Stages of human brain development. Brain. Structural parts of the brain

The newborn is not adapted to the external environment, including biological and social. Brain development depends on hereditary genetic properties, nutrition and the nature of the influence of the surrounding human society. For the full development of the nervous system, the interaction of biological and social factors is necessary. After birth, the body comes into contact with the external environment, which is exposed to a variety of stimuli that influence the development of the central nervous system. Gradually, the thickness of the cerebral cortex increases. The development of the cellular structure of the cerebral cortex occurs mainly before the age of 13. There is no doubt that structural restructuring of the cortex occurs throughout a person’s life, but at a later age these changes are not yet amenable to quantitative and qualitative assessment.

Different areas of the cortex have their own structural cytomyeloarchitectonic features and, therefore, unequal degrees of age-related changes, which are discussed only in the specialized literature. An example of the dynamics of restructuring is the cortex of the central and postcentral regions. In the precentral region, by the age of 10 years, the cortex thickens due to the development of cells of layers III and IV. Only after 10 years do the fibers of these cells become mostly myelinated. In the postcentral region, by the age of 10, the number of myelinated fibers increases 7 times. It has been noted that the myeloarchitecture of the cortex matures later than the body of the neuron or fiber. It is not yet possible to fully imagine the anatomical features of the cortex and reveal the physiological meaning associated with this restructuring. To understand these relationships, it is necessary to study the structure of the brain and its function in a living person throughout his ontogeny. At present, conducting such a study represents a complex technical challenge.

In a newborn, the cerebral hemisphere, the main convolutions of the cortex, are already formed (Fig. 489). After birth, in accordance with the enlargement of the hemispheres and thickening of the cortex, the shape, depth and height of the grooves and convolutions change.

The temporal lobe after birth is better developed than other lobes of the brain, however, noticeable cellular restructuring occurs in it (Fig. 490).

489. Relief of the hemisphere of the brain of a newborn (according to Yu. G. Shevchenko).

490. Age-related features of the cortex of the superior temporal gyrus (field 38).
a - newborn, b - child 6 months old (according to Conel).

By the 6th month, the hippocampal and olfactory gyri shift in the medial direction due to the growth of the temporal lobe at the junction with the parietal and occipital lobes. The superior temporal gyrus is not developed, and the sulci of the temporal lobe are shallow and fragmented; They are issued only by the age of 7.

The occipital lobe is relatively small in proportion to the hemispheres, but contains all the sulci and convolutions. Only the calcarine and parieto-occipital sulci in newborns extend onto the lateral surface of the hemisphere.

Significant changes occur in the inferior parietal and inferior frontal sulcus due to the appearance of many small additional grooves. Only with the improvement of speech motor functions in a child by the age of 5-7 years does the frontal lobe develop so much that it covers the insula of the brain.

In the anterior and posterior central gyri, deep additional grooves of the 1st and 2nd order appear in the first year of life. The interparietal sulcus separates from the postcentral sulcus.

Convolution options. Since the middle of the 19th century, a detailed study of the variability of the gyri and sulci of the human brain began. Many researchers have described their variants in people of different genders, ages, different races and nationalities; The historical evolutionary method was also used. When studying variants of the brain structure, signs of stability, branching, length, depth and shape of the grooves are taken into account. The most stable are the central, fronto-marginal, ascending branch of the lateral sulcus, inferior postcentral, parieto-occipital, calcarine, superior and middle temporal, parieto-occipital sulci. The superior precentral and postcentral sulci change more often.

With the release of the forelimbs in humans, their function changed, especially the right hand, which determined the functional dominance of the left hemisphere of the brain. The mechanism of voluntary speech is also localized in the dominant hemisphere, and the mechanisms of thinking are located in both hemispheres. Right-handedness is not congenital, but develops only through exercise of the right hand. Due to the unevenness of functions, acquired asymmetry of the shape and microstructure of the cerebral hemispheres occurs.

Human brain in sagittal section, with Russian names of large brain structures

Human brain, bottom view, with Russian names of large brain structures

Brain mass

The mass of the human brain ranges from 1000 to more than 2000 grams, which on average represents approximately 2% of body weight. Men's brains weigh on average 100-150 grams more than women's brains, but there is no statistical difference between body size and brain size in adult men and women. It is a common belief that a person’s mental abilities depend on the mass of the brain: the larger the mass of the brain, the more gifted the person. However, it is obvious that this is not always the case. For example, the brain of I. S. Turgenev weighed 2012 g, and the brain of Anatole France - 1017 g. The heaviest brain - 2850 g - was found in an individual who suffered from epilepsy and idiocy. His brain was functionally defective. Therefore, there is no direct relationship between brain mass and the mental abilities of an individual.

However, in large samples, numerous studies have found a positive correlation between brain mass and mental ability, as well as between the mass of certain brain regions and various indicators of cognitive ability. A number of scientists [ Who?], however, cautions against using these studies to support inferences about low mental abilities in some ethnic groups (such as Aboriginal Australians) who have smaller average brain sizes. A number of studies indicate that brain size, which is almost entirely determined by genetic factors, cannot explain most of the differences in IQ. As an argument, researchers from the University of Amsterdam point to a significant difference in cultural level between the civilizations of Mesopotamia and Ancient Egypt and their today's descendants in Iraq and modern Egypt.

