Cardiac muscle tissue develops from. Functions of muscle tissue, types and structure. Functions of striated muscles

Muscle tissue combines the ability to contract.

Structural features: contractile apparatus, which occupies a significant part of the cytoplasm of the structural elements of muscle tissue and consists of actin and myosin filaments, which form organelles for special purposes - myofibrils .

Classification of muscle tissue

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 myotomes of somites) – skeletal muscle tissue (striated);

2) Coelomic type(from the myoepicardial plate of the visceral layer of the splanchnotome) – cardiac muscle tissue (striated);

3) Mesenchymal type(develops from mesenchyme) – smooth muscle tissue;

4) From cutaneous ectoderm And prechordal plate– myoepithelial cells of glands (smooth myocytes);

5) Neural origin (from the neural tube) - myoneural cells (smooth muscles that constrict and dilate the pupil).

Functions of muscle tissue: movement of a body or its parts in space.

SKELETAL MUSCLE TISSUE

Striated (cross-striped) muscle tissue makes up up to 40% of the mass of an adult, is part of the skeletal muscles, muscles of the tongue, larynx, etc. They are classified as voluntary muscles, since their contractions are subject to the will of the person. These are the muscles that are used when playing sports.

Histogenesis. Skeletal muscle tissue develops from myotome cells, myoblasts. There are head, cervical, thoracic, lumbar, and sacral myotomes. They grow in the dorsal and ventral directions. The branches of the spinal nerves grow into them early. Some myoblasts differentiate in place (form autochthonous muscles), while others, from the 3rd week of intrauterine development, migrate into the mesenchyme and, merging with each other, form muscular tubes (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 shifted to the periphery. Cell centers and microtubules disappear, grEPS is significantly reduced. This multi-core structure is called simplast , and for muscle tissue – myosimplast . 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

Let us consider the structure of muscle tissue at several levels of living organization: at the organ level (muscle as an organ), at the tissue level (muscle tissue itself), at the cellular level (the structure of muscle fiber), at the subcellular level (the structure of myofibril) and at the molecular level (the structure of actin and myosin threads).

On the map:

1 - gastrocnemius muscle (organ level), 2 - cross-section of the muscle (tissue level) - muscle fibers, between which the RVST: 3 - endomysium, 4 - nerve fiber, 5 - blood vessel; 6 - cross section of muscle fiber (cellular level): 7 - nuclei of muscle fiber - symplast, 8 - mitochondria between myofibrils, 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 linked together by a system of connective tissue components. Endomysium– PBCT layers 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 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 from 1 to 10-20 cm. Muscle fiber consists of 1) myosymplast(see its formation above, structure - below), 2) small cambial cells - myosatellite cells, adjacent to the surface of the myosymplast and located in the recesses of its plasmalemma, 3) the basement membrane, which covers the plasmalemma. The complex of plasmalemma and basement membrane is called sarcolemma. The muscle fiber is characterized by transverse striations, the nuclei are shifted to the periphery. Between the muscle fibers there are layers of PBST (endomysium).

3) Cellular level: structure muscle fiber (myosymplast).

The term “muscle fiber” implies “myosymplast”, since myosymplast provides the contraction function, myosatellite cells are involved only in regeneration.

Myosimplast, like a cell, consists of 3 components: a nucleus (more precisely, many nuclei), cytoplasm (sarcoplasm) and plasmolemma (which is covered with a basement membrane and is called sarcolemma). Almost the entire volume of the cytoplasm is filled with myofibrils - special-purpose organelles; general-purpose organelles: grEPS, aEPS, mitochondria, Golgi complex, lysosomes, and also nuclei are shifted to the periphery of the fiber.

In the muscle fiber (myosymplast), functional devices are distinguished: membrane, fibrillar(contractive) and trophic.

Trophic apparatus includes nuclei, sarcoplasm and cytoplasmic organelles: mitochondria (energy synthesis), grEPS and 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 with a sarcolemma, where an outer basement membrane and a plasmalemma (under the basement membrane) are distinguished, which forms invaginations ( T-tubes). To each T- the tube is adjacent to two tanks triad: two L-tubes (aEPS tanks) and one T-tubule (invagination of the plasmalemma). AEPS are concentrated in tanks Sa 2+ required for reduction. Myosatellite cells are adjacent to the plasmalemma on the outside. When the basement membrane is damaged, the mitotic cycle of myosatellite cells starts.

