Age-related features of the musculoskeletal system. Features of the development of the child’s muscular system
In the development of a child, the condition of the musculoskeletal system - the bone skeleton, joints, ligaments and muscles - is of greater importance.
The bone skeleton, along with performing a supporting function, performs a protective function: internal organs from adverse effects - various types of injuries. Bone tissue in children contains few salts, it is soft and elastic. The process of bone ossification does not occur during the same period of child development. Especially turbulent perestroika, bone tissue, changes in the skeleton are observed in a child when he begins to walk.
Spine small child consists almost entirely of cartilage and has no bends. When the child begins to hold his head up, he develops a cervical curve, convexly facing forward. At 6-7 months, the child begins to sit, he has a bend in the thoracic part of the spine with a convexity backwards. When walking, a lumbar curvature is formed with a convexity forward. By 3-4 years, the child’s spine has all the curves characteristic of an adult, but the bones and ligaments are still elastic and the curves of the spine are aligned in a supine position. The constancy of the cervical and thoracic curvature of the spine is established by 7 years, and the lumbar curvature by 12 years. Ossification of the spine occurs gradually and is completed only after 20 years.
The chest of a newborn has a rounded-cylindrical shape, its anterior-posterior and transverse diameters are almost the same. When a child begins to walk, the shape of the chest approaches the adult norm. Ribs in children early age have horizontal direction, which limits the excursion (movement) of the chest. By 6-7 years, these features do not appear.
The bones of the arms and legs undergo changes as the child grows. Until the age of 7 years, rapid ossification occurs. For example, ossification nuclei in a child’s femur appear in different areas in different terms: in the epiphyses - still in prenatal period, in the epicondyles - in the 3-8th year of life; in the epiphyses of the tibia - on. 3-6 years, and in the phalanges of the foot - in the 3rd year of life.
The pelvic bones of a newborn child consist of separate parts - iliac, ischial, pubic, the fusion of which begins at 5-6 years of age.
Thus, the skeletal system of children under 7 years of age is characterized by the incompleteness of the bone formation process, which necessitates the need to carefully protect it.
Muscle tissue in early and before school age undergoes morphological growth, functional improvement and differentiation. When standing upright and walking begins, the muscles of the pelvis and lower extremities develop intensively. The muscles of the hands begin to develop rapidly at 6-7 years of age after the structural development of the bone base and under the influence of exercise of the hand muscles as a result of the child’s activities.
Timely development bone- muscular system and motor functions in children of early and preschool age are greatly facilitated by the correct organization of hygienic conditions, environment, nutrition and physical education.
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1. Development, age-related bone characteristics
Bone development occurs in two ways: from connective tissue; from cartilage.
The bones of the vault and lateral parts of the skull, the lower jaw and, according to some, the clavicle (and in lower vertebrates, some others) develop from connective tissue - these are the so-called integumentary or enclosing bones. They develop directly from connective tissue; its fibers thicken somewhat, bone cells appear between them, and lime salts are deposited in the spaces between them. Islands of bone tissue are first formed, which then merge with each other. Most skeletal bones develop from a cartilaginous base that has the same shape as the future bone. Cartilage tissue undergoes a process of destruction, absorption, and instead of it, bone tissue is formed, with the active participation of a special layer of educational cells (osteoblasts). This process can occur both from the surface of the cartilage, from the shell that covers it, the perichondrium, which then turns into the periosteum, and inside it. Usually, the development of bone tissue begins at several points; in tubular bones, the epiphyses and diaphysis have separate points of ossification.
Everyone, of course, knows that the age of a tree can be easily determined by the annual rings of its trunk. But not everyone knows that the condition of the bone in medical practice can determine a person’s age. Not so long ago, bone was generally considered an inert, frozen substance with purely mechanical functions. But electron microscopy, X-ray diffraction analysis, microradiography and others modern methods Studies have shown that bone tissue is dynamic, it has the ability to constantly renew itself, and throughout a person’s life, the quantitative and qualitative relationship between organic and inorganic substances changes in it. Moreover, each period of life is characterized by its own relationships (from which, in particular, age is determined).
U one year old child in bone tissue, organic substances predominate over inorganic ones, which in to a large extent determines the softness and elasticity of his bones. After all, it is organic substances and even water that provide bones with extensibility and elasticity. As a person ages, the percentage of bone tissue increases organic matter and the growing bones become increasingly hard. Bones grow in length due to epiphyseal cartilages located between the body of the bone and its head. When growth ends, and this happens around the age of 20-25, the cartilage is completely replaced by bone tissue. Bone growth in thickness occurs through the application of new masses of bone substance from the periosteum.
But the completion of the formation of the skeleton does not mean that the bone structures have acquired their final, frozen form. The bone tissue continues to leak interconnected processes creation and destruction.
When a person crosses the forty-year mark, so-called involutive processes begin in bone tissue, that is, the destruction of osteons occurs more intensely than their creation. These processes can subsequently lead to the development of osteoporosis, in which the bone crossbars of the spongy substance become thinner, some of them are completely resorbed, the interbeam spaces expand, and as a result, the amount of bone substance decreases and bone density decreases.
With age, not only does there become less bone matter, but the percentage of organic matter in bone tissue decreases. And, in addition, the water content in the bone tissue decreases, it seems to dry out. Bones become brittle, brittle, and even with normal physical activity, cracks may appear in them.
The bones of an elderly person are characterized by marginal bone growths. They are caused by age-related changes that the cartilage tissue that covers the articular surfaces of the bones undergoes, as well as the basis of the intervertebral discs. With age, the interstitial layer of cartilage becomes thinner, which adversely affects the function of the joints. As if trying to compensate for these changes, increase the support area articular surfaces, the bone grows.
Normally, age-related changes in bones develop very slowly, gradually. Signs of osteoporosis usually become apparent after age 60. However, it is often necessary to observe people in whom at the age of 70-75 they are only slightly expressed. But it also happens: depending on the condition skeletal system a person could be given all sixty, but he could only be given forty-five. This premature aging skeletal system, as a rule, occurs in people who lead sedentary lifestyle life, neglecting physical culture, sports.
But bones, no less than muscles, need physical training, under load. Movement - the most important condition normal life the body in general and the musculoskeletal system in particular. Observations have shown that the resorption of bone beams occurs especially intensively in those areas of the bones that experience the least load. While the beams located along the most loaded lines of force, on the contrary, thicken. Therefore, perhaps the main factors in the prevention of pathological age-related changes bone tissue are physical education and physical labor.
In progress physical activity blood supply to bone tissue improves, metabolic processes are activated. Adapting to functional loads, bone tissue changes internal structure, the processes of creation are particularly intense in it; bones become more massive and stronger.
2. Age-related features of the skeleton
musculoskeletal system children
The skeleton of the body consists of the vertebral column and the rib cage. Together with the brain section of the skull, they form the axial skeleton of the body.
