Chapter - 8
BODY MOVEMENTS
The human skeleton is the internal framework which is responsible for giving support, shape and protection to our bodies. It contains 206 bones, each playing an important task. The skeleton can be classified into two parts called as the axial and appendicular.
Limbs: The arms or legs of an animal.
Bones: These are the hard white structures below our skin that protect our internal organs. Bones are incapable of bending.
Cartilage: The part of human skeleton which is not as hard as bones and which can be bent. Example tip of nose and upper part of ear.
Joints: These are defined as the points at which two bones are fitted together. These are the points at which we can rotate and bend our bodies.
Types of Joints
Ball and Socket joint: The joint in which rounded end of one bone fits into the cavity of the other bone. Such a joint allows movement in all directions. Example shoulder joint
Pivotal joint : 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 . In a pivotal joint a cylindrical bone rotates in a ring.
Hinge joint : The joint which show movement only in one direction like the hinge of the door are called hinge joint. Example elbow joint, knee joint
Fixed joint: The bones as such can not move at these joints. Example Joints of skull.
Main Parts of Skeleton
Skull: This is the bony box which protects the brain.
Rib cage: This is the box made of curved ribs joint to chest bone on one side and the backbone other side. It protects the internal body parts of our body.
Backbone: Backbone is the part of axial skeleton made up of small bones called vertebrae. It help us to move our back down and up right and left.
Muscles:
Muscles are attached to the bones and is responsible for the movement of the human body. There is a change in the length of muscle due to contraction and relaxation.
If you move your arm touching your shoulder you will observe the bulging part on your arm, this is muscle due to contraction and it comes back to its normal position if you stretch your arm and muscle come to relax.
Movement in other Animals
Earthworm:
- Earth worms commonly found in soil, feed on dead organic matter (for example: dead leaves, dead animals)
- Earthworms do not have bones.
- The earthworm stretch one part of its body contraction the other and this alternative stretching and contracting movement make its body move forward.
- Their movement in soil makes the soil fertile that’s why earthworms are also called farmers friend.
- Snails commonly found on land or in soil.
- Snail possesses wavy movement with muscular contraction.
- It also secrets sticky substance called mucus which helps to reduce grip between the snail and the ground so that they can move easily.
- It has a shell on its back which is hard but not made of bone and is not helpful in locomotion.
- Movement of snail is called crawling.
Cockroach:
- Cockroaches possess various types of movement like walk, climb, fly.
- The body is divided into three parts—head, thorax, and abdomen. 3 pairs of legs are present in thoracic part which moves by the muscles present near its limbs (legs).
- The body is covered with the outer hard exoskeleton. It uses breast muscles for the movement of wings due to which they can fly.
- Birds fly but few birds can not fly. For example: Penguin, Ostrich cannot fly these are called flightless birds.
- Fore limbs of birds were modified into wings due to which these can fly.
- Hind limbs are legs due to which they can jump, walk or swim as can be seen in ducks.
- The skeleton of birds is hollow to reduce weight and the breastbone muscle use to move the wings up and down.
Fish:
- The head and tail of the fish are smaller than the middle portion of the body, this body shape is called streamlined.
- Fishes swim by moving its body and tail in the opposite direction to each other, they stretch the body and relaxing the tail in the opposite direction this forms a curve, then quickly the body moves other side and the tail on the opposite this creates the jerk and pushes the fish in forward direction.
- This movement is helped by the fins present on tail and also the fins presents on body helps to balance the body while swimming.
- Snakes possess wavy motion it has a long backbone covered with muscles and skin.
- Snakes cannot move on frictionless surface like glass.
- During its movement snakes creates curves in many loops which pushes them to the forward direction, they move very fast but not in straight-line motion created by snakes is called serpentine motion.
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