Muscle tissue is a special tissue of the human body that performs a motor function. Its cells (myocytes) have the ability to contract, thereby ensuring the movement of the human body. Muscle tissue in the embryo begins to form around the 17th day after fertilization, so the baby is born with all the muscles. The human musculature consists of muscle tissues, which make up about 40% of the total mass of the human body.
Kinds
According to their structure, all muscle tissues are divided into striated and smooth. In addition, there is an intermediate option - this is a cardiac striated tissue. It consists of cells interconnected in a network through large branches that make up the likeness of muscle fibers.
striated muscles
Most of the human muscles are striated muscles - all skeletal muscles belong to this group. They consist of oblong muscle fibers with a diameter of 0.01-0.06 mm. The fibers have different lengths (the longest - 10 cm). Connective tissue combines them into larger bundles. The muscles of the connective tissue sheath (fascia) form sheaths for the muscles that protect these bundles from external influences. From both ends, the muscles pass either into short tendons attached to nearby bones, or into long cylindrical ones, heading to further located bones. Each muscle fiber consists of tiny fibers - myofibrils, separate parts of myofibrils - filamentous protein molecules of actin and myosin - always occupy the same position in relation to each other, and when examining myofibrils through a microscope, transverse stripes are visible, which is why the muscles are called striated.
The striated muscles can be affected by an effort of will, with the exception of the heart (although its fibers are striated, their activity does not depend on the will of a person). The structure of the cardiac skeletal muscles varies greatly.
Smooth muscles
They are present in all hollow human organs - in the stomach, intestines, bladder, blood vessels, etc. Muscle fibers of smooth muscles consist of spindle-shaped cells. Most often, the fibers are arranged in thin layers.
Everyone knows the feeling that appears after a lot of physical exertion, when any movement is difficult - this is painful muscle fatigue. Its cause is the accumulation of metabolic products in the muscles, primarily lactic acid. This sensation also occurs due to the rupture of muscle fibers. An effective means of prevention is a hot bath after exercise or special exercises to stretch the muscles.
Functions
Muscles are active organs of the musculoskeletal system, which, by contracting, set the bones and parts of the body in motion. The contraction of the striated muscles is caused by motor (motor) nerves, the function of which a person can influence by willpower. Therefore, striated muscles are also called "dependent on the will of man." Meanwhile, smooth muscle contraction is caused by impulses emanating from the autonomic (autonomic) nervous system, and a person cannot control their contraction.
Striated muscles, which can be strengthened through training, provide regulated human body movements. The name of these muscles may reflect the function they perform: abductors (abductors), adductors (adductors), rotators (rotators), flexors (flexors), extensors (extensors). The task of smooth muscles is to contract, push out its contents from a hollow organ, change the lumen (for example, blood vessels).
Muscle tissues (Latin textus muscularis - “muscle tissue”) are 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 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, in the center there are 1-2 nuclei, 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.
The muscles of the human body are formed mainly by muscle tissue, consisting of muscle cells. Distinguish between smooth and striated muscle tissue. (Under the microscope, striated muscle cells have a transverse striation associated with different optical properties of certain areas of muscle cells: some areas appear darker, others lighter). smooth muscle tissue forms smooth muscles, which is part of some internal organs, and striated forms skeletal muscles. A common property of muscle tissue is its excitability, conduction and contractility(ability to contract).
Striated muscle tissue differs from smooth higher "excitability, conductivity and contractility. The cells of striated muscle have a very small diameter and a large length (up to 10-12 cm). For this reason they are called fibers.
Like other cells, muscle cells have a protoplasm called sarcoplasm(from Greek. sarcos- meat). The membrane of muscle cells is called sarcolemma. Inside the muscle fiber are numerous nuclei and other cell components.
The composition of muscle fibers includes a large number of even thinner fibers - myofibril, which, in turn, consist of the thinnest threads - proto fibrils. Protofibrils are the contractile apparatus of the muscle cell, they are special contractile proteins - myosin and actin. The mechanism of muscle contractions is a complex process of physical and chemical transformations occurring in the muscle fiber with the mandatory participation of the contractile apparatus. The launch of this mechanism is carried out by a nerve impulse, and the energy for the contraction process is supplied by adenosine triphosphoric acid (ATP). In this regard, a feature of the structure of muscle fibers is also a large number of mitochondria, which provide the muscle fiber with the necessary energy. The relaxation of the muscle fiber, according to the assumption of many smart people, is carried out passively, due to the elasticity of the sarcolemma and intramuscular connective tissue.
9.6.2. Structure, shape and classification of skeletal muscles. The anatomical unit of the most active part of the human muscular system - the skeletal, or striated, muscles - is the skeletal muscle. Skeletal muscle is an organ formed by striated muscle tissue and containing, in addition, connective tissue, nerves and blood vessels.
Each muscle is surrounded by a kind of "case" of connective tissue (fascia and outer perimysium). In a cross section of a muscle, clusters of muscle fibers (bundles) are easily distinguished, also surrounded by connective tissue (internal perimysium, or endomysium).