The spinal column is part of the axial skeleton and represents the most important supporting structure of the body, it supports the head and the limbs are attached to it.
Vertebrae (except coccygeal vertebrae) at the end of the second month embryonic period have two cores in an arc, fused from several cores, and one main one in the body. During the first year of life, the nuclei of the arch, developing in the dorsal direction, grow together with each other. This process occurs faster in the cervical vertebrae than in the coccygeal vertebrae. Most often, by the age of seven, the vertebral arches, with the exception of I sacral vertebra, fused (sometimes the sacral section remains uncovered until the age of 15-18). Later comes bony connection arch nuclei with the vertebral body nucleus; this connection appears at the age of 3-6 years and earliest in the thoracic vertebrae. At the age of 8 years in girls and 10 years in boys, epiphyseal rings appear at the edges of the vertebral body, which form the marginal ridges of the vertebral body. During puberty or a little later, ossification of the spinous and transverse processes, which have additional secondary ossification nuclei at their apices, ends. The atlas and axial vertebrae develop somewhat differently. The vertebrae enlarge as intensely as intervertebral discs, and after 7 years relative value disk is significantly reduced. The nucleus pulposus contains a large amount of water and has a significantly big sizes in a child than in an adult. In a newborn, the spinal column is straight in the anteroposterior direction. Subsequently, as a result of a number of factors: the influence of muscle work, independent sitting, heaviness of the head, etc., curves of the spinal column appear. In the first 3 months. life, the formation of a cervical curve occurs ( cervical lordosis). The thoracic curve (thoracic kyphosis) is established by 6-7 months, the lumbar curve (lumbar lordosis) is quite clearly formed by the end of the year of life.
The anlage of the ribs initially consists of mesenchyme, which lies between the muscle segments and is replaced by cartilage. The process of ossification of the ribs occurs, starting from the second month of the intrauterine period, perichondral, and somewhat later - enchondral. Bone tissue in the rib body grows anteriorly, and ossification nuclei in the region of the rib angle and in the head region appear at the age of 15-20 years. The anterior edges of the upper nine ribs are connected on each side by cartilaginous sternal strips, which, approaching each other first in the upper sections and then in the lower ones, are connected to each other, thus forming the sternum. This process occurs during the 3-4th month of the intrauterine period. In the sternum, there are primary ossification nuclei for the manubrium and body and secondary ossification nuclei for the clavicular notches and for the xiphoid process.
The process of ossification in the sternum occurs unevenly in different parts of it. Thus, in the manubrium, the primary ossification nucleus appears in the 6th month of the prenatal period; by the 10th year of life, the fusion of body parts occurs, the fusion of which ends by the age of 18. The xiphoid process, despite the fact that it develops a secondary ossification nucleus by the age of 6 years, often remains cartilaginous.
The sternum as a whole ossifies at the age of 30-35 years, sometimes even later, and not always. Formed by 12 pairs of ribs, 12 thoracic vertebrae and the sternum in conjunction with the articular-ligamentous apparatus, the chest, under the influence of certain factors, goes through a number of stages of development. The development of the lungs, heart, liver, as well as the position of the body in space - lying, sitting, walking - all this, changing with age and functionality, causes changes in the chest. The main formations of the chest - dorsal grooves, lateral walls, upper and lower openings of the chest, costal arch, substernal angle - change their features in one or another period of their development, each time approaching the characteristics of the chest of an adult.
It is believed that the development of the chest goes through four main periods: from birth to two years of age there is very intensive development; in the second stage, from 3 to 7 years, the development of the chest occurs quite quickly, but slower than in the first period; the third stage, from 8 to 12 years, is characterized by somewhat slow development, the fourth stage is the period of puberty, when enhanced development is also noted. After this, slow growth continues until 20-25 years, when it ends.
3. Development, age-related characteristics of the muscular system
The muscular system is a collection of muscle fibers capable of contraction, united in bundles, which form special organs - muscles or are independently part of the internal organs. The mass of muscles is much greater than the mass of other organs: in an adult it is up to 40%.
The muscles of the trunk develop from the dorsal part of the mesoderm lying on the sides of the notochord and brain tube, which is divided into primary segments, or somites. After the release of the scelerotome, which goes towards the formation of the spinal column, the remaining dorsomedial part of the somite forms a myotome, the cells of which (myoblasts) are extended in the longitudinal direction, merge with each other and are subsequently transformed into symplasts of muscle fibers. Some myoblasts differentiate into special cells - myosatellites, lying next to the symplasts. The myotomes grow ventrally and are divided into dorsal and ventral parts. From the dorsal part of the myotomes arises the dorsal (dorsal) muscles of the body, and from the ventral part arises the muscles located on the front and lateral sides of the body and called ventral.
In the embryo, muscles begin to develop at the 6-7th week of pregnancy. Until the age of 5, the child’s muscles are not sufficiently developed, the muscle fibers are short, thin, tender and can hardly be felt in the subcutaneous fat layer.
Children's muscles grow during puberty. In the first year of life they make up 20-25% of body weight, by 8 years - 27%, by 15 years - 15-44%. Increase muscle mass occurs due to changes in the size of each myofibril. In muscle development, an age-appropriate motor regimen plays an important role, and at an older age, playing sports.
Training, repetition, and improving quick skills play a big role in the development of children's muscle activity. As the child grows and muscle fiber develops, the intensity of muscle strength increases. Indicators of muscle strength determined using dynamometry. Highest magnification muscle strength occurs at the age of 17-18 years.
Different muscles develop unevenly. In the first years of life, large muscles of the shoulders and forearms are formed. Up to 5-6 years, motor skills develop; after 6-7 years, the ability to write, sculpt, and draw develops. From 8-9 years of age, the volume of the muscles of the arms, legs, neck, and shoulder girdle increases. During puberty, there is an increase in the volume of the muscles of the arms, back, and legs. At 10-12 years of age, coordination of movements improves.
During puberty, due to an increase in muscle mass, angularity, awkwardness, and abruptness of movements appear. Physical exercises during this period must be of a strictly defined volume.
In the absence of motor load on the muscles (hypokinesia), a delay in muscle development occurs, obesity may develop, vegetative-vascular dystonia, bone growth disorder.
4. Poor posture in children
Poor posture is not easy aesthetic problem. If it is not corrected in time, it can become a source of diseases of the spine and more.
