After eating bitterness in the mouth. Causes of bitterness in the mouth after eating

1) Dorsal induction or Primary neurulation - a period of 3-4 weeks of gestation;
2) Ventral induction - the period of 5-6 weeks of gestation;
3) Neuronal proliferation - a period of 2-4 months of gestation;
4) Migration - a period of 3-5 months of gestation;
5) Organization - a period of 6-9 months of fetal development;
6) Myelination - takes the period from the moment of birth and in the subsequent period of postnatal adaptation.

IN first trimester of pregnancy there are stages of development nervous system fetus:

Dorsal induction or Primary neurulation - due to individual features development may vary in time, but always adheres to 3-4 weeks (18-27 days after conception) of gestation. During this period, the formation of the neural plate occurs, which, after closing its edges, turns into a neural tube (4-7 weeks of gestation).

Ventral induction - this stage of the formation of the fetal nervous system reaches its peak at 5-6 weeks of gestation. During this period, 3 expanded cavities appear at the neural tube (at its anterior end), from which are then formed:

from the 1st (cranial cavity) - the brain;

from the 2nd and 3rd cavity - the spinal cord.

Due to the division into three bubbles, the nervous system develops further and the rudiment of the fetal brain from three bubbles turns into five by division.

From forebrain formed - telencephalon and interstitial brain.

From the posterior cerebral bladder - the laying of the cerebellum and medulla oblongata.

Partial neuronal proliferation also occurs in the first trimester of pregnancy.

The spinal cord develops faster than the brain, and, therefore, it also begins to function faster, which is why it plays more important role during the early stages of fetal development.

But in the first trimester of pregnancy, the development of the vestibular analyzer deserves special attention. He is a highly specialized analyzer, which is responsible for the fetus for the perception of movement in space and the sensation of a change in position. This analyzer is formed already at the 7th week of intrauterine development (earlier than other analyzers!), and by the 12th week nerve fibers are already approaching it. myelination nerve fibers begins by the time the fetus first moves - at 14 weeks of gestation. But for conducting impulses from the vestibular nuclei to the motor cells of the anterior horns spinal cord the vestibulo-spinal tract needs to be myelinated. Its myelination occurs after 1-2 weeks (15 - 16 weeks of gestation).

Therefore, due to the early formation of the vestibular reflex, when a pregnant woman moves in space, the fetus moves into the uterine cavity. At the same time, the movement of the fetus in space is an "irritating" factor for the vestibular receptor, which sends impulses for further development fetal nervous system.

Fetal development disorders from exposure various factors during this period leads to violations of the vestibular apparatus in a newborn child.

Until the 2nd month of gestation, the fetus has a smooth surface of the brain, covered with an ependymal layer consisting of medulloblasts. By the 2nd month of intrauterine development, the cerebral cortex begins to form by migration of neuroblasts to the overlying marginal layer, and thus forming the anlage gray matter brain.

All adverse factors in the first trimester of the development of the fetal nervous system lead to severe and, in most cases, irreversible damage functioning and further formation fetal nervous system.

Second trimester of pregnancy.

If in the first trimester of pregnancy the main laying of the nervous system occurs, then in the second trimester its intensive development occurs.

Neuronal proliferation is the main process of ontogeny.

At this stage of development, physiological dropsy of the cerebral vesicles occurs. This is due to the fact that the cerebrospinal fluid, entering the brain bubbles, expands them.

By the end of the 5th month of gestation, all the main sulci of the brain are formed, and Luschka's foramina also appear, through which the cerebrospinal fluid enters the outer surface of the brain and washes it.

Within 4-5 months of brain development, the cerebellum develops intensively. It acquires its characteristic sinuosity, and divides across, forming its main parts: anterior, posterior and follicle-nodular lobes.

Also in the second trimester of pregnancy, the stage of cell migration takes place (month 5), as a result of which zonality appears. The fetal brain becomes more similar to the brain of an adult child.

When exposed adverse factors on the fetus in the second period of pregnancy, there are violations that are compatible with life, since the laying of the nervous system took place in the first trimester. At this stage, disorders are associated with underdevelopment of brain structures.

Third trimester of pregnancy.

During this period, the organization and myelination of brain structures occurs. Furrows and convolutions in their development are approaching the final stage (7-8 months of gestation).

Under the organization stage nervous structures understand morphological differentiation and the emergence of specific neurons. In connection with the development of the cytoplasm of cells and an increase in intracellular organelles, there is an increase in the formation of metabolic products that are necessary for the development of nervous structures: proteins, enzymes, glycolipids, mediators, etc. In parallel with these processes, the formation of axons and dendrites occurs to ensure synoptic contacts between neurons.

Myelination of nerve structures begins from 4-5 months of gestation and ends by the end of the first, beginning of the second year of a child's life, when the child begins to walk.

When exposed to adverse factors in the third trimester of pregnancy, as well as during the first year of life, when the processes of myelination of the pyramidal tracts end, serious violations does not occur. There may be slight changes in the structure, which are determined only by histological examination.

The development of cerebrospinal fluid and the circulatory system of the brain and spinal cord.

In the first trimester of pregnancy (1 - 2 months of gestation), when five brain bubbles, the formation of vascular plexuses occurs in the cavity of the first, second and fifth cerebral bladder. These plexuses begin to secrete highly concentrated CSF, which is, in fact, nutrient medium due to the high content of protein and glycogen in its composition (exceeds 20 times, unlike adults). Liquor - in this period is the main source nutrients for the development of the structures of the nervous system.

While the development of brain structures supports the cerebrospinal fluid, at 3-4 weeks of gestation, the first vessels of the circulatory system are formed, which are located in the soft arachnoid membrane. Initially, the oxygen content in the arteries is very low, but during the 1st to 2nd month of fetal development circulatory system takes on a more mature look. And in the second month of gestation blood vessels start to grow into medulla forming a circulatory network.

By the 5th month of development of the nervous system, the anterior, middle and posterior cerebral arteries appear, which are interconnected by anastomoses, and represent a complete structure of the brain.

The blood supply to the spinal cord comes from more sources than to the brain. Blood to the spinal cord comes from two vertebral arteries, which branch into three arterial tracts, which, in turn, run along the entire spinal cord, feeding it. The anterior horns receive more nutrients.

The venous system eliminates the formation of collaterals and is more isolated, which contributes to the rapid removal of the end products of metabolism through the central veins to the surface of the spinal cord and into the venous plexus of the spine.

A feature of the blood supply to the third, fourth and lateral ventricles in the fetus is the wider size of the capillaries that pass through these structures. This leads to slower blood flow, which leads to more intense nutrition.

Samara branch of Moscow State Pedagogical University

Abstract on the topic:

Critical periods in the development of the central nervous system in a child

Completed by: 3rd year student

Faculty of Psychology and Education

Kazakova Elena Sergeevna

Checked:

Korovina Olga Evgenievna

Samara 2013

Development of the nervous system.

The nervous system of higher animals and humans is the result of a long development in the process of adaptive evolution of living beings. The development of the central nervous system took place primarily in connection with the improvement in the perception and analysis of influences from the external environment.

At the same time, the ability to respond to these influences with a coordinated, biologically expedient reaction was also improved. The development of the nervous system also proceeded in connection with the complication of the structure of organisms and the need to coordinate and regulate the work of internal organs. To understand the activity of the human nervous system, it is necessary to get acquainted with the main stages of its development in phylogenesis.

The emergence of the central nervous system.

The lowest organized animals, for example, the amoeba, still have neither special receptors, nor a special motor apparatus, nor anything resembling a nervous system. An amoeba can perceive irritation with any part of its body and react to it with a peculiar movement by the formation of an outgrowth of protoplasm, or pseudopodia. By releasing a pseudopodium, the amoeba moves towards a stimulus, such as food.

In multicellular organisms, in the process of adaptive evolution, specialization of various parts of the body arises. Cells appear, and then organs adapted for the perception of stimuli, for movement, and for the function of communication and coordination.

The appearance of nerve cells not only made it possible to transmit signals over a greater distance, but also became the morphological basis for the rudiments of coordination of elementary reactions, which leads to the formation of a holistic motor act.

