The most important pentoses. The structure of monosaccharides. Self-study questions

Rapid changes in body size and proportions are visible evidence of the growth of a child, but in parallel with this, invisible physiological changes occur in the brain. When children reach the age of 5, their brains become almost the same size as those of an adult. Its development facilitates the implementation of more complex processes of learning, problem solving and language use; in turn, perceptual and motor activity contribute to the creation and strengthening of interneuronal 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 almost completed by the time of delivery. Glial cells that isolate neurons and increase the efficiency of transmission of nerve impulses continue to grow throughout the entire 2nd year of life. The rapid growth in neuron size, glial cell count, and the complexity of synapses (interneuronal contact areas) is responsible for intensive brain development from infancy to age 2, which continues (albeit at a slightly slower pace) throughout early childhood. The intensive development of the brain is a time of significant plasticity or flexibility, during which the child is much faster and more likely to recover from brain damage than at an older age; adults are not plastic (Nelson & Bloom, 1997).

Early childhood maturation of the central nervous system (CNS) also includes myelination(the 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

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

At the same time, specialization resulting from the unique experiences of each child increases the number of synapses of some neurons and destroys or “cuts off” the synapses of others. As Alison Gopnik and her colleagues explain (Gopnik, Meltzoff & Kuhl, 1999), neurons in the brain of a newborn have an average of about 2500 synapses, and by the age of 2-3 years, their number in each neuron reaches a maximum level of 15,000, which, in turn, much more than is typical of the adult brain. As the researchers say: What happens to these neural connections as we get older? The brain is not constantly making 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 as creating new ones. The synapses that carry the most messages become stronger and survive, while the weak synaptic connections are cut ... Between the age of 10 and the onset of puberty, the brain mercilessly destroys its weakest synapses, retaining only the proven usefulness (Gopnik, Meltzoff & Kuhl 19996 p. 186-187).

The emergence of knowledge about early brain development has led many researchers to the conclusion that interventions and corrective measures for children who are at increased risk 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(main start), for example, begins during a period called the “window of opportunity” of brain development, that is, during the first 3 years of life. As Craig, Sharon Ramay and colleagues (Ramey, Campbell & Ramey, 1999; Ramey, Ramey, 1998) have noted, major projects involving infants have had a far greater impact than interventions launched 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's visits to special centers lead to better results (NICHD, 2000), and this approach should be intensively used in areas such as proper nutrition and other needs related to health, social and cognitive development, child and family functioning. The magnitude of the benefits obtained from passing the program, according to the researcher Ramey (Ramey, Ramey, 1998, p. 112), depends on the following factors.

‣‣‣ The program is culturally appropriate 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 shut down in any way. The qualitative changes that occur in older age are also beneficial, and, as many researchers have emphasized (eg Bruer, 1999), learning and corresponding brain development continues throughout life. In the process of improving our knowledge of early brain development, we understand the importance of the first 3 years of life for any child, regardless of whether he is at risk or not. It is imperative for researchers to go a long way before they can conclude which experiences and experiences at which point in a given period are decisive.

Literalization. Surface of the brain, or cerebral cortex(cerebral cortex), divided into two hemispheres - right and left. Each hemisphere is specialized in information processing and behavior management; this phenomenon is called lateralization. In the 1960s, Roger Sperry and his colleagues confirmed the presence of lateralization by studying the effects of surgical procedures aimed at treating people with epileptic seizures. Scientists have found that dissecting nerve tissue (corpus callosum (), connecting the two hemispheres can significantly reduce the frequency of seizures, while leaving most of the abilities necessary for daily functioning intact. In this case, the left and right hemispheres of a person are largely independent and cannot establish communication with each other (Sperry, 1968). Today, the surgery associated with the treatment of epileptic seizures is much more specific and subtle.

The left hemisphere controls motor behavior on the right side of the body, and the right hemisphere controls 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 performed in right-handers; in left-handers, some functions may be reversed. It must be remembered that most of the functioning of normal people is associated with activity. all brain (Hellige, 1993). Lateralized (or otherwise specialized) functions indicate a greater degree of activity in this area than in others.

