What are the functions of muscle tissue in the body? Muscle tissues, their structure and significance

Muscle is a group of tissues of animals and humans, main function which is a contraction, which, in turn, causes the movement in space of the organism or its parts. This function corresponds to the structure of the main elements of muscle tissue, which have an elongated shape and longitudinal orientation of myofibrils, which include contractile proteins - actin and myosin. Like the epithelial muscle is a prefabricated tissue group, since its main components develop from various embryonic rudiments.
Depending on the structure of its contractile apparatus, muscle tissue is divided into striated (skeletal) and smooth tissues, consisting of various histogenetic types that differ in structure. The following scheme gives a general idea of the classification of muscle tissue:

striated muscle tissue

The source of its development is the cells of myotomes, which are formed from the dorsal mesoderm. Striated muscle tissue consists of elongated formations - muscle fibers, which look like cylinders with pointed ends. The fibers reach 80 microns in diameter and 12 cm in length. In the center of the muscle fibers there are multinuclear formations (symplasts), to which cells, myosatelites, adjoin from the outside. The fibers are limited by the sarcolemma formed by the basement membrane and the plasmolemma symplast.
Myosatelliotocytes are located under the basement membrane of the muscle fiber so that their plasmolemma touches the symplast plasmolemma. These cells represent the cambial reserve of skeletal muscle tissue, due to which the regeneration of its fibers is carried out.
In addition to the plasmolemma, myosymplasts include the cytoplasm (sarcoplasm) and numerous nuclei located along the periphery. In the perinuclear region, there is a poorly developed granular endoplasmic reticulum and the Golgi complex. A muscle fiber with its sheath, nerve endings, blood and lymphatic capillaries is called a muscle unit (Mion).
A characteristic feature of skeletal muscle fibers is transverse banding, due to the alternation of double-breaking (anisotropic) A-disks and single-breaking (isotropic) I-disks. The composition of the disks includes myofibrils, which form the contractile apparatus of the fibers. Myofibrils are composed of ordered filaments of the contractile proteins actin and myosin. These threads are fixed by transversely located telophragms and mesophragms,
that are made up of other proteins. The segment of myofibril between adjacent telophragms is called a sarcomere. It is a morphofunctional unit of the contractile apparatus of the fiber. In its middle part there is a mesophragm (M-line on longitudinal sections). Thick (about 11 nm in diameter) myosin filaments extend from the mesophragm towards the telophragm, and thin (about 5 nm) actin filaments extend from the telophragm towards them.
Myosin filaments - main component dark disks, and actin filaments - light disks. In the dark disc, actin and myosin filaments are arranged in parallel. The middle section of the A-disk has only myosin filaments and is called the H-band (light zone).
For the convenience of considering the structure of the contractile apparatus of the muscle fiber, it is necessary to remember the so-called sarcomere formula, which reflects the sequential placement of its main components and looks like this: telophragm + 1/2 disk 1 + 1/2 disk A + stripe M + + 1/2 disk A + 1/2 disc I + telophragma.
The cytolemma of the symplastic part of the muscle fiber at the level of the telophragms forms deep protrusions - transverse or T-tubules (from Latin Transversus - transverse). Parallel to these tubules are dilated portions of the tubules of the agranular endoplasmic reticulum (terminal cisterns), which accompany them on both sides. Together with T-tubules, they form triads.
Calcium ions accumulate in the terminal cisterns of the agranular endoplasmic reticulum in a relaxed state of the muscle fiber. Under the influence of distribution along the cytolemma of the fiber and T-tubules of the action potential, calcium ions leave the terminal cisterns entering the myofibrils and, interacting with special reticular proteins - troponin and tropomyosin, begin to actively contract. At the same time, the actin and myosin filaments, interacting with each other, move towards each other. Actin filaments enter between myosin filaments, approach the M-line, and therefore, when the muscle fiber contracts, the width of the H-band and H-disk decreases. The width of the A-disk remains unchanged. (The structure of different functional types of muscle fibers is discussed in textbooks on histology).

