Topic 3

3.1. Features of the functions and structure of the musculoskeletal system

The organs of movement are a single system, where each part and organ is formed and functions in constant interaction with each other. The elements that make up the system of organs of movement are divided into two main categories: passive (bones, ligaments and joints) and active elements of the organs of movement (muscles).

The size and shape of the human body is largely determined by the structural basis - the skeleton. The skeleton provides support and protection for the entire body and individual organs. The skeleton has a system of movably articulated levers, set in motion by muscles, due to which various movements of the body and its parts in space are performed. Separate parts of the skeleton serve not only as a container for vital organs, but also provide their protection. For example, the skull, chest and pelvis serve as protection for the brain, lungs, heart, intestines, etc.

Until recently, the prevailing opinion was that the role of the skeleton in the human body is limited to the function of supporting the body and participating in movement (this was the reason for the appearance of the term "musculoskeletal system"). Thanks to modern research, the understanding of the functions of the skeleton has expanded significantly. For example, the skeleton is actively involved in metabolism, namely in maintaining the mineral composition of the blood at a certain level. Substances included in the skeleton, such as calcium, phosphorus, citric acid and others, if necessary, easily enter into exchange reactions. The function of the muscles is also not limited to the inclusion of bones in movement and the performance of work, many muscles, surrounding the body cavities, protect the internal organs.

General information about the skeleton. Bone Shape. The human skeleton is similar in structure to the skeleton of higher animals, but has a number of features that are associated with upright posture, movement on two limbs, and high development of the arm and brain.

The human skeleton is a system consisting of 206 bones, of which 85 are paired and 36 unpaired. Bones are the organs of the body. The weight of the skeleton in a man is approximately 18% of the body weight, in a woman - 16%, in a newborn - 14%. The skeleton consists of bones of various sizes and shapes.

According to their shape, bones are divided into:

a) long (located in the skeleton of the limbs);

b) short (located in the wrist and tarsus, i.e., where greater strength and mobility of the skeleton are simultaneously required); c) wide or flat (they form the walls of cavities in which internal organs are located - the pelvic bone, the bones of the skull); d) mixed (have different shapes).

Bone connections. Bones articulate in a variety of ways. According to the degree of mobility, joints are distinguished:

a) motionless;

b) sedentary; c) movable bone joints, or joints.

An immovable joint is formed as a result of the fusion of bones, while movements may be extremely limited or completely absent. For example, the immobility of the bones of the brain skull is ensured by the fact that numerous protrusions of one bone enter the corresponding recess of the other. This connection of bones is called a suture.

The presence of elastic cartilage pads between the bones provides little mobility. For example, such pads are available between individual vertebrae. During muscle contraction, the pads are compressed, and the vertebrae are drawn together. During active movements (walking, running, jumping), cartilage acts as a shock absorber, thereby softening sharp shocks and protecting the body from shaking.

Movable joints of bones are more common, which is provided by the joints. The ends of the bones that form the joint are covered with hyaline cartilage 0,2 to 0,6 mm thick. This cartilage is very elastic, has a smooth shiny surface, so the friction between the bones is significantly reduced, which greatly facilitates their movement.

From a very dense connective tissue, an articular bag (capsule) is formed, which surrounds the articulation area of ​​\uXNUMXb\uXNUMXbthe bones. A strong outer (fibrous) layer of the capsule firmly connects the articulating bones. Inside the capsule is lined with a synovial membrane. The joint cavity contains synovial fluid, which acts as a lubricant and also helps to reduce friction.

Outside, the joint is reinforced with ligaments. A number of joints are strengthened by ligaments and inside. In addition, inside the joints there are special devices that increase the articulating surfaces: lips, discs, menisci from connective tissue and cartilage.

The joint cavity is hermetically closed. The pressure between the articular surfaces is always negative (less than atmospheric), and therefore the external atmospheric pressure prevents their divergence.

Types of joints. According to the shape of the articular surface and the axes of rotation, joints are distinguished:

a) with three;

b) with two; c) with one axis of rotation.

The first group consists of spherical joints - the most mobile (for example, the joint between the scapula and the humerus). The joint between the innominate and the thigh, called the walnut, is a type of ball and socket joint.

The second group consists of elliptical (for example, the joint between the skull and the first cervical vertebra) and saddle joints (for example, the joint between the metacarpal bone of the first finger and the corresponding bone of the wrist).

The third group includes block-shaped (joints between the phalanges of the fingers), cylindrical (between the ulna and radius) and helical joints (forming the elbow joint).

Any loose body has six degrees of freedom, because it produces three translational and three rotational movements along the coordinate axes. A fixed body can only perform rotations. Since all links of the body are fixed, joints with three axes of rotation are the most mobile and have three degrees of freedom. Joints with two axes of rotation are less mobile, therefore they have two degrees of freedom. One degree of freedom, which means that joints with one axis of rotation have the least mobility.

Bone structure. Each bone is a complex organ consisting of bone tissue, periosteum, bone marrow, blood and lymphatic vessels and nerves. With the exception of the connecting surfaces, the entire bone is covered with periosteum - a thin connective tissue membrane rich in nerves and vessels that penetrate from it into the bone through special openings. Ligaments and muscles are attached to the periosteum. The cells that make up the inner layer of the periosteum grow and multiply, which ensures the growth of the bone in thickness, and in the event of a fracture, the formation of a callus.

Sawing a tubular bone along its long axis, one can see that a dense (or compact) bone substance is located on the surface, and under it (in depth) - spongy. In short bones, such as vertebrae, spongy matter predominates. Depending on the load experienced by the bone, the compact substance forms a layer of different thickness. The spongy substance is formed by very thin bony crossbars oriented parallel to the lines of the main stresses. This allows the bone to withstand significant loads.

The dense layer of bone has a lamellar structure and is similar to a system of cylinders inserted into each other, which also gives the bone strength and lightness. Bone tissue cells lie between the plates of bone substance. Bone plates make up the intercellular substance of bone tissue.

A tubular bone consists of a body (diaphysis) and two ends (epiphyses). On the epiphyses are the articular surfaces, which are covered with cartilage involved in the formation of the joint. On the surface of the bones are tubercles, tubercles, grooves, ridges, notches, to which the tendons of the muscles are attached, as well as holes through which the vessels and nerves pass.

Chemical composition of bone. Dried and defatted bone has the following composition: organic matter - 30%; minerals - 60%; water - 10%.

The organic substances of the bone include fibrous protein (collagen), carbohydrates and many enzymes.

Bone minerals are represented by salts of calcium, phosphorus, magnesium and many trace elements (such as aluminum, fluorine, manganese, lead, strontium, uranium, cobalt, iron, molybdenum, etc.). The skeleton of an adult contains about 1200 g of calcium, 530 g of phosphorus, 11 g of magnesium, i.e. 99% of all calcium present in the human body is contained in the bones.

In children, organic substances predominate in the bone tissue, so their skeleton is more flexible, elastic, easily deformed during prolonged and heavy load or incorrect body positions. The amount of minerals in the bones increases with age, and therefore the bones become more fragile and more likely to break.

Organic and mineral substances make the bone strong, hard and elastic. The strength of the bone is also ensured by its structure, the location of the bone crossbars of the spongy substance in accordance with the direction of the forces of pressure and tension.

Bone is 30 times harder than brick and 2,5 times harder than granite. Bone is stronger than oak. It is nine times stronger than lead and almost as strong as cast iron. In a vertical position, the human femur can withstand the pressure of a load of up to 1500 kg, and the tibia - up to 1800 kg.

Development of the skeletal system in childhood and adolescence. During prenatal development in children, the skeleton consists of cartilage tissue. Ossification points appear after 7-8 weeks. The newborn has ossified diaphysis of the tubular bones. After birth, the ossification process continues. The timing of the appearance of ossification points and the end of ossification varies for different bones. Moreover, for each bone they are relatively constant; they can be used to judge the normal development of the skeleton in children and their age.

The skeleton of a child differs from the skeleton of an adult in its size, proportions, structure and chemical composition. The development of the skeleton in children determines the development of the body (for example, the musculature develops more slowly than the skeleton grows).

There are two ways of bone development.

1. Primary ossification, when bones develop directly from the embryonic connective tissue - mesenchyme (bones of the cranial vault, facial part, partly the clavicle, etc.). First, a skeletal mesenchymal syncytium is formed. Cells are laid in it - osteoblasts, which turn into bone cells - osteocytes, and fibrils impregnated with calcium salts and turn into bone plates. Thus, bone develops from connective tissue.

2. Secondary ossification, when the bones are initially laid down in the form of dense mesenchymal formations that have the approximate outlines of future bones, then turn into cartilaginous tissues and are replaced by bone tissues (bones of the base of the skull, trunk and limbs).

With secondary ossification, the development of bone tissue occurs by replacement both outside and inside. Outside, the formation of bone substance occurs by osteoblasts of the periosteum. Inside, ossification begins with the formation of ossification nuclei, gradually the cartilage resolves and is replaced by bone. As the bone grows, it is resorbed from the inside by special cells called osteoclasts. The growth of bone substance comes from the outside. Bone growth in length occurs due to the formation of bone substance in the cartilage located between the epiphysis and diaphysis. These cartilages are gradually shifted towards the epiphysis.

