1. Muscles 12/6/2011

2. Bell Ringer Stand up, push in your chair or stool, and jump up and down in place FIVE times. In your notebook, write down all the things that happened in your body during the jumps. What do you think muscles are made of?

3. What are muscles? Muscles are made of bundles of long string-like cells called fibers. Muscle fibers have the unique ability to contract (draw together). Nerves stimulate muscles to contract. When a muscle contracts, it gets shorter and pulls on the attached bone to move the body part.

4. How do muscles work? Muscles do work when they contract (they exert a force and move your bones over a distance). Glucose is your muscles’ main fuel. Chemical energy stored in glucose changes to mechanical energy in muscles, allowing them to contract.

5. What is skeletal muscle? Skeletal muscle is the kind of muscle that moves bones. At movable joints, skeletal muscles are attached to bones by tendons. You decide when to contract or relax your skeletal muscles. All outward body movements, like pushups, are possible because of skeletal muscles.

6. What is cardiac muscle? Cardiac muscle is what forms the walls of your heart. Cardiac muscle pumps blood through the heart and forces blood through the rest of the body.

7. What is smooth muscle? Smooth muscle is found in many places in your body such as your stomach and intestines. The movement of food through your intestines and the distribution of blood within your blood vessels are due to your smooth muscles. You do not have control of your smooth muscle actions.

8. What is a tendon? A tendon is a strong elastic band of tissue connecting muscle to bone.

9. How do skeletal muscles work together? Skeletal muscles work in pairs. When one contracts, its partner relaxes. FOR EXAMPLE, when you raise your arm, you contract your biceps muscle, which pulls on your arm bone. Your triceps relaxes and allows the bone to be pulled up.

10. Building Muscle Strength Muscle use over time, such as through regular exercise, will increase your muscle strength. When you exercise, the size of your muscle fibers increases and that increases your muscle strength. Exercise also increases muscle tone, which is the state of readiness of your muscles to contract. Even when you think you aren’t moving, some of your muscle fibers are contracting and relaxing to maintain tone.