Muscle tissue (lat. textus muscularis - “muscle tissue”) - tissues that are different in structure and origin, but similar in their ability to undergo pronounced contractions. Consist of elongated cells that receive irritation from nervous system and answer it with an abbreviation. They ensure movement in space of the body as a whole, its movement of organs within the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the ability to change shape, but in muscle tissue this ability becomes the main function.
The main morphological characteristics of muscle tissue elements: elongated shape, the presence of longitudinally located myofibrils and myofilaments - special organelles that ensure contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.
Special contractile organelles - myofilaments or myofibrils - provide contraction, which occurs when two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide energy for these processes. The reserve of energy sources is formed by glycogen and lipids. Myoglobin is a protein that ensures the binding of oxygen and the creation of its reserve at the time of muscle contraction, when the blood vessels are compressed (the oxygen supply drops sharply).
In origin and structure, muscle tissue differs significantly from each other, but they are united by the ability to contract, which ensures the motor function of organs and the body as a whole. The muscle elements are elongated and connected either with other muscle elements or with supporting structures.
There are smooth, striated muscle tissue and cardiac muscle tissue.
Smooth muscle tissue.
This tissue is formed from mesenchyme. The structural unit of this tissue is the smooth muscle cell. It has an elongated spindle-shaped shape and is covered with a cell membrane. These cells adhere tightly to each other, forming layers and groups separated from each other by loose, unformed connective tissue.
The cell nucleus has an elongated shape and is located in the center. Myofibrils are located in the cytoplasm; they run along the periphery of the cell along its axis. They consist of thin threads and are the contractile element of the muscle.
The cells are located in the walls of blood vessels and most internal hollow organs (stomach, intestines, uterus, bladder). The activity of smooth muscles is regulated by the autonomic nervous system. Muscle contractions are not subject to human will and therefore smooth muscle tissue is called involuntary muscles.
Striated muscle tissue.
This tissue is formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is striated muscle fiber. This cylindrical body is a symplast. It is covered with a membrane - sarcolemma, and the cytoplasm is called sarcoplasm, which contains numerous nuclei and myofibrils. Myofibrils form a bundle of continuous fibers running from one end of the fiber to the other parallel to its axis. Each myofibril consists of discs that have a different chemical composition and appear dark and light under a microscope. The homogeneous disks of all myofibrils coincide, and therefore the muscle fiber appears striated. Myofibrils are the contractile apparatus of muscle fiber.
All skeletal muscles are built from striated muscle tissue. Musculature is voluntary, because its contraction may occur under the influence of neurons in the motor zone of the cerebral cortex.
Muscle tissue of the heart.
The myocardium - the middle layer of the heart - is built from striated muscle cells (cardiomyocytes). There are two types of cells: typical contractile cells and atypical cardiac myocytes that make up the conduction system of the heart.
Typical muscle cells perform a contractile function; they are rectangular in shape, there are 1-2 nuclei in the center, myofibrils are located along the periphery. There are intercalary discs between adjacent myocytes. With their help, myocytes are collected into muscle fibers, separated from each other by fine fibrous connective tissue. Connective fibers pass between adjacent muscle fibers, which ensure contraction of the myocardium as a whole.
The conduction system of the heart is formed by muscle fibers consisting of atypical muscle cells. They are larger than contractile ones, richer in sarcoplasm, but poorer in myofibrils, which often intersect. The nuclei are larger and are not always in the center. The fibers of the conduction system are surrounded by a dense plexus of nerve fibers.
Muscle tissues are tissues that differ both in their structure and origin. However, what they have in common is that they are capable of pronounced contractions. Muscle tissue is based on elongated cells, which receive impulses from the central nervous system, and the reaction to this is their contraction. Thanks to muscle tissue, the body and internal organs and systems (heart, lungs, intestines, etc.) of which it consists are able to move, changing their position in space. Cells of other tissues also have the ability to change shape and contract. However, in muscle tissue this function is basic.