Typically, poor posture occurs during periods of rapid growth: at 5-8, and especially at 11-12 years. This is the time when bones and muscles increase in length, and the mechanisms for maintaining posture have not yet adapted to the changes that have occurred. Deviations are observed in most children aged 7-8 years (56-82% junior schoolchildren). There are many factors that cause spinal curvature. For example, poor nutrition and diseases often disrupt the proper growth and development of muscle, bone and cartilage tissue, which negatively affects the formation of posture. An important factor is congenital pathologies musculoskeletal system. For example, with bilateral congenital dislocation hip joints, there may be an increase in lumbar curve. An important role in the formation of deviations is played by the uneven development of certain muscle groups, especially against the background of general muscle weakness. For example, hunched shoulders are the result of a predominant force. pectoral muscles And insufficient strength muscles that bring the shoulder blades together, and “dangling shoulders” are the result of insufficient work of the trapezius muscle of the back. An important role is played by overload of certain muscles with unilateral work, for example, incorrect position of the torso during games or activities. All these reasons lead to an increase or decrease in existing physiological bends spine. As a result, the position of the shoulders and shoulder blades changes, resulting in an asymmetrical position of the body. Incorrect posture gradually becomes habitual and can become fixed. You should definitely pay attention to how the child sits at the table during classes: whether he puts one leg under him. Perhaps he is slouching or “leaning” to one side, leaning on the elbow of his bent arm. TO incorrect position body when sitting, it should be attributed to a landing in which the torso is turned, tilted to the side or strongly bent forward. The reason for this situation may be that the chair is far away from the table or the table itself is too low. Or maybe the book the baby is looking at lies too far from him. An asymmetrical position of the shoulder girdle can be formed as a result of the habit of sitting with the shoulder raised high. right shoulder. The weakness of the muscular corset in children is primarily due to the lack of adequate physical activity, while with rapid growth, the strength of the abdominal and back muscles is simply necessary.
5. Flat feet in children
Flat feet are one of the most common diseases of the musculoskeletal system in children. This is a deformation of the foot with a flattening of its arch (in children, the longitudinal arch is usually deformed, which is why the sole becomes flat and its entire surface touches the floor).
It is possible to accurately determine whether a child has flat feet or not only when the child turns five (or even six) years old. Why? Firstly, children up to of a certain age The bone structure of the foot is not yet strong, it is partly a cartilaginous structure, the ligaments and muscles are weak and susceptible to stretching. Secondly, the soles appear flat, since the arch of the foot is filled with a fatty soft “pad” that masks bone base. At normal development of the musculoskeletal system, by the age of five to six years, the arch of the foot acquires the shape necessary for proper functioning. However, in some cases, a developmental deviation occurs, which causes flat feet.
Factors influencing the development of flat feet:
· heredity (if one of your relatives has/had this disease, you need to be especially careful: the child should be regularly shown to an orthopedic doctor),
· wearing “wrong” shoes (flat soles, no heels, too narrow or wide),
Excessive stress on the legs (for example, when lifting heavy objects or with increased body weight),
Excessive flexibility (hypermobility) of joints,
· paralysis of the muscles of the foot and leg (due to polio or cerebral palsy),
· foot injuries.
Flat feet is a disease that, in the absence of adequate therapy, leads to serious complications and severe deformation of the bones of the foot, as well as diseases of the musculoskeletal system. Timely treatment and prevention will return the child to health and confidence in his attractiveness!
6. Musculoskeletal hygienedevices for children in preschool educational institutions and in the family
Any children's furniture must meet sanitary and hygienic requirements aimed at ensuring long-term performance, harmonious physical development, prevention of posture and vision disorders in children. When using correctly selected, high-quality furniture in kindergartens and schools, children maintain visual and hearing acuity, stable body balance is observed, cardiovascular, respiratory, and respiratory systems function normally. digestive system, muscle tension and the possibility of premature fatigue are reduced.
The hygienic requirements for children's furniture primarily concern the size of tables and chairs, as well as the ratio of the main elements: table top, back and chair seat.
During the learning process, children experience stress due to the need to long time maintain a working posture. This load increases sharply if the furniture is arranged incorrectly and its size does not correspond to the height and proportions of the body. Therefore, furniture must be selected in accordance with the distribution of children by height groups. As a result special research For children of toddler and preschool age up to 100 cm tall, a height scale is adopted with an interval of 10 cm, for school-age children taller than 100 cm - 15 cm.
For children in the younger nursery group (from 7 months to 1 year 8 months), feeding tables with a ratio of elements corresponding to group A furniture can be used.
In nurseries, three types of children's tables should be used: four-seater for children 1.5 - 5 years old, two-seater with a variable tilt of the lid and drawers for teaching aids for children 5 - 7 years old; double trapezoidal for children 1.5 - 4 years old.
It is equally important to select children’s tables and chairs not only according to the child’s height this moment, but also taking into account the fact that children grow differently. Therefore, if you are selecting, for example, school furniture for junior classes, it is worth paying attention to height-adjustable student tables and chairs, the size of which can vary from 2 to 4 or from 4 to 6 height groups. The price of such furniture is slightly higher than usual, but its purchase eliminates the need to purchase furniture for groups of different heights, and therefore avoids additional costs in the future.
Hygienic requirements for children's shoes.
From a hygienic point of view, children's shoes must protect the body from hypothermia and overheating, protect the foot from physical damage, provide assistance to muscles and tendons, and keep the arch of the foot in place. correct position, provide a suitable climate around the foot, help maintain the desired temperature in all weather conditions. Children's shoes must meet hygienic requirements - be comfortable, light, not restrict movement, and be suitable for the size and shape of the foot. Then the toes are placed freely and can be moved. But she can be the reason huge amount foot diseases Narrow and small children's shoes complicate gait, pinch the leg, impair blood circulation, cause pain and over time change the shape of the foot, disrupt its normal growth, change the shape of the toes, contribute to the formation of difficult-to-heal ulcers, and in winter period- frostbite. Very loose children's shoes are also harmful. Walking in it quickly becomes tiring, and there is every chance of abrasions, especially in the instep area. Children are not recommended to wear narrow shoes. Wearing it often leads to ingrown nails, bent fingers, the formation of calluses and contributes to the development of flat feet. Flat feet are also observed when wearing shoes without heels for a long time, for example, slippers. Daily wearing of shoes with high (above 4 cm) heels is not recommended for teenage girls, because... complicates walking by shifting the center of gravity forward. The emphasis is transferred to the toes. The support area and stability are reduced. The man leans back. Such a deviation, at a young age, when the bones of the pelvis have not yet fused, entails a change in its shape, and even changes the position of the pelvis. This may subsequently have a negative impact on reproductive function. At this time, a large lumbar curve is formed. The foot moves forward, the toes are compressed in the narrow toe, the load is on anterior section The size of the foot increases, eventually developing flattening of the arch of the foot and deformation of the toes. In high-heeled shoes, it’s easy to twist your foot in the joint and it’s easy to lose your balance.
Organization of physical activity (while walking).
Planning work on the development of movements during a walk should help consolidate, improve games and physical exercises, and increase the motor activity of children. It is important to choose the right time for games and exercises. Organized motor activity should not be allowed to take place at the expense of children’s independent activity time.