Many bones in the human body are not formed entirely, but in separate parts, which then merge into a single bone. For example, the pelvic bone first consists of three parts, merging together by the age of 14-16. The tubular bones are also laid in three main parts (ossification nuclei in the places where bone protrusions are formed are not taken into account). For example, the tibia in the embryo initially consists of a continuous hyaline cartilage. Ossification begins in the middle part at about the eighth week of intrauterine life. Replacement on the bone of the diaphysis occurs gradually and goes first from the outside, and then from the inside. At the same time, the epiphyses remain cartilaginous. The nucleus of ossification in the upper epiphysis appears after birth, and in the lower epiphysis - in the second year of life. In the middle part of the epiphyses, the bone first grows from the inside, then from the outside, as a result of which two layers of epiphyseal cartilage remain separating the diaphysis from the epiphyses.

In the upper epiphysis of the femur, the formation of bone trabeculae occurs at the age of 4-5 years. After 7-8 years, they lengthen and become uniform and compact. The thickness of the epiphyseal cartilage by the age of 17-18 reaches 2-2,5 mm. By the age of 24, the growth of the upper end of the bone ends and the upper epiphysis fuses with the diaphysis. The lower epiphysis grows to the diaphysis even earlier - by the age of 22. With the end of ossification of tubular bones, their growth in length stops.

Ossification process. General ossification of the tubular bones is completed by the end of puberty: in women - by 17-21 years, in men - by 19-24 years. Because men reach puberty later than women, they are taller on average.

From five months to one and a half years, that is, when the child gets on his feet, the main development of the lamellar bone occurs. By the age of 2,5-3 years, the remnants of coarse fibrous tissue are already absent, although during the second year of life, most of the bone tissue has a lamellar structure.

Decreased function of the endocrine glands (anterior pituitary, thyroid, parathyroid, thymus, genital) and lack of vitamins (especially vitamin D) can cause delayed ossification. Acceleration of ossification occurs with precocious puberty, increased function of the anterior part of the adenohypophysis, thyroid gland and adrenal cortex. Delay and acceleration of ossification most often appear before the age of 17-18, and the difference between "bone" and passport ages can reach 5-10 years. Sometimes ossification occurs faster or slower on one side of the body than on the other.

With age, the chemical composition of bones changes. The bones of children contain more organic matter and less inorganic matter. With growth, the amount of salts of calcium, phosphorus, magnesium and other elements increases significantly, the ratio between them changes. So, in young children, calcium is retained in the bones the most, but as they grow older, there is a shift towards greater retention of phosphorus. Inorganic substances in the composition of the bones of a newborn make up one-half of the bone weight, in an adult - four-fifths.

A change in the structure and chemical composition of bones also entails a change in their physical properties. In children, the bones are more elastic and less brittle than in adults. Cartilage in children is also more plastic.

Age-related differences in the structure and composition of bones are especially pronounced in the number, location, and structure of the Haversian canals. With age, their number decreases, and the location and structure change. The older the child, the more dense matter in his bones, in young children there is more spongy substance. By the age of 7, the structure of tubular bones is similar to that of an adult, however, between 10-12 years, the spongy substance of the bones changes even more intensively, its structure stabilizes by the age of 18-20.

The younger the child, the more the periosteum is fused to the bone. The final demarcation between bone and periosteum occurs by the age of 7. By the age of 12, the dense substance of the bone has an almost homogeneous structure; by the age of 15, single areas of resorption of the dense substance completely disappear, and by the age of 17, large osteocytes predominate in it.

From 7 to 10 years, the growth of the bone marrow cavity in the tubular bones sharply slows down, and it is finally formed from 11-12 to 18 years. The increase in the bone marrow canal occurs in parallel with the uniform growth of the dense substance.

Between the plates of the spongy substance and in the medullary canal is the bone marrow. Due to the large number of blood vessels in the tissues, newborns have only red bone marrow - hematopoiesis occurs in it. From six months, a gradual process of replacing the tubular bones in the diaphysis of the red bone marrow with yellow, consisting mostly of fat cells, begins. Replacement of the red brain is completed by 12-15 years. In adults, red bone marrow is stored in the epiphyses of tubular bones, in the sternum, ribs and spine and is approximately 1500 cubic meters. cm.

The union of fractures and the formation of callus in children occurs after 21-25 days, in infants this process occurs even faster. Dislocations in children under 10 years of age are rare due to the high extensibility of the ligamentous apparatus.

3.2. Types and functional features of the muscle tissue of children and adolescents

General information about muscles. There are about 600 skeletal muscles in the human body. The muscular system makes up a significant part of the total human body weight. So, at the age of 17-18 years it is 43-44%, and in people with good physical fitness it can even reach 50%. In newborns, total muscle mass accounts for only 23% of body weight.

The growth and development of individual muscle groups occur unevenly. First of all, the abdominal muscles develop in infants, and a little later, the masticatory muscles. The muscles of a child, unlike the muscles of an adult, are paler, softer and more elastic. By the end of the first year of life, the muscles of the back and limbs noticeably increase, at this time the child begins to walk.

During the period from birth to the end of the growth of the child, the mass of muscles increases by 35 times. At the age of 12-16 years (puberty), due to the lengthening of the tubular bones, the tendons of the muscles also intensively lengthen. At this time, the muscles become long and thin, which is why teenagers look long-legged and long-armed. At 15-18 years of age, transverse muscle growth occurs. Their development continues up to 25-30 years.

Muscle structure. The muscle is divided into a middle part - the belly, consisting of muscle tissue, and the end sections - tendons, formed by dense connective tissue. Tendons attach muscles to bones, but this is not necessary. Muscles can also attach to various organs (the eyeball), to the skin (muscles of the face and neck), etc. In the muscles of a newborn, the tendons are rather poorly developed, and only by the age of 12-14 are the muscle-tendon relationships that are characteristic of muscles established adult. The muscles of all higher animals are the most important working organs - effectors.

Muscles are smooth and striated. In the human body, smooth muscles are found in the internal organs, blood vessels and skin. They are almost not controlled by the central nervous system, so they (as well as the heart muscle) are sometimes called involuntary. These muscles have automatism and their own nervous network (intramural, or metasympathetic), which largely ensures their autonomy. The regulation of the tone and motor activity of smooth muscles is carried out by impulses coming through the autonomic nervous system and humorally (i.e., through tissue fluid). Smooth muscles are able to carry out rather slow movements and long tonic contractions. The motor activity of smooth muscles often has a rhythmic character, for example, pendulum and peristaltic bowel movements. Prolonged tonic contractions of smooth muscles are very clearly expressed in the sphincters of hollow organs, which prevents the release of contents. This ensures the accumulation of urine in the bladder and bile in the gallbladder, the formation of feces in the large intestine, etc.

The smooth muscles of the walls of blood vessels, especially arteries and arterioles, are in a state of constant tonic contraction. The tone of the muscle layer of the walls of the arteries regulates the size of their lumen and thus the level of blood pressure and blood supply to the organs.

Striated muscles consist of many individual muscle fibers, which are located in a common connective tissue sheath and are attached to tendons, which, in turn, are connected to the skeleton. Striated muscles are divided into two types:

a) parallel-fibrous (all fibers are parallel to the long axis of the muscle);

b) pinnate (the fibers are located obliquely, attached on one side to the central tendon cord, and on the other to the outer tendon sheath).

Muscle strength is proportional to the number of fibers, i.e., the area of ​​the so-called physiological cross-section of the muscle, the surface area that intersects all active muscle fibers. Each skeletal muscle fiber is a thin (10 to 100 microns in diameter), long (up to 2-3 cm) multinuclear formation - a symplast - arising in early ontogenesis from the fusion of myoblast cells.

The main feature of a muscle fiber is the presence in its protoplasm (sarcoplasm) of a mass of thin (about 1 micron in diameter) filaments - myofibrils, which are located along the longitudinal axis of the fiber. Myofibrils consist of alternating light and dark areas - discs. Moreover, in the mass of neighboring myofibrils in striated fibers, the same-name disks are located at the same level, which gives regular transverse striation (striation) to the entire muscle fiber.

A complex of one dark and two halves of light discs adjacent to it, limited by thin Z-lines, is called a sarcomere. Sarcomeres are the smallest element of the contractile apparatus of a muscle fiber.

The membrane of the muscle fiber - the plasmalemma - has a similar structure to the nerve membrane. Its distinguishing feature is that it produces regular T-shaped invaginations (50 nm diameter tubes) approximately at the sarcomere boundaries. Invaginations of the plasmalemma increase its area and, consequently, the total electric capacitance.

Inside the muscle fiber between the bundles of myofibrils, parallel to the longitudinal axis of the symplast, there are systems of tubules of the sarcoplasmic reticulum, which is a branched closed system that is closely adjacent to the myofibrils and its blind ends (terminal cisterns) to the T-shaped protrusions of the plasmalemma (T-system). The T-system and the sarcoplasmic reticulum are the apparatus for transmitting excitation signals from the plasmalemma to the contractile apparatus of the myofibrils.

Outside, the entire muscle is enclosed in a thin connective tissue sheath - fascia.

Contractility as the main property of muscles. Excitability, conductivity and contractility are the main physiological properties of muscles. Muscle contractility consists of shortening the muscle or developing tension. During the experiment, the muscle responds with a single contraction in response to a single stimulus. In humans and animals, muscles from the central nervous system receive not single impulses, but a series of impulses, to which they respond with a strong, prolonged contraction. This muscle contraction is called tetanic (or tetanus).

When muscles contract, they perform work that depends on their strength. The thicker the muscle, the more muscle fibers in it, the stronger it is. Muscle in terms of 1 square. cm cross-section can lift a load up to 10 kg. The strength of the muscles also depends on the features of their attachment to the bones. Bones and the muscles attached to them are a kind of leverage. The strength of a muscle depends on how far from the fulcrum of the lever and closer to the point of application of gravity it is attached.