smooth muscle tissue

Smooth muscle tissue of mesenchymal origin forms muscle membranes internal organs. Smooth myocytes often have a spindle shape, their length is from 15 to 500 microns, and their thickness is from 5 to 8 MNM. Cell nuclei are elongated. With the reduction of cells, they can gain the appearance of a gimlet. The organelles in these cells are poorly developed. The cytolemma, stretching out, forms numerous pinocytic vesicles, which transmit irritation inside the cell, which, in turn, causes its contraction.
The contractile apparatus of smooth myocytes (myofibrils) consists of thin myofilaments, formed by actin, and thick, formed by myosin. Myocytes are limited by a basement membrane, as well as collagen (reticular) elastic fibers. These structural components of smooth muscle tissue are formed by smooth myocytes. Efferent (motor) innervation of smooth myocytes is carried out by postganglionic fibers of the autonomic nervous system. Neighboring myocytes through holes in the basement membrane form slit-like communications (nexus) with each other, which provide functional cell interactions.
Smooth muscle tissue of epidermal origin is formed by myoepithelial cells, which are formed from the skin mesoderm. They have a stellate (bucket) shape and are part of the sweat, mammary and salivary glands. Located between the epithelial cells and the basement membrane of the secretory sections of the glands and small excretory ducts, they, by contracting, contribute to the excretion of the secret.
Smooth muscle tissue of neural origin is formed during the embryonic development of the eyeball from the cells of the wall of the eyecup. It is part of the muscles of the iris of the eyeball, which dilate or constrict the pupil.

Muscle tissues (Latin textus muscularis - “muscle tissue”) are tissues that are different in structure and origin, but similar in ability to pronounced contractions. They consist of elongated cells that receive irritation from the nervous system and respond to it with a contraction. They provide movement in the space of the body as a whole, its movement of organs inside the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the property of changing shape, but in muscle tissues this ability becomes the main function.

Main morphological features elements of muscle tissue: an elongated shape, the presence of longitudinally arranged myofibrils and myofilaments - special organelles that provide contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.

Special contractile organelles - myofilaments or myofibrils - provide contraction, which occurs when the two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide energy for these processes. The supply of energy sources is formed by glycogen and lipids. Myoglobin is a protein that binds oxygen and creates its reserve at the time of muscle contraction, when blood vessels are compressed (oxygen supply drops sharply).

By origin and structure, muscle tissues differ significantly from each other, but they are united by the ability to contract, which ensures the motor function of organs and the body as a whole. The muscle elements are elongated and connected either with other muscle elements or with supporting formations.

Distinguish smooth, striated muscle tissue and muscle tissue of the heart.

Smooth muscle tissue.

This tissue is formed from mesenchyme. The structural unit of this tissue is a smooth muscle cell. It has an elongated fusiform shape and is covered with a cell membrane. These cells are tightly adjacent to each other, forming layers and groups, separated from each other by a loose, unformed connective tissue.

The cell nucleus has an elongated shape and is located in the center. Myofibrils are located in the cytoplasm, they go along the periphery of the cell along its axis. They consist of thin threads and are the contractile element of the muscle.

Cells are located in the walls of blood vessels and most of the internal hollow organs (stomach, intestines, uterus, Bladder). Activity smooth muscles regulated by the autonomic nervous system. Muscle contractions do not obey the will of a person and therefore smooth muscle tissue is called involuntary muscles.

Striated muscle tissue.

This tissue was formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is the striated muscle fiber. This cylindrical body is a symplast. It is covered with a membrane - sarcolemma, and the cytoplasm is called - sarcoplasm, in which there are numerous nuclei and myofibrils. Myofibrils form a bundle of continuous fibers running from one end of the fiber to the other parallel to its axis. Each myofibril consists of discs that have a different chemical composition and appear dark and light under a microscope. Homogeneous discs of all myofibrils coincide, and therefore the muscle fiber appears to be striated. Myofibrils are the contractile apparatus of the muscle fiber.

All skeletal muscles are built from striated muscle tissue. Musculature is arbitrary, because. its contraction may occur under the influence of neurons in the motor cortex of the cerebral hemispheres.

Muscular tissue of the heart.

Myocardium - the middle layer of the heart - is built from striated muscle cells (cardiomyocytes). There are two types of cells: typical contractile cells and atypical cardiac myocytes, which make up the conduction system of the heart.

Typical muscle cells perform a contractile function; they are rectangular in shape, there are 1-2 nuclei in the center, myofibrils are located along the periphery. There are intercalated discs between adjacent myocytes. With their help, myocytes are collected into muscle fibers, separated from each other by fine-fibred connective tissue. Connecting fibers pass between adjacent muscle fibers, which provide contraction of the myocardium as a whole.