The degree of brain development can be assessed, in particular, by the ratio of the mass of the spinal cord to the brain. So, in cats it is 1:1, in dogs - 1:3, in lower monkeys - 1:16, in humans - 1:50. In Upper Paleolithic people, the brain was noticeably (10-12%) larger than the brain of a modern person - 1:55-1:56.

Brain structure

The brain volume of most people is in the range of 1250-1600 cubic centimeters and accounts for 91-95% of the capacity of the skull. There are five sections in the brain: medulla oblongata, hindbrain, which includes the pons and cerebellum, pineal gland, midbrain, diencephalon and forebrain, represented by the cerebral hemispheres. Along with the above division into sections, the entire brain is divided into three large parts:

• cerebral hemispheres;
• cerebellum;
• brain stem.

The cerebral cortex covers two hemispheres of the brain: right and left.

Meninges of the brain

The brain, like the spinal cord, is covered with three membranes: soft, arachnoid and hard.

The dura mater is built of dense connective tissue, lined from the inside with flat, moist cells, and tightly fuses with the bones of the skull in the area of ​​its internal base. Between the hard and arachnoid membranes there is a subdural space filled with serous fluid.

Structural parts of the brain

Medulla

At the same time, despite the existence of differences in the anatomical and morphological structure of the brain of women and men, there are no decisive features or their combinations that allow us to talk about a specifically “male” or specifically “female” brain. There are brain features that are more common among women, and others that are more often observed in men, however, both of them can also appear in the opposite sex, and there are practically no stable ensembles of such features observed.

Brain Development

Prenatal development

Development that occurs before birth, intrauterine development of the fetus. During the prenatal period, intensive physiological development of the brain, its sensory and effector systems occurs.

Natal state

The differentiation of cerebral cortex systems occurs gradually, which leads to uneven maturation of individual brain structures.

At birth, the child’s subcortical formations are practically formed and the projection areas of the brain are close to the final stage of maturation, in which the nerve connections coming from the receptors of various sense organs (analyzer systems) end and motor pathways originate.

These areas act as a conglomerate of all three brain blocks. But among them, the structures of the block regulating brain activity (the first block of the brain) reach the highest level of maturation. In the second (block of receiving, processing and storing information) and third (block of programming, regulation and control of activity) blocks, the most mature are only those areas of the cortex that belong to the primary lobes that receive incoming information (second block) and form outgoing motor impulses (3rd block).

Other areas of the cerebral cortex do not reach a sufficient level of maturity by the time the child is born. This is evidenced by the small size of the cells included in them, the small width of their upper layers that perform an associative function, the relatively small size of the area they occupy and the insufficient myelination of their elements.

Period from 2 to 5 years

Aged from two before five years, the maturation of secondary, associative fields of the brain occurs, part of which (secondary gnostic zones of the analytical systems) is located in the second and third blocks (premotor area). These structures support the processes of perception and the execution of a sequence of actions.

Period from 5 to 7 years

The tertiary (associative) fields of the brain mature next. First, the posterior associative field develops - the parietotemporal-occipital region, then the anterior associative field - the prefrontal region.

Tertiary fields occupy the highest position in the hierarchy of interaction between various brain zones, and here the most complex forms of information processing are carried out. The posterior associative area ensures the synthesis of all incoming multimodal information into a supramodal holistic reflection of the reality surrounding the subject in the entirety of its connections and relationships. The anterior associative area is responsible for the voluntary regulation of complex forms of mental activity, including the selection of necessary, essential information for this activity, the formation of activity programs on its basis and control over their correct course.

Thus, each of the three functional blocks of the brain reaches full maturity at different times, and maturation proceeds in sequence from the first to the third block. This is the path from bottom to top - from underlying formations to overlying ones, from subcortical structures to primary fields, from primary fields to associative fields. Damage during the formation of any of these levels can lead to deviations in the maturation of the next one due to the lack of stimulating influences from the underlying damaged level.

The brain from the point of view of cybernetics

American scientists tried to compare the human brain with a computer hard drive and calculated that human memory can contain about 1 million gigabytes (or 1 petabyte) (for example, the Google search engine processes about 24 petabytes of data daily). Considering that to process such a large amount of information, the human brain spends only 20 watts of energy, it can be called the most efficient computing device on Earth.

