1. THE CONCEPT OF THE PROPERTIES OF THE NERVOUS SYSTEM The problem of individual psychological differences between people has always been considered in Russian psychology as one of the fundamental. The greatest contribution to the development of this problem was made by B.M. Teplev and V.D. Nebylitsyn, as well as their

§ 3. Functional organization of the nervous system The nervous system is necessary for the rapid integration of the activity of various organs of a multicellular animal. In other words, the union of neurons is a system for the efficient use of momentary

§ 5. Energy expenditure of the nervous system Comparing the size of the brain and body size of animals, it is easy to establish a pattern according to which an increase in body size clearly correlates with an increase in brain size (see Table 1; Table 3). However, the brain is only part

§ 24. Evolution of the ganglionic nervous system At the dawn of the evolution of multicellular organisms, a group of coelenterates with a diffuse nervous system was formed (see Fig. II-4, a; Fig. II-11, a). A possible scenario for the emergence of such an organization is described at the beginning of this chapter. When

§ 26. The origin of the chordate nervous system The most frequently discussed hypotheses of origin cannot explain the appearance of one of the main signs of chordates - the tubular nervous system, which is located on the dorsal side of the body. I would like to use

§ 47. Features of the mammalian nervous system The central nervous system in mammals is more developed than in any other group of animals. The diameter of the spinal cord is usually slightly larger than that of other tetrapods (see Fig. III-18, a). It has two thickenings in the chest and

Trends in the evolution of the nervous system The brain is the structure of the nervous system. The emergence of the nervous system in animals gave them the ability to quickly adapt to changing environmental conditions, which, of course, can be regarded as an evolutionary advantage. The general

8.1. Principles of functioning of the nervous system The nervous system includes nervous tissue and auxiliary elements which are derived from all other fabrics. The functioning of the nervous system is based on reflex activity. Reflex concept

The nervous system of higher animals and humans is the result of 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 of 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 response was also improved. The development of the nervous system also proceeded in connection with the complication of the structure of organisms and the need for coordination and regulation of 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 using fluids inside and outside the body - humoral or pre-nervous, a form of regulation.

Later, 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 - reticular nervous system... At this stage, the (coelenterate) nervous system, for example, 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 irritated, the excitement 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 - nodular nervous system... At this stage (invertebrate) nerve cells converge into separate clusters or groups, and from clusters of cell bodies, nerve nodes - centers, and from clusters of processes - nerve trunks - nerves. Moreover, in each cell the number of processes decreases and they receive a certain direction. According to the segmental structure of the animal's body, for example, in the annelid worm, in each segment there are segmental nerve nodes and nerve trunks. The latter connect the nodes in two directions: the transverse trunks connect the nodes of a given segment, and the longitudinal ones - the nodes of different segments. Due to this, nerve impulses arising at any point in the body do not spread throughout the body, but propagate along the transverse trunks within this segment. The longitudinal trunks connect the 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, sense organs develop, in connection with which the head nodes develop more strongly than the rest, giving rise to the development of the future brain. A reflection of this stage is the preservation of primitive traits in humans (scattered nodes and microganglia on the periphery) in the structure of the autonomic nervous system.

Stage III - tubular nervous system. At the initial stage of development of animals, a particularly large role was played by the apparatus of movement, on the perfection of which the main condition for the existence of an animal - nutrition (movement in search of food, capture and absorption of it) - depended. In lower multicellular organisms, a peristaltic mode of movement 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, that is, movement using 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) it arose in the form of a metamerically constructed 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 associated with the improvement, first of all, of the motor apparatus of the animal. Already the lancelet also has receptors (olfactory, light). Further development of the nervous system and the emergence of the brain is mainly due to the improvement of the receptor apparatus.

Since most of the sensory organs arise at that end of the animal's body, which is facing towards the movement, i.e., forward, for the perception of external stimuli coming through them, the front end of the trunk brain develops and the brain is formed, which coincides with the isolation of the front end of the body into the form of a head - cephalization.

