What type of cells does smooth muscle tissue have? Smooth muscle tissue. The structure of smooth muscle tissue. Electrochemical stage of muscle contraction

Muscle tissue (textus muscularis) is a type of tissue that carries out motor processes in the human body (movement of blood and lymph through vessels, movement of food during digestion, movement of the body in space, maintaining posture, changing the volume of organs, etc.) with the help of special contractile muscles. structures - myofibrils.

Functional Features muscle tissue: excitability, conductivity and contractility.

There are:

1. smooth

2. striated

1) skeletal

2) cardiac tissue

	Smooth	Skeletal p-p	Heart p-p
Tissue structure	Cells (myocytes) are mononuclear up to 0.5 mm long with pointed ends, myofibrils are filaments d = 1-2 µm, located parallel to each other Myocytes ® bundles ® muscle layers ® muscle layers	Multinucleate cells are cylindrical in shape, up to 10 cm long, striated with transverse stripes. Long up to 10-12 cm, d up to 100 µm multi-nuclear muscle fibers. Nuclei on the periphery. Myofibrils in the form of bundles in the center of the fiber (from sarcomeres)	Cardiomyocytes are connected to each other using intercalary discs. It has a small number of nuclei located in the center of the fiber. Has good blood supply
Location	Walls of internal organs, blood and lymph vessels, skin muscles	Skeletal muscles of the musculoskeletal system and some internal organs: tongue, pharynx, initial part of the esophagus	Heart muscle
Abbreviation type	Tonic Involuntarily, slowly, do not get tired for a long time, high ability to regenerate	Tetanic voluntary	Tonic Involuntary, less tired
Functions	Involuntary contractions of the walls of internal organs. Raising hair on the skin. Controlled by the ANS	Voluntary movements, facial expressions, speech Controlled by somatics. NS	Involuntary contractions (automatism) Controlled by the somatic system. NS

The section of myofibril located between adjacent light stripes is a sarcomere.

The contractile proteins of striated muscle fiber (myosin, actin, tropomyosin, troponin) are contained in myofibrils in the form of 2 types of protein filaments: thin - actin, thick - myosin. The sliding of actin filaments relative to myosin filaments in the longitudinal direction during nervous excitation of the muscle fiber leads to shortening and thickening of sarcomeres - reduction of striated muscle fibers.

The sarcoplasm of muscle fibers contains a respiratory pigment - myoglobin, which determines the red color of muscles. Depending on the myoglobin content, red, white and intermediate muscle fibers are distinguished. Red ones are capable of longer contractions, white ones provide rapid motor function. The composition of almost all human muscles is mixed.

Tetanus is a strong, prolonged contraction of a muscle.

Tone is irregular muscle contractions that maintain the muscle in a state of constant partial contraction.

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

The main morphological characteristics of muscle tissue elements: elongated shape, the presence of longitudinally located myofibrils and myofilaments - special organelles that ensure 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 two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide these processes with energy. The supply of energy sources is formed by glycogen and lipids. Myoglobin is a protein that ensures the binding of oxygen and the creation of its reserve at the time of muscle contraction, when the blood vessels are compressed (the oxygen supply drops sharply).

Properties of muscle tissue

Contractility

Types of muscle tissue

Smooth muscle tissue

Consists of mononuclear cells - spindle-shaped myocytes with a length of 20-500 microns. Their cytoplasm in a light microscope looks uniform, without transverse striations. This muscle tissue has special properties: it contracts and relaxes slowly, is automatic, and is involuntary (that is, its activity is not controlled by the will of a person). It is part of the walls of internal organs: blood and lymphatic vessels, urinary tract, digestive tract (contraction of the walls of the stomach and intestines).

Striated skeletal muscle tissue

Consists of myocytes that are long (up to several centimeters) and have a diameter of 50-100 microns; these cells are multinucleated, containing up to 100 or more nuclei; in a light microscope, the cytoplasm looks like alternating dark and light stripes. The properties of this muscle tissue are high speed of contraction, relaxation and volition (that is, its activity is controlled by the will of the person). This muscle tissue is part of the skeletal muscles, as well as the wall of the pharynx, the upper part of the esophagus, it forms the tongue, and the extraocular muscles. Fibers are 10 to 12 cm long.

Striated cardiac muscle tissue

Consists of 1 or 2 nuclear cardiomyocytes with transverse striations of the cytoplasm (along the periphery of the cytolemma). Cardiomyocytes are branched and form connections with each other - intercalary discs, in which their cytoplasm is united. There is also another intercellular contact - anostamosis (invagination of the cytolemma of one cell into the cytolemma of another) This type of muscle tissue forms the myocardium of the heart. Develops from the myoepicardial plate (visceral layer of the splanchnotome of the fetal neck). A special property of this tissue is automaticity - the ability to rhythmically contract and relax under the influence of excitation that occurs in the cells themselves (typical cardiomyocytes). This tissue is involuntary (atypical cardiomyocytes). There is a 3rd type of cardiomyocytes - secretory cardiomyocytes (they do not have fibrils). They synthesize the hormone troponin, which lowers blood pressure and dilates the walls of blood vessels.

