Tissue is a collection of similar cells that share common functions. Almost all are made up of different types of fabrics.
Classification
In animals and humans, the following types of tissues are present in the body:
- epithelial;
- nervous;
- connecting;
- muscular.
These groups combine several varieties. So, connective tissue is adipose, cartilage, bone. It also includes blood and lymph. Epithelial tissue is multi-layered and single-layered, depending on the structure of the cells, squamous, cubic, cylindrical epithelium, etc. can also be distinguished. There is only one type of nervous tissue. And we will talk about it in more detail in this article.
Types of muscle tissue
In the body of all animals, its three varieties are distinguished:
- striated muscles;
- cardiac muscle tissue.
The functions of smooth muscle tissue differ from those of striated and cardiac tissue, so it has a different structure. Let's take a closer look at the structure of each type of muscle.
General characteristics of muscle tissue
Since all three species belong to the same type, they have a lot in common.
Muscle tissue cells are called myocytes, or fibers. Depending on the type of tissue, they may have a different structure.
Another common feature of all types of muscles is that they are able to contract, but this process occurs individually in different species.
Features of myocytes
Cells of smooth muscle tissue, as well as striated and cardiac, have an elongated shape. In addition, they have special organelles called myofibrils, or myofilaments. They contain (actin, myosin). They are necessary in order to ensure the movement of the muscle. A prerequisite for the functioning of the muscle, in addition to the presence of contractile proteins, is also the presence of calcium ions in the cells. Therefore, insufficient or excessive consumption of foods high in this element can lead to incorrect functioning of the muscles - both smooth and striated.
In addition, another specific protein, myoglobin, is present in cells. It is necessary in order to bind with oxygen and store it.
As for organelles, in addition to the presence of myofibrils, a special feature for muscle tissues is the content of a large number of mitochondria in the cell - two-membrane organelles responsible for cellular respiration. And this is not surprising, since the muscle fiber needs a large amount of energy generated during respiration by mitochondria to contract.
In some myocytes, more than one nucleus is also present. This is typical for striated muscles, the cells of which can contain about twenty nuclei, and sometimes this figure reaches one hundred. This is due to the fact that the striated muscle fiber is formed from several cells, subsequently combined into one.
The structure of striated muscles
This type of tissue is also called skeletal muscle. The fibers of this type of muscle are long, collected in bundles. Their cells can reach several centimeters in length (up to 10-12). They contain many nuclei, mitochondria and myofibrils. The main structural unit of each myofibril of striated tissue is the sarcomere. It is made up of a contractile protein.
The main feature of this muscle is that it can be controlled consciously, in contrast to smooth and cardiac.
The fibers of this tissue are attached to the bones with the help of tendons. That is why such muscles are called skeletal.
The structure of smooth muscle tissue
Smooth muscles line some of the internal organs, such as the intestines, uterus, bladder, and blood vessels. In addition, sphincters and ligaments are formed from them.
Smooth muscle fibers are not as long as striated fibers. But its thickness is greater than in the case of skeletal muscles. Cells of smooth muscle tissue have a spindle-like shape, and not filamentous, like striated myocytes.
The structures that provide smooth muscle contraction are called protofibrils. Unlike myofibrils, they have a simpler structure. But the material from which they are built is the same contractile proteins actin and myosin.
There are also fewer mitochondria in smooth muscle myocytes than in striated and cardiac cells. In addition, they contain only one core.
Features of the heart muscle
Some researchers define it as a subspecies of striated muscle tissue. Their fibers are indeed very similar in many ways. Heart cells - cardiomyocytes - also contain several nuclei, myofibrils and a large number of mitochondria. This tissue, as well as being able to contract much faster and stronger than smooth muscles.
However, the main feature that distinguishes the heart muscle from the striated muscle is that it cannot be controlled consciously. Its contraction occurs only automatically, as is the case with smooth muscles.
In the heart tissue, in addition to typical cells, there are also secretory cardiomyocytes. They do not contain myofibrils and do not contract. These cells are responsible for the production of the hormone atriopeptin, which is necessary for the regulation of blood pressure and control of circulating blood volume.
Functions of the striated muscles
Their main task is to move the body in space. It is also the movement of body parts relative to each other.
Of the other functions of the striated muscles, one can note the maintenance of the posture, the depot of water and salts. In addition, they perform a protective role, which is especially true for the abdominal muscles, which prevent mechanical damage to internal organs.
The functions of striated muscles can also include temperature regulation, since with active muscle contraction, a significant amount of heat is released. That is why, when freezing, the muscles begin to tremble involuntarily.
Functions of smooth muscle tissue
The muscles of this type perform an evacuation function. It lies in the fact that the smooth muscles of the intestine push the feces to the place of their excretion from the body. Also, this role is manifested during childbirth, when the smooth muscles of the uterus push the fetus out of the organ.
The functions of smooth muscle tissue are not limited to this. Their sphincter role is also important. Special circular muscles are formed from the tissue of this type, which can close and open. Sphincters are present in the urinary tract, in the intestines, between the stomach and esophagus, in the gallbladder, in the pupil.
Another important role played by smooth muscles is the formation of the ligamentous apparatus. It is necessary to maintain the correct position of the internal organs. With a decrease in the tone of these muscles, omission of some organs may occur.
This is where the functions of smooth muscle tissue end.
Purpose of the heart muscle
Here, in principle, there is nothing special to talk about. The main and only function of this tissue is to ensure blood circulation in the body.
Conclusion: differences between the three types of muscle tissue
To clarify this issue, we present a table:
| smooth muscle | striated muscles | cardiac muscle tissue |
| Shrinks automatically | Can be controlled consciously | Shrinks automatically |
| Cells elongated, spindle-shaped | Cells are long, filamentous | elongated cells |
| Fibers do not bundle | The fibers are bundled | The fibers are bundled |
| One nucleus per cell | Multiple nuclei in a cell | Multiple nuclei in a cell |
| Relatively few mitochondria | Lots of mitochondria | |
| Myofibrils are missing | Myofibrils are present | There are myofibrils |
| Cells are able to divide | Fibers cannot divide | Cells cannot divide |
| Contract slowly, weakly, rhythmically | Decrease quickly, strongly | Contract quickly, strongly, rhythmically |
| They line internal organs (intestines, uterus, bladder), form sphincters | Attached to the skeleton | Shape the heart |
That's all the main characteristics of striated, smooth and cardiac muscle tissue. Now you are familiar with their functions, structure and main differences and similarities.