A person is able to maintain the same posture for a long time. This is called static muscle tension. For example, when a person simply stands or holds his head upright (i.e., makes the so-called static efforts), his muscles are in a state of tension. Some exercises on rings, parallel bars, holding a raised bar require such static work, which requires the simultaneous contraction of almost all muscle fibers. Of course, such a state cannot be prolonged due to developing fatigue.

During dynamic work, various muscle groups contract. At the same time, the muscles that perform dynamic work contract quickly, work with great tension and therefore soon get tired. Usually, during dynamic work, different groups of muscle fibers contract in turn. This gives the muscle the ability to do work for a long time.

By controlling the work of the muscles, the nervous system adapts their work to the current needs of the body, in connection with this, the muscles work economically, with a high efficiency. Work will become maximum, and fatigue will develop gradually, if for each type of muscular activity an average (optimal) rhythm and load value is selected.

The work of muscles is a necessary condition for their existence. If the muscles are inactive for a long time, muscle atrophy develops, they lose their efficiency. Training, that is, constant, fairly intense work of the muscles, helps to increase their volume, increase strength and performance, and this is important for the physical development of the body as a whole.

Muscle tone. In humans, muscles are somewhat contracted even at rest. A condition in which tension is maintained for a long time is called muscle tone. Muscle tone may decrease slightly and the body may relax during sleep or anesthesia. Complete disappearance of muscle tone occurs only after death. Tonic muscle contraction does not cause fatigue. The internal organs are held in their normal position only due to muscle tone. The amount of muscle tone depends on the functional state of the central nervous system.

The tone of skeletal muscles is directly determined by the supply of nerve impulses from the motor neurons of the spinal cord to the muscle with a large interval. The activity of neurons is supported by impulses coming from the overlying sections of the central nervous system, from receptors (proprioceptors) that are located in the muscles themselves. The role of muscle tone in ensuring coordination of movements is great. In newborns, the tone of the flexors of the arm predominates; in children of 1-2 months - the tone of the extensor muscles, in children of 3-5 months - the balance of the tone of the antagonist muscles. This circumstance is associated with increased excitability of the red nuclei of the midbrain. As the functional maturation of the pyramidal system, as well as the cerebral cortex of the brain, muscle tone decreases.

The increased muscle tone of the legs of the newborn gradually decreases (this occurs in the second half of the child's life), which is a necessary prerequisite for the development of walking.

Fatigue. During prolonged or strenuous work, muscle performance decreases, which is restored after rest. This phenomenon is called physical fatigue. With pronounced fatigue, prolonged shortening of the muscles and their inability to completely relax (contracture) develop. This is primarily due to changes that occur in the nervous system, disruption of the conduction of nerve impulses at synapses. When tired, the reserves of chemical substances that serve as sources of contraction energy are depleted, and metabolic products (lactic acid, etc.) accumulate.

The rate of onset of fatigue depends on the state of the nervous system, the frequency of the rhythm in which the work is performed, and on the magnitude of the load. Fatigue can be associated with an unfavorable environment. Uninteresting work quickly causes fatigue.

The younger the child, the faster he gets tired. In infancy, fatigue occurs after 1,5-2 hours of wakefulness. Immobility, prolonged inhibition of movements tire children.

Physical fatigue is a normal physiological phenomenon. After rest, working capacity is not only restored, but may also exceed the initial level. In 1903 I.M. Sechenov found that the performance of tired muscles of the right hand is restored much faster if, during rest, work is done with the left hand. Such a rest, in contrast to the simple rest of I.M. Sechenov called active.

Thus, the alternation of mental and physical labor, outdoor games before classes, physical culture breaks during lessons and during breaks increase the efficiency of students.

3.3. Growth and muscle work

During fetal development, muscle fibers are formed heterochronously. Initially, the muscles of the tongue, lips, diaphragm, intercostal and dorsal are differentiated, in the limbs - first the muscles of the arms, then the legs, in each limb first - the proximal sections, and then the distal ones. Muscles of embryos contain less proteins and more (up to 80%) water. The development and growth of different muscles after birth also occur unevenly. Earlier and more muscles begin to develop, providing motor functions that are extremely important for life. These are the muscles that are involved in breathing, sucking, grasping objects, i.e., the diaphragm, muscles of the tongue, lips, hands, intercostal muscles. In addition, the muscles involved in the process of teaching and nurturing certain skills in children are trained and developed more.

A newborn has all the skeletal muscles, but they weigh 37 times less than an adult. Skeletal muscles grow and develop until about 20-25 years of age, influencing the growth and formation of the skeleton. The increase in muscle weight with age occurs unevenly, this process is especially fast during puberty.

Body weight increases with age, mainly due to an increase in skeletal muscle weight. The average weight of skeletal muscles as a percentage of body weight is distributed as follows: in newborns - 23,3; at 8 years old - 27,2; at 12 years old - 29,4; at the age of 15 - 32,6; at 18 years old - 44,2.

Age-related features of growth and development of skeletal muscles. The following pattern of growth and development of skeletal muscles is observed at different age periods.

Period up to 1 year: more than the muscles of the pelvis, hips and legs, the muscles of the shoulder girdle and arms are developed.

The period from 2 to 4 years: in the arm and shoulder girdle, the proximal muscles are much thicker than the distal ones, the superficial muscles are thicker than the deep ones, the functionally active muscles are thicker than the less active ones. The fibers grow especially fast in the longissimus dorsi muscle and in the gluteus maximus muscle.

The period from 4 to 5 years: the muscles of the shoulder and forearm are developed, the muscles of the hands are not sufficiently developed. In early childhood, the muscles of the trunk develop much faster than the muscles of the arms and legs.

The period from 6 to 7 years: there is an acceleration in the development of the muscles of the hand, when the child begins to do light work and learn to write. The development of the flexors is ahead of the development of the extensors.

In addition, the weight and physiological diameter of the flexors are greater than those of the extensors. The muscles of the fingers, especially the flexors that are involved in the capture of objects, have the greatest weight and physiological diameter. Compared with them, the flexors of the hand have a relatively smaller weight and physiological diameter.

Period up to 9 years: the physiological diameter of the muscles that cause finger movements increases, while the muscles of the wrist and elbow joints grow less intensively.

Period up to 10 years: the diameter of the long flexor of the thumb by the age of 10 reaches almost 65% of the length of the diameter of an adult.

Period from 12 to 16 years: the muscles that ensure the vertical position of the body grow, especially the iliopsoas, which plays an important role in walking. By the age of 15-16, the thickness of the fibers of the iliopsoas muscle becomes the largest.

The anatomical diameter of the shoulder in the period from 3 to 16 years increases in boys by 2,5-3 times, in girls - less.

The deep muscles of the back in the first years of life in children are still weak, their tendon-ligamentous apparatus is also underdeveloped, however, by the age of 12-14, these muscles are strengthened by the tendon-ligamentous apparatus, but less than in adults.

The abdominal muscles in newborns are not developed. From 1 year to 3 years, these muscles and their aponeuroses differ, and only by the age of 14-16 the anterior wall of the abdomen is strengthened almost in the same way as in an adult. Up to 9 years, the rectus abdominis muscle grows very intensively, its weight increases almost 90 times compared to the weight of a newborn, the internal oblique muscle - more than 70 times, the external oblique - 67 times, the transverse - 60 times. These muscles resist the gradually increasing pressure of the internal organs.

In the biceps muscle of the shoulder and the quadriceps muscle of the thigh, muscle fibers thicken: by 1 year - twice; by 6 years - five times; by the age of 17 - eight times; by the age of 20 - 17 times.

Muscle growth in length occurs at the junction of muscle fibers and tendons. This process continues until the age of 23-25. From 13 to 15 years, the contractile part of the muscle grows especially quickly. By the age of 14-15, muscle differentiation reaches a high level. The growth of fibers in thickness continues up to 30-35 years. The diameter of the muscle fibers thickens: by 1 year - twice; by 5 years - five times; by the age of 17 - eight times; by the age of 20 - 17 times.

Muscle mass especially intensively increases in girls at 11-12 years old, in boys - at 13-14 years old. In adolescents, in two to three years, the mass of skeletal muscles increases by 12%, while in the previous 7 years - only by 5%. The weight of skeletal muscles in adolescents is approximately 35% in relation to body weight, while muscle strength increases significantly. The muscles of the back, shoulder girdle, arms and legs develop significantly, which causes increased growth of tubular bones. The correct selection of physical exercises contributes to the harmonious development of skeletal muscles.

Age-related features of the structure of skeletal muscles. The chemical composition and structure of skeletal muscles also change with age. The muscles of children contain more water and less dense substances than those of adults. The biochemical activity of red muscle fibers is greater than white ones. This is explained by differences in the number of mitochondria or in the activity of their enzymes. The amount of myoglobin (an indicator of the intensity of oxidative processes) increases with age. In a newborn, skeletal muscle contains 0,6% myoglobin, in adults it is 2,7%. In addition, children contain relatively less contractile proteins - myosin and actin. With age, this difference decreases.

Muscle fibers in children contain relatively more nuclei, they are shorter and thinner, but with age, both their length and thickness increase. Muscle fibers in newborns are thin, tender, their transverse striation is relatively weak and surrounded by large layers of loose connective tissue. Relatively more space is occupied by tendons. Many nuclei within muscle fibers do not lie near the cell membrane. Myofibrils are surrounded by clear layers of sarcoplasm.

The following dynamics of changes in the structure of skeletal muscles depending on age is observed.

