Muscle tissues (Latin textus muscularis - “muscle tissue”) are tissues that are different in structure and origin, but similar in ability to pronounced contractions. Consist of elongated cells that receive irritation from nervous system and answer it with an abbreviation. They provide movement in the space of the body as a whole, its movement of organs inside the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the property of changing shape, but in muscle tissues this ability becomes the main function.
The main morphological features of muscle tissue elements are: an elongated shape, the presence of longitudinally arranged myofibrils and myofilaments - special organelles that provide contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.
Special contractile organelles - myofilaments or myofibrils - provide contraction that occurs when the two main fibrillar proteins interact in them - actin and myosin - with the obligatory participation of calcium ions. Mitochondria provide energy for these processes. The supply of energy sources is formed by glycogen and lipids. Myoglobin is a protein that binds oxygen and creates its reserve at the time of muscle contraction, when blood vessels are compressed (oxygen supply drops sharply).
By origin and structure, muscle tissues differ significantly from each other, but they are united by the ability to contract, which ensures the motor function of organs and the body as a whole. The muscle elements are elongated and connected either with other muscle elements or with supporting formations.
Distinguish smooth, striated muscle tissue and muscle tissue of the heart.
Smooth muscle tissue.
This tissue is formed from mesenchyme. The structural unit of this tissue is a smooth muscle cell. It has an elongated fusiform shape and is covered with a cell membrane. These cells are tightly adjacent to each other, forming layers and groups, separated from each other by a loose, unformed connective tissue.
The cell nucleus has an elongated shape and is located in the center. Myofibrils are located in the cytoplasm, they go along the periphery of the cell along its axis. They consist of thin threads and are the contractile element of the muscle.
Cells are located in the walls of blood vessels and most of the internal hollow organs (stomach, intestines, uterus, bladder). Smooth muscle activity is regulated by the autonomic nervous system. Muscle contractions do not obey the will of a person and therefore smooth muscle tissue is called involuntary muscles.
Striated muscle tissue.
This tissue was formed from myotomes, derivatives of the mesoderm. The structural unit of this tissue is the striated muscle fiber. This cylindrical body is a symplast. It is covered with a membrane - sarcolemma, and the cytoplasm is called - sarcoplasm, in which there are numerous nuclei and myofibrils. Myofibrils form a bundle of continuous fibers running from one end of the fiber to the other parallel to its axis. Each myofibril consists of discs that have a different chemical composition and appear dark and light under a microscope. Homogeneous discs of all myofibrils coincide, and therefore the muscle fiber appears to be striated. Myofibrils are the contractile apparatus of the muscle fiber.
All skeletal muscles are built from striated muscle tissue. Musculature is arbitrary, because. its contraction may occur under the influence of neurons in the motor cortex of the cerebral hemispheres.
Muscular tissue of the heart.
Myocardium - the middle layer of the heart - is built from striated muscle cells (cardiomyocytes). There are two types of cells: typical contractile cells and atypical cardiac myocytes, which make up the conduction system of the heart.
Typical muscle cells perform a contractile function; they are rectangular in shape, there are 1-2 nuclei in the center, myofibrils are located along the periphery. There are intercalated discs between adjacent myocytes. With their help, myocytes are collected into muscle fibers, separated from each other by fine-fibrous connective tissue. Connecting fibers pass between adjacent muscle fibers, which provide contraction of the myocardium as a whole.
The conduction system of the heart is formed by muscle fibers, consisting of atypical muscle cells. They are larger than contractile ones, richer in sarcoplasm, but poorer in myofibrils, which often intersect. The nuclei are larger and not always in the center. The fibers of the conducting system are surrounded by a dense plexus of nerve fibers.
Muscle tissues are tissues that differ both in their structure and origin. However, at the same time they are united by the fact that they are capable of pronounced contractions. At the heart of muscle tissues are oblong cells, to which impulses are received from the central nervous system, and their contraction becomes a reaction to this. 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 the main one.
Features of the structure of muscle tissue
The most important features of the main components of muscle tissue are their oblong shape, the presence of elongated and appropriately located myofilaments and myofibrils (which provide 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 are mitochondria, lipids and glycogen. Oxygen is bound and stored through a protein such as myoglobin, which occurs at the time of muscle contraction and simultaneous squeezing of blood vessels.