In the external structure of the muscle, there is a tendon head corresponding to the beginning of the muscle, the belly of the muscle, or the body formed by muscle fibers, and the tendon end of the muscle, or tail, with which the muscle is attached to another bone. Usually, the tail of the muscle is a movable point of attachment, and the beginning is fixed. In the process of movement, their functions can change: moving points become fixed and vice versa.
In addition to the above main components of skeletal muscle, there are various auxiliary
Formations contributing to the optimal implementation of movements.
The shape of the muscles is very diverse and largely depends on the functional purpose of the muscle. There are long, short, wide, rhomboid, square, trapezius and other muscles. If the muscle has one head, it is called simple, if two or more - complex (for example, biceps, triceps and quadriceps muscles).
Muscles may have two or more median parts, such as the rectus abdominis; several terminal parts, for example, the flexor of the fingers of the hand has four tendon tails.
An important morphological feature is the arrangement of muscle fibers. There are parallel, oblique, transverse and circular arrangement of fibers (in the sphincters). If, with an oblique arrangement of muscle fibers, they are attached only on one side by tendons, then the muscles are called single-feathered, if on both sides they are double-feathered.
Depending on the number of joints which the muscle sets in motion, one can distinguish single-joint, two-joint and multi-joint muscles. functional muscles can be divided into flexors and extensors, outward rotators (arch supports) and inward rotators (pronators), adductors and abductors. There are also synergistic and antagonistic muscles. The former form a group of muscles that perform a movement in a friendly manner, the contraction of the latter causes opposite movements.
According to the location of the muscles i.e., according to their topographic and anatomical features, the muscles of the back, chest, abdomen, head, neck, upper and lower extremities are distinguished. In total, anatomists distinguish 327 skeletal muscles (paired) and 2 unpaired. Together, they average about 40% of a person's body weight (Fig. 65).
Rice. 65. Human muscles. A - front view; B - side view (according to A. I. Fadeeva et al., 1982):
1 - long palmar muscle, 2 - flexor of the fingers, 3, 21 - flexors of the hand, 4, 44 - triceps muscle of the shoulder, 5 - beak-shoulder muscle, 6 - m large circular muscle, 7 - wide back muscle, 8 - serratus anterior, 9-external oblique muscle of the abdomen, 10- iliopsoas muscle, // - rectus femoris, 12-tailor muscle, 13 - internal broad muscle, 14, 19 - anterior tibial muscle, 15 - calcaneal tendon, 16 - gastrocnemius muscle, 17 - tender muscle, 18 - cruciate ligament, 20 - peroneal muscles, 22 - brachioradialis muscle, 23, 24 - biceps muscle of the shoulder, 25 - deltoid muscle, 26 - pectoralis major muscle, 27 - sternohyoid muscle, 28 - sternum clavicular-mastoid muscle, 29 - chewing muscle, 30 - circular muscle of the eye, 31 - trapezius muscle, 32 - extensor of the hand, 33, 38 - extensor of the fingers, 34 - gluteus maximus muscle, 35 - biceps femoris muscle, 36 - soleus muscle, 37, 39 - long peroneal muscle, 40, 41 - wide fascia of the thigh, 42 - rhombus id muscle, 43 - infraspinatus muscle, 45 - shoulder muscle
9.6.3. Contractility as the main property of a muscle
Contractility is characterized by the ability of a muscle to shorten or develop muscle tension. This ability of the muscle is associated with the peculiarities of its structure and functional properties.
The structure of the neuromuscular apparatus and motor units. Muscle contraction occurs under the influence of nerve impulses coming from various centers of the brain. The direct connection of the muscles and the control nerve centers is carried out through the lower parts of the central nervous system located in the spinal cord. There are special neurons here (motor neurons) sending their axons to skeletal muscles. Axons, having reached the muscle, branch out, forming special endings that transmit excitation from the nerve fiber to the muscle (neuromuscular synapse, or motor plate). The structure of the neuromuscular synapse is generally similar to the synapses located in the central nervous system, but the postsynaptic membrane is located on the muscle fiber. The transmission of nerve impulses is also carried out chemically with the help of mediators (acetylcholine).
As a rule, one axon gives rise to many nerve endings that form synapses on various muscle fibers, their number ranges from 5 to 2000. As a result, excitation of one motor neuron leads to excitation and contraction of all muscle fibers innervated by it. This combination of motor neuron, neuromuscular synapses and muscle fibers is called motor unit, which, in fact, is the functional unit of the muscle. In muscles that perform subtle and complex movements, motor units include a small number of muscle fibers (muscles of the eyes, fingers); the muscles involved in the implementation of gross movements have motor units that include a large number of muscle fibers. The contraction of the muscle fibers that make up one motor unit occurs almost simultaneously, but the motor units of one muscle contract asynchronously, which ensures the smoothness of its contraction. Usually the number of motor units depends on the functional role of a given muscle and varies considerably.