The conduction system of the heart is formed by muscle fibers, consisting of atypical muscle cells. They are larger than contractile ones, richer in sarcoplasm, but poorer in myofibrils, which often intersect. The nuclei are larger and not always in the center. The fibers of the conducting system are surrounded by a dense plexus of nerve fibers.

Muscle tissue (Latin name - textus muscularis) forms muscles that provide motor functions living organism. These formations are different in form and properties. The structure of muscle tissue is cellular. Muscles are complexes of elongated elastic elements capable of responding to impulses sent by the nervous system. Irritant signals from the central nervous system cause muscle tissue to contract and set in motion the human musculoskeletal system. The structure of muscle tissue allows the body to make energy reserves, and then use them for independent movement for a long time. Smooth muscles, like other residents of the body, receive complex nutrition, consisting of nutrients and oxygen, which are delivered through the bloodstream. This is a complex biochemical process focused on the strengthening and development of myocytes - the cells that underlie the structure of muscle tissue. Successful replacement of energy resources lost as a result of active human life is the key to the further full functioning of all organs. Muscle tissue accumulates energy for a short time, the need for its use arises almost every minute.

myocytes

The main motor functions of the body are assigned by nature to muscular formations, the name of which is "smooth muscle tissue". In its biological structure, mononuclear spindle-shaped cells predominate. These are myocytes - the structural unit of smooth muscle tissue. Their length ranges from 15 to 500 microns, which allows the muscles to act in a fairly wide range of contractions. The nervous system of the body is tuned to use all the possibilities of myocyte structures. Smooth muscle tissue functions predominantly in a slow contraction mode, due to the interaction of myosin with actin. Relaxation is also gradual. At the same time, smooth muscle tissue, whose functions are quite diverse, is capable of contractions of great force. For example, during childbirth, the muscles of the uterus create a strong tension aimed at pushing the fetus out. Contractions continuously follow one after another for a long time, while each cell of the smooth muscle tissue of the uterus carries a charge of inexhaustible energy, as a result of which labor pains, in some cases, last for hours. The process is programmed by nature as "mandatory". At the same time, smooth muscle tissue, whose functions are quite complex, is completely beyond intellectual control and obeys exclusively impulses coming from the central nervous system. This circumstance creates certain difficulties for doctors and paramedical personnel, who are deprived of the opportunity to influence the process.

Reflex automatism

Smooth muscle tissue forms the walls of many internal organs: the stomach, intestines, large blood vessels. Each part of the body, the activity of which is associated with contractile functions, contains one or another amount of muscle fibers. The strength of muscle contractions directly depends on its intended purpose. For example, the smooth muscles of the back can be sharply activated when a person lifts a heavy load, a bag of cement, or a box full of vegetables. There will be a very powerful contraction muscle mass, the energy will be transferred to the skeleton. Moreover, this will happen automatically, without any intellectual intervention of the loader himself.

Regeneration capabilities

Smooth muscle tissue, whose functions are quite universal, acts as a link between individual fragments of the body. It connects them with peculiar elastic bridges. The integrity of structural formations in the human body is largely ensured precisely by the muscle layers located everywhere. The dislocation of muscles is rational, the logic of their presence is unambiguous. There are no duplicating organs in the human body, with the exception of external ones, which are assigned the functions of the main senses, for example, these are the eyes and ears. Nature provided for the possibility of losing some part, while the function is preserved at the expense of an understudy. Muscular formations exist only in one copy, with the loss of one of them, partial disability occurs. Human muscles do not have the ability to regenerate lost or damaged structures, as occurs in lizards and some other amphibians and reptiles. The disturbed area simply dies off or enters a state of low activity. In some cases, the loss of activity of the muscular structure ends in the death of the whole organism. This happens when the activity of the heart muscle is lost, which, for some reason of a pathological nature, loses its ability to function. The result is cardiological failure, incompatible with life.

Smooth and striated muscle tissue

IN human body several types of muscular formations function. Cross-striped muscle tissue consists of myocytes up to 4-5 centimeters long. Their diameter ranges from 50 to 120 microns. There are a large number of nuclei in cells, 100 or more units. The cytoplasm of these myocytes looks under a microscope as a mass lined with alternating dark and light stripes. Unlike smooth, striated muscles have a high rate of contraction and relaxation, it forms a complex skeletal muscle, upper part esophagus, tongue and moves the larynx. The fibers of the striated muscles reach a length of 10-12 centimeters.