Muscle tissues They are a group of tissues of different origin and structure, united on the basis of a common feature - a pronounced contractile ability, 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. Structural elements of muscle tissues (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 the plasmolemma. (sarcolemma) performing a supporting function. In part of muscle tissue, myofilaments form organelles of special significance - myofibrils. Muscle contraction requires a significant amount of energy, therefore, in the structural elements of muscle tissues there are a large number of mitochondria and trophic inclusions (lipid drops, glycogen granules) containing substrates - energy sources. Since muscle contraction proceeds with the participation of calcium ions, the structures that carry out its accumulation and release are well developed in muscle cells and fibers - the agranular endoplasmic reticulum. (sarcoplasmic reticulum), caveolae.
Muscle tissue classification based on features of their (a) structure and function (morphofunctional classification) and (b) origin (histogenetic classification).
Morphofunctional classification of muscle tissues highlights striated (striated) muscle tissue and smooth muscle tissue. Striated muscle tissues are formed by structural elements (cells, fibers), which have a transverse striation due to a special ordered mutual arrangement of actin and myosin myofilaments in them. The striated muscle tissues are skeletal and cardiac muscle tissue. Smooth muscle tissue consists of cells that do not have transverse 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 tissues identifies three main types of muscle tissue: somatic(skeletal muscle tissue) coelomic(heart muscle) 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 (striated) muscle tissue in its mass exceeds any other tissue of the body and is the most common muscle tissue of the human body. It ensures the movement of the body and its parts in space and the maintenance of a posture (part of the locomotor apparatus), forms the oculomotor muscles, muscles of the wall of the oral cavity, tongue, pharynx, larynx. A similar structure has non-skeletal visceral striated muscle tissue, which is found in the upper third of the esophagus, is part of the external anal and urethral sphincters.
Skeletal striated muscle tissue develops in the embryonic period from myotomes somites, giving rise to actively dividing myoblasts- cells that are arranged in chains and merge with each other at the ends to form muscle tubules (myotubules), turning into muscle fibres. Such structures, formed by a single giant cytoplasm and numerous nuclei, are traditionally referred to in Russian literature as symplasts(in this case - myosymplasts), however, this term does not exist in accepted international terminology. Some myoblasts do not fuse with others, being located on the surface of the fibers and giving rise to myosatellitocytes- small cells, which are the cambial elements of skeletal muscle tissue. Skeletal muscle tissue is made up of 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 belonging to a particular 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 seen in transverse sections (see Fig. 87). Between the muscle fibers are thin layers of loose fibrous connective tissue that carry blood vessels and nerves - endomysium. The transverse striation of skeletal muscle fibers is due to the alternation of dark anisotropic discs (bands A) and bright isotropic disks (bands I). Each isotropic disk is cut in two by a thin dark line Z - telophragm(Fig. 88). The nuclei of the muscle fiber are relatively light, with 1-2 nucleoli, diploid, oval, flattened - they lie on its periphery under the sarcolemma and are located along the fiber. Outside, the sarcolemma is covered with a thick basement membrane, into which reticular fibers are woven.
Myosatellitocytes (myosatellite cells) - small flattened cells located in shallow depressions of the muscle fiber sarcolemma and covered with a common basement membrane (see Fig. 88). The nucleus of the myosatellitocyte is dense, relatively large, the organelles are small and few. These cells are activated when muscle fibers are damaged and provide their reparative regeneration. Merging with the rest of the fiber under increased load, myosatellitocytes 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 identified on the cross sections of the fibers in the form of small dots (see Fig. 87 and 88).
Myofibrils have their own transverse striation, and in the muscle fiber they are arranged in such an orderly manner that the isotropic and anisotropic disks of different myofibrils coincide with each other, causing the transverse striation of the entire fiber. Each myofibril is formed by thousands of repeating successively interconnected structures - sarcomeres.
Sarcomere (myomer) is a structural and functional unit of a myofibril and is 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 mesophragma (line M) and are concentrated in an anisotropic disk,
and thin myofilaments are attached to telophragms (Z lines), form isotropic disks and partially penetrate the anisotropic disk between thick filaments up to light H stripes at the center of the anisotropic disk.
The mechanism of muscle contraction described the 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 are pushed into the gaps between thick ones without changing their length. In this case, the width of the anisotropic disks does not change, while the width of the isotropic disks and H bands 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, elements of which braid each myofibril, after receiving a signal from the sarcolemma through 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, strong and smooth sheath made of dense fibrous connective tissue, extending deeper into the organ thinner connective tissue septa - perimysium, which surrounds the bundles of muscle fibers. From the perimysium inside the bundles of muscle fibers depart the thinnest layers of loose fibrous connective tissue 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 setting up histochemical reactions for detecting enzymes - for example, ATPase, lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) (Fig. 91), etc. In a generalized form, three main types of muscle fibers can be conditionally distinguished, between which there are transitional options.
Type I (red)- slow, tonic, resistant to fatigue, with a small force of contraction, 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 (which determines their red color), large mitochondria and lipid inclusions, rich blood supply. Numerically predominate in muscles performing long-term tonic loads.
Type IIB (white)- fast, tetanic, easily tiring, with great force of contraction, glycolytic. They are characterized by 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 (which determines their light color), a significant amount of glycogen, relatively poor blood supply. They predominate in muscles that perform fast movements, for example, the muscles of the limbs.
Type IIA (intermediate)- fast, resistant to fatigue, with great strength, oxidative-glycolytic. On preparations, they resemble type I fibers. They are equally capable of using the energy obtained by 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, which are distributed in them in a mosaic pattern (see Fig. 91).