Fibrillar apparatus.Most of the cytoplasm of the 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 - discs. Dark disks are birefringent and are called anisotropic disks, or A- disks. Light-colored disks are not birefringent and are called isotropic, or I-disks.

In the middle of the disk A there is a lighter area - N- a zone where only thick filaments of the myosin protein are contained. In the middle N-zones (which means A-disk) the darker one stands out M-line consisting of myomesin (necessary 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 using the protein desmin, and therefore all the named lines and disks of neighboring myofibrils coincide and a picture of striated muscle fiber is created.

The structural unit of the myofibril is sarcomere (S) — it is a bundle of myofilaments enclosed between two Z-lines. The myofibril consists of many sarcomeres. Formula describing the structure of the sarcomere:

S = Z 1 + 1/2 I 1 + A + 1/2 I 2 + Z 2

5) Molecular level: structure actin And myosin filaments .

Under an electron microscope, myofibrils appear as aggregates of thick, or myosin, and thin, or actin, filaments. Between the thick filaments there 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 protein of muscle, 300-400 myosin molecules in each strand. The myosin molecule is a hexamer consisting of two heavy and four light chains. Heavy chains are two helically twisted polypeptide strands. They bear spherical heads at their ends. Between the head and the heavy chain there is a hinge section with which the head can change its configuration. In the area of ​​the heads there are light chains (two on each). Myosin molecules are arranged in a thick filament in such a way that their heads face 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), formed by three proteins: actin, troponin and tropomyosin. The main protein by mass 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 - A-disc, thin occupy I- discs and partially insert between thick myofilaments. N-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 the unblocking of the myosin-binding regions of actin molecules.

Motor innervation of 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, the 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, the muscle fibers shorten, but the length of the actin and myosin filaments in the myofibrils does not change, but they move relative to each other: myosin filaments move into the spaces between actin filaments, actin filaments - between myosin filaments. As a result, the width is reduced I-disk, H-stripes and the length of the sarcomere decreases; width A-disk does not change.

Sarcomere formula at full contraction: S = Z 1 + A+ Z 2

Molecular mechanism of muscle contraction

1. The passage of a nerve impulse through the neuromuscular synapse and depolarization of the plasmalemma of the muscle fiber;

2. The depolarization wave travels along T-tubules (invaginations of the plasmalemma) to L-tubules (cisterns 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 connections between actin and myosin during movement, while the actin filaments are pulled into the space between the myosin filaments towards M-lines, bringing two together Z-lines;

7. Relaxation: Sa 2+ -ATPase of the sarcoplasmic reticulum pumps Sa 2+ from sarcoplasm into cisterns. In the sarcoplasm the concentration Sa 2+ becomes low. Troponin bonds are broken WITH 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 receptors for skeletal muscle. A spindle capsule is formed on the outside. When striated (striated) muscle fibers contract, the tension of the connective tissue capsule of the spindle changes and the tone of the intrafusal (located under the capsule) muscle fibers changes accordingly. A nerve impulse is formed. When a muscle is overstretched, a feeling of pain occurs.

Classification and types of muscle fibers

1. By the nature of the contraction: phasic and tonic muscle fibers. Phasic are capable of performing rapid contractions, but cannot maintain the achieved level of shortening for a long time. Tonic muscle fibers (slow) ensure the maintenance of static tension or tone, which plays a role in maintaining a certain position of the body in space.

2. By biochemical characteristics and color allocate red and white muscle fibers. The color of the muscle is determined by the degree of vascularization and myoglobin content. A characteristic feature of red muscle fibers is the presence of numerous mitochondria, the chains of which are located between the myofibrils. In white muscle fibers there are fewer mitochondria and they are located evenly in the sarcoplasm of the muscle fiber.

3. By type of oxidative metabolism : oxidative, glycolytic and intermediate. 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. Release muscle fibers A-type (glycolytic) with low SDH activity, WITH-type (oxidative) with high SDH activity. Muscle fibers IN-types occupy an intermediate position. Transition of muscle fibers from A-type in WITH-type marks changes from anaerobic glycolysis to oxygen-dependent metabolism.

For sprinters (athletes, when a quick short contraction is needed, bodybuilders), training and nutrition are aimed at the development of glycolytic, fast, white muscle fibers: they have a lot of glycogen reserves and energy is produced primarily through the anaeolbic pathway (white meat in chicken). Stayers (athletes - marathon runners, in those sports where endurance is required) have a predominance of oxidative, slow, red fibers in the muscles - they have a lot of mitochondria for aerobic glycolysis, blood vessels (they need oxygen).

