Functions of the human cerebral cortex briefly. The cerebral cortex, structure and functions

CORTEX (cortexencephali) - all surfaces of the cerebral hemispheres, covered with a cloak (pallium), formed by gray matter. Together with other departments of c. n. with. the bark is involved in the regulation and coordination of all body functions, plays an extremely important role in mental, or higher nervous activity (see).

In accordance with the stages of evolutionary development of c. n. with. the bark is divided into old and new. The old cortex (archicortex - the old cortex itself and paleocortex - the ancient cortex) is a phylogenetically older formation than the new cortex (neocortex), which appeared during the development of the cerebral hemispheres (see Architectonics of the cerebral cortex, Brain).

Morphologically, K. m. is formed by nerve cells (see), their processes and neuroglia (see), which has a support-trophic function. In primates and humans in the cortex, there are approx. 10 billion neurocytes (neurons). Depending on the shape, pyramidal and stellate neurocytes are distinguished, which are characterized by great diversity. The axons of pyramidal neurocytes are sent to the subcortical white matter, and their apical dendrites - to the outer layer of the cortex. Star-shaped neurocytes have only intracortical axons. Dendrites and axons of stellate neurocytes branch abundantly near the cell bodies; some of the axons approach the outer layer of the cortex, where, following horizontally, they form a dense plexus with the tops of the apical dendrites of pyramidal neurocytes. Along the surface of the dendrites there are reniform outgrowths, or spines, which represent the region of axodendritic synapses (see). The cell body membrane is the area of ​​axosomatic synapses. In each area of ​​the cortex there are many input (afferent) and output (efferent) fibers. Efferent fibers go to other areas K. of m, to subcrustal educations or to the motive centers of a spinal cord (see). Afferent fibers enter the cortex from the cells of the subcortical structures.

The ancient cortex in humans and higher mammals consists of a single cell layer, poorly differentiated from the underlying subcortical structures. Actually the old bark consists of 2-3 layers.

The new bark has a more complex structure and takes (in humans) approx. 96% of the entire surface of K. g. m. Therefore, when they talk about K. g. m., they usually mean a new bark, which is divided into the frontal, temporal, occipital and parietal lobes. These lobes are divided into areas and cytoarchitectonic fields (see Architectonics of the cerebral cortex).

The thickness of the cortex in primates and humans varies from 1.5 mm (on the surface of the gyri) to 3-5 mm (in the depth of the furrows). On the sections painted across Nissl, the layered structure of bark is visible, a cut depends on grouping of neurocytes at its different levels (layers). In the bark, it is customary to distinguish 6 layers. The first layer is poor in cell bodies; the second and third - contain small, medium and large pyramidal neurocytes; the fourth layer is the zone of stellate neurocytes; the fifth layer contains giant pyramidal neurocytes (giant pyramidal cells); the sixth layer is characterized by the presence of multiform neurocytes. However, the six-layer organization of the cortex is not absolute, since in reality in many parts of the cortex there is a gradual and uniform transition between layers. The cells of all layers, located on the same perpendicular with respect to the surface of the cortex, are closely connected with each other and with subcortical formations. Such a complex is called a column of cells. Each such column is responsible for the perception of predominantly one type of sensitivity. For example, one of the columns of the cortical representation of the visual analyzer perceives the movement of an object in a horizontal plane, the neighboring one - in a vertical one, etc.

Similar cell complexes of the neocortex have a horizontal orientation. It is assumed that, for example, small cell layers II and IV consist mainly of receptive cells and are “entrances” to the cortex, large cell layer V is an “exit” from the cortex to subcortical structures, and middle cell layer III is associative, connects different areas of the cortex.

Thus, several types of direct and feedback connections between the cellular elements of the cortex and subcortical formations can be distinguished: vertical bundles of fibers that carry information from subcortical structures to the cortex and back; intracortical (horizontal) bundles of associative fibers passing at different levels of the cortex and white matter.

The variability and originality of the structure of neurocytes indicate the extreme complexity of the apparatus of intracortical switching and the methods of connections between neurocytes. This feature of the structure of K. g. m should be considered as morfol, the equivalent of its extreme reactivity and funkts, plasticity, providing it with higher nervous functions.

An increase in the mass of the cortical tissue occurred in a limited space of the skull; therefore, the surface of the cortex, which was smooth in lower mammals, was transformed into convolutions and furrows in higher mammals and humans (Fig. 1). It was with the development of the cortex already in the last century that scientists associated such aspects of brain activity as memory (see), intelligence, consciousness (see), thinking (see), etc.

I. P. Pavlov defined 1870 as the year "from which scientific fruitful work on the study of the cerebral hemispheres begins." This year, Fritsch and Gitzig (G. Fritsch, E. Hitzig, 1870) showed that electrical stimulation of certain areas of the anterior section of the CG of dogs causes a contraction of certain groups of skeletal muscles. Many scientists believed that when stimulated by K. m., the “centers” of voluntary movements and motor memory are activated. However still Ch. Sherrington preferred to avoid funkts, interpretations of this phenomenon and was limited only by the statement that the area of ​​bark, irritation a cut causes reduction of muscle groups, is intimately connected with a spinal cord.