Excitability, bioelectric phenomena in muscles, muscle lability. In response to irritation, a process of excitation develops in the muscle. As noted above, this ability of the tissue is called excitability(See section 4.4.1). The level of muscle excitability is one of the most important functional indicators characterizing the functional state of the entire neuromuscular apparatus. The process of excitation of the muscle is accompanied by a change in the metabolism in the cells of the muscle tissue and, accordingly, a change in its bioelectrical features. The basis of the bioelectrical phenomena of the muscle, as well as in the nervous tissue, is the redistribution of K + and Na + ions between the internal contents of the cell and the extracellular space. As a result, at rest in muscle cells, a resting potential of 90 mV is determined. When a muscle cell is excited, an action potential of 30-40 mV appears, propagating throughout the entire muscle fiber. The maximum speed of excitation conduction is only about 5 m/s, i.e., much less than in nerve fibers (see Section 4.6).
Bioelectrical processes in muscles can be recorded using a special device - an electromyograph, and the method of recording muscle biocurrents is called electromyography. The idea of this method was first proposed in 1884 by the famous Russian physiologist N. E. Vvedensky, who managed to detect the action potentials of skeletal muscles using a telephone. Currently, this method has become widespread and is used to diagnose various muscle diseases.
Muscle activity is largely characterized by its lability- the speed or duration of the excitation process in the excitable tissue (N. E. Vvedensky). Muscle fibers have much less lability than nerve fibers, but more than the lability of synapses.
The levels of excitability and lability of the muscle are not constant and change under the influence of various factors. For example, some physical activity early exercise) increases the excitability and lability of the neuromuscular apparatus, and significant physical and mental stress - lower.
Isotonic and isometric muscle contraction. Muscle contraction may be accompanied by its shortening, but the tension remains constant. This reduction is called isotonic. If the muscle is tensed, but shortening does not occur, then muscle contraction is called isometric(for example, when trying to lift a heavy load).
Under natural conditions, muscle contractions are always mixed and human movements are accompanied by both isotonic and isometric muscle contractions. Therefore, when characterizing natural muscle contractions, one can only speak of the relative predominance of the isotonic or isometric mode of muscle activity.
Thus, under the influence of a nerve impulse that enters the muscle through the neuromuscular synapse, biochemical and bioelectrical changes occur in the muscle, which cause its tension or contraction. Under experimental conditions, one nerve impulse is sufficient for muscle contraction. This muscle contraction is called single, it proceeds very quickly, within a few tens of milliseconds. Under natural conditions in the body, a series of impulses is always sent to the muscle. As a result, the muscle does not have time to completely relax after the excitation caused by the previous impulse, as a new impulse again causes its tension, etc. In other words, single contractions are summed up into one longer contraction, which is called titanic contraction or tetanus. It is tetanus that ensures the duration and smoothness of muscle contractions that we encounter in the natural conditions of our physical activity.
The reflex nature of muscle contractions. Human movements, which are based on muscle contractions, have a reflex nature. The contractile mechanisms of muscle fibers work under the influence of nerve impulses coming from the nerve centers. The activity of the latter, in turn, is determined by stimuli coming from the environment due to the activity of the sense organs. In addition, in the process of the movement itself, the brain, on the basis of feedback, constantly receives signals about the progress of its implementation. reflex ring, which is a continuous stream of nerve impulses coming from peripheral receptors (proprioreceptors) to the brain, from it to the executive organs (muscles), the contractions of which are recorded by peripheral receptors, and from there again the stream of nerve impulses rushes to the nerve centers (see Sec. 4.7).
9.6.4. Muscle strength. The strength of a muscle is measured by the maximum tension that it can develop under conditions of isometric contraction. For example, if, under experimental conditions, an animal muscle is isolated and irritated by suspending various loads, then a moment will come when the muscle will not be able to lift the load, but is able to hold it without changing its length. This load will characterize maximum strength. Its value will depend primarily on the number and thickness of the muscle fibers that form the muscle. Quantity and thickness muscle fibers are usually determined by physio logical the cross section of the muscle which is understood as the area of the transverse section of the muscle (cm 2), passing through all the muscle fibers. The thickness of the muscle does not always coincide with its physiological diameter. For example, with equal thickness, muscles with a parallel and pinnate arrangement of fibers differ significantly in physiological diameter. The pennate muscles have a larger diameter and have a greater contraction force. At the same time, the anatomical thickness of the muscle (anatomical diameter), which is the area of its cross section, also characterizes the strength of the muscle. The thicker the muscle, the stronger it is.
Important for the manifestation of muscle strength are the nature of attachment of the muscle to the bones and the point of application of force in the mechanical levers formed by muscles, joints and bones. Muscle strength largely depends on its functional state - excitability, lability, nutrition. The maximum strength of the individual muscles of a person in total and the strength developed by a person with his maximum effort differ significantly. If all the muscles of a person contracted simultaneously and to the maximum, then the force developed by them would reach 25 tons. Under natural conditions, the arbitrary maximum force of a person is always significantly less, since its manifestation is associated not only with the angles of application of muscle traction in the bone levers, which reduce in eventually maximum strength, but also depends on intramuscular and intermuscular coordination. Intramuscular coordination is related to the degree of synchrony of the contraction of the motor units of the muscle, and intermuscular- with the degree of coordination of the muscles involved in the work, The higher the degree of intra- and intermuscular coordination, the greater the maximum human strength. Sports workout significantly contribute to the improvement of their coordination mechanisms, therefore, a trained person has a greater maximum and relative strength, i.e., muscle strength referred to 1 kg of body weight.
