How the human body is adapted for movement.
The Human Body – Movement
There are 206 bones in an ordinary human skeleton. Our skeleton gives the general shape to our body, but also protects delicate organs like the heart and the lungs. These are protected by the rib cage. Bones are strong so they can withstand pressure and hard blows. They are also light in weight to make them easier to move. To be strong and lightweight, larger bones are made up of hard, dense substance that are hollow in the middle. The hollow section is filled with bone marrow. Red blood cells are produced in bone marrow. Where two or more bones meet, a joint is formed which allows the movement of the skeleton. Bones in a joint are held together by strong fibres called ligaments. Movement at joints are controlled by muscles. Each end of a muscle is connected to a bone by a tendon, which will not stretch. One end of the muscle is attached to the bone, which does not move, and the other is fixed to the bone that moves.
The muscle pulls on the bone by contracting. This means the muscle gets shorter and fatter. When a muscle relaxes it gets longer, but cannot exert a pulling force. Another muscle is needed to contract and pull the bone in the opposite direction. Many bones in the body act as levers, which enable a relatively small force to lift a greater object. A small force applied on the contraction of the muscle in the forearm pulls on the bone. The far end of the bone, which is carrying the weight, is moved through a larger distance.
The triceps and biceps work in unison to bend and straighten the arm. Muscles all over the body are arranged in pairs in a similar way. Because they work in opposite directions they are known as antagonistic muscle pairs. Most joints in the body allow for considerable freedom. These joints are synovial joints. They have features, which reduce friction between the bones and allow bones to slide easily over each other. The surfaces of the bones in contact are covered with a smooth layer of elasticised cartilage. The joints are enclosed by a tough capsule containing synovial fluid, which is an extremely good lubricant. This is how the human body is adapted for movement.