Notes

1. Frederico A.C. Azevedo, Ludmila R.B. Carvalho, Lea T. Grinberg, José Marcelo Farfel, Renata E.L. Ferretti. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain // The Journal of Comparative Neurology. - 2009-04-10. - Vol. 513, iss. 5 . - P. 532-541. - DOI:10.1002/cne.21974.
2. Williams R. W., Herrup K. The control of neuron number. (English) // Annual review of neuroscience. - 1988. - Vol. 11. - P. 423-453. - DOI:10.1146/annurev.ne.11.030188.002231. - PMID 3284447.[to correct]
3. Azevedo F. A., Carvalho L. R., Grinberg L. T., Farfel J. M., Ferretti R. E., Leite R. E., Jacob Filho W., Lent R., Herculano-Houzel S. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. (English) // The Journal of comparative neurology. - 2009. - Vol. 513, no. 5 . - P. 532-541. - DOI:10.1002/cne.21974. - PMID 19226510.[to correct]
4. Evgenia Samokhina“Burner” of energy // Science and life. - 2017. - No. 4. - P. 22-25. - URL: https://www.nkj.ru/archive/articles/31009/
5. Ho, K. C.; Roessmann, U; Straumfjord, J. V.; Monroe, G. Analysis of brain weight. I. Adult brain weight in relation to sex, race, and age (English) // Archives of pathology & laboratory medicine (English) Russian: journal. - 1980. - Vol. 104, no. 12 . - P. 635-639. - PMID 6893659.
6. Paul Browardel. Procès-verbal de l "autopsie de Mr. Yvan Tourgueneff. - Paris, 1883.
7. W. Ceelen, D. Creytens, L. Michel. The Cancer Diagnosis, Surgery and Cause of Death of Ivan Turgenev (1818-1883) (English) // Acta chirurgica Belgica: journal. - 2015. - Vol. 115, no. 3. - P. 241-246. - DOI:10.1080/00015458.2015.11681106.
8. Guillaume-Louis, Dubreuil-Chambardel. Le cerveau d"Anatole France (undefined) // Bulletin de l"Académie nationale de médecine. - 1927. - T. 98. - pp. 328-336.
9. Elliott G.F.S. Prehistoric Man and His Story. - 1915. - P. 72.
10. Kuzina S., Savelyev S. Weight in society depends on brain weight (undefined) . Science: secrets of the brain. Komsomolskaya Pravda (July 22, 2010). Retrieved October 11, 2014.
11. Neuroanatomical Correlates of Intelligence
12. Intelligence and brain size in 100 postmortem brains: sex, lateralization and age factors. Witelson S.F., Beresh H., Kigar D.L. Brain. 2006 Feb;129(Pt 2):386-98.
13. Brain size and human intelligence (from R. Lynn’s book “Races. Peoples. Intelligence”)
14. Hunt, Earl; Carlson, Jerry. Considerations relating to the study of group differences in intelligence // Perspectives on Psychological Science (English) Russian: journal. - 2007. - Vol. 2, no. 2. - P. 194-213. - DOI:10.1111/j.1745-6916.2007.00037.x.
15. Brody, Nathan. Jensen's Genetic Interpretation of Racial Differences in Intelligence: Critical Evaluation // The Scientific Study of General Intelligence: Tribute to Arthur Jensen. - Elsevier Science, 2003. - P. 397–410.
16. Why national IQs do not support evolutionary theories of intelligence (English) // Personality and Individual Differences (English) Russian: journal. - 2010. - January (vol. 48, no. 2). - P. 91-96. - DOI:10.1016/j.paid.2009.05.028.
17. Wicherts, Jelte M.; Borsboom, Denny; Dolan, Conor V. Evolution, brain size, and the national IQ of peoples around 3000 years B.C (English) //

The nervous system develops from the outer germ layer - the ectoblast. At the end of the third week of development, the ectoderm of the embryo begins to thicken along the initial stripe and notochord anlage. This is called sweat sweating neural plate . Soon it deepens with uneven cell growth in the neural groove; the edge of the groove rises upward, forming neural ridges. In the anterior section of the groove, the neural ridges are much larger than in the middle and behind, and this is already the initial development of the brain. In a three-week embryo this is already clearly noticeable. The nerve ridges, increasing in size, gradually come closer to each other and, finally, converge and ripple, forming neural tube . Since the roll consists of a medial part - cells of the neural groove and a lateral part - cells of unchanged ectoderm, the medial plates grow together, closing the neural tube, a. The laterals form a continuous ectodermal plate, which is initially adjacent to the neural tube. Later, the neural tube deepens and loses connection with the ectoderm, and the latter grows together over it.

The anterior end of the neural tube expands and forms three successive primary brain vesicles, separated by small interceptions, namely: anterior medullary vesicle, middle and rhomboid . These three bubbles represent the anlages of the entire brain. They do not lie in one plane, but are very curved, and three bends are formed. Some of them disappear with subsequent development. A more stable bend is the bend in the area of ​​the middle bubble, which is called parietal flexure . At the end of the fourth week of development, signs of future separation of the anterior and posterior bladders appear. At the sixth week of development there are already five brain vesicles. The anterior bladder is divided into telencephalonі diencephalon, the midbrain is not divided, but the rhomboid vesicle is divided into hindbrain and medulla oblongata . In the telencephalon, two lateral structures are formed, from which the cerebral hemispheres arise. From the side walls of the intermediate bladder, visual tubercles are formed, from its bottom - a gray tubercle with a funnel and the back part of the pituitary gland, and from the back wall - the epiphysis. The midbrain gives rise to the cerebral peduncles and the four-hump body. In the rhomboid vesicles, the cerebellum and medulla oblongata are distinguished. The pons is formed from the abdominal walls of the hindbrain, and the cerebellar peduncles to the pons are formed from the lateral walls

The cavities of the brain vesicles turn into the ventricles of the formed brain. The cavities of the outgrowths of the telencephalon form two lateral ventricles. The third ventricle arises from the cavity of the diencephalon. The cavity of the midbrain develops less, forming the aqueduct of Sylvius, and the fourth ventricle is formed from the cavity of the entire rhomboid vesicle. The spinal cord remains tubular for life. Only during embryonic development do the walls become so thick in their lateral parts that they converge, leaving between them an anterior median fissure and a posterior median groove. The cavity of the tube remains very small, from which the central canal of the spinal cord and medulla oblongata originates.