In the future, as the evolution of the animal world, the development and improvement of the apparatus of reception, movement and coordination takes place. There are various sense organs adapted for the perception of mechanical, chemical, temperature, light and other stimuli. A complex motor apparatus appears, adapted, depending on the lifestyle of the animal, to swimming, crawling, walking, jumping, flying, etc. As a result of the concentration, or centralization, of scattered nerve cells into compact organs, a central nervous system and peripheral nervous systems arise. way. Nerve impulses are transmitted along one of these pathways from receptors to the central nervous system, along others - from centers to effectors.

General structure of the human body.

The human body is a complex system of numerous and closely interconnected elements, united in several structural levels. The concept of the growth and development of an organism is one of the fundamental concepts in biology. The term "growth" is currently understood as an increase in the length, volume and body weight of children and adolescents, associated with an increase in the number of cells and their number. Development is understood as qualitative changes in the child's body, consisting in the complication of its organization, i.e. in the complication of the structure and function of all tissues and organs, the complication of their relationships and the processes of their regulation. Growth and development of the child, i.e. Quantitative and qualitative changes are closely interconnected with each other. Gradual quantitative and qualitative changes that occur during the growth of the organism lead to the appearance of new qualitative features in the child.

The entire period of development of a living being, from the moment of fertilization to the natural end of an individual life, is called ontogeny (Greek ONTOS - being, and GINESIS - origin). In ontogenesis, two relative stages of development are distinguished:

1. Prenatal - begins from the moment of conception to the birth of a child.

2. Postnatal - from the moment of birth to the death of a person.

Along with the harmony of development, there are special stages of the most abrupt spasmodic atom-physiological transformations.

In postnatal development, there are three such " critical period or "age crisis":

	Changing Factors	Consequences
from 2 to 4	Development of the sphere of communication with the outside world. The development of the form of speech. The development of a form of consciousness.	Increasing educational requirements. Increasing motor activity
from 6 to 8 years	New people. New friends. New responsibilities	Decreased motor activity
from 11 to 15 years old	Change hormonal balance with the maturation and restructuring of the work of the endocrine glands. Expanding the circle of communication	Conflicts in the family and at school. Hot temper

An important biological feature in the development of a child is that the formation of their functional systems occurs much earlier than they need.

The principle of advanced development of organs and functional systems in children and adolescents is a kind of "insurance" that nature gives to a person in case of unforeseen circumstances.

A functional system is a temporary association of various organs of a child's body, aimed at achieving a result useful for the existence of the organism.

Purpose of the nervous system.

The nervous system is the leading physiological system of the body. Without it, it would be impossible to connect countless cells, tissues, organs into a single hormonal working whole.

The functional nervous system is divided "conditionally" into two types:

Thus, thanks to the activity of the nervous system, we are connected with the surrounding world, we are able to admire its perfection, to learn the secrets of its material phenomena. Finally, thanks to the activity of the nervous system, a person is able to actively influence the surrounding nature, transform it in the desired direction.

At the highest stage of its development, the central nervous system acquires another function: it becomes an organ of mental activity, in which sensations, perceptions and thinking appear on the basis of physiological processes. The human brain is an organ that provides the possibility of social life, communication of people with each other, knowledge of the law of nature and society and their use in social practice.

Let us give some idea of conditioned and unconditioned reflexes.

Features of unconditional and conditioned reflexes.

The main form of activity of the nervous system is reflex. All reflexes are usually divided into unconditional and conditional.

Unconditioned reflexes- these are congenital, genetically programmed reactions of the body, characteristic of all animals and humans. The reflex arcs of these reflexes are formed in the process of prenatal development, and in some cases, in the process of postnatal development. For example, sexual innate reflexes are finally formed in a person only by the time of puberty in adolescence. Unconditioned reflexes have conservative, little-changing reflex arcs, passing mainly through the subcortical regions of the central nervous system. The participation of the cortex in the course of many unconditioned reflexes is not necessary.

Conditioned reflexes- individual, acquired reactions of higher animals and humans, developed as a result of learning (experience). Conditioned reflexes are always individually unique. Reflex arcs of conditioned reflexes are formed in the process of postnatal ontogenesis. They are characterized by high mobility, the ability to change under the influence of environmental factors. Reflex arcs of conditioned reflexes pass through the higher part of the brain - CGM.

Classification of unconditioned reflexes.

The question of classifying unconditioned reflexes is still open, although the main types of these reactions are well known. Let us dwell on some especially important unconditioned human reflexes.

1. Food reflexes. For example, salivation when food enters the oral cavity or sucking reflex in a newborn baby.

2. Defensive reflexes. Reflexes that protect the body from various adverse effects, an example of which can be a hand withdrawal reflex during pain irritation of the finger.

3. Orienting reflexes. Any new unexpected stimulus draws the photograph of a person to itself.

4. Game reflexes. This type of unconditioned reflexes is widely found in various representatives of the animal kingdom and also has an adaptive value. Example: puppies, playing,. hunt each other, sneak up and attack their "opponent". Consequently, during the game, the animal creates models of possible life situations and carries out a kind of "preparation" for various life surprises.

While retaining its biological foundations, children's play acquires new qualitative features - it becomes an active tool for understanding the world and, like any other human activity, acquires a social character. The game is the very first preparation for future work and creative activity.

The game activity of the child appears from 3-5 months of postnatal development and underlies the development of his ideas about the structure of the body and the subsequent isolation of himself from the surrounding reality. At 7-8 months play activity acquires an "imitative or teaching" character and contributes to the development of speech, the improvement of the emotional sphere of the child and the enrichment of his ideas about the surrounding reality. From the age of one and a half, the child's play becomes more and more complicated, the mother and other people close to the child are introduced into the game situations, and thus the foundations for the formation of interpersonal, social relations are created.

In conclusion, it should also be noted sexual and parental unconditioned reflexes associated with the birth and feeding of offspring, reflexes that ensure the movement and balance of the body in space, and reflexes that maintain the homeostasis of the body.

instincts. A more complex, unconditionally reflex activity is the instincts, the biological nature of which is still unclear in its details. In a simplified form, instincts can be represented as a complex interconnected series of simple innate reflexes.

Physiological mechanisms of formation of conditioned reflexes.

The following essential conditions are necessary for the formation of a conditioned reflex:

1) The presence of a conditioned stimulus

2) The presence of unconditional reinforcement

The conditioned stimulus must always somewhat precede the unconditioned reinforcement, i.e., serve as a biologically significant signal; the conditioned stimulus must be weaker than the unconditioned stimulus in terms of the strength of its effect; finally, for the formation of a conditioned reflex, a normal (active) functional state of the nervous system, especially its leading department - the brain, is necessary. Any change can be a conditioned stimulus! Powerful factors contributing to the formation of conditioned reflex activity are rewards and punishments. At the same time, we understand the words "encouragement" and "punishment" in a broader sense than simply "satisfaction of hunger" or "painful effect". It is in this sense that these factors are widely used in the process of teaching and raising a child, and every teacher and parent is well aware of their effective action. True, up to 3 years for the development of useful reflexes in a child, “food reinforcement” also has a leading role. However, then the leading role as a reinforcement in the development of useful conditioned reflexes acquires "verbal encouragement." Experiments show that in children older than 5 years, with the help of praise, you can develop any useful reflex in 100% of cases.

Thus, educational work, in its essence, is always associated with the development in children and adolescents of various conditioned reflex reactions or their complex interconnected systems.

Classification of conditioned reflexes.

The classification of conditioned reflexes is difficult due to their large number. There are exteroceptive conditioned reflexes that are formed when the exteroreceptors are stimulated; interoceptive reflexes, which are formed when receptors located in the internal organs are stimulated; and proprioceptive, arising from stimulation of muscle receptors.

There are natural and artificial conditioned reflexes. The first are formed under the action of natural unconditioned stimuli on the receptors, the second - under the action of indifferent stimuli. For example, salivation in a child at the sight of favorite sweets is a natural conditioned reflex, and salivation that occurs in a hungry child at the sight of dinner utensils is an artificial reflex.

The interaction of positive and negative conditioned reflexes is important for adequate interaction of the organism with external environment. Such an important feature of the child's behavior as discipline is associated precisely with the interaction of these reflexes. In physical education lessons, to suppress reactions of self-preservation and a sense of fear, for example, when performing gymnastic exercises on the uneven bars, defensive negative conditioned reflexes are inhibited in students and positive motor reflexes are activated.