Classification of muscle fibers
Given 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. Phase fibers are designed to guarantee the ability to perform fast contractions, but at the same time they are not able to keep the shortening of the muscle fiber at a certain level for a long time. Taking into account biochemical characteristics, as well as color, white and red fibers are distinguished. The color of muscle tissue determines the concentration of myoglobin in it (the so-called degree of vascularization). One of the features of the red muscle fiber is the presence in its composition of mitochondrial chains surrounded by myofibrils. Slightly fewer 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 a low activity of the above enzyme, and oxidative (or C-type fibers), on the contrary, have an increased activity of succinate dehydrogenase. B-type fibers are fibers that occupy an intermediate position. The process of transition from type A fibers to type C fibers is the transition to an oxygen-dependent metabolism from anaerobic glycolysis. An example is the situation when sports training in combination with nutrition, they are aimed at the rapid development and formation of glycolytic muscle fibers, which include 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, in which there are more blood vessels and mitochondria that provide aerobic glycolysis.
Muscle tissues can be of several types, if we consider their sources of development. That is, depending on the type of embryonic buds, they can be mesenchymal (desmal bud), epidermal (prechordal plate or skin ectoderm), coelomic (myoepicardial plate of the so-called visceral splanchnotome), neural (neural tube) or somatic / myotomic.
Types of muscle tissue
There is smooth and striated (skeletal and cardiac) muscle tissue. The composition of the smooth tissue contains mainly myocytes (single-nuclear cells), which have the shape of a spindle. The cytoplasm of such myocytes is homogeneous and does not have transverse bands. Smooth muscle tissue has special properties. First of all, it relaxes and contracts extremely slowly. In addition, she is uncontrollable by a person and usually all her reactions are involuntary. The walls of the vessels of the lymphatic and circulatory systems, urinary tract, stomach and intestines. The striated skeletal tissue is composed of very long multinucleated (from a 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 sufficiently high rate of contraction and relaxation. The activity of a tissue of this type can be controlled by a person, and it itself is present in the composition skeletal muscle, in the upper esophagus, in the tongue, as well as in the muscles responsible for movement 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 strongly branched and form intercalated discs with cytoplasm united in them at the junctions. Cells also contact through cytolemmas, resulting in the formation of anastomoses. The 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 relaxation. Striated cardiac muscle tissue refers to involuntary tissues (the so-called atypical cardiomycytes). There is also a third type of cardiomycytes - these are secretory cardiomyocytes, in which there are no fibrils.
The most important functions of muscle tissue
The main functional features of muscle tissue include such abilities as conductivity, excitability, and contractility. Muscle tissue provides the functions of heat transfer, movement and protection. In addition to the above, one more functional feature of muscle tissues can be distinguished - mimic (or, as it is also called, social). In particular, the facial muscles of a person control his facial expressions, thereby broadcasting a certain information message to other people around him.
Blood supply to muscle tissue
Blood enters the muscle tissue due to its work. Thus, the muscle is provided with the necessary amount of oxygen. When a muscle is at rest, it usually requires much less oxygen (usually this figure is five hundred times less than the figure that reflects the oxygen demand of an actively working muscle). Thus, in the process of active muscle contractions, the volume of blood entering the muscle increases many times over. This is about 300 to 500 capillaries per cubic millimeter, or about twenty times more than the amount of blood needed by a muscle at rest.
Muscular tissue (textus muscularis) is a type of tissue that carries out motor processes in the human body (the movement of blood and lymph through the vessels, the movement of food during digestion, the movement of the body in space, maintaining posture, changing the volume of organs, etc.) with the help of special contractile structures - myofibrils.
Functional features of muscle tissue: excitability, conductivity and contractility.
Distinguish:
1. smooth
2. striated
1) skeletal
2) heart tissue
| Smooth | Skeletal p-p | Heart p-p | |
| Fabric structure | Cells (myocytes) are uninuclear up to 0.5 mm long with pointed ends, myofibrils are filaments d = 1-2 microns, located parallel to each other Myocytes ® bundles ® muscle layers ® muscle layers | Multinucleated cylindrical cells up to 10 cm long, striated with transverse stripes. Long up to 10-12 cm, d up to 100 microns, multi-nuclear muscle fibers. Kernels on the periphery. Myofibrils in the form of bundles in the center of the fiber (from sarcomeres) | Cardiomyocytes are interconnected by intercalated discs. It has a small number of nuclei located in the center of the fiber. Has a good blood supply |
| Location | Walls internal organs, blood and lymph vessels, skin muscles | Skeletal muscles of the musculoskeletal system and some internal organs: tongue, pharynx, initial part of the esophagus | cardiac muscle |
| Reduction type | Tonic Involuntarily, slowly, do not get tired for a long time, high ability to regenerate | Tetanic arbitrarily | Tonic Involuntary, less tired |
| Functions | Involuntary contractions of the walls of internal organs. Raising hair on the skin. Controlled by VNS | Arbitrary movements, facial expressions, speech Controlled by somat. NS | Involuntary contractions (automatism) Controlled by somat. NS |
The area of the myofibril located between adjacent light stripes is the sarcomere.