At the first stage The development of the brain consists of three sections: the posterior, middle and anterior, and of these divisions, in the first place (in lower fish), the posterior, or rhomboid, brain especially develops. The development of the hindbrain occurs under the influence of receptors for acoustics and gravity (receptors of the VIII pair of cranial nerves, which are of leading importance 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 adaptation of the body to environment by changing the metabolism in the hindbrain, as the most developed department of the central nervous system at this stage, centers for controlling vital life processes arise, associated, in particular, with the gill apparatus (respiration, blood circulation, digestion, etc.). Therefore, in the medulla oblongata, the nuclei of the branchial nerves arise (group X of the pair - the vagus nerve). These vital centers of respiration and blood 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 the nuclei of the vagus nerve and the respiratory center create the basis for the formation hind brain.

In the second stage(even in fish) under the influence of the visual receptor, the midbrain develops especially. 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.

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

Under the influence of the olfactory receptor, the forebrain, the prosencephalon, develops, at first having the character of a purely olfactory brain. Subsequently, the forebrain grows and differentiates into intermediate and terminal. In the endbrain, as in the higher part of the central nervous system, centers for all types of sensitivity appear. 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 appear, subjugating the old ones. There is, as it were, a movement of functional centers to the head end and a simultaneous subordination of phylogenetically old primordia to new ones. As a result, the centers of hearing that first appeared in the hindbrain are also present in the middle and anterior, the centers of vision that have arisen in the middle are also present in the anterior, 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 - old bark.

The improvement of receptors leads to the progressive development of the forebrain, which gradually becomes the organ that controls all the behavior of the animal. There are two forms of animal behavior: instinctive, based on species 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 endbrain: basal ganglia having the structure of nuclei (nuclear centers), and gray matter bark, which has a solid screen structure (screen centers). In this case, the "subcortex" develops first, and then the cortex. The bark appears during the transition of an animal from an aquatic to a terrestrial lifestyle and is clearly found in amphibians and reptiles. Further evolution of the nervous system is characterized by the fact that the cerebral cortex more and more subordinates to itself the functions of all underlying centers, there is a gradual corticolization of functions... The growth of the new cortex in mammals is so intense that the old and ancient cortex is pushed medially towards the septum. The rapid growth of the bark 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 enhanced development of the neocortex, the terminal brain in higher vertebrates surpasses all other parts of the brain, covering them like a cloak. The developing new brain pushes back into the depths the old brain (olfactory), which, as it were, coagulates, but still remains 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. The new cortex is in black, the old olfactory part is in dashed lines¸

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

Further development of the human brain is subject to other laws associated with its social nature. In addition to the natural organs of the body, which are also available in animals, man began to use tools. The tools of labor, which have become artificial organs, supplemented the natural organs of the body and constituted the technical "armament" of man. With the help of this "equipment" man acquired the ability 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, labor, and then with it articulate speech were the two most important stimuli, under the influence of which the monkey's brain gradually turned into a human brain, which, with 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 final brain, especially its cortex - the neocortex.

In addition to analyzers that perceive various stimuli of the external world and constitute the material substrate of concrete-visual thinking characteristic of animals (the first signal system for reflecting reality, but I.P. Pavlov), a person developed the ability of 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 material substrate of the second signaling system was the surface layers of the neocortex. Therefore, the cortex of the telencephalon reaches its highest development in humans.

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

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 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 provides a rapid transmission of excitation addressed to well-defined targets.

The nervous system of invertebrates

The nervous system as a specialized system of integration on the way of structural and functional development goes through several stages, which in primary and deuterostome animals can be characterized by features of parallelism and phylogenetic plasticity of choice.

Among invertebrates, the most primitive type of the nervous system in the form diffuse nervous network occurs in the type of intestinal cavities. Their neural network is an accumulation of multipolar and bipolar neurons, the processes of which can intersect, 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 nerve networks of coelenterates, can 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.

An example of such centralization and concentration of nerve elements is orthogonal nervous system flatworms. The orthogon of higher turbellaria is an ordered structure that consists of associative and motor cells that together form several pairs of longitudinal strands, or trunks, connected by a large number of transverse and annular commissural trunks. The concentration of nerve elements is accompanied by their immersion deep into the body.