Cardiac striated (striated) muscle tissue occurs in the muscular membrane 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 to spontaneous rhythmic contractions, the activity of which is influenced by hormones and the nervous system. This tissue provides the contractions of the heart that keep the blood circulating in the body. The source of development of cardiac muscle tissue is myoepicardial plate of the visceral leaf of the splanchnotome(coelomic lining in the neck of the embryo). The cells of this plate (myoblasts) actively multiply and gradually turn into cardiac muscle cells - cardiomyocytes (cardiac myocytes). Lined up in chains, cardiomyocytes form complex intercellular connections - insert discs, linking them to cardiac muscle fibers.
Mature cardiac muscle tissue is formed by cells - cardiomyocytes, connected to each other in the region of the intercalated 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 usually have an irregular shape and are smaller. These cells contain one or two nuclei and a sarcoplasm, covered with a sarcolemma, which is surrounded by a basement membrane on the outside. Their nuclei - light, with a predominance of euchromatin, well-marked nucleoli - occupy a central position in the cell. In an adult, a significant part of cardiomyocytes - 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, skeletal muscle tissue fibers similar in structure to myofibrils (see Fig. 94); together they cause transverse striation of cardiomyocytes.
Between the myofibrils at the poles of the nucleus and under the sarcolemma 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 drops and glycogen granules (see Fig. 94).
Types of cardiomyocytes in cardiac muscle tissue differ in structural and functional features, 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, which occupies most of their sarcoplasm;
2)conducting cardiomyocytes have the ability to generate and quickly conduct electrical impulses. They form knots, bundles and fibers conducting system of the heart and are divided into several subtypes. They are characterized by weak development of the contractile apparatus, light sarcoplasm and large nuclei. AT conductive heart fibers(Purkinje) these cells are large (see Fig. 93).
3)secretory (endocrine) cardiomyocytes located in the atria (especially 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, vasodilation, lowering blood pressure).
Insert discs carry out communication of cardiomyocytes with 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 intercalated disk is determined, which is a complex of intercellular connections of several types (see Fig. 94). In the area of transverse (oriented perpendicular to the location of myofibrils) sections of the intercalated disk, neighboring cardiomyocytes form numerous interdigitations connected by contacts of the type desmosome and adhesive fascias. Actin filaments are attached to the transverse sections of the sarcolemma of the intercalated 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 bonding of cardiomyocytes and transmission of the contraction impulse.
smooth muscle tissue part of the wall of hollow (tubular) internal organs - bronchi, stomach, intestines, uterus, fallopian tubes, ureters, bladder (visceral smooth muscle) as well as vessels (vascular smooth muscle). Smooth muscle tissue is also found in the skin, where it forms the muscles that raise the hair, in the capsules and trabeculae of some organs (spleen, testis). Due to the contractile activity of this tissue, the activity of the organs of the digestive tract, the regulation of respiration, blood and lymph flow, the excretion of urine, the transport of germ cells, etc. are ensured. The source of development of smooth muscle tissue in the embryo is mesenchyme. The properties of smooth myocytes are also possessed by some cells of a different origin - myoepithelial cells(modified contractile epithelial cells in some glands) and myoneural cells irises of the eye (develop from the neural bud). The structural and functional unit of smooth muscle tissue is smooth myocyte (smooth muscle cell).
Smooth myocytes (smooth muscle cells) - elongated cells predominantly faith-
tenoid shape, not having transverse striation 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 bodies(see Fig. 97) - structures homologous to Z lines in striated tissues; similar formations associated with the inner surface of the sarcolemma are called dense plates.
The contraction of smooth myocytes is provided by the interaction of myofilaments and develops in accordance with the model of sliding filaments. As in striated muscle tissues, the contraction of smooth myocytes is induced by the influx of Ca 2+ into the sarcoplasm, which is released in these cells. sarcoplasmic reticulum and caveoli- Numerous flask-shaped protrusions of the surface of the sarcolemma. Due to their pronounced synthetic activity, smooth myocytes produce and secrete (like fibroblasts) collagens, elastin, and components of an amorphous substance. They are also able to synthesize and secrete 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 interdigitations, adhesive and gap junctions. The arrangement of smooth myocytes in layers is such that the narrow part of one cell is adjacent to the wide part of the other. 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 sections of myocytes, cut in the wide part and in the region of 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 - fields of myofibrils (Konheim); 1.3 - nuclei of the muscle fiber; 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 - myosatellitocyte; 4 - the core of the myosymplast; 5 - isotropic disk: 5.1 - telophragm; 6 - anisotropic disk; 7 - myofibrils
Rice. 89. Plot 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 band; 3 - sarcomere
Rice. 90. Skeletal muscle (cross section)
Stain: 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 the detection of succinate dehydrogenase (SDH)
1 - fibers of type I (red fibers) - with high activity of SDH (slow, oxidative, resistant to fatigue); 2 - IIB type fibers (white fibers) - with low SDH activity (fast, glycolytic, fatigued); 3 - fibers of type IIA (intermediate fibers) - with moderate activity of SDH (fast, oxidative-glycolytic, resistant to fatigue)
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 drops; 4 - core; 5 - insert disk.
B - cardiomyocyte of the conduction system of the heart (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 - insert 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 - insert disc
Rice. 94. Ultrastructural organization of the region of the intercalated disc 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 - bright H band, 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 drops, 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
Stain: 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
stain: hematoxylin
1 - core; 2 - sarcoplasm; 3 - sarcolemma
Rice. 97. Ultrastructural organization of a smooth myocyte (section of a cell)
Drawing with EMF
1 - sarcolemma; 2 - sarcoplasm: 2.1 - mitochondria, 2.2 - dense bodies; 3 - core; 4 - basement membrane
Muscle tissues combines the ability to reduce.
Structural features: the contractile apparatus, which occupies a significant part in the cytoplasm of the structural elements of muscle tissue and consists of actin and myosin filaments, which form special-purpose organelles - myofibrils .
Muscle tissue classification
1. Morphofunctional classification:
1) Striated or striated muscle tissue: skeletal and cardiac;
2) Unstriated muscle tissue: smooth.
