Excitable tissues in the human body include nervous, secretory and muscle tissues. However, the latter differs from the others in the unique property of contractility due to the presence in the cell structure of microfilaments from specialized proteins - myosin, actin, tropomyosin.
Due to this, the human posture is maintained, moving in space, the advancement of the food lump in the gastrointestinal tract, blood circulation and much more. Depending on the histological features, the functions performed and the origin, there is a classification into smooth and striated muscle tissue, also some authors distinguish cardiac as a third subspecies for features. However, it should be understood that contractile elements constitute only the basis of these tissues, and they could not fully work without a dense network of blood vessels that provide the delivery of a large amount of oxygen, a protective and energetically significant membrane - sarcolemma, as well as reinforcing loose unformed
connective tissue.Striated
Cross-striped muscle tissue, mainly, make up the whole skeletal muscle and provide movement of joints and maintaining posture. Their structural and functional unit is the sarcomere, and they, in turn, consist of myosymplasts - fibers formed during the fusion of several individual cells in the process of differentiation. On a histological specimen, striated muscle tissue is easily distinguished by multinucleation and striation, which is why they got their name. Another important function of them is heat generation, in connection with which a shiver occurs when a person lowers temperature. The striated
muscle tissue also forms the structure of the myocardium, only cardiomyocytes are characterized by the absence of symplasts. When microscopic, they are mononuclear spindle cells. According to their functions, they are divided into workers (prevailing in number), conducting and secretory. It is thanks to the second that cardiac striated muscle tissues have the property of automatism, that is, they have the ability to contract independently, which ensures the continuous operation of the heart. The third type of cell is the site of the synthesis of hormone-like substances, in particular, it is an atrial natriuretic factor, which contributes to increased diuresis.
Smooth
If the muscular tissue of a person providing movement is striated, then the peristalsis of the gastrointestinal and genitourinary tract, the contraction of the vascular and bronchial walls provides smooth muscles. It is characterized by rhythm, relative slowness, a high degree of extensibility and regenerative abilities, as well as vegetative innervation. These are elongated mononuclear cells, without striation, and with a large amount of actin and collagen in the structure. Each such myocyte is covered with a thin basement membrane, and groups with endomysium from loose unformed connective tissue.