By observing how and in what sequence children exercise their skills and abilities, we notice that the development of the cerebral hemispheres is not synchronous (Tratcher, Walker & Guidice, 1987). For example, linguistic abilities develop very rapidly between the ages of 3 and 6, and the left hemisphere of most children responsible for them grows rapidly at this time. On the other hand, maturation of the right hemisphere in early childhood proceeds at a slower pace and accelerates somewhat during middle childhood (8-10 years). The specialization of the cerebral hemispheres continues throughout childhood and ends in adolescence.

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

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

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 infinity 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 processes inherent in humans, one way or another, occur within a small space of the cranium. The work of the human brain and its study are connected much more strongly than any other objects and methods of research. In this case, they practically coincide. 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 of a walnut, covered with a thin gray shell. This is the cerebral cortex. Each of the halves is conventionally divided into several parts. The most evolutionarily ancient parts of the brain, the limbic system and the trunk, 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 the remaining elements into a single whole, and also take part in strengthening 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 that transmit information from the neuron body further, and short dendrites that receive a signal from other cells. The contiguous axons and dendrites form synapses, places where information is transmitted. The long process releases a neurotransmitter into the synapse cavity, a chemical that affects the functioning of the cell, it gets on the dendrite and leads to inhibition or excitation of the neuron. The signal is transmitted to all connected cells. As a result, the work of a large number of neurons is very quickly excited or inhibited.

Some developmental features

The human brain, like any other organ of the body, goes through certain stages of its formation. The 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 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 it acquires many strong and orderly connections between the remaining ones. "Extra" neurons that have not found a place in the formed structures die. How much the human brain works, apparently, depends on the quality of the connections, and not on the number of cells.

Common myth

Understanding the features of the development of the brain helps to determine the discrepancy between the reality of some of the usual 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 is mysteriously dormant. If you re-read the above, it becomes clear that unused neurons cannot exist for a long time - they die. Most likely, such a mistake is the result of the perception that existed some time ago that only those neurons that transmit an impulse work. However, in a unit of time, only some cells are in a similar 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, for a certain time, the whole 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 the brain's work so much desired by many, can lead to a kind of short circuit: a person will hallucinate, experience pain and all possible sensations, shudder with the whole body.

Connections

It turns out that you cannot say that some part of the brain is not working. However, the abilities of the human brain are, indeed, not fully utilized. The point, however, is not in "dormant" neurons, but in the number and quality of connections between cells. Any repetitive action, sensation or thought is anchored at the neuronal level. The more reps, the stronger the bond. Accordingly, a more complete use of the brain presupposes the building of new connections. Learning is built on this. The child's brain does not yet have stable connections; they are formed and consolidated in the process of the child's acquaintance with the world. With age, it becomes more difficult to make changes in the existing structure, so children learn more easily. Nevertheless, if you wish, you can develop the abilities of the human brain at any age.

Unbelievable but true

The ability to forge new connections and retrain has been amazing. There are cases when she overcame all the boundaries of the possible. The human brain is a non-linear structure. With all certainty, it is impossible to single out zones in it that perform one specific function and nothing else. Moreover, if necessary, parts of the brain can take on the "duties" of the injured areas.

This happened to Howard Rocket, who was doomed to a wheelchair as a result of a stroke. He didn’t want to give up and, through a series of exercises, tried to develop a 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 was very slowly and gradually reconfigured 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 characteristic that amazes scientists. Neuroscientists do not ignore such phenomena as telepathy or clairvoyance. In laboratories, experiments are carried out to prove or disprove the possibility of such abilities. Studies by American and British scientists provide interesting results that suggest 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 the possible, 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 babies, and in adults it is an extremely rare phenomenon. However, the human brain is an organ and, like any other part of the body, it lends itself to training. This means that memory can be improved, intellect can be tightened, and creative thinking can be developed. It is only important to remember that the development of the human brain is not a matter of one day. Exercise should be regular regardless of your goals.

