Stages of development of the nervous system. Stages of development of the central nervous system

The main stages of the evolution of the CNS.

The nervous system of higher animals and humans is the result of a long development in the process of adaptive evolution of living beings. The development of the central nervous system took place, first of all, in connection with the improvement in the perception and analysis of influences from the external environment. At the same time, the ability to respond to these influences with a coordinated, biologically expedient reaction was also improved. The development of the nervous system also proceeded in connection with the complication of the structure of organisms and the need to coordinate and regulate the work of internal organs.

The simplest unicellular organisms (amoeba) do not yet have a nervous system, and communication with the environment is carried out with the help of fluids that are inside and outside the body, - humoral or prenervous, form of regulation.

In the future, when the nervous system arises, another form of regulation appears - nervous. As it develops, it more and more subjugates the humoral, so that a single neurohumoral regulation with the leading role of the nervous system. The latter in the process of phylogenesis goes through a number of main stages.

Stage I - net nervous system. At this stage, the (intestinal) nervous system, such as hydra, consists of nerve cells, the numerous processes of which are connected to each other in different directions, forming a network that diffusely permeates the entire body of the animal. When any point of the body is stimulated, the excitation spreads throughout the entire nervous network and the animal reacts with the movement of the whole body. The diffuse nervous network is not divided into central and peripheral sections and can be localized in the ectoderm and endoderm.

Stage II - nodal nervous system. At this stage, (invertebrate) nerve cells converge into separate clusters or groups, and clusters of cell bodies produce nerve nodes - centers, and clusters of processes - nerve trunks - nerves. At the same time, the number of processes in each cell decreases and they receive a certain direction. According to the segmental structure of the body of an animal, for example, in an annelids, in each segment there are segmental nerve nodes and nerve trunks. The latter connect the nodes in two directions: the transverse shafts connect the nodes of a given segment, and the longitudinal ones connect the nodes of different segments. Due to this, nerve impulses that occur at any point in the body do not spread throughout the body, but spread along transverse trunks within this segment. Longitudinal trunks connect nerve segments into one whole. At the head end of the animal, which, when moving forward, comes into contact with various objects of the surrounding world, sensory organs develop, and therefore the head nodes develop more strongly than the others, giving rise to the development of the future brain. A reflection of this stage is the preservation of primitive features in humans (dispersion of nodes and microganglia on the periphery) in the structure of the autonomic nervous system.

Stage III - tubular nervous system. At the initial stage of animal development, a particularly important role was played by the apparatus of movement, on the perfection of which depended the main condition for the existence of an animal - nutrition (movement in search of food, capturing and absorbing it). In lower multicellular organisms, a peristaltic mode of locomotion has developed, which is associated with involuntary muscles and its local nervous apparatus. At a higher level, the peristaltic method is replaced by skeletal motility, i.e., movement with the help of a system of rigid levers - over the muscles (arthropods) and inside the muscles (vertebrates). The consequence of this was the formation of voluntary (skeletal) muscles and the central nervous system, which coordinates the movement of individual levers of the motor skeleton.

Such central nervous system in chordates (lancelet) arose in the form of a metamerically built neural tube with segmental nerves extending from it to all segments of the body, including the apparatus of movement, the trunk brain. In vertebrates and humans, the trunk brain becomes the spinal cord. Thus, the appearance of the trunk brain is connected with the improvement, first of all, of the motor apparatus of the animal. The lancelet already has receptors (olfactory, light). The further development of the nervous system and the emergence of the brain is due mainly to the improvement of the receptor apparatus.

Since most of the sense organs arise at the end of the animal’s body that is turned in the direction of movement, i.e. forward, the anterior end of the trunk brain develops to perceive the external stimuli coming through them and the brain is formed, which coincides with the isolation of the anterior end of the body in the form of the head cephalization.

At the first stage development, the brain consists of three sections: posterior, middle and anterior, and from these sections in the first place (in lower fish) the posterior, or rhomboid brain, especially develops. The development of the hindbrain occurs under the influence of acoustic and gravity receptors (receptors of the VIII pair of cranial nerves having leading value for orientation in the aquatic environment). In the process of further evolution, the hindbrain differentiates into the medulla oblongata and the hindbrain proper, from which the cerebellum and pons develop.

In the process of adapting the body to the environment by changing the metabolism in the hindbrain, as the most developed section of the central nervous system at this stage, there are control centers for vital life processes associated, in particular, with the gill apparatus (respiration, blood circulation, digestion, etc.). .). Therefore, nuclei of the gill nerves arise in the medulla oblongata (group X of the pair - the vagus nerve). These vital centers of respiration and circulation remain in the human medulla oblongata. The development of the vestibular system associated with the semicircular canals and lateral line receptors, the emergence of nuclei of the vagus nerve and the respiratory center create the basis for the formation hindbrain.

At the second stage(still in fish) under the influence of the visual receptor, the midbrain especially develops. On the dorsal surface of the neural tube, a visual reflex center develops - the roof of the midbrain, where the fibers of the optic nerve come.

At the third stage, in connection with the final transition of animals from the aquatic environment to the air, the olfactory receptor is intensively developing, perceiving chemicals contained in the air, signaling prey, danger and other vital phenomena of the surrounding nature.

Under the influence of the olfactory receptor, the forebrain, prosencephalon, develops, initially having the character of a purely olfactory brain. In the future, the forebrain grows and differentiates into the intermediate and final. In the telencephalon, as in the higher part of the central nervous system, there appear centers for all kinds of sensitivity. However, the underlying centers do not disappear, but remain, obeying the centers of the overlying floor. Consequently, with each new stage in the development of the brain, new centers arise that subjugate the old ones. There is a kind of movement of functional centers to the head end and the simultaneous subordination of phylogenetically old rudiments to new ones. As a result, the hearing centers that first appeared in the hindbrain are also present in the middle and forebrain, the centers of vision that arose in the middle are also in the forebrain, and the centers of smell are only in the forebrain. Under the influence of the olfactory receptor, a small part of the forebrain, called the olfactory brain, develops, which is covered with a gray matter cortex - the old cortex.

The improvement of the receptors leads to the progressive development of the forebrain, which gradually becomes the organ that controls the entire behavior of the animal. There are two forms of animal behavior: instinctive, based on specific reactions (unconditioned reflexes), and individual, based on the experience of the individual (conditioned reflexes). According to these two forms of behavior, 2 groups of gray matter centers develop in the telencephalon: basal ganglia having the structure of nuclei (nuclear centers), and cortex of gray matter, which has the structure of a continuous screen (screen centers). In this case, the “subcortex” develops first, and then the cortex. The bark arises during the transition of an animal from an aquatic to a terrestrial lifestyle and is clearly found in amphibians and reptiles. The further evolution of the nervous system is characterized by the fact that the cerebral cortex more and more subjugates the functions of all underlying centers, there is a gradual function corticolization. The growth of the new cortex in mammals is so intense that the old and ancient cortex is pushed in the medial direction to the cerebral septum. The rapid growth of the crust is compensated by the formation of folding.

The necessary structure for the implementation of higher nervous activity is new bark, located on the surface of the hemispheres and acquiring a 6-layer structure in the process of phylogenesis. Due to the increased development of the new cortex, the telencephalon in higher vertebrates surpasses all other parts of the brain, covering them like a cloak. The developing new brain pushes the old brain (olfactory) into the depths, which, as it were, collapses, but remains as before the olfactory center. As a result, the cloak, that is, the new brain, sharply prevails over the rest of the brain - the old brain.

Rice. 1. Development of the telencephalon in vertebrates (according to Eddinger). I - human brain; II - rabbit; III - lizards; IV - sharks. Black indicates the new cortex, dotted line - the old olfactory part¸

So, the development of the brain takes place under the influence of the development of receptors, which explains the fact that the highest part of the brain: the brain - the cortex (gray matter) is a collection of cortical ends of the analyzers, that is, a continuous perceiving (receptor) surface.

The further development of the human brain is subject to other patterns associated with its social nature. In addition to the natural organs of the body, which are also found in animals, man began to use tools. Tools of labor, which became artificial organs, supplemented the natural organs of the body and constituted the technical "weapon" of man. With the help of this “weapon”, man acquired the opportunity not only to adapt himself to nature, as animals do, but also to adapt nature to his needs. Labor, as already noted, was a decisive factor in the formation of a person, and in the process of social labor, a means necessary for communication between people arose - speech. “First work, and then articulate speech along with it, were the two most important stimuli under the influence of which the brain of the monkey gradually turned into a human brain, which, for all its resemblance to the monkey, far surpasses it in size and perfection.” (K. Marx, F. Engels). This perfection is due to the maximum development of the telencephalon, especially its cortex - the new cortex.

In addition to analyzers that perceive various stimuli of the outside world and constitute the material substrate of concrete-visual thinking characteristic of animals (the first signal system for reflecting reality, but to I.P. Pavlov), a person has the ability to abstract, abstract thinking with the help of a word, first heard (oral speech) and later visible (written speech). This constituted the second signaling system, according to I.P. Pavlov, which in the developing animal world was “an extraordinary addition to the mechanisms of nervous activity” (I.P. Pavlov). The surface layers of the new crust became the material substrate of the second signaling system. Therefore, the cerebral cortex reaches its highest development in humans.

Thus, the evolution of the nervous system is reduced to the progressive development of the telencephalon, which in higher vertebrates and especially in humans, due to the complication of nervous functions, reaches enormous proportions. In the process of development, there is a tendency to move the leading integrative centers of the brain in the rostral direction from the midbrain and cerebellum to the forebrain. However, this trend cannot be absolutized, since the brain is an integral system in which the stem parts play an important functional role at all stages of the phylogenetic development of vertebrates. In addition, starting from cyclostomes, projections of various sensory modalities are found in the forebrain, indicating the participation of this brain region in the control of behavior already at the early stages of vertebrate evolution.

