Moveable joints

 

The skull contains both fixed joints and moveable joints.

Fixed and moveable joints

A joint is a place where two bones meet. We have two main types of a

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. Chis 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

The shoulder is a ball-and-socket joint.

Your shoulder joint can move in almost all directions. You can swing. your arm round in the complete circle.

This is because the shoulder port joint is a

ball-and-socket joint. A ball on one bone fits Info 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.

 

The elbow is a hinge joint.

Structure of a moveable joint

The diagram shows what the elbow joint would look like if you could cut through it.

It is important that joints can move easily.

When two surfaces move against each other, a force called friction tries to stop them. You can read more about friction on page 136.

To reduce friction:

. the ends of the bones are covered with a very smooth, slippery material called cartilage

. a thick, slippery fluid called synovial fluid fills the spaces between the two bones. The synovial fluid helps to lubricate the Joint, like oil in the moving parts of an engine or bicycle.