1. At 2-3 years old, muscle fibers are twice as thick as in newborns, they are denser, the number of myofibrils increases, and the number of sarcoplasms decreases, the nuclei are adjacent to the membrane.

2. At 7 years old, the thickness of muscle fibers is three times thicker than in newborns, and their transverse striation is clearly expressed.

3. By the age of 15-16, the structure of muscle tissue becomes the same as in adults. By this time, the formation of the sarcolemma is completed.

The maturation of muscle fibers can be traced by a change in the frequency and amplitude of biocurrents recorded from the biceps muscle of the shoulder when holding the load:

▪ in children 7-8 years old, as the time of holding the load increases, the frequency and amplitude of biocurrents decrease more and more. This proves the immaturity of some of their muscle fibers;

▪ in children 12-14 years old, the frequency and amplitude of biocurrents do not change during 6-9 seconds of holding the load at maximum height or decrease at a later date. This indicates the maturity of the muscle fibers.

In children, unlike adults, the muscles are attached to the bones further from the axes of rotation of the joints, therefore, their contraction is accompanied by less loss of strength than in adults. With age, the ratio between the muscle and its tendon, which grows more intensively, changes significantly. As a result, the nature of the attachment of the muscle to the bone changes, therefore, the efficiency increases. Approximately by the age of 12-14, the "muscle-tendon" relationship, which is typical for an adult, stabilizes. In the girdle of the upper extremities up to 15 years, the development of the muscular belly and tendons occurs equally intensively, after 15 and up to 23-25 ​​years the tendon grows more intensively.

The elasticity of children's muscles is about twice as high as that of adults. When contracted, they shorten more, and when stretched, they lengthen more.

Muscle spindles appear on the 10-14th week of uterine life. An increase in their length and diameter occurs in the first years of a child's life. In the period from 6 to 10 years, the transverse size of the spindles changes slightly. In the period of 12-15 years, muscle spindles complete their development and have the same structure as in adults at the age of 20-30.

The beginning of the formation of sensitive innervation occurs at 3,5-4 months of uterine life, and by 7-8 months the nerve fibers reach significant development. By the time of birth, afferent nerve fibers are actively myelinated.

The muscle spindles of a single muscle have the same structure, but their number and the level of development of individual structures in different muscles are not the same. The complexity of their structure depends on the amplitude of movement and the force of muscle contraction. This is due to the coordination work of the muscle: the higher it is, the more muscle spindles in it and the more difficult they are. In some muscles, there are no muscle spindles that are not subject to stretching. Such muscles, for example, are the short muscles of the palm and foot.

Motor nerve endings (myoneural apparatus) appear in a child in the uterine period of life (at the age of 3,5-5 months). In different muscles they develop in the same way. By the time of birth, the number of nerve endings in the muscles of the arm is greater than in the intercostal muscles and muscles of the lower leg. In a newborn, the motor nerve fibers are covered with a myelin sheath, which thickens greatly by the age of 7. By the age of 3-5, the nerve endings become much more complicated, by the age of 7-14 they are even more differentiated, and by the age of 19-20 they reach full maturity.

Age-related changes in muscle excitability and lability. For the functioning of the muscular system, not only the properties of the muscles themselves are important, but also age-related changes in the physiological properties of the motor nerves that innervate them. To assess the excitability of nerve fibers, a relative indicator expressed in time units is used - chronaxy. In newborns, a more elongated chronaxia is observed. During the first year of life, the level of chronaxy decreases by approximately 3-4 times. In subsequent years, the value of chronaxy gradually shortens, but in school-age children it still exceeds the chronaxy of an adult. Thus, a decrease in chronaxy from birth to the school period indicates that the excitability of nerves and muscles increases with age.

For children 8-11 years old, as well as for adults, the excess of flexor chronaxy over extensor chronaxy is characteristic. The difference in the chronaxy of the antagonist muscles is most pronounced on the arms than on the legs. The chronaxia of the distal muscles exceeds that of the proximal muscles. For example, the chronaxia of the muscles of the shoulder is approximately two times shorter than the chronaxia of the muscles of the forearm. Less toned muscles have a longer chronaxy than more toned ones. For example, the biceps femoris and tibialis anterior have longer chronaxies than their antagonists, the quadriceps femoris and gastrocnemius. The transition from light to darkness lengthens the chronaxy, and vice versa.

During the day, in children of primary school age, chronaxy changes. After 1-2 general education lessons, there is a decrease in motor chronaxy, and by the end of the school day it often recovers to its previous level or even increases. After easy general education lessons, motor chronaxia most often decreases, and after difficult lessons it increases.

As we grow older, fluctuations in motor chronaxy gradually decrease, while chronaxy of the vestibular apparatus increases.

Functional mobility, or lability, in contrast to chronaxy, determines not only the shortest time required for the onset of excitation, but also the time required for completion of excitation and restoration of the tissue's ability to give new subsequent excitation impulses. The faster the skeletal muscle reacts, the more excitation impulses pass through it per unit time, the greater its lability. Consequently, muscle lability increases with an increase in the mobility of the nervous process in motor neurons (acceleration of the transition of excitation into inhibition), and vice versa - with an increase in the speed of muscle contraction. The slower the muscles react, the less their lability. In children, lability increases with age, by the age of 14-15 it reaches the level of adult lability.

Change in muscle tone. In early childhood, there is significant tension in certain muscles, such as the hands and hip flexors, due to the involvement of skeletal muscles in generating heat at rest. This muscle tone is of reflex origin and decreases with age.

The tone of skeletal muscles is manifested in their resistance to active deformation during compression and stretching. At the age of 8-9 years, in boys, muscle tone, for example, the muscles of the back of the thigh, is higher than in girls. By the age of 10-11, muscle tone decreases, and then again increases significantly. The greatest increase in skeletal muscle tone is observed in adolescents aged 12-15, especially boys, in whom it reaches youthful values. With the transition from pre-preschool to preschool age, there is a gradual cessation of the participation of skeletal muscles in heat production at rest. At rest, the muscles become more and more relaxed.

In contrast to the voluntary tension of skeletal muscles, the process of their voluntary relaxation is more difficult to achieve. This ability increases with age, so the stiffness of movements decreases in boys up to 12-13 years old, in girls - up to 14-15 years old. Then the reverse process occurs: the stiffness of movements increases again from the age of 14-15, while in boys aged 16-18 it is significantly greater than in girls.

Sarcomere structure and mechanism of muscle fiber contraction. A sarcomere is a repeating segment of myofibril, consisting of two halves of a light (optically isotropic) disk (I-disc) and one dark (anisotropic) disk (A-disc). Electron microscopic and biochemical analysis revealed that the dark disk is formed by a parallel bundle of thick (diameter about 10 nm) myosin filaments, the length of which is about 1,6 μm. The molecular weight of the myosin protein is 500 D. The heads of myosin molecules (000 nm long) are located on the myosin filaments. The light discs contain thin filaments (20 nm in diameter and 5 µm in length), which are built from protein and actin (molecular weight - 1 D), as well as tropomyosin and troponin. In the region of the Z-line, delimiting adjacent sarcomeres, a bundle of thin filaments is held together by a Z-membrane.

The ratio of thin and thick filaments in the sarcomere is 2: 1. The myosin and actin filaments of the sarcomere are arranged so that the thin filaments can freely enter between the thick ones, i.e., “move” into the A-disk, this happens during muscle contraction. Therefore, the length of the light part of the sarcomere (I-disk) can be different: with passive stretching of the muscle, it increases to a maximum, with contraction, it can decrease to zero.

The mechanism of contraction is the movement (pulling) of thin filaments along the thick filaments to the center of the sarcomere due to the "rowing" movements of the myosin heads, which periodically attach to the thin filaments, forming transverse actomyosin bridges. Investigating the movements of the bridges using the X-ray diffraction method, it was determined that the amplitude of these movements is 20 nm, and the frequency is 5-50 oscillations per second. In this case, each bridge either attaches and pulls the thread, then detaches in anticipation of a new attachment. A huge number of bridges work randomly, so their total thrust is uniform in time. Numerous studies have established the following mechanism for the cyclic operation of the myosin bridge.

1. At rest, the bridge is charged with energy (myosin is phosphorylated), but it cannot connect to the actin filament, since a system of tropomyosin filament and troponin globule is wedged between them.

2. Upon activation of the muscle fiber and the appearance of Ca + 2 ions in the myoplasm (in the presence of ATP), troponin changes its conformation and moves the tropomyosin thread away, opening up the possibility for the myosin head to connect with actin.

3. The connection of the head of phosphorylated myosin with actin sharply changes the conformation of the bridge (its "bending" occurs) and moves the actin filaments by one step (20 nm), and then the bridge breaks. The energy required for this appears as a result of the breakdown of the macroergic phosphate bond included in phosphoryl lactomyosin.

4. Then, due to a drop in the local concentration of Ca + 2 and its detachment from troponin, tropomyosin again blocks actin, and myosin is again phosphorylated due to ATP. ATP not only charges the systems for further work, but also contributes to the temporary separation of the threads, that is, it plasticizes the muscle, making it capable of stretching under the influence of external forces. It is believed that one ATP molecule is consumed per working movement of one bridge, and actomyosin plays the role of ATPase (in the presence of Mg + 2 and Ca + 2). With a single contraction, a total of 0,3 μM ATP is spent per 1 g of muscle.

Thus, ATP plays a dual role in muscle work: on the one hand, by phosphorylation of myosin, it provides energy for contraction, on the other hand, being in a free state, it provides muscle relaxation (its plasticization). If ATP disappears from the myoplasm, a continuous contraction develops - contracture.