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 proprioceptors - neuromuscular spindles.

Factors that determine the structure and function of skeletal muscle are the influence of nervous tissue, hormonal influence, location of the muscle, level of vascularization and motor activity.

CARDIAC MUSCLE TISSUE

Cardiac muscle tissue is located in the muscular layer 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 (visceral layer 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. The structural unit of cardiac muscle tissue is a cell cardiomyocyte. Between the cells there are layers of PBCT with blood vessels and nerves.

Types of cardiomyocytes : 1) typical ( workers, 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 contacts and nexuses (slit-like contacts) 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, sarcoplasm and plasmalemma, surrounded by a basement membrane. There are functional apparatuses, the same as in muscle fiber: membrane, fibrillar(contractile), trophic, and energetic.

Trophic apparatus includes the nucleus, sarcoplasm and cytoplasmic organelles: grEPS and Golgi complex (synthesis of proteins - structural components of myofibrils), lysosomes (phagocytosis of 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 breakdown 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 in the form of triglycerides in lipid droplets; 2) glycogen, located in granules located between fibrils.

Membrane apparatus : Each cell is covered with a membrane consisting of a plasmalemma complex and a basement membrane. The shell forms invaginations ( T-tubes). To each T-the tubule is adjacent to one tank (unlike the muscle fiber - there are 2 tanks) sarcoplasmic reticulum(modified aEPS), forming dyad: one L-tube (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 the 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. When relaxed, 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-tube and one tank network), which converge in the area Z-lines.

Cardiomyocytes, connecting with the help of intercalary discs, form contractile complexes that contribute to the synchronization of contraction; lateral anastomoses are formed between cardiomyocytes of neighboring contractile complexes.

Function of typical cardiomyocytes: providing the force of contraction of the heart muscle.

Conducting (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 cells (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. The cells do not have T-tubules or cross-striations because the myofibrils are arranged in a disorderly manner.

Function of atypical cardiomyocytes– generation of impulses and transmission to working cardiomyocytes, ensuring 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 loss of sodium and water in the urine, dilation of blood vessels, decreased blood pressure, and inhibition of the secretion of aldosterone, cortisol, and vasopressin.

Function of secretory cardiomyocytes: endocrine.

Regeneration of cardiomyocytes. Cardiomyocytes are characterized only by intracellular regeneration. Cardiomyocytes are not capable of division; they lack cambial cells.

SMOOTH MUSCLE TISSUE

Smooth muscle tissue forms the walls of internal hollow organs and blood vessels; characterized by a lack of striations and involuntary contractions. Innervation is carried out by the autonomic nervous system.

Structural and functional unit of non-striated smooth muscle tissue - smooth muscle cell (SMC), or smooth myocyte. The cells are spindle-shaped, 20-1000 µm long and 2 to 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, cytoplasm with organelles and sarcolemma (plasmolemma and basement membrane complex). In the cytoplasm at the poles there is a Golgi complex, many mitochondria, ribosomes, and a developed sarcoplasmic reticulum. 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. Myosin monomers (micromyosin) are located near the actin filaments. Having different lengths, they are much shorter than thin threads.

Contraction of smooth muscle cells occurs through the interaction of actin filaments and myosin. The signal traveling along the nerve fibers causes the release of a mediator, which changes the state of the plasmalemma. It forms flask-shaped invaginations (caveolae), where calcium ions are concentrated. Contraction of SMCs is induced by the influx of calcium ions into the cytoplasm: caveolae are detached and, together with calcium ions, enter the cell. This leads to the polymerization of myosin and its interaction with actin. Actin filaments and dense bodies come closer together, 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; the contraction stops.

Special types of muscle cells

Myoepithelial cells are derivatives of ectoderm and do not have striations. They surround the secretory sections and excretory ducts of the glands (salivary, mammary, lacrimal). They are connected to glandular cells by desmosomes. By contracting, they promote secretion. In the terminal (secretory) sections, the shape of the cells is branched and stellate. The nucleus is in the center, in the cytoplasm, mainly in the processes, myofilaments are localized, which form the contractile apparatus. These cells also contain cytokeratin intermediate filaments, which emphasizes their similarity to epithelial cells.