Functions of muscle tissue

Motor. Protective. Heat exchange. You can also highlight one more function - facial (social). Facial muscles, controlling facial expressions, transmit information to others.

Notes

Biological tissues
Cell
Animals	Epithelial Connective (bone, cartilage, fat, blood and lymph) Nervous Muscular Pokrovnaya
Plants	Educational (meristem) Integumentary Mechanical Adsorption Assimilation Conducting Secretory Aerenchyma
see also	Histology Intercellular substance
Organ

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See what “Muscle tissue” is in other dictionaries:

MUSCLE- (testus muscularis), constitutes the main. muscle mass and performs their contraction and function. There are striated M. t. skeletal and cardiac muscles (sometimes cardiac M. t. is distinguished separately), smooth and with double oblique striations. In vertebrates... ... Biological encyclopedic dictionary

muscle- ▲ tissue of the animal body muscle muscle tissue develops from mesoderm (striated #) and mesenchyme (smooth #). sarcoplasm. muscle. myocardium, myocardium. ↓ myoblasts. myofibrils. MUSCULAR SYSTEM, heart... Ideographic Dictionary of the Russian Language

MUSCLE- makes up the bulk of the muscles and carries out their contractile function. Depending on the structure of muscle tissue, cardiac, smooth and transverse muscles are distinguished... Big Encyclopedic Dictionary

muscle- makes up the bulk of the muscles and carries out their contractile function. Depending on the structure of muscle tissue, cardiac, smooth and striated muscles are distinguished. * * * MUSCLE TISSUE MUSCLE TISSUE makes up the bulk of muscles and... ... encyclopedic Dictionary

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Muscle- tissue that makes up the bulk of muscles and performs their contractile function. There are striated muscles (skeletal and cardiac muscles), smooth and with double oblique striations. Almost all skeletal M. t. in vertebrates... ... Great Soviet Encyclopedia

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MUSCLE- constitutes the main muscle mass and reduces them. function. Depending on the structure of the muscle tissue, cardiac, smooth and striated muscles are distinguished... Natural science. encyclopedic Dictionary

MUSCLE- the main component of the mass of muscles and individual organs, performing their contractile function. There are transversely striated muscles (skeletal and cardiac muscles), smooth and with double oblique striations (see Types of muscles) ... Psychomotorics: dictionary-reference book

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

Consists of mononuclear cells - spindle-shaped myocytes with a length of 20-500 microns. Their cytoplasm in a light microscope looks uniform, without transverse striations. This tissue has special properties: it contracts and relaxes slowly, is automatic, and is involuntary (that is, its activity is not controlled by the will of a person). It is part of the walls of internal organs: blood and lymphatic vessels, urinary tract, digestive tract (contraction of the walls of the stomach and intestines).

Consists of myocytes that are long (up to several centimeters) and have a diameter of 50-100 microns; these cells are multinucleated, containing up to 100 or more nuclei; in a light microscope, the cytoplasm appears as alternating dark and light stripes. The properties of this muscle tissue are high speed of contraction, relaxation and volition (that is, its activity is controlled by the will of the person). This muscle tissue is part of the skeletal muscles, as well as the wall of the pharynx, the upper part of the esophagus, it forms the tongue, and the extraocular muscles. The fibers are 10 to 12 cm long.

Muscle tissue represent a group of tissues of different origin and structure, united on the basis of a common feature - pronounced contractility, thanks to which they can perform their main function - to move the body or its parts in space.

The most important properties of muscle tissue. The structural elements of muscle tissue (cells, fibers) have an elongated shape and are capable of contraction due to the powerful development of the contractile apparatus. The latter is characterized by a highly ordered arrangement actin And myosin myofilaments, creating optimal conditions for their interaction. This is achieved by the connection of contractile structures with special elements of the cytoskeleton and plasmalemma (sarcolemma), performing a supporting function. In some muscle tissues, myofilaments form organelles of special importance - myofibrils. For muscle contraction a significant amount of energy is required, therefore, in the structural elements of muscle tissue there is a large number of mitochondria and trophic inclusions (lipid droplets, glycogen granules) containing substrates - sources of energy. Since muscle contraction occurs with the participation of calcium ions, structures that accumulate and release calcium are well developed in muscle cells and fibers - the agranular endoplasmic reticulum (sarcoplasmic reticulum), caveolae.