All these phenomena can be demonstrated on isolated actomyosin filament complexes: such filaments harden without ATP (rigor is observed), in the presence of ATP they relax, and when Ca+2 is added they produce a reversible contraction similar to normal.

Muscles are permeated with blood vessels, through which nutrients and oxygen come to them with blood, and metabolic products are carried out. In addition, the muscles are also rich in lymphatic vessels.

Muscles have nerve endings - receptors that perceive the degree of contraction and stretching of the muscle.

Major muscle groups of the human body. The shape and size of muscles depend on the work they perform. The muscles are distinguished between long, broad, short and circular. Long muscles are located on the limbs, short ones - where the range of movement is small (for example, between the vertebrae). The broad muscles are located mainly on the torso, in the walls of the body cavities (for example, the abdominal muscles, back, chest). Circular muscles - sphincters - lie around the openings of the body, narrowing them when contracting.

By function, the muscles are divided into flexors, extensors, adductors and abductors, as well as muscles that rotate inward and outward.

I. The muscles of the trunk include:

1) chest muscles;

2) abdominal muscles;

3) back muscles.

II. The muscles located between the ribs (intercostal), as well as other muscles of the chest, are involved in the function of breathing. They are called respiratory muscles. These include the diaphragm, which separates the chest cavity from the abdominal cavity.

III. Well-developed chest muscles move and strengthen the upper limbs on the body. These include:

1) pectoralis major muscle;

2) pectoralis minor muscle;

3) serratus anterior muscle.

IV. The abdominal muscles perform various functions. They form the wall of the abdominal cavity and, due to their tone, keep the internal organs from moving, lowering and falling out. By contracting, the abdominal muscles act on the internal organs as the abdominal press, contributing to the release of urine, feces and childbirth. The contraction of the abdominal muscles also helps the movement of blood in the venous system, the implementation of respiratory movements. The abdominal muscles are involved in forward flexion of the spinal column.

Due to the possible weakness of the abdominal muscles, not only the prolapse of the abdominal organs occurs, but also the formation of hernias. A hernia is the exit of internal organs (intestines, stomach, greater omentum) from the abdominal cavity under the skin of the abdomen.

V. The muscles of the abdominal wall include:

1) rectus abdominis muscle;

2) pyramidalis muscle;

3) quadratus lumborum muscle;

4) broad abdominal muscles (external and internal, oblique and transverse).

VI. A dense tendon cord runs along the midline of the abdomen - the so-called white line. On the sides of it is the rectus abdominis muscle, which has a longitudinal direction of the fibers.

VII. On the back are numerous muscles along the spinal column. These are deep back muscles. They are attached mainly to the processes of the vertebrae and are involved in the movements of the spinal column back and to the side.

VIII. The superficial back muscles include:

1) trapezius muscle of the back;

2) latissimus dorsi muscle. They provide movement of the upper limbs and chest.

IX. Among the muscles of the head, there are:

1) chewing muscles. These include: temporal muscle; chewing muscle; pterygoid muscles. Contractions of these muscles cause complex chewing movements of the lower jaw;

2) facial muscles. These muscles with one or sometimes two ends are attached to the skin of the face. When contracted, they displace the skin, creating a certain facial expression, that is, one or another facial expression. The facial muscles also include the circular muscles of the eye and mouth.

X. The muscles of the neck throw back the head, tilt and turn it.

XI. The scalene muscles raise the ribs, thus participating in inspiration.

XII. The muscles attached to the hyoid bone, during contraction, change the position of the tongue and larynx when swallowing and pronouncing various sounds.

XIII. The belt of the upper limbs is connected to the body only in the area of ​​the sternoclavicular joint. It is strengthened by the muscles of the torso:

1) trapezius muscle;

2) pectoralis minor muscle;

3) rhomboid muscle;

4) serratus anterior muscle;

5) the levator scapulae muscle.

XIV. The muscles of the limb girdle move the upper limb in the shoulder joint. The most important of these is the deltoid muscle. When contracted, this muscle flexes the arm at the shoulder joint and abducts the arms to a horizontal position.

XV. In the area of ​​​​the shoulder in front there is a group of flexor muscles, in the back - extensor muscles. Among the muscles of the anterior group, the biceps of the shoulder is distinguished, the back - the triceps of the shoulder.

XVI. The muscles of the forearm on the front surface are represented by flexors, on the back - by extensors.

XVII. Among the muscles of the hand are:

1) palmaris longus muscle;

2) flexors of the fingers.

XVIII. The muscles located in the lower extremity belt area move the leg at the hip joint, as well as the spinal column. The anterior muscle group is represented by one large muscle - the iliopsoas. The posterior external group of muscles of the pelvic girdle includes:

1) large muscle;

2) gluteus medius muscle;

3) gluteus minimus muscle.

XIX. The legs have a more massive skeleton than the arms. Their musculature has more strength, but less variety and limited range of motion.

On the thigh in front is the longest in the human body (up to 50 cm) tailor muscle. It flexes the leg at the hip and knee joints.

The quadriceps femoris muscle lies deeper than the sartorius muscle, while it fits the femur from almost all sides. The main function of this muscle is to extend the knee joint. When standing, the quadriceps muscle does not allow the knee joint to bend.

On the back of the lower leg is the gastrocnemius muscle, which flexes the lower leg, flexes and somewhat rotates the foot outward.

3.4. The role of muscle movements in the development of the body

Studies have shown that from the first years of life, the movements of the child play a significant role in the functioning of speech. It has been proven that the formation of speech in interaction with the motor analyzer is particularly successful.

Physical education, which consists in strengthening the health and physical improvement of children, significantly affects the development of thinking, attention and memory. This is not just a biological meaning: there is an expansion of human capabilities in the perception, processing and use of information, the assimilation of knowledge, a versatile study of the surrounding nature and oneself.

Physical exercises improve the muscular system and vegetative functions (respiration, blood circulation, etc.), without which it is impossible to perform muscular work. In addition, exercise stimulates the functions of the central nervous system.

However, physical exercises are the leading, but not the only factor influencing the body in the course of physical education. It is very important to remember the general rational mode, proper organization of nutrition and sleep. Of great importance is hardening, etc.

Age-related patterns of motor development. Age-related physiology has collected a huge amount of factual material about age-related patterns of development of motor skills in children and adolescents.

The most significant changes in motor function are observed in primary school age. In accordance with the morphological data, the nervous structures of the child's motor apparatus (spinal cord, pathways) mature at the earliest stages of ontogenesis. With regard to the central structures of the motor analyzer, it has been established that their morphological maturation occurs at the age of 7 to 12 years. In addition, by this time, the sensory and motor endings of the muscular apparatus reach full development. The development of the muscles themselves and their growth continue until the age of 25-30, which explains the gradual increase in the absolute strength of the muscles.

Thus, we can say that the main tasks of school physical education must be solved as fully as possible in the first eight years of schooling, otherwise the most productive age periods for the development of children's motor abilities will be missed.

Period 7-11 years. Studies show that schoolchildren during this period have relatively low levels of muscle strength. Strength and especially static exercises cause them to quickly fatigue. Children of primary school age are more adapted to short-term speed-strength exercises, but they should be gradually taught to maintain static postures, which has a positive effect on posture.

Period 14-17 years. This period is characterized by the most intensive growth of muscle strength in boys. In girls, the growth of muscle strength begins somewhat earlier. This difference in the dynamics of the development of muscle strength is most pronounced at 11-12 years of age. The maximum increase in relative strength, i.e. strength per kilogram of mass, is observed up to 13-14 years. Moreover, by this age, the indicators of the relative muscle strength of boys significantly exceed the corresponding indicators for girls.

Endurance. Observations show that children 7-11 years old have a low level of endurance for dynamic work, but from 11-12 years old boys and girls become more resilient. By age 14, muscular endurance is 50-70%, and by age 16, it is about 80% of adult endurance.

Interestingly enough, there is no relationship between endurance to static loads and muscle strength. However, the level of endurance depends, for example, on the degree of puberty. Experience shows that walking, slow running, skiing are good means of developing endurance.

The time when the level of motor qualities can be raised with the help of physical education means is adolescence. However, it should be remembered that this period coincides with the biological restructuring of the body associated with puberty. Therefore, the teacher requires exceptional attention to the correct planning of physical activity.

Physical activity planning. At the age of 7-11, there is an intensive development of speed of movements (frequency, speed of movements, reaction time, etc.), therefore, in adolescence, schoolchildren adapt very well to high-speed loads, which is expressed in high performance in running, swimming, i.e. Where speed and responsiveness are of paramount importance. Also during this period, there is greater mobility of the spinal column and high elasticity of the ligamentous apparatus. All these morphofunctional prerequisites are important for the development of such a quality as flexibility (note that by the age of 13-15 this indicator reaches its maximum).

At the age of 7-10 years, dexterity of movements develops at an accelerated pace. At this age, the mechanism of regulation of movements in children is still insufficiently perfect; nevertheless, they successfully master the basic elements of such complex actions as swimming, skating, cycling, etc. At the same time, preschool children and younger schoolchildren acquire skills related to with the accuracy of hand movements, reproduction of the given efforts. These parameters reach a relatively high level of development by adolescence.

By the age of 12-14, the accuracy of throws, throwing at a target, and the accuracy of jumps increase. At the same time, according to some data, there is a deterioration in the coordination of movements in adolescents associated with morphological and functional changes during puberty.