Features of the structure of muscle tissue
The most important features of the main components of muscle tissue are their elongated shape, the presence of elongated and appropriately arranged myofilaments and myofibrils (which ensure muscle contractility), as well as the presence of mitochondria, lipids, glycogen and myoglobin. Inside the contractile organelles, myosin and actin interact (with the simultaneous participation of Ca ions in the reaction), resulting in muscle contraction. The source of energy for contractile processes is mitochondria, lipids and glycogen. Oxygen is bound and stored through a protein called myoglobin, which occurs when muscle contraction and simultaneous compression of blood vessels.
Classification of muscle fibers
Taking into account the nature of the contraction, tonic and phasic muscle fibers are distinguished. In particular, the first type of fibers is designed to provide tone (or static muscle tension), which is especially important for maintaining a particular body position relative to spatial coordinates. Phasic fibers are designed to ensure the ability to perform rapid contractions, but are not able to maintain the shortening of the muscle fiber at a certain level for a long time. Taking into account the biochemical characteristics, as well as color, white and red fibers are distinguished. The color of muscle tissue is determined by the concentration of myoglobin in it (the so-called degree of vascularization). One of the features of red muscle fiber is the presence in its composition of chains of mitochondria surrounded by myofibrils. Slightly lower number of mitochondria in white muscle fiber. They are usually evenly distributed in the sarcoplasm.
Depending on the characteristics of oxidative metabolism, muscle fibers can be glycolytic, oxidative and intermediate. Fibers are distinguished based on information about the degree of activity of the SDH enzyme, which is a marker for the so-called Krebs cycle and mitochondria. The intensity of energy metabolism can be determined by the degree of activity of this enzyme. Glycolytic fibers (or A-type fibers) are characterized by low activity of the above enzyme, while oxidative (or C-type fibers), on the contrary, have increased succinate dehydrogenase activity. B-type fibers are fibers that occupy intermediate position. The process of transition from type A fibers to type C fibers is a transition to oxygen-dependent metabolism from anaerobic glycolysis. An example would be a situation where sports training in combination with nutrition, are aimed at the rapid development and formation of glycolytic muscle fibers, which contain: large quantities glycogen, and energy production is carried out anaerobically. This type of training is usually reserved for bodybuilders or sprinters. At the same time, for those sports that require endurance, it is necessary to develop oxidative muscle fibers, which have more blood vessels and mitochondria that provide aerobic glycolysis.
Muscle tissue can be of several types, if we consider their sources of development. That is, depending on the type of embryonic rudiments, they can be mesenchymal (desmal rudiment), epidermal (prechordal plate or cutaneous ectoderm), coelomic (myoepicardial plate of the so-called visceral section of the splanchnotome), neural (neural tube) or somatic/myotome.
Types of muscle tissue
There are smooth and striated (skeletal and cardiac) muscle tissue. The smooth tissue contains predominantly myocytes (mononuclear cells) having the shape of a spindle. The cytoplasm of such myocytes is homogeneous and does not have transverse stripes. Smooth muscle tissue has special properties. First of all, it relaxes and contracts extremely slowly. In addition, she is uncontrollable by humans and usually all her reactions are involuntary. The walls of lymphatic and circulatory systems, urinary tract, stomach and intestines. Striated skeletal tissue contains very long multinucleated (one hundred or more nuclei) myocytes. If you examine the cytoplasm under a microscope, it will look like alternating light and dark stripes. Striated skeletal muscle tissue is characterized by a fairly high rate of contraction and relaxation. The activity of this type of tissue can be controlled by a person, and it itself is present in the composition skeletal muscles, in the upper esophagus, in the tongue, as well as in the muscles responsible for the movements of the eyeball.
The composition of striated cardiac muscle tissue includes cardiomyocytes with one or two nuclei, as well as cytoplasm, striated along the periphery of the cytolemma with transverse stripes. Cardiomyocytes are quite highly branched and form intercalated discs with cytoplasm integrated into them at the junctions. Cells also contact through cytolemmas, resulting in the formation of anastomoses. Striated cardiac muscle tissue is found in the myocardium. The most important feature of this tissue is the ability, in the case of cellular excitation, to rhythmic contractions and subsequent relaxations. Striated cardiac muscle tissue belongs to involuntary tissues (so-called atypical cardiomycytes). There is also a third type of cardiomycytes - these are secretory cardiomycytes, which lack fibrils.