9.6.5. Dynamic and static muscle work. Physical performance of the body. Contracting and straining, the muscle produces mechanical work, which in the simplest case can be determined by the formula A = PH, where A is mechanical work (kgm), P is the weight of the load (kg), R is the height of the load (m).
Thus, the work of the muscles is measured by the product of the weight of the lifted load by the amount of shortening of the muscle. From the formula it is easy to deduce the so-called rule of average loads, according to which the maximum work can be done at average loads. Indeed, if P \u003d 0, i.e., the muscle contracts without load, then A \u003d 0. At H \u003d 0, which can be observed when the muscle is not able to lift too heavy a load, the work will also be equal to 0.
Natural human movements are very diverse. In the process of these movements, the muscles, contracting, perform work, which is accompanied by both their shortening and their isometric tension. In this regard, a distinction is made between dynamic and static muscle work. Dynamic work is associated with muscular work, during which muscle contractions are always combined with their shortening. Static work is associated with muscle tension without shortening them. In real conditions, human muscles never perform dynamic or static work in a strictly isolated form. Muscle work is always mixed. However, human movements can be dominated by either the dynamic or static nature of muscle work. Therefore, often, when characterizing muscle activity as a whole, one speaks of its static or dynamic nature. For example, a student's work in a lecture can be characterized as static, although here one can find many elements of dynamic work. On the other hand, playing football is a dynamic job, but players have to perform static efforts as well.
The ability of a person to perform physical work for a long time is called physical performance. The physical performance of a person can be determined using special devices - ergometers (for example, bicycle ergometers). Its unit of measurement is kgm/min. The more a person is able to perform work per unit of time, the higher his physical performance. The value of a person's physical performance depends on age, gender, fitness, environmental factors (temperature, time of day, oxygen content in the air, etc.), and the functional state of the body. For a comparative characteristic of the physical performance of various people, the total amount of work done in 1 minute is calculated, divided by body weight (kg) and relative physical performance is obtained (kgm / min per 1 kg of mass, i.e. kgm - kg / min). On average, the level of physical performance of a 20-year-old boy is 15.5 kgm > kg / min, and for a young athlete of the same age, it reaches 25.
In recent years, the determination of the level of physical performance has been widely used to characterize the general physical development and health status of children and adolescents.
9.6.6. Influence of muscular work on functional
the state of the physiological systems of the body. Muscular work requires the active state of not only the muscles and nerve cells that regulate movement. It is associated with high energy costs of the body and, in this regard, has a significant impact on all aspects of its life: the intensity of metabolism and energy increases, the flow of oxygen into the body increases, the cardiovascular system begins to function more intensely, etc. If energy
body costs at rest average 4.18 kJ / kg of mass, then light work (teachers, clerical workers, etc.) requires more than 8.36 kJ / kg of mass, work of medium severity (painters, turners, locksmiths, etc. ) - 16.74 kJ/kg. Hard physical work increases energy consumption to 29.29 kJ/kg. At rest, the amount of air that has passed through the lungs in 1 minute is 5-8 liters, with physical exertion it can increase up to 50-100 liters! Muscular work also increases the load on the heart. At rest, with each contraction, it ejects up to 60-80 ml of blood into the aorta, with increased
work, this amount increases to 200 ml.
Thus, muscular work has a wide activating effect on all aspects of the life of the body, which is of great physiological significance: the high functional activity of all physiological systems is maintained, the overall reactivity of the body and its immune qualities are significantly increased, and adaptive reserves increase. Finally, as already mentioned, movements are a necessary factor in the normal physical and mental development of the child.
9.6.7. Processes of physical fatigue. Prolonged and intense muscle loads lead to a temporary decrease in the physical performance of the body. This physiological state of the body is called fatigue. The physiological nature of fatigue is still a mystery. It has now been shown that the fatigue process primarily affects the central nervous system, then the neuromuscular junction, and lastly the muscle. For the first time, the leading role of the nervous system in the development of fatigue processes in the body was noted by I. M. Sechenov. “The source of the sensation of fatigue is usually placed in the working muscles,” he wrote, “I place it ... exclusively in the central nervous system.” The proof of the validity of such a conclusion is not only experiments in the laboratory, but also numerous examples from life. Everyone knows that interesting work does not cause fatigue for a long time, and uninteresting work very quickly, although muscle loads in the first case may even exceed the work done by the same person in the second case. amputation of an arm or leg, they feel their presence for a long time.If such people are given the task to mentally work with the missing limb, they soon declare their fatigue.Consequently, the processes of fatigue in such people develop in the central nervous system, since there is no muscular work in this case is not performed.
