Year 7 Joint and Muscles (PDF)

## 1.3 The human skeleton Your skeleton supports your body and helps it to move. It also protects some of the soft organs inside you. The diagram shows the main bones in the skeleton. **This is an X-ray of a mink.** ### Questions 1. List three functions of the skeleton. 2. Look at the diagram of...

## 1.3 The human skeleton Your skeleton supports your body and helps it to move. It also protects some of the soft organs inside you. The diagram shows the main bones in the skeleton. **This is an X-ray of a mink.** ### Questions 1. List three functions of the skeleton. 2. Look at the diagram of the skeleton. How are the bones in the arms and legs similar? 3. How many ribs does a person have? (Remember that there are the same number on both sides of the body.) 4. As well as supporting the body, some bones protect other organs. Name the bones that protect: brain, heart and lungs. 5. Look at the X-ray of a mink. Do you think a mink has the same bones as a human? What evidence do you have for your answer? ## 1.4 Joints ### Fixed and moveable joints A joint is a place where two bones meet. We have two main types of joints in our bodies: - fixed joints - moveable joints. The skull has fixed joints in the cranium. The cranium is made up of several bones firmly joined together. This helps the cranium to protect the brain. The jawbone is joined to the rest of the skull by a moveable joint. This allows the jaw to move up and down and from side to side when you chew, talk or yawn. ### Hinge joints and ball-and-socket joints Your shoulder joint can move in almost all directions. You can swing your arm round in a complete circle. This is because the shoulder joint is a ball-and-socket joint. A ball on one bone fits into a socket on the other. Your elbow joint is a hinge joint. It can move in only one direction. It moves like a door on a hinge. ### Questions 1. State one place in the body where you have a fixed joint. Why is it useful to have a fixed joint in this place? 2. Name the bones that form the ball-and-socket joint in your shoulder. 3. Name the bones that form the hinge joint at your elbow. ## 1.5 Muscles Muscles are organs that help us to move. The diagram shows the two main muscles in the upper arm. The muscles are attached to the bones by tendons. Tendons are very strong, and they do not stretch. ### Questions 1. Name the bones that the biceps muscle is attached to. 2. Name the bones that the triceps muscle is attached to. 3. 'Bi' means 'two'. "Tri' means three. Look carefully at the diagram, and suggest why the biceps and triceps are given their names. ### How muscles work Muscles can get shorter. This is called contraction. When muscles contract, they produce a pulling force. Look at the diagram of the muscles in the arm. When the biceps muscle contracts, it pulls on the radius and scapula. The pulling force is transmitted to these bones through the strong tendons. The radius is pulled upwards, towards the scapula. The arm bends. ### Questions: 4. Predict what will happen if the biceps stops contracting, and the triceps contracts. 5. *Explain why it is important that tendons do not stretch.* ## Antagonistic muscles Muscles can contract and make themselves shorter. However, muscles cannot make themselves get longer. When a muscle is not contracting, we say that it is relaxed. A relaxed muscle does not do anything by itself. But if a force pulls on it, the force can make the relaxed muscle get longer. The top diagram shows what happens when the biceps muscle contracts and the triceps muscle relaxes. The contracting biceps muscle makes the arm bend at the elbow joint. It also pulls the relaxed triceps muscle and makes it longer. The next diagram shows how the arm can be made straight again. To do this, the triceps muscle contracts, and the biceps muscle relaxes. You can see that the biceps and triceps work as a team. When one of them contracts, the other one relaxes. When one of them contracts, it pulls the bones in one direction, and when the other contracts, it pulls the bones in the opposite direction. A pair of muscles that work together like this are called antagonistic muscles. ### Question: 6. Explain why the biceps muscle alone cannot make the arm straighten. ### Summary - Muscles produce a pulling force when they contract. - They can only pull. They cannot push. - Muscles are joined bones by tendons. - Antagonistic muscles are a pair of muscles working together, pulling in opposite directions.