The most important functions of muscle tissue
The main functional features of muscle tissue include its abilities such as conductivity, excitability, and contractility. Muscle tissue provides the functions of heat exchange, movement and protection. In addition to the above, one more functional feature of muscle tissue can be identified - facial (or, as it is also called, social). In particular, a person’s facial muscles control his facial expressions, thereby transmitting a certain information message to other people around him.
Blood supply to muscle tissue
Blood enters muscle tissue due to its work. This provides the muscle with the necessary amount of oxygen. If a muscle is at rest, then it, as a rule, requires much less oxygen (usually this figure is five hundred times less than the figure reflecting the oxygen requirement of an actively working muscle). Thus, during active muscle contractions, the volume of blood entering the muscle increases many times over. This is approximately 300 to 500 capillaries per cubic millimeter, or approximately twenty times more than the amount of blood required by a muscle at rest.
Muscle tissue (textus muscularis) is a type of tissue that carries out motor processes in the human body (movement of blood and lymph through vessels, movement of food during digestion, movement of the body in space, maintaining posture, changing the volume of organs, etc.) with the help of special contractile muscles. structures - myofibrils.
Functional Features muscle tissue: excitability, conductivity and contractility.
There are:
1. smooth
2. striated
1) skeletal
2) cardiac tissue
| Smooth | Skeletal p-p | Heart p-p | |
| Tissue structure | Cells (myocytes) are mononuclear up to 0.5 mm long with pointed ends, myofibrils are filaments d = 1-2 µm, located parallel to each other Myocytes ® bundles ® muscle layers ® muscle layers | Multinucleate cells are cylindrical in shape, up to 10 cm long, striated with transverse stripes. Long up to 10-12 cm, d up to 100 µm multi-nuclear muscle fibers. Nuclei on the periphery. Myofibrils in the form of bundles in the center of the fiber (from sarcomeres) | Cardiomyocytes are connected to each other using intercalary discs. It has a small number of nuclei located in the center of the fiber. Has good blood supply |
| Location | Walls internal organs, blood and lymphatic vessels, skin muscles | Skeletal muscles of the musculoskeletal system and some internal organs: tongue, pharynx, initial part of the esophagus | Heart muscle |
| Abbreviation type | Tonic Involuntarily, slowly, do not get tired for a long time, high ability to regenerate | Tetanic voluntary | Tonic Involuntary, less tired |
| Functions | Involuntary contractions of the walls of internal organs. Raising hair on the skin. Controlled by the ANS | Voluntary movements, facial expressions, speech Controlled by somatics. NS | Involuntary contractions (automatism) Controlled by the somatic system. NS |
The section of myofibril located between adjacent light stripes is the sarcomere.
The contractile proteins of striated muscle fiber (myosin, actin, tropomyosin, troponin) are contained in myofibrils in the form of 2 types of protein filaments: thin - actin, thick - myosin. The sliding of actin filaments relative to myosin filaments in the longitudinal direction during nervous stimulation of the muscle fiber leads to shortening and thickening of the sarcomeres - contraction of striated muscle fibers.
The sarcoplasm of muscle fibers contains a respiratory pigment - myoglobin, which determines the red color of muscles. Depending on the myoglobin content, red, white and intermediate muscle fibers are distinguished. Red ones are capable of longer contractions, white ones provide rapid motor function. The composition of almost all human muscles is mixed.
Tetanus is a strong, prolonged muscle contraction.
Tone – irregular muscle contractions, maintaining the muscle in a state of constant partial contraction.
Muscle tissue- this is a group of animal and human tissues, the main function of which is contraction, which, in turn, causes the movement of the body or its parts in space. This function corresponds to the structure of the main elements of muscle tissue, which have an elongated shape and longitudinal orientation of myofibrils, which include contractile proteins - actin and myosin. Like epithelial tissue, muscle tissue is a composite tissue group, since its main components develop from various embryonic rudiments.
