Certain animals when coming out of water loose their shape such as, jellyfish and worms, this means they have a softer skeleton.
Other animals such as, insects have an external skeleton made from chitin.
Fish, frogs, bird and humans all have an internal skeleton, made from cartlidge or bones.
Human skeleton is made from bones, apart from the outer ear, nose, and the ends of long bones are made from cartlidge.
Although a shark is made from all cartlidge as its easier to bend because its more flexible.
An internal skeleton is better than an external skeleton, because..
- it forms a frame for the human body to work in
- it grows when the body grows
- it allows muscles to easily be attached
- many joints so that the body is still flexible
- is made from living tissue such as bone cells and blood cells
Structure of a long bone
The long bones in the human body such as the arms and legs are hollow this means they are less likely to break than if they were solid bones.
Each end of the long bone has a head which is covered in cartlidge. Cartlidge is aimed to absort the shock and helps bones to slide over each other.
Repair and Growth of a bone
when a bone or cartlidge is damaged it can become infected by microorganisms.
bone and cartlidge are living tissues so they will repair themselves.
When a baby is born, there internal structure is made from cartlidge. As the body grows older, the cartlidges change to bone by calcium salts and phosphates that have depostited in the body making them hard. this is called ossification.
You can tell from an x ray if you have stopped growing by seeing if there is anymore cartlidge between the head of the bone and the main shaft. If there is no more cartlidge, the human body has stopped growing.
A broken bone is called a fracture. when you have an x ray the bones are clearly visible so you can see where the break is.
the different kinds of fractures are:
- greenstick fracture - when the bone isnt completely broken
- simple fracture - when the bone is clearly broken
- compound fracture - when the bone has broken and broke through the skin
a joint is when two or more bones meet at one place.
- fixed joints, found in the skull, where the bone cannot move
- hinge joints, found in the elbow and knee
- ball and socket joints, found in the shoulder and hip.
Instead of breaking a bone, you could also damage a ligament which connects two bones together or a tendon which connects a muscle to a bone.
More on Bones
Elderly people have to take more care of their bodies because there bones are softer due to osteoporosis.
this is when bones degenerates.
by making sure that they have a rich Vitamin-C diet helps there bones to stay strong and healthy.
most elderly people have to have their hips and knees replaced because the hip is a ball joint and socket and the knee is a hinge. They are called synovial joints because it contains synovial fluid.
How the arm moves
Biceps and triceps work as a pair of muscles called antagonistic muscles that bend or straighten the arm.
when one muscle contracts the other muscle relaxes. this produces precise movements to do complex activities.
when the forearm is been raised the biceps contract and the triceps relax.
when the forearm is been lowered the biceps relax and triceps contracts.