Classification of muscle tissue based on the characteristics of their (a) structure and function (morphofunctional classification) and (b) origin (histogenetic classification).

Morphofunctional classification of muscle tissue highlights striated (striated) muscle tissue And smooth muscle tissue. Cross-striated muscle tissue is formed by structural elements (cells, fibers) that have cross-striations due to the special ordered mutual arrangement of actin and myosin myofilaments in them. Striated muscle tissues include skeletal And cardiac muscle tissue. Smooth muscle tissue consists of cells that do not have cross-striations. The most common type of this tissue is smooth muscle tissue, which is part of the walls of various organs (bronchi, stomach, intestines, uterus, fallopian tube, ureter, bladder and blood vessels).

Histogenetic classification of muscle tissue There are three main types of muscle tissue: somatic(skeletal muscle tissue), coelomic(cardiac muscle tissue) and mesenchymal(smooth muscle tissue of internal organs), as well as two additional ones: myoepithelial cells(modified epithelial contractile cells in the terminal sections and small excretory ducts of some glands) and myoneural elements(contractile cells of neural origin in the iris).

Skeletal striated muscle tissue Its mass exceeds any other tissue in the body and is the most common muscle tissue in the human body. It ensures the movement of the body and its parts in space and maintains posture (part of the locomotor apparatus), forms the oculomotor muscles, muscles of the wall of the oral cavity, tongue, pharynx, and larynx. Non-skeletal visceral striated muscle tissue, which is found in the upper third of the esophagus and is part of the external anal and urethral sphincters, has a similar structure.

Skeletal striated muscle tissue develops in the embryonic period from myotomes somites that give rise to actively dividing myoblasts- cells that are arranged in chains and merge with each other at the ends to form muscular tubes (myotubules), turning into muscle fibers. Such structures, formed by a single giant cytoplasm and numerous nuclei, are traditionally called in the Russian literature simplasts(in this case - myosymplasts), however, this term is not in accepted international terminology. Some myoblasts do not merge with others, being located on the surface of the fibers and giving rise to myosatellite cells- small cells that are cambial elements of skeletal muscle tissue. Skeletal muscle tissue is formed in bundles striated muscle fibers(Fig. 87), which are its structural and functional units.

Muscle fibers skeletal muscle tissue are cylindrical formations of variable length (from millimeters to 10-30 cm). Their diameter also varies widely depending on the specific muscle and type, functional state, degree of functional load, nutritional status

and other factors. In muscles, muscle fibers form bundles in which they lie parallel and, deforming each other, often acquire an irregular multifaceted shape, which is especially clearly visible in cross sections (see Fig. 87). Between the muscle fibers there are thin layers of loose fibrous connective tissue, bearing vessels and nerves - endomysium. The transverse striation of skeletal muscle fibers is due to the alternation of dark anisotropic disks (bands A) and light isotropic disks (strips I). Each isotropic disk is cut in two by a thin dark line Z - telophragm(Fig. 88). The nuclei of the muscle fiber - relatively light, with 1-2 nucleoli, diploid, oval, flattened - lie on its periphery under the sarcolemma and are located along the fiber. On the outside, the sarcolemma is covered with a thick basement membrane, into which reticular fibers are woven.

Myosatellite cells (myosatellite cells) - small flattened cells located in shallow depressions of the sarcolemma of the muscle fiber and covered with a common basement membrane (see Fig. 88). The nucleus of the myosatellite cell is dense, relatively large, the organelles are small and few in number. These cells are activated when muscle fibers are damaged and provide their reparative regeneration. Merging with the rest of the fiber under increased load, myosatellite cells participate in its hypertrophy.

Myofibrils form the contractile apparatus of the muscle fiber, are located in the sarcoplasm along its length, occupying the central part, and are clearly visible on cross sections of the fibers in the form of small dots (see Fig. 87 and 88).

Myofibrils have their own transverse striations, and in the muscle fiber they are located in such an orderly manner that the isotropic and anisotropic disks of different myofibrils coincide with each other, causing the transverse striations of the entire fiber. Each myofibril is formed by thousands of repeating, sequentially interconnected structures - sarcomeres.

Sarcomere (myomer) is a structural and functional unit of the myofibril and represents its section located between two telophragms (Z lines). It includes an anisotropic disk and two halves of isotropic disks - one half on each side (Fig. 89). The sarcomere is formed by an ordered system thick (myosin) And thin (actin) myofilaments. Thick myofilaments are associated with mesophragm (line M) and are concentrated in an anisotropic disk,

and thin myofilaments are attached to telophragms (Z lines), form isotropic disks and partially penetrate into the anisotropic disk between thick threads up to the light stripes H at the center of the anisotropic disk.

