Movement of our body and its organs is provided by activity of muscles. The above was described striated muscle tissue that their forms. The ability to produce movement based on the fact that muscle fibers under the influence of the nerve impulse, or in response to a stimulus reduced, i.e. become shorter and at the same time thicker. Their length can be reduced in two times. The ability of the muscle to contract represents one of the most amazing natural phenomena. Muscle man in appearance and structure is fundamentally no different from that of animals. We know a lot about the structure of muscles, their chemical composition, complex chemical transformations, that occur when the voltage, but the mystery of the mechanism of muscle contraction largely remains unsolved till the end. Isn't it amazing that the muscle, with a gelatinous consistency, while reducing becomes solid and able to do a great job?! Is it not likely ability of muscle fibers to lift cargo, in thousand times more than their own weight?! And because of muscle contraction can be repeated many times - up to several hundred times per second (for example, some insects).
According to modern science, the act of muscle contraction appears to be as follows. Above it was mentioned that the contractile muscle elements associated with the presence in its composition of fibrous structures - myofibrils. These formations are composed of proteins actin and myosin. Both substances form a filamentary structure, able to stretch and shrink like a spring. Electron microscope strengthened the human eye to such an extent that he was able to observe large protein molecules; this allowed scientists to see the reduction of protein actomyosin threads. Shortening their occurs as a result of convergence of individual sites (links) molecules. It requires a great expenditure of energy, which is produced by the breakdown of adenosine triphosphate (ATP)contained in the muscles, but also due to the very complex oxidation processes. We are talking about the "burning" of organic substances - particularly glycogen * - to carbon dioxide and water that occurs in the muscles, provided oxygen supply.
The resulting energy is only 30% is used for mechanical work (traffic, heavy lifting, etc.,), 70% of it is converted to heat. Thus, the muscles are powerful generator heat. Muscular activity as a result of complex transformations of many substances affects the blood and tissue fluids, thus producing the effect on many important life processes.
Fig. 27. Building muscles:
a - muscle in cross section:
1 - a bundle of muscle fibers;
2 - single muscle fiber.
b - the General view of skeletal muscle:
1 - abdomen;
2 - tendon.
Every muscle consists of separate fibers which are connected with connective tissue in beams (Fig. 27). Connective tissue that connects the individual elements of the muscles at the ends forms the sinews used for attaching them to the bones. All the muscles get rich blood supply and innervation by which regulated the most complex processes of metabolism and manage their work. Chemical and physical phenomena that occur in the muscles, accompanied by the formation of electric currents, which were discovered in the XVIII century by using modern equipment, you can register these currents of muscles and by their nature to perceive the subtle changes that occur in the body, can make the diagnosis in various diseases. This type of study found especially in wide use in diseases of the muscles and the heart (electromyography and electrocardiography).
Outside the muscles covered with special thick shell - bands that are like a soft outer skeleton. They are bright, dense film, lying between the individual muscles. Muscles can have different shapes depending on their functions.
* Glycogen is a complex carbohydrate; it is called "animal starch".