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

Plant and animal organisms differ not only externally, but, of course, internally. However, the main distinguishing feature of lifestyle is that animals are able to actively move in space. This is ensured due to the presence in them of special tissues - muscle. We will consider them in more detail later.

Animal tissue

In the body of mammals, animals and humans there are 4 types of tissues that line all organs and systems, form blood and perform vital functions.

1. Epithelial . Forms integument of organs, external walls of blood vessels, lines mucous membranes, forms serous membranes.
2. Nervous . It forms all the organs of the same system, has the most important features - excitability and conductivity.
3. Connective . It exists in various manifestations, including in liquid form - blood. Forms tendons, ligaments, fatty layers, fills bones.
4. Muscle tissue, the structure and functions of which allow animals and humans to perform a wide variety of movements, and many internal structures - to contract and expand (blood vessels and so on).
   
   

The combined combination of all these species ensures the normal structure and functioning of living things.

Muscle tissue: classification

A special role in the active life of humans and animals is played by a specialized structure. Its name is muscle tissue. Its structure and functions are very peculiar and interesting.

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

• smooth;
• striated;
• heart.

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

Muscle cell structure

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

Firstly, it is elongated (sometimes up to 14 cm), that is, it stretches along the entire muscle organ. Secondly, it is multi-core, since it is in these cells that the processes of protein synthesis, the formation and breakdown of ATP molecules proceed most intensively.

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

Features of muscle tissue of any type is that their cells (myocytes) form entire clusters - bundles of fibers, or symplasts. Each of them is lined with whole clusters of fibrils from the inside, while the smallest structure itself consists of the above proteins. If you look figuratively at this structural mechanism, it turns out, like a nesting doll, - smaller in larger, and so on until the very bundles of fibers, united by 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 nuclei and their orientation not in the center of the fiber, but in the peripheral part. It also lies in the fact that division does not occur due to 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 - restoration of tissue integrity.

Muscle tissue properties

Like any other structure, these types of fabrics have their own characteristics 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 the muscles, they can quickly perceive signal impulses. This property is called excitability.

Also, the structural features of muscle tissue allow it to quickly respond to any irritation, sending a response impulse to the cortex of the brain and spinal cord. This is the property of conductivity. This is very important, since the ability to respond in time to threatening influences (chemical, mechanical, physical) is an important condition for the normal safe life of any organism.

Muscle tissue, the structure and the functions that it performs - all 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 happens due to the work of protein myofibrils (actin and myosin filaments). They can stretch and thin out almost to invisibility, and then quickly restore their structure again.

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

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

The structure of muscle tissue, the possession of the listed properties, distinctive features are the main reasons for their performance of a number of important functions in animal and human organisms.

Smooth fabric

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

Protoplast is characterized by the absence of sarcolemma. The core is one, but there are many mitochondria. The localization of genetic material, separated from the cytoplasm by the karyolemma, is in the center of the cell. The plasma membrane is simple enough, complex proteins and lipids are not observed. Near mitochondria and throughout the cytoplasm, myofibrillar rings are scattered, containing actin and myosin in small amounts, but sufficient to contract tissue. The endoplasmic reticulum and the Golgi complex are somewhat simplified and reduced compared to 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 submits to the control of the autonomic nervous system, that is, it contracts, is excited without conscious control of the body.

In some organs, smooth muscles are formed thanks to individual single cells with special innervation. Although this phenomenon is quite rare. In general, two main types of smooth muscle cells can be distinguished:

• secretory myocytes, or synthetic;
• smooth.
  

The first group of cells is poorly differentiated, contains many mitochondria, a well-expressed Golgi apparatus. In the cytoplasm, bundles of contractile myofibrils and microfilaments are clearly visible.

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

Places of localization in the body

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

• 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.

Functions Performed

The structure of muscle tissue leaves a direct imprint on the functions they perform. So, smooth muscles are needed for the following operations:

• the implementation of contraction and relaxation of organs;
• narrowing and expansion of the lumen of blood and lymph vessels;
• eye movement in different directions;
• control over the tone of the bladder and other hollow organs;
• providing a response to the action of hormones and other chemicals;
• high plasticity and the connection of the processes of excitation and contraction.
  

The gall bladder, the place where the stomach enters the intestine, 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, strictly autonomous.

Striated muscle tissue

The types of muscle tissue discussed above are not subject to control by the human mind and are not responsible for its movement. This is the prerogative of the next type of fiber - striated.

First, we will understand why they were given such a name. When viewed through a microscope, you can see that these structures have a pronounced striation across certain strands - the actin and myosin protein strands that form myofibrils. This was the reason for this name of the fabric.

Cross-muscle tissue has myocytes that contain many nuclei and are the result of the fusion of several cellular structures. Such a phenomenon is denoted by the terms "simplast" or "syncytium". The appearance of the fibers is represented by long, elongated cylindrical cells tightly interconnected by a common intercellular substance. By the way, there is a certain tissue that forms this medium for the articulation of all myocytes. It has a smooth muscle. Connective tissue is the basis of intercellular substance, which can be either dense or loose. It also forms a number of tendons, with the help of which the striated skeletal muscles are attached to the bones.

Myocytes of the tissue in question, in addition to a significant size, have several more features:

• sarcoplasm of cells contains a large number of clearly distinguishable microfilaments and myofibrils (actin and myosin at the base);
• these structures are combined into large groups - muscle fibers, which, in turn, form directly the skeletal muscles of different groups;
• there are many nuclei, a well-defined reticulum and Golgi apparatus;
• numerous mitochondria are well developed;
• innervation is carried out under the control of the somatic nervous system, that is, consciously;
• the fatigue of the fibers is high, but also the performance;
• lability is above average, rapid recovery after refraction.

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

At a young age of animals and humans, skeletal muscles contain more dense connective tissue between myocytes. Over time and aging, it is replaced by loose and fatty, so the muscles become flabby and weak. In general, skeletal muscle occupies up to 75% of the total mass. It is she who makes the meat of animals, birds, fish, which a person eats. The nutritional value is very high due to the high content of various protein compounds.

A variety of striated muscles, in addition to skeletal, is the heart. Its structural features are expressed in the presence of two types of cells: ordinary myocytes and cardiomyocytes. Ordinary have the same structure as skeletal. They are responsible for the autonomous contraction of the heart and its vessels. But cardiomyocytes are special elements. They have a small amount of myofibrils, which means actin and myosin. This indicates a low ability to contract. But that is not their task. The main role is the fulfillment of the function of conducting excitability in the heart, the implementation of rhythmic automation.

Cardiac muscle tissue is formed due to the multiple branching of myocytes included in its composition and the subsequent unification into the general structure of these branches. Another difference from the striated skeletal muscle is that the heart cells contain nuclei in their central part. Myofibrillar sites are localized on the periphery.

What organs does it form?

The whole skeletal muscle of the body is striated muscle tissue. A table reflecting the location of this tissue in the body is given below.

Value for the body

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

Consider what other functions the striated muscle performs in the human and animal body.

1. He is responsible for complex facial expressions, expression of emotions, external manifestations of complex feelings.
2. Maintains body position in space.
3. It performs the function of protecting the abdominal organs (from mechanical influences).
4. Cardiac muscle provides rhythmic contractions of the heart.
5. Skeletal muscles are involved in swallowing, form the vocal cords.
6. Regulate the movement of the tongue.

Thus, we can draw the following conclusion: muscle tissue is an important structural element of any animal organism, endowing it with certain unique abilities. The properties and structure of different types of muscles provide vital functions. The structure of any muscle is based on a myocyte - a fiber formed from the protein filaments of actin and myosin.