The choice of time and exercises during the walk depends on previous work in the group. If a physical education or music lesson was held in the first half of the day, then it is advisable to organize games and exercises in the middle or end of the walk, and at the very beginning to provide children with the opportunity to play independently and practice with a variety of aids.
On other days, it is advisable to organize the motor activity of children at the beginning of the walk, which will enrich the content of their independent activity.
On the days of physical education classes, children are organized with one outdoor game and some physical exercise ( sports exercise or an exercise in the main type of movement). On other days, when there is no lesson, an outdoor game, sports exercise and exercise in the main form of movement (jumping, climbing, throwing, throwing and catching a ball, etc.) are planned.
When conducting exercises and basic types of movements, different methods of organization should be used (frontal, subgroup, individual). The most appropriate is mixed use different ways organizations.
Due to the peculiarities of performing some movements (climbing a gymnastic ladder, balance exercises, long and high jumps from a running start), continuous and individual methods are used.
The combination of different methods of organization significantly increases the effectiveness of games and exercises during a walk. For example, a climbing exercise is performed by children one by one, and an exercise with balls is performed frontally, i.e. by all children at the same time.
It is advisable to organize children’s exercises in the main types of movements into subgroups, depending on the degree of mobility of the children. Each subgroup performs its own task. For example, children of the first and second subgroups (with high and average levels of mobility) perform exercises that require concentration, coordination and dexterity, while the teacher exercises control. Children of the third subgroup (with a low level of mobility) practice different types jumping rope.
The duration of organized motor activity is 30-35 minutes.
Formation correct posture - when sittingwalking, walking, standing, lying down
Preschool age is the period of formation of posture, and it should be noted that deficiencies in posture in preschoolers are still unstable. The child can accept correct posture, if he is reminded of this, but his muscles, especially the back and abdomen, are unable to hold the spine in an upright position for a long time, as they quickly tire. Therefore, sufficient muscle strength, as well as their development and strengthening, play an important role in the formation of correct posture. Work on developing correct posture should be constantly carried out with all children, and not just with those who have any deviations.
Systematic physical exercise in the form of daily morning exercises, physical education classes, and outdoor games in groups. Medical workers carry out special classes in exercise therapy, hardening, herbal medicine. It is very important to monitor the posture of preschool children and develop the ability to sit and stand correctly:
- posture at the table when drawing, looking at illustrations, when playing board games, it should be comfortable: the elbows of both hands are on the table, the forearms are symmetrical and free (according to upper third a little lower elbow joints), lie on the table surface. The shoulders are at the same level, the head is slightly tilted forward, the distance from the eyes to the table is 30-35 cm. The child should sit with an equal load on both buttocks, without tilting to one side. Feet are on the floor. Ankle, knee and hip joints form a right angle;
- posture during sleep. It is best if the child sleeps on his back, on a small pillow. Sleeping on your side bends the spine, as does the habit of standing with support on one leg;
- standing posture. You have to stand with uniform distribution body weight on both legs;
- walking posture. Keep your shoulders at the same level, straighten your chest, pull your shoulder blades back without tension, tighten your stomach, look straight without lowering your head.
The main means of preventing postural disorders in preschoolers is physical exercise.
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The child's skeleton undergoes complex transformations in the process of growth and development. Bone tissue in a child infancy It has fibrous structure, poor in mineral salts, rich in water and blood vessels. Each bone in a child is represented as several bones, which are subsequently fused together. If an adult has 206 of them, then a newborn has 350. After another 14 years, bone fusion continues. For example, in the first years of a child, the pelvic bone consists of three individual bones, connected to each other by layers of cartilage, which are gradually replaced by bone tissue, and the bones grow together
After birth, bones continue to grow in thickness by layering bone tissue on the outside and breaking down from the inside. This is most of the bones of the brain and facial skull. Otherwise, long bones of the limbs grow, in which it is customary to distinguish middle part, or diaphysis, and the ends of the bone, or epiphyses. First, bone tissue forms in the middle of the diaphysis. In long bones, cartilaginous layers remain between the diaphysis and epiphysis for a long time ( growth zones). Ossification begins from the middle part of the bone - from the diaphysis, where, thanks to the activity of bone cells, a bone cuff is formed. It increases towards the epiphyses, causing the bone to grow in length. At the same time, its thickness increases due to the formation of new layers of bone tissue. When the cartilaginous layer ossifies, bone growth in length becomes impossible. In the majority long bones and vertebrae, the cartilaginous layer between the diaphysis and epiphyses persists up to 17-20 years, and in some up to 22-25 years.
There are many cartilaginous parts in the skeleton of a newborn child. The epiphyses, that is, the ends of the long bones of the limbs, remain cartilaginous. In many bones, cartilaginous areas are preserved between individual ossification centers (Fig. 4.8).
The bones of the skull are not in contact with each other throughout. The gap between the frontal and two parietal bones is especially large - large fontanel, which is overgrown by the year. Small fontanelle- the space between the occipital and two parietal bones. It overgrows in the first month of life, and more often before birth (Fig. 4.9.). The skull grows unevenly. Grows rapidly in the first year: head circumference increases by 30%, and transverse diameter by more than 40%. Volume brain skull increases by 2.5 times. The size of the facial skull increases. The volume of the cranium continues to increase and by the age of three it reaches 80% of the volume of an adult. By this time, cranial sutures begin to form. The base of the skull continues to grow significantly, and by the age of 7-8 it becomes the same as that of an adult. The facial skull also continues to grow. As dairy and permanent teeth the upper and lower jaws grow.
Development vertical position body leads to a number of significant changes in the motor system: firstly, the tone and contractility extensor muscles; secondly, curves of the spine appear, which help maintain balance, have a springing effect when walking, running, jumping and facilitate muscle work while maintaining an upright body position for a long time.
The spine in newborns is straightened and has no physiological bends. The first curve - cervical (lordosis) appears at two months of age, when the child begins to hold his head up. The forward-facing convexity of the cervical spine becomes well defined much later, when the child independently maintains a sitting position for a long time. The constancy of the cervical curvature is established by 7 years. At the same time, the backward-facing convexity of the middle part of the spine—the thoracic curve—is more clearly revealed. A thoracic curve (kyphosis) appears by 6 months, when the child can sit. Kyphosis- a bend directed convexly backwards. The sitting position, and especially the standing position, contributes to the formation of the lumbar curve, convexity facing forward. A bend directed convexly forward is called lordosis. It appears after a year, when the child begins to walk. With the formation of lumbar lordosis, the center of gravity moves posteriorly, preventing the body from falling in an upright position. Usually this bend becomes noticeable at the 2nd year of life.