Cardiology

A special place in the body is occupied by striated muscle tissue, which consists of cardiomyocytes with transverse striation of the cytoplasm. The cells have a branched structure and form specific compounds - intercalary discs. There is also another intercellular structure - the anastomosis, in which the cytolemmas of individual cells stick together. This type of muscle tissue is the material for the formation of the myocardium of the heart. A special property of such a tissue is the ability to rhythmic contractions under the influence of excitation that occurs directly in the cells themselves. There is another type of cardiomyocytes - secretory, characterized by the absence of fibrils. These cells produce the hormone troponin, which lowers blood pressure.

Smooth muscles differ from striated muscles in that relatively few calories are expended on their activity and, thus, the appearance of fatigue syndrome is delayed. This factor is one of the most significant in the life of the organism. However, smooth muscle tissue, whose structural features are conducive to saving energy, nevertheless has the ability to actively function due to the simultaneous release of a caloric charge. This is enough for one or two contractions, which in some cases is enough. In general, smooth muscle is predisposed to slow actions that are not associated with extreme situations. In this case, its operation is stable and reliable.

Structure

The nuclei of tissue cells - myocytes have a rod-shaped form. Their location in the very center of parental formation is due to the presence of heterofromatin. During cell contraction, the elongated nucleus bends, and with a particularly intense reaction to a signal from the central nervous system, it even twists. At the nuclear poles at this moment, a significant number of mitochondria are collected, which are a kind of organelles, auxiliary intracellular structures.

Smooth muscles do not have transverse structuring, their cellular cytoplasm contains many different agents, including: fat, pigment, carbohydrate. There are also caveolae and pinocytic vesicles that attract calcium ions. The cytoplasm of smooth muscle cells under microscopic examination reveals myosin myofilaments, thick and thin actin, located along the long cell axis. Due to the intermolecular interaction with myosin, the filaments approach each other, the process is transferred to the cytolem, the plasma membrane, and only after that does the muscle contraction occur.

Since the structure of smooth muscle tissue is cellular, myocytes are present in a wide range throughout the body. In the uterus, endocardium, bladder, aorta and many other organs, they are present in the form of process cells that closely interact with each other. The process of reproduction of new myocytes obeys the logic of biochemical regeneration, but at the same time it is distinguished by a certain ability to filter elements. Thus, newly emerged myocytes are subject to selection, only healthy ones survive. Such a system fully justifies itself, since in this case the muscle tissue is fully updated in a continuous mode.

motor functions

Features of smooth muscle tissue are also that the shell of each myocyte is enveloped by a basement membrane that attracts collagen fibrils. There are holes in the membrane through which cells come into contact with each other. The interaction can be conditional or reproductive. Myocytes are also surrounded by reticular collagen fibers, which form a mesh endomysium that binds neighboring cells.

The functionality of the body depends on how the human muscles work, smoothly or spontaneously. Entire cells are formed by smooth muscle tissue motor complexes, which are triggered reflexively, by means of one or two impulses sent by the central nervous system. This applies only to habitual, often repetitive body movements. In other, extraordinary manifestations of human life, the muscles are in constant readiness for action. The surprise factor is taken into account at the level of psychology, if necessary, there is a sharp activation of the muscles, adequately to the situation.

Protective functions

Smooth muscle tissue also forms various schemes for counteracting external stimuli. At the same time, the body copes with problems that have come from outside, without the direct participation of the intellect, only due to muscular reflexes. In this case, the contractile function of the smooth muscle mass is fully used. After the normalization of the situation, its relaxation begins.

Facial expression

A person is constantly surrounded by the so-called society, during the day he is in contact with colleagues at work, in the evening he stays with his family, and on weekends he visits public places. The people with whom the individual communicates see his face, reflecting feelings, mood, joy or sadness, anger or fun. Changes are clearly visible to others. All processes that change facial expressions are controlled by facial muscles. Smooth muscle tissue, located in the front of the head, provides a full range of changes regarding the emotional state of a person in a certain period of time.