2. Histogenetic classification (depending on the sources of development):
1) Somatic type(from somite myotomes) - skeletal muscle tissue (striated);
2) coelomic type(from the myoepicardial plate of the visceral leaf of the splanchnotome) - cardiac muscle tissue (striated);
3) Mesenchymal type(develops from mesenchyme) - smooth muscle tissue;
4) From skin ectoderm and prechordal plate- myoepithelial cells of glands (smooth myocytes);
5) neural origin (from the neural tube) - myoneural cells (smooth muscles that constrict and expand the pupil).
Functions of muscle tissue: movement of a body or its parts in space.
SKELETAL MUSCLE TISSUE
striated (striated) muscle tissue makes up to 40% of the mass of an adult, is part of the skeletal muscles, muscles of the tongue, larynx, etc. They belong to arbitrary muscles, since their contractions obey the will of a person. It is these muscles that are involved in sports.
Histogenesis. Skeletal muscle tissue develops from myotome cells of myoblasts. There are head, cervical, thoracic, lumbar, sacral myotomes. They grow in dorsal and ventral directions. Branches of the spinal nerves grow into them early. Some myoblasts differentiate in situ (form autochthonous muscles), while others from the 3rd week of intrauterine development migrate into the mesenchyme and, merging with each other, form myotubes (myotubes)) with large centrally oriented nuclei. In myotubes, differentiation of special organelles of myofibrils occurs. Initially, they are located under the plasmalemma, and then fill most of the myotube. The nuclei are displaced to the periphery. Cell centers and microtubules disappear, GREP is significantly reduced. Such a multi-core structure is called symplast , and for muscle tissue - myosymplast . Some myoblasts differentiate into myosatellitocytes, which are located on the surface of myosymplasts and subsequently take part in the regeneration of muscle tissue.
The structure of skeletal muscle tissue
Consider the structure of muscle tissue at several levels of organization of the living: at the organ level (muscle as an organ), at the tissue level (directly muscle tissue), at the cellular (muscle fiber structure), at the subcellular (myofibril structure) and at the molecular level (structure of actin and myosin threads).
On the card:
1 - gastrocnemius muscle (organ level), 2 - cross section of the muscle (tissue level) - muscle fibers, between which RVST: 3 - endomysium, 4 - nerve fiber, 5 - blood vessel; 6 - cross section of the muscle fiber (cellular level): 7 - the nucleus of the muscle fiber - simplast, 8 - mitochondria between myofibrils, in blue - sarcoplasmic reticulum; 9 — cross section of myofibril (subcellular level): 10 — thin actin filaments, 11 — thick myosin filaments, 12 — heads of thick myosin filaments.
1) Organ level: structure muscles as an organ.
Skeletal muscle consists of bundles of muscle fibers connected together by a system of connective tissue components. Endomysius- layers of RVST between muscle fibers, where blood vessels and nerve endings pass . Perimysium- surrounds 10-100 bundles of muscle fibers. Epimysium- the outer shell of the muscle, represented by a dense fibrous tissue.
2) Tissue level: structure muscle tissue.
The structural and functional unit of skeletal striated (striated) muscle tissue is muscle fiber- a cylindrical formation with a diameter of 50 microns and a length of 1 to 10-20 cm. Muscle fiber consists of 1) myosymplast(see its formation above, its structure below), 2) small cambial cells - myosatellitocytes, adjacent to the surface of the myosymplast and located in the recesses of its plasmolemma, 3) the basement membrane, which covers the plasmolemma. The complex of plasmalemma and basement membrane is called sarcolemma. The muscle fiber is characterized by transverse striation, the nuclei are displaced to the periphery. Between the muscle fibers - layers of RVST (endomysium).
3) Cellular level: structure muscle fiber (myosymplast).
The term "muscle fiber" implies "myosymplast", since the myosymplast provides the function of contraction, myosatellitocytes are involved only in regeneration.
Myosymplast, like a cell, consists of 3 components: the nucleus (more precisely, many nuclei), the cytoplasm (sarcoplasm) and the plasmolemma (which is covered with a basement membrane and is called the sarcolemma). Almost the entire volume of the cytoplasm is filled with myofibrils - special-purpose organelles, general-purpose organelles: rEPS, aEPS, mitochondria, the Golgi complex, lysosomes, and nuclei are displaced to the periphery of the fiber.
In the muscle fiber (myosymplast), functional apparatuses are distinguished: membrane, fibrillar(contractile) and trophic.
Trophic apparatus includes nuclei, sarcoplasm and cytoplasmic organelles: mitochondria (energy synthesis), GREP and the Golgi complex (synthesis of proteins - structural components of myofibrils), lysosomes (phagocytosis of worn out structural components of the fiber).
Membrane apparatus: each muscle fiber is covered by a sarcolemma, where the outer basement membrane is distinguished and the plasmolemma (under the basement membrane), which forms invaginations ( T- tubules). To each T-tubule adjoined by two tanks triad: two L- tubules (AEPS tanks) and one T tubule (invagination of the plasmalemma). In tanks, AEPS are concentrated Sa 2+ , required for contraction. Myosatellitocytes are adjacent to the plasmolemma. When the basement membrane is damaged, the mitotic cycle of myosatellitocytes starts.
fibrillar apparatus.Most of the cytoplasm of striated fibers is occupied by special-purpose organelles - myofibrils, oriented longitudinally, providing the contractile function of the tissue.
4) Subcellular level: structure myofibrils.
When examining muscle fibers and myofibrils under a light microscope, there is an alternation of dark and light areas in them - disks. Dark discs are birefringent and are called anisotropic discs, or BUT- disks. Light discs do not have birefringence and are called isotropic, or I-disks.
In the middle of the disk BUT there is a lighter area - H-a zone containing only thick filaments of the protein myosin. In the middle H-zones (and therefore BUT-disk) stands out darker M- a line consisting of myomesin (required for the assembly of thick filaments and their fixation during contraction). In the middle of the disk I there is a dense line Z, which is built from protein fibrillar molecules. Z-line is connected to neighboring myofibrils with the help of the desmin protein, and therefore all the named lines and disks of neighboring myofibrils coincide and a picture of striated striation of the muscle fiber is created.