Unusual

New connections are formed at the moment when a person does something differently. The simplest example: you can get to work in several ways, but out of habit we always choose the same one. The challenge is to choose a new road 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.

The number of such trainings can be attributed to the use of the left hand where the right one is accustomed (and vice versa, for left-handed people). Writing, typing, holding the 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 fantasy. They are matched by crosswords, puzzles, logic games, chess. They stimulate thinking, make us use those capabilities of the brain that are usually not in demand.

Physical exercise

How much the human brain works, at full capacity or not, 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 from regular exercise improves overall well-being 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 the beginning 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 original stripe and notochord anlage. This sweat is called neural plate ... Soon it deepens the uneven growth of cells in the nerve groove, the edge of the groove rises upward, forming nerve rolls. In the anterior part of the groove, the nerve rolls 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 visible. The nerve rolls, increasing, gradually approach each other and, finally, converge and mikayutsya, forming neural tube ... Since the roll consists of the medial part - the cells of the neural groove and the lateral - the cells of the unchanged ectoderm, the medial plates grow together, closing the neural tube, and. Lateral form a continuous ectodermal plate, which is first adjacent to the neural tube. Later, the neural tube deepens and loses its connection with the ectoderm, and this latter grows together over it.

The anterior end of the neural tube expands and forms three sequential initial cerebral vesicles, separated by small interceptions, namely: anterior cerebral bladder, middle and rhomboid ... These three bubbles represent the bookmarks of the entire brain. They do not lie in the same plane, but are very curved, and three bends are formed. Some of them disappear with subsequent development. More stable viya is the bend in the area of the middle bubble, which is called parietal bend ... At the end of the fourth week of development, signs of future separation of the anterior and posterior vesicles appear. At the sixth week of development, there are already five brain bubbles. The front bladder is divided into terminal brainі diencephalon, the midbrain is not divided, and the rhomboid bladder is divided into hindbrain and medulla oblongata ... In the terminal brain, two lateral outgrowths are formed, from which the cerebral hemispheres originate. From the lateral walls of the intermediate bladder, visual tubercles are formed, from its bottom - a gray tubercle with a funnel and the posterior part of the pituitary gland, and from the posterior wall - the pineal gland. From the midbrain, the legs of the brain and the four-humped body are formed. In rhomboid vesicles are distinguished strong> bookmarks of the cerebellum and medulla oblongata. From the abdominal walls of the hindbrain, an anlage of the pons is formed, and from the lateral walls - the cerebellar legs to the pons

The cavities of the cerebral vesicles are transformed into the ventricles of the formed brain. The cavities of the outgrowths of the telencephalon form two lateral ventricles. The third ventricle originates from the diencephalon cavity. The cavity of the midbrain develops less, forming the sylvian aqueduct, and the fourth ventricle is formed from the cavity of the entire rhomboid bladder. The spinal cord remains tubular for life. Only during the course of embryonic development do the walls thicken so much in their lateral parts, converge, leaving between themselves the anterior median fissure and the 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 is five small bubbles that develop at the end of the neural tube (future spinal cord). The brain at this stage is remarkably similar to that of a fish (Figure 18). It is interesting that the human embryo now has gills and hvis_st.

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

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

... V four months internally embryonic life, the rudiments of the cerebral cortex are formed at the same time it begins to crumple, as it were - grooves and convolutions are formed

... V six months migrating cells, which "arrived" in place, begin to vigorously grow and develop. The surface of the hemispheres, covered with bark, increases. The bark is divided into layers and areas with different structures (fields)

... By the time the baby is born the brain is almost complete. There are already all the grooves and convolutions. Birth is a watershed moment. The flow of various stimuli that the sensory organs perceive, a sharp change in the way of eating - all this, naturally, leads to large changes in the brain.

