Muscular tissue: structure and function. Features of the structure of muscle tissue

Plant and animal organisms differ not only externally, but also, of course, internally. However, the most important distinguishing feature of the way of life is that animals are able to move actively in space. This is due to the presence in them of special tissues - muscle. We will discuss them in detail later.

Animal tissues

In the organism of mammals, animals and humans are distinguished by 4 types of tissues lining all organs and systems that form blood and carry out vital functions.

1. Epithelial . Forms the integument of the organs, the outer walls of the vessels, lining the mucous membranes, forms serous membranes.
2. Nervous . Forms all the organs of the same name system, has the most important features - excitability and conductivity.
3. Connecting . There are different manifestations, including in liquid form - blood. Forms tendons, ligaments, fat layers, fills the bones.
4. Muscular tissue, the structure and functions of which allow animals and humans to carry out a variety of movements, and many internal structures - to contract and expand (vessels and so on).
   

The cumulative combination of all these species provides a normal structure and functioning of living beings.

Muscular tissue: classification

A specialized structure plays a special role in the active vital activity of humans and animals. Its name is muscle tissue. The structure and its functions are very peculiar and interesting.

In general, this tissue is heterogeneous and has its own classification. It should be considered in more detail. There are such types of muscle tissue as:

• Smooth;
• Striated;
• Heart.

Each of them has its own place of localization in the body and performs strictly defined functions.

The structure of the muscle cell

All three types of muscle tissue have their own structural features. However, it is possible to single out general patterns of the structure of a cell of such a structure.

First, it is elongated (sometimes reaching 14 cm), that is, it extends along the entire muscular organ. Secondly, it is multinucleate, since it is in these cells that the processes of protein synthesis, formation and decomposition of ATP molecules are most intense.

Also features of the structure of muscle tissue is that its cells contain beams of myofibrils formed by two proteins - actin and myosin. They provide the main property of this structure - contractility. Each filamentary fibril includes bands that are visible in the microscope as being lighter and darker. They are protein molecules that form something like strands. Actin forms light, and myosin - dark.

The features of any type of muscle tissue are that their cells (myocytes) form whole clusters - bundles of fibers, or symplasts. Each of them is lined with whole clusters of fibrils from the inside, while the very smallest structure consists of the proteins named above. If we consider this mechanism of the structure in a figurative way, then it turns out, like a nesting doll, smaller in the larger, and so down to the bundles of fibers combined by a loose connective tissue into a common structure - a certain type of muscle tissue.

The internal environment of the cell, that is, the protoplast, contains all the same structural components as any other in the body. The difference is in the number of cores and their orientation not in the center of the fiber, but in the peripheral part. Also, the division does not occur at the expense of the genetic material of the nucleus, but due to special cells called satellites. They are part of the myocyte membrane and actively perform the function of regeneration - restoring the integrity of the tissue.

Properties of muscle tissue

Like any other structure, these types of fabrics have their own peculiarities not only in structure, but also in the functions performed. The main properties of muscle tissue, thanks to which they can do this:

• Reduction;
• excitability;
• Conductivity;
• lability.

Due to the large number of nerve fibers, blood vessels and capillaries that feed muscles, they can quickly perceive signal impulses. This property is called excitability.

Also, the peculiarities of the structure of the muscle tissue allow it to react quickly to any irritations, sending a reciprocal impulse to the cortex of the brain and spinal cord. Thus, the conductivity property is manifested. This is very important, since the ability to react in time to threatening effects (chemical, mechanical, physical) is an important condition for the normal safe functioning of any organism.

Muscular tissue, the structure and functions that it performs - all of this as a whole comes down to the main property, contractility. It implies an arbitrary (controlled) or involuntary (without conscious control) reduction or increase in the length of the myocyte. This is due to the work of protein myofibrils (actin and myosin filaments). They can stretch and thin out almost to invisibility, and then again quickly restore their structure.

This includes the features of any type of muscle tissue. Thus, the work of the heart of man and animals, their vessels, eye muscles, rotating an apple is constructed. It is this property that provides the ability to actively move, move in space. What would a man do if his muscles could not contract? Nothing. Raise and lower the arm, jump, sit down, dance and run, perform various physical exercises - all this helps to do only the muscles. Namely, myofibrils actinic and myosin nature, forming tissue myocytes.

The last property to be mentioned is lability. It implies the ability of the tissue to recover quickly after excitation, to come to absolute efficiency. Better than the myocytes, this can only do axons - nerve cells.

The structure of the muscular tissues, the possession of the listed properties, the distinctive features are the main reasons for the fulfillment of a number of important functions in animal and human organisms.

Smooth cloth

One of the varieties of muscle. Has a mesenchymal origin. It is arranged differently from others. Myocytes are small, slightly elongated, resembling thickened fibers in the center. The average cell size is about 0.5 mm in length and 10 μm in diameter.

Protoplast is distinguished by the absence of a sarcomelem. The kernel is one, but a lot of mitochondria. Localization of genetic material, separated from the cytoplasm by a karyolemma, is in the center of the cell. Plasma membrane is arranged quite simply, complex proteins and lipids are not observed. Near the mitochondria and throughout the cytoplasm are myofibril rings containing actin and myosin in small amounts, but sufficient to reduce tissue. The endoplasmic reticulum and the Golgi complex are somewhat simplified and reduced in comparison with other cells.

Smooth muscle tissue is formed by bundles of myocytes (spindle-shaped cells) of the described structure, innervated by efferent and afferent fibers. It is subordinated to the management of the autonomic nervous system, that is, it is reduced, is excited without conscious control of the organism.