3 Development of the human brain

The first month of embryonic life - five small vesicles that develop at the end of the neural tube (the future spinal cord). The brain at this stage is remarkably similar to the brain of a fish (Figure 18). It is interesting that the human embryo now has gills and a tail.

Fig 18 . Human brain development(for Dorling. Kindersley, 2003)

. IN three months The internal and external structure of the brain changes dramatically. The front of the five bubbles outstrips the others in growth, as if covering them with a cloak, forming the hemispheres of the brain. At the same time, cells inside the brain are intensively growing, and a complex process of their migration begins - moving from internal to external parts.

. IN four months Internally, embryonic life, the rudiments of the cerebral cortex are formed; at the same time, it begins to crumple - grooves and convolutions are formed

. IN six months migrating cells that have “arrived” in place begin to grow and develop rapidly. The surface of the hemispheres, covered with cortex, increases. The bark is divided into layers and areas with different structures (fields)

. By the time the baby is born the brain is almost formed. All the grooves and convolutions are already there. Birth is a turning point. The flow of various irritations that the senses perceive, a sharp change in the way of eating - all this, naturally, leads to great changes in the brain.

. In the third month After birth, the child’s brain already changes noticeably. Many fields of the cortex are divided into subfields, the cells become even larger, and their processes branch out. It is from this time that one can easily produce a conditioned reflex to sound and light. The child begins to follow the object with his eyes, smile, recognize his mother, and babble.

. One year . The child's brain grew larger, and the cortex became even more complex in structure. The child begins to walk and speaks his first words

. Three years . The child's behavior becomes especially complicated - self-awareness and clear speech appear. The baby begins to actively explore the world and poses thousands of questions. It is during this period that the brain mass becomes three times greater than at birth.

. IN seven - twelve years The formation of not only the macro-, but also the microstructure of the brain ends. The child’s memory changes quickly, and the beginnings of independent creativity appear. But even after seven years, some areas of the brain associated with language and complex human mental activity continue to change. Subtle biochemical and molecular rearrangements continue throughout a person’s life.

The brain develops from the anterior, expanded section of the brain tube. Development goes through several stages. In a 3-week embryo, the stage of two brain vesicles is observed - anterior and posterior. The anterior bubble overtakes the chord in growth rates and ends up ahead of it. The rear one is located above the chord. At the age of 4-5 weeks, the third brain vesicle is formed. Next, the first and third brain bubbles are each divided into two, resulting in the formation of 5 bubbles. From the first brain bladder the paired telencephalon develops, from the second - the diencephalon, from the third - the midbrain (mesencephalon), from the fourth - the hindbrain (meten-cephalon), from the fifth - the medulla oblongata (myelencephalon). ). Simultaneously with the formation of 5 bubbles, the brain tube bends in the sagittal direction. In the region of the midbrain, a bend is formed in the dorsal direction - the parietal bend. At the border with the rudiment of the spinal cord, another bend also goes in the dorsal direction - the occipital one; in the region of the hindbrain, a cerebral bend is formed, running in the ventral direction.

In the fourth week of embryogenesis, protrusions in the form of bags are formed from the wall of the diencephalon, which later take the form of glasses - these are the optic glasses. They come into contact with the ectoderm and induce lens placodes in it. The optic cups retain connections with the diencephalon in the form of eyestalks.

Subsequently, the stalks turn into optic nerves. The retina with receptor cells develops from the inner layer of the glass. From the outside - the choroid and sclera. Thus, the visual receptor apparatus is, as it were, a part of the brain located on the periphery.

A similar protrusion of the wall of the anterior medullary bladder gives rise to the olfactory tract and the olfactory bulb.

Heterochronicity of maturation of neural systems of the brain

The sequence of maturation of the neural systems of the brain in embryogenesis is determined not only by the laws of phylogenesis, but is largely determined by the stage-by-stage formation of functional systems (Fig. V. 1). First of all, those structures mature that should prepare the fetus for birth, that is, for life in new conditions, outside the mother’s body.

Several stages can be distinguished in the maturation of the neural systems of the brain.

First stage. Single neurons of the anterior part of the midbrain and cells of the mesencephalic nucleus of the trigeminal (V) nerve mature most early. The fibers of these cells grow into the

direction of the ancient cortex and further - to the neocortex. Thanks to their influence, the neocortex is involved in the implementation of adaptive processes. Mesencephalic neurons are involved in maintaining the relative constancy of the internal environment, primarily the gas composition of the blood, and are involved in the mechanisms of general regulation of metabolic processes. The cells of the mesencephalic nucleus of the trigeminal nerve (V) are also associated with the muscles involved in the act of sucking and are part of the functional system associated with the formation of the sucking reflex.