We can say that adolescence has great potential for improving the motor apparatus. This is confirmed by the achievements of adolescents in rhythmic and artistic gymnastics, figure skating, and other sports. However, when organizing physical education in high school, it should be taken into account that the process of body formation in 16-17-year-old schoolchildren has not yet been completed, therefore, for those who do not systematically go in for sports, it is necessary to dose the loads associated with the manifestation of maximum strength and endurance. These facts, which testify to the heterochronous development of motor qualities, should be taken into account and strive for the harmonious development of different aspects of the motor skills of children, adolescents and young people.

In addition, the development of motor skills varies over a fairly wide range in children of the same age. Therefore, physical education should take into account the functional capabilities of each child, while not forgetting about age characteristics. The child needs to be taught skills and abilities, for the achievement of which he already has morphological and functional prerequisites.

Normalization of physical activity. Normalizing the volume of physical activity at different stages of ontogenesis is another important problem of physical education at school. Of course, the more a child moves daily, the better for the development of his motor functions. The preschooler is on the move almost continuously, except for the periods allocated for sleep and eating. After entering school, children's physical activity is reduced by half. Due to the independent motor activity of students in grades I-III, only 50% of the optimal number of movements is realized. That’s why organized forms of physical exercise are so important at this age.

At the same time, even in healthy, properly developing schoolchildren, only spontaneous motor activity and physical education lessons cannot provide the required daily range of motion. A physical education lesson compensates on average 11% of the required daily number of movements. In total, morning exercises, gymnastics before classes at school, physical education breaks in classes, outdoor games during breaks, walks with games after classes make up to 60% of the required daily range of motion for children 7-11 years old.

Research Institute of Physiology of Children and Adolescents of the Academy of Medical Sciences (now - the Institute of Developmental Physiology of the Russian Academy of Education) proved that 5-6 hours of physical exercise per week (two physical education lessons, daily physical culture and health-improving forms of work, classes in the sports section) contribute to favorable physical development, improvement the general physiological and immune reactivity of the body and are the average optimal and necessary norm. It has been established that daily 15-20-minute outdoor games for children in grades I-II after the third lesson increase mental performance by 3-4 times.

Adolescents need active rest after the third or fourth lesson, as well as before preparing homework, while physical education or outdoor recreation after the fifth or sixth lesson leads to a deterioration in performance indicators and inhibition of the phagocytic activity of blood leukocytes.

The importance of physical culture for the development of the musculoskeletal system. Skeletal muscles influence the course of metabolic processes and the functioning of internal organs: respiratory movements are carried out by the chest muscles and diaphragm, and the abdominal muscles normalize the activity of the abdominal organs, blood circulation and breathing. The power and size of muscles directly depend on exercise and training. This is due to the fact that during work the blood supply to the muscles increases, the regulation of their activity by the nervous system improves, which leads to the growth of muscle fibers, i.e., an increase in muscle mass. The result of training the muscular system is the ability to perform physical work and endurance.

An increase in the physical activity of children and adolescents leads to changes in the skeletal system and a more intensive growth of their body. Exercise strengthens bones and makes them more resistant to stress and injury. No less important is the fact that sports, physical exercises, taking into account the age characteristics of children and adolescents, eliminate posture disorders.

Versatile muscular activity contributes to an increase in the body's working capacity, while reducing the energy costs of the body to perform work. Systematic physical activity forms a more perfect mechanism of respiratory movements. This is expressed in an increase in the depth of breathing, vital capacity of the lungs. During muscular work, pulmonary ventilation can reach up to 120 l / min. Deep breathing of trained people better saturates the blood with oxygen. Blood vessels become more elastic during training, which improves the conditions for the movement of blood.

If a person does not move enough according to the nature of his work, does not go in for sports, then in middle and old age, the elasticity and contractility of his muscles decrease. This leads to a number of unpleasant consequences: his muscles become flabby; as a result of weakness of the abdominal muscles, the internal organs prolapse and the function of the gastrointestinal tract is disturbed; weakness of the back muscles causes a change in posture, stoop gradually develops, coordination of movements is disturbed.

Thus, the favorable effect exerted by physical exercises on the formation of a healthy, strong, hardy person with a correct physique and harmoniously developed muscles is obvious.

3.5. Features of the growth of the bones of the skull

The skull is the skeleton of the head. In accordance with the features of development, structure and functions, two sections of the skull are distinguished: cerebral and facial (visceral). The brain part of the skull forms a cavity inside which the brain is located. The facial region forms the bone base of the respiratory apparatus and the alimentary canal.

The medulla of the skull consists of a roof (or vault of the skull) and a base. The parietal bone of the cranial vault is a quadrangular plate with four serrated edges. Two parietal bones connected by sutures form the parietal tubercle. In front of the parietal bones lies the frontal bone, most of which is represented by scales.

The convex part of the facial part of the skull is formed by the frontal tubercles, below which are the bones that form the walls of the orbits. Between the eye sockets is the nasal part, adjacent to the nasal bones, below which are the cells of the ethmoid bone.

Behind the parietal bones is the occipital bone, thanks to which the base of the skull is formed and the skull is connected to the spine. On the sides of the roof of the skull are two temporal bones, also involved in the formation of the base of the skull. Each of them contains the corresponding sections of the organ of hearing and the vestibular apparatus. At the base of the skull is the sphenoid bone.

The bones of the base of the skull, developed from cartilage, are connected by cartilage tissue, which is replaced by bone tissue with age. The bones of the roof, developed from the connective tissue, are connected by connective tissue sutures, which become bony in old age. This also applies to the facial region of the skull.

The facial section of the skull consists of the upper jaw, zygomatic, lacrimal, ethmoid, palatine, nasal bones, inferior nasal concha, vomer, mandible and hyoid bone.

Age features of the skull. The brain and facial parts of the skull are formed from mesenchyme. The bones of the skull develop in a primary and secondary way (see 3.1). The skull of children differs significantly from the skull of adults in its size compared to body size, structure and proportions of individual parts of the body. In a newborn, the cerebral part of the skull is six times larger than the facial part, in an adult - 2,5 times. In other words, in a newborn, the facial part of the skull is relatively smaller than the brain part. With age, these differences disappear. Moreover, not only the shape of the skull and its constituent bones changes, but also the number of skull bones.

From birth to 7 years of age, the skull grows unevenly. There are three waves of acceleration in the growth of the skull:

1) up to 3-4 years;

2) from 6 to 8 years;

3) from 11 to 15 years.

The fastest growth of the skull occurs in the first year of life. The occipital bone protrudes and, together with the parietal bones, grows especially rapidly. The ratio of the volume of the skull of a child and an adult is as follows: in a newborn, the volume of the skull is equal to one third of the volume of an adult; at 6 months - one second; at 2 years - two-thirds.

During the first year of life, the thickness of the walls of the skull increases three times. In the first or second year of life, fontanelles (areas of connective tissue) are closed and replaced with bone sutures: occipital - in the second month; wedge-shaped - in the second or third month; mastoid - at the end of the first or beginning of the second year; frontal - in the second year of life. By the age of 1,5 years, the fontanelles are completely overgrown, and by the age of four, cranial sutures are formed.

At the age of 3 to 7 years, the base of the skull, together with the occipital bone, grows faster than the vault. At the age of 6-7 years, the frontal bone is completely fused. By the age of 7, the base of the skull and the foramen magnum reach a relatively constant value, and there is a sharp slowdown in the development of the skull. From 7 to 13 years of age, the growth of the base of the skull slows down even more.

At 6-7 and at 11-13 years old, the growth of the bones of the cranial vault increases slightly, and by the age of 10 it basically ends. The capacity of the skull by 10 years is 1300 cubic meters. cm (for comparison: in an adult - 1500-1700 cc).

From 13 to 14 years of age, the frontal bone grows intensively, the development of the facial section of the skull in all directions predominates, and the characteristic features of the physiognomy develop.

At the age of 18-20, the formation of synostosis between the bodies of the occipital and sphenoid bones ends. As a result, the growth of the base of the skull in length stops. Full fusion of the bones of the skull occurs in adulthood, but the development of the skull continues. After 30 years, the sutures of the skull gradually become bony.

The development of the lower jaw is directly dependent on the work of the masticatory muscles and the condition of the teeth. In its growth, two waves of acceleration are observed:

1) up to 3 years;

2) from 8 to 11 years.

Head sizes in schoolchildren increase very slowly. At all ages, boys have a larger average head circumference than girls. The largest increase in the head is observed between the ages of 11 and 17, i.e., during puberty (for girls - by 13-14 years, and for boys - by 13-15).

The ratio of head circumference to height decreases with age. If at 9-10 years old the head circumference is on average 52 cm, then at 17-18 years old it is 55 cm. In men, the capacity of the cranial cavity is approximately 100 cubic meters. see more than women.

There are also individual features of the skull. These include two extreme forms of skull development: long-headed and short-headed.

3.6. Spinal growth. The spine of an adult and a child

The spine consists of 24 free vertebrae (7 cervical, 12 thoracic and 5 lumbar) and 9-10 non-free (5 sacral and 4-5 coccygeal). Free vertebrae, articulated among themselves, are connected by ligaments, between which there are elastic intervertebral discs made of fibrocartilage. The sacral and coccygeal vertebrae are fused to form the sacrum and coccyx. The vertebrae develop from cartilage tissue, the thickness of which decreases with age.

There are four stages in the development of the epiphyses of the vertebrae: up to 8 years - the cartilaginous epiphysis; from 9 to 13 years - calcification of the epiphysis; from 14 to 17 years old - bone epiphysis; after 17 years - the fusion of the epiphysis with the vertebral body.

From 3 to 15 years, the size of the lower lumbar vertebrae increases more than the upper thoracic. This is due to an increase in body weight, its pressure on the underlying vertebrae.

