The most important pentoses. The structure of monosaccharides. Questions for self-study

Rapid changes in body size and proportions are visible evidence of a child's growth, but in parallel, invisible physiological changes occur in the brain. When children reach 5 years of age, their brain becomes almost the same size as that of an adult. Its development facilitates more complex processes of learning, problem solving and language use; in turn, perceptual and motor activity contribute to the creation and strengthening of interneuron connections.

Development neurons, The 100 or 200 billion specialized cells that make up the nervous system begin in the embryonic and fetal periods and are practically completed by the time of birth. Glial cells that perform the function of insulating neurons and increasing the efficiency of transmission of nerve impulses continue to grow throughout the 2nd year of life. Rapid growth in the size of neurons, the number of glial cells, and the complexity of synapses (interneuronal contact areas) is responsible for the rapid growth of the brain from infancy to the 2nd birthday, which continues (albeit at a slightly reduced rate) throughout early childhood. Intensive brain development is a time of significant plasticity or flexibility, during which time a child will recover much faster and is more likely to recover from brain damage than at an older age; adults are not plastic (Nelson & Bloom, 1997).

The maturation of the central nervous system (CNS) that occurs in early childhood also includes myelination(formation of a protective layer of insulating cells - the myelin sheath, which covers the fast-acting pathways of the central nervous system) (Cratty, 1986). Myelination of the pathways of motor reflexes and the visual analyzer occurs in early childhood.

Chapter 7. Early childhood: physical, cognitive and speech development 323

youth. Subsequently, the motor pathways necessary for the organization of more complex movements are myelinated, and, finally, the fibers, pathways and structures that control attention, visual-motor coordination, memory and learning processes. Along with brain development, ongoing myelination of the central nervous system correlates with the growth of the child’s cognitive and motor abilities and qualities in preschool years and later.

At the same time, specialization, resulting from each child's unique experience, increases the number of synapses on some neurons and destroys, or “cuts off” the synapses of others. As explained by Alison Gopnik and her colleagues (Gopnik, Meltzoff & Kuhl, 1999), neurons in the newborn brain have an average of approximately 2,500 synapses, and by the age of 2-3 years, the number of synapses per neuron reaches a maximum of 15,000, which, in turn, much more than is typical for the adult brain. As the researchers say: What happens to these neural connections as we get older? The brain is not constantly creating more and more synapses. Instead, he creates many of the connections he needs and then gets rid of many of them. It turns out that removing old connections is just as important a process as creating new ones. Synapses that carry the most messages become stronger and survive, while weak synaptic connections are cut off... Between the ages of 10 and puberty, the brain mercilessly destroys its weakest synapses, retaining only those that have proven useful in practice (Gopnik, Meltzoff & Kuhl, 19996 p. 186-187).

The emergence of knowledge about early development brain has led many researchers to the conclusion that interventions and corrective measures for children in the zone increased risk the occurrence of cognitive impairment and developmental delays due to living in conditions of material poverty and intellectual hunger should begin at the earliest stages. Traditional programs Head start(primary start), for example, begin during a period called the “window of opportunity” of brain development, i.e., during the first 3 years of life. As noted by Craig, Sharon Ramey, and their colleagues (Ramey, Campbell, & Ramey, 1999; Ramey & Ramey, 1998), flagship projects that began as infants had much greater impact than interventions that began later. Undoubtedly, these and other authors note that in this case, quality is everything (Burchinal et al., 2000; Ramey, Ramey, 1998). It turned out that children visiting special centers leads to better results (NICHD, 2000), and this approach should be used intensively in areas such as nutrition and other needs related to health, social and cognitive development, child and family functioning. The magnitude of the benefits obtained from completing the program, according to researchers Ramey (Ramey, Ramey, 1998, p. 112), depends on the following factors.

‣‣‣ Culturally appropriate program for the child's developmental level.

‣‣‣ Timetable of classes.

‣‣‣ Intensity of training.

‣‣‣ Coverage of topics (breadth of the program).

‣‣‣ Focus on individual risks or violations.

324 Part II. Childhood

This does not mean that the first 3 years of life are a critical period and that after this time the window will somehow slam shut. The qualitative changes that occur in later life are also beneficial, and, as many researchers have emphasized (e.g., Bruer, 1999), learning and associated brain development continue throughout life. As we advance our knowledge of early brain development, we understand the importance of the first 3 years of life for any child, whether at risk or not. It is vital that researchers have a long way to go before they can conclude which experiences at which point in a given period are of decisive importance.