Directions of experimental researches K. of m of the end of the last century were almost always connected with problems a wedge, neurology. On this basis, experiments were started with partial or complete decortication of the brain (see). The first complete decortication in a dog was made by Goltz (F. L. Goltz, 1892). The decorticated dog turned out to be viable, but many of its most important functions were sharply impaired - vision, hearing, orientation in space, coordination of movements, etc. Before I. P. Pavlov discovered the phenomenon of the conditioned reflex (see), interpretation of experiments with both partial extirpations of the cortex suffered from the absence of an objective criterion for their evaluation. The introduction of the conditioned reflex method into the practice of experimenting with extirpations opened up a new era in studies of the structural and functional organization of CG m.

Simultaneously with the discovery of the conditioned reflex, the question arose about its material structure. Since the first attempts to develop a conditioned reflex in decorticated dogs failed, I. P. Pavlov came to the conclusion that C. g. m. is an "organ" of conditioned reflexes. However, further studies showed the possibility of developing conditioned reflexes in decorticated animals. It was found that conditioned reflexes are not disturbed during vertical cuts of various areas of the K. g. m. and their separation from subcortical formations. These facts, along with electrophysiological data, gave reason to consider the conditioned reflex as a result of the formation of a multichannel connection between various cortical and subcortical structures. The shortcomings of the method of extirpation for studying the significance of C. g. m in the organization of behavior prompted the development of methods for reversible, functional, exclusion of the cortex. Buresh and Bureshova (J. Bures, O. Buresova, 1962) applied the phenomenon of the so-called. spreading depression by applying potassium chloride or other irritants to one or another part of the cortex. Since depression does not spread through the furrows, this method can only be used on animals with a smooth surface K. g. m. (rats, mice).

Other way funkts, switching off K. m. - its cooling. The method developed by N. Yu. Belenkov et al. (1969) consists in the fact that, in accordance with the shape of the surface of the cortical areas scheduled for shutdown, capsules are made that are implanted over the dura mater; during the experiment, a cooled liquid is passed through the capsule, as a result of which the temperature of the cortical substance under the capsule decreases to 22-20°C. The assignment of biopotentials with the help of microelectrodes shows that at such a temperature, the impulse activity of neurons stops. The cold decortication method used in hron, experiments on animals demonstrated the effect of an emergency shutdown of the new cortex. It turned out that such a switch-off stops the implementation of previously developed conditioned reflexes. Thus, it was shown that K. g. m. is a necessary structure for the manifestation of a conditioned reflex in an intact brain. Consequently, the observed facts of the development of conditioned reflexes in surgically decorticated animals are the result of compensatory rearrangements occurring in the time interval from the moment of operation to the beginning of the study of the animal in hron, experiment. The compensatory phenomena take place and in case funkts, switching-offs of a new bark. Just like cold shutdown, acute shutdown of the neocortex in rats with the help of spreading depression sharply disrupts conditioned reflex activity.

A comparative evaluation of the effects of complete and partial decortication in various animal species showed that monkeys endure these operations more difficult than cats and dogs. The degree of dysfunction during extirpation of the same areas of the cortex is different in animals at different stages of evolutionary development. For example, the removal of temporal regions in cats and dogs impairs hearing less than in monkeys. Similarly, vision after removal of the occipital lobe of the cortex is affected to a greater extent in monkeys than in cats and dogs. On the basis of these data there was an idea of ​​corticolization of functions in the course of evolution of c. n. N of page, according to Krom phylogenetically earlier links of a nervous system pass to lower level of hierarchy. At the same time, K. g. m. plastically rebuilds the functioning of these phylogenetically older structures in accordance with the influence of the environment.

Cortical projections of afferent systems K. of m represent specialized end stations of ways from sensory organs. Efferent pathways go from K. m. to the motor neurons of the spinal cord as part of the pyramidal tract. They originate mainly from the motor area of ​​the cortex, which in primates and humans is represented by the anterior central gyrus, located anterior to the central sulcus. Behind the central sulcus is the somatosensory area K. m. - the posterior central gyrus. Individual parts of the skeletal muscles are corticolized to varying degrees. The lower limbs and trunk are represented least differentiated in the anterior central gyrus, the representation of the muscles of the hand occupies a large area. An even larger area corresponds to the musculature of the face, tongue and larynx. In the posterior central gyrus, in the same ratio as in the anterior central gyrus, afferent projections of body parts are presented. It can be said that the organism is, as it were, projected into these convolutions in the form of an abstract "homunculus", which is characterized by an extreme preponderance in favor of the anterior segments of the body (Fig. 2 and 3).

In addition, the cortex includes associative, or non-specific, areas that receive information from receptors that perceive irritations of various modalities, and from all projection zones. The phylogenetic development of C. g. m. is characterized primarily by the growth of associative zones (Fig. 4) and their separation from projection zones. In lower mammals (rodents), almost the entire cortex consists of projection zones alone, which simultaneously perform associative functions. In humans, the projection zones occupy only a small part of the cortex; everything else is reserved for associative zones. It is assumed that associative zones play a particularly important role in the implementation of complex forms in c. n. d.