Embryogenesis of the CNS.

Ontogenesis (ontogenesis; Greek op, ontos - existing + genesis - origin, origin) - the process of individual development of the organism from the moment of its inception (conception) to death. Allocate: embryonic (embryonic, or prenatal) - the time from fertilization to birth and postembryonic (post-embryonic, or postnatal) - from birth to death, periods of development.

The human nervous system develops from the ectoderm - the outer germ layer. At the end of the second week of embryonic development, a section of the epithelium separates in the dorsal parts of the body - neural (medullary) plate, cells of which intensively multiply and differentiate. The accelerated growth of the lateral sections of the neural plate leads to the fact that its edges first rise, then approach each other, and finally, at the end of the third week, grow together, forming the primary brain tube. After that, the brain tube gradually sinks into the mesoderm.

Fig.1. Formation of the neural tube.

The neural tube is the embryonic germ of the entire human nervous system. From it, the brain and spinal cord, as well as the peripheral parts of the nervous system, are subsequently formed. When the neural groove closes on the sides in the region of its raised edges (neural folds), a group of cells is isolated on each side, which, as the neural tube separates from the skin ectoderm, forms a continuous layer between the neural folds and the ectoderm - the ganglionic plate. The latter serves as the starting material for cells of sensitive nerve nodes (spinal and cranial ganglia) and nodes of the autonomic nervous system that innervates internal organs.

The neural tube at an early stage of its development consists of one layer of cylindrical cells, which subsequently intensively multiply by mitosis and their number increases; as a result, the wall of the neural tube thickens. At this stage of development, three layers can be distinguished in it: the inner one (later it will form the ependymal lining), the middle layer (the gray matter of the brain, the cellular elements of this layer differentiate in two directions: some of them turn into neurons, the other part into glial cells ) and the outer layer (white matter of the brain).

Fig.2. Stages of development of the human brain.

The neural tube develops unevenly. Due to the intensive development of its anterior part, the brain begins to form, cerebral bubbles form: first two bubbles appear, then the back bubble divides into two more. As a result, in four-week-old embryos, the brain consists of three brain bubbles(front, middle and rhomboid brain). At the fifth week, the anterior cerebral vesicle is subdivided into the telencephalon and diencephalon, and the rhomboid - into the posterior and medulla oblongata ( stage five brain bubbles). At the same time, the neural tube forms several bends in the sagittal plane.

The spinal cord with the spinal canal develops from the undifferentiated posterior part of the medullary tube. Formation occurs from the cavities of the embryonic brain brain ventricles. The cavity of the rhomboid brain is transformed into the IV ventricle, the cavity of the midbrain forms the aqueduct of the brain, the cavity of the diencephalon forms the III ventricle of the brain, and the cavity of the forebrain forms the lateral ventricles of the brain with a complex configuration.

After the formation of five cerebral vesicles in the structures of the nervous system, complex processes of internal differentiation and growth of various parts of the brain take place. At 5-10 weeks, growth and differentiation of the telencephalon is observed: cortical and subcortical centers are formed, and the cortex is stratified. Meninges are formed. The spinal cord acquires a definitive state. At 10-20 weeks, the migration processes are completed, all the main parts of the brain are formed, and differentiation processes come to the fore. The end brain develops most actively. The cerebral hemispheres become the largest part of the nervous system. At the 4th month of human fetal development, a transverse fissure of the large brain appears, at the 6th - the central sulcus and other main sulci, in the following months - secondary and after birth - the smallest sulci.

In the process of development of the nervous system, myelination of nerve fibers plays an important role, as a result of which the nerve fibers are covered protective layer myelin and significantly increases the speed of nerve impulses. By the end of the 4th month of intrauterine development, myelin is detected in the nerve fibers that make up the ascending, or afferent (sensory) systems of the lateral cords of the spinal cord, while in the fibers of the descending, or efferent (motor) systems, myelin is found at the 6th month. At about the same time, myelination of the nerve fibers of the posterior cords occurs. Myelination of nerve fibers of the cortico-spinal tract begins in the last month of intrauterine life and continues for a year after birth. This indicates that the process of myelination of nerve fibers extends first to phylogenetically older structures and then to younger structures. The order of formation of their functions depends on the sequence of myelination of certain nerve structures. The formation of function and also depends on the differentiation of cellular elements and their gradual maturation, which lasts for the first decade.

By the time the baby is born, nerve cells reach maturity and are no longer capable of dividing. As a result, their number will not increase in the future. In the postnatal period, the final maturation of the entire nervous system gradually occurs, in particular its most complex section - the cerebral cortex, which plays a special role in the brain mechanisms of conditioned reflex activity, which is formed from the first days of life. Another milestone in ontogenesis, this is the period of puberty, when the sexual differentiation of the brain also passes.

Throughout a person's life, the brain is actively changing, adapting to the conditions of the external and internal environment, some of these changes are genetically programmed, some are a relatively free reaction to the conditions of existence. The ontogenesis of the nervous system ends only with the death of a person.

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

IN first trimester of pregnancy the following stages of development of the nervous system of the fetus occur:

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

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

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

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

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

From the forebrain, the telencephalon and the diencephalon are formed.

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

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

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

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

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

Violations of the development of the fetus from the influence of various factors during this period leads to violations of the vestibular apparatus in a newborn child.

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

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

Second trimester of pregnancy.

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

Neuronal proliferation is the main process of ontogeny.

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

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

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

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

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

Third trimester of pregnancy.

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

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

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

Under the influence of unfavorable factors in the third trimester of pregnancy, as well as during the first year of life, when the processes of myelination of the pyramidal tracts end, no serious disturbances occur. There may be slight changes in the structure, which are determined only by histological examination.

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

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

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

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

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

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

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

The nervous system is of ectodermal origin, i.e., it develops from an external germinal sheet with a thickness of a single-cell layer due to the formation and division of the medullary tube.

In the evolution of the nervous system, the following stages can be schematically distinguished:

1. Reticulate, diffuse, or asynaptic, nervous system. It arises in freshwater hydra, has the shape of a grid, which is formed by the connection of process cells and is evenly distributed throughout the body, thickening around the oral appendages. The cells that make up this network differ significantly from the nerve cells of higher animals: they are small in size, do not have a nucleus and a chromatophilic substance characteristic of a nerve cell. This nervous system conducts excitations diffusely, in all directions, providing global reflex reactions. At further stages of the development of multicellular animals, it loses its significance as a single form of the nervous system, but in the human body it remains in the form of the Meissner and Auerbach plexuses of the digestive tract.

2. The ganglionic nervous system (in worm-like) is synaptic, conducts excitation in one direction and provides differentiated adaptive reactions. This corresponds to the highest degree of evolution of the nervous system: special organs of movement and receptor organs develop, groups of nerve cells appear in the network, the bodies of which contain a chromatophilic substance. It tends to disintegrate during cell excitation and recover at rest. Cells with a chromatophilic substance are located in groups or nodes of ganglia, therefore they are called ganglionic. So, at the second stage of development, the nervous system from the reticular system turned into the ganglion-network. In humans, this type of structure of the nervous system has been preserved in the form of paravertebral trunks and peripheral nodes (ganglia), which have vegetative functions.

3. The tubular nervous system (in vertebrates) differs from the nervous system of worm-like ones in that skeletal motor apparatuses with striated muscles arose in vertebrates. This led to the development of the central nervous system, the individual parts and structures of which are formed in the process of evolution gradually and in a certain sequence. First, the segmental apparatus of the spinal cord is formed from the caudal, undifferentiated part of the medullary tube, and the main parts of the brain are formed from the anterior part of the brain tube due to cephalization (from the Greek kephale - head).

A reflex is a natural reaction of the body in response to irritation of receptors, which is carried out by a reflex arc with the participation of the central nervous system. This is an adaptive reaction of the body in response to a change in internal or environment. Reflex reactions ensure the integrity of the body and the constancy of its internal environment, the reflex arc is the main unit of integrative reflex activity.

A significant contribution to the development of the reflex theory was made by I.M. Sechenov (1829-1905). He was the first to use the reflex principle to study the physiological mechanisms of mental processes. In the work "Reflexes of the brain" (1863) I.M. Sechenov argued that the mental activity of humans and animals is carried out according to the mechanism of reflex reactions that occur in the brain, including the most complex of them - the formation of behavior and thinking. Based on his research, he concluded that all acts of conscious and unconscious life are reflex. Reflex theory I.M. Sechenov served as the basis on which the teachings of I.P. Pavlov (1849-1936) on higher nervous activity.

The method of conditioned reflexes developed by him expanded the scientific understanding of the role of the cerebral cortex as a material substratum of the psyche. I.P. Pavlov formulated a reflex theory of the brain, which is based on three principles: causality, structure, unity of analysis and synthesis. PK Anokhin (1898-1974) proved the importance of feedback in the reflex activity of the organism. Its essence lies in the fact that during the implementation of any reflex act, the process is not limited to the effector, but is accompanied by the excitation of the receptors of the working organ, from which information about the consequences of the action is supplied by afferent pathways to the central nervous system. There were ideas about the "reflex ring", "feedback".

Reflex mechanisms play an essential role in the behavior of living organisms, ensuring their adequate response to environmental signals. For animals, reality is signaled almost exclusively by stimuli. This is the first signal system of reality, common to man and animals. I.P. Pavlov proved that for a person, unlike animals, the object of display is not only the environment, but also social factors. Therefore, for him, the second signal system acquires decisive importance - the word as a signal of the first signals.