Mechanism of muscle contraction described theory of sliding threads, according to which the shortening of each sarcomere (and, consequently, myofibrils and the entire muscle fiber) during contraction occurs due to the fact that, as a result of the interaction of actin and myosin in the presence of calcium and ATP, thin filaments move into the spaces between thick ones without changing their length. In this case, the width of the anisotropic disks does not change, but the width of the isotropic disks and H stripes decreases. The strict spatial ordering of the interaction of many thick and thin myofilaments in the sarcomere is determined by the presence of a complexly organized supporting apparatus, which, in particular, includes the telophragm and mesophragm. Calcium is released from sarcoplasmic reticulum, the elements of which entwine each myofibril, after receiving a signal from the sarcolemma along T-tubules(the set of these elements is described as sarcotubular system).

Skeletal muscle as an organ consists of bundles of muscle fibers connected together by a system of connective tissue components (Fig. 90). Covers the outside of the muscle epimysium- a thin, durable and smooth cover made of dense fibrous connective tissue, extending thinner connective tissue septa deeper into the organ - perimysium, which surrounds bundles of muscle fibers. From the perimysium, into the muscle fiber bundles, thin layers of loose fibrous connective tissue extend, surrounding each muscle fiber - endomysium.

Types of muscle fibers in skeletal muscle - varieties of muscle fibers with certain structural, biochemical and functional differences. Typing of muscle fibers is carried out on preparations when staging histochemical reactions to identify enzymes - for example, ATPase, lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) (Fig. 91), etc. In a generalized form, we can conditionally distinguish three main types of muscle fibers, between which there are transitional options.

Type I (red)- slow, tonic, fatigue-resistant, with low contraction force, oxidative. Characterized by small diameter, relatively thin myofibrils,

high activity of oxidative enzymes (for example, SDH), low activity of glycolytic enzymes and myosin ATPase, predominance of aerobic processes, high content of myoglobin pigment (determining their red color), large mitochondria and lipid inclusions, rich blood supply. Numerically predominant in muscles performing long-term tonic loads.

Type IIB (white)- fast, tetanic, easily fatigued, with great contraction force, glycolytic. They are characterized by a large diameter, large and strong myofibrils, high activity of glycolytic enzymes (for example, LDH) and ATPase, low activity of oxidative enzymes, predominance of anaerobic processes, relatively low content of small mitochondria, lipids and myoglobin (determining their light color), a significant amount of glycogen, relatively weak blood supply. Predominant in muscles that perform rapid movements, for example, muscles of the limbs.

Type IIA (intermediate)- fast, fatigue-resistant, with great strength, oxidative-glycolytic. The preparations resemble type I fibers. Equally capable of using energy obtained through oxidative and glycolytic reactions. According to their morphological and functional characteristics, they occupy a position intermediate between type I and IIB fibers.

Human skeletal muscles are mixed, that is, they contain fibers of various types that are distributed in them in a mosaic manner (see Fig. 91).

Cardiac striated muscle tissue found in the muscular lining of the heart (myocardium) and the mouths of the large vessels associated with it. The main functional property of cardiac muscle tissue is the ability for spontaneous rhythmic contractions, the activity of which is influenced by hormones and the nervous system. This tissue enables the heart to contract, which keeps blood circulating throughout the body. The source of development of cardiac muscle tissue is myoepicardial plate of the visceral layer of the splanchnotome(coelomic lining in the cervical part of the embryo). The cells of this plate (myoblasts) actively multiply and gradually turn into cardiac muscle cells - cardiomyocytes (cardiac myocytes). Arranging in chains, cardiomyocytes form complex intercellular connections - insert discs, connecting them in cardiac muscle fibers.

Mature cardiac muscle tissue is formed by cells - cardiomyocytes, connected to each other in the area of the intercalary discs and forming a three-dimensional network of branching and anastomosing cardiac muscle fibers(Fig. 92).

Cardiomyocytes (cardiac myocytes) - cylindrical or branching cells, larger in the ventricles. In the atria they are usually irregular in shape and smaller in size. These cells contain one or two nuclei and sarcoplasm, covered with a sarcolemma, which is externally surrounded by a basement membrane. Their nuclei - light, with a predominance of euchromatin, clearly visible nucleoli - occupy a central position in the cell. In an adult, a significant proportion of cardiomyocytes are polyploid, more than half - dual-core. The sarcoplasm of cardiomyocytes contains numerous organelles and inclusions, in particular, a powerful contractile apparatus, which is highly developed in contractile (working) cardiomyocytes (especially in ventricular ones). The contractile apparatus is presented cardiac striated myofibrils, similar in structure to the myofibrils of fibers of skeletal muscle tissue (see Fig. 94); together they cause the transverse striation of cardiomyocytes.