Second phase. Under the influence of cells maturing at the first stage, the underlying structures of the brain stem of cells maturing at the first stage develop. These are separate groups of neurons of the reticular formation of the medulla oblongata, the posterior part of the pons and neurons of the motor nuclei of the cranial nerves. (V, VII, IX, X, XI, XII), ensuring the coordination of the three most important functional systems: sucking, swallowing and breathing. This entire system of neurons is characterized by an accelerated rate of maturation. They quickly outstrip neurons maturing at the first stage in terms of maturity.

At the second stage, early maturing neurons of the vestibular nuclei, localized at the bottom of the rhomboid fossa, become active. The vestibular system develops at an accelerated pace in humans. Already by 6-7 months of embryonic life, it reaches the degree of development characteristic of an adult.

Third stage. The maturation of neural ensembles of the hypothalamic and thalamic nuclei also occurs heterochronously and is determined by their inclusion in various functional systems. For example, the nuclei of the thalamus, involved in the thermoregulation system, develop rapidly.

In the thalamus, the neurons of the anterior nuclei are the latest to mature, but the rate of their maturation jumps sharply before birth. This is due to their participation in the integration of olfactory impulses and impulses from other modalities that determine survival in new environmental conditions.

Fourth stage. Maturation first of the reticular neurons, then of the remaining cells of the paleocortex, archicortex and basal forebrain. They are involved in the regulation of olfactory reactions, maintaining homeostasis, etc. The ancient and old cortex, which occupies a very small surface area of ​​the human hemisphere, is already fully formed by birth.

Fifth stage. Maturation of neural ensembles of the hippocampus and limbic cortex. This occurs at the end of embryogenesis, and the development of the limbic cortex continues into early childhood. The limbic system is involved in organizing and regulating emotions and motivations. For a child, these are primarily food and drink motivations, etc.

In the same sequence in which the parts of the brain mature, myelination of the corresponding fiber systems occurs. Neurons of early maturing systems and brain structures send their processes to other areas, as a rule, in the oral direction and, as it were, induce the subsequent stage of development.

The development of the neocortex has its own characteristics, but it also follows the principle of heterochrony. Thus, according to the phylogenetic principle, the ancient bark appears earliest in evolution, then the old bark, and only after that the new bark. During embryogenesis in humans, the new cortex is formed before the old and ancient cortex, but the latter develop at a rapid pace and reach maximum area and differentiation by the middle of embryogenesis. Then they begin to shift to the medial and basal surface and are partially reduced. The insular region, which is only partially occupied by the neocortex, quickly begins its development and matures by the end of the prenatal period.

Those areas of the neocortex that are associated with phylogenetically older vegetative functions, for example, the limbic area, mature most quickly. Then the areas that form the so-called projection fields of various sensory systems mature, where sensory signals from the senses come. Thus, the occipital region is formed in the embryo at 6 lunar months, and its full maturation is completed by 7 years of life.

Somewhat later, associative fields mature. The last to mature are the phylogenetically youngest and functionally most complex fields, which are associated with the implementation of specifically human functions of a high order - abstract thinking, articulate speech, gnosis, praxis, etc. These are, for example, speech-motor fields 44 and 45. Cortex The frontal region is formed in a 5-month-old fetus, full maturation is delayed until 12 years of life. Fields 44 and 45 require a longer time to develop, even at high ripening rates. They continue to grow and develop throughout the first years of life, into adolescence and even into adulthood. The number of nerve cells does not increase, but the number of processes and the degree of their branching, the number of spines on dendrites, the number of synapses increase, and myelination of nerve fibers and plexuses occurs. The development of new areas of the cortex is facilitated by educational programs that take into account the characteristics of the functional organization of the child’s brain.

As a result of the uneven growth of areas of the cortex during ontogenesis (both pre- and postnatal), in some areas there is a kind of pushing back of certain sections into the depths of the grooves due to the influx of neighboring, functionally more important ones above them. An example of this is the gradual immersion of the insula into the depths of the Sylvian fissure due to the powerful growth of neighboring sections of the cortex, which develop with the appearance and improvement of the child’s articulate speech - the frontal and temporal operculum - respectively, the speech-motor and speech-auditory centers. The ascending and horizontal anterior branches of the Sylvian fissure are formed from the influx of the triangular gyrus and develop in humans in the very late stages of the prenatal period, but this can also occur postnatally, quite in adulthood.

In other areas, the uneven growth of the cortex is manifested in patterns of the opposite order: a deep furrow seems to unfold, and new sections of the cortex, previously hidden in the depths, come to the surface. This is how, in the later stages of prenatal ontogenesis, the transverse occipital sulcus disappears, and the parieto-occipital gyri, the cortical sections associated with the implementation of more complex, visual-gnostic functions, come to the surface; the projection visual fields are moved to the medial surface of the hemisphere.