Not only facial expression, but also the eye depends on the interaction of the muscle group that controls the facial components, since smooth muscles move the eyeballs and regulate the diameter of the pupil. The eyelids are also under its influence, microscopic muscles are present even under the eyelashes, their function is to provide correct position hairs. Some muscle groups have the ability to function automatically. For example, upper eyelids periodically close for a fraction of a second, then to return to its original position. This is because the eye needs to renew the corneal mucosa and the entire front of the eyeball. The eyes "blink" with an interval of 10-15 seconds and this cycle is set by the muscle tissue itself, an impulse arises in the depths of its fibers, which initiates blinking. If a foreign body, even microscopic in size, gets on the mucous membrane of the eyeball, this becomes the reason for frequent, intense blinking, which continues until the cause of irritation is eliminated.

Nervous tic

Sometimes the cyclicity is broken and random lowering occurs. upper eyelid often of a convulsive nature. This can happen simultaneously in both eyes or only in one. The phenomenon is called a "nervous tic" and is considered a rather painful harbinger of a pathological disorder. You must immediately consult a doctor.

Nervous tics can also appear in other areas, such as the cheeks. It is expressed in the periodic twitching of the muscles at certain points. As a rule, such phenomena disturb a person. The aesthetics of the face suffers, in addition, there is a feeling of discomfort. To get rid of discomfort, you should first massage the problem area, and then consult a doctor. The subcutaneous location of the flat muscles of the face suggests massage as a means to raise the overall tone. There are techniques specially developed by specialists that are focused on smoothing wrinkles and giving elasticity to the skin. However, it is necessary to control mimic emotions. For example, a smile should be restrained enough so that the skin on the face does not gather into folds.

In some cases, the smooth muscle tissue of the face loses stability and begins to twitch due to a psychological reason, insomnia or general nervous tension can be the cause. Then you need to calm down, take light pharmaceuticals and consult a doctor.

2. Striated skeletal tissue

3. Histogenesis and regeneration of muscle tissue

4. Innervation and blood supply of skeletal muscles

5. Cardiac striated muscle tissue

6. Smooth muscle tissue

7. Special smooth muscle tissues

1. Contractibility property almost all types of cells possess, due to the presence in their cytoplasm of the contractile apparatus, represented by a network of thin microfilaments (5-7 nm), consisting of contractile proteins - actin, myosin, tropomyosin and others. Due to the interaction of these microfilament proteins, contractile processes are carried out and the movement of hyaloplasm, organelles, vacuoles in the cytoplasm, the formation of pseudopodia and plasmolemma invaginations, as well as the processes of phago- and pinocytosis, exocytosis, cell division and movement are ensured. The content of contractile elements, and, consequently, contractile processes are not equally expressed in different types of cells. Contractile structures are most pronounced in cells whose main function is contraction. Such cells or their derivatives form muscle tissues, which provide contractile processes in hollow internal organs and vessels, movement of body parts relative to each other, maintaining posture and moving the body in space. In addition to movement during contraction, a large amount of heat is released, and, therefore, muscle tissues are involved in the thermoregulation of the body. Muscle tissues they are not the same in structure, sources of origin and innervation, in functional features. Finally, it should be noted that any kind of muscle tissue, in addition to contractile elements (muscle cells and muscle fibers), includes cellular elements and fibers of loose fibrous connective tissue and vessels that provide trophism of muscle elements, transfer the forces of contraction of muscle elements to the skeleton. However, the functionally leading elements of muscle tissues are muscle cells or muscle fibers.

Muscle tissue classification

Smooth (non-striated) - mesenchymal;

special - neural origin and epidermal origin;

Cross-striped (striated) - skeletal;

cardiac.

As can be seen from the presented classification, muscle tissue is divided according to its structure into two main groups - smooth and striated. Each of the two groups, in turn, is divided into varieties, both according to sources of origin, and according to structure and functional features. smooth muscle tissue, which is part of the internal organs and blood vessels, develops from the mesenchyme. Special muscle tissues of neural origin include smooth muscle cells of the iris, epidermal origin - myoepithelial cells of the salivary, lacrimal, sweat and mammary glands.

striated muscle tissue subdivided into skeletal and cardiac. Both of these varieties develop from the mesoderm, but from different parts of it: the skeletal one - from the myotomes of the somites, the cardiac one - from the visceral leaf of the splanchnotome.