Between the myofibrils at the poles of the nucleus and under the sarcolemma there are very numerous and large mitochondria (see Fig. 93 and 94). Myofibrils are surrounded by elements of the sarcoplasmic reticulum associated with T-tubules (see Fig. 94). The cytoplasm of cardiomyocytes contains the oxygen-binding pigment myoglobin and accumulations of energy substrates in the form of lipid droplets and glycogen granules (see Fig. 94).

Types of cardiomyocytes in cardiac muscle tissue differ in structural and functional characteristics, biological role and topography. There are three main types of cardiomyocytes (see Fig. 93):

1)contractile (working) cardiomyocytes form the main part of the myocardium and are characterized by a powerfully developed contractile apparatus, occupying most of their sarcoplasm;

2)conducting cardiomyocytes have the ability to generate and quickly conduct electrical impulses. They form knots, bundles and fibers cardiac conduction system and are divided into several subtypes. They are characterized by weak development of the contractile apparatus, light sarcoplasm and large nuclei. IN conductive cardiac fibers(Purkinje) these cells are large in size (see Fig. 93).

3)secretory (endocrine) cardiomyocytes located in the atria (especially the right

vom) and are characterized by a process form and weak development of the contractile apparatus. In their sarcoplasm near the poles of the nucleus there are dense granules surrounded by a membrane containing atrial natriuretic peptide(a hormone that causes loss of sodium and water in the urine, dilation of blood vessels, lowering blood pressure).

Insert discs communicate between cardiomyocytes and each other. Under a light microscope, they look like transverse straight or zigzag stripes crossing the cardiac muscle fiber (see Fig. 92). Under an electron microscope, the complex organization of the intercalary disc is determined, which is a complex of intercellular connections of several types (see Fig. 94). In the region of transverse (oriented perpendicular to the location of myofibrils) sections of the intercalary disc, neighboring cardiomyocytes form numerous interdigitations connected by contacts like desmosomes And adhesive fascia. Actin filaments attach to the transverse portions of the sarcolemma of the intercalary disc at the level Z lines. On the sarcolemma of the longitudinal sections of the intercalary disc there are numerous gap junctions (nexuses), providing ionic communication between cardiomyocytes and transmission of the contraction impulse.

Smooth muscle tissue is part of the wall of hollow (tubular) internal organs - bronchi, stomach, intestines, uterus, fallopian tubes, ureters, bladder (visceral smooth muscle tissue), as well as blood vessels (vascular smooth muscle tissue). Smooth muscle tissue is also found in the skin, where it forms the muscles that lift the hair, in the capsules and trabeculae of some organs (spleen, testicle). Thanks to the contractile activity of this tissue, the activity of the digestive tract organs, regulation of respiration, blood and lymph flow, urine excretion, transport of germ cells, etc. is ensured. The source of development of smooth muscle tissue in the embryo is mesenchyme. Some cells of a different origin also have the properties of smooth myocytes - myoepithelial cells(modified contractile epithelial cells in some glands) and myoneural cells irises of the eye (develop from the neural rudiment). The structural and functional unit of smooth muscle tissue is smooth myocyte (smooth muscle cell).

Smooth myocytes (smooth muscle cells) - elongated cells are predominantly ver-

shadow-shaped, not transversely striated and forming numerous connections with each other (Fig. 95-97). Sarcolemma each smooth myocyte is surrounded basement membrane, into which thin reticular, collagen and elastic fibers are woven. Smooth myocytes contain one elongated diploid nucleus with a predominance of euchromatin and 1-2 nucleoli, located in the central thickened part of the cell. In the sarcoplasm of smooth myocytes, moderately developed organelles of general importance are located together with inclusions in cone-shaped areas at the poles of the nucleus. Its peripheral part is occupied by the contractile apparatus - actin And myosin myofilaments, which in smooth myocytes do not form myofibrils. Actin myofilaments are attached in the sarcoplasm to oval or fusiform dense corpuscles(see Fig. 97) - structures homologous to Z lines in striated tissues; similar formations associated with inner surface sarcolemmas are called dense plates.

The contraction of smooth myocytes is ensured by the interaction of myofilaments and develops in accordance with the sliding filament model. As in striated muscle tissues, contraction of smooth myocytes is induced by the influx of Ca 2+ into the sarcoplasm, which is released in these cells sarcoplasmic reticulum And caveolae- numerous flask-shaped invaginations of the surface of the sarcolemma. Due to their pronounced synthetic activity, smooth myocytes produce and secrete (like fibroblasts) collagens, elastin and amorphous substance components. They are also capable of synthesizing and secreting a number of growth factors and cytokines.