The structural unit of a myofibril is sarcomere (S) — is a bundle of myofilaments enclosed between two Z-lines. The myofibril is made up of many sarcomeres. Formula describing the structure of the sarcomere:
S = Z 1 + 1/2 I 1 + BUT + 1/2 I 2 + Z 2
5) Molecular level: structure actin and myosin filaments .
Under an electron microscope, myofibrils are aggregates of thick, or myosin, and thin, or actin, filaments. Between the thick filaments are thin filaments (diameter 7-8 nm).
Thick filaments or myosin filaments(diameter 14 nm, length 1500 nm, distance between them 20-30 nm) consist of myosin protein molecules, which is the most important contractile muscle protein, 300-400 myosin molecules in each thread. The myosin molecule is a hexamer consisting of two heavy and four light chains. Heavy chains are two helically twisted polypeptide filaments. They carry spherical heads at their ends. Between the head and the heavy chain there is a hinge section, with the help of which the head can change its configuration. In the area of \u200b\u200bthe heads there are light chains (two on each). Myosin molecules are stacked in a thick filament in such a way that their heads are turned outward, protruding above the surface of the thick filament, and the heavy chains form the core of the thick filament.
Myosin has ATPase activity: the released energy is used for muscle contraction.
Thin filaments or actin filaments(diameter 7-8 nm) are formed by three proteins: actin, troponin and tropomyosin. The main protein is actin, which forms a helix. Tropomyosin molecules are located in the groove of this helix, troponin molecules are located along the helix.
Thick filaments occupy the central part of the sarcomere - BUT-disc, thin occupied I- discs and partially enter between thick myofilaments. H- zone consists only of thick threads.
At rest interaction of thin and thick filaments (myofilaments) impossible, because The myosin-binding sites of actin are blocked by troponin and tropomyosin. At a high concentration of calcium ions, conformational changes in tropomyosin lead to unblocking of the myosin-binding regions of actin molecules.
Motor innervation of the muscle fiber. Each muscle fiber has its own innervation apparatus (motor plaque) and is surrounded by a network of hemocapillaries located in the adjacent RVST. This complex is called mion. A group of muscle fibers innervated by a single motor neuron is called neuromuscular unit. In this case, muscle fibers may not be located nearby (one nerve ending can control from one to dozens of muscle fibers).
When nerve impulses arrive along the axons of motor neurons, muscle fiber contraction.
Muscle contraction
During contraction, muscle fibers shorten, but the length of actin and myosin filaments in myofibrils does not change, but they move relative to each other: myosin filaments move into the spaces between actin a, actin filaments - between myosin filaments. As a result, the width is reduced I-disk, H-strips and the length of the sarcomere decreases; width BUT-disk does not change.
Sarcomere formula at full contraction: S = Z 1 + BUT+ Z 2
Molecular mechanism of muscle contraction
1. The passage of a nerve impulse through the neuromuscular synapse and depolarization of the plasmolemma of the muscle fiber;
2. The wave of depolarization passes through T-tubules (invagination of the plasmalemma) to L tubules (cistern of the sarcoplasmic reticulum);
3. Opening of calcium channels in the sarcoplasmic reticulum and release of ions Sa 2+ into sarcoplasm;
4. Calcium diffuses to the thin filaments of the sarcomere, binds to troponin C, leading to conformational changes in tropomyosin and freeing active centers for binding myosin and actin;
5. Interaction of myosin heads with active centers on the actin molecule with the formation of actin-myosin "bridges";
6. Myosin heads “walk” along actin, forming new bonds of actin and myosin during movement, while actin filaments are pulled into the space between myosin filaments to M-lines, bringing two Z-lines;
7. Relaxation: Sa The 2+-ATPase of the sarcoplasmic reticulum pumps Sa 2+ from sarcoplasm to cisterns. In the sarcoplasm, the concentration Sa 2+ becomes low. Troponin bonds are broken FROM with calcium, tropomyosin closes the myosin-binding sites of thin filaments and prevents their interaction with myosin.
Each movement of the myosin head (attachment to actin and detachment) is accompanied by the expenditure of ATP energy.
Sensory innervation(neuromuscular spindles). Intrafusal muscle fibers, together with sensory nerve endings, form neuromuscular spindles, which are skeletal muscle receptors. The spindle capsule is formed outside. With the contraction of striated (striated) muscle fibers, the tension of the connective tissue capsule of the spindle changes and, accordingly, the tone of the intrafusal (located under the capsule) muscle fibers changes. A nerve impulse is formed. With excessive stretching of the muscle, a feeling of pain occurs.
Classification and types of muscle fibers
1. By the nature of the reduction: phasic and tonic muscle fibres. Phase ones are able to carry out rapid contractions, but cannot maintain the achieved level of shortening for a long time. Tonic muscle fibers (slow) provide maintenance of static tension or tone, which plays a role in maintaining a certain position of the body in space.
2. According to biochemical features and color allocate red and white muscle fibers. The color of the muscle is determined by the degree of vascularization and the content of myoglobin. A characteristic feature of red muscle fibers is the presence of numerous mitochondria, the chains of which are located between the myofibrils. There are fewer mitochondria in white muscle fibers and they are located evenly in the sarcoplasm of the muscle fiber.
3. According to the type of oxidative exchange : oxidative, glycolytic and intermediate. The identification of muscle fibers is based on the activity of the enzyme succinate dehydrogenase (SDH), which is a marker for mitochondria and the Krebs cycle. The activity of this enzyme indicates the intensity of energy metabolism. Separate muscle fibers BUT-type (glycolytic) with low activity of SDH, FROM-type (oxidative) with high activity of SDH. Muscle fibers AT-type occupy an intermediate position. The transition of muscle fibers from BUT-type in FROM-type marks the change from anaerobic glycolysis to oxygen dependent metabolism.