Myoneural cells develop from the cells of the outer layer of the optic cup and form the muscle that constricts the pupil and the muscle that dilates the pupil. The structure of the first muscle is similar to SMCs of mesenchymal origin. The muscle that dilates the pupil is formed by cell processes located radially, and the nuclear-containing 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 we can consider 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 are modified SMCs that represent 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 granules and enters the blood through the mechanism of exocytosis.

Regeneration of smooth muscle tissue. Smooth myocytes are characterized by intracellular regeneration. With an increase in functional load, myocyte hypertrophy and hyperplasia (cellular regeneration) occur in some organs. Thus, during pregnancy, the smooth muscle cells of the uterus can increase 300 times.

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. Muscle contraction requires a significant amount of energy, therefore the structural elements of muscle tissue contain 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 intertwine 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 skeletal muscle tissue fibers (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 the inner surface of the sarcolemma 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 interdigitations, 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 - insert 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 - 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 - 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

This tissue is localized in the muscular layer of the heart (myocardium) and the mouths of the large vessels associated with it.

Functional Features

1) automaticity,

2) rhythmicity,

3) involuntariness,

4) low fatigue.

The activity of contractions is influenced by hormones and the nervous system (sympathetic and parasympathetic).

B.2.1. Histogenesis of cardiac muscle tissue

The source of development of cardiac muscle tissue is the myoepicardial plate of the visceral layer of the splanchnotome. It produces SCMs (stem cells of myogenesis), which differentiate into cardiomyoblasts that actively multiply by mitosis. In their cytoplasm, myofilaments are gradually formed, forming myofibrils. With the advent of the latter, cells are called cardiomyocytes(or cardiac myocytes). The ability of human cardiomyocytes to undergo complete mitotic division is lost at the time of birth or in the first months of life. Processes begin in these cells polyploidization. Cardiac myocytes line up in chains, but do not merge with each other, as happens during the development of skeletal muscle fiber. Cells form complex intercellular connections - intercalary discs that connect cardiomyocytes in functional fibers(functional syncytium).

The structure of cardiac muscle tissue

As already noted, 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 functional fibers.

Types of cardiomyocytes

1. contractile

1) ventricular (prismatic)

2) atrial (processes)

2. cardiomyocytes of the cardiac conduction system

1) pacemakers (P-cells, 1st order pacemakers)

2) transitional (2nd order pacemakers)

3) conductive (3rd order pacemakers)

3. secretory (endocrine)

Cardiomyocytes of the cardiac conduction system (CCS)

Irregular prismatic shape

Length size 8-20 microns, width 2-5 microns

Poor development of all organelles (including myofibrils)

Intercalated discs have fewer desmosomes

Secretory (endocrine) cardiomyocytes

Process form

Length size 15-20 microns, width 2-5 microns

General plan of the building (see above SKMC)

Organelles for export synthesis are developed

Many secretory granules

Myofibrils are poorly developed

Structural and functional apparatus of cardiomyocytes

1. Contractile apparatus(most developed in SKMC)

Presented myofibrils , each of which consists of thousands of telophragms connected in series sarcomeres containing actinic e(thin) and myosin (thick) myofilaments. The terminal sections of myofibrils are attached from the cytoplasmic side to the intercalary discs using adhesion strips(splitting and weaving of actin filaments into the submembrane areas of the plasmalemma of myocytes

Provides strong rhythmic energy-dense calcium-dependent contraction ↔ relaxation (“sliding thread model”)

2. Transport apparatus(developed at SKMC) - similar to that in skeletal muscle fibers

3. Support apparatus

Imagine n sarcolemma, intercalated discs, stripes of adhesion, anastomoses, cytoskeleton, telophragms, mesophragms.

Provides formative, frame, locomotor And integration functions.

4. Trophic-energetic apparatus – presented sarcosomes and inclusions of glycogen, myoglobin and lipids.

5. Apparatus for synthesis, structuring and regeneration.

Presented free ribosomes, EPS, kg, lysosomes, secretory granules(in secretory cardiomyocytes)

Provides resynthesis contractile and regulatory proteins of myofibrils, other endoreproductive processes, secretion components of the basement membrane and PNUF (secretory cardiomyocytes)

6. Nervous apparatus

Presented nerve fibers, receptor and motor nerve endings autonomic nervous system.

Provides adaptive regulation of contractile and other functions of cardiomyocytes.