In primates and humans, the frontal (prefrontal) region reaches the greatest development. It is phylogenetically the youngest structure directly related to the highest mental functions. However, attempts to project these functions to separate areas of the frontal cortex have not been successful. Obviously, any part of the frontal cortex can be included in the implementation of any of the functions. The effects observed during the destruction of various parts of this area are relatively short-lived or often completely absent (see Lobectomy).

The confinement of separate structures of K. of m to certain functions, considered as a problem of localization of functions, remains till now one of the most difficult problems of neurology. Noting that in animals, after the removal of the classical projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved, I. P. Pavlov hypothesized the existence of a "core" of the analyzer and its elements, "scattered" throughout the C. g. By means of microelectrode research methods (see) it was succeeded to register activity of the specific neurocytes responding to incentives of a certain touch modality in various areas K. of m. Superficial assignment of bioelectric potentials reveals distribution of primary evoked potentials on the considerable areas K. of m - outside of the corresponding projection zones and cytoarchitectonic fields. These facts, along with the polyfunctionality of disturbances upon removal of any sensory area or its reversible shutdown, indicate a multiple representation of functions in C.g.m. Motor functions are also distributed over large areas of C.g.m. tract, are located not only in the motor areas, but also beyond them. In addition to sensory and motor cells, in K. m. there are also intermediate cells, or interneurocytes, which make up the bulk of K. g. m. and concentrated ch. arr. in association areas. Multimodal excitations converge on interneurocytes.

Experimental data indicate, thus, the relativity of the localization of functions in C. g. m., the absence of cortical "centers" reserved for one or another function. The least differentiated in funkts, the relation are the associative areas possessing especially expressed properties of plasticity and interchangeability. However, it does not follow from this that associative regions are equipotential. The principle of equipotentiality of the cortex (the equivalence of its structures), expressed by Lashley (K. S. Lashley) in 1933 on the basis of the results of extirpations of a poorly differentiated rat cortex, as a whole cannot be extended to the organization of cortical activity in higher animals and humans. I. P. Pavlov contrasted the principle of equipotentiality with the concept of dynamic localization of functions in C.G.M.

The solution to the problem of the structural and functional organization of C. g. m. is largely hampered by the identification of the localization of symptoms of extirpations and stimulations of certain cortical zones with the localization of the functions of K. g. m. This question already concerns the methodological aspects of neurophysiol, experiment, since from a dialectical point From the point of view of any structural-functional unit in the form in which it appears in each given study, it is a fragment, one of the aspects of the existence of the whole, a product of the integration of structures and connections of the brain. For example, the position that the function of motor speech is "localized" in the lower frontal gyrus of the left hemisphere is based on the results of damage to this structure. At the same time, electrical stimulation of this "center" of speech never causes an act of articulation. It turns out, however, that the utterance of entire phrases can be induced by stimulation of the rostral thalamus, which sends afferent impulses to the left hemisphere. Phrases caused by such stimulation have nothing to do with arbitrary speech and are not adequate to the situation. This highly integrated stimulation effect indicates that ascending afferent impulses are transformed into a neuronal code effective for the higher coordination mechanism of motor speech. In the same way, complexly coordinated movements caused by stimulation of the motor area of ​​the cortex are organized not by those structures that are directly exposed to irritation, but by neighboring or spinal and extrapyramidal systems excited along descending pathways. These data show that there is a close relationship between the cortex and subcortical formations. Therefore, it is impossible to oppose cortical mechanisms to the work of subcortical structures, but it is necessary to consider specific cases of their interaction.

With electrical stimulation of individual cortical areas, the activity of the cardiovascular system, the respiratory apparatus, went. - kish. a path and other visceral systems. K. M. Bykov also substantiated the influence of C. m. on the internal organs by the possibility of the formation of visceral conditioned reflexes, which, along with vegetative shifts with various emotions, was put by him as the basis for the concept of the existence of cortico-visceral relations. The problem of cortico-visceral relations is solved in terms of studying the modulation of the activity of subcortical structures by the cortex, which are directly related to the regulation of the internal environment of the body.

An essential role is played by communications K. of m with a hypothalamus (see).

The level of activity of K. m. is mainly determined by ascending influences from the reticular formation (see) of the brain stem, which is controlled by cortico-fugal influences. The effect of the last has dynamic character and is a consequence of the current afferent synthesis (see). Studies with the help of electroencephalography (see), in particular corticography (i.e., the assignment of biopotentials directly from K. g. m.), It would seem that they confirmed the hypothesis of the closure of the temporary connection between the foci of excitations arising in the cortical projections of the signal and unconditioned stimuli in the process of formation of a conditioned reflex. However, it turned out that as the behavioral manifestations of the conditioned reflex become stronger, the electrographic signs of the conditioned connection disappear. This crisis of the technique of electroencephalography in the knowledge of the mechanism of the conditioned reflex was overcome in the studies of M. N. Livanov et al. (1972). They showed that the spread of excitation along C. g. m. and the manifestation of a conditioned reflex depend on the level of distant synchronization of biopotentials taken from spatially remote points of C. g. m. An increase in the level of spatial synchronization is observed with mental stress (Fig. 5). In this state, synchronization areas are not concentrated in certain areas of the cortex, but are distributed over its entire area. Correlation relations cover points of the entire frontal cortex, but at the same time, increased synchrony is also recorded in the precentral gyrus, in the parietal region, and in other parts of the C. g. m.