In sprinters (athletes, when a quick short contraction is needed, bodybuilders), training and nutrition are aimed at developing glycolytic, fast, white muscle fibers: they have a lot of glycogen stores and energy is obtained mainly in an anaerobic way (white meat in chicken). Stayers (athletes - marathon runners, in those sports where endurance is needed) are dominated by oxidative, slow, red fibers in the muscles - they have a lot of mitochondria for aerobic glycolysis, blood vessels (oxygen is needed).
4. In striated muscles, two types of muscle fibers are distinguished: extrafusal, which predominate and determine the actual contractile function of the muscle and intrafusal, which are part of the proprioceptors - neuromuscular spindles.
The factors that determine the structure and function of skeletal muscle are the influence of nervous tissue, hormonal influence, location of the muscle, the level of vascularization and motor activity.
HEART MUSCLE TISSUE
Cardiac muscle tissue is located in the muscular membrane of the heart (myocardium) and in the mouths of the large vessels associated with it. It has a cellular type of structure and the main functional property is the ability to spontaneous rhythmic contractions (involuntary contractions).
It develops from the myoepicardial plate (the visceral sheet of the splanchnotome of the mesoderm in the cervical region), the cells of which multiply by mitosis and then differentiate. Myofilaments appear in the cells, which further form myofibrils.
Structure. Structural unit of cardiac muscle tissue - cell cardiomyocyte. Between the cells are layers of RVST with blood vessels and nerves.
Types of cardiomyocytes : 1) typical ( working, contractile), 2) atypical(conductive), 3) secretory.
Typical cardiomyocytes
Typical (working, contractile) cardiomyocytes- cylindrical cells, up to 100-150 microns long and 10-20 microns in diameter. Cardiomyocytes form the main part of the myocardium, connected to each other in chains by the bases of the cylinders. These zones are called insert discs, in which desmosomal junctions and nexuses (gap junctions) are distinguished. Desmosomes provide mechanical cohesion that prevents cardiomyocytes from separating. Gap junctions facilitate the transmission of contraction from one cardiomyocyte to another.
Each cardiomyocyte contains one or two nuclei, a sarcoplasm and a plasma membrane surrounded by a basement membrane. There are functional devices, the same as in the muscle fiber: membrane, fibrillar(contractile), trophic, as well as energy.
Trophic apparatus includes the nucleus, sarcoplasm and cytoplasmic organelles: rEPS and the Golgi complex (protein synthesis - the structural components of myofibrils), lysosomes (phagocytosis of the structural components of the cell). Cardiomyocytes, like fibers of skeletal muscle tissue, are characterized by the presence in their sarcoplasm of the iron-containing oxygen-binding pigment myoglobin, which gives them a red color and is similar in structure and function to erythrocyte hemoglobin.
Energy apparatus represented by mitochondria and inclusions, the splitting of which provides energy. Mitochondria are numerous, lying in rows between fibrils, at the poles of the nucleus and under the sarcolemma. The energy required by cardiomyocytes is obtained by splitting: 1) the main energy substrate of these cells - fatty acids, which are deposited as triglycerides in lipid drops; 2) glycogen, located in the granules located between the fibrils.
Membrane apparatus : each cell is covered with a membrane consisting of a complex of plasmolemm and basement membrane. The shell forms invaginations ( T- tubules). To each T- one tank adjoins the tubule (unlike the muscle fiber - there are 2 tanks) sarcoplasmic reticulum(modified aEPS), forming dyad: one L- tubule (aEPS tank) and one T tubule (invagination of the plasmalemma). In AEPS tanks, ions Sa 2+ do not accumulate as actively as in muscle fibers.
Fibrillar (contractile) apparatus .Most of the cytoplasm of a cardiomyocyte is occupied by special-purpose organelles - myofibrils, oriented longitudinally and located along the periphery of the cell. The contractile apparatus of working cardiomyocytes is similar to skeletal muscle fibers. During relaxation, calcium ions are released into the sarcoplasm at a low rate, which ensures automaticity and frequent contractions of cardiomyocytes. T tubules are wide and form dyads (one T-tubule and one cistern network), which converge in the area Z-lines.
Cardiomyocytes, communicating with the help of intercalated discs, form contractile complexes that contribute to the synchronization of contraction, lateral anastomoses are formed between the cardiomyocytes of neighboring contractile complexes.
Function of typical cardiomyocytes: ensuring the force of contraction of the heart muscle.
Conductive (atypical) cardiomyocytes have the ability to generate and quickly conduct electrical impulses. They form nodes and bundles of the conduction system of the heart and are divided into several subtypes: pacemakers (in the sinoatrial node), transitional (in the atrioventricular node) and cells of the His bundle and Purkinje fibers. Conducting cardiomyocytes are characterized by weak development of the contractile apparatus, light cytoplasm and large nuclei. There are no T-tubules and transverse striation in the cells, since the myofibrils are arranged randomly.
Function of atypical cardiomyocytes- generation of impulses and transmission to working cardiomyocytes, ensuring the automaticity of myocardial contraction.
Secretory cardiomyocytes
Secretory cardiomyocytes are located in the atria, mainly in the right; characterized by a process form and weak development of the contractile apparatus. In the cytoplasm, near the poles of the nucleus, there are secretory granules containing natriuretic factor, or atriopeptin(a hormone that regulates blood pressure). The hormone causes the loss of sodium and water in the urine, vasodilation, pressure reduction, inhibition of the secretion of aldosterone, cortisol, vasopressin.
Function of secretory cardiomyocytes: endocrine.
Regeneration of cardiomyocytes. Only intracellular regeneration is characteristic of cardiomyocytes. Cardiomyocytes are not capable of division, they lack cambial cells.
SMOOTH MUSCLE
Smooth muscle tissue forms the walls of internal hollow organs, vessels; characterized by the absence of striation, involuntary contractions. Innervation is carried out by the autonomic nervous system.
Structural and functional unit of unstriated smooth muscle tissue - smooth muscle cell (SMC), or smooth myocyte. The cells are spindle-shaped, 20–1000 µm long and 2–20 µm thick. In the uterus, the cells have an elongated process shape.