Smooth muscle tissue in organs usually represented by layers, bundles and layers of smooth myocytes (see Fig. 95), within which the cells are connected by interdigitation, adhesive and gap junctions. The arrangement of smooth myocytes in the layers is such that the narrow part of one cell is adjacent to the wide part of another. This contributes to the most compact packing of myocytes, ensuring the maximum area of their mutual contacts and high tissue strength. In connection with the described arrangement of smooth muscle cells in the layer, cross sections are adjacent to sections of myocytes cut in the wide part and in the narrow edge (see Fig. 95).

MUSCLE TISSUE

Rice. 87. Skeletal striated muscle tissue

1 - muscle fiber: 1.1 - sarcolemma, covered with a basement membrane, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.2.2 - myofibril fields (Conheim); 1.3 - muscle fiber nuclei; 2 - endomysium; 3 - layers of loose fibrous connective tissue between bundles of muscle fibers: 3.1 - blood vessels, 3.2 - fat cells

Rice. 88. Skeletal muscle fiber (diagram):

1 - basement membrane; 2 - sarcolemma; 3 - myosatellite cell; 4 - myosymplast core; 5 - isotropic disk: 5.1 - telophragm; 6 - anisotropic disk; 7 - myofibrils

Rice. 89. Section of myofibril fiber of skeletal muscle tissue (sarcomere)

Drawing with EMF

1 - isotropic disk: 1.1 - thin (actin) myofilaments, 1.2 - telophragm; 2 - anisotropic disk: 2.1 - thick (myosin) myofilaments, 2.2 - mesophragm, 2.3 - H strip; 3 - sarcomere

Rice. 90. Skeletal muscle (cross section)

Staining: hematoxylin-eosin

1 - epimysium; 2 - perimysium: 2.1 - blood vessels; 3 - bundles of muscle fibers: 3.1 - muscle fibers, 3.2 - endomysium: 3.2.1 - blood vessels

Rice. 91. Types of muscle fibers (cross section of skeletal muscle)

Histochemical reaction for detecting succinate dehydrogenase (SDH)

1 - type I fibers (red fibers) - with high SDH activity (slow, oxidative, fatigue resistant); 2 - type IIB fibers (white fibers) - with low SDH activity (fast, glycolytic, fatigue); 3 - type IIA fibers (intermediate fibers) - with moderate SDH activity (fast, oxidative-glycolytic, fatigue resistant)

Rice. 92. Cardiac striated muscle tissue

Stain: iron hematoxylin

A - longitudinal section; B - cross section:

1 - cardiomyocytes (form cardiac muscle fibers): 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.3 - nucleus; 2 - insert disks; 3 - anastomoses between fibers; 4 - loose fibrous connective tissue: 4.1 - blood vessels

Rice. 93. Ultrastructural organization of cardiomyocytes of various types

Drawings with EMF

A - contractile (working) cardiomyocyte of the ventricle of the heart:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - lipid droplets; 4 - core; 5 - insertion disk.

B - cardiomyocyte of the cardiac conduction system (from the subendocardial network of Purkinje fibers):

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria; 3.3 - glycogen granules, 3.4 - intermediate filaments; 4 - cores; 5 - insertion disk.

B - endocrine cardiomyocyte from the atrium:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - secretory granules; 4 - core; 5 - insertion disk

Rice. 94. Ultrastructural organization of the intercalary disc region between neighboring cardiomyocytes

Drawing with EMF

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.1.1 - sarcomere, 3.1.2 - isotropic disk, 3.1.3 - anisotropic disk, 3.1.4 - light stripe H, 3.1.5 - telophragm, 3.1.6 - mesophragm, 3.2 - mitochondria, 3.3 - T-tubules, 3.4 - elements of the sarcoplasmic reticulum, 3.5 - lipid droplets, 3.6 - glycogen granules; 4 - intercalary disc: 4.1 - interdigitation, 4.2 - adhesive fascia, 4.3 - desmosome, 4.4 - gap junction (nexus)

Rice. 95. Smooth muscle tissue

Staining: hematoxylin-eosin

A - longitudinal section; B - cross section:

1 - smooth myocytes: 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.3 - nucleus; 2 - layers of loose fibrous connective tissue between bundles of smooth myocytes: 2.1 - blood vessels

Rice. 96. Isolated smooth muscle cells

Staining: hematoxylin

1 - core; 2 - sarcoplasm; 3 - sarcolemma

Rice. 97. Ultrastructural organization of a smooth myocyte (cell region)

Drawing with EMF

1 - sarcolemma; 2 - sarcoplasm: 2.1 - mitochondria, 2.2 - dense bodies; 3 - core; 4 - basement membrane

The muscular layer of the walls of all cavity internal organs is built from smooth muscle tissue; it is also found in the walls of blood vessels and in the skin. This tissue contracts relatively slowly and does not tire for a long time. Contractions are rhythmic, at regular intervals. This tissue develops from mesenchyme, the cells of which are stretched in one direction, acquiring a spindle-shaped shape, approach each other and form a dense layer. Threads-protofibrils appear in the cytoplasm of cells. With natural physiological wear and tear and damage, the tissue is restored due to the amitotic division of muscle cells, as well as due to poorly differentiated elements that are always present in it.

