8th Grade Chapter 13 Lesson 1: Skeletal & Muscular Systems PDF

Your Skeletal System MAIN IDEA​ ​Your skeletal system provides your body with a framework​. Your skeletal system is made up of bones, joints, and various connective tissue. You can feel bones in your hands, arms, legs, and feet. All of your bones make up your skeleton. Your body has more than 200 b...

Your Skeletal System MAIN IDEA​ ​Your skeletal system provides your body with a framework​. Your skeletal system is made up of bones, joints, and various connective tissue. You can feel bones in your hands, arms, legs, and feet. All of your bones make up your skeleton. Your body has more than 200 bones. Bones are attached to muscles. Each movement you make is caused by your bones and muscles working together. You can see many bones in the figure in the Lesson Resources panel. The skeletal system has important functions. Bones provide support. Are you sitting right now? If so, your bones and muscles are working to hold you in your sitting position. If you raise your hand to speak in class, your bones and muscles cause the movement. Touch your head. The hard part on the top of your head protects your brain. Other bones protect your spinal cord, lungs, and other internal organs. The figure in the Lesson Resources panel shows how the skull protects your brain. Another function of bones is to produce and store materials needed by your body. Red blood marrow makes millions of blood cells each day. Bones store fat and calcium. Calcium is needed for strong bones and teeth and for many cellular processes. Several kinds of connective tissues help move and protect your bones. Bones work together at joints. Joints provide flexibility and enable the skeleton to move. A ligament connects bones to other bones. When the bones in joints move, ligaments stretch and work to keep the bones together. Ligaments connect bones but do not protect them. Bones are protected by cartilage​. ​Cartilage protects bones, such as those connected by your knee joint. Your elbows and shoulders are also protected by cartilage. The figure in the Lesson Resources panel shows how cartilage protects the bones in your knee joint. A tendon​ ​can also protect your bones. Tendons help to stabilize joints and keep them from moving out of place. Your skeletal system contains two types of joints—immovable joints and movable joints. Immovable joints do not move. For example, your skull contains several immovable joints. Movable joints allow you to move your hands and feet and bend parts of your body such as your knees and elbows. READING CHECK Compare​ Identify two types of joints and give an example of each. Your Muscular System MAIN IDEA​ ​Your muscular system allows your body to move and helps keep it stable​. You use muscles when you walk and stretch. Movement is an important part of the muscular system​.​ Muscles also provide your body with stability and protection. Muscles attached to bones support your body to provide stability and balance. If you stumble and lose your balance, your muscles pull you back to a stable position. Muscles cover most of your skeleton like a layer of padding. Muscles cover your abdomen, chest, and back to protect your internal organs. Muscles also work to keep your body at its normal temperature of around 37°C. When you are cold, your muscles contract quickly and cause you to shiver. When you are too warm or have exercised, your body may sweat. In either case, when your body is too cold or too warm, your muscles work to turn chemical energy into thermal energy to keep your body at a safe temperature. Many of your muscles are attached to bones by tendons to enable your skeleton to move. The movement of your body can be fast, such as when you run, or slow, such as when you stretch. Muscles are made of strong tissue that can contract in an orderly way. When a muscle contracts, the cells of the muscle become shorter. When the muscle relaxes, those cells return to their original length. See the figure in the Lesson Resource panel for an example. Many of your muscles are not attached to bones. As these muscles contract, they cause blood and food to move through your body. These are the muscles that cause your heart to beat. These types of muscles also make the hair on your arms stand on end when you get goose bumps. READING CHECK Explain​ How do muscles work? Types of Muscles Your body has three different types of muscles: skeletal, cardiac, and smooth. Each of these muscle tissues has a specific function. Skeletal muscle is voluntary muscle. This means that you control the skeletal muscles to make your body move. The figure in the Lesson Resources panel shows the major skeletal muscles. Your heart is made of cardiac muscle. Cardiac muscle is involuntary muscle. Cardiac muscles work on their own, without your control. When cardiac muscles contract and relax, they pump blood through your heart and blood vessels throughout your body. Smooth muscle is involuntary muscle named for its smooth appearance. Blood vessels in your body are lined with smooth muscles. Your stomach, bladder, and intestines also contain smooth muscles. Contraction of the smooth muscles controls the movement of blood through the vessels. They also move other materials through the body, such as food in the stomach. READING CHECK Differentiate​ Explain the difference between ​voluntary​ and ​involuntary​ muscles. How Muscles Work Together Skeletal muscles work by pulling bones. They do not push on your bones. Each movement that you make involves your muscles pulling on your bones. Muscles often work together to help your body move. Muscles contract and expand to pull on bones and create movement at a joint. The process of two muscles working together is called paired movement. For example, when you pull up your lower arm at the elbow, your biceps muscle contracts. When you then lower your arm, your biceps muscle relaxes and the triceps muscle contracts in order to pull the arm down. The figure in the Lesson Resources panel shows how muscles work together. Problems with Bones and Muscles MAIN IDEA​ ​Your bones and muscles can develop problems​. Your bones, muscles, and connective tissues are strong, but they need your care. Problems can develop because of injury, infection, poor posture, and lack of nutritious foods. Some problems of the skeletal system can include: Fracture.​ A fracture is a break in a bone caused by an injury. Dislocation.​ This occurs when a bone is pushed out of its joint. Dislocation can stretch or tear a ligament. Sprain.​ A sprain is an injury to the ligament connecting bones at a joint. This occurs when a ligament is stretched or twisted and causes swelling. Strain.​ This is a small tear in a muscle or tendon. Strains can occur when a muscle has been overstretched. A strain may be referred to as a pulled muscle. Overuse injuries.​ Injuries as a result of overuse occur over a period of time. An example of overuse is a shin splint, which can develop in runners. Osteoporosis.​ This condition results in brittle or porous bones. Osteoporosis can be caused by long-term lack of nutrition or exercise.  Scoliosis.​ This is a curving of the backbone. The spine curves to one side of the body in an S-shape or C-shape. Muscular dystrophy.​ This disorder weakens muscles over time. It is usually inherited and causes skeletal muscle tissue to gradually waste away. READING CHECK Summarize​ What are the most frequent causes of injuries to bones and muscles? Caring for Your Bones and Muscles MAIN IDEA​ ​You can help keep your bones and muscles healthy. Your good health habits can keep your bones and muscles strong and healthy. Bone and muscle health requires energy from the foods you eat. A diet that is rich in nutrients such as protein, fiber, potassium, and vitamin C can help keep your muscles strong. Physical activity also helps keep muscles healthy and strong. Decreased muscle strength can increase the risk of heart disease and injury, and make joints less stable. Do flexibility exercises so you can move more easily and work out more safely. Choose activities that strengthen your muscles and bones. Improve your cardiovascular endurance to give your heart and lungs more power. Warm up before and cool down after physical activity. If you feel pain, stop and give your body time to recover. Also important is your posture, or the way you hold your body. Good posture means the bones and joints in your back stay in place and your muscles are used properly. To prevent too much strain on your back, avoid carrying a heavy backpack. Bend and use your legs, not your back, when you lift something heavy. Running, walking, cycling, and swimming can help keep your back strong and healthy. READING CHECK Explain​ Tell how good posture contributes to bone and muscle strength. What causes paralysis?​ The nervous system can be affected by injury or disease. A spinal cord injury causes the nervous system to lose the ability to send messages to the muscles. Muscular disorders such as muscular dystrophy cause the muscular system to lose the ability to respond to messages from the nervous system.