From the age of 3, the vertebrae grow equally in height and width; from 5-7 years old - more in height.

At the age of 6-8 years, ossification centers are formed in the upper and lower surfaces of the vertebral bodies and at the ends of the spinous and transverse processes. Up to 5 years, the spinal canal develops especially rapidly. Since the vertebral bodies grow faster than the arches, the capacity of the canal decreases relatively, which corresponds to a decrease in the relative size of the spinal cord.

By the age of 10, the development of the spinal canal is completed, but the structure of the vertebral body continues to develop in children of senior school age.

By the age of 25, ossification of the cervical, thoracic and lumbar vertebrae ends, by the age of 20 - the sacral, by the age of 30 - the coccygeal vertebrae.

The length of the spine increases especially sharply during the first and second years of life, then the growth of the spine slows down and accelerates again from 7 to 9 years (more in girls than in boys). From 9 to 14 years old, the increase in the length of the spine in boys and girls slows down several times, and from 14 to 20 years old even more.

In boys, the growth of the spine ends after 20 years, in girls it grows up to 18 years, i.e., the growth of the spine in women stops earlier than in men. The average length of the spine in men is 70-73 cm, in women - 66-69 cm. By the end of puberty, the growth of the length of the spine is almost completed (approximately equal to 40% of the body length).

The mobility of the spine depends on the height of the intervertebral cartilage discs and their elasticity, as well as on the frontal and sagittal size of the vertebral bodies. In an adult, the total height of the intervertebral discs is equal to one fourth of the height of the movable part of the spine. The higher the intervertebral discs, the greater the mobility of the spine. The height of the discs in the lumbar region is one third of the height of the body of the adjacent vertebra, in the upper and lower parts of the thoracic region - one fifth, in its middle part - one sixth, in the cervical region - one fourth, therefore, in the cervical and lumbar regions, the spine has the greatest mobility.

By the age of 17-25, as a result of the replacement of intervertebral discs with bone tissue, the spine becomes immobile in the sacral region.

The flexion of the spine is greater than its extension. The greatest flexion of the spine occurs in the cervical region (70°), less in the lumbar, and the least in the thoracic region. Tilts to the side are greatest between the thoracic and lumbar regions (100°). The greatest circular motion is observed in the cervical spine (75°), it is almost impossible in the lumbar spine (5°). Thus, the cervical spine is the most mobile, the lumbar is less mobile, and the thoracic is the least mobile, because its movements are inhibited by the ribs.

The mobility of the spine in children, especially 7-9 years old, is much greater than in adults. This depends on the relatively larger size of the intervertebral discs and their greater elasticity. The development of intervertebral discs takes a long time and ends by the age of 17-20.

Physiological curves of the spine. After birth, the spine acquires four physiological curves. At 6-7 weeks, with the raising of the child’s head, anterior bending (lordosis) occurs in the cervical region. At 6 months, as a result of sitting, posterior curves (kyphosis) are formed in the thoracic and sacral regions. At 1 year of age, with the onset of standing, lordosis forms in the lumbar region. Initially, these physiological curves of the spine are held by the muscles, and then by the ligaments, cartilage and bones of the vertebrae.

By the age of 3-4 years, the curves of the spine gradually increase as a result of standing, walking, gravity and muscle work. By the age of 7, cervical lordosis and thoracic kyphosis are finally formed; by the age of 12 - lumbar lordosis, which is finally formed by the period of puberty. Lifting excessive weights increases lumbar lordosis.

In adults, the physiological curves of the spine are distributed as follows.

1. Cervical bend: moderate lordosis, formed by all cervical and upper thoracic vertebrae; the greatest bulge falls on the fifth or sixth cervical vertebrae.

2. Strong thoracic kyphosis, the greatest bulge falls on the sixth-seventh thoracic vertebrae.

3. Strong lumbar lordosis, formed by the last thoracic and all lumbar vertebrae.

4. Strong sacrococcygeal kyphosis.

Due to the spring movement of the spine, the magnitude of its bends can change. As a result of changes in the curvature of the spine and the height of the intervertebral discs, the length of the spine also changes: with age and during the day. During the day, a person's height varies within 1 cm, and sometimes 2-2,5 cm and even 4-6 cm. In the prone position, the length of the human body is 2-3 cm longer than in the standing position.

3.7. Chest development

The chest is made up of 12 pairs of ribs. The true ribs (the first - the seventh pair) are connected to the sternum with the help of cartilages, of the remaining five false ribs, the cartilaginous ends of the eighth, ninth and tenth pairs are connected to the cartilage of the overlying rib, and the eleventh and twelfth pairs do not have costal cartilages and have the greatest mobility, since end freely. The second - seventh pairs of ribs are connected to the sternum by small joints.

The ribs are connected to the vertebrae by joints, which, when the chest is raised, determine the movement of the upper ribs mainly forward, and the lower ribs to the sides.

The sternum is an unpaired bone in which three parts are distinguished: the handle, the body and the xiphoid process. The handle of the sternum articulates with the clavicle with the help of a joint containing an intracartilaginous disk (by the nature of the movements, it approaches the spherical joints).

The shape of the chest depends on age and gender. In addition, the shape of the chest changes due to the redistribution of the force of gravity of the body when standing and walking, depending on the development of the muscles of the shoulder girdle.

Age-related changes in the formation of the chest. The ribs develop from mesenchyme, which transforms into cartilage in the second month of uterine life. Their ossification begins in the fifth to eighth week, and that of the sternum in the sixth month. Ossification nuclei in the head and tubercle appear in the upper ten ribs at 5-6 years, and in the last two ribs at 15 years. The fusion of parts of the rib ends by the age of 18-25.

Up to 1-2 years, the rib consists of a spongy substance. From 3-4 years of age, a compact layer develops in the middle of the rib. From the age of 7, the compact layer grows along the entire rib. From the age of 10, the compact layer continues to grow in the region of the corner. By the age of 20, ossification of the ribs is completed.

In the xiphoid process, the nucleus of ossification appears at the age of 6-12 years. At the age of 15-16, the lower segments of the body of the sternum fuse. At the age of 25, the xiphoid process fuses with the body of the sternum.

The sternum develops from many paired ossification points that merge extremely slowly. Ossification of the manubrium and body of the sternum ends by the age of 21-25, the xiphoid process - by the age of 30. The fusion of the three parts of the sternum into one bone occurs much later, and not in all people. Thus, the sternum is formed and develops later than all other bones of the skeleton.

Chest shape. In humans, there are two extreme shapes of the chest: long, narrow and short, wide. The shape of the sternum also corresponds to them. Among the main shapes of the chest, there are conical, cylindrical and flat shapes.

The shape of the chest changes significantly with age. After birth and for the first few years of life, the ribcage is cone-shaped with the base facing down. From the age of 2,5-3 years, the growth of the chest goes parallel to the growth of the body, in connection with this, its length corresponds to the thoracic spine. Then the growth of the body accelerates, and the chest becomes relatively shorter. In the first three years, there is an increase in the circumference of the chest, which leads to the predominance of the transverse diameter in the upper part of the chest.

Gradually, the chest changes its conical shape and approaches that of an adult, that is, it takes the form of a cone with the base turned upward. The chest acquires its final shape by the age of 12-13, but is smaller than in adults.

Sex differences in chest shape and circumference. Sex differences in the shape of the chest appear from about 15 years of age. From this age, an intensive increase in the sagittal size of the chest begins. In girls, during inhalation, the upper ribs rise sharply, in boys - the lower ones.

Gender differences are also observed in the growth of the circumference of the chest. In boys, the circumference of the chest from 8 to 10 years old increases by 1-2 cm per year, by puberty (from 11 years old) - by 2-5 cm. In girls up to 7-8 years old, the chest circumference exceeds half the size of their growth. In boys, this ratio is observed up to 9-10 years, from this age half of the height becomes larger than the size of the chest circumference. From the age of 11, in boys, its growth is less than in girls.

Exceeding half of the height above the circumference of the chest depends on the growth rate of the body, which is greater than the growth rate of the circumference of the chest. The growth of the circumference of the chest is inferior to the addition of body weight, so the ratio of body weight to the circumference of the chest gradually decreases with age. The chest circumference grows most rapidly during puberty and in the summer-autumn period. Normal nutrition, good hygienic conditions and physical exercise have a dominant influence on the growth of the chest circumference.

The parameters of the development of the chest depend on the development of skeletal muscles: the more developed the skeletal muscles, the more developed the chest. Under favorable conditions, the circumference of the chest in children 12-15 years old is 7-8 cm more than under unfavorable conditions. In the first case, the circumference of the chest will equal half the height on average by the age of 15, and not by the age of 20-21, as in children who were in unfavorable living conditions.

Improper seating of children at a desk can lead to chest deformity and, as a result, a violation of the development of the heart, large vessels and lungs.

3.8. Features of the development of the pelvis and lower extremities. Skeleton of the lower extremities

The pelvic girdle consists of the pubic, ilium, and ischium bones, which develop independently and merge with age to form a pelvis, posteriorly connected to the sacral spine. The pelvis serves as a support for the internal organs and legs. Due to the mobility of the lumbar spine, the pelvis increases the range of motion of the leg.

The leg skeleton consists of the femur (thigh skeleton), the tibia and fibula (tibia skeleton) and the bones of the foot.