Fatigue is a normal physiological process developed in the process of evolution to protect physiological systems from systematic overwork, which is a pathological process and is characterized by a disorder in the activity of the nervous system and other physiological systems of the body. Rational rest quickly restores the lost working capacity of the body. However, rest should be active. In other words, after physical work it is useful to change the type of activity, since complete rest restores strength much more slowly. For example, after sports training it is useful to sit down for books, and vice versa, after training sessions - to play football or clean the room.
9.7. DEVELOPMENT OF THE MUSCULAR SYSTEM
The muscular system of a child undergoes significant structural and functional changes in the process of ontogenesis. The formation of muscle cells and the formation of muscles as structural units of the muscular system occurs heterochronously, i.e., first those skeletal muscles are formed that are necessary for the normal functioning of the child's body at this age stage. The process of "rough" muscle formation ends by the 7-8th week of prenatal development. At this stage, irritation of the skin receptors already causes response motor reactions of the fetus, which indicates the establishment of a functional relationship between tactile reception and the muscular system. In the following months, the functional maturation of muscle cells is intensively associated with an increase in the number of myofibrils and their thickness. After birth, the maturation of muscle tissue continues. In particular, intensive fiber growth is observed up to 7 years and in the puberty period. Starting from the age of 14-15, the microstructure of muscle tissue practically does not differ from that of an adult. However, the thickening of muscle fibers can last up to 30-35 years.
The development of the muscles of the upper extremities usually precedes the development of the muscles of the lower extremities. Larger muscles are always formed before small ones. For example, the muscles of the shoulder and forearm are formed faster than the small muscles of the hand. In a one-year-old baby, the muscles of the arms and shoulder girdle are better developed than the muscles of the pelvis and legs. The muscles of the hands develop especially intensively at the age of 6-7 years. The total muscle mass increases rapidly during puberty: in boys - at 13-14 years old, and in girls - at 11-12 years old. Below are data characterizing the mass of skeletal muscles in the process of postnatal development of children and adolescents.
Table 14. Age-related changes in the maximum frequency of movements reproduced by sound signals for 10 s (in terms of 1 min (according to A.I. Vasyutnaya and A.P. Tambiyeva, 1989)
| Boys and youths | Girls | and girls | ||
| Age, | average frequency | relative | average | relative |
| years | movements | frequency | frequency | frequency |
| movements, % | movements | movements, % | ||
The functional properties of muscles also change significantly in the process of ontogenesis. Increased excitability and lability of muscle tissue. Muscle tone changes. "The newborn has increased muscle tone, and the muscles that cause flexion of the limbs predominate over the extensor muscles. As a result, the arms and legs of infants are more often in a bent state. They have a poorly expressed ability of muscles to relax, which with age This is usually associated with stiffness of movements in children and adolescents.Only after 15 years, movements become more plastic.
By the age of 13-15, the formation of all departments of the motor analyzer is completed, which is especially intensive at the age of 7-12 years. In the process of development of the musculoskeletal system, the motor qualities of the muscles change: speed, strength, agility and endurance. Their development is uneven. First of all, speed and dexterity of movements develop. The speed (speed) of movements is characterized by the number of movements that the child is able to produce per unit of time. The speed is determined by three indicators: the speed of a single movement, the time of the motor reaction and the frequency of movements. The speed of a single movement increases significantly in children from 4-5 years old and by the age of 13-14 reaches the level of an adult. By the age of 13-14, the time of a simple motor reaction reaches the level of an adult, which is determined by the speed of physiological processes in the neuromuscular apparatus. The maximum voluntary frequency of movements increases from 7 to 13 years old, and in boys at 7-10 years old it is higher than in girls, and from 13-14 years old the frequency of movements of girls exceeds this indicator in boys. Finally, the maximum frequency of movements in a given rhythm also increases sharply at 7–9 years of age (Table 14).
Until the age of 13-14, the development of dexterity is mainly completed, which is associated with the ability of children and adolescents to carry out accurate, coordinated and fast movements. Consequently, dexterity is associated, firstly, with the spatial accuracy of movements, secondly, with temporal accuracy, and, thirdly, with the speed of solving complex motor tasks. The most important for the development of dexterity is the preschool and primary school period. So, for example, the greatest increase in the accuracy of movements is observed from 4-5 to 7-8 years. Moreover, the ability to reproduce the amplitude of movements up to 40-50 ° maximizes at 7-10 years and after 12 practically does not change, and the accuracy of reproduction of small angular displacements (up to 10-15 °) increases up to 13-14 years. Interestingly, sports training has a significant impact on the development of agility, and in 15-16-year-old athletes, the accuracy of movements is twice as high as in untrained adolescents of the same age.
Thus, up to 6-7 years old, children are not able to make fine precise movements in an extremely short time. Then the spatial accuracy of movements gradually develops, followed by the temporal accuracy. Finally, the ability to quickly solve motor problems in various situations improves (Fig. 66). Agility continues to improve until age 17.
The greatest increase in strength is observed in middle and senior school age, strength increases especially intensively from 10-12 to 13-15 years (Table 15). In girls, the increase in strength occurs somewhat earlier, from 10-12 years old, and in boys - from 13-14. Nevertheless, boys surpass girls in this indicator in all age groups, but the difference is especially clear at 13-14 years old.