The brain consists of two symmetrical parts (hemispheres) interconnected by commissures consisting of nerve fibers. Both hemispheres of the brain are united by the largest commissure - the corpus callosum (see). Its fibers connect identical points of the K. g. m. The corpus callosum ensures the unity of the functioning of both hemispheres. When it is cut, each hemisphere begins to function independently of one another.

In the process of evolution, the human brain acquired the property of lateralization, or asymmetry (see). Each of its hemispheres specialized to perform certain functions. In most people, the left hemisphere is dominant, providing the function of speech and control over the action of the right hand. The right hemisphere is specialized for the perception of form and space. At the same time funkts, differentiation of hemispheres is not absolute. However, extensive damage to the left temporal lobe is usually accompanied by sensory and motor speech disorders. Obviously, lateralization is based on innate mechanisms. However, the potential of the right hemisphere in organizing the function of speech can manifest itself when the left hemisphere is damaged in newborns.

There are reasons to consider lateralization as an adaptive mechanism that developed as a result of the complication of brain functions at the highest stage of its development. Lateralization prevents the interference of various integrative mechanisms in time. It is possible that cortical specialization counteracts the incompatibility of various functional systems (see), facilitates decision-making about the purpose and mode of action. The integrative activity of the brain is not limited, therefore, to the external (summative) integrity, understood as the interaction of the activities of independent elements (be it neurocytes or entire brain formations). Using the example of the development of lateralization, one can see how this integral, integrative activity of the brain itself becomes a prerequisite for the differentiation of the properties of its individual elements, endowing them with functionality and specificity. Consequently, the funkts, the contribution of each individual structure of the C. g. m., in principle, cannot be assessed in isolation from the dynamics of the integrative properties of the whole brain.

Pathology

The cerebral cortex is rarely affected in isolation. Signs of its defeat to a greater or lesser extent usually accompany the pathology of the brain (see) and are part of its symptoms. Usually patol, not only K. of m, but also white matter of hemispheres is surprised by processes. Therefore, pathology K. of m is usually understood as its primary lesion (diffuse or local, without a strict boundary between these concepts). The most extensive and intense lesion of K. m. is accompanied by the disappearance of mental activity, a complex of both diffuse and local symptoms (see Apallic syndrome). Along with nevrol, symptoms of damage to the motor and sensitive spheres, symptoms of damage to various analyzers in children is a delay in the development of speech and even the complete impossibility of the formation of the psyche. In this case, changes in cytoarchitectonics are observed in the form of a violation of layering, up to its complete disappearance, foci of loss of neurocytes with their replacement by growths of glia, heterotopia of neurocytes, pathology of the synaptic apparatus and other pathomorphol changes. Lesions of K. m. hereditary and degenerative diseases of the brain, disorders of cerebral circulation, etc.

Studying of EEG at localization patol, the center in K. of m reveals dominance of focal slow waves which are considered as a correlate of guarding braking more often (U. Walter, 1966). Weak expressiveness of slow waves in the field patol, the center is a useful diagnostic sign in a preoperative assessment of a condition of patients. As N. P. Bekhtereva's (1974) researches which are carried out jointly with neurosurgeons showed, absence of slow waves in the field patol, the center is an adverse prognostic sign of consequences of surgical intervention. For an assessment patol, K.'s state of m also the test for interaction of EEG in a zone of focal defeat with the caused activity is used in response to positive and differentiating conditional irritants. The bioelectric effect of such an interaction can be both an increase in focal slow waves, and a weakening of their severity or an increase in frequent oscillations such as pointed beta waves.

Bibliography: Anokhin P.K. Biology and neurophysiology of the conditioned reflex, M., 1968, bibliogr.; Belenkov N. Yu. Structural integration factor in brain activity, Usp. fiziol, sciences, t. 6, century. 1, p. 3, 1975, bibliogr.; Bekhtereva N. P. Neurophysiological aspects of human mental activity, L., 1974; Gray Walter, The Living Brain, trans. from English, M., 1966; Livanov MN Spatial organization of brain processes, M., 1972, bibliogr.; Luria A. R. Higher cortical functions of a person and their disturbances in local lesions of the brain, M., 1969, bibliogr.; Pavlov I.P. Complete works, vol. 3-4, M.-L., 1951; Penfield V. and Roberts L. Speech and brain mechanisms, trans. from English, L., 1964, bibliography; Polyakov G. I. Fundamentals of the systematics of neurons in the new human cerebral cortex, M., 1973, bibliogr.; Cytoarchitectonics of the human cerebral cortex, ed. S. A. Sarkisova and others, p. 187, 203, M., 1949; Sade J. and Ford D. Fundamentals of neurology, trans. from English, p. 284, M., 1976; M a s t e g t o n R. B. a. B e r k 1 e y M. A. Brain function, Ann. Rev. Psychol., at. 25, p. 277, 1974, bibliogr.; S h about 1 1 D. A. The organization of cerebral cortex, L.-N. Y., 1956, bibliogr.; Sperry R. W. Hemisphere deconnection and unity in conscious awareness, Amer. Psychol., v. 23, p. 723, 1968.