Literalization. surface of the brain, or cerebral cortex(cerebral cortex), is divided into two hemispheres - right and left. Each hemisphere has its own specialization in information processing and behavior control; this phenomenon is called lateralization. In the 60s of the 20th century, Roger Sperry and his colleagues confirmed the presence of lateralization by studying the consequences of surgical operations aimed at treating people suffering from epileptic seizures. Scientists have discovered that cutting nerve tissue (corpus callosum(), connecting the two hemispheres can significantly reduce the frequency of seizures while leaving most of the abilities needed for daily functioning intact. In this case, the left and right hemispheres of a person turn out to be largely independent and cannot establish connections with each other (Sperry, 1968). Today surgery related treatment epileptic seizures, is much more specific and subtle.

The left hemisphere controls motor behavior right side body, and the right - the left side (Cratty, 1986; Hellige, 1993). In some aspects of functioning, however, one hemisphere must be more active than the other. Figure 7.2 is an illustration of these hemispheric functions as they occur in right-handed people; in left-handers, some functions may have reverse localization. It must be remembered that most of the functioning normal people related to activities in total brain (Hellige, 1993). Lateralized (or otherwise specialized) functions indicate a greater degree of activity in a given area than in others.

By observing how and in what sequence children demonstrate their skills and abilities, we notice that the development of the brain hemispheres does not occur synchronously (Tratcher, Walker, & Guidice, 1987). For example, linguistic abilities develop very quickly between 3 and 6 years of age, and left hemisphere Most children, responsible for them, grows rapidly at this time. Maturation of the right hemisphere in early childhood, on the contrary, proceeds at a slower pace and accelerates somewhat during middle childhood (8-10 years). Specialization of the cerebral hemispheres continues throughout childhood and ends in adolescence.

Handedness. Scientists have long been interested in the question of why children, as a rule, prefer to use one hand (and foot) more than the other, usually the right one. For most children, this “right-sided” choice is associated with a strong dominance of the left hemisphere of the brain. But even with such dominance

Corpus callosum (lat.) - corpus callosum. - Note translation

Chapter 7, Early childhood: physical some, cognitive and speech development 325

Rice. 7.2. Functions of the left and right hemispheres.

The biggest mystery for scientists is not the vastness of space or the formation of the Earth, but the human brain. Its capabilities exceed those of any modern computer. Thinking, forecasting and planning, emotions and feelings, finally, consciousness - all these inherent in man processes, one way or another, take place within a small space of the cranium. The work of the human brain and its study are much more closely related than any other objects and methods of research. In this case they are almost identical. The human brain is studied using the human brain. The ability to understand the processes occurring in the head actually depends on the ability of the “thinking machine” to know itself.

Structure

Today, quite a lot is known about the structure of the brain. It consists of two hemispheres resembling halves walnut, covered with a thin gray shell. This is the cerebral cortex. Each of the halves is conventionally divided into several shares. The most ancient parts of the brain in evolutionary terms, the limbic system and brainstem, are located under the corpus callosum, which connects the two hemispheres.

The human brain is made up of several types of cells. Most of them are glial cells. They perform the function of connecting other elements into a single whole, and also take part in amplifying and synchronizing electrical activity. About a tenth of brain cells are neurons of various shapes. They transmit and receive electrical impulses using processes: long axons, which transmit information from the neuron body further, and short dendrites, which receive signals from other cells. Contacting axons and dendrites form synapses, places where information is transmitted. Long shoot releases a neurotransmitter into the synapse cavity, Chemical substance, affecting the functioning of the cell, it reaches the dendrite and leads to inhibition or excitation of the neuron. The signal is transmitted throughout all connected cells. As a result, the work of a large number of neurons is very quickly excited or inhibited.

Some development features

The human brain, like any other organ of the body, goes through certain stages of its formation. A child is born, so to speak, not in full combat readiness: the process of brain development does not end there. Its most active departments during this period are located in the ancient structures responsible for reflexes and instincts. The cortex functions less well because it consists of a large number of immature neurons. With age, the human brain loses some of these cells, but acquires many strong and orderly connections between the remaining ones. “Extra” neurons that have not found a place in the resulting structures die. How much the human brain works appears to depend on the quality of connections rather than the number of cells.