Table 15. Maximum strength of various muscle groups in untrained individuals of different ages, kg (according to A. V. Korobkov, 1958)
| Part of the body | Traffic | Age, years | |||||
| 4-5 | 6-7 | 9-11 | 13-14 | 16-17 | 20-30 | ||
| Finger | bending | 2,2 | 2,8 | 4,8 | 6,2 | ||
| Extension | - | - | 0,6 | 0,6 | 1,1 | 0,6 | |
| Brush | bending | 5,2 | 8,0 | 9,8 | 13,8 | 26,2 | 27,2 |
| Extension. | 4,6 | 5,5 | 9,1 | 12,9 | 15,3 | 22,5 | |
| Forearm | bending | 5,4 | 7,3 | 15,0 | 16,3 | 27,7 | 32,3 |
| Extension | 5,0 | 6,1 | 14,8 | 14,7 | 22,4 | 28,5 | |
| Shoulder | bending | 5,5 | 7,7 | 20,0 | 22,8 | 46,1 | 47,9 |
| Extension | 5,5 | 7,7 | 17,7 | 22,4 | 41,9 | 46,5 | |
| torso | bending | 8,2 | 10,2 | 21,3 | 21,5 | 43,3 | 44,9 |
| Extension | 14,6 | 24,2 | 57,5 | 83,1 | 147,8 | 139,0 | |
| Neck | bending | 4,6 | 7,7 | 10,6 | 16,5 | 17,4 | 20,0 |
| Extension | 5,5 | 7,3 | 14,0 | 13,8 | 35,8 | 36,2 | |
| Hip | bending | 6,0 | 7,9 | 19,5 | 25,8 | 33,9 | 32,4 |
| Extension | 7,9 | 13,8 | 37,1 | 49,3 | 95,4 | 108,2 | |
| Shin | bending | 4,6 | 5,0 | 12,1 | 15,2 | 22,7 | 25,2 |
| Extension | 6,7 | 8,4 | 17,7 | 28,0 | 47,6 | 59,8 | |
| Foot | bending | ||||||
| (rear) | - | - | 14,6 | 16,2 | 29,2 | 38,5 | |
| bending | |||||||
| (plantar) | 9,1 | 20,9 | 40,7 | 59,2 | 110,7 | 98,5 |
Later than other physical qualities, endurance develops, which is characterized by the time during which a sufficient level of body performance is maintained. There are age, sex and individual differences in endurance. Endurance of preschool children is at a low level, especially for static work. An intensive increase in endurance to dynamic work is observed from 11 -
12 years. So, if we take the volume of dynamic work of 7-year-old schoolchildren as 100%, then for 10-year-olds it will be 150%, and for 14-15-year-olds - more than 400% (M. V. Antropova, 1968). Schoolchildren's endurance to static loads also grows intensively from the age of 11-12 (Fig. 67). In general, by the age of 17-19, the endurance of schoolchildren is about 85% of the adult level. It reaches its maximum level by 25-30 years.
9.8. DEVELOPMENT OF MOTOR ACTIVITY AND MOVEMENT COORDINATION
Motor activity and coordination of movements in a newborn is far from perfect. The set of his movements is very limited and has only an unconditional reflex basis. Of particular interest is the swimming reflex, which also has an unconditional reflex nature. The maximum manifestation of the swimming reflex is observed by the 40th day of postnatal development. At this age, the child is able to make swimming movements in the water and stay on it for up to 15 minutes. Naturally, the child's head must be supported, as his own neck muscles are still very weak. In the future, the swimming reflex and other unconditioned motor reflexes fade away, and various motor skills are formed to replace them.
The development of the child's movements is due not only to the maturation of the musculoskeletal and nervous systems, it also depends on the conditions of education. All the basic natural movements inherent in a person (walking, climbing, running, jumping, etc.) and their coordination are formed in a child up to 3-5 years old. At the same time, the first weeks of life are of great importance for the normal development of movements. Naturally, the coordination mechanisms at preschool age are still imperfect. The well-known Soviet physiologist N. A. Bernstein described the motor skills of preschool age as "graceful clumsiness." Despite the fact that the movements of the preschooler are poorly coordinated and awkward, children are able to master relatively complex movements. In particular, it is at this age that children learn tool movements, that is, motor skills and the ability to use a tool (hammer, scissors, wrench, etc.). From the age of 6-7, children master writing and other movements that require fine coordination. The formation of coordination mechanisms of movements ends by adolescence, and all types of movements become available to boys and girls (V. S. Farfel, 1959). Of course, the improvement of movements and their coordination during systematic exercises can continue into adulthood, for example, among musicians, athletes, circus performers, etc. (see Fig. 66).
Thus, the development of movements and mechanisms of their coordination is most intensive in the first years of life and up to adolescence. Their improvement is always closely connected with the development of the child's nervous system, so any delay in the development of movements should alert the educator. In such cases, it is necessary to seek help from doctors and check the functional state of the nervous system of children. In adolescence, coordination of movements due to hormonal changes in the child's body is somewhat disturbed. However, this is a temporary phenomenon, which usually disappears without a trace after 15 years. The general formation of all coordination mechanisms ends in adolescence, and by the age of 18-25 they fully correspond to the level of an adult. The age of 18-30 years is considered "golden" in the development of human motor skills. This is the heyday of his motor skills.