H. Yu. Belenkov.

Layer of gray matter covering the cerebral hemispheres of the cerebrum. The cerebral cortex is divided into four lobes: frontal, occipital, temporal, and parietal. The part of the cortex that covers most of the surface of the cerebral hemispheres is called the neocortex because it was formed during the final stages of human evolution. The neocortex can be divided into zones according to their functions. Different parts of the neocortex are associated with sensory and motor functions; the corresponding areas of the cerebral cortex are involved in the planning of movements (frontal lobes) or are associated with memory and perception (occipital lobes).

Cortex

Specificity. The upper layer of the cerebral hemispheres, consisting primarily of nerve cells with a vertical orientation (pyramidal cells), as well as bundles of afferent (centripetal) and efferent (centrifugal) nerve fibers. In neuroanatomical terms, it is characterized by the presence of horizontal layers that differ in width, density, shape and size of the nerve cells included in them.

Structure. The cerebral cortex is divided into a number of areas, for example, in the most common classification of cytoarchitectonic formations by K. Brodman, 11 areas and 52 fields are identified in the human cerebral cortex. Based on phylogenesis data, a new cortex, or neocortex, old, or archicortex, and ancient, or paleocortex, are distinguished. According to the functional criterion, three types of areas are distinguished: sensory areas that provide reception and analysis of afferent signals coming from specific relay nuclei of the thalamus, motor areas that have bilateral intracortical connections with all sensory areas for the interaction of sensory and motor areas, and associative areas that do not have direct afferent or efferent connections with the periphery, but associated with sensory and motor areas.

CORTEX

The surface covering the gray matter that forms the uppermost level of the brain. In an evolutionary sense, this is the newest neural formation, and approximately 9-12 billion of its cells are responsible for basic sensory functions, motor coordination and control, participation in the regulation of integrative, coordinated behavior and, most importantly, for the so-called "higher mental processes" of speech. , thinking, problem solving, etc.

CORTEX

English cerebral cortex) - the surface layer covering the cerebral hemispheres, formed mainly by vertically oriented nerve cells (neurons) and their processes, as well as bundles of afferent (centripetal) and efferent (centrifugal) nerve fibers. In addition, the cortex includes neuroglia cells.

A characteristic feature of the structure of C. g. m. is horizontal layering, due to the ordered arrangement of the bodies of nerve cells and nerve fibers. In K. m., 6 (according to some authors, 7) layers are distinguished, differing in width, arrangement density, shape and size of their constituent neurons. Due to the predominantly vertical orientation of the bodies and processes of neurons, as well as bundles of nerve fibers, K. m. has a vertical striation. For the functional organization of K. m., the vertical, columnar arrangement of nerve cells is of great importance.

The main type of nerve cells that make up the K. m. are pyramidal cells. The body of these cells resembles a cone, from the top of which one thick and long, apical dendrite departs; heading towards the surface of the K. g. m., it becomes thinner and fan-shaped divided into thinner terminal branches. Shorter basal dendrites and an axon depart from the base of the body of the pyramidal cell, heading to the white matter, located under the K. m., or branching within the cortex. The dendrites of pyramidal cells bear a large number of outgrowths, the so-called. spines, which take part in the formation of synaptic contacts with the endings of afferent fibers that come to K. g. m. from other parts of the cortex and subcortical formations (see Synapses). The axons of the pyramidal cells form the main efferent pathways coming from the C. g. m. The size of the pyramidal cells varies from 5-10 microns to 120-150 microns (Betz giant cells). In addition to pyramidal neurons, stellate, fusiform, and some other types of interneurons, which are involved in the reception of afferent signals and the formation of functional interneuronal connections, are part of the cgm.

Based on the peculiarities of the distribution in the layers of the cortex of nerve cells and fibers of various sizes and shapes, the entire territory of the K. g. fields that differ in their cellular structure and functional significance. The classification of cytoarchitectonic formations of K. g. m., proposed by K. Brodman, who divided the entire K. g. m. of a person into 11 regions and 52 fields, is generally accepted.

Based on the data of phylogenesis, K. g. m. is divided into new (neocortex), old (archicortex) and ancient (paleocortex). In the phylogenesis of the KGM, there is an absolute and relative increase in the territories of the new crust, with a relative decrease in the area of ​​the ancient and old. In humans, the new cortex accounts for 95.6%, while the ancient one occupies 0.6%, and the old one - 2.2% of the entire cortical territory.

Functionally, there are 3 types of areas in the cortex: sensory, motor, and associative.