Regeneration of cardiac muscle tissue

A. Mechanisms

1. Endoreproduction

2. Synthesis of basement membrane components

3. Cardiomyocyte proliferation possible in embryogenesis

B. Species

1. Physiological

Occurs continuously, ensures age-related (including in children) increase in myocardial mass (working hypertrophy of myocytes without hyperplasia)

Increases with increasing load on the myocardium → working hypertrophy myocytes without hyperplasia (in people with manual labor, in pregnant women)

2. Reparative

The defect in muscle tissue is not replenished by cardiomyocytes (a connective tissue scar is formed at the site of damage)

Regeneration of cardiomyocytes (both physiological and reparative) is carried out only by the mechanism of endoreproduction. Causes:

1) there are no poorly differentiated cells,

2) cardiomyocytes are not capable of division,

3) they are not capable of dedifferentiation.

· Has a structure of myofibrils and protofibrils and a mechanism of muscle contraction similar to skeletal muscle tissue (there are few myofibrils, they are thin, weak transverse striations)

Features of cardiac striated muscle tissue:

o Muscle fiber consists of chains of individual cells – cardiomyocytes(cells do not fuse)

o All heart cells are connected by membrane contacts (intercalated discs) into a single muscle fiber, which ensures contraction of the myocardium as a whole (separately the atrial myocardium and ventricular myocardium)

o Fibers have a small number of cores

· Cardiac muscle tissue is divided into two types:

o working muscle tissue– makes up 99% of the mass of the heart myocardium (provides heart contraction)

o conductive muscle tissue– consists of modified, incapable of contraction, atypical cells

Forms nodes in the myocardium where electrical impulses for heart contractions are generated and distributed from – conduction system of the heart

Functions of cardiac striated muscle tissue

1. Generation and propagation of electrical impulses to contract the myocardium of the heart

2. Involuntary rhythmic contractions of the myocardium of the heart to push blood (myocardial automation)

Smooth muscle tissue

· Localized only in internal organs (walls of the digestive tract, walls of the respiratory tract, blood and lymphatic vessels, bladder, uterus, oblique muscles of the hair of the skin, muscles surrounding the pupil)

· Cells are solitary, long, spindle-shaped, mononuclear, dividing throughout life

· The internal structure of the cell is the same as that of muscle fibers of striated tissue (myofibrils, consisting of protofibrils and the proteins actin and myosin)

· Light areas of actin and dark areas of myosin of different myofibrils lie disorderly, which leads to the absence of cross-striations of smooth muscle cells

· Form ribbons, layers, cords in the walls of internal organs (do not form separate muscles)

Innervated by autonomic nerves

Smooth muscles of internal organs are weak, contract involuntarily without the fate of consciousness, slowly, do not get tired, capable of being in a state of contraction for a very long time (hours, days) – tonic contractions (consume little energy to operate)

Functions of smooth muscles

1. Work (motor function) of internal organs (peristalsis, urine excretion, childbirth, etc.)

2. Tone of blood and lymphatic vessels (changes in the diameter of blood vessels lead to changes in blood pressure and velocity)

Nervous tissue

· During embryogenesis, it is formed by division of ectoderm cells

Properties of nervous tissue – excitability And conductivity

Organs formed by nervous tissue: brain, spinal cord, ganglia, nerves

· Comprises nerve cells (neurons)– 15% of all cells and neuroglia(intercellular substance)

Neuroglia have cells (gliocytes) - 85% of all cells

Functions of neuroglia

1. Trophic (supply of neurons with everything necessary for life)

2. Supporting (skeleton of nervous tissue)

3. Insulating, protective (protection from adverse conditions and electrical insulation of neurons)

4. Regeneration of nerve cell processes

· Nerve cells - neurons- mononuclear, with processes, not dividing 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 shoots

· In neurons many mitochondria, the Golgi complex and the system of support-transport microtubules are very well developed - neurofibrils for transport of substances (neurotransmitters)

· There are two types of shoots:

o Axon– always one, long (up to 1.5 m), not branching (extends beyond the limits of the nervous system organ)

Axon functions– carrying out 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

Neuron structure:


Structure of a multipolar neuron:
1 - dendrites; 2 - neuron body; 3 - core; 4 - axon; 5 - myelin sheath; 6 – axon branches

· The gray matter of the brain is a collection of neuron cell bodies- substance of the cerebral cortex, cerebellar cortex, horns of gray matter of the spinal cord and nerve nodes (ganglia)

· White matter of the brain - a set of neuron processes (axons and dendrites)

Types of neurons(by number of shoots)