9.9. PHYSIOLOGY OF WORK PROCESSES AND PHYSICAL EXERCISES
The formation of labor and sports movements is based on the formation of systems of temporary connections in the cerebral cortex and the subsequent formation of complex dynamic cortical stereotypes from them. The dominant phenomenon observed in the process of labor and sports activity is also important (A. A. Ukhtomsky, 1923; S. A. Kosilov, 1965). Simultaneously with the improvement of the nervous processes, there is their finest coordination with the functional activity of the motor apparatus and the entire vegetative sphere. Such broad functional changes occurring in the body of children and adolescents in the process of labor and sports activities have a beneficial effect on their physical and mental development. Naturally, labor and physical exercises stimulate the processes of growth and development of the child only when the solution of pedagogical problems is combined properly with the functional capabilities of the child's body, with the degree of maturity of its physiological systems.
The reasonable organization of physical exercises already in infancy contributes to the physical development of the child, improves its basic nervous processes, increases attention, stimulates the development of speech and creates a favorable emotional background (A. F. Tur, 1960; K-D. Hubert, M. T. Ryss , 1970). In parallel with the improvement of the nervous system, physical labor and physical exercises significantly increase the functionality of the physiological systems of the child's body, increase its efficiency and resistance to diseases.
Unfortunately, some teachers and parents, paying much attention to the intellectual and aesthetic education of children and adolescents, underestimate the role of physical education in their overall physical and mental development. This opposition of physical and mental education is deeply erroneous and causes irreparable harm to the development of children and adolescents. According to modern physiological and psychological research, there is a direct and close connection between the physical and mental activity of the child, which remains in his subsequent life. In particular, a close correlation was shown between the child's motor system and his school performance. It turned out that about 30% of underachieving primary school students have various disorders in the motor sphere. A direct relationship between the motor activity of the child, his mental development and mental performance was revealed. The more active the child is in motor activity, the more intensively his mental development goes. This dependence does not lose its significance in the life of an adult: the more active he is in motor activity, the more active and productive he is in mental activity, the more significant person he becomes in work and social life. This connection between the general physical development of children and adolescents and their mental abilities was noted even by the great materialist thinkers of the past. “If you want to educate the mind of your student,” wrote J. J. Rousseau in one of his philosophical and pedagogical works, “educate the forces (bodily) that he must control. Constantly exercise his body; make him healthy and strong to make him smart and sensible; let him work, act, run, shout; let it always be in motion; let him be a man according to strength, and soon he will become one according to reason.
Thus, the properly organized upbringing of children and adolescents in the family and school should combine all educational influences into a single system that contributes to the proper extent to the physical and mental development of the younger generation.
In conclusion, it should be noted that physical labor and physical exercises are necessary for a person of any age, since at any age they are an important condition for strengthening and maintaining human health. The role of physical labor and sports is especially growing at the present time, when urban transport, a dense network of highways and railways, sea and air liners have made the life of a modern person sedentary. Modern production does not require physical endurance and muscular strength from a person. The labor of a worker turns into the work of an operator who monitors the readings of instruments and, with the help of automatic systems, manages production.
Muscle tissues (lat. textus muscularis) - 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).
It consists of mononuclear cells - spindle-shaped myocytes 20-500 microns long. Their cytoplasm in a light microscope looks uniform, without transverse striation. This tissue has special properties: it slowly contracts and relaxes, has automaticity, 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).
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 a high speed of 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. Fibers are 10 to 12 cm long.
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.
Tissue is a collection of similar cells that share common functions. Almost all are made up of different types of fabrics.
Classification
In animals and humans, the following types of tissues are present in the body:
- epithelial;
- nervous;
- connecting;
- muscular.
These groups combine several varieties. So, connective tissue is adipose, cartilage, bone. It also includes blood and lymph. Epithelial tissue is multi-layered and single-layered, depending on the structure of the cells, squamous, cubic, cylindrical epithelium, etc. can also be distinguished. There is only one type of nervous tissue. And we will talk about it in more detail in this article.
Types of muscle tissue
In the body of all animals, its three varieties are distinguished:
- striated muscles;
- cardiac muscle tissue.
The functions of smooth muscle tissue differ from those of striated and cardiac tissue, so it has a different structure. Let's take a closer look at the structure of each type of muscle.
General characteristics of muscle tissues
Since all three species belong to the same type, they have a lot in common.
Muscle tissue cells are called myocytes, or fibers. Depending on the type of tissue, they may have a different structure.
Another common feature of all types of muscles is that they are able to contract, but this process occurs individually in different species.
Features of myocytes
Cells of smooth muscle tissue, as well as striated and cardiac, have an elongated shape. In addition, they have special organelles called myofibrils, or myofilaments. They contain (actin, myosin). They are necessary in order to ensure the movement of the muscle. A prerequisite for the functioning of the muscle, in addition to the presence of contractile proteins, is also the presence of calcium ions in the cells. Therefore, insufficient or excessive consumption of foods high in this element can lead to incorrect functioning of the muscles - both smooth and striated.