A rapid increase in the area of ​​the neocortex leads to the appearance of grooves that separate the hemispheres into convolutions. (There is another explanation for the formation of grooves - this is the germination of blood vessels). The deepest grooves (cracks) are formed first. For example, from 2 months of embryogenesis, the Sylvian fossa appears and the formation of the calcarine groove occurs. Less deep primary and secondary grooves appear later and create a general plan for the structure of the hemisphere. After birth, tertiary grooves appear - small, varying in shape, they individualize the pattern of grooves on the surface of the hemisphere. In general, the order of furrow formation is as follows. By the 5th month of embryogenesis, the central and transverse occipital sulci appear, by the 6th month - the upper and lower frontal, marginal and temporal sulci, by the 7th month - the upper and lower pre- and postcentral, as well as interparietal sulci, by the 8th month. month - middle frontal.

By the time a child is born, different parts of his brain are developed differently. The structures of the spinal cord, the reticular formation and some nuclei of the medulla oblongata (nuclei of the trigeminal, vagus, hypoglossal nerves, vestibular nuclei), midbrain (red nucleus, substantia nigra), individual nuclei of the hypothalamus and limbic system are more differentiated. The neuronal complexes of phylogenetically younger areas of the cortex - the temporal, inferior parietal, frontal, as well as the striopallidal system, the visual thalamus, many nuclei of the hypothalamus and cerebellum - are relatively far from final maturation.

The sequence of maturation of brain structures is determined by the timing of the onset of activity of the functional systems in which these structures are included. Thus, the vestibular and auditory apparatus begin to form relatively early. Already at the stage of 3 weeks, thickenings of the ectoderm are visible in the embryo, which turn into auditory placodes. By the 4th week, an auditory vesicle is formed, consisting of the vestibular and cochlear sections. By the 6th week, the semicircular canals differentiate. At 6.5 weeks, afferent fibers maturing from the vestibular ganglion to the rhomboid fossa. At 7-8 weeks, the cochlea and spiral ganglion develop.

In the auditory system, at birth, a hearing aid is formed that is capable of perceiving irritations.

Along with the olfactory system, the hearing aid plays a leading role already from the first months of life. The central auditory pathways and cortical hearing zones mature later.

By the time of birth, the apparatus that provides the sucking reflex has fully matured. It is formed by the branches of the trigeminal (V pair), facial (VII pair), glossopharyngeal (IX pair) and vagus (X pair) nerves. All fibers are myelinated at birth.

The visual apparatus is partially developed at the time of birth. The central visual pathways are myelinated at birth, while the peripheral ones (the optic nerve) are myelinated after birth. The ability to see the world around us is the result of learning. It is determined by the conditioned reflex interaction of vision and touch. Hands are the first object of one’s own body that comes into the child’s field of vision. It is interesting that the position of the hand, which allows the eye to see it, is formed long before birth, in the embryo at 6-7 weeks (see Fig. VIII. 1).

As a result of myelination of the optic, vestibular and auditory nerves, a 3-month-old child has an accurate alignment of the head and eyes to the source of light and sound. A 6-month-old child begins to manipulate objects under visual control.

The brain structures that ensure the improvement of motor reactions also mature consistently. At the 6-7th week, the red nucleus of the midbrain matures in the embryo, which plays an important role in organizing muscle tone and in the implementation of adjustment reflexes when coordinating posture in accordance with the rotation of the torso, arms, and head. By 6-7 months of prenatal life, the higher subcortical motor nuclei - the striatum - mature. The role of tone regulator in different positions and involuntary movements passes to them.

The movements of the newborn are imprecise and undifferentiated. They are provided by influences coming from the striatum. In the first years of a child’s life, fibers grow from the cortex to the striatum, and the activity of the striatum begins to be regulated by the cortex. Movements become more precise and differentiated.

Thus, the extrapyramidal system comes under the control of the pyramidal system. The process of myelination of the central and peripheral pathways of the functional movement system occurs most intensively up to 2 years. During this period, the child begins to walk.

The age from birth to 2 years is a special period during which the child also acquires a unique ability for articulate speech. The development of a child’s speech occurs only through direct communication with people around him and about the learning process. The apparatus that regulates speech includes complex innervation of various organs of the head, larynx, lips, tongue, myelinated pathways in the central nervous system, as well as the formed specifically human complex of speech fields of the cortex of 3 centers - speech-motor, speech-auditory, speech-visual, united by a system of bundles of associative fibers into a single morphofunctional system of speech. Human speech is a specifically human form of higher nervous activity.

Brain mass: age, individual and sex variability

The weight of the brain changes unevenly during embryogenesis. In a 2-month-old fetus it is ~ 3 g. Over the period up to 3 months, the brain mass increases by ~ 6 times and amounts to 17 g, by 6 lunar months - another 8 times: -130 g. In a newborn, the brain mass reaches: 370 g - for boys and 360 g - for girls. By 9 months, it doubles: 400 g. By 3 years, the brain mass triples. By the age of 7, it reaches 1260 g in boys and 1190 g in girls. Maximum brain mass is achieved in the 3rd decade of life. In older ages it decreases.