The conditioned reflex underlies the higher nervous activity of man and animals. It is always included as an essential component in the most complex manifestations of behavior. However, not all forms of behavior of a living organism can be explained from the point of view of the reflex theory, which reveals only the mechanisms of action. The reflex principle does not answer the question of the expediency of human and animal behavior, does not take into account the result of the action.

Therefore, over the past decades, on the basis of reflex ideas, a concept has been formed regarding the leading role of needs as the driving force behind the behavior of humans and animals. The presence of needs is a necessary prerequisite for any activity. The activity of the organism acquires a certain direction only if there is a goal that meets this need. Each behavioral act is preceded by needs that arose in the process of phylogenetic development under the influence of environmental conditions. That is why the behavior of a living organism is determined not so much by the reaction to external influences how much the need to implement the intended program, plan, aimed at meeting a particular need of a person or animal.

PC. Anokhin (1955) developed the theory of functional systems, which provides a systematic approach to the study of the mechanisms of the brain, in particular, the development of problems of the structural and functional basis of behavior, the physiology of motivations and emotions. The essence of the concept is that the brain can not only adequately respond to external stimuli, but also foresee the future, actively plan its behavior and implement them. The theory of functional systems does not exclude the method of conditioned reflexes from the sphere of higher nervous activity and does not replace it with something else. It makes it possible to delve deeper into the physiological essence of the reflex. Instead of the physiology of individual organs or structures of the brain, the systematic approach considers the activity of the organism as a whole. For any behavioral act of a person or animal, such an organization of all brain structures is needed that will provide the desired end result. So, in the theory of functional systems, the useful result of an action occupies a central place. Actually, the factors that are the basis for achieving the goal are formed according to the type of versatile reflex processes.

One of the important mechanisms of the activity of the central nervous system is the principle of integration. Thanks to the integration of somatic and autonomic functions, which is carried out by the cerebral cortex through the structures of the limbic-reticular complex, various adaptive reactions and behavioral acts are realized. The highest level of integration of functions in humans is the frontal cortex.

An important role in the mental activity of humans and animals is played by the principle of dominance, developed by O. O. Ukhtomsky (1875-1942). Dominant (from Latin dominari to dominate) is an excitation that is superior in the central nervous system, which is formed under the influence of stimuli from the environment or internal environment and at a certain moment subordinates the activity of other centers.

The brain with its highest department - the cerebral cortex - is a complex self-regulating system built on the interaction of excitatory and inhibitory processes. The principle of self-regulation is carried out at different levels of the analyzer systems - from the cortical sections to the level of receptors with the constant subordination of the lower sections of the nervous system to the higher ones.

Studying the principles of the functioning of the nervous system, not without reason, the brain is compared with an electronic computer. As you know, the basis of the operation of cybernetic equipment is the reception, transmission, processing and storage of information (memory) with its further reproduction. Information must be encoded for transmission and decoded for playback. Using cybernetic concepts, we can assume that the analyzer receives, transmits, processes and, possibly, stores information. In the cortical sections, its decoding is carried out. This is probably enough to make it possible to attempt to compare the brain with a computer.

At the same time, the work of the brain cannot be identified with a computer: “... the brain is the most capricious machine in the world. Let us be modest and cautious with conclusions” (I.M. Sechenov, 1863). A computer is a machine and nothing more. All cybernetic devices operate on the principle of electrical or electronic interaction, and in the brain, which was created through evolutionary development, in addition, complex biochemical and bioelectrical processes take place. They can only be carried out in living tissue. The brain, unlike electronic systems, does not function according to the principle of “all or nothing”, but takes into account a great many gradations between these two extremes. These gradations are due not to electronic, but to biochemical processes. This is the essential difference between the physical and the biological.

The brain has qualities that go beyond those that a computer has. It should be added that the behavioral reactions of the body are largely determined by intercellular interactions in the central nervous system. As a rule, processes from hundreds or thousands of other neurons approach one neuron, and it, in turn, branches off into hundreds or thousands of other neurons. No one can say how many synapses are in the brain, but the number 10 14 (one hundred trillion) does not seem incredible (D. Hubel, 1982). The computer contains much fewer elements. The functioning of the brain and the vital activity of the body are carried out in specific environmental conditions. Therefore, the satisfaction of certain needs can be achieved provided that this activity is adequate to the existing external environmental conditions.

For the convenience of studying the basic patterns of functioning, the brain is divided into three main blocks, each of which performs its own specific functions.

The first block is the phylogenetically most ancient structures of the limbic-reticular complex, which are located in the stem and deep parts of the brain. They include the cingulate gyrus, the seahorse (hippocampus), the papillary body, the anterior nuclei of the thalamus, the hypothalamus, and the reticular formation. They provide the regulation of vital functions - respiration, blood circulation, metabolism, as well as general tone. With regard to behavioral acts, these formations are involved in the regulation of functions aimed at ensuring nutritional and sexual behavior, species conservation processes, in the regulation of systems that provide sleep and wakefulness, emotional activity, memory processes. The second block is a set of formations located behind central sulcus: somatosensory, visual and auditory areas of the cerebral cortex.

Their main functions are receiving, processing and storing information. The neurons of the system, which are located mainly anterior to the central sulcus and are associated with effector functions, the implementation of motor programs, constitute the third block. Nevertheless, it should be recognized that it is impossible to draw a clear line between the sensory and motor structures of the brain. The postcentral gyrus, which is a sensitive projection area, is closely interconnected with the precentral motor area, forming a single sensorimotor field. Therefore, it is necessary to clearly understand that one or another human activity requires the simultaneous participation of all parts of the nervous system. Moreover, the system as a whole performs functions that go beyond the functions inherent in each of these blocks.

Anatomical and physiological characteristics and pathology of the cranial nerves

The cranial nerves, which extend from the brain in an amount of 12 pairs, innervate the skin, muscles, organs of the head and neck, as well as some organs of the chest and abdominal cavities. Of these, III, IV,

VI, XI, XII pairs are motor, V, VII, IX, X are mixed, pairs I, II and VIII are sensitive, providing, respectively, specific innervation of the organs of smell, vision and hearing; Pairs I and II are derivatives of the brain, they do not have nuclei in the brain stem. All other cranial nerves exit or enter the brain stem where their motor, sensory, and autonomic nuclei are located. So, the nuclei of III and IV pairs of cranial nerves are located in the brain stem, V, VI, VII, VIII pairs - mainly in the pons, IX, X, XI, XII pairs - in the medulla oblongata.

cerebral cortex

The brain (encephalon, cerebrum) includes the right and left hemispheres and the brain stem. Each hemisphere has three poles: frontal, occipital and temporal. Four lobes are distinguished in each hemisphere: frontal, parietal, occipital, temporal and insula (see Fig. 2).

The hemispheres of the brain (hemispheritae cerebri) are called even more, or the final brain, the normal functioning of which predetermines signs specific to a person. The human brain consists of multipolar nerve cells - neurons, the number of which reaches 10 11 (one hundred billion). This is approximately the same as the number of stars in our Galaxy. The average mass of the brain of an adult is 1450 g. It is characterized by significant individual fluctuations. For example, such prominent people as the writer I.S. Turgenev (63 years old), the poet Byron (36 years old), it was 2016 and 2238, respectively, for others, no less talented - the French writer A. France (80 years old) and the political scientist and philosopher G.V. Plekhanov (62 years old) - respectively 1017 and 1180. The study of the brain of great people did not reveal the secret of intelligence. There was no dependence of brain mass on the creative level of a person. The absolute mass of the brain of women is 100-150 g less than the mass of the brain of men.

The human brain differs from the brain of apes and other higher animals not only in greater mass, but also in the significant development of the frontal lobes, which makes up 29% of the total mass of the brain. Significantly outpacing the growth of other lobes, the frontal lobes continue to increase throughout the first 7-8 years of a child's life. Obviously, this is due to the fact that they are associated with motor function. It is from the frontal lobes that the pyramidal path originates. The importance of the frontal lobe and in the implementation of higher nervous activity. In contrast to the animal, in the parietal lobe of the human brain, the lower parietal lobule is differentiated. Its development is associated with the appearance of speech function.

The human brain is the most perfect of all that nature has created. At the same time, it is the most difficult object for knowledge. What apparatus, in general terms, enables the brain to perform its extremely complex function? The number of neurons in the brain is about 10 11 , the number of synapses, or contacts between neurons, is about 10 15 . On average, each neuron has several thousand separate inputs, and it itself sends connections to many other neurons (F. Crick, 1982). These are just some of the main provisions of the doctrine of the brain. Scientific research on the brain is progressing, albeit slowly. However, this does not mean that at some point in the future there will not be a discovery or series of discoveries that will reveal the secrets of how the brain works.

This question concerns the very essence of man, and therefore fundamental changes in our views on the human brain will significantly affect ourselves, the world around us and other areas of scientific research, will give an answer to whole line biological and philosophical questions. However, these are still prospects for the development of brain science. Their implementation will be similar to those revolutions that were made by Copernicus, who proved that the Earth is not the center of the universe; Darwin, who established that man is related to all other living beings; Einstein, who introduced new concepts regarding time and space, mass and energy; Watson and Crick, who showed that biological heredity can be explained by physical and chemical concepts (D. Huebel, 1982).

The cerebral cortex covers its hemispheres, has grooves that divide it into lobes and convolutions, as a result of which its area increases significantly. On the upper lateral (outer) surface of the cerebral hemisphere there are two largest primary sulci - the central sulcus (sulcus centralis), which separates the frontal lobe from the parietal, and the lateral sulcus (sulcus lateralis), which is often called the sylvian sulcus; it separates the frontal and parietal lobes from the temporal (see Fig. 2). On the medial surface of the cerebral hemisphere, a parietal-occipital sulcus (sulcus parietooccipitalis) is distinguished, which separates the parietal lobe from the occipital lobe (see Fig. 4). Each cerebral hemisphere also has a lower (basal) surface.

