The four types of joints are ball and socket joint, pivotal joint, hinge joint and fixed joint.
In ball and socket joint, the rounded end of one bone fits into the cavity (hollow space) of the other bone. Such a joint allows movements in all directions.
Ball and socket joint is present in our shoulders.
The joint where our neck joins the head is a pivotal joint. It allows us to bend our head forward and backward and turn the head to our right or left.
The elbow has a hinge joint that allows only a back and forth movement.
Some joints between bones are fixed and didn’t move at all are known as fixed joints.
The framework of bones that give shape to our body is known as skeleton.
The small bones which are present at our wrist are known as carples.
Ribs join the chest bone and the backbone together to form a box. This is called the rib cage.
There are 12 ribs on each side of chest.
Backbone is made up of many small bones called vertebrae. The backbone consists of 33 vertebrae.
The additional parts of the skeleton that are not as hard as the bones and which can be bent. These are called cartilage.
Muscles work in pairs.
When one of them contracts, the bone is pulled in that direction. The other muscle of the pair relaxes.
To move the bone in the opposite direction, the relaxed muscle contracts to pull the bone towards its original position, while the first relaxes.
The body of an earthworm is made up of many rings joined end to end.
During movement, the earthworm first extends the front part of the body, keeping the rear portion fixed to the ground. Then it fixes the front end and releases the rear end. It then shortens the body and pulls the rear end forward. This makes it move forward by a small distance.
Under its body, it has a large number of tiny bristles (hair like structures) projecting out. The bristles help to get a good grip on the ground.
The outer skeleton of the snail is known as shell.
The muscular foot of snail releases mucus which helps it to move.
Cockroaches have three pairs of legs and a hard outer skeleton.
There are two pairs of wings attached to the body behind head.
The bones of birds are hollow which makes them light weighted and help them in flying.
The forelimbs of birds are modified into wings. The breastbones are modified to hold muscles of flight which are used to move the wings up and down.
The shape of a fish’s body is streamlined.
The skeleton of the fish is covered with strong muscles.
During swimming, muscles make the front part of the body curve to one side and the tail part swings towards the opposite side. Then, quickly, the body and tail curve to the other side. This makes a jerk and pushes the body forward. A series of such jerks make the fish swim ahead. This is helped by the fins of the tail.
Fish also have other fins on their body which mainly help to keep the balance of the body and to keep direction, while swimming.
Snakes have a long backbone. They have many thin muscles. They are connected to each other even though they are far from one another. Muscles also interconnect the backbone, ribs and skin.
The snake’s body curves into many loops. Each loop of the snake gives it a forward push by pressing against the ground. Since its long body makes many loops and each loop gives it this push, the snake moves forward very fast and not in a straight line.