The brain weight of an adult male is 1150-1700 g. Throughout life, the brain weight of men is higher than that of women. Brain mass has noticeable individual variability, but cannot serve as an indicator of the level of development of a person’s mental abilities. It is known, for example, that I.S. Turgenev's brain mass was 2012 g, Cuvier's - 1829, Byron's - 1807, Schiller's - 1785, Bekhterev's - 1720, I.P. Pavlova - 1653, D.I. Mendeleev - 1571, A. France - 1017

To assess the degree of brain development, a “cerebralization index” was introduced (the degree of brain development with the influence of body weight excluded). According to this index, humans differ sharply from animals. It is very significant that during human ontogenesis a special period in development can be distinguished, which is characterized by a maximum “cerebralization index.” This period corresponds to the period of early childhood, from 1 year to 4 years. After this period, the index declines. Changes in the cerebralization index are confirmed by neurohistological data. For example, the number of synapses per unit area of ​​the parietal cortex after birth increases sharply only up to 1 year, then decreases slightly until 4 years and sharply falls after 10 years of a child’s life. This indicates that the period of early childhood is a time of a huge number of possibilities inherent in the nervous tissue of the brain. The further development of a person’s mental abilities largely depends on their implementation.

At the end of the chapters on the development of the human brain, it should be emphasized once again that the most important specifically human feature is the unique heterochrony of the formation of the neocortex, in which the development and final maturation of brain structures associated with the implementation of higher-order functions occur for a fairly long time after birth. Perhaps this was the greatest aromorphosis that determined the separation of the human branch in the process of anthropogenesis, since it “introduced” the process of learning and education into the formation of the human personality.

INTRODUCTION

Some of the modern sciences have a completely finished form, others are intensively developing or are just becoming established. This is understandable, since science evolves, just like the nature it studies. One of the promising areas of natural science is the study of the human brain and the connection between mental processes and physiological ones.

At birth, the brain is the most undifferentiated organ of the body. It is important to know that the brain does not function “properly” until its development is “complete.” However, the brain never becomes “complete” as it continues to reintegrate itself. Brain plasticity, that is, its sensitivity to environmental influences, is a characteristic particularly common to the human brain.

The study of higher nervous activity is possible using physical, chemical methods, hypnosis, etc. Among the topics interesting from a natural science point of view are:

1) direct impact on brain centers;

2) experiments with drugs (LSD, in particular);

3) coding of behavior at a distance.

The purpose of my work is the study of basic issues of brain development, as well as consideration of the basic mental properties of a person.

To get the job done The following tasks are highlighted:

- Consideration of human brain development;

- The study of human mental properties (temperament, abilities, motivation, character).

To write a paper Various educational sources were studied and analyzed. Preference was given to the following authors: Gorelov A.A., Grushevitskaya T.G., Sadokhin A.P., Uspensky P.D., Maklakov A.G.

Human brain development

The brain is that part of the nervous system that evolved evolutionarily based on the development of distant receptor organs.

The goal of studying the brain is to understand the mechanisms of behavior and learn to control them. Knowledge about the processes occurring in the brain is necessary for better use of mental abilities and achievement of psychological comfort.

What does natural science know about brain activity? Even in the last century, the outstanding Russian physiologist Sechenov wrote that physiology has data on the relationship of mental phenomena with nervous processes in the body. Thanks to Pavlov, everything became accessible to the physiological study of the brain, including consciousness and memory. Gorelov A.A. Concepts of modern natural science: A course of lectures., M.: Center, 1998. - p. 156.

The brain is considered as a control center consisting of neurons, pathways and synapses (there are 10 interconnected neurons in the human brain).

Brain Research

The cerebral cortex and subcortical structures are associated with external mental functions, with human thinking and consciousness. It is through the nerves emerging from the brain and spinal cord that the central nervous system is connected to all organs and tissues. Nerves carry information from the external environment to the brain and bring it back to the parts and organs.

Nowadays there are technical possibilities for experimental research of the brain. The method of electrical stimulation is aimed at this, through which the parts of the brain responsible for memory, problem solving, pattern recognition, etc. are studied, and the influence can be remote. You can artificially induce thoughts and emotions - hostility, fear, anxiety, pleasure, the illusion of recognition, hallucinations, obsessions. Modern technology can literally make a person happy by acting directly on the pleasure centers of the brain.

Research has shown that:

1) Not a single behavioral act is possible without the occurrence of negative potentials at the cellular level, which are accompanied by electrical and chemical changes and depolarization of the membrane;

2) Processes in the brain can be of two types: excitatory and inhibitory;

3) Memory is like links in a chain and you can pull out a lot by pulling one;

4) The so-called psychic energy is the sum of the physiological activity of the brain and information received from the outside;

5) The role of the will comes down to putting already established mechanisms into action.

A special role in the brain is played by the left and right hemispheres, as well as their main lobes: frontal, parietal, occipital and temporal. I.P. Pavlov first introduced the concept of an analyzer based on a complex of brain and other organic structures involved in the perception, processing and storage of information. He identified a relatively autonomous organic system that ensures the processing of specific information at all levels of its passage through the central nervous system. Maklakov A.G. General psychology: St. Petersburg: Peter 2002.- p. 38.