The formed smooth muscle tissue consists of elongated

Rice. 6L Loose network of endocardial smooth muscle cells.

Cells tightly adjacent to each other (Fig. 61). Thanks to thin layers of reticular and connective tissue, the cells are combined into bundles, between which there are coarser layers of connective tissue with vessels and nerves. Smooth muscle cells most often have the shape of highly elongated spindles, often ending in branching ends. The length of the cells, depending on the organ, ranges from 20 to 500 microns. According to the shape of the cell, its nucleus is also elongated and lies almost in the center of the cell. Around it are located the usual organelles for any cell: centrosome, mitochondria, lamellar complex, cytoplasmic reticulum, glycogen inclusions. When studied under a light microscope, formed myofibrils are detected, although electron microscopic studies show that in the cytoplasm of these cells there are only contractile elements in the form of thin myofilaments, oriented longitudinally, usually not formed into bundles. On the surface, the smooth muscle cell is surrounded by a membrane - the myolemma, and is also covered by a basement membrane, to the outer surface of which collagen and argyrophilic fibers are attached. Smooth muscle tissue is innervated by the vegetative (autonomous) nervous system, and its action does not directly depend on the cerebral cortex, although it is controlled by it.

STRIPED MUSCLE TISSUE

All somatic, or skeletal, muscles of mammals are built from this type of tissue, as well as the muscles of the tongue, the muscles that move the eyeball, the muscles of the larynx and some others. Striated muscles differ sharply from smooth muscles in that they contract much faster (fractions of a second); this contraction occurs irregularly; striated fabric characterized by rapid fatigue.

Striated muscle tissue develops from myotomes, which are part of the somites of the mesoderm. Myotomes contain elongated cells - myoblasts, which grow, merge with each other, and form multinucleated symplastic formations called myotubes. The nuclei in them are located in the center, and weak fibrillarity is noticeable in the cytoplasm. Subsequently, myofibrils intensively develop in the central part of the myotubes, and the nuclei are pushed towards the sarcolemmas. The endomysium is formed from the surrounding mesenchyme, and in this way the muscle fiber is finally formed.

Rice. 62. Striated muscle tissue:

A - structure diagram; B - muscles of the tongue in a transverse section (a) and a longitudinal section (b).

Striated tissue consists of striated muscle fibers united by loose connective tissue into rays. Muscle fibers (Fig. 62) are non-cellular symplastic formations of an elongated cylindrical shape. They range from a few millimeters to 10-12 cm or more. Their thickness ranges from 10 to 200 microns and depends on the type, breed, age and physiological activity of the animal, as well as on the type of anatomical structure of the muscles. In one muscle, along with small ones, there are also large fibers (P. A. Glagolev,

N. N. Morozova, V. S. Sysoev, M. M. Streb-kova). Each muscle fiber is covered with a sheath - sarcolemma (sarcos - meat, lemma - sheath), consisting of two main layers. The plasmalemma, similar to cell membranes, is directly adjacent to the fiber. Outer part The sarcolemma is composed of a structureless membrane resembling the basement membrane of the epithelium. On the outside, the sarcolemma, more precisely the basement membrane, is entwined with collagen fibers, which at some distance from the muscle fiber pass into the collagen fibers of the surrounding connective tissue. The contents of the fiber are similar to the cytoplasm of cells and are called sarcoplasm.

Rice. 63. Scheme of the structure of a section of striated muscle fiber:

/ - basement membrane; 2- plasmalemma; 3 - mitochondria; 4 - lateral cistern and 5 - tubular channels of the cytoplasmic reticulum; 6 - T-system channels; 7 - triad; 8 - thick protofibrils; 9 - thin protofibrils; 10 - I-disks; 11 - A-discs; 12 - Z-stripe; 13 - H-strip.

Sarcoplasm contains nuclei, organelles, and inclusions. The nuclei in the fiber are located differently in different animals: in mammals they are located on the periphery of the fiber under the sarcolemma, and in birds - in the center of the fiber. One fiber can have over a hundred cores. They have the shape of highly elongated oval bodies and are poor in chromatin. A large number of large mitochondria (sarcosomes) are noted in the sarcoplasm. There are especially many sarcosomes between myofibrils. Thanks to the enzymes they contain, sarcosomes take an active part in processes related to energy production. In addition, the muscle fiber contains a lamellar complex and the sarcoplasmic reticulum, similar to the cytoplasmic network of other cells - a system of tubules, vesicles, cisterns located along the fiber, between the myofibrils (Fig. 63-4, 5).