The cerebral cortex is evolutionarily the most young education, the most complex in structure and function. It is extremely important in the organization of the life of the body. The cerebral cortex developed as an apparatus for adapting to changing environmental conditions. Adaptive reactions are determined by the interaction of somatic and vegetative functions. It is the cerebral cortex that ensures the integration of these functions through the limbic-reticular complex. It does not have a direct connection with receptors, but receives the most important afferent information, partially already processed at the level of the spinal cord, in the brain stem and subcortical region. In the cortex, sensitive information lends itself to analysis and synthesis. Even according to the most cautious estimates, about 10 11 elementary operations are carried out in the human brain during 1 second (O. Forster, 1982). It is in the cortex that nerve cells, interconnected by many processes, analyze the signals that enter the body, and decisions are made regarding their implementation.

Emphasizing the leading role of the cerebral cortex in neurophysiological processes, it should be noted that this higher department of the central nervous system can function normally only with close interaction with subcortical formations, the reticulate formation of the brain stem. Here it is appropriate to recall the statement of P.K. Anokhin (1955) that, on the one hand, the cerebral cortex develops, and, on the other hand, its energy supply, i.e., network formation. The latter controls all the signals that are sent to the cerebral cortex, skips a certain number of them; excess signals are cumulated, and in case of information hunger are added to the general flow.

Cytoarchitectonics of the cerebral cortex

The cerebral cortex is the gray matter of the surface of the cerebral hemispheres 3 mm thick. It reaches its maximum development in the precentral gyrus, where its thickness approaches 5 mm. The human cerebral cortex contains about 70% of all neurons of the central nervous system. The mass of the cerebral cortex in an adult is 580 g, or 40% of the total mass of the brain. The total area of ​​the cortex is about 2200 cm 2, which is 3 times the area of ​​the inner surface of the cerebral skull, to which it is adjacent. Two-thirds of the area of ​​the cerebral cortex is hidden in a large number of furrows (sulci cerebri).

The first rudiments of the cerebral cortex are formed in the human embryo at the 3rd month of embryonic development, at the 7th month most of the cortex consists of 6 plates, or layers. The German neurologist K. Brodmann (1903) gave the following names to the layers: molecular plate (lamina molecularis), outer granular plate (lamina granulans externa), outer pyramidal plate (lamina pyramidal is externa), inner granular plate (lamina granulans interna), internal pyramidal plate (lamina pyramidalis interna seu ganglionaris) and multiform plate (lamina miltiformis).

The structure of the cerebral cortex:

a - layers of cells; b - layers of fibers; I - molecular plate; II - external granular plate; III - external pyramidal plate; IV - internal granular plate; V - internal pyramidal (ganglion) plate; VI - multiform plate (Via - triangular cells; VIb - spindle-shaped cells)

The morphological structure of the cerebral cortex in its different parts was described in detail by Professor of Kyiv University I.O. Betz in 1874. He first described giant pyramidal cells in the fifth layer of the cortex of the precentral gyrus. These cells are known as Betz cells. Their axons are sent to the motor nuclei of the brainstem and spinal cord, forming a pyramidal pathway. IN. Betz first introduced the term "cytoarchitecture of the cortex". This is the science of the cellular structure of the cortex, the number, shape and arrangement of cells in its different layers. The cytoarchitectonic features of the structure of different parts of the cerebral cortex are the basis for its distribution into areas, subareas, fields and subfields. Individual fields of the cortex are responsible for certain manifestations of higher nervous activity: speech, vision, hearing, smell, etc. The topography of the fields of the human cerebral cortex was studied in detail by K. Brodman, who compiled the corresponding maps of the cortex. The entire surface of the cortex, according to K. Brodman, is divided into 11 sections and 52 fields, which differ in the features of the cellular composition, structure and executive function.

In humans, there are three formations of the cerebral cortex: new, ancient and old. They differ significantly in their structure. The new cortex (neocortex) makes up approximately 96% of the entire surface of the cerebrum and includes the occipital lobe, superior and inferior parietal, precentral and postcentral gyrus, as well as the frontal and temporal lobes of the brain, the insula. This is a homotopic cortex, it has a lamellar type of structure and consists mainly of six layers. Records vary in the power of their development in different fields. In particular, in the precentral gyrus, which is the motor center of the cerebral cortex, the outer pyramidal, inner pyramidal and multiform plates are well developed, and worse - the outer and inner granular plates.

The ancient cortex (paleocortex) includes the olfactory tubercle, the transparent septum, the periamygdala and prepiriform regions. It is connected with the ancient functions of the brain, relating to smell, taste. The ancient bark differs from the bark of the new formation in that it is covered with a white layer of fibers, part of which consists of fibers of the olfactory pathway (tractus olfactorius). The limbic cortex is also an ancient part of the cortex, it has a three-layer structure.

Old bark (archicortex) includes ammonium horn, dentate gyrus. It is closely connected with the area of ​​the hypothalamus (corpus mammillare) and the limbic cortex. The old bark differs from the ancient one in that it is clearly separated from the subcortical formations. Functionally, it is connected with emotional reactions.

The ancient and aged cortex makes up approximately 4% of the cerebral cortex. It does not pass in the embryonic development of the period of the six-layer structure. Such a cortex has a three- or one-layer structure and is called heterotopic.

Almost simultaneously with the study of the cellular architectonics of the cortex, the study of its myeloarchitectonics began, that is, the study of the fibrous structure of the cortex from the point of view of determining those differences that exist in its individual sections. Myeloarchitectonics of the cortex is characterized by the presence of six layers of fibers within the boundaries of the cerebral cortex with different lines of their myelination (Fig. b). different hemispheres, and projection, connecting the cortex with the lower parts of the central nervous system.

Thus, the cerebral cortex is divided into sections and fields. All of them have a special, specific, inherent structure. As for functions, there are three main types of cortical activity. The first type is associated with the activities of individual analyzers and provides the simplest forms of cognition. This is the first signal system. The second type includes a second signaling system, the operation of which is closely related to the function of all analyzers. This is a more complex level of cortical activity, which directly concerns the speech function. Words for a person are the same conditioned stimulus as signals of reality. The third type of cortical activity provides purposefulness of actions, the possibility of their long-term planning, which is functionally connected with the frontal lobes of the cerebral hemispheres.

Thus, a person perceives the world around him on the basis of the first signal system, and logical, abstract thinking is associated with the second signal system, which is the highest form of human nervous activity.

Autonomic (vegetative) nervous system

As already noted in previous chapters, the sensory and motor systems perceive irritation, carry out a sensitive connection of the body with the environment, and provide movement by contracting skeletal muscles. This part of the general nervous system is called the somatic. At the same time, there is a second part of the nervous system, which is responsible for the process of nutrition of the body, metabolism, excretion, growth, reproduction, circulation of fluids, i.e., regulates the activity of internal organs. It is called the autonomic (vegetative) nervous system.

There are different terminological designations for this part of the nervous system. According to the International Anatomical Nomenclature, the generally accepted term is "autonomous nervous system". However, in the domestic literature, the former name is traditionally used - the autonomic nervous system. The division of the general nervous system into two closely interconnected parts reflects its specialization while maintaining the integrative function of the central nervous system as the basis of the body's integrity.

Functions of the autonomic nervous system:

Trophotropic - regulation of the activity of internal organs, maintaining the constancy of the internal environment of the body - homeostasis;

Ergotropic vegetative provision of the processes of adaptation of the body to environmental conditions, i.e., the provision of various forms of mental and physical activity of the body: increased blood pressure, increased heart rate, deepening of breathing, increased blood glucose levels, release of adrenal hormones and other functions. These physiological functions are regulated independently (autonomously), without arbitrary control of them.

Thomas Willis singled out a borderline sympathetic trunk from the vagus nerve, and Jacob Winslow (1732) described in detail its structure, connection with internal organs, noting that "... one part of the body affects another, sensations arise - sympathy." This is how the term “sympathetic system” arose, that is, a system that connects organs to each other and to the central nervous system. In 1800, the French anatomist M. Bisha divided the nervous system into two sections: animal (animal) and vegetative (vegetative). The latter provides the metabolic processes necessary for the existence of both an animal organism and plants. Although at that time such ideas were not fully perceived, and then were generally discarded, but the proposed term "vegetative nervous system" was widely used and has been preserved to this day.

The English scientist John Langley established that different nervous vegetative conductor systems exercise opposite influences on organs. Based on these functional differences in the autonomic nervous system, two divisions were identified: sympathetic and parasympathetic. The sympathetic division of the autonomic nervous system activates the activity of the organism as a whole, provides protective functions(immune processes, barrier mechanisms, thermoregulation), parasympathetic - maintains homeostasis in the body. In its function, the parasympathetic nervous system is anabolic, it contributes to the accumulation of energy.

In addition, some of the internal organs also have metasympathetic neurons that carry out local mechanisms of regulation of internal organs. The sympathetic nervous system innervates all organs and tissues of the body, while the sphere of activity of the parasympathetic nervous system refers mainly to the internal organs. Most internal organs have dual, sympathetic and parasympathetic, innervation. The exceptions are the central nervous system, most of the vessels, the uterus, the adrenal medulla, the sweat glands, which do not have parasympathetic innervation.

The first anatomical descriptions of the structures of the autonomic nervous system were made by Galen and Vesalius, who studied the anatomy and function of the vagus nerve, although they mistakenly attributed other formations to it. In the XVII century.

Anatomy

According to anatomical criteria, the autonomic nervous system is divided into segmental and suprasegmental sections.

The segmental division of the autonomic nervous system provides autonomic innervation of individual segments of the body and the internal organs that belong to them. It is divided into sympathetic and parasympathetic parts.