Each type of muscle tissue has its own structural and functional unit. The structural and functional unit of the smooth muscle tissue of the internal organs and the iris is a smooth muscle cell - myocyte; special muscle tissue of epidermal origin - basket myoepitheliocyte; cardiac muscle tissue cardiomyocyte; skeletal muscle tissue muscle fibre.

They perform a very important function in the organisms of living beings - they form and line all organs and their systems. Of particular importance among them is precisely the muscle, since its importance in the formation of the outer and inner cavities of all structural parts of the body is a priority. In this article, we will consider what smooth muscle tissue is, its structural features, properties.

Varieties of these fabrics

There are several types of muscles in the composition of the animal body:

striated;
smooth muscle tissue.

Both of them have their own characteristic features of the structure, functions performed and properties exhibited. In addition, they are easy to distinguish from each other. After all, both of them have their own unique pattern, which is formed due to the protein components that make up the cells.

Cross-striped is also divided into two main types:

skeletal;
cardiac.

The name itself reflects the main areas of location in the body. Its functions are extremely important, because it is this muscle that provides the contraction of the heart, the movement of the limbs and all other moving parts of the body. However, smooth muscles are no less significant. What are its features, we will consider further.

In general, it can be seen that only the coordinated work performed by smooth and striated muscle tissue allows the entire body to function successfully. Therefore, it is impossible to determine more or less significant of them.

Smooth structural features

The main unusual features of the structure under consideration are the structure and composition of its cells - myocytes. Like any other, this tissue is formed by a group of cells that are similar in structure, properties, composition and functions. General features of the structure can be identified in several points.

Each cell is surrounded by a dense plexus of connective tissue fibers that looks like a capsule.
Each structural unit tightly adjoins the other, intercellular spaces are practically absent. This allows the entire fabric to be tightly packed, structured and strong.
Unlike the striated colleague, this structure may include cells of unequal shape.

This, of course, is not the whole characteristic that the structural features, as already mentioned, lie precisely in the myocytes themselves, their functioning and composition. Therefore, this issue will be discussed in more detail below.

smooth muscle myocytes

Myocytes have different shapes. Depending on the localization in a particular organ, they can be:

oval;
spindle-shaped elongated;
rounded;
process.

However, in any case, their general composition is similar. They contain organelles such as:

well-defined and functioning mitochondria;
Golgi complex;
the core, often elongated in shape;
endoplasmic reticulum;
lysosomes.

Naturally, the cytoplasm with the usual inclusions is also present. An interesting fact is that smooth muscle myocytes are covered on the outside not only with a plasma membrane, but also with a membrane (basal). This provides them additional opportunity to contact each other.

These points of contact constitute the features of smooth muscle tissue. The places of contact are called nexuses. It is through them, as well as through the pores that are in these places in the membrane, that the transmission of impulses between cells, the exchange of information, water molecules and other compounds takes place.

There is another unusual feature that smooth muscle tissue has. The structural features of its myocytes are that not all of them have nerve endings. That's why nexuses are so important. So that not a single cell is left without innervation, and the impulse can be transmitted through the neighboring structure through the tissue.

There are two main types of myocytes.

Secretory. Their main function is the production and accumulation of glycogen granules, the preservation of many mitochondria, polysomes and ribosomal units. These structures got their name because of the proteins contained in them. These are actin filaments and contractile fibrin filaments. These cells are most often localized along the periphery of the tissue.
Smooth They look like spindle-shaped elongated structures containing an oval nucleus, displaced to the middle of the cell. Another name for leiomyocytes. They differ in that they are larger. Some particles of the uterine organ reach 500 microns! This is a fairly significant figure against the background of all other cells in the body, except perhaps the egg.

The function of smooth myocytes is also that they synthesize the following compounds:

glycoproteins;
procollagen;
elastane;
intercellular substance;
proteoglycans.

The joint interaction and well-coordinated work of the indicated types of myocytes, as well as their organization, provide the structure of smooth muscle tissue.