Common Myth

Understanding the features of brain development helps to determine the discrepancy between the reality of some common ideas about the work of this organ. There is an opinion that the human brain works 90-95 percent less than it can, that is, about a tenth of it is used, and the rest mysteriously sleeps. If you re-read the above, it becomes clear that neurons that are not used cannot exist for long - they die. Most likely, such an error is the result of ideas that existed some time ago that only those neurons that transmit an impulse work. However, per unit of time, only a few cells are in such a state, associated with the actions necessary for a person now: movement, speech, thinking. After a few minutes or hours, they are replaced by others who were previously “silent”.

Thus, over a certain period of time, the entire brain participates in the work of the body, first with some of its parts, then with others. The simultaneous activation of all neurons, which implies 100% brain function so desired by many, can lead to a kind of short circuit: a person will hallucinate, experience pain and all possible sensations, and shudder throughout the body.

Connections

It turns out that we cannot say that some part of the brain does not work. However, the abilities of the human brain are indeed not fully used. The point, however, is not in “sleeping” neurons, but in the quantity and quality of connections between cells. Any repeated action, sensation or thought is fixed at the neuronal level. The more repetitions, the stronger the connection. Accordingly, using the brain more fully involves building new connections. This is what training is built on. Children's brain does not yet have stable connections; they are formed and strengthened in the process of the child’s acquaintance with the world. With age, it becomes more and more difficult to make changes to the existing structure, so children learn more easily. However, if you want, you can develop the abilities of the human brain at any age.

Unbelievable but true

The ability to form new connections and relearn produces amazing results. There are cases when she overcame all the limits of the possible. The human brain is a nonlinear structure. With all certainty, it is impossible to identify zones that perform one specific function and no more. Moreover, if necessary, parts of the brain can take over the “responsibilities” of the injured areas.

This is what happened to Howard Rocket, who was doomed to a wheelchair as a result of a stroke. He did not want to give up and, using a series of exercises, tried to develop his paralyzed arm and leg. As a result of everyday hard work, after 12 years he was able not only to walk normally, but also to dance. His brain very slowly and gradually rewired itself so that the unaffected parts of it could perform the functions necessary for normal movement.

Paranormal abilities

The plasticity of the brain is not the only feature that amazes scientists. Neuroscientists do not ignore such phenomena as telepathy or clairvoyance. Experiments are carried out in laboratories to prove or disprove the possibility of such abilities. Research by American and English scientists provides interesting results suggesting that their existence is not a myth. However, neuroscientists have not yet made a final decision: for official science there are still certain boundaries of what is possible, and the human brain, as it is believed, cannot cross them.

Work on yourself

In childhood, as neurons that have not found a “place” die off, the ability to remember everything at once disappears. The so-called eidetic memory occurs quite often in children, but in adults it is an extremely rare phenomenon. However, the human brain is an organ and, like any other part of the body, it can be trained. This means that you can improve your memory, improve your intelligence, and develop creative thinking. It is only important to remember that the development of the human brain is not a matter of one day. Training should be regular, regardless of your goals.

Unusual

New connections are formed at the moment when a person does something differently than usual. The simplest example: there are several ways to get to work, but out of habit we always choose the same one. The task is to choose a new path every day. This elementary action will bear fruit: the brain will be forced not only to determine the path, but also to register new visual signals coming from previously unknown streets and houses.

Such training also includes using the left hand where the right hand is accustomed (and vice versa, for left-handed people). Writing, typing, holding a mouse is so inconvenient, but, as experiments show, after a month of such training, creative thinking and imagination will significantly increase.

Reading

We have been told about the benefits of books since childhood. And these are not empty words: reading increases brain activity, as opposed to watching TV. Books help develop imagination. Crosswords, puzzles, logic games, and chess match them. They stimulate thinking and force us to use those brain capabilities that are usually not in demand.

Physical exercise

How much the human brain works, at full capacity or not, also depends on the load on the whole body. It has been proven that physical training by enriching the blood with oxygen has a positive effect on brain activity. In addition, the pleasure that the body receives during regular exercise improves overall health and mood.

There are many ways to increase brain activity. Among them there are both specially designed and extremely simple ones, which we, without knowing it, resort to every day. The main thing is consistency and regularity. If you do each exercise once, there will be no significant effect. The feeling of discomfort that occurs at first is not a reason to quit, but a signal that this exercise makes the brain work.

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 anterior section the groove of the nerve ridges is much larger than in the middle and behind, and this is already initial development 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, midbrain does not divide, but the diamond-shaped bladder divides 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 bumps are formed, from its bottom - a gray bump with a funnel and rear end g pituitary gland, and c back wall- pineal gland The midbrain gives rise to the cerebral peduncles and the four-hump body. In the rhomboid vesicles, the cerebellar anlage and medulla oblongata. WITH abdominal walls the hindbrain forms the anlage of the pons, and from the lateral brain the cerebellar peduncles to the pons

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 difficult process their migrations - moving from internal parts to external ones.