Throughout preschool age, bends in strong degree depend on body position. After lying for a long time, for example, after a night's sleep, the cervical curve and especially the lumbar curve can completely disappear, reappearing and intensifying towards the end of the day under the influence of sitting and walking. Even at primary school age, the curves flatten significantly during the night. By the age of 7, there are already clearly defined cervical and thoracic curves. Fixation of the lumbar curve occurs at 12-14 years. The curves of the spine are specific feature human and arose in connection with the vertical position of the body. Thanks to the bends, the spinal column is springy. Impacts and shocks when walking, running, jumping are weakened and attenuated, which protects the brain from concussions (Fig. 4.10.).
The growth of the spine in length occurs especially rapidly in the first two years and during puberty. Between the vertebrae there are discs of cartilage that promote mobility of the spinal column. With age, the height of the discs changes. Ossification of the vertebrae continues throughout childhood.
In newborns and infants up to 6 months, the chest has the shape of a cylinder or a truncated cone. The diameter of its lower section exceeds the diameter upper section. The ribs are located horizontally. The chest appears shortened in the first months. Then it changes, and physiological drooping of the ribs appears. The ribs take a more oblique direction, the intercostal spaces become narrower. The features of the child’s chest are smoothed out by 6-7 years, its final formation occurs by 12-13 years.
The rib cage forms the bony base chest cavity. It protects the heart, lungs, liver and serves as an attachment site respiratory muscles and muscles upper limbs. According to the change in the chest, the volume of the lungs increases. Changing the position of the ribs helps to increase the movements of the chest, which makes breathing movements more effective.
The lumbar girdle forms the sacrum and 2 pelvic bones. Each pelvic bone in newborns consists of three bones; their fusion begins at 5-6 years of age and is completed by 17-18 years of age.
In newborns, the carpal bones are just emerging, becoming clearly visible by the age of 7, and their ossification is completed by the age of 12. Ossification of the phalanges of the fingers is completed by the age of 11. An unformed hand gets tired quickly
By the age of two years, the structure of a child’s bones is close to the bones of an adult, and by the age of 12 they are no longer different from them.
With the help of the musculoskeletal system it is carried out most important function body - movement. Physical activity plays a vital role in metabolic processes, has a positive effect on the functioning of all internal organs.
The muscles of a newborn and infant are poorly developed. They make up 25% of body weight, whereas in an adult it is 40-43%. The size of muscles depends on the work they perform. As a child develops, muscle groups grow unevenly. In infants, first of all, the abdominal muscles develop. By the age of one year, due to crawling and the beginning of walking, the muscles of the back and limbs noticeably grow. Over the entire period of child growth, muscle mass increases 35 times. An increase in muscle mass is achieved by lengthening and thickening them, due to an increase in the diameter of the fibers. In newborns it does not exceed 10-15 thousandths of a millimeter, and by 3-4 years it increases 2-2.5 times. In subsequent years, the diameter of muscle fibers largely depends on individual characteristics body, and mainly from physical activity.
Already in the first days of life, the child shows great motor activity. Basically, these are random movements of the limbs.
In children of the first months of life there is increased tone muscles. The flexor tone prevails over the extensor tone. During normal development of a child, motor skills are formed sequentially.
At 1-2 months the child holds his head in an upright position. When lying on his stomach, he raises his head, and by the end of the second month, leaning on his hands, he raises not only his head, but also his chest.
Three month old baby begins to roll over from back to stomach. At 3-3.5 months, with support from the armpits, he rests his feet. At the age of 4-5 months, movements begin to be well controlled by vision: seeing new item, the child reaches out to him, grabs him and, as a rule, drags him into his mouth.
At 6 months – sits independently. At 7-8 months he crawls. By 7 months, the child maintains a sitting position well, and after another month he sits down independently and, holding on to various objects, rises to his feet. Gradually he begins to crawl on all fours. At 10 months – standing without support. At 12 months, the child takes his first independent steps.
Maintaining an upright body position requires the well-coordinated activity of nearly three hundred large and small muscles. Each muscle must contract with a strictly defined force in order, together with other muscles, to secure the movably connected bones of the skeleton in a certain position. Muscle work is especially difficult when walking and running. During walking, about 50 muscles are involved in moving the leg forward. While one leg takes a step forward, the muscles of the other, together with the muscles of the torso, ensure the maintenance of balance, which is complicated by the continuous movement of the center of gravity.
In a child, coordination of muscle work when standing and walking is not immediately established: At first, the child walks with his legs spread wide and balancing with his arms spread to the sides. Only gradually, by the age of 3-4 years, the coordination of movements becomes so precise that the child easily walks and runs while maintaining balance.
At the age of 4-5 years, a child can jump, hop on one leg, slide along ice paths, skate, and do various gymnastic and acrobatic exercises.
The movements of the small muscles of the hand begin to be mastered by the end of the first and beginning of the 2nd year of life. The child can grasp and hold small items not only with the whole hand, but with the thumb and forefinger. By the age of 3-5, a wide variety of well-coordinated and precise finger movements are available to him: a child can learn to draw, play the piano, and cut with scissors. We can assume that the coordination of movements of various muscle groups characteristic of an adult is established by the age of 6. Intensive muscle growth and an increase in their strength are observed after 6 years. By the age of 8 years, muscles already make up about 27% of body weight, which is explained by their natural training.
Another property of muscles develops very slowly - their endurance. The endurance of the musculoskeletal system is determined by the performance of the muscles, their ability to perform dynamic and static work for a long time. Children are better suited to perform dynamic work than static work, since the latter causes rapid muscle fatigue. Preschool children are very mobile. A rough calculation shows that in a day, especially in the summer, a child, moving, covers up to 15-20 km. In other words, significant natural training of the motor system occurs. A 3-4 year old child is usually not able to walk for a long time at a calm, even pace. His movements are constantly changing. The static tension of his muscles can only remain unchanged for a short time.
In older preschool age physical activity more diverse. The muscles become much stronger, and movements become well coordinated. Endurance increases somewhat, but still the child moves very quickly from one activity to another. When walking, his movements acquire the correct rhythm, but only for a while, for example for 5, 10 or 15 minutes. The ability to maintain a stationary posture increases, especially when sitting, but not for long. Endurance remains especially low in relation to maximum force tension. Muscle endurance increases from 8-10 years. Endurance to dynamic work depends not only on the degree of muscle development, but also on the performance of internal organs, especially the circulatory and respiratory systems, therefore any physical activity(outdoor and sports games, gymnastics, walks) must be strictly dosed. The greatest endurance for dynamic work is achieved by the age of 25-30.
Thus, in preschool and primary school age, the growth and development of the musculoskeletal system is far from complete. Teachers should remember this and try to fulfill the hygienic requirements for organizing the child’s living conditions.
Consists of the skeleton (bones), muscles, ligaments and joints. These structures form cavities for internal organs, protect internal organs, and also provide motor acts.