Sensory (or projection) cortical zones receive and analyze afferent signals along fibers coming from specific relay nuclei of the thalamus. Sensory zones are localized in certain areas of the cortex: visual is located in the occipital (fields 17, 18, 19), auditory in the upper parts of the temporal region (fields 41, 42), somatosensory, analyzing the impulse coming from the receptors of the skin, muscles, joints, - in the region of the postcentral gyrus (fields 1, 2, 3). Olfactory sensations are associated with the function of phylogenetically older parts of the cortex (paleocortex) - the hippocampal gyrus.

The motor (motor) area - field 4 according to Brodman - is located on the precentral gyrus. The motor cortex is characterized by the presence in layer V of giant Betz pyramidal cells, the axons of which form the pyramidal tract, the main motor tract descending to the motor centers of the brain stem and spinal cord and providing cortical control of voluntary muscle contractions. The motor cortex has bilateral intracortical connections with all sensory areas, which ensures close interaction between sensory and motor areas.

association areas. The human cerebral cortex is characterized by the presence of a vast territory that does not have direct afferent and efferent connections with the periphery. These areas, connected through an extensive system of associative fibers with sensory and motor areas, are called associative (or tertiary) cortical areas. In the posterior cortex, they are located between the parietal, occipital, and temporal sensory areas, and in the anterior, they occupy the main surface of the frontal lobes. The associative cortex is either absent or poorly developed in all mammals up to primates. In humans, the posterior associative cortex occupies about half, and the frontal regions a quarter of the entire surface of the cortex. In terms of structure, they are distinguished by a particularly powerful development of the upper associative layers of cells in comparison with the system of afferent and efferent neurons. Their feature is also the presence of polysensory neurons - cells that perceive information from various sensory systems.

In the associative cortex there are also centers associated with speech activity (see Broca's center and Wernicke's center). Associative areas of the cortex are considered as structures responsible for the synthesis of incoming information, and as an apparatus necessary for the transition from visual perception to abstract symbolic processes.

Clinical neuropsychological studies show that damage to the posterior associative areas disrupts complex forms of orientation in space, constructive activity, makes it difficult to perform all intellectual operations that are carried out with the participation of spatial analysis (counting, perception of complex semantic images). With the defeat of speech zones, the ability to perceive and reproduce speech is impaired. Damage to the frontal areas of the cortex leads to the impossibility of implementing complex behavioral programs that require the selection of significant signals based on past experience and foreseeing the future. See Blocks of the brain, Cortpicalization, Brain, Nervous system, Development of the cerebral cortex, Neuro-psychological syndromes. (D. A. Farber.)

glial cells; it is located in some parts of the deep brain structures, the cortex of the cerebral hemispheres (as well as the cerebellum) is formed from this substance.

Each hemisphere is divided into five lobes, four of which (frontal, parietal, occipital and temporal) are adjacent to the corresponding bones of the cranial vault, and one (insular) is located deep in the fossa that separates the frontal and temporal lobes.

The cerebral cortex has a thickness of 1.5–4.5 mm, its area increases due to the presence of furrows; it is connected with other parts of the central nervous system, thanks to the impulses that neurons conduct.

The hemispheres make up approximately 80% of the total mass of the brain. They carry out the regulation of higher mental functions, while the brain stem is lower, which are associated with the activity of internal organs.

Three main regions are distinguished on the hemispheric surface:

• convex upper lateral, which is adjacent to the inner surface of the cranial vault;
• lower, with the anterior and middle sections located on the inner surface of the cranial base and the posterior ones in the region of the cerebellum;
• the medial is located at the longitudinal fissure of the brain.

Features of the device and activities

The cerebral cortex is divided into 4 types:

• ancient - occupies a little more than 0.5% of the entire surface of the hemispheres;
• old - 2.2%;
• new - more than 95%;
• the average is about 1.5%.

The phylogenetically ancient cerebral cortex, represented by groups of large neurons, is pushed aside by the new one to the base of the hemispheres, becoming a narrow strip. And the old one, consisting of three cell layers, shifts closer to the middle. The main region of the old cortex is the hippocampus, which is the central department of the limbic system. The middle (intermediate) crust is a formation of a transitional type, since the transformation of old structures into new ones is carried out gradually.

The human cerebral cortex, unlike that of mammals, is also responsible for the coordinated work of internal organs. Such a phenomenon, in which the role of the cortex in the implementation of all the functional activities of the body increases, is called the corticalization of functions.

One of the features of the cortex is its electrical activity, which occurs spontaneously. Nerve cells located in this section have a certain rhythmic activity, reflecting biochemical, biophysical processes. Activity has a different amplitude and frequency (alpha, beta, delta, theta rhythms), which depends on the influence of numerous factors (meditation, sleep phases, stress, the presence of convulsions, neoplasms).

Structure

The cerebral cortex is a multilayer formation: each of the layers has its own specific composition of neurocytes, a specific orientation, and the location of processes.

The systematic position of neurons in the cortex is called "cytoarchitectonics", the fibers arranged in a certain order are called "myeloarchitectonics".

The cerebral cortex consists of six cytoarchitectonic layers.