Smooth myocyte
A smooth myocyte consists of a rod-shaped nucleus located in the center, a cytoplasm with organelles, and a sarcolemma (a complex of plasmolemma and basement membrane). In the cytoplasm at the poles is the Golgi complex, many mitochondria, ribosomes, and the sarcoplasmic reticulum is developed. Myofilaments are located obliquely or along the longitudinal axis. In SMCs, actin and myosin filaments do not form myofibrils. There are more actin filaments and they are attached to dense bodies, which are formed by special cross-linking proteins. Next to the actin filaments are myosin monomers (micromyosin). Possessing different lengths, they are much shorter than thin threads.
Contraction of smooth muscle cells is carried out by the interaction of actin filaments and myosin. The signal traveling along the nerve fibers causes the release of the neurotransmitter, which changes the state of the plasmalemma. It forms flask-shaped invaginations (caveoles), where calcium ions are concentrated. SMC contraction is induced by the influx of calcium ions into the cytoplasm: the caveolae are laced off and enter the cell together with calcium ions. This leads to the polymerization of myosin and its interaction with actin. Actin filaments and dense bodies approach, the force is transferred to the sarcolemma and the SMC is shortened. Myosin in smooth myocytes is able to interact with actin only after phosphorylation of its light chains by a special enzyme, light chain kinase. After the signal stops, calcium ions leave the caveolae; Myosin depolarizes and loses its affinity for actin. As a result, the myofilament complexes disintegrate; contraction stops.
Special types of muscle cells
Myoepithelial cells are derivatives of the ectoderm, do not have striation. Surround the secretory sections and excretory ducts of the glands (salivary, milk, lacrimal). They are connected to glandular cells by desmosomes. Reducing, contribute to the secretion. In the terminal (secretory) sections, the shape of the cells is process-like, stellate. The nucleus in the center, in the cytoplasm, mainly in the processes, myofilaments are localized, which form the contractile apparatus. These cells also have cytokeratin intermediate filaments, which emphasizes their similarity to epitheliocytes.
myoneural cells develop from the cells of the outer layer of the eyecup and form the muscle that narrows the pupil and the muscle that expands the pupil. In structure, the first muscle is similar to the MMC of mesenchymal origin. The muscle dilating the pupil is formed by processes of cells located radially, and the nucleated part of the cell is located between the pigment epithelium and the stroma of the iris.
Myofibroblasts belong to loose connective tissue and are modified fibroblasts. They exhibit the properties of fibroblasts (synthesize intercellular substance) and smooth myocytes (have pronounced contractile properties). As a variant of these cells can be considered myoid cells as part of the wall of the convoluted seminiferous tubule of the testicle and the outer layer of the theca of the ovarian follicle. During wound healing, some fibroblasts synthesize smooth muscle actins and myosins. Myofibroblasts provide contraction of the wound edges.
Endocrine smooth myocytes - These are modified SMCs, representing the main component of the juxtaglomerular apparatus of the kidneys. They are located in the wall of the arterioles of the renal corpuscle, have a well-developed synthetic apparatus and a reduced contractile apparatus. They produce the enzyme renin, which is located in the granules and enters the bloodstream by the mechanism of exocytosis.
Regeneration of smooth muscle tissue. Smooth myocytes are characterized by intracellular regeneration. With an increase in functional load, myocyte hypertrophy occurs and in some organs hyperplasia (cellular regeneration). So, during pregnancy, the smooth muscle cells of the uterus can increase 300 times.
Muscular tissue (Latin name - textus muscularis) forms muscles that provide the motor functions of a 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 reduction in muscle mass, 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. Muscle 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
There are several types of muscle formations in the human body. 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 muscle has a high rate of contraction and relaxation, it forms a complex of skeletal muscles, the upper part of the 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 that form a mesh endomysium that binds neighboring cells.
The functionality of the body depends on how the human muscles work, smoothly or spontaneously. Entire motor complexes are formed by smooth muscle tissue, 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 the expression of the face, 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 ensure the correct position of the hairs. Some muscle groups have the ability to function automatically. For example, the upper eyelids periodically close for a fraction of a second, then to return to their 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 cycle is broken and there is an indiscriminate lowering of the 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.
It has a structure of myofibrils and protofibrils similar to skeletal muscle tissue and a mechanism of muscle contraction (myofibrils are few, they are thin, weak transverse striation)
Features of cardiac striated muscle tissue:
o Muscle fiber consists of chains of individual cells - cardiomyocytes(cells do not merge)
o All heart cells are connected by membrane contacts (intercalary discs) into a single muscle fiber, which ensures contraction of the myocardium as a whole (separately atrial myocardium and ventricular myocardium)
o Fibers have a small number of nuclei
Cardiac muscle tissue is divided into two types:
o working muscle tissue- makes up 99% of the mass of the myocardium of the heart (provides contraction of the heart)
o conductive muscle tissue- consists of modified, incapable of reduction, atypical cells
Forms nodes in the myocardium, where electrical impulses are generated and from where they propagate for heart contractions - conduction system of the heart
Functions of cardiac striated muscle tissue
1. Generation and propagation of electrical impulses for contraction of the myocardium of the heart
2. involuntary rhythmic contractions of the myocardium of the heart to push blood (automatic myocardium)
smooth muscle tissue
Localized only in the internal organs (the walls of the digestive tract, the walls of the respiratory tract, blood and lymphatic vessels, the bladder, uterus, oblique muscles of the hair of the skin, the muscles surrounding the pupil)
Cells solitary, long, spindle-shaped, mononuclear, dividing throughout life
The internal structure of the cell is the same as that of the muscle fibers of striated tissue (myofibrils, consisting of protofibrils and proteins of actin and myosin)
Light areas of actin and dark areas of myosin of different myofibrils are disordered, which leads to the absence of transverse striation of smooth muscle cells
They form ribbons, layers, strands in the walls of internal organs (do not form separate muscles)
Innervated by autonomic nerves
The smooth muscles of the internal organs are weak, shrink involuntarily without the participation of consciousness, slowly, do not get tired, are able to be in a state of contraction for a very long time (hours, days) - tonic contractions (consume little power to operate)