The skeleton forms the structural basis of the body, determines its shape and size. In the skeleton of an adult there are more than 200 bones, which primarily perform a supporting function and are a kind of levers when carrying out motor acts. At the same time, bones actively participate in metabolic processes: they accumulate mineral salts and, if necessary, supply them to the body (mainly calcium and phosphorus salts). Bones also contain hematopoietic tissue - red bone marrow.
Bones contain approximately 60% minerals, 30% organic components (mainly ossein protein and osteoblastic bone cell bodies) and 10% water. This combination of substances in the structure of bones provides them with significant strength (30 times stronger than brick and 2.5 times stronger than granite) and greater elasticity, elasticity and viscosity (9 times the viscosity of lead). Bones are characterized by a significant margin of safety (for example, the femur can withstand a load of 1.5 tons). In children tubular bones They grow in length due to the cartilage between the ends of the bones (epiphysis) and their body (diaphysis), and in thickness due to the surface tissue - the periosteum. Flat bones grow in all directions only due to the periosteum. When the human body stops growing, the cartilage in many bones is replaced by bone tissue. Skeletal development in men ends at 20-24 years, and in women at 17-21 years.
Individual bones and even parts of the skeleton mature at different periods. Thus, until the age of 14, only the middle parts of the vertebrae are covered by ossification, while their other parts remain cartilaginous and only at the age of 21-23 do they completely become bone. By the same period, ossification of most other bones of the skeleton is basically completed.
An important stage in the development of the human skeleton is the formation and strengthening of the bends of the spine, which are divided into those that are directed with the convex side forward and are called lordosis (occur in the neck and lumbar spine) and those that are directed backward and are called kyphosis (thoracic and sacral). parts of the spine). The presence of lordosis and kyphosis is a necessary phenomenon due to the upright posture of a person when standing and walking; this is also necessary to maintain body balance and provide shock absorption function when moving, jumping, etc. Sagittal (when viewed from the side) bends of the spine appear from the moment when children begin to raise their heads, sit down, stand up and walk (up to the age of one year) . Until 5-6 years of age, the bends of the spine are slightly fixed, and if the child lies down, then most often these bends disappear (even out). The strengthening of the bends of the spine occurs gradually: up to 7-8 years only the cervical and thoracic curves are formed, and at 12-14 years - lordosis of the lumbar spine and kyphosis of the sacral spine. The final consolidation of lordosis and kyphosis is completed with ossification of the spinal vertebrae (17-20 years). In the frontal projection (when viewed from the front or rear), a normally developed spine should be straight.
Growth and development of bones. IN During the embryonic period of development, the skeleton is formed as a connective tissue formation. In some bones, foci of ossification appear directly in the connective tissue skeleton, i.e., the bone passes the cartilaginous stage in its development. Such bones are called primary(bones of the skull). Most bones are characterized by the replacement of connective tissue with cartilage, after which the cartilage is destroyed and bone tissue is formed in its place. This is how they are formed secondary bones.
Ossification occurs in two ways: enchondral ossification, when foci of ossification appear within the cartilage, and peri-chondral, starting from its surface.-
The collagen fibers of the developing bone tissue (in certain areas of them) contain active crystallization centers with reactive groups. It is believed that the calcification process begins with the interaction of the amino acid lysine, which is part of the reaction group of collagen, with phosphate ions. At the first stages of mineralization, crystals of inorganic salts are not oriented relative to the axes of collagen fibrils. But as mineralization proceeds, the resulting crystals are oriented with their long axes parallel to the axes of the collagen fibrils with which they are associated. In the epiphyses, in short bones, in the processes of bones, ossification is carried out according to the enchondral type, and in the diaphyses - according to the perichondral type. Ossification begins in the middle part of the diaphysis, where a bone cuff is formed due to the activity of osteoblasts. The bony cuff grows towards the epiphyses. At the same time, its thickness increases due to the formation of more and more new layers of bone tissue. At the same time, cartilage and bone tissue are reabsorbed inside, and a bone marrow cavity is formed. Thus, from the outside, new layers of bone tissue are layered, and from the inside, the remains of cartilage and bone tissue are destroyed. Due to this, the bone grows in thickness. At a certain stage of embryonic development, foci of ossification appear in the epiphyses. However, for a long time, a cartilaginous zone remains at the border of the diaphysis and epiphysis - growth plate, determining the ability of bones to grow in length.
To carry out the complex process of bone formation
It is necessary to have nutrition that is complete in both qualitative and quantitative terms. The child's food must contain sufficient amounts of salts P and Ca, without which the calcification process is impossible, as well as the required amount of vitamins. Thus, a lack of vitamin A causes a narrowing of the vessels of the periosteum and an associated malnutrition of the developing bone tissue, as a result of which the bone stops growing. With a lack of vitamin C, bone plates do not form. For vitamin deficiency IN the exchange of phosphorus and calcium is disrupted. The disease occurs rahit, manifested in disruption of the process of bone tissue formation. This
the disease is characterized by softening of bone tissue, and resulting deformation of the bones, as well as increased growth of tissue, which differs from bone in its structure and chemical composition (Fig. 91).
Age-related features of bone structure. Ossification begins in the prenatal period of development, when primary ossification nuclei. A significantly larger number of ossification nuclei appear after the birth of a child. These kernels are called secondary. In total, 806 ossification nuclei are formed in the human skeleton during development.
Only in the skull almost all ossification nuclei appear in the prenatal period of development. In all other parts of the skeleton, the number of secondary nuclei is greater than the number of primary ones. In an adult, the number of bones is significantly less than in a 14-year-old teenager: in an adult - 206, in a 14-year-old - 356. It follows that even after 14 years of age, bone fusion continues.
The bone of a newborn is characterized by a large amount of cartilaginous tissue, a large thickness of the periosteum, a rich vascular network, and an irregular arrangement of the Haversian canals. Apatite crystals are very small in size, and the diameter of collagen fibers is small. Newly formed bone tissue is rich in water. Inorganic bone matter makes up only half of its mass. All this makes the bone less dense, porous, more elastic, elastic and flexible.
Rice. 91. Skeletal changes with rickets:
A- curvature of the legs; IN- deformation of the skull, spine, chest.
Age-related features of the skull skeleton. The skull begins to differentiate in the 2nd month of intrauterine life. The bones of the skull develop in both primary and secondary ways. By the time of birth, ossification nuclei are present in all bones of the skull, but their growth and fusion occurs in the postnatal period. In a newborn, the volume of the brain skull is 8 times larger than the facial skull, and in an adult it is only 2-2.5 times larger. At 2 years the face/skull ratio is 1:6, at 5 years it is 1:4, at 10 years it is 1:3 (Fig. 92, B). The smaller size of the facial skull in newborns depends on the underdevelopment of the facial, mainly jaw, bones. As teeth grow, these ratios approach those of an adult.
