Explain the Role of Joints in Movement

Did you know there are more joints in the body than there are bones?

There are roughly 360 joints in the human body and 206 bones that fit together to form our skeleton!

So what exactly is a joint? 

Some of our bones meet at points called joints.  Joints allow the skeleton to move. 

Joints have ligaments, tendons and muscles and these allow us to bend and twist, for example our knee cap (or the patella) allows us to bend our legs. 

Most joints have ligaments and these connect a bone to another bone. They keep our bones in line and bend as they should. 

Tendons attach muscles to the bone.  When a muscle gets squeezed (contracts) it pulls on a tendon, which then pulls on a bone making it move. The knee has a tendon attached to the knee cap (patella). Can you see it in the image below?

The ends of bones in a joint have a soft tissue called cartilage covering it. Cartilage stops bones rubbing against one another. Like sandpaper wears away wood, the bones in a joint will wear away if there isn't something protecting it. There's also a fluid called synovial fluid which coats the end of the bones and cartilage, to reduce friction. A bit like oil on a bike chain prevents friction, the synovial fluid also reduces the friction between the bones in a joint.

There are four types of joints in the human skeleton, these are called hinge joints, pivot joints, ball and socket joints and fixed joints.

A hinge joint allows movement in two directions (180° movement), like a door hinge! For example, the knee and elbow both have hinge joints. 

Pivot joints allow bones to rotate around each other. The wrist bones in the image above have pivot joints - these rotate when trying to open a jar.

The skull is actually made of different bones. However, these fit tightly together and can't move at these fixed joints. Babies don't have fixed joints in their skull, so their bones are actually separate - their skull becomes fused as they grow.

Can you find the shoulder in the x-ray image above?

You can see the ball-shaped end of the upper arm bone. This sits in the shoulder blade (the 'socket') and allows the arm to move around 360°. Ball and socket joints allow the most movement in comparison to the other joints.

In this activity, we're going to look at how joints allow the skeleton to move.