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 Intercalary (associative)– analysis, biological meaning of information received from receptors, development of a response command, connection of sensory neurons with motor neurons and other neurons (one neuron can connect to 20 thousand other neurons); 60% of all neurons are multipolar

o Propulsive (centrifugal, motor, effector)– transmission of the interneuron command 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 of the 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 pulpless

o Hundreds and thousands of pulpal and non-pulmonary nerve fibers extending beyond the central nervous system, covered with connective tissue, form nerves (nerve trunks)

Types of nerves

o Sensory nerves - formed exclusively by dendrites, they serve to conduct sensitive information from the body’s receptors to the brain (into sensory neurons)

o Motor nerves– formed from axons: they serve to carry out brain commands from the 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 is the point of contact of an axon with another process or body of another cell (nerve or somatic), in which the transmission of a nerve (electrical) impulse occurs

o The transmission of nerve impulses at the synapse is carried out using chemicals - neurotransmitters(adrenaline, norepinephrine, acetylcholine, serotonin, dopamine, etc.)

o Synapses are located on the branches of the axon terminal

o The number of synapses on one neuron can reach up to 10,000, so the total number of contacts in the nervous system is approaching an astronomical figure

o It is possible that the number of contacts and multipolar neurons in the nervous system is one of the indicators of a person’s mental development and labor specialization. With age, the number of contacts decreases significantly

Animal tissue(human tissue)

Reflex. Reflex arc

Reflex – the body’s response 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 idea 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 this term “reflex” to science

v I.P. Pavlov, Russian academician (XX century) divided the reflex into unconditional ( congenital, specific, group) and conditional (purchased, individual)

The structural units of cardiac muscle tissue are cells - cardiomyocytes, covered with a basement membrane.

There are 5 types of cardiomyocytes: contractile (working), or typical, and atypical: sinus (pacemaker), transitional, conductive and secretory.

Working cardiomyocytes have the shape of an elongated cylinder with a length of about 100-150 microns and a diameter of up to 20 microns. They contain one, or less often two, nuclei located in the center of the cell, and myofibrils (Conheim's fields) are localized in groups around the nuclei. The structure of myofibrils is the same as in skeletal muscle tissue, but they lack triads. Cardiomyocytes connect end to end to form functional muscle fibers. In the area of ​​cardiomyocyte junctions, intercalated discs are clearly visible at the light-optical level.

In Insert discs distinguish between longitudinal and transverse sections:

IN Transverse sections there are many intercellular contacts - Desmos , they ensure the strength of the connection of cardiomyocytes; V Longitudinal Plots there are many intercellular contacts like Nexus , which form narrow channels between neighboring cells, water and ions are able to pass through these channels, which creates conditions for the free passage of electric current from one cardiomyocyte to another; Thus, the presence of nexuses ensures the electrical coupling of cardiomyocytes, necessary for the rapid spread of excitation throughout the entire mass of the myocardium and for its synchronous contraction

Pacemaker cardiomyocytes (P-cells) are located in the sinus region. They are able to contract rhythmically and transmit control signals through transitional and conductive cardiomyocytes to workers, which contract with a given rhythm.

Transitional and Conductive cardiomyocytes They transmit excitation of the heart rhythm from β-cells to contractile cardiomyocytes.

Secretory cardiomyocytes They produce atrial natriuretic factor, which regulates urine formation and is a renin antagonist (increases diuresis and reduces blood pressure).

Common to the morphology of skeletal and cardiac muscle tissue is the presence of striations, detected at the light-optical level, and the so-called T-tubules, detected by ultramicroscopic examination.

T-tubules are tube-shaped invaginations of the cytomembrane that go inside the muscle fiber and cardiomyocyte, that is, they are located transversely relative to their length. Approximately at the level of the Z-lines, they come close to the endoplasmic reticulum.

Smooth muscle tissue

In smooth muscle tissue of mesenchymal origin, the structural unit is the myocyte, which has a spindle-shaped shape, its nucleus is elongated, and is localized in the center of the cell. The length of myocytes ranges from 20-500 microns, and the width in the abdominal region is only 5-8 microns. The contractile apparatus is represented by actin filaments, forming a three-dimensional network, next to which myosin monomers are located.

In smooth muscle tissue there is no troponin-tropomyosin complex; the myosin head has light chains that must first be phosphorylated in order for it to cleave and attach ATP and interact with actin.

The structural unit of smooth muscles of ectodermal origin is the myoepitheliocyte of the exocrine glands, and the structural unit of neural origin is the myoneural cells m. m. sphincter et dilatator pupille.