Four kinds of joint

The idea

Ball-and-socket joints (shoulder: a rounded bone end in a hollow) allow free movement, including circular; hinge joints (elbow, knee) bend one way only; a pivot joint (skull on backbone) turns the head sideways; fixed joints (skull) allow no movement.

Four movements

You can swing your arm in a circle at the shoulder. Your elbow bends one way. Your head turns side to side. The bones of your skull do not move at all.

What does this tell you about the joints that do these jobs?

• There are different types of joints
• All joints are exactly the same
• Only the shoulder is a joint

Meet the joints

Choose each joint in turn.

Shape decides movement

In the shoulder, a rounded bone end sits in a hollow, so the arm moves freely. The elbow works like a door hinge. The skull turns on the backbone like a doorknob in its socket. The bones of the skull are fixed together, so they do not move.

Ball-and-socket joints (shoulder: a rounded bone end in a hollow) allow free movement, including circular; hinge joints (elbow, knee) bend one way only; a pivot joint (skull on backbone) turns the head sideways; fixed joints (skull) allow no movement.

Notes

Ball-and-socket (shoulder): free movement. Hinge (elbow, knee): one way. Pivot (skull on backbone): head turns sideways. Fixed (skull): no movement.

Check yourself

Which joint allows free movement, including circular movement?

The elbow and the knee are…

How is the skull connected to the backbone?

• The hinge joint. A hinge joint bends and straightens in one direction only, like a door hinge.
• The fixed joint. Fixed joints allow no movement.
• The ball-and-socket joint — correct. Yes!
• hinge joints — correct. Yes!
• ball-and-socket joints. The shoulder is a ball-and-socket joint. The elbow and knee bend one way, like a door hinge.
• pivot joints. A pivot joint turns the head sideways. The elbow and knee bend in one direction only.
• By a hinge joint that bends one way. The skull is connected to the backbone through a pivot joint.
• By a pivot joint, which lets the head turn side to side — correct. Yes!
• By fixed joints that allow no movement. Fixed joints join the bones of the skull to each other. The head does move on the backbone.