If you have every seen a scary movie or listened in the Science class, or broken a bone, you will know what a skeleton looks like. Those are the bones that are on the inside of out body and there are 206 bones that makes up this frame work.
A baby has 305 bones and it is only later that some of these bones join together and form the 206 bones that an adult has.
Why do we need a skeleton
Besides from the obvious fact that a skeleton gives us form and holds us upright (without one you would be like a blob of jelly), the skeleton also plays an important role in protecting some very important organs like the lungs and kidneys and brain and heart and is also responsible to make blood cells.
We find different types of blood cells in our bodies and the most important ones are the red blood cells that carries the oxygen and the white blood cells the fights infection in the body.
These blood cells are produced on the inside of the bone in the bone marrow. The bone marrow is very soft and is protected by the hard outer part of the bone.
Bones look different from one another.
The bones differ in their built - some bones cannot bend like the bones in the skull that are flat plates that are joined together. We have bones in our body that are connected with a joint and can bend with the help of these joints and the muscles that are connected to it, like the elbow and knee.
The type of joint that connects the knee is called the "synovial joint".
Have a look at the sketch - you have two bones that has cartilage at the end. This is a rubbery type of substance to prevent the bones from rubbing against each other. Around it is has fluid which keeps the area slippery and help to make the movement easier. It is not on the sketch but the two bones are hold together and in place with ligaments which prevent the bones and joint to fall apart.
There are many types of synovial joint, depending on their function and where in the body it is found.
Do the bones move by themselves?
We will not be able to move our bones if we do not have muscles attached to it - the muscles are like the strings you need if you want to move a puppet - in the same way if a muscle pull together we say it contracts and then the arm will bend or the leg will lift up. The muscle is connected to the bone with tendons.
We need muscles that work together in pair to do different jobs - the one muscle bends the arm and the other muscle helps to make the arm straight again. A muscle can only pull, it cannot push, that is why we need the muscles working in pairs.
There are many types of muscles, some of them only work when your brain sends a message like lifting your leg and we call the "voluntary muscles" and we also have muscles that work without you thinking about it like your heart beating and those we call "involuntary muscles".