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

... One year ... The baby's brain has grown, and the cortex has become even more complex in structure. The child begins to walk, pronounces the first words

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

... V seven to twelve years the formation of not only the macro-, but also the microstructure of the brain ends. The child's memory is rapidly changing, the beginnings of independent creativity appear. But even after seven years, some parts of the brain associated with language and complex mental activity of a person 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 over 2000 grams, which on average is approximately 2% of body weight. The brains of men have an average mass of 100-150 grams more than the brains of women, but there was no statistical difference between the ratio of body-to-brain size in adult men and women. It is widely believed that the mental abilities of a person depend on the mass of the brain: the greater the mass of the brain, the more gifted a person is. 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 the mass of the brain and the mental abilities of an individual 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 parts of the brain and various indicators of cognitive ability. A number of scientists [ who?], however, cautions against using these studies to support the conclusion about low intelligence in some ethnic groups (such as Australian Aborigines) with smaller average brains. A number of studies indicate that brain size, which is almost entirely dependent on genetic factors, cannot explain much of the difference in IQ. As an argument, researchers from the University of Amsterdam point to a significant cultural difference between the civilizations of Mesopotamia and Ancient Egypt and their present-day descendants in Iraq and modern Egypt.

The degree of development of the brain 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 people of the Upper Paleolithic, the brain was noticeably (10-12%) larger than the brain of a modern person - 1: 55-1: 56.

The structure of the brain

The volume of the brain of most people is in the range of 1250-1600 cubic centimeters and is 91-95% of the capacity of the skull. In the brain, five sections are distinguished: the medulla oblongata, the posterior one, which includes the bridge and the cerebellum, the pineal gland, the middle, diencephalon and forebrain, represented by the large hemispheres. Along with the above division into divisions, the entire brain is divided into three large parts:

cerebral hemispheres;
cerebellum;
brain stem.

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

The 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 with flat moist cells from the inside, tightly fused with the bones of the skull in the area of its inner 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 brains of women and men, no decisive signs or their combinations are observed, allowing to speak of a specifically “male” or specifically “female” brain. There are brain features that are more common among women, and there are - more often observed in men, however, both of them can manifest themselves in the opposite sex, and there are practically no stable ensembles of this kind of signs.

Brain development

Prenatal development

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

Natal condition

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

At birth, the child has practically formed subcortical formations 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 different sensory organs (analyzer systems) end, and the motor pathways begin.

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

Other areas of the cerebral cortex do not reach a sufficient level of maturity by the time a child is born. This is evidenced by the small size of the cells included in them, the small width of their upper layers, which perform 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 secondary, associative fields of the brain mature, some of which (secondary gnostic zones of the analytic systems) are located in the second and third blocks (premotor region). These structures provide processes of perception and execution of a sequence of actions.

Period from 5 to 7 years

The next to mature are the tertiary (associative) fields of the brain. 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 of various brain zones, and here the most complex forms of information processing are carried out. The back associative area provides the synthesis of all incoming heterogeneous information into a supra-modal holistic reflection of the reality surrounding the subject in the totality of its connections and relationships. The anterior associative area is responsible for the arbitrary regulation of complex forms of mental activity, including the choice of information necessary, essential 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 the bottom up - from the underlying formations to the overlying ones, from the subcortical structures to the primary fields, from the primary fields to the associative ones. Damage during the formation of any of these levels can lead to deviations in the maturation of the next one due to the absence of stimulating effects from the underlying damaged level.

The brain from the point of view of cybernetics

American scientists tried to compare the human brain with the hard drive of a computer 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 the human brain spends only 20 watts of energy to process such a large amount of information, it can be called the most efficient computing device on Earth.

Notes (edit)

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abstract

On the topic of:

"The main stages of brain development"

Moscow 2009

Introduction

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

Brain functions include processing sensory information from the senses, planning, decision making, coordination, movement control, positive and negative emotions, attention, memory. The human brain performs the highest function - thinking. Also, one of the most important functions of 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 function.