. 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 crucial moment. 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.

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. Most heavy brain- 2850 g - was discovered 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 conclusions about low mental abilities some ethnic groups(such as Australian Aborigines) who have the average size less brain. 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 modern man - 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 made of dense connective tissue, lined from the inside with flat, moistened cells, 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 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, their small width upper layers, performing an associative function, the relatively small size of the area they occupy and 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, search system Google processes about 24 petabytes of data every day). 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

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.
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]
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]
Evgenia Samokhina“Burner” of energy // Science and life. - 2017. - No. 4. - P. 22-25. - URL: https://www.nkj.ru/archive/articles/31009/
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Paul Browardel. Procès-verbal de l "autopsie de Mr. Yvan Tourgueneff. - Paris, 1883.
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.
Guillaume-Louis, Dubreuil-Chambardel. Le cerveau d"Anatole France (undefined) // Bulletin de l"Académie nationale de médecine. - 1927. - T. 98. - pp. 328-336.
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Neuroanatomical Correlates of Intelligence
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.
Brain size and human intelligence (from R. Lynn’s book “Races. Peoples. Intelligence”)
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Essay

On the topic of:

"Main stages of brain development"

Moscow 2009

Introduction

The human brain, the organ that coordinates and regulates everything vital functions body and controls behavior. All our thoughts, feelings, sensations, desires and movements are associated with the functioning of the brain, and if it does not function, a person goes into vegetative state: the ability to perform any actions, sensations or reactions to external influences is lost.

Brain functions include processing sensory information from the senses, planning, decision making, coordination, motor control, positive and negative emotions, attention, memory. The human brain performs higher function- thinking. Also one of essential functions The human brain is the perception and generation of speech.

Embryonic development of the brain is one of the keys to understanding its structure and functions.

Brain structure

The brain is a part of the nervous system contained in the cranial cavity. It consists of various organs.

The cerebrum: the most voluminous part of the brain, occupies almost the entire skull. Consists of two halves, or hemispheres, separated by a longitudinal fissure, each hemisphere is divided laterally by the Rolandic or Sylvian fissures. Thus, the brain is divided into four parts, or lobes: frontal, parietal, temporal and occipital. The brain consists of several layers.

The cerebral cortex, or gray matter, is outer layer formed by the bodies of nerve cells - neurons. White matter makes up the rest of the brain tissue and is made up of dendrites, or cell processes. Corpus callosum, located in the inner part, between the two hemispheres, is formed by various nerve channels. Finally, the ventricles of the brain are four interconnected cavities through which cerebrospinal fluid circulates.

Cerebellum: small organ, located under occipital part brain. The main function of the cerebellum is to maintain balance and coordinate movements of the musculoskeletal system.

Pons medullaris: Also located under the occipital lobe of the brain, in front of the cerebellum. Acts as a transmitting center for sensory and motor pathways.

Medulla oblongata: is a continuation of the medullary pons and directly passes into the spinal cord. Regulates important involuntary functions of the body through respiratory center(respiratory rate), vasomotor center (constriction and expansion blood vessels) and vomiting center.

Because of its extreme importance, the brain is well protected. Apart from the skull, which is durable bone structure, it is protected by three very thin shells: hard, arachnoid and soft meninges, which protect it from direct contact with the bones of the skull. The ventricles of the brain also secrete cerebrospinal fluid, which serves as a shock absorber for blows to the head.

embryonic brain head stage

Brain Development

Embryogenesis of the brain begins with the development in the anterior (rostral) part of the brain tube of two primary brain vesicles, resulting from uneven growth of the walls of the neural tube (archencephalon and deuterencephalon). The deuterencephalon, like the posterior part of the brain tube (later the spinal cord), is located above the notochord. The archencephalon is laid in front of it.

Then, at the beginning of the fourth week, the deuterencephalon of the embryo is divided into the middle (mesencephalon) and rhombencephalon (rhombencephalon) bladders. And the archencephalon turns into the anterior cerebral vesicle (prosencephalon) at this (trivesical) stage. In the lower part of the forebrain, the olfactory lobes protrude (from them the olfactory epithelium of the nasal cavity, olfactory bulbs and tracts develop). Two optic vesicles protrude from the dorsolateral walls of the anterior medullary vesicle. Next, the retina, optic nerves and tracts develop from them.