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

Ganglionization of nerve elements is further developed in higher invertebrates, annelids, molluscs 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 with 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 ladder to chain nervous system. An identical, chain type of structure of the nervous system also exists in arthropods with different severity of the concentration of nerve elements, which can be carried out not only due to the fusion of adjacent ganglia of one segment, but also by the fusion of successive ganglia of different segments.

The evolution of the nervous system of invertebrates proceeds not only along the path of the concentration of nerve elements, but also in the direction of the complication of structural relationships within the ganglia. It is no coincidence that modern literature notes the tendency to compare the abdominal nerve cord with the spinal cord of vertebrates. As in the spinal cord, in the ganglia, the superficial arrangement of the pathways is found, the differentiation of the neuropil into motor, sensory and associative areas. This similarity, which is an example of parallelism in the evolution of tissue structures, does not exclude, however, the originality 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, as is the case in vertebrates.

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

The progressive development of the brain in cephalopods and insects creates a prerequisite for the emergence of a kind of hierarchy of command behavior control systems. 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, higher level of integration, where inter-analytic 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 of the neurons' triggering of segmental centers. Obviously, the interaction of the two levels of integration underlies the plasticity of the behavior of higher invertebrates, including innate and acquired responses.

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 neuroontogenetic studies of invertebrates allow us 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.

In the early stages of phylogenetic development, 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 branchial clefts and a dorsal nerve cord - a neural tube, which is a derivative of the external germ layer - ectoderm. Tubular type of the nervous system in vertebrates, according to the basic principles of organization, it differs from the ganglionic or nodular type of the nervous system of higher invertebrates.

The nervous system of vertebrates

Vertebrate nervous system is laid in the form of a continuous neural tube, which in the process of onto- and phylogenesis differentiates into different sections and is also a source of peripheral sympathetic and parasympathetic nerve nodes. In the most ancient chordates (cranials), the brain is absent and the neural tube is presented in a poorly differentiated state.

According to the views of L.A. Orbeli, S. Herrik, A.I. Karamyan, this critical stage in the development of the central nervous system

stem is denoted as spinal. The neural tube of the modern noncranial (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. 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 a conductive 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 are large Ovsyannikov ganglion cells, which have synaptic contacts with the bipolar sensitive cells of the olfactory fossa. Recently, neurosecretory cells have been identified in the head of the neural tube that resemble the pituitary system of higher vertebrates. However, the analysis of perception and simple forms of learning of the lancelet shows that at this stage of development, the central nervous system functions according to the principle of equipotentiality, and the statement about the specifics of the head section of the neural tube does not have sufficient grounds.

In the course of further evolution, there is a movement of some functions and integration systems 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 cranials to the level of cyclostomes the brain is formed as a superstructure over distant reception systems.

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

The development of distant visual reception gives an impetus to the bookmark midbrain. 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. Finally, the development of olfactory receptors contributes to the formation front or terminal brain, adjoined by an underdeveloped diencephalon.

The above-mentioned direction of the encephalization process is consistent with the course of ontogenetic development of the brain in cyclostomes. In the process of embryogenesis, the head sections of the neural tube give rise to three cerebral vesicles. The terminal and diencephalon is formed from the anterior bladder, the middle bladder differentiates into the midbrain, and an oblong bladder is formed from the posterior bladder

brain and cerebellum. A similar plan for the 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 middle and medulla oblongata, i.e., at this stage of development of the central nervous system, dominates bulbomesencephalic integration system, which replaced the spinal.

For a long time, the forebrain of cyclostomes was considered purely olfactory. However, recent studies have shown that the olfactory inputs to the forebrain are not unique, but supplemented by sensory inputs of 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. In contrast to the cranial neurons of the cutaneous sensitivity, they are secreted 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 pillars have contacts with a powerful dendritic network of motoneurons. Downward connections of the brain with the spinal cord are formed through Müllerian fibers - giant axons of cells lying in the medulla and medulla oblongata.