A special place is occupied by conditioned reflexes for time, the formation of which is associated with regularly repeated stimuli at the same time, for example, with food intake. That is why, by the time of eating, the functional activity of the digestive organs increases, which has a biological meaning. Such rhythmicity of physiological processes underlies the rational organization of the day regimen of preschool and school children and is a necessary factor in the highly productive activity of an adult. Reflexes for time, obviously, should be attributed to the group of so-called trace conditioned reflexes. These reflexes are developed if the unconditioned reinforcement is given 10-20 seconds after the final action of the conditioned stimulus. In some cases, it is possible to develop trace reflexes even after a 1-2 minute pause.

Important in the life of a child are imitation reflexes, which are also a kind of conditioned reflexes. To develop them, it is not necessary to take part in the experiment, it is enough to be its "spectator".

Higher nervous activity in the early and preschool periods of development (from birth to 7 years).

A child is born with a set of unconditioned reflexes. reflex arcs of which begin to form at the 3rd month of prenatal development. So, the first sucking and respiratory movements appear in the fetus precisely at this stage of ontogenesis, and the active movement of the fetus is observed at the 4-5th month of intrauterine development. By the time of birth, most of the innate unconditioned reflexes are formed in the child, providing him with the normal functioning of the vegetative sphere, his vegetative "comfort".

The possibility of simple food conditioned reactions, despite the morphological and functional immaturity of the brain, occurs already on the first or second day, and by the end of the first month of development, conditioned reflexes are formed from the motor analyzer and vestibular apparatus: motor and temporal. All these reflexes are formed very slowly, they are extremely gentle and easily inhibited, which is apparently due to the immaturity of the cortical cells and the sharp predominance of excitatory processes over inhibitory ones and their wide irradiation.

From the second month of life, auditory, visual, and tactile reflexes are formed, and by the 5th month of development, the child develops all the main types of conditioned inhibition. The education of the child is of great importance in the improvement of conditioned reflex activity. The earlier training is started, i.e., the development of conditioned reflexes, the faster their formation subsequently proceeds.

By the end of the first year of development, the child relatively well distinguishes the taste of food, smells, the shape and color of objects, distinguishes voices and faces. Significantly improved movement, some children begin to walk. The child tries to pronounce individual words ("mom", "dad", "grandfather", "aunt", "uncle", etc.), and he develops conditioned reflexes to verbal stimuli. Consequently, already at the end of the first year, the development of the second signaling system is in full swing and its joint activity with the first is being formed.

The development of speech is a difficult task. It requires coordination respiratory muscles, muscles of the larynx, tongue, pharynx and lips. Until this coordination is developed, the child pronounces many sounds and words incorrectly.

It is possible to facilitate the formation of speech by the correct pronunciation of words and grammatical phrases so that the child constantly hears the patterns he needs. Adults, as a rule, when addressing a child, try to copy the sounds that the child utters, believing that in this way they will be able to find a "common language" with him. This is a profound delusion. There is a huge distance between a child's understanding of words and the ability to pronounce them. The lack of the right role models delays the development of the child's speech.

The child begins to understand words very early, and therefore, for the development of speech, it is important to "talk" with the child from the first days after his birth. When changing a vest or a diaper, shifting a child or preparing him for feeding, it is advisable not to do this silently, but to address the child with the appropriate words, naming your actions.

The first signal system is the analysis and synthesis of direct, specific signals of objects and phenomena of the surrounding world, coming from visual, auditory and other receptors of the body and components

The second signaling system is (only in humans) the connection between verbal signals and speech, the perception of words - heard, spoken (aloud or to oneself) and visible (when reading).

In the second year of the child's development, all types of conditioned reflex activity are improved and the formation of the second signal system continues, the vocabulary increases significantly (250-300 words); direct stimuli or their complexes begin to cause verbal reactions. If in a one-year-old child conditioned reflexes to direct stimuli are formed 8-12 times faster than to a word, then at the age of two, words acquire a signal value.

Of decisive importance in the formation of the child's speech and the entire second signaling system as a whole is the communication of the child with adults, i.e. Environment social environment and learning processes. This fact is another proof of the decisive role of the environment in the unfolding of the potential possibilities of the genotype. Children deprived of a linguistic environment, communication with people, do not speak, moreover, their intellectual abilities remain at a primitive animal level. At the same time, the age from two to five is "critical" in mastering speech. Cases are known that children abducted by wolves in early childhood and returned to human society after five years, are able to learn to speak only to a limited extent, and those returned only after 10 years are not able to utter a single word.

The second and third years of life are distinguished by lively orientation and research activities. “At the same time,” writes M. M. Koltsova, “the essence of the orienting reflex of a child of this age can be more correctly characterized not by the question “what is it?”, but by the question “what can be done with it?”. The child reaches out to each object, touches it, feels it, pushes it, tries to lift it, etc."

Thus, the described age of the child is characterized by the "objective" nature of thinking, that is, by the decisive importance of muscular sensations. This feature is largely associated with the morphological maturation of the brain, since many motor cortical zones and zones of skin-muscle sensitivity already reach a sufficiently high functional usefulness by the age of 1-2 years. The main factor stimulating the maturation of these cortical zones are muscle contractions and high physical activity child. Limitation of its mobility at this stage of ontogenesis significantly slows down mental and physical development.

The period up to three years is also characterized by the extraordinary ease of formation of conditioned reflexes to a wide variety of stimuli, including the size, heaviness, distance and color of objects. Pavlov considered these types of conditioned reflexes to be prototypes of concepts developed without words ("grouped reflection of the phenomena of the external world in the brain").

A notable feature of a two-three-year-old child is the ease of developing dynamic stereotypes. Interestingly, each new stereotype is developed more easily. M. M. Koltsova writes: “Now not only the daily regimen becomes important for the child: the hours of sleep, wakefulness, nutrition and walks, but also the sequence in putting on or taking off clothes or the order of words in a familiar fairy tale and song - everything becomes important. Obviously , that with insufficiently strong and mobile nervous processes children need stereotypes that make it easier to adjust to their environment."

Conditional connections and dynamic stereotypes in children up to three years of age are distinguished by extraordinary strength, therefore their alteration for a child is always an unpleasant event. An important condition in educational work at this time is a careful attitude to all stereotypes developed.

The age from three to five years is characterized by the further development of speech and the improvement of nervous processes (their strength, mobility and balance increase), the processes of internal inhibition become dominant, but delayed inhibition and a conditioned brake are developed with difficulty. Dynamic stereotypes are developed just as easily. Their number increases every day, but their alteration no longer causes disturbances in higher nervous activity, which is due to the above functional changes. The orienting reflex to extraneous stimuli is longer and more intense than in school-age children, which can be used effectively for inhibition in children bad habits and skills.

Thus, truly inexhaustible possibilities open up before the creative initiative of the educator during this period. Many outstanding teachers (D. A. Ushinsky, A. S. Makarenko) empirically considered the age from two to five to be especially responsible for the harmonious formation of all the physical and mental capabilities of a person. Physiologically, this is based on the fact that the conditional connections and dynamic stereotypes that arise at this time are exceptionally strong and are carried by a person through his entire life. At the same time, their constant manifestation is not necessary, they can be inhibited for a long time, but under certain conditions they are easily restored, suppressing the conditional connections developed later.

By the age of five to seven, the role of the signaling system of words increases even more, and children begin to speak freely. "A word at this age already has the meaning of a "signal of signals", that is, it acquires a general meaning close to that which it has for an adult."

This is due to the fact that only by the age of seven postnatal development does the material substratum of the second signaling system mature functionally. In this regard, it is especially important for educators to remember that only by the age of seven can a word be effectively used to form conditional connections. Abuse of a word before this age without its sufficient connection with direct stimuli is not only ineffective, but also causes functional damage to the child, forcing the child's brain to work in non-physiological conditions.

Higher nervous activity of schoolchildren

The existing few data of physiology indicate that the primary school age (from 7 to 12 years old) is a period of relatively "quiet" development of higher education. nervous activity. The strength of the processes of inhibition and excitation, their mobility, balance, and mutual induction, as well as the reduction in the strength of external inhibition, provide opportunities for broad learning for the child. This is the transition "from reflex emotionality to the intellectualization of emotions"

However, only on the basis of teaching writing and reading does the word become an object of the child's consciousness, moving further and further away from the images of objects and actions associated with it. A slight deterioration in the processes of higher nervous activity is observed only in the 1st grade due to the processes of adaptation to school. It is interesting to note that in the younger school age on the basis of the development of the second signaling system, the conditioned reflex activity of the child acquires a specific character, characteristic only of man. For example, during the development of vegetative and somato-motor conditioned reflexes in children, in some cases, a response is observed only to an unconditioned stimulus, and the conditioned one does not cause a reaction. So, if the subject was given a verbal instruction that after the call he would receive cranberry juice, then salivation begins only upon presentation of an unconditioned stimulus. Such cases of "non-formation" of the conditioned reflex manifest themselves the more often, the older the subject is, and among children of the same age - among the more disciplined and capable.