1. Surface molecular, in which there are not very many nerve cells. Their processes are located in himself, and they do not go beyond.
2. The outer granular is formed from pyramidal and stellate neurocytes. The processes leave this layer and go to the next ones.
3. Pyramidal consists of pyramidal cells. Their axons go down where they end or form association fibers, and their dendrites go up to the second layer.
4. The internal granular is formed by stellate cells and small pyramidal. The dendrites go into the first layer, the lateral processes branch out within their own layer. Axons extend into the upper layers or into the white matter.
5. Ganglionic is formed by large pyramidal cells. Here are the largest neurocytes of the cortex. The dendrites are directed to the first layer or distributed in their own. Axons leave the cortex and begin to be fibers that connect various departments and structures of the central nervous system with each other.
6. Multiform - consists of various cells. Dendrites go to the molecular layer (some only up to the fourth or fifth layers). Axons are sent to the overlying layers or exit the cortex as association fibers.

The cerebral cortex is divided into regions - the so-called horizontal organization. There are 11 of them in total, and they include 52 fields, each of which has its own serial number.

Vertical organization

There is also a vertical division - into columns of neurons. In this case, small columns are combined into macro columns, which are called a functional module. At the heart of such systems are stellate cells - their axons, as well as their horizontal connections with the lateral axons of pyramidal neurocytes. All nerve cells in the vertical columns respond to the afferent impulse in the same way and together send an efferent signal. Excitation in the horizontal direction is due to the activity of transverse fibers that follow from one column to another.

He first discovered units that unite neurons of different layers vertically in 1943. Lorente de No - with the help of histology. Subsequently, this was confirmed using methods of electrophysiology on animals by W. Mountcastle.

The development of the cortex in fetal development begins early: as early as 8 weeks, the embryo has a cortical plate. First, the lower layers differentiate, and at 6 months, the unborn child has all the fields that are present in an adult. The cytoarchitectonic features of the cortex are fully formed by the age of 7, but the bodies of neurocytes increase even up to 18. For the formation of the cortex, coordinated movement and division of precursor cells from which neurons emerge are necessary. It has been established that this process is influenced by a special gene.

Horizontal organization

It is customary to divide the areas of the cerebral cortex into:

• associative;
• sensory (sensitive);
• motor.

When studying localized areas and their functional characteristics, scientists used a variety of methods: chemical or physical stimulation, partial removal of brain areas, development of conditioned reflexes, registration of brain biocurrents.

sensitive

These areas occupy approximately 20% of the cortex. The defeat of such zones leads to a violation of sensitivity (reduction of vision, hearing, smell, etc.). The area of ​​the zone directly depends on the number of nerve cells that perceive the impulse from certain receptors: the more there are, the higher the sensitivity. Allocate zones:

• somatosensory (responsible for skin, proprioceptive, autonomic sensitivity) - it is located in the parietal lobe (postcentral gyrus);
• visual, bilateral damage that leads to complete blindness - located in the occipital lobe;
• auditory (located in the temporal lobe);
• taste, located in the parietal lobe (localization - postcentral gyrus);
• olfactory, bilateral violation of which leads to loss of smell (located in the hippocampal gyrus).

Violation of the auditory zone does not lead to deafness, but other symptoms appear. For example, the impossibility of distinguishing short sounds, the meaning of everyday noises (steps, pouring water, etc.) while maintaining the difference in pitch, duration, and timbre. Amusia can also occur, which consists in the inability to recognize, reproduce melodies, and also distinguish between them. Music can also be accompanied by unpleasant sensations.

Impulses going along afferent fibers from the left side of the body are perceived by the right hemisphere, and from the right side - by the left (damage to the left hemisphere will cause a violation of sensitivity on the right side and vice versa). This is due to the fact that each postcentral gyrus is connected to the opposite part of the body.

Motor

The motor areas, the irritation of which causes the movement of the muscles, are located in the anterior central gyrus of the frontal lobe. Motor areas communicate with sensory areas.

The motor pathways in the medulla oblongata (and partially in the spinal cord) form a decussation with a transition to the opposite side. This leads to the fact that the irritation that occurs in the left hemisphere enters the right half of the body, and vice versa. Therefore, damage to the cortex of one of the hemispheres leads to a violation of the motor function of the muscles on the opposite side of the body.

The motor and sensory areas, which are located in the region of the central sulcus, are combined into one formation - the sensorimotor zone.

Neurology and neuropsychology have accumulated a lot of information about how damage to these areas leads not only to elementary movement disorders (paralysis, paresis, tremors), but also to disturbances in voluntary movements and actions with objects - apraxia. When they appear, movements during writing may be disturbed, spatial representations may be disturbed, and uncontrolled patterned movements may appear.

Associative

These zones are responsible for linking the incoming sensory information with the one that was previously received and stored in memory. In addition, they allow you to compare information that comes from different receptors. The response to the signal is formed in the associative zone and transmitted to the motor zone. Thus, each associative area is responsible for the processes of memory, learning and thinking.. Large associative zones are located next to the corresponding functional sensory zones. For example, any associative visual function is controlled by the visual association area, which is located next to the sensory visual area.

Establishing the laws of the brain, analyzing its local disorders and checking its activity is carried out by the science of neuropsychology, which is located at the intersection of neurobiology, psychology, psychiatry and computer science.