The central link of the sympathetic part of the autonomic nervous system is the Jacobson's nucleus neurons of the lateral horns of the spinal cord from the lower cervical (C8) to the lumbar (L2-L4) segments. The axons of these cells leave the spinal cord as part of the anterior spinal roots. Then they in the form of preganglionic fibers (white connecting branches) go to the sympathetic nodes of the border (sympathetic) trunk, where they break.

The sympathetic trunk is located on both sides of the spine and is formed by paravertebral nodes, of which 3 are cervical, 10-12 thoracic, 3-4 lumbar and 4 sacral. In the nodes of the sympathetic trunk, part of the fibers (preganglionic) ends. The other part of the fibers, without interruption, goes to the prevertebral plexuses (on the aorta and its branches - the abdominal, or solar plexus). From the sympathetic trunk and intermediate nodes originate postgangio fibers (gray connecting branches), which do not have a myelin sheath. They innervate various organs and tissues.

Scheme of the structure of the segmental division of the autonomic (vegetative) nervous system:

1 - craniobulbar division of the parasympathetic nervous system (nuclei III, VII, IX, X pairs of cranial nerves); 2 - sacral (sacral) section of the parasympathetic nervous system (lateral horns of S2-S4 segments); 3 - sympathetic department (lateral horns of the spinal cord at the level of C8-L3 segments); 4 - ciliary knot; 5 - pterygopalatine node; 6 - submaxillary node; 7 - ear knot; 8 - sympathetic trunk.

In the lateral horns of the spinal cord at the level of C8-T2 is the ciliospinal center Budge, from which the cervical sympathetic nerve originates. The preganglionic sympathetic fibers from this center are sent to the superior cervical sympathetic ganglion. From it, the postganglionic fibers rise up, form the sympathetic plexus of the carotid artery, the ophthalmic artery (a. ophtalmica), then penetrate into the orbit, where they innervate the smooth muscles of the eye. With damage to the lateral horns at this level or the cervical sympathetic nerve, Bernard-Horner syndrome occurs. The latter is characterized by partial ptosis (narrowing of the palpebral fissure), miosis (narrowing of the pupil) and enophthalmos (retraction of the eyeball). Irritation of sympathetic fibers leads to the appearance of the opposite Pourfure du Petit syndrome: expansion of the palpebral fissure, mydriasis, exophthalmos.

Sympathetic fibers that start from the stellate ganglion (cervical-thoracic ganglion, gangl. stellatum) form the plexus of the vertebral artery and the sympathetic plexus in the heart. They provide innervation of the vessels of the vertebrobasilar basin, and also give branches to the heart and larynx. The thoracic section of the sympathetic trunk gives off branches that innervate the aorta, bronchi, lungs, pleura, and abdominal organs. From the lumbar nodes, sympathetic fibers are sent to the organs and vessels of the small pelvis. On the extremities, sympathetic fibers go along with the peripheral nerves, spreading in the distal sections along with small arterial vessels.

The parasympathetic part of the autonomic nervous system is divided into craniobulbar and sacral divisions. The craniobulbar region is represented by neurons of the nuclei of the brain stem: III, UP, IX, X pairs of cranial nerves. The vegetative nuclei of the oculomotor nerve - the accessory (Yakubovich's nucleus) and the central posterior (Perlia's nucleus) are located at the level of the midbrain. Their axons, as part of the oculomotor nerve, go to the ciliary ganglion (gangl. ciliarae), which is located in the posterior part of the orbit. From it, postganglionic fibers as part of short ciliary nerves (nn. ciliaris brevis) innervate the smooth muscles of the eye: the muscle that narrows the pupil (m. sphincter pupillae) and the ciliary muscle (t. ciliaris), the contraction of which provides accommodation.

In the region of the bridge there are secretory lacrimal cells, the axons of which, as part of the facial nerve, go to the pterygopalatine ganglion (gangl. pterygopalatinum) and innervate the lacrimal gland. The upper and lower secretory salivary nuclei are also localized in the brain stem, the axons from which go with the glossopharyngeal nerve to the parotid node (gangl. oticum) and with the intermediate nerve to the submandibular and sublingual nodes (gangl. submandibularis, gangl. sublingualis) and innervate the corresponding salivary glands.

At the level of the medulla oblongata is the posterior (visceral) nucleus of the vagus nerve (nucl. dorsalis n.vagus), the parasympathetic fibers of which innervate the heart, alimentary canal, gastric glands and other internal organs (except for the pelvic organs).

Scheme of efferent parasympathetic innervation:

1 - parasympathetic nuclei of the oculomotor nerve; 2 - upper salivary nucleus; 3 - lower salivary nucleus; 4 - posterior nucleus of a wandering non-ditch; 5 - lateral intermediate nucleus of the sacral spinal cord; b - oculomotor nerve; 7 - facial nerve; 8 - glossopharyngeal nerve; 9 - vagus nerve; 10 - pelvic nerves; 11 - ciliary knot; 12 - pterygopalatine node; 13 - ear knot; 14 - submandibular node; 15 - sublingual node; 16 - nodes of the pulmonary plexus; 17 - nodes of the cardiac plexus; 18 - abdominal nodes; 19 - nodes of the gastric and intestinal plexuses; 20 - nodes of the pelvic plexus.

On the surface or inside the internal organs there are intraorganic nerve plexuses (the metasympathetic division of the autonomic nervous system), which act as a collector - switch and transform all the impulses that come to the internal organs and adapt their activity to the changes that have occurred, i.e. e. provide adaptive and compensatory processes (for example, after surgery).

The sacral (sacral) part of the autonomic nervous system is represented by cells that are located in the lateral horns of the spinal cord at the level of S2-S4 segments (lateral intermediate nucleus). The axons of these cells form the pelvic nerves (nn. pelvici), which innervate the bladder, rectum and genitals.

The sympathetic and parasympathetic part of the autonomic nervous system has the opposite effect on the organs: dilatation or contraction of the pupil, acceleration or deceleration of the heartbeat, opposite changes in secretion, peristalsis, etc. An increase in the activity of one department under physiological conditions leads to a compensatory tension in another . This returns the functional system to its original state.

The differences between the sympathetic and parasympathetic divisions of the autonomic nervous system are as follows:

1. The parasympathetic ganglia are located near or in the organs that they innervate, and the sympathetic ganglia are at a considerable distance from them. Therefore, the postganglionic fibers of the sympathetic system are of considerable length, and when they are stimulated, the clinical symptoms are not local, but diffuse. The manifestations of the pathology of the parasympathetic part of the autonomic nervous system are more local, often covering only one organ.

2. Different nature of mediators: the mediator of preganglionic fibers of both departments (sympathetic and parasympathetic) is acetylcholine. In the synapses of the postganglionic fibers of the sympathetic part, sympathy is released (a mixture of adrenaline and norepinephrine), parasympathetic - acetylcholine.

3. The parasympathetic department is evolutionarily older, it performs a trophotropic function and is more autonomous. The sympathetic department is newer, performs an adaptive (ergotropic) function. It is less autonomous, depends on the function of the central nervous system, endocrine system and other processes.

4. The scope of functioning of the parasympathetic part of the autonomic nervous system is more limited and concerns mainly the internal organs; sympathetic fibers provide innervation to all organs and tissues of the body.

The suprasegmental division of the autonomic nervous system is not divided into sympathetic and parasympathetic parts. In the structure of the supra-segmental department, ergotropic and trophotropic systems are distinguished, as well as systems proposed by the English researcher Ged. The ergotropic system intensifies its activity at moments that require a certain tension from the body, vigorous activity. In this case, blood pressure rises, the coronary arteries expand, the pulse quickens, the respiratory rate increases, the bronchi expand, pulmonary ventilation increases, intestinal peristalsis decreases, the kidney vessels constrict, the pupils expand, the excitability of receptors and attention increase.

The body is ready to defend or to resist. To implement these functions, the ergotropic system mainly includes segmental apparatuses of the sympathetic part of the autonomic nervous system. In such cases, humoral mechanisms are also included in the process - adrenaline is released into the blood. Most of these centers are located in the frontal and parietal lobes. For example, the motor centers of innervation of smooth muscles, internal organs, blood vessels, sweating, trophism, and metabolism are located in the frontal lobes of the brain (fields 4, 6, 8). The innervation of the respiratory organs is associated with the cortex of the insula, the abdominal organs - with the cortex of the postcentral gyrus (field 5).

The trophotropic system helps to maintain internal balance and homeostasis. It provides nutritional benefits. The activity of the trophotropic system is associated with the state of rest, rest, sleep, and the processes of digestion. In this case, the heart rate, breathing slows down, blood pressure decreases, the bronchi narrow, the peristalsis of the intestines and the secretion of digestive juices increase. The actions of the trophotropic system are realized through the formation of the segmental division of the parasympathetic part of the autonomic nervous system.

The activity of both these functions (ergo- and trophotropic) proceeds synergistically. In each specific case, the predominance of one of them can be noted, and the adaptation of the organism to changing environmental conditions depends on their functional relationship.

Supra-segmental autonomic centers are located in the cerebral cortex, subcortical structures, cerebellum and brain stem. For example, such vegetative centers as the innervation of smooth muscles, internal organs, blood vessels, sweating, trophism, and metabolism are located in the frontal lobes of the brain. A special place among the higher vegetative centers is occupied by the limbic-reticular complex.

The limbic system is a complex of brain structures, which includes: the cortex of the posterior and mediobasal surface of the frontal lobe, the olfactory brain (olfactory bulb, olfactory pathways, olfactory tubercle), hippocampus, dentate, cingulate gyrus, septal nuclei, anterior thalamic nuclei , hypothalamus, amygdala. The limbic system is closely related to the reticular formation of the brain stem. Therefore, all these formations and their connections are called the limbic-reticular complex. The central parts of the limbic system are the olfactory brain, the hippocampus, and the amygdala.