Verbal instruction greatly accelerates the formation of conditioned reflexes and in some cases does not even require unconditional reinforcement: conditioned reflexes are formed in humans in the absence of direct stimuli. These features of conditioned reflex activity determine the enormous importance of verbal pedagogical influence in the process of educational work with younger schoolchildren.

The central nervous system, together with the peripheral parts of the distant analyzers, develops from the outer germ layer - the ectoderm. The laying of the neural tube occurs at the 4th week of embryonic development; subsequently, the cerebral vesicles and the spinal cord are formed from it. The most intensive formation of the structures of the central nervous system occurs on the 15-25th day of pregnancy (Table 10-2).

The structural design of the brain regions is closely related to the processes of differentiation of nerve elements occurring in them and the establishment of morphological and functional connections, as well as with the development of peripheral nervous apparatus (receptors, afferent and efferent pathways, etc.). By the end of the embryonic period of development, the first manifestations of nervous activity are found in the fetus, which are expressed in elementary forms of motor activity.

Functional maturation of the CNS occurs during this period in the caudal-cranial direction, i.e. from the spinal cord to the cerebral cortex. In this regard, the functions of the fetal body are regulated mainly by the structures of the spinal cord.

By the 7-10th week of the intrauterine period, functional control over the more mature spinal cord begins to exercise medulla. From 13-14 weeks there are signs of control of the underlying parts of the central nervous system by the midbrain.

Brain bubbles form cerebral hemispheres, up to 4 one month old During prenatal development, their surface is smooth, then the primary furrows of the sensory fields of the cortex appear, at the 6th month - the secondary ones, and the tertiary ones continue to form after birth. In response to cortical stimulation hemispheres fetus, up to 7 months of its development, no reactions occur. Therefore, at this stage, the cerebral cortex does not determine the behavior of the fetus.

During the embryonic and fetal periods of ontogeny, there is a gradual complication of the structure and differentiation of neurons and glial cells.

Table 10-2.

Brain development in the antenatal period


age, weeks	length, mm	Features of brain development
		There is a neural groove
		The well-defined neural groove quickly closes; the neural crest has the appearance of a continuous ribbon
		The neural tube is closed; 3 primary cerebral vesicles formed; nerves and ganglia are formed; the formation of the ependymal, mantle and marginal layers has ended
		5 brain bubbles are formed; cerebral hemispheres are outlined; nerves and ganglia are more pronounced (the adrenal cortex is isolated)
		3 primary bends of the neural tube are formed; nerve plexuses are formed; visible epiphysis (pineal body); sympathetic nodes form segmental clusters; planned meninges
		The cerebral hemispheres reach big size; well expressed striatum and visual tubercle; the funnel and Rathke's pocket are closed; choroid plexuses appear (adrenal medulla begins to penetrate into the cortex)
		Typical nerve cells appear in the cerebral cortex; olfactory lobes are noticeable; the hard, soft and arachnoid membranes of the brain are clearly expressed; chromaffin bodies appear
		The definitive internal structure of the spinal cord is formed
		Common structural features of the brain appear; cervical and lumbar thickening is visible in the spinal cord; cauda equina and filum terminalis of the spinal cord are formed, differentiation of neuroglial cells begins
		The hemispheres cover most of the brain stem; lobes of the brain become visible; tubercles of the quadrigemina appear; the cerebellum becomes more pronounced
		The formation of brain commissures is completed (20 weeks); myelination of the spinal cord begins (20 weeks); typical layers of the cerebral cortex appear (25 weeks); furrows and convolutions of the brain develop rapidly (28-30 weeks); myelination of the brain occurs (36-40 weeks)

The neocortex is already divided into layers in a fetus of 7-8 months of age, but the highest rates of growth and differentiation of the cellular elements of the cortex are observed in the last 2 months of pregnancy and in the first months after birth. The pyramidal system, which provides voluntary movements, matures later than the extrapyramidal system, which controls involuntary movements. An indicator of the degree of maturity of nerve structures is the level of myelination of its conductors. Myelination in the embryonic brain begins at the 4th month of intrauterine life from the anterior roots of the spinal cord, preparing motor activity; then the posterior roots are myelinated, the pathways of the spinal cord, the afferents of the acoustic and labyrinth systems. In the brain, the process of myelination of conductive structures continues in the first 2 years of a child's life, remaining in adolescents and even adults.

The earliest (7.5 weeks) the fetus has a well-defined local reflex to irritation of the lips. The reflexogenic zone of the sucking reflex by the 24th week of intrauterine development expands significantly and is evoked from the entire surface of the face, hand, and forearm. In postnatal ontogenesis, it decreases to the zone of the surface of the lips.

Reflexes to tactile stimulation of the skin of the upper extremities appear in the fetus by 11 weeks. The skin reflex during this period is most clearly evoked from the palmar surface and looks like isolated finger movements. By 11 weeks, these finger movements are accompanied by flexion of the wrist, forearm, and pronation of the hand. By the 15th week, stimulation of the palm leads to flexion and fixation in this position of the fingers, the previously generalized reaction disappears. By the 23rd week, the grasping reflex intensifies and becomes strictly local. By the 25th week, all tendon reflexes of the hand become distinct.

Reflexes when stimulating the lower extremities appear by the 10-11th week of fetal development. The flexor reflex of the toes to irritation of the sole appears first. By 12-13 weeks, the flexor reflex to the same irritation is replaced by a fan-shaped dilution of the fingers. After 13 weeks, the same movement to stimulate the sole is accompanied by movements of the foot, lower leg, and thigh. At an older age (22-23 weeks), irritation of the sole causes mainly flexion of the toes.

By the 18th week, a trunk flexion reflex appears with irritation of the lower abdomen. By the 20-24th week, muscle reflexes appear abdominal wall. By the 23rd week, respiratory movements can be induced in the fetus by irritation of various parts of the skin surface. By the 25th week, the fetus can breathe on its own, but the respiratory movements that ensure the survival of the fetus are established only after 27 weeks of its development.

Thus, the reflexes of the skin, motor and vestibular analyzers appear already on early stages intrauterine development. In the later stages of intrauterine development, the fetus is able to respond with facial movements to taste and smell irritations.

Within 3 recent months prenatal development in the fetus, the reflexes necessary for the survival of the newborn child mature: cortical regulation of orientation, protective, and other reflexes begins to be realized, the newborn already has protective and food reflexes; reflexes from muscles and skin become more localized and focused. In the fetus and newborn, due to the small amount of inhibitory mediators, generalized excitation easily occurs in the central nervous system even with very small stimulus forces. The strength of inhibitory processes increases as the brain matures.

The stage of generalization of response reactions and the spread of excitation throughout the structures of the brain persists until birth and for some time after it, but it does not prevent the development of complex vital reflexes. For example, by 21-24 weeks, the sucking and grasping reflex is well developed.

In the fetus already at the 4th month of its development, the proprioceptive muscular system is well developed, tendon and vestibular reflexes, at 3-5 months there are already labyrinth and cervical tonic position reflexes. The tilt and turn of the head is accompanied by the extension of the limbs of the side in which the head is turned.

The reflex activity of the fetus is provided mainly by the mechanisms of the spinal cord and brain stem. However, the sensorimotor cortex already reacts with excitation to irritations of the trigeminal nerve receptors on the face, receptors on the skin surface of the extremities; in a 7-8 month old fetus visual cortex there are reactions to light stimuli, but during this period, the cortex, perceiving signals, is excited locally and does not transfer the significance of the signal to other, except for the motor cortex, brain structures.

In the last weeks of intrauterine development, the fetus alternates between REM and non-REM sleep, with REM sleep accounting for 30-60% of total sleep time.

The intake of nicotine, alcohol, drugs, medicines and viruses into the bloodstream of the fetus affects the health of the unborn child, and in some cases can lead to intrauterine death of the fetus.