The emergence 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 skin and muscle-articular (proprioceptive) sensitivity. In the spinal ganglia, specialized neurons appear to perform these functions.

In the efferent part of the spinal cord of cartilaginous fish, progressive transformations are also observed. The path of motor axons inside the spinal cord is shortened, further differentiation of its pathways occurs. The ascending pathways of the lateral pillars in cartilaginous fish reach the medulla oblongata and cerebellum. At the same time, the ascending pathways of the posterior columns of the spinal cord are not yet 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 cerebellar spinal tracts).

At the same time, in the medulla oblongata, there is a complication of the system of the 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 shark cerebellum has two-way connections with the spinal cord, medulla oblongata and the lining of the midbrain. Functionally, it is divided into two parts: the old cerebellum (archycerebellum), associated with the vestibulo-lateral system, and the ancient cerebellum (fingercerebellum), included in the proprioceptive sensitivity analysis system. An essential point in the structural organization of the cerebellum of cartilaginous fish is its multilayer structure. In the gray matter of the shark cerebellum, the molecular layer, the Purkinje cell layer and the granular layer have been identified.

Another multilayered structure of the brain stem of cartilaginous fish is roof of the midbrain, where afferents of various modalities (visual, somatic) fit. The morphological organization of the midbrain itself testifies to 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 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 forebrain hemispheres of sharks. In addition to the olfactory system, a representation of the visual and somatic sensory systems was found here. Obviously, the old and ancient bark can be involved in the regulation of search, food, sexual and defense reflexes in cartilaginous fish, many of which are active predators.

Thus, in cartilaginous fishes, the main features of the ichthyopid type of brain organization are formed. His hallmark 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 allows us to talk about mesencephalocerebellar 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 lower regions.

The transition of vertebrates from aquatic to terrestrial mode of life is associated with a number of rearrangements in the central nervous system. For example, in amphibians, two thickenings appear in the spinal cord, corresponding to the upper and lower girdles of the limbs. In the spinal ganglia, instead of bipolar sensory neurons, unipolar ones with a T-shaped branching process are concentrated, providing a higher rate of excitation conduction without the participation of the cellular body. At the periphery, in the skin of amphibians, specialized receptors and receptor fields, providing discriminatory sensitivity.

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

Compared to fish, amphibians, which have a 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 division of the visual analyzer integration - additional tubercles appear - predecessors of the rear hills of the quadruple.

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

In the hemispheres of the forebrain, further differentiation of the old and ancient cortex takes place. In the old cortex (archicortex), stellate and pyramidal cells are found. In between the old and ancient bark, a strip of 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 diencephalo-telencephalic, 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 reptile brain and marks the following stage of morphofunctional evolution of the brain .

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

Ascending appears in the lateral columns of the reptile's spinal cord. spinothalamic tract, which conducts information about temperature and pain sensitivity to the brain. Here, in the side pillars, 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 multilink system combines the influence of the forebrain, cerebellum, reticular formation of the trunk, nuclei of the vestibular complex and coordinates motor activity.

In reptiles, as truly terrestrial animals, the role of visual and acoustic information increases, the need arises

comparing this information with the olfactory and gustatory, In accordance with these biological changes in the brain stem of reptiles occurs whole line structural changes. 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 a quadruple, in the posterior hills of which the acoustic centers are localized.

There is a further differentiation of the connections between the roof of the midbrain and the optic hillock - the thalamus, which is, as it were, a vestibule before the entrance to 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.

Ultimate brain 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 retained in mammals.

Striatal type of organization, characteristic of modern lizards, is distinguished by the dominant development of the basal ganglia located in the depths of the hemispheres, in particular the striatum. The development of the brain in birds follows this path. 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 these associations receive the same afferentation, and this makes them similar to neurons combined into vertical columns in the mammalian neocortex. At the same time, identical cellular 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 the rapid growth of the neocortex, which is in close functional connection with the optic tubercle of the diencephalon. In the cortex, efferent pyramidal cells are laid, sending their long axons to the motor neurons of the spinal cord.