Depending on the structure of its contractile apparatus, muscle tissue is divided into striated (skeletal) and smooth fabric, consisting of various histogenetic types that differ in structure. The following scheme gives a general idea of the classification of muscle tissue:
Striated muscle tissue
The source of its development are myotome cells formed from the dorsal mesoderm. Striated muscle tissue consists of elongated formations - muscle fibers, which look like cylinders with pointed ends. The fibers reach 80 microns in diameter and 12 cm in length. In the center of the muscle fibers there are multinucleated formations (symplasts), to which cells - myosatelites - are adjacent on the outside. The fibers are limited by the sarcolemma formed by the basement membrane and the plasmolemma simplast.Myosatelliotocytes are located under the basement membrane of the muscle fiber so that their plasmalemma touches the symplast plasmalemma. These cells represent the cambial reserve of skeletal muscle tissue, due to which the regeneration of its fibers is carried out.
In addition to the plasmalemma, myosimplasts include cytoplasm (sarcoplasm) and numerous nuclei located along the periphery. In the perinuclear region there is a poorly developed granular endoplasmic reticulum and Golgi complex. A muscle fiber with its sheath, nerve endings, blood and lymphatic capillaries is called a muscle unit (Mion).
A characteristic feature of skeletal muscle fibers is transverse striation, caused by the alternation of double-folding (anisotropic) A-disks and single-folding (isotropic) I-discs. The discs contain myofibrils, which form the contractile apparatus of the fibers. Myofibrils are composed of ordered filaments of the contractile proteins actin and myosin. These threads are secured by transversely located telophragms and mesophragms,
which are made up of other proteins. The segment of myofibril between adjacent telophragms is called a sarcomere. It is a morphofunctional unit of the fiber contractile apparatus. In its middle part there is a mesophragm (M-line on longitudinal sections). Thick (about 11 nm in diameter) myosin filaments extend from the mesophragm towards the telophragm, and thin (about 5 nm) actin filaments extend from the telophragm towards them.
Myosin filaments are the main component of dark disks, and actin filaments are the main component of light disks. Within the dark disk, actin and myosin filaments are located in parallel. The middle segment of the A-disc has only myosin filaments and is called the H-stripe (light zone).
For the convenience of considering the structure of the contractile apparatus of the muscle fiber, it is necessary to remember the so-called sarcomere formula, which reflects the sequential placement of its main components and looks like this: telophragm + 1/2 disk 1 + 1/2 disk A + stripe M + + 1/2 disk A + 1/2 disk I + telophragm.
The cytolemma of the symplastic part of the muscle fiber at the level of the telophragm is formed by deep protrusions - transverse or T-tubules (from the Latin Transversus - transverse). Parallel to these tubes are located expanded sections of the tubules of the agranular endoplasmic reticulum (terminal cisterns), which accompany them on both sides. Together with T-tubules they form triads.
In the terminal cisterns of the agranular endoplasmic reticulum, calcium ions accumulate in the relaxed state of the muscle fiber. Under the influence of the propagation of the action potential along the cytolemma of the fiber and T-tubules, calcium ions leave the terminal cisterns entering the myofibrils and, interacting with special reticular proteins - troponin and tropomyosin, begin to actively contract. In this case, the actin and myosin filaments, interacting with each other, move towards each other. Actin filaments come between the myosin filaments and approach the M-line, and therefore, when the muscle fiber contracts, the width of the H-strip and H-disk decreases. The width of the A-disc remains unchanged. (The structure of different functional types of muscle fibers is discussed in histology textbooks).
Smooth muscle tissue
Smooth muscle tissue of mesenchymal origin forms the muscular membranes of internal organs. Smooth myocytes are often spindle-shaped, their length ranges from 15 to 500 μm, and their thickness ranges from 5 to 8 MNM. Cell nuclei elongate in length. As cells shrink, they can take on a gimlet-like appearance. The organelles in these cells are poorly developed. The cytolemma, stretching, forms numerous pinocytotic vesicles, which transmit irritation into the cell, which, in turn, causes its contraction.The contractile apparatus of smooth myocytes (myofibrils) consists of thin myofilaments formed by actin and thick ones formed by myosin. Myocytes are bounded by a basement membrane as well as collagen (reticular) elastic fibers. These structural components of smooth muscle tissue are formed by smooth myocytes. Efferent (motor) innervation of smooth myocytes is carried out by postganglionic fibers of the autonomic nervous system. Neighboring myocytes, through holes in the basement membrane, form slit-like communications (nexus) with each other, which ensure functional cell interactions.