In some organs, smooth muscles are formed by individual single cells with a special innervation. Although this phenomenon is rare. In general, there are two main types of smooth muscle cells:

• Secretory myocytes, or synthetic;
• Smooth.

The first group of cells is poorly differentiated, contains a lot of mitochondria, a well-expressed Golgi apparatus. Beams of contractile myofibrils and microfilaments are clearly seen in the cytoplasm.

The second group of myocytes specializes in the synthesis of polysaccharides and complex combinative high-molecular substances, from which collagen and elastin are subsequently built. They also produce a significant part of the intercellular substance.

Locations in the body

Smooth muscle tissue, the structure and functions that it performs, allow it to concentrate in different organs in an unequal number. Since the innervation is not subject to control on the part of the directed activity of the person (his consciousness), the places of localization will be corresponding. Such as:

• Walls of blood vessels and veins;
• Most of the internal organs;
• leather;
• Eyeball and other structures.

In this regard, the nature of the activity of smooth muscle tissue is high-speed low.

Performed functions

The structure of the muscular tissues imposes a direct imprint on the functions performed by them. So, smooth muscles are needed for the following operations:

• The reduction and relaxation of organs;
• Narrowing and widening of the lumen of blood and lymphatic vessels;
• Movement of the eyes in different directions;
• Control over the tone of the bladder and other hollow organs;
• The reaction to the action of hormones and other chemicals;
• High plasticity and the connection between the processes of excitation and contraction.

The gall bladder, the places of the stomach into the bowel, the bladder, lymphatic and arterial vessels, veins and many other organs - all of them are able to function normally only due to the properties of smooth muscles. Management, once again make a reservation, strictly autonomous.

Striated muscle tissue

The types of muscle tissue considered above do not obey control from the side of human consciousness and are not responsible for its movement. It is the prerogative of the next type of fiber - cross-striped.

First we will understand, for what they were given such a name. When viewed in a microscope, it can be seen that these structures have a pronounced striation across certain strands - the threads of the actin and myosin protein forming myofibrils. This was the reason for this name of the fabric.

The transverse-muscular tissue has myocytes containing many nuclei and are the result of the fusion of several cellular structures. This phenomenon is denoted by the terms "symplast" or "syncytium". The appearance of the fibers is represented by long, elongated cylindrical cells, tightly connected together by a common intercellular substance. By the way, there is a certain tissue that forms this environment for the articulation of all myocytes. She has a smooth and muscular. Connective tissue is the basis of intercellular substance, which can be either dense or loose. It also forms a series of tendons, by means of which the striated skeletal musculature is attached to the bones.

The myocytes of the tissue in question, apart from a considerable size, have several more features:

• Sarcoplasm contains a large number of well-distinguishable microfilaments and myofibrils (actin and myosin in the base);
• These structures are combined into large groups - muscle fibers, which, in turn, form directly skeletal muscles of different groups;
• There are many nuclei, a well-expressed reticulum and the Golgi apparatus;
• Well developed numerous mitochondria;
• Innervation is carried out under the control of the somatic nervous system, that is, consciously;
• Fatigue of the fibers is high, however, and performance is also;
• Lability above average, rapid recovery after refraction.

In the body of animals and humans, the striated musculature is red. This is due to the presence in the fibers of myoglobin, a specialized protein. Each myocyte is covered from the outside with an almost invisible transparent membrane - the sarcolemma.

At a young age, animals and human skeletal muscles contain more dense connective tissue between the myocytes. With the passage of time and aging, it is replaced by a loose and fatty, so the muscles become flabby and weak. In general, the skeletal musculature occupies up to 75% of the total mass. It is she who makes meat of animals, birds, fishes, which a person consumes. Nutritional value is very high because of the large content of various protein compounds.

A variant of the striated muscles, in addition to the skeletal muscles, is the heart muscle. Features of its structure are expressed in the presence of two types of cells: ordinary myocytes and cardiomyocytes. Ordinary have the same structure as skeletal ones. They are responsible for the autonomous contraction of the heart and its vessels. But cardiomyocytes are special elements. They contain a small number of myofibrils, which means, actin and myosin. This indicates a low ability to reduce. But their task is not this. The main role - the performance of the function of carrying out excitability by heart, the implementation of rhythmic automation.

Cardiac muscular tissue is formed due to multiple branching of the myocytes entering into its composition and subsequent integration into the general structure of these branches. Another difference from the striated skeletal musculature is that the cardiac cells contain nuclei in their central part. Myofibrillar regions are localized around the periphery.

What organs forms?

All the skeletal muscles of the body are striated muscle tissue. A table showing the localization of this tissue in the body is given below.

Importance for the body

The role played by cross-striped muscles is difficult to overestimate. After all, it is she who is responsible for the most important distinctive property of plants and animals - the ability to actively move. A person can perform a lot of the most difficult and simple manipulations, and all of them will depend on the work of skeletal muscles. Many people are engaged in thorough training their muscles, achieve this in great success due to the properties of muscle tissue.

Let us consider what other functions are performed by the striated muscle in the body of man and animals.

1. Responsible for complex mimic cuts, expression of emotions, external manifestations of complex feelings.
2. Supports the position of the body in space.
3. Performs the function of protecting the abdominal cavity (from mechanical effects).
4. Cardiac musculature provides rhythmic contractions of the heart.
5. Skeletal muscles participate in swallowing acts, form vocal cords.
6. Adjust the movements of the tongue.

Thus, we can draw the following conclusion: Muscle tissues are important structural elements of any animal organism, giving it certain unique abilities. The properties and structure of different types of muscles provide vital functions. At the heart of the structure of any muscle is the myocyte - a fiber formed from protein threads of actin and myosin.