Thus, along with the multilink extrapyramidal system, straight pyramidal pathways appear, which provide direct control over motor acts. Cortical regulation of motility 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. Neocerebellum acquires two-way bonds with the neocortex.

The growth of the new cortex in mammals is so intense that the old and ancient cortex is pushed medially towards the septum. The rapid growth of the bark is compensated by the formation of folding. In the lowest organized monotremes (platypus), the first two permanent grooves are laid on the surface of the hemisphere, while the rest of the surface remains smooth (lissencephalic type of cortex).

As shown by neurophysiological studies, the brain of monotremes and marsupials is still devoid of the connecting hemisphere of the corpus callosum and is characterized by overlapping sensory projections in the neocortex. There is no clear localization of motor, visual and auditory projections.

In placental mammals (insectivores and rodents) *, the development of a more distinct localization of projection zones in the cortex is noted. Along with the projection zones, associative zones are formed in the new cortex, but the boundaries of the former and the latter may 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 appear 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 demonstrate the highest level of organization of the cerebral cortex. The bark of primates is characterized by six layers, the absence of overlapping 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 reduced simply to a linear increase in size. In different evolutionary lines of vertebrates, independent processes of increase in size and complication of cytoarchitectonics of different parts of the brain could take place. An example of this is the comparison of striatal and cortical types of organization of the forebrain of vertebrates.

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

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3. General course of human and animal physiology in 2 books. Ed. A.D. Nozdracheva. M., "High School", 1991.

The main stages of the development of the nervous system

The nervous system is of ectodermal origin, that is, it develops from an external rudimentary layer into a single-celled layer as a result of the formation and division of the medullary tube. In the evolution of the nervous system, such stages can be schematically distinguished.

1. Network-like, diffuse, or asynaptic, nervous system. It occurs in a freshwater hydra, has the shape of a mesh, 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 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 the importance of a single form of the nervous system, but in the human body it is preserved in the form of Meissner's and Auerbach's plexuses of the digestive tract.

2. The ganglionic nervous system (in the vermiform) 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 the excitation of cells and recover at rest. Cells with a chromatophilic substance are located in groups or ganglia nodes, therefore they are called ganglion cells. So, at the second stage of development, the nervous system from reticular to ganglion-reticular. 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 autonomic functions.

3. The tubular nervous system (in vertebrates) differs from the worm-like nervous system in that skeletal motor apparatus 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, from the caudal, undifferentiated part of the medullary tube, the segmental apparatus of the spinal cord is formed, and from the anterior part of the cerebral tube, due to cephalization (from the Greek kephale - head), the main parts of the brain are formed. In human ontogeny, they develop sequentially according to a well-known scheme: first, three primary cerebral vesicles are formed: anterior (prosencephalon), middle (mesencephalon) and rhomboid, or posterior (rhombencephalon). In the future, from the anterior cerebral bladder, the final (telencephalon) and intermediate (diencephalon) bubbles are formed. The rhomboid cerebral bladder is also fragmented into two: posterior (metencephalon) and oblong (myelencephalon). Thus, the stage of three bubbles is replaced by the stage of formation of five bubbles, from which different parts of the central nervous system are formed: from the telencephalon the cerebral hemispheres, diencephalon diencephalon, mesencephalon - the midbrain, metencephalon - the brain bridge and cerebellum, myelencephalon - the medulla oblongata (Fig. see 1).

The evolution of the vertebrate nervous system led to the development of a new system capable of forming temporary connections of functioning elements, which are provided by the division of the central nervous apparatus into separate functional units of neurons. Consequently, with the emergence of skeletal motility in vertebrates, a neural cerebrospinal nervous system developed, to which more ancient formations are subordinated, which have been preserved. Further development of the central nervous system led to the emergence of special functional relationships between the brain and spinal cord, which are built on the principle of subordination, or subordination. The essence of the principle of subordination is that evolutionarily new nerve formations not only regulate the functions of more ancient, lower nervous structures, but also subordinate them to themselves by inhibition or excitation. Moreover, subordination exists not only between new and ancient functions, between the brain and spinal cord, but is also observed between the cortex and the subcortex, between the subcortex and the brainstem and, to a certain extent, even between the cervical and lumbar enlargements of the spinal cord. With the advent of new functions of the nervous system, the ancients do not disappear. With the loss of new functions, ancient forms of reaction appear, due to the functioning of more ancient structures. An example is the appearance of subcortical or foot pathological reflexes when the cerebral cortex is affected.

