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Watch the fragment of the film. Pay attention to the new information about the skeletal and muscular systems.

Without bone’s supporters giving lever up to our muscles we would be immobile mass of flash. Our skeleton weights about 12 kilograms. It makes up less than 20 percent of the body’s weight. The sharp of each bone is ideally checked to perform some functions. The complex structure of the limbs makes them rather flexible and movable. The arms are supported by the bone framework across the shoulders only use and connected to the rest of the skeleton. The shoulders plates are not connected to the chest, that’s why they can do so large movements.

But bones are not only the building material and levers. The proverb “dry as bone” is not completely true. The third of bone’s weight is made up the living tissue with the microscopical network of blood vessels and nerves. The central part of some bones is filled in with the bone marrow, which manufactures blood cells. This microscopical architecture lays in base of many our bones and their structure combines straight and lightness. Bones are not permanent. Materials composed the most part of bone – calcium and phosphorus – gradually break down and are carried away by the blood stream. At the same time some minerals carried by the blood stream through the thin blood vessels begin to build the new bone. As a result our skeleton is totally replaced every two years. The crystals of new bone are layers to provide strength similar of the construction of the carbon fiber of an oar. They must work against axis of movement, that’s why they serve as levers to the human body.

The most complex joints of the body are the knees the must be flex while carrying heavy weight. The muscles of the knees must bend well around the knee joint, To keep friction to the minimum bones are divided with the soft pad. It is filled in with the natural dense fluid. Without it we would move like robots. Joints and bones work together to provide the motions of our muscles. The central part of the elbow makes the movements of bone in the upper part of arm possible.

But the human hand is the most amazing piece of bioengineering. We are different from other animal world by the thumb which gives strong but sensitive seizure. The three other long fingers are operated by the forearm. Their power is transferred by long tendons. The fragile bone of fingers must do delicate work, that’s why they are rather elegant. In contrast the massive spine bones have to support the weight of the upper part of the body. Besides, it protects the spinal cord and nerves carrying information between the brain and other part of the body. At the end of the spinal cord the coccyx without nerves is situated. It is the rest of ex-tail. It’s your back. It supports the spinal muscles, holding the human bone together. 24 bony elements of the spinal cord are separated by the discs. The weight of our body compresses the discs when we stand. During the day our height becomes less on 2 cm. But at night we become taller again.

Our legs keep our bony structure. They consist of the strongest bones of the body which can hold 1 ton of weight. Bones of legs are copy the bones of arms, but they perform other functions. Short toes ensure flexible and other bone divide the weight of our body. The skeleton protects the heart, lungs, and other organs inside our body. Ribs help to divide exertion. The skull protects the brain.

TASK № 5

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