The contractile proteins of the striated muscle fiber (myosin, actin, tropomyosin, troponin) are contained in myofibrils in the form of protein filaments of 2 types: thin - actin, thick - myosin. The sliding of actin filaments relative to myosin filaments in the longitudinal direction during nervous excitation of the muscle fiber leads to shortening and thickening of the sarcomeres - a contraction of striated muscle fibers.
The sarcoplasm of muscle fibers contains a respiratory pigment - myoglobin, which causes the red color of the muscles. Depending on the content of myoglobin, red, white and intermediate muscle fibers are distinguished. Reds are capable of a longer contraction, whites provide a fast motor function. The composition of almost all human muscles is mixed.
Tetanus is a strong prolonged contraction of a muscle.
tone - irregular muscle contractions that maintain the muscle in a state of constant partial contraction.
Muscle- this is a group of tissues of animals and humans, the main function of which is contraction, which, in turn, causes the movement of the organism 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 prefabricated tissue group, since its main components develop from various embryonic buds.
Depending on the structure of its contractile apparatus, muscle tissue is divided into striated (skeletal) and smooth fabric, consisting of various histogenetic types differing in structure. The following scheme gives a general idea of the classification of muscle tissue:
striated muscle tissue
The source of its development is the cells of myotomes, which are formed from the dorsal mesoderm. Striated muscle tissue consists of elongated formations - muscle fibers, which look like cylinders with pointed ends. The fibers reach 80 microns in diameter and 12 cm in length. In the center of the muscle fibers there are multinuclear formations (symplasts), to which cells, myosatelites, adjoin from the outside. The fibers are limited by the sarcolemma formed by the basement membrane and the plasmolemma symplast.Myosatelliotocytes are located under the basement membrane of the muscle fiber so that their plasmolemma touches the symplast plasmolemma. These cells represent the cambial reserve of skeletal muscle tissue, due to which the regeneration of its fibers is carried out.
In addition to the plasmolemma, myosymplasts include the cytoplasm (sarcoplasm) and numerous nuclei located along the periphery. In the perinuclear region, there is a poorly developed granular endoplasmic reticulum and the Golgi complex. A muscle fiber with its sheath, nerve endings, blood and lymphatic capillaries is called muscle unit(Mion).
A characteristic feature of skeletal muscle fibers is transverse banding, due to the alternation of double-breaking (anisotropic) A-disks and single-breaking (isotropic) I-disks. The composition of the disks includes myofibrils, which form the contractile apparatus of the fibers. Myofibrils are composed of ordered filaments of the contractile proteins actin and myosin. These threads are fixed by transversely located telophragms and mesophragms,
that are made up of other proteins. The segment of myofibril between adjacent telophragms is called a sarcomere. It is a morphofunctional unit of the contractile apparatus of the fiber. In its middle part there is a mesophragm (M-line on longitudinal sections). Thick (about 11 nm in diameter) myosin filaments extend from the mesophragm towards the telophragm, and thin (about 5 nm) actin filaments extend from the telophragm towards them.
Myosin filaments are the main component of dark discs, and actin filaments are the main component of light discs. In the dark disc, actin and myosin filaments are arranged in parallel. The middle section of the A-disk has only myosin filaments and is called the H-band (light zone).
For the convenience of considering the structure of the contractile apparatus of the muscle fiber, it is necessary to remember the so-called sarcomere formula, which reflects the sequential placement of its main components and looks like this: telophragm + 1/2 disk 1 + 1/2 disk A + strip 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 telophragms forms deep protrusions - transverse or T-tubules (from Latin Transversus - transverse). Parallel to these tubules, there are dilated portions of the tubules of the agranular endoplasmic reticulum (terminal cisterns), which accompany them on both sides. Together with T-tubules, they form triads.