Thus, in the process of evolution of the nervous system, several main stages can be distinguished, which are the main ones in its morphological and functional development. Among the morphological stages, one should name the centralization of the nervous system, cephalization, corticalization in chordates, the appearance of symmetrical hemispheres in higher vertebrates. Functionally, these processes are associated with the principle of subordination and the increasing specialization of centers and cortical structures. Functional evolution corresponds to morphological evolution. At the same time, phylogenetically younger brain structures are more vulnerable and less able to recover.

The nervous system has a neural type of structure, that is, it consists of nerve cells - neurons that develop from neuroblasts.

The neuron is the main morphological, genetic and functional unit of the nervous system. It has a body (perikarion) and a large number of processes, among which an axon and dendrites are distinguished. Axon, or neurite, is a long process that conducts a nerve impulse in the direction from the cell body and ends with a terminal branching. He is always only one in the cage. Dendrites are a large number of short, tree-like branched processes. They transmit nerve impulses towards the cell body. The body of a neuron consists of cytoplasm and a nucleus with one or more nucleoli. Special components of nerve cells are chromatophilic substance and neurofibrils. The chromatophilic substance has the form of lumps and grains of different sizes, is contained in the body and dendrites of neurons and is never detected in the axons and initial segments of the latter. It is an indicator of the functional state of the neuron: it disappears in the event of depletion of the nerve cell and is restored during the rest period. Neurofibrils are thin filaments that are placed in the cell body and its processes. The cytoplasm of the nerve cell also contains a lamellar complex (Golji mesh apparatus), mitochondria and other organelles. The concentration of the bodies of nerve cells form the nerve centers, or the so-called gray matter.

Nerve fibers are extensions of neurons. Within the boundaries of the central nervous system, they form pathways - the white matter of the brain. Nerve fibers consist of an axial cylinder, which is a process of a neuron, and a sheath formed by oligodendroglial cells (neurolemocytes, Schwann cells). Depending on the structure of the sheath, nerve fibers are divided into myelin and non-myelin. Myelinated nerve fibers are part of the brain and spinal cord, as well as peripheral nerves. They consist of an axial cylinder, myelin sheath, neurolema (Schwann's sheath) and basement membrane. The axon membrane serves to conduct an electrical impulse and releases a mediator in the area of ​​axonal endings, and the dendrite membrane reacts to a mediator. In addition, it enables the recognition of other cells during embryonic development. Therefore, each cell looks for a specific place in the network of neurons. The myelin sheaths of nerve fibers are not continuous, but are interrupted by intervals of narrowing - nodes (nodal interceptions of Ranvier). Ions can penetrate into the axon only in the area of ​​the interceptions of Ranvier and in the segment of the initial segment. Myelin-free nerve fibers are typical of the autonomic (autonomic) nervous system. They have a simple structure: they consist of an axial cylinder, a neurolemma and a basement membrane. The speed of transmission of a nerve impulse by myelinic nerve fibers is much higher (up to 40-60 m / s) than nonmyelinated (1-2 m / s).

The main functions of a neuron are the perception and processing of information, transferring it to other cells. Neurons also perform a trophic function, affecting the metabolism in axons and dendrites. There are the following types of neurons: afferent, or sensitive, which perceive irritation and transform it into a nerve impulse; associative, intermediate, or interneurons, which transmit a nerve impulse between neurons; efferent, or motor, which provide the transmission of a nerve impulse to the working structure. This classification of neurons is based on the position of the nerve cell in the reflex arc. Nervous excitement is transmitted along it in only one direction. This rule is called physiological, or dynamic, polarization of neurons. An isolated neuron is capable of conducting impulses in any direction. The neurons of the cerebral cortex are morphologically divided into pyramidal and non-pyramidal.