Nicotine, getting from the mother's blood into the blood of the fetus, and then into the nervous system, affects the development of inhibitory processes, and thus the reflex activity, differentiation, which will subsequently affect the processes of memory, concentration. The action of alcohol also causes gross violations of the maturation of the nervous system, disrupts the sequence of development of its structures. Drugs used by mother depress him physiological centers, which form natural endorphins, which can subsequently lead to dysfunction of the sensory system, hypothalamic regulation.

10.2 . Features of the development and functioning of the central nervous system in postnatal ontogenesis.

The general plan of the structure of the cortex in a newborn child is the same as in an adult. The mass of his brain is 10-11% of body weight, and in an adult - only 2%.

The total number of neurons in the brain of a newborn is equal to the number of neurons in an adult, but the number of synapses, dendrites and collaterals of axons, their myelination in newborns is significantly behind the brain of adults (Table 10-1).

The cortical zones of the newborn mature heterochronously. The somatosensory and motor cortex matures the earliest. This is explained by the fact that the somatosensory cortex of all sensory systems receives the largest amount of afferent impulses, the motor cortex also has a significantly greater afferent than other systems, since it has connections with all sensory systems and has the largest number of polysensory neurons.

By the age of 3, almost all areas of the sensory and motor cortex, with the exception of the visual and auditory ones, mature. The associative cortex of the brain matures most late. A jump in the development of associative areas of the cerebral cortex is noted at the age of 7. The maturation of associative zones proceeds at an increasing pace until puberty, and then slows down and ends by 24-27 years of age. Later than all of the associative zones of the cortex, the associative areas of the frontal and parietal cortex complete the maturation.

The maturation of the cortex means not only the implementation of the establishment of the interaction of cortical, but also the establishment of the interaction of the cortex with subcortical formations. These relationships are established by the age of 10-12, which is very important for regulating the activity of body systems during puberty, when the activity of the hypothalamic-pituitary system increases, as well as systems related to sexual development, the development of glands internal secretion.

Period newborns (neonatal period). The maturation of the child's cerebral cortex in the process of postembryonic development at the cellular level occurs due to a gradual increase in the size of the primary, secondary and tertiary cortical zones. The older the child, the larger these cortical zones occupy, and the more complex and diverse becomes his mental activity. In a newborn, the associative neuronal layers of the cerebral cortex are poorly developed and improve only with its normal development. In congenital dementia, the upper layers of the cerebral cortex remain underdeveloped.

Already in the first hours after birth, the child has developed tactile and other reception systems, so the newborn has a number of protective reflexes to painful and tactile stimuli, reacts vividly to temperature stimuli. Of the distant analyzers, the auditory is most well developed in a newborn child. The least developed visual analyzer. Only by the end of the neonatal period are coordinated movements of the left and right eyeballs. However, the reaction of the pupils to light takes place already in the first hours after birth (congenital reflex). By the end of the neonatal period, the ability to converge the eyes appears (Table 10-3).

Table 10-3.

Evaluation (points) age development newborn (1st week)

Index	Response score

Dynamic features
The relationship between sleep and wakefulness		Sleeps calmly, wakes up only for feeding or when wet, falls asleep quickly	Sleeps calmly and does not wake up wet and for feeding or full and dry does not fall asleep	Does not wake up hungry and wet, but full and dry does not fall asleep or often screams for no reason	Very difficult to wake up or sleeps little, but does not scream or screams constantly
		The cry is loud, clear with a short inhalation and an extended exhalation	The cry is quiet, weak, but with a short inhalation and an extended exhalation	Cry painful, piercing or separate sobs on inspiration	There is no cry, or separate screams, or an aphonic cry
Unconditioned reflexes		All unconditioned reflexes are evoked, symmetrical	Require longer stimulation or rapidly deplete or are not consistently asymmetric	All are called, but after a long latent period and repeated stimulation, they are quickly depleted or persistently asymmetric	Most reflexes are not triggered
Muscle tone		Symmetric flexor tone overcome by passive movements	Mild asymmetry or tendency to hypo- or hypertension without affecting posture or movement	Permanent asymmetries, hypo- or hyper-limiting spontaneous movements	Postures of opistho-tonus or embryo or frog
Asymmetric cervical tonic reflex (ASTR)		When turning the head to the side, it unsteadily unbends the “front” arm		Constant extension or no extension of the arm when turning the head to the side	Swordsman Pose
Chain symmetrical reflex		Absent
Sensory reactions		Squints and worries in bright light; turns his eyes to the source of light and shudders at a loud sound	One of the responses is questionable	One of the response evaluation reactions 3 is absent or 2-3 reactions are doubtful	All response score 3 responses are missing

The motor activity of a newborn child is erratic and uncoordinated. The neonatal period of a full-term baby is characterized by predominant activity of the flexor muscles. The chaotic movements of the child are due to the activity of the subcortical formations and the spinal cord, which is not coordinated by the cortical structures.

From the moment of birth, the most important unconditioned reflexes begin to function in a newborn (Table 10-4). The first cry of a newborn, the first exhalation are reflex. In a full-term baby, three unconditioned reflexes are well expressed - food, defensive and indicative. Therefore, already in the second week of life, conditioned reflexes are developed in him (for example, a position reflex for feeding).

Table 10-4.

Reflexes of the newborn.

	Definition method	A brief description of
Babinsky	Light foot stroking from heel to toes	Bends the first toe and extends the rest
	Unexpected noise (such as clapping your hands) or the baby's head dropping quickly	Spreads the arms to the sides, and then crosses them on the chest
closure (closing eyelids)	Flash Light	Closes eyes
Prehensile	Place a finger or pencil in the child's hand	Grabs a finger (pencil) with fingers

In the neonatal period, there is a rapid maturation of reflexes already existing before birth, as well as the appearance of new reflexes or their complexes. The mechanism of reciprocal inhibition of spinal, symmetric and reciprocal reflexes is enhanced.

In a newborn, any irritation causes an orienting reflex. Initially, it manifests itself as a general shuddering of the body and inhibition of motor activity with a delay in breathing, subsequently, a motor reaction of the arms, legs, head, torso occurs to external signals. At the end of the first week of life, the child reacts to signals with an orienting reaction with the presence of some vegetative and exploratory components.

A significant turning point in the development of the nervous system is the stage of the emergence and consolidation of antigravitational reactions and the acquisition of the ability to carry out purposeful locomotor acts. Starting from this stage, the nature and degree of intensity of the implementation of motor behavioral reactions determine the characteristics of the growth and development of a given child. In this period, a phase of up to 2.5-3 months stands out, when the child first fixes first antigravity reaction, characterized by the ability to hold the head in a vertical position. The second phase lasts from 2.5-3 to 5-6 months, when the child makes the first attempts to realize second antigravity reaction- sitting posture. The direct emotional communication of the child with the mother increases his activity, becomes the necessary basis for the development of his movements, perception, thinking. Lack of communication negatively affects its development. Children who ended up in an orphanage lag behind in mental development (even with good hygienic care), their speech appears late.

Mother's milk hormones are necessary for the child for the normal maturation of the mechanisms of his brain. So, for example, more than half of women who received artificial feeding in early childhood suffer from infertility due to a lack of prolactin. Prolactin deficiency in mother's milk disrupts the development of the dopaminergic system of the child's brain, which leads to underdevelopment of the inhibitory systems of his brain. In the postnatal period, the need of the developing brain for anabolic and thyroid hormones is high, since at this time the synthesis of proteins of the nervous tissue is carried out and the process of its myelination takes place.

The development of the central nervous system of the child is greatly facilitated by thyroid hormones. In newborns and during the first year of life, the level of thyroid hormones is maximum. A decrease in the production of thyroid hormones in the fetal or early postnatal periods leads to cretinism due to a decrease in the number and size of neurons and their processes, inhibition of the development of synapses, their transition from potential to active. The process of myelination is provided not only by thyroid hormones, but also by steroid hormones, which is a manifestation of the body's reserve capabilities in the regulation of brain maturation.

For the normal development of various centers of the brain, it is necessary to stimulate them with signals that carry information about external influences. The activity of brain neurons is a prerequisite for the development and functioning of the central nervous system. In the process of ontogenesis, those neurons will not be able to function, which, due to a deficiency of afferent inflow, have not established a sufficient number of effective synaptic contacts. The intensity of the sensory influx predetermines the ontogeny of behavior and mental development. So, as a result of raising children in a sensory enriched environment, there is an acceleration of mental development. Adaptation to the external environment and education of deaf-blind-mute children are possible only with an increased influx of afferent impulses from the preserved skin receptors into the CNS.