Calcium ions accumulate in the terminal cisterns of the agranular endoplasmic reticulum in a relaxed state of the muscle fiber. Under the influence of distribution along the cytolemma of the fiber and T-tubules of the action potential, calcium ions leave the terminal cisterns entering the myofibrils and, interacting with special reticular proteins - troponin and tropomyosin, begin to actively contract. At the same time, the actin and myosin filaments, interacting with each other, move towards each other. Actin filaments enter between myosin filaments, approach the M-line, and therefore, when the muscle fiber contracts, the width of the H-band and H-disk decreases. The width of the A-disk remains unchanged. (The structure of different functional types of muscle fibers is discussed in textbooks on histology).
smooth muscle tissue
Smooth muscle tissue of mesenchymal origin forms the muscular membranes of internal organs. Smooth myocytes often have a spindle shape, their length is from 15 to 500 microns, and their thickness is from 5 to 8 MNM. Cell nuclei are elongated. With the reduction of cells, they can gain the appearance of a gimlet. The organelles in these cells are poorly developed. The cytolemma, stretching out, forms numerous pinocytic vesicles, which transmit irritation inside the cell, which, in turn, causes its contraction.The contractile apparatus of smooth myocytes (myofibrils) consists of thin myofilaments, formed by actin, and thick, formed by myosin. Myocytes are limited by a basement membrane, as well as collagen (reticular) elastic fibers. These structural components of smooth muscle tissue are formed by smooth myocytes. Efferent (motor) innervation of smooth myocytes is carried out by postganglionic fibers of the autonomic nervous system. Neighboring myocytes through holes in the basement membrane form slit-like communications (nexus) with each other, which provide functional cell interactions.
Smooth muscle tissue of epidermal origin is formed by myoepithelial cells, which are formed from the skin mesoderm. They have a stellate (bucket) shape and are part of the sweat, mammary and salivary glands. Located between the epithelial cells and the basement membrane of the secretory sections of the glands and small excretory ducts, they, by contracting, contribute to the excretion of the secret.
Smooth muscle tissue of neural origin is formed during the embryonic development of the eyeball from the cells of the wall of the eyecup. It is part of the muscles of the iris of the eyeball, which dilate or constrict the pupil. textus muscularis) are called tissues that are different in structure and origin, but similar in ability to pronounced contractions. They consist of elongated cells that receive irritation from the nervous system and respond to it with a contraction. They provide movement in the space of the body as a whole, its movement of organs inside the body (heart, tongue, intestines, etc.) and consist of muscle fibers. Cells of many tissues have the property of changing shape, but in muscle tissues this ability becomes the main function.
The main morphological features of muscle tissue elements are: an elongated shape, the presence of longitudinally arranged myofibrils and myofilaments - special organelles that provide contractility, the location of mitochondria next to the contractile elements, the presence of inclusions of glycogen, lipids and myoglobin.
Special contractile organelles - myofilaments or myofibrils - provide contraction that occurs when the 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 binds oxygen and creates its reserve at the time of muscle contraction, when blood vessels are compressed (oxygen supply drops sharply).
properties of muscle tissue
- Contractility
Types of muscle tissue
smooth muscle tissue
It consists of mononuclear cells - spindle-shaped myocytes 20-500 microns long. Their cytoplasm in a light microscope looks uniform, without transverse striation. This muscle tissue has special properties: it slowly contracts and relaxes, it has automaticity, it 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 (reduction of the walls of the stomach and intestines).
striated skeletal muscle tissue
Consists of myocytes, having a large length (up to several centimeters) and a diameter of 50-100 microns; these cells are multinucleated, containing up to 100 or more nuclei; Under a light microscope, the cytoplasm looks like alternating dark and light stripes. The properties of this muscle tissue are high speed contraction, relaxation and arbitrariness (that is, its activity is controlled by the will of a person). This muscle tissue is part of the skeletal muscles, as well as the walls of the pharynx, the upper part of the esophagus, it forms the tongue, oculomotor muscles. The fibers are 10 to 12 cm long.
striated cardiac muscle tissue
Consists of 1 or 2 nuclear cardiomyocytes with transverse striation of the cytoplasm (along the periphery of the cytolemma). Cardiomyocytes are branched and form connections between themselves - intercalary discs in which their cytoplasm is combined. There is also another intercellular contact - anostamosis (an invagination of the cytolemma of one cell into the cytolemma of another). This type of muscle tissue forms the myocardium of the heart. It develops from the myoepicardial plate (the visceral sheet of the splanchnotome of the neck of the embryo). 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 expands the walls of blood vessels.
Functions of muscle tissue
Motor. Protective. Heat exchange. You can also highlight another function - mimic (social). The muscles of the face, controlling facial expressions, transmit information to others.
Notes
| biological tissues | |
|---|---|
| Cell | |
| Animals | Epithelial Connective (bone, cartilage, fat, blood and lymph) Nervous muscular Integumentary |
| Plants | Educational (meristem) Integumentary Mechanical Adsorption Assimilation Conductive Secretory Aerenchyma |
| see also | Histology Intercellular substance |
| Organ | |
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