Smooth muscle functions
1. Work (motor function) of internal organs (peristalsis, excretion of urine, childbirth, etc.)
2. The tone of the blood and lymphatic vessels (a change in the diameter of the vessels leads to a change in pressure and blood velocity)
nervous tissue
In the process of embryogenesis, it is formed by cell division of the ectoderm
properties of nervous tissue excitability and conductivity
Organs formed by nervous tissue: brain, spinal cord, ganglions (ganglia), nerves
· Comprises nerve cells (neurons)– 15% of all cells and neuroglia(intercellular substance)
Neuroglia has cells (gliocytes) - 85% of all cells
Functions of neuroglia
1. Trophic (supplying neurons with everything necessary for life)
2. Support (skeleton of nervous tissue)
3. Isolating, protective (protection from adverse conditions and electrical insulation of neurons)
4. Regeneration of nerve cell processes
· Nerve cells - neurons- mononuclear, with processes that do not divide after birth (the total number of neurons in the human nervous system, according to various estimates, ranges from 100 billion to 1 trillion)
· Have body(contains granules, lumps) and processes
In neurons many mitochondria, the Golgi complex and the system of support-transport microtubules are very well developed - neurofibrils for the transport of substances (neurotransmitters)
Distinguish two types of processes:
o axon- always one, long (up to 1.5 m), not branching (goes beyond the organ of the nervous system)
Axon functions- conducting a command (in the form of an electrical impulse) from a neuron to other neurons or to working tissues and organs
o Dendrites- numerous (up to 15), short, branched (have sensitive nerve endings at the ends - receptors)
Functions of dendrites- perception of irritation and conduction of an electrical impulse (information) from receptors to the body of a neuron (to the brain)
· Nerve fibers
Structure of a neuron:
The structure of a multipolar neuron:
1 - dendrites; 2 - neuron body; 3 - core; 4 - axon; 5 - myelin sheath; 6 - branching of the axon
· The gray matter of the brain is a collection of bodies of neurons- the substance of the cerebral cortex, the cerebellar cortex, the horns of the gray matter of the spinal cord and nerve nodes (ganglia)
· The white matter of the brain set of processes of neurons (axons and dendrites)
Types of neurons(according to the number of processes)
o Unipolar- have one process (axon)
o Bipolar- have two processes (one axon and one dendrite)
o Multipolar - have many processes (one axon and many dendrites) - neurons of the spinal cord and brain
Types of neurons(by function)
o Sensitive (centripetal, sensory, efferent) - perceive irritations from receptors, form feelings, sensations (bipolar)
o Insertion (associative)- analysis, the biological meaning of information received from receptors, the development of a response command, connection of sensory neurons with motor and other neurons (one neuron can connect to 20 thousand other neurons); 60% of all neurons, multipolar
o Motor (centrifugal, motor, effector)- transmission of the command of the intercalary neuron to the working organs (muscles, glands); multipolar, with a very long axon
o Brake
o Some neurons are capable of synthesizing hormones: oxytocin and prolactin ( neurosecretory cells hypothalamus diencephalon)
· Nerve fibers- processes of nerve cells covered with connective tissue membranes
There are two types of nerve fibers (depending on the structure of the sheath): pulpy and non-pulpy
| Pulmonary (myelinated) nerve fibers | Unmyelinated (unmyelinated) nerve fibers |
| 1. Sheathed with neuroglial cells (Schwann cells) to electrically insulate the fiber | 1. Too |
| 2. Membranes Schwann cell membranes contain a substance - myelin(significantly increases electrical insulation) | 2. Do not contain myelin (less effective electrical insulation) |
| 3. The fiber has areas without a sheath - intercepts of Ranvier (accelerate the conduction of a nerve impulse along the fiber) | 3. No |
| 4. Thick | 4. Thin |
| 5. The speed of nerve impulses up to 120 m / s | 5. The speed of the nerve impulse is about 10 m / s |
| 6. Form the nerves of the central nervous system | 6. Form nerves of the autonomic nervous system |
o Hundreds and thousands of pulpy and non-pulmonic nerve fibers that extend beyond the CNS, covered with connective tissue form nerves (nerve trunks)
Types of nerves
o Sensory nerves - formed exclusively by dendrites, serve to conduct sensitive information from the body's receptors to the brain (to sensitive neurons)
o motor nerves- formed from axons: they serve to conduct a brain command from a motor neuron to working tissues and organs (effectors)
o mixed nerves- consist of dendrites and axons; also serve to conduct sensitive information to the brain and brain commands to working organs (for example, 31 pairs of spinal nerves)
Communication and interaction between nerve cells is carried out using synapses
Synapse - the place of contact of an axon with another process or body of another cell (nervous or somatic), in which the transmission of a nerve (electrical) impulse occurs
o The transmission of a nerve impulse in the synapse is carried out with the help of chemicals - neurotransmitters(adrenaline, norepinephrine, acetylcholine, serotonin, dopamine, etc.)
o Synapses are located on the branches of the end of the axon
o The number of synapses on one neuron can reach up to 10,000, so the total number of contacts in the nervous system approaches an astronomical figure
o It is possible that the number of contacts and multipolar neurons in the nervous system are one of the indicators of a person's mental development and labor specialization. With age, the number of contacts decreases significantly
animal tissue(human tissues)
Reflex. reflex arc
Reflex - response of the body to irritation (change) of the external and internal environment, carried out with the participation of the nervous system
o the main form of activity of the central nervous system
v The founder of the concept of reflexes as unconscious automatic acts associated with the lower parts of the nervous system is the French philosopher and naturalist R. Descartes (XVII century). In the XVIII century. Czech anatomist and physiologist G. Prohaska introduced the science of this term "reflex"
v I.P. Pavlov, Russian academician (XX century) divided the reflex into unconditional ( congenital, species, group) and conditional (purchased, individual)