In a newborn, between the bones of the skull there are spaces of about 3 mm in size, filled with connective tissue. They are called seams. During postnatal development, the width of the sutures decreases, so that the connective tissue layer becomes barely visible. After 30 years, ossification of the sutures occurs.
The corners of the skull bones do not ossify at the time of birth, and the places where they connect are also filled with connective tissue. These areas are called fontanelles(Fig. 92, A). There are anterior, posterior and lateral fontanelles. Anterior, frontal fontanel located between the frontal and parietal bones, its size is 2.5-5 cm. It progressively decreases by 6 months of postnatal development and completely closes by 1.5-2 years. Posterior, occipital fontanel located between the occipital and parietal bones, it is up to 1 cm in size. Usually it is already closed at the time of birth, but sometimes persists for up to 4-8 weeks. Lateral frontniya fontanelle located at the convergence of the frontal, parietal, main and temporal bones, A lateral rear- between the occipital and temporal bones. Their closure occurs either in the intrauterine period of development or in the first weeks after birth. With rickets, closure of the fontanelles occurs at a later date.
Rice. 92. Features of the skull of newborns:
L - location of fontanelles: / -- frontal; 2 - occipital; 3 - rear side;
4 - front side; B- the relationship between the facial and cerebral parts of the skull
in newborns and adults / - in a newborn; 2 - in an adult
Rice. 93. Development of the frontal sinus(A) and sinuses of the maxilla(B).
Long-term persistence of fontanelles is considered one of the symptoms of this disease. The presence of fontanelles and sutures at the time of birth is of great importance, because it allows the bones of the baby’s skull to move during birth, thereby facilitating passage through the mother’s birth canal.
The occipital bone in newborns consists of four non-fused bones, the temporal bone - of three, the lower jaw - of two halves, the frontal - of two, in sphenoid bone The front and back parts of its body, as well as the wings and the body, are not fused. In the first year of life, the large wings fuse with the body of the sphenoid bone; the fusion of the anterior and posterior parts of its body occurs only at 13 years of age. The halves of the lower jaw grow together by the age of 2 years. The fusion of individual parts of the temporal bone occurs in 2-3 years, the occipital bone - in 4-5 years. Fusion of two halves frontal bone ends by the end of the 3rd year of life, the seam between them disappears at 7-8 years.
Sinuses in the bones of the skull are formed mainly after the birth of a child. The newborn has only a rudiment topmaxillary, or maxillary, cavity. The formation of sinuses ends only in mature age. Figure 93 clearly shows changes in the size of the sinuses during different periods of postnatal development.
In a newborn, the skull bones are very thin, their thickness is 8 times less than in an adult. However, thanks to the intensive process of bone formation, already in the first year of life the wall thickness increases 3 times.
The volume of the skull changes quite quickly: in a newborn it is 1/3> at 6 months - "/g. and by 2 years - 2/3 of the volume of the adult’s skull. From 10-12 years, its size changes little.
Age-related features of the trunk skeleton. The vertebrae that form the spinal column develop as secondary bones, i.e. they go through a cartilaginous stage. Ossification nuclei appear in them in the 2nd month of intrauterine development. The process of ossification of the spinal column occurs in a strictly defined order. Foci of ossification first appear in the thoracic vertebrae, and then ossification spreads towards the cervical and coccygeal spine.
On the 40-50th day of intrauterine development, an ossification nucleus appears in the body of the 12th thoracic vertebra; by the end of the 4th month, the bodies of all thoracic vertebrae, cervical, lumbar and the first two sacral vertebrae have ossification nuclei. During the same period, ossification nuclei appear in the vertebral arches. The fusion of the ossification nuclei of the right and left halves of the vertebral arches occurs only after birth. The newborn's spine is open at the back along the line of all vertebral arches. Only by the age of 7 are all arches closed. The only exception may be the arch of the first sacral vertebra. Sometimes it closes later. The anterior arch of the atlas can remain open for up to 9 years.
At 8-11 years of age, ossification nuclei appear in the epiphyseal cartilaginous discs that bound the vertebrae above and below. From 15 to 24 years of age, fusion of the bony epiphyseal discs with the vertebral body occurs. This occurs first in the thoracic spine, then in the cervical and lumbar spine. Complete fusion of the processes with the vertebral body occurs at the age of 18-24 years.
The vertebral bodies in newborns are flattened so that their transverse diameter is greater than the longitudinal one and the ratio between the diameters is 5:3. During puberty, this ratio becomes 4:3, and in adults it is 3:3. In general, over the entire period of development, the length of the spine increases by 3.5 times. During the first 2 years, the growth of the spine is very intense, then it slows down and again becomes more intense during puberty, increasing by 3.5 times.
Rice. 94. Curves of the spine:
A- the shape of the adult spine; B- the appearance of bends in children: / - due to holding the head; 2 - when sitting; 3 - when standing.
During the first 2 years, the growth of the spine is very intense, then it slows down and again becomes more intense during puberty.
The spinal column of a newborn has only a slight sacral curve (Fig. 94). The first to appear is the cervical curve at the age of 2.5-3 months, when the child begins to hold his head. A bend directed convexly forward is called lordosis. Therefore, the first one to appear is cervical lordosis. At about 6 months of age, when the baby begins to sit, a bend in the thoracic region, convexly directed backwards. Such bends, convexly directed backwards, are called kyphosis. By the time you start walking, a lumbar curve. This is accompanied by a change in the position of the center of gravity, which prevents the body from falling when moving to a vertical position. Thus, by the age of one year all the curves of the spine are already present. At first, the resulting bends are not fixed and disappear when the muscles relax. Fixation of bends in the cervical and thoracic spine occurs at 6-7 years, and in the lumbar spine - by 12 years.
Ossification of the sternum occurs in a secondary way, and the first ossification nuclei appear in the manubrium and its body even in the prenatal period of development. In the xiphoid process, the ossification nucleus appears only at 6-12 years of age.
Complete fusion of all bone areas of the sternum occurs after 25 years.
Ossification of cartilaginous ribs begins at 6-8 weeks of intrauterine development. Nuclei appear first in the middle ribs. Secondary nuclei appear at 8-11 years of age. The fusion of the bony parts of the rib occurs at the age of 18-19 years, and the head and body of the rib - at 20-25 years.
In newborns, the chest is bell- or pear-shaped. The upper part of the chest is narrow, the lower part is widened due to the high location of the internal organs, its anterior-posterior diameter is greater than the transverse one (Fig. 95). With the development of the lungs, which begin to occupy a large space, the upper ribs, which were located obliquely, begin to occupy a horizontal position.
Rice. 95. Various shapeschest:
A- in newborns; B- in adults.