Any dosed effects on the senses, propulsion system, speech centers perform multi-purpose functions. Firstly, they have a system-wide effect, regulating the functional state of the brain, improving its work; secondly, they contribute to a change in the rate of brain maturation processes; thirdly, they ensure the deployment of complex programs of individual and social behavior; fourthly, they facilitate the processes of association during mental activity.

Thus, the high activity of sensory systems accelerates the maturation of the CNS and ensures the implementation of its functions as a whole.

At the age of about 1 year, the child is fixed third antigravity reaction- implementation of the standing posture. Prior to its implementation, the physiological functions of the body mainly ensure growth and preferential development. After the implementation of the standing posture, the child has new opportunities in the coordination of movements. The standing posture contributes to the development of motor skills, the formation of speech. A critical factor for the development of appropriate cortical structures in a given age period is the preservation of the child's communication with his own kind. Isolation of a child (from people) or inadequate upbringing conditions, for example, among animals, despite the genetically determined maturation of brain structures to this critical stage of ontogenesis, the body does not begin to interact with environmental conditions specific to humans, which would stabilize and promote the development of mature structures. Therefore, the emergence of new human physiological functions and behavioral responses is not realized. In children who grew up in isolation, the function of speech is not realized, even when isolation from people ends.

In addition to critical age periods, there are sensitive periods in the development of the nervous system. This term refers to periods of greatest sensitivity to certain specific influences. The sensitive period of speech development lasts from one to three years, and if this stage is missed (there was no verbal communication with the child), it is almost impossible to compensate for losses in the future.

In the age period 1 year to 2.5-3 years . In this age period, the development of locomotor acts in the environment (walking and running) takes place in connection with the improvement of reciprocal forms of inhibition of the antagonist muscles. The development of the child's central nervous system is greatly influenced by afferent impulses from proprioceptors that occur during contraction skeletal muscle. There is a direct relationship between the level of development of the musculoskeletal system, the motor analyzer of the child and his general physical and mental development. The influence of motor activity on the development of the child's brain functions manifests itself in specific and non-specific forms. The first is related to the fact that the motor areas of the brain are a necessary element of its activity as a center for organizing and improving movements. The second form is associated with the influence of movements on the activity of cortical cells of all brain structures, an increase in which contributes to the formation of new conditioned reflex connections and the implementation of old ones. The subtle movements of the fingers of children play a leading role in this. In particular, the formation of motor speech is influenced by coordinated movements of the fingers: when training precise movements, voice reactions in children of 12-13 months develop not only more intensively, but also turn out to be more perfect, speech becomes clearer, complex phrases are easier to reproduce. As a result of training fine finger movements, children master speech very quickly, significantly outperforming the group of children in which these exercises were not carried out. The influence of proprioceptive impulses from the muscles of the hand on the development of the cerebral cortex is most pronounced in childhood, while the speech motor zone of the brain is being formed, but it persists at older ages.

Thus, the movements of the child are not only an important factor in physical development, but are also necessary for normal mental development. Restriction of mobility or muscle overload violate the harmonious functioning of the body and can be a pathogenetic factor in the development of a number of diseases.

3 years - 7 years. 2.5–3 years is another turning point in the development of the child. Intense physical and mental development the child leads to the intense work of the physiological systems of his body, and in the case of too high requirements - to their "breakdown". The nervous system is especially vulnerable, its overstrain leads to the appearance of a syndrome of small brain dysfunctions, inhibition of the development of associative thinking, etc.

The nervous system of a preschool child is extremely plastic and sensitive to various external influences. Early preschool age is most favorable for improving the activity of the sense organs, the accumulation of ideas about the world around. Many connections between the nerve cells of the neocortex, even those present at birth and due to hereditary growth mechanisms, must be reinforced during the period of communication of the organism with the environment, i.e. these connections must be claimed in time. Otherwise, these links will no longer be able to function.

One of the objective indicators of the degree of functional maturity of the child's brain can be functional interhemispheric asymmetry. The first stage of formation of interhemispheric interaction lasts from 2 to 7 years and corresponds to the period of intensive structural maturation of the corpus callosum. Until the age of 4, the hemispheres are relatively separated, however, by the end of the first period, the possibilities of transmitting information from one hemisphere to another increase significantly.

The preference for the right or left hand is clearly revealed already at the age of 3 years. The degree of asymmetry progressively increases from 3 to 7 years, further increase in asymmetry is insignificant. The rate of progressive growth of asymmetry in the interval of 3-7 years is higher in left-handers than in right-handers. With age, when comparing preschoolers and younger schoolchildren, the degree of preference for using the right arm and leg increases. At the age of 2-4 years, right-handed people make up 38%, and by the age of 5-6 years - already 75%. In abnormal children, the development of the left hemisphere is significantly delayed and functional asymmetry is weakly expressed.

Among the exogenous factors that cause the occurrence of signs of impaired development of the central nervous system, environment. A neuropsychological examination of children aged 6-7 years in cities with an unfavorable environmental situation reveals a deficiency in motor coordination, auditory-motor coordination, stereognosis, visual memory, and speech functions. Motor awkwardness, decrease in auditory perception, slowness of thinking, weakening of attention, insufficient formation of skills of intellectual activity were noted. A neurological examination reveals microsymptomatics: anisoreflexia, muscular dystonia, impaired coordination. A relationship has been established between the frequency of disorders in the neuropsychological development of children with pathology of their perinatal period and deviations in health at this time of parents employed in environmentally unfavorable industries.

7 - 12 years old. The next stage of development - 7 years (the second critical period of postnatal ontogenesis) - coincides with the beginning of schooling and is caused by the need for the child's physiological and social adaptation to school. The spread of the practice of primary education in expanded and in-depth programs in pursuit of the growth of educational and pedagogical indicators of children leads to a significant disruption of the neuropsychic status of the child, which is manifested by a decrease in working capacity, deterioration of memory and attention, changes in the functional state of the cardiovascular and nervous systems, disorders vision in first graders.

In most preschool children, right-hemispheric dominance is normally noted, even in the implementation of speech, which, apparently, indicates the predominance of their figurative, concrete perception of the outside world, carried out mainly by the right hemisphere. In children of primary school age (7-8 years old), the most common is a mixed type of asymmetry, i.e. according to some functions, the activity of the right hemisphere prevailed, according to others - the activity of the left. However, the complication and steady development of second-signal conditional relationships with age, apparently, causes an increase in the degree of interhemispheric asymmetry, as well as an increase in the number of cases of left hemispheric asymmetry in 7 and especially in 8-year-old children. Thus, in this segment of ontogenesis, a change in phase relations between the hemispheres and the formation and development of the dominance of the left hemisphere can be clearly seen. Electroencephalographic (EEG) studies of left-handed children indicate a lower degree of maturity of their neurophysiological mechanisms compared to right-handed children.

At 7-10 years old, the corpus callosum increases in volume due to ongoing myelination, the relationship of callosal fibers with the neural apparatus of the cortex becomes more complicated, which expands the compensatory interactions of symmetrical brain structures. By the age of 9–10 years, the structure of interneuronal connections of the cortex becomes much more complicated, ensuring the interaction of neurons both within the same ensemble and between neuronal ensembles. If in the first years of life the development of interhemispheric relations is determined by the structural maturation of the corpus callosum, i.e. interhemispheric interaction, then after 10 years the dominant factor is the formation of intra- and interhemispheric organization of the brain.

12 - 16 years old. Period - puberty, or adolescence, or senior school age. It is usually characterized as age crisis, in which there is a rapid and rapid morphophysiological transformation of the body. This period corresponds to the active maturation of the neural apparatus of the cerebral cortex, the intensive formation of the ensemble functional organization of neurons. At this stage of ontogenesis, the development of associative intrahemispheric connections of various cortical fields is completed. Improvement with age of morphological intrahemispheric connections creates conditions for the formation of specialization in the implementation of various activities. The increasing specialization of the hemispheres leads to the complication of functional interhemispheric connections.

Between the ages of 13 and 14, there is a pronounced divergence in developmental characteristics between boys and girls.

17 years - 22 years (juvenile period). Adolescence in girls begins at 16, and in boys at 17 years old and ends in boys at 22-23 years old, and in girls at 19-20 years old. During this period, the onset of puberty is stabilized.