In some places, the sarcolemma protrudes into the fiber, forming transverse tubes - T-systems or T-channels. Through them, water enters the fiber, and they participate in the propagation of the nerve impulse, and also, together with the sarcoplasmic reticulum, take part in the process of fiber contraction (6). The complex of the T-channel and the elements of the sarcoplasmic reticulum adjacent to it on both sides is called the triad.

The sarcoplasm of striated muscle fiber also contains trophic inclusions, such as fat, glycogen and myoglobin (protein).

The amount of fat varies in different fibers. The color of the muscle depends on myoglobin - hence the red and white muscles. There is more of it in dark red muscles. This protein easily binds oxygen, with its participation respiratory phosphorylation occurs, delivering a large amount of energy. Lighter-colored muscles have less myoglobin and the anaerobic process of carbohydrate metabolism predominates in them, resulting in less energy being released. In light of the above, it becomes clear why animals living in conditions of oxygen deficiency, an example of which are aquatic mammals and inhabitants

Rice. 64. Muscle fibers in cross section:

A - uniform and B - uneven distribution.

At high altitudes, there is especially a lot of myoglobin. The muscles of wild animals contain more myoglobin than those of domestic animals. The muscles of an ox working intensively are more colored than those of an ox working less intensively; in young animals it is weaker than in adults. Chickens that have lost the ability to fly pectoral muscles, associated with the movement of the wing, are weakly colored, while the actively working muscles of the pelvic limbs are dark red.

The contractile elements of muscle fiber are myofibrils.

Each myofibril is a filament with a thickness of 0.5 to 2 microns, and the length corresponds to the length of the fiber. It consists of areas that refract light differently and therefore appear on the preparation as dark (anisotropic) disks A and light (isotropic) disks I. In one fiber, the myofibrils are arranged so that their dark disks are opposite the dark ones, and the light ones are against the light ones. A Z strip or a T strip (telophragm) (12) passes through the middle of each isotropic disk, and an M strip (mesophragm) passes through the middle of an anisotropic disk. In a relaxed muscle, in the middle of the anisotropic disk, a light zone (H strip) is found, in the center of which the M strip is located. The area of the myofibril between the two Z strips is called a sarcomere. It includes half an isotropic disk, a whole anisotropic disk, and half of another isotropic disk. Due to the fact that there are a lot of myofibrils in the fiber and they lie very closely, it is not possible to distinguish individual fibrils under a microscope, and to the eye, the light disks of all myofibrils merge into a continuous transverse light stripe, and the dark disks into a dark transverse stripe on the muscle fiber. Hence the latter received the name striated. Under an electron microscope, it was discovered that myofibrils are a bundle of protofibrils (myofilaments) of two types (§, 9). Some of them, thinner ones, originate from the telophragm and consist of the actin protein; they form I disks, but also extend slightly into A disks. Others, protofibrils, forming “overlapping zones”, are thicker, consist of myosin and are located only in disk A. In the overlap zones between thick (myosin) and thin (actin) protofibrils there are short transversely oriented processes (bridges). During contraction, thin protofibrils are introduced between thick ones, moving towards the mesophragms inside the H stripe, while thick myosin strands approach the Z stripes, resting against them at the end of contraction, so that the I disk seems to disappear.

In the muscles of most animals, myofibrils are located in a dense bundle in the middle of the fiber (dense type of fiber structure), and in other animals in several bundles separated by layers

Rice. 65. Diagram of muscle structure:

1 - external perimysium; 2 - internal perimysium; 3 - blood vessels; 4 - nerve; 5 - fat cells; 6 - endomysium; 7 - muscle fibers in cross section (dots indicate myo-

fibrils in muscle fibers).

Groups of striated muscle fibers with the help of connective tissue (endomysium) are connected into bundles of the first order (primary muscle bundle). Several bundles of the first order with a larger amount of connective tissue (internal perimysium) are combined into bundles of the second order (secondary muscle bundle). Bundles of the second order, connecting with each other using new layers of connective tissue, form bundles of the third order (tertiary muscle bundle), etc. Finally, the outermost layers of connective tissue envelop the entire muscle (external perimysium). All layers of connective tissue passing between bundles of different orders, as well as between individual fibers in a bundle, are connected and form a single connective tissue framework - the muscle stroma (Fig. 65). A large number of blood and lymphatic vessels, as well as nerves, pass through the layers of connective tissue. Striated muscle tissue is innervated by cranial and spinal nerves. The latter contain both motor fibers, which transmit excitation from the brain to the muscle, and sensory fibers, which transmit excitation from the muscle to the brain. The work of muscles is controlled directly by the cerebral cortex.