Smooth muscle tissue of epidermal origin is formed by myoepithelial cells, which are formed from the skin mesoderm. They have a star-shaped (bucket-shaped) shape and are part of the sweat, mammary and salivary glands. Located between the epithelial cells and the basement membrane of the secretory sections of the glands and small excretory ducts, they, by contracting, contribute to the excretion of secretions.
Smooth muscle tissue of neural origin is formed during the embryonic development of the eyeball from the cells of the wall of the optic cup. It is part of the muscles of the iris of the eyeball, which dilate or constrict the pupil. textus muscularis) are tissues that are different in structure and origin, but similar in their ability to undergo pronounced contractions. They consist of elongated cells that receive irritation from the nervous system and respond to it with contraction. They ensure movement in space of the body as a whole, its movement of organs within the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the ability to change shape, but in muscle tissue this ability becomes the main function.
The main morphological characteristics of muscle tissue elements: elongated shape, the presence of longitudinally located myofibrils and myofilaments - special organelles that ensure contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.
Special contractile organelles - myofilaments or myofibrils - provide contraction, which occurs when two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide these processes with energy. The supply of energy sources is formed by glycogen and lipids. Myoglobin is a protein that ensures the binding of oxygen and the creation of its reserve at the time of muscle contraction, when the blood vessels are compressed (the oxygen supply drops sharply).
Properties of muscle tissue
- Contractility
Types of muscle tissue
Smooth muscle tissue
Consists of mononuclear cells - spindle-shaped myocytes with a length of 20-500 microns. Their cytoplasm in a light microscope looks uniform, without transverse striations. This muscle tissue has special properties: it contracts and relaxes slowly, is automatic, and is involuntary (that is, its activity is not controlled by the will of a person). It is part of the walls of internal organs: blood and lymphatic vessels, urinary tract, digestive tract (contraction of the walls of the stomach and intestines).
Striated skeletal muscle tissue
Consists of myocytes that are long (up to several centimeters) and have a diameter of 50-100 microns; these cells are multinucleated, containing up to 100 or more nuclei; in a light microscope, the cytoplasm looks like alternating dark and light stripes. The properties of this muscle tissue are high speed contractions, relaxations and voluntariness (that is, its activities are controlled by the will of a person). This muscle tissue is part of the skeletal muscles, as well as the wall of the pharynx, the upper part of the esophagus, it forms the tongue, oculomotor muscles. Fibers are 10 to 12 cm long.
Striated cardiac muscle tissue
Consists of 1 or 2 nuclear cardiomyocytes with transverse striations of the cytoplasm (along the periphery of the cytolemma). Cardiomyocytes are branched and form connections with each other - intercalary discs, in which their cytoplasm is combined. There is also another intercellular contact - anostamoses (invagination of the cytolemma of one cell into the cytolemma of another) This type of muscle tissue forms the myocardium of the heart. Develops from the myoepicardial plate (visceral layer of the splanchnotome of the fetal neck). A special property of this tissue is automaticity - the ability to rhythmically contract and relax under the influence of excitation that occurs in the cells themselves (typical cardiomyocytes). This tissue is involuntary (atypical cardiomyocytes). There is a 3rd type of cardiomyocytes - secretory cardiomyocytes (they do not have fibrils). They synthesize the hormone troponin, which lowers blood pressure and dilates the walls of blood vessels.
Functions of muscle tissue
Motor. Protective. Heat exchange. You can also highlight one more function - facial (social). Facial muscles, controlling facial expressions, transmit information to others.
Notes
| Biological tissues | |
|---|---|
| Cell | |
| Animals | Epithelial Connective (bone, cartilage, fat, blood and lymph) Nervous Muscular Pokrovnaya |
| Plants | Educational (meristem) Integumentary Mechanical Adsorption Assimilation Conducting Secretory Aerenchyma |
| See also | Histology Intercellular substance |
| Organ | |
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