The whole complex of structures of the limbic system, despite their phylogenetic and morphological differences, ensures the integrity of many body functions. At this level, the primary synthesis of all sensitivity takes place, the state of the internal environment is analyzed, elementary needs, motivations, and emotions are formed. The limbic system provides integrative functions, the interaction of all motor, sensory, and vegetative systems of the brain. The level of consciousness, attention, memory, the ability to navigate in space, motor and mental activity, the ability to perform automated movements, speech, the state of alertness or sleep depend on its state.

A significant place among the subcortical structures of the limbic system is assigned to the hypothalamus. It regulates the function of digestion, respiration, cardiovascular, endocrine systems, metabolism, thermoregulation.

Ensures the constancy of the indicators of the internal environment (BP, blood glucose, body temperature, gas concentration, electrolytes, etc.), i.e., is the main central mechanism for the regulation of homeostasis, ensures the regulation of the tone of the sympathetic and parasympathetic divisions of the autonomic nervous system. Thanks to connections with many structures of the central nervous system, the hypothalamus integrates the somatic and autonomic functions of the body. Moreover, these connections are carried out on the principle of feedback, bilateral control.

An important role among the structures of the suprasegmental division of the autonomic nervous system is played by the reticular formation of the brain stem. It has an independent meaning, but is a component of the limbic-reticular complex - the integrative apparatus of the brain. The nuclei of the reticular formation (there are about 100 of them) form suprasegmental centers of vital functions: respiration, vasomotor, cardiac activity, swallowing, vomiting, etc. In addition, it controls the state of sleep and wakefulness, phasic and tonic muscle tone, deciphers information signals from environment. The interaction of the reticular formation with the limbic system ensures the organization of expedient human behavior to changing environmental conditions.

Sheaths of the brain and spinal cord

The brain and spinal cord are covered with three membranes: hard (dura mater encephali), arachnoid (arachnoidea encephali) and soft (pia mater encephali).

The hard shell of the brain consists of dense fibrous tissue, in which the outer and inner surfaces are distinguished. Its outer surface is well vascularized and is directly connected to the bones of the skull, acting as an internal periosteum. In the cavity of the skull, the hard shell forms folds (duplicatures), which are commonly called processes.

There are such processes of the dura mater:

The crescent of the brain (falx cerebri), located in the sagittal plane between the cerebral hemispheres;

The sickle of the cerebellum (falx cerebelli), located between the hemispheres of the cerebellum;

The tentorium of the cerebellum (tentorium cerebelli), stretched in a horizontal plane above the posterior cranial fossa, between top corner the pyramids of the temporal bone and the transverse groove of the occipital bone and delimits the occipital lobes of the cerebrum from the upper surface of the cerebellar hemispheres;

Aperture of the Turkish saddle (diaphragma sellae turcicae); this process is stretched over the Turkish saddle, it forms its ceiling (operculum sellae).

Between the sheets of the dura mater and its processes are cavities that collect blood from the brain and are called the sinuses of the dura matris (sinus dures matris).

There are the following sinuses:

Superior sagittal sinus (sinus sagittalis superior), through which blood is discharged into the transverse sinus (sinus transversus). It is located along the protruding side of the upper edge of the greater falciform process;

The lower sagittal sinus (sinus sagittalis inferior) lies along the lower edge of the large crescent process and flows into the straight sinus (sinus rectus);

The transverse sinus (sinus transversus) is contained in the sulcus de occipital bone of the same name; bending around the mastoid angle of the parietal bone, it passes into the sigmoid sinus (sinus sigmoideus);

The direct sinus (sinus rectus) runs along the line of connection of the large falciform process with the cerebellum tenon. Together with the superior sagittal sinus, it brings venous blood into the transverse sinus;

Cavernous sinus (sinus cavernosus) is located on the sides of the Turkish saddle.

In cross section, it looks like a triangle. Three walls are distinguished in it: upper, outer and inner. The oculomotor nerve passes through the upper wall (p.

Nervous system - a set of formations (nerves, ganglia, sensory organs, brain) in animals and humans, which perceives stimuli acting on the body, analyzes them and provides a coordinated response. It regulates the work of all organs, ensures the interconnection of various organ systems, adapting the activity of the whole organism as a whole to the influences of the external environment.

Nervous regulation differs from humoral regulation (with the help of chemical substances) precise and fast action. The maximum speed of propagation of a nerve impulse along the nerves is 120 m/s, and the highest speed of delivery of chemicals by the bloodstream is only 0.5 m/s.

The structural and functional unit of the nervous system is the nerve cell, or neuron (Fig. 1). A person has 50 billion neurons, united in a complex network with numerous interneuronal contacts. The neuron consists of a body, strongly branching short processes - dendrites, a long process - an axon, and axon endings that look like buttons or bulbs with a specific structure - synapses (Fig. 2). Synapses provide the transmission of excitation to other neurons or muscles and glands. The coordination of processes in the body largely depends on their functional state.

The activity of the nervous system is largely carried out according to the reflex principle (Fig. 3).

This principle was formulated in 1863 by I. M. Sechenov in his work “Reflexes of the brain” (see Reflexes, Irritability, Receptors). Reflex reactions are very diverse and depend on the level of development of the nervous system.

In the course of evolution, the nervous system went through three stages of development (Fig. 4).

The most ancient, diffuse, or reticular, nervous system is found in intestinal animals. In this case, the nerve cells are connected into a network in which the conduction of excitation is carried out uniformly in different directions, gradually fading as it moves away from the site of irritation. Many connections provide broad interchangeability and greater reliability of activity, but the reactions are inaccurate, diffuse.

The nodal type of the nervous system is characteristic of worms, insects, mollusks, and crustaceans. The bulk of the neurons of the nodal system is concentrated on the ventral side in the nodes interconnected with receptors and executive formations using bundles of nerve fibers. In the most mobile animals, the nodes are mainly located at the head end. Here is the largest number of receptors. It looks like a brain. The connections of this type of nervous system are rigidly fixed, excitation is transmitted in a certain direction. This gives a gain in the speed and accuracy of responses.

In vertebrates, the nervous system is laid down on the dorsal side in the form of a neural tube, from which the spinal cord is then formed (Fig. 5). Sections of the brain are formed as thickenings at the head end of the neural tube in the form of cerebral vesicles (Fig. 6). In different classes of vertebrates, the formation of cerebral vesicles occurs according to the same type, only the degree of their development is different. The brain consists of the medulla oblongata, pons, cerebellum, midbrain, diencephalon and cerebral hemispheres (Fig. 7).

The spinal cord and brain are composed of gray and white matter. Gray matter is formed by the bodies and processes of neurons, and white matter is formed by nerve fibers covered with a whitish fat-like myelin sheath. Nonsynthetic fibers form ascending and descending pathways. All this makes up the central part of the nervous system.

The peripheral section is formed by nerves and nerve nodes - an accumulation of nerve cells outside the spinal cord and brain.

The part of the nervous system that regulates the activity of the skeletal muscles of the body is called somatic (from the Greek word soma - body).

The autonomic nervous system is the part that regulates the activity of internal organs (Fig. 8). Its name comes from the Latin word vegetativus - vegetable; it was previously believed that the internal organs provide growth processes.

It consists of the so-called sympathetic and parasympathetic fibers. Unlike somatic nerves, they have a smaller diameter and consist of two neurons, so the speed of excitation in the autonomic nerves is less. The sympathetic and parasympathetic nerves basically have opposite regulatory effects, providing a fine adaptation of the activity of the internal organs to various conditions. So, during sleep, parasympathetic nerves slow down the rhythm and weaken the strength of heart contractions. During physical exertion and emotional arousal, sympathetic nerves increase heart contractions.

This is the general plan of the structure of the tubular nervous system. In the process of evolution, it acquired new progressive qualities in comparison with the diffuse and nodal systems. Nerve cells formed a compact central system with specific functions. There was an increase in the development of the head sections of the brain, the structure of the central nervous system (CNS) became more complicated, the underlying sections of the CNS functionally obeyed the overlying ones, and all sections began to be controlled by the cerebral cortex.

Intensively developed sense organs, which produced a subtle analysis of existing stimuli, which made it possible to more successfully adapt to changing living conditions.

As the central nervous system became more complex, reflex reactions became more complicated. This can be seen in the example of the regulation of motor and vegetative reflexes by various parts of the CNS. The spinal cord regulates the simplest motor reactions: flexion, extensor, stepping and other reflexes. This section of the central nervous system has vegetative centers that regulate sweating, blood vessel tone, heart activity, excretory functions, etc.

The medulla oblongata and the bridge regulate motor reflexes that ensure the body's posture is maintained at rest and during movement, and complex autonomic processes: the regulation of respiration, the cardiovascular system, the secretory function of the digestive glands, etc. The midbrain regulates orienting reflexes (to light, sound , the reaction of "alarm") and others, which helps to quickly respond to sudden irritations. The same department regulates the movement of the fingers, the act of chewing and swallowing, etc. The cerebellum influences complex unconditioned motor and autonomic reflexes. When the cerebellum is removed, the coordination of movements and the activity of the respiratory, cardiovascular and other systems are disturbed. The diencephalon regulates temperature, pain, taste sensitivity, auditory and visual sensations, emotional states (joy, pleasure, anger, fear, etc.), states of sleep and wakefulness, feelings of hunger and thirst, and other processes.

The cerebral cortex carries out fine conditioned reflex regulation of all motor and vegetative processes, the most complex behavioral reactions. The human cerebral cortex provides higher mental processes: thinking, consciousness, memory, speech.