The tarsus is made up of the talus, calcaneus, navicular, cuboid, and three cuneiform bones. The metatarsus is made up of five metatarsal bones. The toes consist of phalanges: two phalanges in the first toe and three phalanges in the remaining fingers. Sesamoid ossicles are located, as in the hand, but are much better expressed. The largest sesamoid bone of the leg skeleton is the patella, located inside the tendon of the quadriceps femoris. It increases the shoulder strength of this muscle and protects the knee joint from the front.

Development of the pelvic bones. The most intensive growth of the pelvic bones is observed in the first three years of life. In the process of fusion of the pelvic bones, several stages can be distinguished: 5-6 years (beginning of fusion); 7-8 years (pubic and ischial bones fuse); 14-16 years (pelvic bones are almost fused); 20-25 years (end of complete fusion).

These terms must be taken into account in labor movements and physical exercises (especially for girls). With sharp jumps from a great height and when wearing high-heeled shoes, the non-united pelvic bones are displaced, which leads to their improper fusion and narrowing of the exit from the pelvic cavity, leading to difficulty in childbirth. Cohesion disorders are also caused by excessive improper sitting or standing, carrying heavy loads, especially when the load is unevenly distributed.

The size of the pelvis in men is smaller than in women. Distinguish between the upper (large) pelvis and the lower (small) pelvis. The transverse size of the entrance to the small pelvis in girls changes abruptly in several stages: at 8-10 years old (it increases very quickly); at 10-12 years old (there is some slowdown in its growth); from 12 to 14-15 years (growth increases again). The anteroposterior size increases more gradually; from the age of 9 it is less than the transverse. In boys, both sizes of the pelvis increase evenly.

Development of lower limb bones. By the time of birth, the femur consists of cartilage, only the diaphysis is bone. Synostosis in long bones ends between the ages of 18 and 24 years. The kneecap takes on the shape characteristic of an adult by the age of 10.

The development of the bones of the tarsus occurs much earlier than the bones of the wrist, the ossification nuclei in them (in the calcaneus, talus and cuboid bones) appear even in the uterine period. In the sphenoid bones, they occur at 1-3-4 years, in the scaphoid - at 4,5 years. At the age of 12-16, the ossification of the calcaneus ends.

The bones of the metatarsus ossify later than the bones of the tarsus, at the age of 3-6 years. Ossification of the phalanges of the foot occurs in the third or fourth year of life. The final ossification of the bones of the legs occurs: femoral, tibial and fibular - by 20-24 years; metatarsal - to 17-21 in men and to 14-19 in women; phalanges - by 15-21 in men and by 13-17 years in women.

From the age of 7, the legs grow faster in boys. The greatest ratio of leg length to body is achieved in boys by the age of 15, in girls - by 13 years.

The human foot forms an arch that rests on the calcaneus and the anterior ends of the metatarsal bones. The general arch of the foot is made up of the longitudinal and transverse arches. The formation of the arch of the foot in humans occurred as a result of upright walking.

For the formation of the arch of the foot, the development of the muscles of the legs, in particular those that hold the longitudinal and transverse arches, is of great importance. The arch allows you to evenly distribute the weight of the body, acts like a spring, softening the shock and shock of the body while walking. It protects the muscles, vessels and nerves of the plantar surface from pressure. Flattening of the arch (flat feet) develops with prolonged standing, carrying heavy weights, and wearing narrow shoes. Flat feet leads to violations of posture, the mechanics of walking.

3.9. Upper limb bone development

The skeleton of the upper limbs includes the shoulder girdle and the skeleton of the hand. The shoulder girdle consists of the scapula and collarbone, the skeleton of the arm consists of the shoulder, forearm and hand. The hand is divided into the wrist, metacarpus and fingers.

The shoulder blade is a flat, triangular-shaped bone located on the back. The clavicle is a tubular bone, one end of which articulates with the sternum and ribs, and the other with the scapula. The costoclavicular joint appears in children from 11-12 years old; it reaches its greatest development in adults.

The arm skeleton consists of the humerus (shoulder skeleton), the ulna and radius (forearm skeleton), and the bones of the hand.

The wrist consists of eight small bones arranged in two rows, forming a groove on the palm and a bulge on its back surface.

The metacarpus consists of five small tubular bones, of which the shortest and thickest is the thumb bone, the longest is the second bone, and each of the following bones is smaller than the previous one. The exception is the thumb (first) finger, which consists of two phalanges. The other four fingers have three phalanges. The largest phalanx is proximal, the smaller is the middle, and the smallest is the distal.

On the palmar surface, there are permanent sesamoid bones - inside the tendons between the metacarpal bone of the thumb and its proximal phalanx, and non-permanent - between the metacarpal bone and the proximal phalanx of the second and fifth fingers. The pisiform bone of the wrist is also a sesamoid bone.

The joints of the wrist, metacarpus and fingers are reinforced with a powerful ligamentous apparatus.

Age-related features of the development of the upper limbs. In a newborn, the clavicle is almost completely bone, the formation of an ossification nucleus in its sternal region occurs at 16-18 years, fusion with its body - at 20-25 years. Fusion of the ossification nucleus of the coracoid process with the body of the scapula occurs at 16-17 years. Synestosis of the acromial process with its body ends at 18-25 years.

All long bones in a newborn, such as the humerus, radius, ulna, have cartilaginous epiphyses and bone diaphyses. There are no bones in the wrist, and cartilage ossification begins: in the first year of life - in the capitate and hamate bones; at 2-3 years old - in a trihedral bone; at 3-4 years - in the lunate bone; at 4-5 years old - in the navicular bone; at 4-6 years old - in a large polygonal bone; at 7-15 years old - in the pisiform bone.

Sesamoid bones in the first metacarpophalangeal joint appear at 12-15 years of age. At the age of 15-18, the lower epiphysis of the humerus merges with its body, and the upper epiphyses merge with the bodies of the bones of the forearm. In the third year of life, ossification of the proximal and distal epiphyses of the phalanges occurs. "Bone age" determines the centers of ossification of the hand.

Ossification of the bones of the upper limbs ends: at 20-25 years old - in the collarbone, scapula and humerus; at 21-25 years old - in the radius; at 21-24 years old - in the ulna; at 10-13 years old - in the bones of the wrist; at 12 years old - in the metacarpus; at 9-11 years old - in the phalanges of the fingers.

Ossification ends in men on average two years later than in women. The last centers of ossification can be found in the clavicle and scapula at 18-20 years old, in the humerus - at 12-14 years old, in the radius - at 5-7 years old, in the ulna - at 7-8 years old, in the metacarpal bones and phalanges fingers - in 2-3 years. Ossification of sesamoid bones usually begins during puberty: in boys - at 13-14 years old, in girls - at 12-13. The beginning of the fusion of parts of the first metacarpal bone indicates the beginning of puberty.

3.10. Effect of furniture on posture. Hygienic requirements for school equipment

School furniture should correspond to the age-related changes in the growth and proportions of the children's body, exclude the possibility of damage to the body and be easy to keep clean.

Desk. This is the main type of school furniture. Selecting a desk that matches the child’s height and proper seating are the prevention of posture and vision problems. The standards approve five table numbers according to student height (in cm): A - 115-130, B - 130-145, C - 145-160, D - 160-175, D - 175-190.

For normal reading and writing conditions, the slope of the desk top should be 14-15°. A book or notebook should be placed freely on the table top of the school desk at an angle of 25 ° to its edge.

Chair. The back of the chair provides an additional point of support for the body in the lumbosacral region. The curve of the chair back should be at the level of the lumbar curve of the spine and correspond to its height.

The chair back distance is the distance from the edge of the table top to the back of the chair. For the correct calculation of the distance, it is necessary to add 3-5 cm to the diameter of the student's torso.

The anteroposterior size of the seat of the chair should correspond to 2/3-3/4 of the thigh, the height of the chair above the floor should correspond to the length of the lower leg to the popliteal cavity with an addition of 2 cm and taking into account the height of the heel.

The seat distance is the distance from the edge of the table top to the front edge of the seat. A negative distance is recommended, at which the front edge of the seat extends 2-3 cm beyond the edge of the table top, as it eliminates spinal curvature and visual impairment.

The difference between the height of the edge of the table top and the height of the seat is called the desk differential. It should be equal to the distance from the seat to the elbow of the hand pressed to the body, with the addition of 2-2,5 cm.

The most rational ratios of the height of children and the workplace with a height of 110-119 cm are: table height - 51 cm, seat height - 30 cm, seat depth - 24-25 cm. For every 10 cm increase in height, the corresponding dimensions increase by 4, 3 and 2 cm, respectively, starting from a height of 150-159 cm, the seat depth increases by 4 cm.

Correct seating at the desk: a straight position of the torso with a slight tilt of the head forward, support on the back of the seat (without chest support on the edge of the desk cover), legs bent at a straight or slightly larger (100-110 °) angle resting on the floor or the footboard of the desk.

Note that the seating of students, taking into account their physiological characteristics, plays an equally important role. So, schoolchildren with hearing loss are recommended to be seated at the front desks, and short-sighted - at the windows.

Author: Antonova O.A.

<< Back: The influence of heredity and environment on the development of the child’s body (Heredity and its role in the processes of growth and development. Man and plants. Man and animals. The influence of viruses on the human body. Hygiene of clothing and footwear)

>> Forward: Development of the body's regulatory systems (The significance and functional activity of the elements of the nervous system. Age-related changes in the morphofunctional organization of the neuron. Properties of excitation impulses in the central nervous system. Bioelectric phenomena. Processes of excitation and inhibition in the central nervous system. Structure and functioning of the spinal cord. Structure and functioning of the brain. Functions of the autonomic department nervous system. Endocrine glands. Their relationship and functions. Development of the child’s genital organs. Puberty)

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