Origin of this muscle

There is more than one source of formation of this type of muscle in the body. There are three main origins. This explains the differences that the structure of smooth muscle tissue has.

mesenchymal origin. most of the smooth fibers have this. It is from the mesenchyme that almost all the tissues lining the inner part hollow organs.
epidermal origin. The name itself speaks of the places of localization - these are all skin glands and their ducts. It is they that are formed by smooth fibers that have this variant of appearance. Sweat, salivary, milk, lacrimal - all these glands secrete their secret due to irritation of the cells of myoepitheliocytes - the structural particles of the organ in question.
neural origin. Such fibers are localized in one specific place - this is the iris, one of the membranes of the eye. The contraction or expansion of the pupil is innervated and controlled by these smooth muscle cells.

Despite the different origins, the internal composition and performance properties of all in the tissue under consideration remain approximately the same.

The main properties of this fabric

The properties of smooth muscle tissue correspond to those of striated muscle tissue. In this they are united. This:

conductivity;
excitability;
lability;
contractility.

At the same time, there is one rather specific feature. If the striated skeletal muscles are able to contract rapidly (this is a good illustration of the trembling in the human body), then the smooth one can be held in a compressed state for a long time. In addition, its activities are not subject to the will and mind of man. Because it innervates her

A very important property is the ability to long-term slow stretching (contraction) and the same relaxation. So, this is the basis of the work of the bladder. Under the influence of biological fluid (its filling), it is able to stretch and then contract. Its walls are lined with smooth muscle.

Cell proteins

The myocytes of the tissue in question contain many different compounds. However, the most important of them, providing the functions of contraction and relaxation, are precisely protein molecules. Of these, here are:

myosin filaments;
actin;
nebulin;
connectin;
tropomyosin.

These components are usually located in the cytoplasm of cells isolated from each other, without forming clusters. However, in some organs in animals, bundles or strands called myofibrils are formed.

The location in the tissue of these bundles is mainly longitudinal. Moreover, both myosin fibers and actin fibers. As a result, a whole network is formed in which the ends of some are intertwined with the edges of other protein molecules. This is important for rapid and correct contraction of the entire tissue.

The contraction itself occurs as follows: in the composition of the internal environment of the cell there are pinocytic vesicles, which necessarily contain calcium ions. When a nerve impulse arrives, indicating the need for contraction, this bubble approaches the fibril. As a result, the calcium ion irritates actin and it moves deeper between the myosin filaments. This leads to the involvement of the plasmalemma and as a result, the myocyte is reduced.

Smooth muscle tissue: drawing

If we talk about striated tissue, then it is easy to recognize it by its striation. But with regard to the structure we are considering, this does not happen. Why does smooth muscle tissue have a completely different pattern than its close neighbor? This is due to the presence and location of protein components in myocytes. In the composition of smooth muscles, the filaments of myofibrils of different nature are localized chaotically, without a definite ordered state.

That is why the fabric pattern is simply absent. In the striated filament, actin is successively replaced by transverse myosin. As a result, a pattern arises - striation, thanks to which the fabric got its name.

Under the microscope, the smooth tissue looks very even and ordered, due to the longitudinally located elongated myocytes tightly adjacent to each other.

Areas of spatial arrangement in the body

Smooth muscle tissue forms a sufficiently large number of important internal organs in the animal body. So, she was educated:

intestines;
genitals;
blood vessels of all types;
glands;
organs of the excretory system;
Airways;
parts of the visual analyzer;
organs of the digestive system.

Obviously, the localization sites of the tissue in question are extremely diverse and important. In addition, it should be noted that such muscles form mainly those organs that are subject to automatic control.

Recovery methods

Smooth muscle tissue forms structures that are important enough to have the ability to regenerate. Therefore, it is characterized by two main ways of recovery from damage of various kinds.

Mitotic division of myocytes until the required amount of tissue is formed. The most common simple and fast way regeneration. This is how the restoration of the internal part of any organ formed by smooth muscles occurs.
Myofibroblasts are capable of transforming into smooth tissue myocytes when needed. This is a more complex and rare way of regeneration of this tissue.

Smooth muscle innervation

Smooth performs its own regardless of the desire or unwillingness of a living being. This is due to the fact that its innervation is carried out by the vegetative nervous system, as well as the processes of the nerves of the ganglia (spinal).

An example of this and proof is the reduction or increase in the size of the stomach, liver, spleen, stretching and contraction of the bladder.

Functions of smooth muscle tissue

What is the meaning of this structure? Why do you need the following:

prolonged contraction of the walls of organs;
development of secrets;
the ability to respond to stimuli and exposure with excitability.