOINT 282 Fibula ---'1;'.'_ _ Tibia HINGE JOINT It hours your 1 asleep Or ar Wi muscl alive. pump des al ,ints allow Ich as the .. These !lows you or your s the ver ~ r. t!l-and ovements ou to lre made to the name anQ the body? turn them possible by It urning ng-shaped g board, ~ r type of - -- Ulna joint, a hinge joint. The hinge joint, also found at the elbow, allows for forward and backward move ment. See Figure 12-10. SECTION REVIEW Figure 12-11 The X-ray of a shoulder (right) shows how a bone can be forced out of a joint in a dislocation. In the X-ray of a lower arm (left), you can see a break in the radius. What is the other bone in the lower arm called? 1. ""hat are the five functions of the skeletal system? 2. What is a ligament? 3. List four places in the body where cartilage is found. 4. What is marrow? 5. Compare the movements of four types of mova ble joints. 6. Suggest a reason why the ribs are attached to the sternum, or breastbone, by cartilage. PIVOT JOINT 12-3 The Muscu'lar System - - - Femur Tibia HINGE JOINT It is 3 A.M. and you have been asleep for several hours. All day you walked, ran, and played , using your muscles in a variety of ways. Now that you are asleep, all the muscles in your body are also at rest. Or are they? Without waking you, many of the more than 600 muscles in your body are still working to keep you alive. The muscles of your heart are contracting to pump blood throughout the body. Your chest mus cles are working to help move air in and out of Section Objective To describe the three types of muscles 283 The Skeletal System -------= Although you may not be aware of all your bones, your body actually contains about 206 bones of different shapes and sizes. All of these bones are arranged in a very orderly way. They are fastened together by stringy connective tissues called ligaments. Together, your bones and the ligaments that hold them in place help make up most of your skeletal system. The skeletal system has five impor tant functions: it provides shape, allows movement, protects organs, produces blood cells, and stores certain materials. Functions of the Skeleton Without your skeletal system, your body would look like little more than a mass of jelly. Besides giv ing the body shape and support, the skeletal system al·o serves four other important functions. One of SkUII~ ~L Mandible Clavicle Scapula Humerus -5!i>-iiT-ii + - - Sternum ~~~~tJ-Ribs Radius- - T / Ulna 4ia'-~rr-- Vertebra --J#! -n---'iT-- Pelvis n +---Femur Metacarpals t\u'----Patelia tt----Fibula n I - t l - - - - Tibia Tarsals- - ___~ Section Objective To describe the structure and function of the skeletal system Figure 12-4 Your body contains about 206 bones . Working together, the bones and the muscles to which most of the bones are attached allow you ta do many things, including play basketball like Magic Johnson. What is the name of the connective tissue that connects bone to bone?
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