The structure of the brain

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

Large brain: the most voluminous part of the brain, occupies almost the entire skull. Consists of two halves, or hemispheres, separated by a longitudinal slit, each hemisphere is divided laterally by a Roland or Sylvian groove. Thus, four parts, or lobes, are distinguished in the brain: frontal, parietal, temporal, and occipital. The brain is made up of several layers.

The cerebral cortex, or gray matter, is the outer layer formed by the bodies of nerve cells - neurons. The white matter makes up the rest of the brain tissue and consists of dendrites, or cell processes. The 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: A small organ located under the occipital region of the brain. The main function of the cerebellum is to maintain balance and coordinate movements of the musculoskeletal system.

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

The medulla oblongata: is a continuation of the medullary bridge and goes directly into the spinal cord. Regulates important involuntary body functions through the respiratory center (respiration rate), the vasomotor center (narrowing and dilation of blood vessels) and the vomiting center.

Because of its extreme importance, the brain is well protected. In addition to the skull, which is a strong bony structure, it is protected by three very thin membranes: hard, arachnoid and pia mater, which protect it from direct contact with the bones of the skull. Also, the ventricles of the brain 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 cerebral tube of two primary cerebral vesicles resulting from the uneven growth of the walls of the neural tube (archencephalon and deuterancephalon). Deuterencephalon, like the posterior part of the brain tube (later the spinal cord), is located above the notochord. Archephalon is laid in front of her.

Then, at the beginning of the fourth week in the embryo, the deuterencephalon is divided into the middle (mesencephalon) and rhomboid (rhombencephalon) bubbles. At this (three-vesicular) stage, archencephalon turns into the anterior cerebral bladder (prosencephalon). 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 eye vesicles protrude from the dorsolateral walls of the anterior cerebral bladder. Further, the retina of the eyes, optic nerves and tracts develop from them.

At the sixth week of embryonic development, the anterior and rhomboid vesicles divide into two, and the five-vesicle stage begins.

The anterior bladder - the telencephalon - is divided by a longitudinal slit 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 cracks. 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 fetal brain, the membranes of the brain develop. Gray matter is located on the periphery, forming the cerebral cortex, and at the base of the hemispheres, forming subcortical nuclei.

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

The third cerebral bladder turns into the midbrain, which develops most easily and lags behind in growth. Its walls thicken evenly, and the cavity turns into a narrow channel - the Sylvian aqueduct connecting the third and fourth ventricles. From the dorsal wall, the quadruple develops, and from the ventral, the midbrain legs.

The rhomboid brain is divided into posterior and accessory. From the posterior, the cerebellum is formed - first the cerebellar worm, and then the hemisphere, as well as the bridge. The accessory brain becomes the medulla oblongata. The walls of the rhomboid brain thicken - both from the sides and at the bottom, only the roof remains in the form of the thinnest plate. The cavity turns into the IV ventricle, which communicates with the Sylvian aqueduct and with the central canal of the spinal cord.

As a result of the uneven development of the cerebral vesicles, the cerebral tube begins to bend (at the level of the midbrain - the parietal deflection, in the hindbrain region - the pontine and at the place where the accessory brain passes into the spinal cord - the occipital deflection). The parietal and occipital deflections are turned outward, and the pavement - inward.

The structures of the brain that form from the primary cerebral bladder: the middle, posterior and accessory brains - make up the brain stem. It is a rostral extension of the spinal cord and has structural features in common with it. The paired border groove passing along the lateral walls of the spinal cord and brainstem divides the cerebral 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 base plate. Above the border groove, sensory structures (posterior horns of the spinal cord, sensory nuclei of the brainstem) develop from the pterygoid plate, within the border groove itself, the centers of the autonomic nervous system.

Archencephalon derivatives (telencephalon and diencephalon) create subcortical structures and cortex. There is no main plate (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 a child is born.

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. 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. For 20 to 60 years, the mass and volume remain maximum and constant for each individual.

Listliterature

1. Anatomy of the central nervous system: a 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 vols. 2nd ed., Rev. and add. M., 1999.

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

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