The achievements of neurophysiology include the discovery of asymmetry in the functioning of the brain. California Institute of Technology professor R. Sperry in the early 50s proved the functional difference of the cerebral hemispheres with almost complete identical anatomy. Gorelov A.A. Concepts of modern natural science: A course of lectures.. - M.: Center, 1998. - p. 157.

Left hemisphere- analytical, rational, consistently acting, more aggressive, active, leading, controlling the motor system.

Right- synthetic, holistic, intuitive; cannot express itself in speech, but controls vision and shape recognition. Pavlov said that all people can be divided into artists and thinkers. In the former, therefore, the right hemisphere dominates, in the latter, the left hemisphere dominates.

A clearer understanding of the mechanisms of the central nervous system allows us to solve the problem of stress. Stress is a concept that characterizes, according to G. Selye, the rate of wear and tear of the human body, and is associated with the activity of a nonspecific defense mechanism that increases resistance to external factors.

Stress syndrome goes through three stages:

1) “alarm reaction”, during which defensive forces are mobilized;

2) “resilience stage,” reflecting complete adaptation to the stressor;

“the stage of exhaustion,” which inexorably sets in when the stressor is strong enough and lasts long enough, since “adaptive energy,” or the adaptability of a living being, is always finite.”

Much about brain activity remains unclear. Electrical stimulation of the motor zone of the cerebral cortex is not capable of causing the precise and dexterous movements inherent in humans, and therefore there are more subtle and complex mechanisms responsible for movement. There is no convincing physicochemical model of consciousness, and therefore it is unknown what consciousness is as a functional entity and what thought is as a product of consciousness. One can only conclude that consciousness is the result of a special organization, the complexity of which creates new, so-called emergent properties that the constituent parts do not have.

The question of the beginning of consciousness is controversial. According to one view, there is a plane of consciousness before birth, not a ready-made consciousness. “The development of the brain,” says X. Delgado, “determines the individual’s attitude towards the environment even before the individual becomes able to perceive sensory information about the environment. Consequently, the initiative remains with the body.” Gorelov A.A. Concepts of modern natural science: A course of lectures., M.: Center, 1998. - p. 158.

There is a so-called “advanced morphological maturation”: even before birth in the dark, the eyelids rise and fall. But newborns are deprived of consciousness and only acquired experience leads to recognition of objects.

The reactions of newborns are so primitive that they can hardly be considered signs of consciousness. And at birth there is no brain at all. Therefore, humans are born less developed than other animals and require a certain postnatal period of growth. Instinctive activity can exist even in the absence of experience, mental activity - never.

It is important to note that the functioning of the hand had a major influence on the development of the brain. The hand, as a developing specialized organ, should also have formed a representation in the brain. This caused not only an increase in the mass of the brain, but also a complication of its structure.

Insufficient sensory input negatively affects the physiological development of the child. The ability to understand what is visible is not an innate property of the brain. Thinking does not develop on its own. Personality formation, according to Piaget, ends at three years of age, but brain activity depends on sensory information throughout life. “Animals and people need novelty and a constant stream of varied stimuli from the external environment.” A decrease in the supply of sensory information, as experiments have shown, leads to the appearance of hallucinations and delusions after a few hours.

The question of how much a continuous sensory stream determines human consciousness is as complex as the question of the relationship between intellect and feelings. Spinoza also believed that “human freedom, the possession of which everyone boasts,” is no different from the capabilities of a stone, which “receives a certain amount of movement from some external cause.” Modern behaviorists are trying to substantiate this point of view. The fact that consciousness can change dramatically under the influence of external causes (and in the direction of strengthening foresight and the formation of new properties and abilities) is proven by the behavior of people who have received severe skull injuries. Indirect (for example, advertising) and direct (operational) influence on consciousness leads to coding.

Three areas of neurophysiology attract the greatest interest:

1) influence on consciousness through irritation of certain brain centers using psychotropic and other means;

2) surgical and medication coding;

3) study of unusual properties of consciousness and their influence on society. These important but dangerous areas of research are often kept secret.

Brain structure

Brain, encephalon (cerebrum), with the surrounding membranes is located in the cavity of the brain skull. The convex superolateral surface of the brain corresponds in shape to the internal concave surface of the cranial vault. The lower surface, the base of the brain, has a complex relief corresponding to the cranial fossae of the inner base of the skull. Human Anatomy: Textbook. / R.P. Samusev, Yu.M. Celine. - M.: Medicine, 1990. - p. 376.

The mass of the brain of an adult varies from 1100 to 2000. From 20 to 60 years, the mass and volume remain maximum and constant for each given individual (brain mass on average in men is 1394 g, in women - 1245 g), and after 60 years they decrease somewhat.

When examining a specimen of the brain, its three largest components are clearly visible. These are the paired cerebral hemispheres, the cerebellum and the brain stem.

The cerebral hemispheres in an adult are the most highly developed, largest and functionally most important part of the central nervous system. The divisions of the hemispheres cover all other parts of the brain. The right and left hemispheres are separated from each other by a deep longitudinal fissure of the cerebrum, reaching the greater commissure of the brain, or corpus callosum.

brain psyche temperament character