Perm Institute of Humanities and Technology

Faculty of Humanities

TEST

in the discipline "ANATOMY OF THE CNS"

on the topic

"The main stages of the evolutionary development of the central nervous system"

Perm, 2007

Stages of development of the central nervous system

The emergence of multicellular organisms was the primary stimulus for the differentiation of communication systems that ensure the integrity of the body's reactions, the interaction between its tissues and organs. This interaction can be carried out both in a humoral way through the entry of hormones and metabolic products into the blood, lymph and tissue fluid, and due to the function of the nervous system, which ensures the rapid transmission of excitation addressed to well-defined targets.

Nervous system of invertebrates

The nervous system as a specialized system of integration on the path of structural and functional development passes through several stages, which in protostomes and deuterostomes can be characterized by features of parallelism and phylogenetic plasticity of choice.

Among invertebrates, the most primitive type of nervous system in the form diffuse neural network found in the intestinal type. Their nervous network is an accumulation of multipolar and bipolar neurons, the processes of which can cross, adjoin each other and lack functional differentiation into axons and dendrites. The diffuse nervous network is not divided into central and peripheral sections and can be localized in the ectoderm and endoderm.

epidermal nerve plexuses resembling the nervous networks of coelenterates can also be found in more highly organized invertebrates (flat and annelids), but here they occupy a subordinate position in relation to the central nervous system (CNS), which stands out as an independent department.

As an example of such centralization and concentration of nerve elements, one can cite orthogonal nervous systemflatworms. The orthogon of higher turbellarians is an ordered structure, which consists of associative and motor cells, which together form several pairs of longitudinal cords, or trunks, connected by a large number of transverse and annular commissural trunks. The concentration of nerve elements is accompanied by their immersion into the depths of the body.

Flatworms are bilaterally symmetrical animals with a well-defined longitudinal body axis. Movement in free-living forms is carried out mainly towards the head end, where receptors are concentrated, signaling the approach of a source of irritation. These turbellarian receptors include pigment eyes, olfactory pits, statocysts, and sensory cells of the integument, the presence of which contributes to the concentration of nervous tissue at the anterior end of the body. This process leads to the formation head ganglion, which, according to the apt expression of Ch. Sherrington, can be considered as a ganglion superstructure over the systems of reception at a distance.

Ganglionization of nerve elements is further developed in higher invertebrates, annelids, mollusks and arthropods. In most annelids, the abdominal trunks are ganglionized in such a way that one pair of ganglia is formed in each segment of the body, connected by connectives to another pair located in the adjacent segment.

The ganglia of one segment in primitive annelids are interconnected by transverse commissures, and this leads to the formation ladder nervous system. In more advanced orders of annelids, there is a tendency for the abdominal trunks to converge up to the complete fusion of the ganglia of the right and left sides and the transition from the scalene to chain nervous system. An identical, chain type of structure of the nervous system also exists in arthropods with a different concentration of nerve elements, which can be carried out not only due to the fusion of neighboring ganglia of one segment, but also due to the fusion of successive ganglia of different segments.

The evolution of the nervous system of invertebrates goes not only along the path of concentration of nerve elements, but also in the direction of complication of structural relationships within the ganglia. It is no coincidence that modern literature notes the tendency to compare the ventral nerve cord with the spinal cord of vertebrates. As in the spinal cord, in the ganglia, a superficial arrangement of pathways is found, and the neuropil is differentiated into motor, sensory, and associative areas. This similarity, which is an example of parallelism in the evolution of tissue structures, does not, however, exclude the peculiarity of the anatomical organization. For example, the location of the trunk brain of annelids and arthropods on the ventral side of the body determined the localization of the motor neuropil on the dorsal side of the ganglion, and not on the ventral side, as is the case in vertebrates.

The process of ganglionization in invertebrates can lead to the formation scattered-nodular nervous system, found in molluscs. Within this numerous phylum there are phylogenetically primitive forms with a nervous system comparable to the orthogon of flatworms (lateral nerve molluscs) and advanced classes (cephalopods) in which fused ganglia form a differentiated brain.

The progressive development of the brain in cephalopods and insects creates a prerequisite for the emergence of a kind of hierarchy of command systems for controlling behavior. The lowest level of integration in the segmental ganglia of insects and in the subpharyngeal mass of the brain of mollusks, it serves as the basis for autonomous activity and coordination of elementary motor acts. At the same time, the brain is the following, a higher level of integration, where inter-analyzer synthesis and assessment of the biological significance of information can be carried out. On the basis of these processes, descending commands are formed that provide the variability in the launch of neurons of segmental centers. Obviously, the interaction of two levels of integration underlies the plasticity of the behavior of higher invertebrates, including innate and acquired reactions.

In general, speaking about the evolution of the nervous system of invertebrates, it would be an oversimplification to represent it as a linear process. The facts obtained in neurodevelopmental studies of invertebrates make it possible to assume a multiple (polygenetic) origin of the nervous tissue of invertebrates. Consequently, the evolution of the nervous system of invertebrates could proceed on a broad front from several sources with initial diversity.

At the early stages of phylogenetic development, a the second trunk of the evolutionary tree, which gave rise to echinoderms and chordates. The main criterion for distinguishing the type of chordates is the presence of a notochord, pharyngeal gill slits and a dorsal nerve cord - the neural tube, which is a derivative of the outer germ layer - the ectoderm. Tubular type of nervous system vertebrates, according to the basic principles of organization, is different from the ganglionic or nodal type of the nervous system of higher invertebrates.

Nervous system of vertebrates

Nervous system of vertebrates is laid in the form of a continuous neural tube, which in the process of ontogenesis and phylogenesis differentiates into various sections and is also a source of peripheral sympathetic and parasympathetic ganglions. In the most ancient chordates (non-cranial), the brain is absent and the neural tube is presented in an undifferentiated state.

According to the ideas of L. A. Orbeli, S. Herrick, A. I. Karamyan, this critical stage in the development of the central nervous system is designated as spinal. The neural tube of a modern non-cranial (lancelet), like the spinal cord of more highly organized vertebrates, has a metameric structure and consists of 62-64 segments, in the center of which passes spinal canal. The abdominal (motor) and dorsal (sensory) roots depart from each segment, which do not form mixed nerves, but go in the form of separate trunks. In the head and tail sections of the neural tube, giant Rode cells are localized, the thick axons of which form the conduction apparatus. The light-sensitive eyes of Hess are associated with Rode cells, the excitation of which causes negative phototaxis.

In the head part of the neural tube of the lancelet there are large ganglionic cells of Ovsyannikov, which have synaptic contacts with bipolar sensory cells of the olfactory fossa. Recently, neurosecretory cells resembling the pituitary system of higher vertebrates have been identified in the head of the neural tube. However, an analysis of the perception and simple forms of learning in the lancelet shows that at this stage of development the CNS functions according to the principle of equipotentiality, and the statement about the specificity of the head section of the neural tube does not have sufficient grounds.

In the course of further evolution, there is a shift of some functions and systems of integration from the spinal cord to the brain - encephalization process, which was considered on the example of invertebrates. During the period of phylogenetic development from the level of non-cranial to the level of cyclostomes the brain is formed as a superstructure over systems of distant reception.

A study of the central nervous system of modern cyclostomes shows that their rudimentary brain contains all the main structural elements. The development of the vestibulolateral system associated with the semicircular canals and lateral line receptors, the emergence of nuclei of the vagus nerve and the respiratory center create the basis for the formation hindbrain. The hindbrain of the lamprey includes the medulla oblongata and cerebellum in the form of small protrusions of the neural tube.

The development of distant visual reception gives impetus to laying midbrain. On the dorsal surface of the neural tube, the visual reflex center develops - the roof of the midbrain, where the fibers of the optic nerve come. And finally, the development of olfactory receptors contributes to the formation front or telencephalon, which is adjacent to the underdeveloped intermediate brain.

The direction of the encephalization process indicated above is consistent with the course of the ontogenetic development of the brain in cyclostomes. During embryogenesis, the head sections of the neural tube give rise to three cerebral vesicles. The telencephalon and diencephalon form from the anterior bladder, the middle bladder differentiates into the midbrain, and the medulla oblongata and cerebellum form from the posterior bladder. A similar plan of ontogenetic development of the brain is preserved in other classes of vertebrates.

Neurophysiological studies of the brain of cyclostomes show that its main integrative level is concentrated in the midbrain and medulla oblongata, i.e., at this stage of development, the central nervous system dominates bulbomesencephalic system of integration, replacing spinal.

Forebrain of cyclostomes long time considered purely olfactory. However, recent studies have shown that the olfactory inputs to the forebrain are not the only ones, but are complemented by sensory inputs from other modalities. Obviously, already at the early stages of vertebrate phylogenesis, the forebrain begins to participate in information processing and behavior control.

At the same time, encephalization as the main direction of brain development does not exclude evolutionary transformations in the spinal cord of cyclostomes. Unlike non-cranial neurons of skin sensitivity are isolated from the spinal cord and concentrated in the spinal ganglion. Improvement of the conductive part of the spinal cord is observed. The conductive fibers of the lateral columns have contacts with a powerful dendritic network of motor neurons. Downward connections of the brain with the spinal cord are formed through the Müllerian fibers - giant axons of cells lying in the midbrain and medulla oblongata.

The appearance of more complex forms of motor behavior in vertebrates, it is associated with the improvement of the organization of the spinal cord. For example, the transition from stereotypical undulating movements of cyclostomes to locomotion with the help of fins in cartilaginous fish (sharks, rays) is associated with the separation of cutaneous and musculo-articular (proprioceptive) sensitivity. Specialized neurons appear in the spinal ganglia to perform these functions.