22 years - 60 years. The period of puberty, or the childbearing period, within which the morphophysiological characteristics established before it remain more or less unambiguous, is a relatively stable period. Damage to the nervous system at this age can be caused by infectious diseases, strokes, tumors, injuries, and other risk factors.

Over 60 years old. Stationary childbearing period is changing regressive period personal development, which includes next steps: 1st stage - the period of old age, from 60 to 70-75 years; 2nd stage - the period of senile age from 75 to 90 years; Stage 3 - centenarians - over 90 years old. It is generally accepted that changes in morphological, physiological and biochemical parameters are statistically correlated with an increase in chronological age. The term "aging" refers to the progressive loss of regenerative and adaptive responses that serve to maintain normal functionality. For the CNS, aging is characterized by an asynchronous change in the physiological state various structures brain.

With aging, there quantitative and qualitative changes in the structures of the central nervous system. The progressive decrease in the number of neurons begins at the age of 50-60. By the age of 70, the cerebral cortex loses 20%, and by the age of 90 - 44-49% of its cellular composition. The greatest losses of neurons occur in the frontal, lower temporal, and associative areas of the cortex.

In connection with the specialization of the neural structures of the brain, a decrease in its cellular composition in one of them affects the activity of the central nervous system as a whole.

Along with degenerative-atrophic processes during aging, mechanisms develop that help maintain the functionality of the central nervous system: the surface of the neuron, organelles, the volume of the nucleus, the number of nucleoli, and the number of contacts between neurons increase.

Along with the death of neurons, an increase in gliosis occurs, which leads to an increase in the ratio of the number of glial cells to nerve cells, which favorably affects the trophism of the neuron.

It should be noted that there is no direct relationship between the number of dead neurons and the degree of functional changes in the activity of a particular brain structure.

Weaken with age descending influences of the brain on the spinal cord. In old age, spinal cord injuries have a less prolonged inhibitory effect on spinal cord reflexes. The weakening of the central influence on the reflexes of the brain stem is shown in relation to the cardiovascular, respiratory and other systems.

Intercentral relations of brain structures during aging affect the weakening of reciprocal mutual inhibitory influences. The spread of synchronized, convulsive activity is caused by lower doses of corazole, cordiamine, etc. than in young people. At the same time, convulsive seizures in the elderly are not accompanied by violent vegetative reactions, as is the case in young people.

Aging is accompanied by an increase in the cerebellum gliocyte-neuron ratio from 3.6+0.2 to 5.9+0.4. By the age of 50 in humans, compared with 20 years, the activity of choline acetyltransferase decreases by 50%. The amount of glutamic acid decreases with age. Non-functional changes in the cerebellum itself are most pronounced with aging. The changes mainly concern the cerebellar-frontal relations. This makes it difficult or completely levels out in the elderly the possibility of mutual compensation of dysfunctions of one of these structures.

IN limbic system of the brain with aging, the total number of neurons decreases, the amount of lipofuscin in the remaining neurons increases, and intercellular contacts worsen. Astroglia grows, the number of axosomatic and axodendritic synapses on neurons decreases significantly, and the spiny apparatus decreases.

With the destruction of brain tissues, the reinnervation of cells in old age is slow. The mediator metabolism in the limbic system is significantly more disturbed with aging than in other brain structures at the same age.

The duration of circulation of excitation through the structures of the limbic system decreases with age, and this affects short-term memory and the formation of long-term memory, behavior, and motivation.

Striopallidary system brain, with its dysfunctions, causes various motor disorders, amnesia, vegetative disorders. With aging, after 60 years, there are dysfunctions of the striopallidary system, which is accompanied by hyperkinesis, tremor, hypomimia. The cause of such disorders are two processes: morphological and functional. With aging, the volume of striopallidar nuclei decreases. The number of interneurons in the neostriatum becomes smaller. Due to morphological destruction, the functional connections of the striatal systems through the thalamus with the extrapyramidal cortex are disrupted. But this is not the only cause of functional disorders. These include changes in mediator metabolism and receptor processes. Striatal nuclei are related to the synthesis of dopamine, one of the inhibitory mediators. With aging, the accumulation of dopamine in striatal formations decreases. Aging leads to dysregulation on the part of the striopallidum of fine, precise movements of the limbs, fingers, impaired muscle strength, and the possibility of maintaining a high muscle tone for a long time.

brain stem is the most stable formation in age aspect. This is apparently due to the importance of its structures, the wide duplication and redundancy of their functions. The number of neurons in the brain stem changes little with age.

The most important in the regulation of vegetative functions is hypothalamic-pituitary complex.

Structural and ultrastructural changes in the hypothalamic-pituitary formations are as follows. The nuclei of the hypothalamus do not age synchronously. Signs of aging are expressed in the accumulation of lipofuscin. The earliest expressed aging appears in the anterior hypothalamus. Neurosecretion in the hypothalamus decreases. The rate of catecholamine metabolism is halved. The pituitary gland increases the secretion of vasopressin in old age, which accordingly stimulates an increase in blood pressure.

The functions of the spinal cord change significantly with aging. The main reason for this is a decrease in its blood supply.

With aging, the long-axon neurons of the spinal cord are the first to change. By the age of 70, the number of axons in the roots of the spinal cord decreases by 30%, lipofuscin accumulates in neurons, and various kinds inclusion, the activity of choline acetyltransferase decreases, the transmembrane transport of K + and Na + is disturbed, the incorporation of amino acids into neurons is difficult, the RNA content in neurons decreases especially actively after 60 years. At the same age, the axoplasmic flow of proteins and amino acids slows down. All these changes in the neuron reduce its lability, the frequency of generated impulses decreases by 3 times, and the duration of the action potential increases.

Monosynaptic reflexes of the spinal cord with latent periods (LP) of 1.05 ms account for 1%. The LP of these reflexes doubles in old age. Such a lengthening of the reflex time is due to a slowdown in the formation and release of the neurotransmitter in the synapses of this reflex arc.

In the multineuronal reflex arc of the spinal cord, the reaction time increases due to the slowing down of mediator processes in synapses. Mentioned changes in synaptic transmission lead to a decrease in the strength of tendon reflexes, an increase in their LP. In persons aged 80, Achilles reflexes sharply decrease or even disappear. For example, the latency of the Achilles reflex in young people is 30-32 ms, and in old people it is 40-41 ms. Such slowdowns are also characteristic of other reflexes, which results in a slowdown in motor reactions in an elderly person.

Age changes nervous system.

The body of children in the first years of life is significantly different from the body of older people. Already in the very first days of adaptation to life outside the mother's body, the child must master the most necessary nutrition skills, adapt to various thermal environmental conditions, respond to the surrounding faces, etc. All reactions of adaptation to the conditions of a new environment require the rapid development of the brain, especially its higher sections - the cerebral cortex.

However various zones barks do not ripen at the same time. Earlier In total, in the very first years of life, the projection zones of the cortex mature ( primary fields) - visual, motor, auditory, etc., then secondary fields (the periphery of the analyzers) and last of all, up to the adult state - tertiary, associative fields of the cortex (zones higher analysis and synthesis). Thus, the motor zone of the cortex (primary field) is mainly formed by the age of 4, and the associative fields of the frontal and lower parietal cortex in terms of the territory occupied, the thickness and degree of cell differentiation by the age of 7-8 years mature only by 80%, especially lagging behind in development. in boys compared to girls.

Formed the fastest functional systems, including vertical connections between the cortex and peripheral organs and providing vital skills - sucking, defensive reactions(sneezing, blinking, etc.), elementary movements. Very early in infants in the region of the frontal region, a center for the identification of familiar faces is formed. However, the development of processes of cortical neurons and myelination of nerve fibers in the cortex, the processes of establishing horizontal intercentral relationships in the cerebral cortex, are slower. As a result, the first years of life are characterized by lack of interconnections in the body (for example, between the visual and motor systems, which underlies the imperfection of visual motor reactions).

Children in their first years of life need a significant amount of sleep with short breaks for wakefulness. The total duration of sleep is 16 hours at the age of 1 year, 12 hours for 4-5 years, 10 hours for 7-10 years, and 7-8 hours for adults. At the same time, the duration of the phase is especially large in children of the first years of life. REM sleep(with activation metabolic processes, electrical activity of the brain, autonomic and motor functions and rapid eye movements) compared with the phase " slow-motion sleep(when all these processes slow down). The severity of REM sleep is associated with the ability of the brain to learn, which corresponds to the active knowledge of the outside world in childhood.