In addition, another specific protein, myoglobin, is present in cells. It is necessary in order to bind with oxygen and store it.
As for organelles, in addition to the presence of myofibrils, a special feature for muscle tissues is the content of a large number of mitochondria in the cell - two-membrane organelles responsible for cellular respiration. And this is not surprising, since the muscle fiber needs a large amount of energy generated during respiration by mitochondria to contract.
In some myocytes, more than one nucleus is also present. This is typical for striated muscles, the cells of which can contain about twenty nuclei, and sometimes this figure reaches one hundred. This is due to the fact that the striated muscle fiber is formed from several cells, subsequently combined into one.
The structure of striated muscles
This type of tissue is also called skeletal muscle. The fibers of this type of muscle are long, collected in bundles. Their cells can reach several centimeters in length (up to 10-12). They contain many nuclei, mitochondria and myofibrils. The main structural unit of each myofibril of striated tissue is the sarcomere. It is made up of a contractile protein.
The main feature of this muscle is that it can be controlled consciously, in contrast to smooth and cardiac.
The fibers of this tissue are attached to the bones with the help of tendons. That is why such muscles are called skeletal.
The structure of smooth muscle tissue
Smooth muscles line some of the internal organs, such as the intestines, uterus, bladder, and blood vessels. In addition, sphincters and ligaments are formed from them.
Smooth muscle fibers are not as long as striated fibers. But its thickness is greater than in the case of skeletal muscles. Cells of smooth muscle tissue have a spindle-like shape, and not filamentous, like striated myocytes.
The structures that provide smooth muscle contraction are called protofibrils. Unlike myofibrils, they have a simpler structure. But the material from which they are built is the same contractile proteins actin and myosin.
There are also fewer mitochondria in smooth muscle myocytes than in striated and cardiac cells. In addition, they contain only one core.
Features of the heart muscle
Some researchers define it as a subspecies of striated muscle tissue. Their fibers are indeed very similar in many ways. Heart cells - cardiomyocytes - also contain several nuclei, myofibrils and a large number of mitochondria. This tissue, as well as being able to contract much faster and stronger than smooth muscles.
However, the main feature that distinguishes the heart muscle from the striated muscle is that it cannot be controlled consciously. Its contraction occurs only automatically, as is the case with smooth muscles.
In the heart tissue, in addition to typical cells, there are also secretory cardiomyocytes. They do not contain myofibrils and do not contract. These cells are responsible for the production of the hormone atriopeptin, which is necessary for the regulation of blood pressure and control of circulating blood volume.
Functions of the striated muscles
Their main task is to move the body in space. It is also the movement of body parts relative to each other.
Of the other functions of the striated muscles, one can note the maintenance of the posture, the depot of water and salts. In addition, they perform a protective role, which is especially true for the abdominal muscles, which prevent mechanical damage to internal organs.
The functions of striated muscles can also include temperature regulation, since with active muscle contraction, a significant amount of heat is released. That is why, when freezing, the muscles begin to tremble involuntarily.
Functions of smooth muscle tissue
The muscles of this type perform an evacuation function. It lies in the fact that the smooth muscles of the intestine push the feces to the place of their excretion from the body. Also, this role is manifested during childbirth, when the smooth muscles of the uterus push the fetus out of the organ.
The functions of smooth muscle tissue are not limited to this. Their sphincter role is also important. Special circular muscles are formed from the tissue of this type, which can close and open. Sphincters are present in the urinary tract, in the intestines, between the stomach and esophagus, in the gallbladder, in the pupil.
Another important role played by smooth muscles is the formation of the ligamentous apparatus. It is necessary to maintain the correct position of the internal organs. With a decrease in the tone of these muscles, omission of some organs may occur.
This is where the functions of smooth muscle tissue end.
Purpose of the heart muscle
Here, in principle, there is nothing special to talk about. The main and only function of this tissue is to ensure blood circulation in the body.
Conclusion: differences between the three types of muscle tissue
To clarify this issue, we present a table:
| smooth muscle | striated muscles | cardiac muscle tissue |
| Shrinks automatically | Can be controlled consciously | Shrinks automatically |
| Cells elongated, spindle-shaped | Cells are long, filamentous | elongated cells |
| Fibers do not bundle | The fibers are bundled | The fibers are bundled |
| One nucleus per cell | Multiple nuclei in a cell | Multiple nuclei in a cell |
| Relatively few mitochondria | Lots of mitochondria | |
| Myofibrils are missing | Myofibrils are present | There are myofibrils |
| Cells are able to divide | Fibers cannot divide | Cells cannot divide |
| Contract slowly, weakly, rhythmically | Decrease quickly, strongly | Contract quickly, strongly, rhythmically |
| They line internal organs (intestines, uterus, bladder), form sphincters | Attached to the skeleton | Shape the heart |
That's all the main characteristics of striated, smooth and cardiac muscle tissue. Now you are familiar with their functions, structure and main differences and similarities.