Explain How Joints are like Pivots

Did you know that we have roughly 206 bones in our body?!

These 206 bones fit together to form our skeleton.

Our bones are pretty awesome - believe it or not, they’re actually living! Possibly, when we think of bones, we tend to think of bones that have been dead and buried for thousands of years, like dinosaur bones! Bones are living because they can grow and if we were to accidentally break, or fracture a bone, it would be able to repair itself. 

The bones in our skeleton are all important of course, but some of the main bones to remember are our vertebrae, which are small bones that make up our backbone, the rib cage in our chest, our skull and the femur in our thigh.

Can you find these bones in the image above?

Did you know that the femur is actually the longest and strongest bone in the body? The femur helps to carry our body weight and allows us to move around easily. This is known as the function or job, of this particular bone. Our bones can have many different functions.

One main function of our skeleton is to allow movement. Some of our bones meet at points called joints. 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're made of a tough elastic tissue and keep our bones in line, limiting the bone's movement so it bends as it should. 

Tendons are a strong flexible tissue which attach muscles to the bone.  When a muscle 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 above?

To help allow movement our bones can act as a lever. A lever in everyday life is usually a beam or bar used to move something, especially something heavy.

You can see in the image above that the blue bar is the lever. It is resting on something called a pivot (sometimes called a fulcrum). The blue bar moves around the top of the pivot. What do you think will happen to the red wheel (this is known as the load) when we push down on the opposite end of the lever?

It will move and lift up. Using a lever helps this to happen much more easily - it would be very difficult to move the object using just our strength! 

In our body, the bones are the lever and our joints act as the pivot. We have different types of joints that allow movement - hinge, ball and socket and pivot joints. These three joints allow movement at the joints in different ways.  Though they have different names, all joints act as a pivot in some way and in doing so, allow movement of a bone.

Pivot joints allow bones to rotate around each other. One bone is normally fixed and doesn't move while the other does. The wrist bones in the image above have pivot joints - these rotate when trying to open a jar. Pivot joints in our neck also allow us to move our head from side to side. 

A hinge joint allows movement in two directions. It allows 180° movement, like a door hinge! The knee and elbow both have hinge joints. 

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 which is known as the 'socket' and allows the arm to move around 360°. Ball and socket joints allow the most movement in comparison to the other joints. Our shoulder is the most mobile but also most at risk of damage!

The load is the body part that is being moved or anything it's carrying. Our muscles provide the effort or force needed to lift the weight. You might remember that when muscles contract they squeeze together, pulling on a tendon which then pulls on the bone they're attached to. That pull is the force.

In this picture, the arm bone is the lever. The elbow joint is the pivot and the dumbbell is the load. The muscles in the arm produce the force needed to lift the dumbbell.

We call this interaction between bones and muscles biomechanics.

In this activity, we're going to look at how the bones and joints of the skeleton act like levers and pivots.