Where bones meet

The idea

A joint is a junction between two or more bones; joints allow movement but cannot move bones on their own, and the type of joint decides the directions in which a part can move.

Shoulder and elbow

You can swing your arm in many directions at the shoulder, but your elbow bends only one way.

What do you think decides the directions in which a body part can move?

• The type of joint
• The colour of the bone
• The size of the muscle

Can a joint move a bone

Try a strong pull with the muscle off. Then switch the muscle on.

Joint and muscle

With the muscle off, the bone stayed in place. A joint is only the place where two or more bones meet. It lets the bones move, but a muscle has to pull them. The kind of joint then decides the directions of the movement.

A joint is a junction between two or more bones. Joints allow movement but cannot move bones on their own, and the type of joint decides the directions in which a part can move.

Notes

A joint is a junction between bones. It allows movement but cannot move bones on its own, and its type decides the directions of movement.

Check yourself

What is a joint?

Can a joint move the bones on its own?

Some body parts move in many directions and others in only one. What is this due to?

In the picture the bone moved only when the muscle was on. What does this show?

• A band that connects a muscle to a bone. That is a tendon.
• A junction between two or more bones — correct. Yes!
• A soft, jelly-like tissue that cushions. That describes cartilage.
• Yes, a joint pushes the bones by itself. Joints allow movement but cannot move bones on their own. A muscle pulls on a bone.
• Yes, a joint pulls the bones when a ligament contracts. Ligaments connect bones to bones and prevent excessive movement. They do not move bones.
• No, joints allow movement but cannot move the bones on their own — correct. Yes!
• The types of joints present — correct. Yes!
• The length of the bones. The difference is due to the types of joints present.
• The amount of blood in the part. The difference is due to the types of joints present, not to the blood.
• The joint alone moves the bone. With the muscle off, the bone did not move.
• A joint allows movement, but a muscle must pull the bone — correct. Yes!
• The muscle is the junction between the bones. The junction between two bones is the joint, and the muscle is what pulls.