In this regard, the chest takes on a barrel-shaped shape. The upper edge of the sternum in an infant is at the level of the first thoracic vertebra. The curvature of the ribs is slight. The angle between the ribs and the spine, as well as between the ribs and the sternum, is large. Thus, the costovertebral angle in a newborn is 82°, and at 3 years old it is 62°. The shape of the chest during this period corresponds to the phase of maximum inspiration. From this it is clear that breathing at this age is carried out mainly through the diaphragm. By 3-4 years, the upper edge of the sternum drops to the level of the 3-4th thoracic vertebra (as in adults). Together with the sternum, the ribs descend, their curvature increases, the costovertebral angle and the angle between the ribs and the sternum decrease. This leads to an increasing dependence of the act of breathing on changes in chest volume. This dependence is already clearly evident in a 3-year-old child.
The chest acquires the shape of an adult by the age of 12-13 years.
Age-related features of the limb skeleton. All the bones of the belt upper limbs, with the exception of the collarbone, they go through the flaccid stage. IN collarbone precartilaginous tissue is immediately replaced by bone. The process of ossification, which began in the 6th week of intrauterine development, is almost completely completed by the time of birth. Only the sternal end of the clavicle does not have an ossification nucleus. It appears only by the age of 16-22, and its fusion with the body occurs by the age of 25.
In most bones of the free upper limbs, primary ossification nuclei appear within 2-3 months of embryonic development. In the bones of the wrist they appear after birth: in the capitate and hamate - at the 4-5th month, and in the rest - in the period from 2 to 11 years. The fusion of primary and secondary ossification nuclei in the bones of the girdle ends by 16 - 25 years.
In almost all bones lower limb belts Primary ossification nuclei also appear in the embryonic period of development. Only in the tarsal bones (scaphoid, cuboid and sphenoid) do they form in the period from 3 months after birth to 5 years.
Pelvis in a newborn it has the shape of a funnel. Its anteroposterior size is larger than the transverse one. The lower opening of the pelvis is very small. The entrance plane is located much more vertically than in an adult. The pelvis of a newborn consists of separate, unfused bones. Ossification nuclei in the ilium, ischium and pubis appear in the period from 3.5 to 4.5 months of intrauterine development. From 12 to 19 years, secondary ossification nuclei appear. The fusion of all three pelvic bones occurs at 14-16 years of age, and the secondary nuclei are connected to the previously formed and fused pelvic bones only by the age of 25.
In the postnatal period, the shape and size of the pelvis changes under the influence of a variety of factors: under the influence of pressure exerted by body weight and abdominal organs,
under the influence of muscles, as a result of pressure from the head of the femur, under the influence of sex hormones, etc. As a result of these various influences, the anteroposterior diameter of the pelvis increases (from 2.7 cm in a newborn to 8.5 cm at 6 years and 9.5 cm at 12 years old), its transverse size increases, which at 13-14 years old becomes the same as in adults. The plane of the pelvis in transverse diameter becomes oval at this age.
After 9 years, there is a difference in the shape of the pelvis in boys and girls: boys have a higher and narrower pelvis than girls.
Thus, not only in preschool age, but also in school age, the growth and development of the skeleton is far from complete. Teachers, educators, and parents should remember this and try to fulfill all the hygienic requirements that apply to organizing the child’s living conditions. Furniture that does not correspond to the height of the child, poor lighting in the room during his activities, uncomfortable shoes, high-heeled shoes, limited physical activity, insufficient time in the fresh air, improper nutrition in quantitative and qualitative terms can cause certain disorders in the formation of the skeleton. , which in turn can cause pathology of internal organs. Thus, pronounced kyphosis (stooped back) often leads to disruption of the respiratory system. Deformation of the sternum can negatively affect the functioning of the heart, etc. Sometimes lateral curvature of the spine occurs - scoliosis. They can also cause problems with the functioning of the chest organs.
AGE FEATURES OF SKELETAL MUSCLE
Changes in the macro- and microstructure of skeletal muscles with WHOgrowing up. The formation of skeletal muscles occurs at very early stages of development. At the 8th week of intrauterine development, all muscles are already distinguishable, and by the 10th week their tendons develop. The connection between the primary formation of muscles and the corresponding nerves is detected already in the 2nd month of development. However, motor nerve endings first appear only in the 4th month of intrauterine development.
The maturation of muscle fibers is associated with an increase in the number of myofibrils, the appearance of transverse striations, and an increase in the number of nuclei. It occurs in different muscle fibers at different speeds. The first to differentiate are the fibers of the muscles of the tongue, lips, intercostal muscles, back muscles and diaphragm. Then - the muscles of the upper limb and, lastly, the muscles of the lower limb.
In newborns, muscle mass is 23.3% (in adults - 44.2%) of the total body mass. The tendon part of the muscle is poorly developed and makes up a smaller part of the entire length of the muscle than in adults; fascia and tendons broad muscles very thin, fragile, easy to separate from them. The connective tissue that forms the intramuscular septa differs from the connective tissue of adult muscles in the larger number of cells and fewer fibers. Striated muscle fibers are characterized by very a large number kernels that are oval in shape. The longitudinal diameter is related to the transverse diameter as 2:1. Various muscle fibers in newborns differ little in their diameter. The sarcolemma begins to appear by the 6th month of intrauterine development. In a newborn, it is clearly expressed and is characterized by the presence of a large number of thin fibers, in the arrangement of which there are no signs of order.
During postnatal development, further changes occur in both the macro- and microstructure of skeletal muscles. Different muscles and even different fiber bundles of the same muscle mature at different rates. This speed is determined by the function that a given anatomical formation performs at a particular age stage. As a rule, functionally active muscles mature first. In general, muscle mass increases by approximately 21% over the entire period of development. By the age of 8, muscle mass in relation to the mass of the whole body becomes equal to 27.2%, by the period of puberty - 32.6%, and at 17-18 years - 44.2%. It follows that the most intense weight gain occurs during puberty. By the time a child is born, the muscles of the trunk, head, and upper limbs reach their greatest development. Their mass makes up about 40% of the mass of all muscles (in adults - up to 30%).
The mass of the muscles of the upper extremities in relation to the mass of the muscles of the whole body increases from birth to 23-25 years, when the ontogenetic maturation of muscles ends, by only 2%. Consequently, by the time of birth they already have a fairly large mass, and its further increase was in full accordance with the increase in the mass of the entire body. At the same time, the muscle mass of the lower extremities in relation to body weight increases over the entire period of development by more than 16%. In the muscles of the upper extremities, the mass of those that cause finger movements increases especially sharply in preschool and primary school age. The mass of the extensor muscles increases more intensively than the flexors, since by the time of birth the flexors, which determine the characteristic fetal position during intrauterine development, are already significantly developed. The extensors that ensure the vertical position of the body mature intensively after the birth of a child.
Muscles that provide a large range of movement rapidly grow in length, and muscles whose function requires contractions of great strength increase in diameter. Their development is characterized by an increase in the degree of featheriness.