Nerve cells are in contact with each other through the synapses of specialized structures, where the nerve impulse passes from neuron to neuron. For the most part, synapses form between the axons of one cell and the dendrites of another. There are also other types of synaptic contacts: axosomatic, axoaxonal, dendrodentritic. So, any part of a neuron can form a synapse with different parts of another neuron. A typical neuron can have 1,000 to 10,000 synapses and receive information from 1,000 other neurons. As part of the synapse, two parts are distinguished - the presynaptic and the postsynaptic, between which there is a synaptic cleft. The presynaptic part is formed by the terminal branch of the axon of the nerve cell that transmits the impulse. For the most part, it looks like a small button and is covered with a presynaptic membrane. In the presynaptic endings are vesicles, or vesicles, which contain so-called neurotransmitters. Mediators, or neurotransmitters, are various biologically active substances. In particular, acetylcholine is the mediator of cholinergic synapses, while norepinephrine and adrenaline are the mediator of adrenergic synapses. The postsynaptic membrane contains a special neurotransmitter receptor protein. The release of the neurotransmitter is influenced by the mechanisms of neuromodulation. This function is performed by neuropeptides and neurohormones. The synapse provides a one-sided conduction of a nerve impulse. According to their functional features, two types of synapses are distinguished - excitatory, which contribute to the generation of impulses (depolarization), and inhibitory, which can inhibit the action of signals (hyperpolarization). Nerve cells have a low level of arousal.

The Spanish neurohistologist Ramon y Cajal (1852-1934) and the Italian histologist Camillo Golgi (1844-1926) were awarded the Nobel Prize in Medicine and Physiology (1906) for the development of the doctrine of the neuron as a morphological unit of the nervous system. The essence of the neural doctrine they developed is as follows.

1. A neuron is an anatomical unit of the nervous system; it consists of a nerve cell body (perikarion), a neuron nucleus, and an axon / dendrites. The body of the neuron and its processes are covered with a cytoplasmic partially permeable membrane that performs a barrier function.

2. Each neuron is a genetic unit, it develops from an independent embryonic neuroblast cell; the genetic code of a neuron precisely determines its structure, metabolism, connections that are genetically programmed.

3. A neuron is a functional unit capable of perceiving a stimulus, generating it and transmitting a nerve impulse. The neuron functions as a unit only in the communication link; in an isolated state, the neuron does not function. A nerve impulse is transmitted to another cell through a terminal structure - a synapse, with the help of a neurotrans-mitter, which can inhibit (hyperpolarization) or excite (depolarization) subsequent neurons on the line. A neuron generates or does not generate a nerve impulse in accordance with the "all or nothing" law.

4. Each neuron conducts a nerve impulse in only one direction: from the dendrite to the body of the neuron, axon, synaptic connection (dynamic polarization of neurons).

5. The neuron is a pathological unit, that is, it reacts to damage as a unit; with severe damage, the neuron dies as a cell unit. The process of degeneration of an axon or myelin sheath distal to the site of injury is called Wallerian degeneration (rebirth).

6. Each neuron is a regenerative unit: in humans, neurons of the peripheral nervous system are regenerated; pathways within the central nervous system do not effectively regenerate.

Thus, in accordance with neural doctrine, a neuron is an anatomical, genetic, functional, polarized, pathological and regenerative unit of the nervous system.

In addition to neurons that form the parenchyma of the nervous tissue, an important class of cells in the central nervous system are glial cells (astrocytes, oligodendrocytes and microgliocytes), the number of which is 10-15 times greater than the number of neurons and which form neuroglia. Its functions are: supporting, delimiting, trophic, secretory, protective. Glial cells are involved in higher nervous (mental) activity. With their participation, the synthesis of mediators of the central nervous system is carried out. The neuroglia also play an important role in synaptic transmission. It provides structural and metabolic protection for the neuronal network. So, there are various morphofunctional connections between neurons and glial cells.