At the sixth week of embryonic development, the anterior and rhomboid vesicles each divide into two and the pentavesicular stage begins.

The anterior vesicle, the telencephalon, is divided by a longitudinal fissure into two hemispheres. The cavity also divides to form the lateral ventricles. The medulla increases unevenly, and numerous folds are formed on the surface of the hemispheres - convolutions, separated from each other by more or less deep grooves and fissures. Each hemisphere is divided into four lobes; in accordance with this, the cavities of the lateral ventricles are also divided into 4 parts: the central section and the three horns of the ventricle. From the mesenchyme surrounding the embryonic brain, the membranes of the brain develop. Gray matter is located both on the periphery, forming the cerebral cortex, and at the base of the hemispheres, forming the subcortical nuclei.

The posterior part of the anterior bladder remains undivided and is now called the diencephalon. Functionally and morphologically it is connected with the organ of vision. At the stage when the boundaries with the telencephalon are poorly defined, paired outgrowths are formed from the basal part of the lateral walls - optic vesicles, which are connected to their place of origin with the help of eye stalks, which subsequently turn into optic nerves. The greatest thickness reaches the lateral walls of the diencephalon, which are transformed into the visual thalamus, or thalamus. In accordance with this cavity III ventricle turns into a narrow sagittal fissure. In the ventral region (hypothalamus), an unpaired protrusion is formed - a funnel, from the lower end of which the posterior medullary lobe of the pituitary gland - the neurohypophysis - arises.

The third brain vesicle turns into the midbrain, which develops most simply and lags behind in growth. Its walls thicken evenly, and the cavity turns into a narrow canal - the Sylvian aqueduct, connecting the III and IV ventricles. The quadrigemina develops from the dorsal wall, and the midbrain peduncle develops from the ventral wall.

The rhombencephalon is divided into the hindbrain and the accessory brain. The cerebellum is formed from the posterior one - first the cerebellar vermis, and then the hemispheres, as well as the pons. The accessory brain becomes the medulla oblongata. The walls of the rhomboid brain thicken - both on the sides and on the bottom, only the roof remains in the form of a thin plate. The cavity turns into the IV ventricle, which communicates with the aqueduct of Sylvius and the central canal of the spinal cord.

As a result of the uneven development of the brain vesicles, the brain tube begins to bend (at the level of the midbrain - the parietal deflection, in the region of the hindbrain - the pavement, and at the point of transition of the accessory cord into the spinal cord - the occipital deflection). The parietal and occipital deflections face outward, and the pavement faces inward.

The structures of the brain that form from the primary brain vesicle: the midbrain, hindbrain and accessory brain - make up the brainstem. It is a rostral continuation of the spinal cord and has with it common features buildings. The paired boundary groove, running along the lateral walls of the spinal cord and brainstem, divides the brain tube into the main (ventral) and pterygoid (dorsal) plates. Motor structures (anterior horns of the spinal cord, motor nuclei of the cranial nerves) are formed from the main plate. Above the border groove, sensory structures develop from the pterygoid plate ( rear horns spinal cord, sensory nuclei of the brain stem), within the border sulcus itself - the centers of the autonomic nervous system.

Derivatives of the archencephalon (telencephalon and diencephalon) create subcortical structures and cortex. There is no main plate here (it ends in the midbrain), therefore, there are no motor and autonomic nuclei. The entire forebrain develops from the pterygoid plate, so it contains only sensory structures.

Postnatal ontogenesis of the human nervous system begins from the moment of birth of a child.

The brain of a newborn weighs 300-400 g. Soon after birth, the formation of new neurons from neuroblasts stops; the neurons themselves do not divide.

By the eighth month after birth, the weight of the brain doubles, and by 4-5 years it triples. The brain mass grows mainly due to an increase in the number of processes and their myelination.

The mass of the adult human brain ranges from 1100 to 2000. Over the course of 20 to 60 years, the mass and volume remain maximum and constant for each individual.

Listliterature

1. Anatomy of the central nervous system: Textbook for university students / N.V. Voronova, H.M. Klimova, A.M. Mendzheritsky. - M.: AspectPress, 2005.

2. Sanin M.P., Bilich G.L. Human Anatomy: In 2 books. 2nd ed., revised. and additional M., 1999.

3. Kurepina M.M., Ozhigova A.P., Nikitina A.A. Human anatomy: textbook. For students Higher Textbook Establishments. - M.: Humanite. Ed. VLADOS center, 2002.

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