What is the Skeletal System?

The skeletal system is the name for all the bones and joints that make up the internal structure of our body. There are 206 bones in the human body.

What are bones made of?

The outer layer of a bone is called the periosteum. It is a thin, strong layer containing nerves and blood vessels which nourish the bone.

Compact bone is the shiny white layer of bone that we imagine when we think of a skeleton.  This layer gives the bone its strength and structure.

Cancellous bone, also known as spongybone, is the spongy-looking layer of bone underneath the Compact Bone. This is designed to be strong but light, so that we can move around easily.

Protected in the centre of some bones (such as the femur, or thigh bone), we can find bonemarrow.  This is where our body makes blood cells.

What do our bones do?

The skeleton is the scaffold for our bodies. It provides a stable, strong structure for our muscles to attach to, and gives us shape.

Muscles and bones act together so that we can move. They act as levers – for example when we lift things, or kick balls – without too much effort.

Our organs are protected by our skeleton. For example: the skull protects our brain, while the rib cage protects our heart and lungs.

Blood cells are produced deep inside flat bones (such as the skull or hip bones) and long bones (such as thigh or arm bones).

Essential minerals and substances are stored in our bones for use when needed. The most important of these is calcium.

Bones change and develop as we grow.  When we are born, we have about 300 bones. As we grow, some of them grow together (fuse). Other ‘bones’ are made of a substance called ‘cartilage’ when we are born, and slowly absorb calcium and turn into adult bone as we grow up. This process happens at a certain rate, and is completed by the time we are 25 years old. This explains why archaeologists can sometimes tell how old a person was, just from their skeleton.

Bone cells release a hormone that regulates blood sugar and fat deposits.

What are joints?

The point of contact between two bones is called a joint. We have several different types:

• A fixed joint doesn’t move at all. A flat plate in the skull fused to another plate is an example of a fixed joint.
• A hinge joint is where the bones can only move in one direction, such as the elbow.
• A ball and socket joint can move in many directions. The shoulder and the hips are ball and socket joints.

Most joints in our body are synovial joints. The space where two bones meet is covered with a kind of capsule which holds liquid called synovial fluid. This fluid acts like oil to stop friction and allow the bones to move.

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