Progressive transformations are also observed in the efferent part of the spinal cord of cartilaginous fishes. The path of motor axons inside the spinal cord is shortened, further differentiation of its pathways occurs. The ascending pathways of the lateral columns in cartilaginous fish reach the medulla oblongata and cerebellum. At the same time, the ascending pathways of the posterior columns of the spinal cord have not yet been differentiated and consist of short links.

The descending pathways of the spinal cord in cartilaginous fish are represented by a developed reticulospinal tract and pathways connecting the vestibulolateral system and the cerebellum with the spinal cord (vestibulospinal and cerebellospinal tracts).

At the same time, in the medulla oblongata there is a complication of the system of nuclei of the vestibulolateral zone. This process is associated with further differentiation of the lateral line organs and with the appearance in the labyrinth of the third (external) semicircular canal in addition to the anterior and posterior.

The development of general motor coordination in cartilaginous fish is associated with intensive development of the cerebellum. The massive cerebellum of the shark has bilateral connections with the spinal cord, medulla oblongata, and midbrain tegmentum. Functionally, it is divided into two parts: the old cerebellum (archicerebellum), associated with the vestibulo-lateral system, and the ancient cerebellum (fingerecerebellum), included in the proprioceptive sensitivity analysis system. An essential aspect of the structural organization of the cerebellum of cartilaginous fishes is its multi-layered nature. In the gray matter of the shark cerebellum, a molecular layer, a layer of Purkinje cells, and a granular layer were identified.

Another multilayer structure of the brainstem of cartilaginous fish is midbrain roof, where afferents of various modalities fit (visual, somatic). The very morphological organization of the midbrain indicates its important role in integrative processes at this level of phylogenetic development.

In the diencephalon of cartilaginous fish, differentiation of the hypothalamus, which is the most ancient formation of this part of the brain. The hypothalamus has connections with the telencephalon. The telencephalon itself grows and consists of olfactory bulbs and paired hemispheres. In the hemispheres of sharks, there are the rudiments of the old cortex (archicortex) and the ancient cortex (paleocortex).

The paleocortex, closely associated with the olfactory bulbs, serves mainly for the perception of olfactory stimuli. The archicortex, or hippocampal cortex, is designed for more complex processing of olfactory information. At the same time, electrophysiological studies have shown that olfactory projections occupy only part of the hemispheres of the forebrain in sharks. In addition to the olfactory, representation of the visual and somatic sensory systems was found here. Obviously, the old and ancient bark can participate in the regulation of search, feeding, sexual, and defensive reflexes in cartilaginous fishes, many of which are active predators.

Thus, in cartilaginous fishes, the main features of the ichthyopsid type of brain organization are formed. Its distinguishing feature is the presence of a suprasegmental integration apparatus that coordinates the work of motor centers and organizes behavior. These integrative functions are performed by the midbrain and cerebellum, which makes it possible to speak of mesenzphalocerebellar integration system at this stage of the phylogenetic development of the nervous system. The telencephalon remains predominantly olfactory, although it is involved in the regulation of the functions of the underlying sections.

The transition of vertebrates from an aquatic to a terrestrial way of life is associated with a number of rearrangements in the central nervous system. So, for example, in amphibians, two thickenings appear in the spinal cord, corresponding to the upper and lower limb girdle. In the spinal ganglia, instead of bipolar sensory neurons, unipolar neurons with a T-shaped branching process are concentrated, providing a higher rate of excitation without the participation of the cell body. On the periphery in the skin of amphibians are formed specialized receptors and receptor fields, providing discrimination sensitivity.

Structural changes also occur in the brain stem due to the redistribution of the functional significance of various departments. In the medulla oblongata, there is a reduction of the lateral line nuclei and the formation of a cochlear, auditory nucleus, which analyzes information from the primitive organ of hearing.

Compared to fish, amphibians, which have rather stereotyped locomotion, show a significant reduction in the cerebellum. The midbrain, like in fish, is a multilayer structure in which, along with the anterior colliculus, the leading part of the integration of the visual analyzer, additional tubercles appear - precursors of the posterior colliculi of the quadrigemina.

The most significant evolutionary changes occur in the diencephalon of amphibians. Here is isolated visual tubercle - thalamus, structured nuclei appear (external geniculate body) and ascending pathways connecting the visual tubercle with the cortex (thalamocortical tract).

In the hemispheres of the forebrain, further differentiation of the old and ancient cortex occurs. In the old cortex (archicortex), stellate and pyramidal cells are found. In the gap between the old and ancient bark, a strip of a cloak appears, which is the forerunner new cortex (neocortex).

In general, the development of the forebrain creates the prerequisites for the transition from the cerebellar-mesencephalic integration system characteristic of fish to diencephalotelencephalic, where the forebrain becomes the leading department, and the visual tubercle of the diencephalon turns into a collector of all afferent signals. This integration system is fully represented in the sauropsid type of the brain in reptiles and marks the next stage of morphofunctional evolution of the brain .

The development of the thalamocortical system of connections in reptiles leads to the formation of new conducting pathways, as if pulling up to phylogenetically young brain formations.

In the lateral columns of the spinal cord of reptiles, an ascending spinothalamic tract, which conducts information about temperature and pain sensitivity to the brain. Here, in the side columns, a new descending tract is formed - rubrospinal(Monakova). It connects the motor neurons of the spinal cord with the red nucleus of the midbrain, which is included in the ancient extrapyramidal system of motor regulation. This multi-link system combines the influence of the forebrain, cerebellum, brainstem reticular formation, nuclei of the vestibular complex and coordinates motor activity.

In reptiles, as truly terrestrial animals, the role of visual and acoustic information increases, and it becomes necessary to compare this information with olfactory and gustatory information. Corresponding to these biological changes, a number of structural changes occur in the reptile brainstem. In the medulla oblongata, the auditory nuclei differentiate, in addition to the cochlear nucleus, an angular nucleus appears, connected with the midbrain. In the midbrain, the colliculus is transformed into the quadrigemina, in the posterior hills of which the acoustic centers are localized.

There is a further differentiation of the connections of the roof of the midbrain with the thalamus, which is, as it were, a vestibule before entering the cortex of all ascending sensory pathways. In the thalamus itself, there is a further separation of nuclear structures and the establishment of specialized connections between them.

telencephalon reptiles can have two types of organization:

cortical and striatal. cortical type of organization, characteristic of modern turtles, is characterized by the predominant development of the forebrain hemispheres and the parallel "development of new sections of the cerebellum. In the future, this direction in the evolution of the brain is preserved in mammals.

Striatal type of organization, characteristic of modern lizards, it is distinguished by the dominant development of the basal ganglia located in the depths of the hemispheres, in particular the striatum. This path is followed by the development of the brain in birds. It is of interest that in the striatum in birds there are cell associations or associations of neurons (from three to ten), separated by oligodendroglia. The neurons of such associations receive the same afferentation, and this makes them similar to neurons arranged in vertical columns in the neocortex of mammals. At the same time, identical cell associations have not been described in the striatum of mammals. Obviously, this is an example of convergent evolution, when similar formations developed independently in different animals.

In mammals, the development of the forebrain was accompanied by rapid growth of the neocortex, which is in close functional connection with the thalamus opticus of the diencephalon. Efferent pyramidal cells are laid in the cortex, sending their long axons to the motor neurons of the spinal cord.

Thus, along with the multilink extrapyramidal system, direct pyramidal pathways appear that provide direct control over motor acts. Cortical regulation of motor skills in mammals leads to the development of the phylogenetically youngest part of the cerebellum - the anterior part of the posterior lobes of the hemispheres, or neocerebellum. The neocerebellum acquires bilateral connections with the neocortex.

The growth of the new cortex in mammals is so intense that the old and ancient cortex is pushed in the medial direction to the cerebral septum. The rapid growth of the crust is compensated by the formation of folding. In the most poorly organized monotremes (platypus), the first two permanent furrows are laid on the surface of the hemisphere, while the rest of the surface remains smooth. (lissencephalic type of cortex).

Neurophysiological studies have shown that the brain of monotremes and marsupials lacks the corpus callosum that still connects the hemispheres and is characterized by overlapping sensory projections in the neocortex. There is no clear localization of motor, visual and auditory projections here.

Placental mammals (insectivores and rodents) develop a more distinct localization of projection zones in the cortex. Along with the projection zones, associative zones are formed in the neocortex, however, the boundaries of the first and second ones can overlap. The brain of insectivores and rodents is characterized by the presence of a corpus callosum and a further increase in the total area of ​​the neocortex.

In the process of parallel-adaptive evolution, predatory mammals develop parietal and frontal associative fields, responsible for evaluating biologically significant information, motivating behavior and programming complex behavioral acts. Further development of folding of the new crust is observed.

Finally, primates show the highest level of organization of the cerebral cortex. The bark of primates is characterized by six layers, the absence of overlap of associative and projection zones. In primates, connections are formed between the frontal and parietal associative fields and, thus, an integral integrative system of the cerebral hemispheres arises.

In general, tracing the main stages of the evolution of the vertebrate brain, it should be noted that its development was not limited to a linear increase in size. In different evolutionary lines of vertebrates, independent processes of increasing the size and complication of the cytoarchitectonics of various parts of the brain could take place. An example of this is a comparison of the striatal and cortical types of organization of the vertebrate forebrain.

In the process of development, there is a tendency to move the leading integrative centers of the brain in the rostral direction from the midbrain and cerebellum to the forebrain. However, this trend cannot be absolutized, since the brain is an integral system in which the stem parts play an important functional role at all stages of the phylogenetic development of vertebrates. In addition, starting from cyclostomes, projections of various sensory modalities are found in the forebrain, indicating the participation of this brain region in the control of behavior already at the early stages of vertebrate evolution.

Bibliographic list

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