Electrical activity of the brain (EEG) reflects the disunity of various areas of the cortex and the immaturity of cortical neurons - it is irregular, does not have dominant rhythms and pronounced foci of activity, slow waves predominate. In children under the age of 1 year, there are mainly waves with a frequency of 2-4 oscillations per 1 second. Then the predominant frequency of oscillations of electrical potentials increases: at 2-3 years - 4-5 oscillations / s; at 4-5 years old - 6 fluctuations / s; at 6-7 years old - 6 and 10 fluctuations / s; at 7-8 years old - 8 fluctuations / s; at 9 years old - 9 fluctuations / s; the interconnectedness of the activity of various cortical zones increases (Khrizman T. P., 1978). By the age of 10 years, the basic rhythm of rest is established -10 oscillations / s (alpha rhythm), characteristic of an adult organism.

For the nervous system children of preschool and primary school age characterized by high excitability and weakness of inhibitory processes, which leads to a wide irradiation of excitation along the cortex and insufficient coordination of movements. However, long-term maintenance of the excitation process is still impossible, and children quickly get tired. When organizing classes with younger students, and especially with preschoolers, long instructions and instructions, lengthy and monotonous tasks should be avoided. It is especially important to strictly dose the loads, since children of this age are different. underdeveloped sense of fatigue. They are bad at assessing change. internal environment organism during fatigue and cannot fully reflect them in words even with complete exhaustion.

With the weakness of cortical processes in children, subcortical processes of excitation predominate. Children at this age are easily distracted by any external stimulus. In such an extreme severity of the orienting reaction (according to I.P. Pavlov, the reflex “What is it?”) Is reflected involuntary nature of their attention. Arbitrary attention is very short-term: children 5-7 years old are able to focus only for 15-20 minutes.

In a child of the first years of life subjective sense of time is poorly developed. Most often, he cannot correctly measure and reproduce the given intervals, keep within time when performing various tasks. Insufficient synchronization of internal processes in the body and little experience in comparing own activity with external synchronizers (estimation of the duration of the flow various situations, change of day and night, etc.). With age, the sense of time improves: for example, only 22% of 6-year-olds, 39% of 8-year-olds and 49% of 10-year-olds accurately reproduce the interval of 30 seconds.

Body scheme is formed in a child by the age of 6, and more complexspatial representations - by 9-10 years, which depends on the development of the cerebral hemispheres and the improvement of sensorimotor functions.

Insufficient development of the frontal programming zones of the cortex causes weak development of extrapolation processes. The ability to foresee the situation at 3-4 years old is practically absent in a child (it appears at 5-6 years old). It is difficult for him to stop running at a given line, to substitute his hands in time to catch the ball, etc.

Higher nervous activity children of preschool and primary school age is characterized by a slow generation th piecework conditioned reflexes and the formation of dynamic stereotypes, as well as the particular difficulty of their alteration. Great importance for the formation of motor skills has the use of imitative reflexes, the emotionality of classes, gaming activities.

Children 2-3 are distinguished by a strong stereotypical attachment to an unchanged environment, to familiar faces around them and to acquired skills. Alteration of these stereotypes occurs with great difficulty, often leading to disruptions in higher nervous activity. In 5-6-year-old children, the strength and mobility of nervous processes increase. They are able to consciously build programs of movements and control their implementation, it is easier to rebuild programs.

At primary school age, the predominant influences of the cortex on subcortical processes already arise, the processes of internal inhibition and voluntary attention are intensified, the ability to master complex programs of activity appears, and characteristic individual-typological features of the child's higher nervous activity are formed.

Of particular importance in the behavior of the child is speech development. Until the age of 6, reactions to direct signals predominate in children (the first signal system, according to I.P. Pavlov), and from the age of 6, speech signals begin to dominate (the second signal system).

In middle and senior school age, significant development is noted in all higher structures of differentiation of the central nervous system. By the period of puberty, the weight of the brain in comparison with the newborn increases by 3.5 times and by 3 times in girls.

Until the age of 13-15, development continues diencephalon. There is an increase in the volume and nerve fibers of the thalamus, the nuclei of the hypothalamus. By the age of 15, the cerebellum reaches adult size.

In the cerebral cortex total length furrows by the age of 10 increases by 2 times, and the area of the cortex - by 3 times. In adolescents, the process of myelination of the nerve pathways ends.

The period from 9 to 12 years is characterized by a sharp increase in the relationship between various cortical centers, mainly due to the growth of processes of neurons in horizontal direction. This creates a morphological and functional basis for the development of the integrative functions of the brain, the establishment of intersystem relationships.

At the age of 10-12 years, the inhibitory effects of the cortex on the subcortical structures increase. Cortical-subcortical relationships close to the adult type are formed with the leading role of the cerebral cortex and the subordinate role of the subcortex.

In the EEG, by the age of 10-12, an adult type of electrical activity is established. with stabilization of the amplitude and frequency of cortical potentials, a pronounced dominance of the alpha rhythm (8-12 vibrations / s) and a characteristic distribution of rhythmic activity over the surface of the cortex.

In various types of activity, with an increase in age from 10 to 13 years, the EEG recorded a sharp increase in the spatial synchronization of the potentials of different cortical zones, which reflects the establishment of functional relationships between them. Created functional basis for system processes in the cortex, providing high level extracting useful information from afferent messages, building complex multi-purpose behavioral programs. In 13-year-old adolescents, the ability to process information, make quick decisions, and increase the efficiency of tactical thinking are significantly improved. The time for solving tactical tasks is significantly reduced in comparison with 10-year ones. It changes little by the age of 16, but does not yet reach adult values.

The noise immunity of behavioral reactions and motor skills reaches an adult level by the age of 13 years. This ability has great individual differences, it is genetically controlled and changes little during training.

The smooth improvement of brain processes in adolescents is disturbed as they enter puberty - in girls at 11-13 years old, in boys at 13-15 years old. This period is characterized weakening of the inhibitory influences of the cortex on the underlying structures and the "violence" of the subcortex, causing strong arousal for throughout the cortex and increased emotional reactions in adolescents. Increasing activity sympathetic department nervous system and the concentration of adrenaline in the blood. The blood supply to the brain is deteriorating.

Such changes lead to a violation of the fine mosaic of excited and inhibited areas of the cortex, disrupt the coordination of movements, impair memory and sense of time. Adolescents' behavior becomes unstable, often unmotivated and aggressive. Significant changes also occur in interhemispheric relations - the role of the right hemisphere in behavioral responses is temporarily enhanced. In a teenager, the activity of the second signaling system (speech functions) worsens, the importance of visual-spatial information increases. Violations of higher nervous activity are noted - all types of internal inhibition are violated, the formation of conditioned reflexes, the consolidation and alteration of dynamic stereotypes are hindered. There are sleep disorders.

A decrease in the controlling influences of the cortex on behavioral reactions leads to the suggestibility and lack of independence of a number of adolescents who easily adopt bad habits, trying to imitate older comrades. It is at this age that most often there is a craving for smoking, alcoholism, and taking drugs. The contingent of those infected with the human immunodeficiency virus (HIV) and suffering from this AIDS (acquired immunodeficiency syndrome) is especially growing. The systematic use of hard drugs leads to lethal outcome already 4 years after the start of admission. The highest frequency of deaths is recorded in drug addicts around the age of 21. The life of AIDS patients goes on a little longer. An increase in the number of people with AIDS last years requires increased attention to prevent and control this condition. One of the most important means of preventing bad habits is exercise. exercise and sports.

Hormonal and structural changes in the transitional period slow down the growth of the body in length, reduce the rate of development of strength and endurance.

With the end of this period of restructuring in the body (after 13 years in girls and 15 years in boys), the leading role of the left hemisphere of the brain again increases, cortical-subcortical relations are being established with the leading role of the cortex. The increased level of cortical excitability decreases and the processes of higher nervous activity are normalized.

The transition from the age of adolescents to adolescence is marked by an increased role of the anterior frontal tertiary fields and transition of the dominant role from the right to the left hemisphere (in right-handers). This leads to a significant improvement in abstract-logical thinking, the development of a second signal system and extrapolation processes. The activity of the central nervous system is very close to the adult level.