Features of localization by fields

The cerebral cortex is plastic, which affects the transition of the functions of one department, if it is disturbed, to another. This is due to the fact that the analyzers in the cortex have a core, where the highest activity takes place, and a periphery, which is responsible for the processes of analysis and synthesis in a primitive form. Between the analyzer cores there are elements that belong to different analyzers. If the damage touches the nucleus, peripheral components begin to take responsibility for its activity.

Thus, the localization of functions possessed by the cerebral cortex is a relative concept, since there are no definite boundaries. However, cytoarchitectonics suggests the presence of 52 fields that communicate with each other through pathways:

• associative (this type of nerve fibers is responsible for the activity of the cortex in the region of one hemisphere);
• commissural (connect symmetrical areas of both hemispheres);
• projection (contribute to the communication of the cortex, subcortical structures with other organs).

Table 1

		Relevant fields
Motor
sensitive
visual
Olfactory
Taste
Speech motor, which includes centers:	Wernicke, which allows you to perceive oral speech
	Broca - responsible for the movement of the tongue muscles; defeat threatens with a complete loss of speech
	Perception of speech in writing

So, the structure of the cerebral cortex involves considering it in a horizontal and vertical orientation. Depending on this, vertical columns of neurons and zones located in the horizontal plane are distinguished. The main functions performed by the cortex are reduced to the implementation of behavior, regulation of thinking, consciousness. In addition, it ensures the interaction of the body with the external environment and takes part in the control of the work of internal organs.

The reticular formation of the brain stem occupies a central position in the medulla oblongata, pons varolii, midbrain and diencephalon.

The neurons of the reticular formation do not have direct contacts with the body's receptors. When the receptors are excited, nerve impulses arrive at the reticular formation along the collaterals of the fibers of the autonomic and somatic nervous system.

Physiological role. The reticular formation of the brain stem has an ascending effect on the cells of the cerebral cortex and a descending effect on the motor neurons of the spinal cord. Both of these influences of the reticular formation can be activating or inhibitory.

Afferent impulses to the cerebral cortex come in two ways: specific and nonspecific. specific neural pathway necessarily passes through the visual tubercles and carries nerve impulses to certain areas of the cerebral cortex, as a result, any specific activity is carried out. For example, when the photoreceptors of the eyes are stimulated, impulses through the visual tubercles enter the occipital region of the cerebral cortex and visual sensations arise in a person.

Nonspecific neural pathway necessarily passes through the neurons of the reticular formation of the brain stem. Impulses to the reticular formation come through the collaterals of a specific nerve pathway. Due to numerous synapses on the same neuron of the reticular formation, impulses of different values ​​(light, sound, etc.) can converge (converge), while they lose their specificity. From the neurons of the reticular formation, these impulses do not arrive at any particular area of ​​the cerebral cortex, but spread like a fan through its cells, increasing their excitability and thereby facilitating the performance of a specific function.

In experiments on cats with electrodes implanted in the region of the reticular formation of the brainstem, it was shown that stimulation of its neurons causes the awakening of a sleeping animal. With the destruction of the reticular formation, the animal falls into a long sleepy state. These data indicate the important role of the reticular formation in the regulation of sleep and wakefulness. The reticular formation not only affects the cerebral cortex, but also sends inhibitory and excitatory impulses to the spinal cord to its motor neurons. Due to this, it is involved in the regulation of skeletal muscle tone.

In the spinal cord, as already mentioned, there are also neurons of the reticular formation. It is believed that they maintain a high level of activity of neurons in the spinal cord. The functional state of the reticular formation itself is regulated by the cerebral cortex.

Cerebellum

Features of the structure of the cerebellum. Connections of the cerebellum with other parts of the central nervous system. The cerebellum is an unpaired formation; it is located behind the medulla oblongata and the pons, borders on the quadrigemina, is covered from above by the occipital lobes of the cerebral hemispheres, the middle part is distinguished in the cerebellum - worm and located on the sides of it two hemisphere. The surface of the cerebellum consists of gray matter called the cortex, which includes the bodies of nerve cells. Inside the cerebellum is white matter, representing the processes of these neurons.

The cerebellum has extensive connections with various parts of the central nervous system due to three pairs of legs. lower legs connect the cerebellum to the spinal cord and medulla oblongata medium- with the pons and through it with the motor area of ​​the cerebral cortex, upper with midbrain and hypothalamus.

The functions of the cerebellum were studied in animals in which the cerebellum was removed partially or completely, as well as by recording its bioelectrical activity at rest and during stimulation.

When half of the cerebellum is removed, an increase in the tone of the extensor muscles is noted, therefore, the limbs of the animal are extended, a bend of the body and a deviation of the head to the operated side are observed, sometimes rocking movements of the head. Often the movements are made in a circle in the operated direction (“manege movements”). Gradually, the marked violations are smoothed out, but some awkwardness of movements remains.

When the entire cerebellum is removed, more pronounced movement disorders occur. In the first days after the operation, the animal lies motionless with its head thrown back and elongated limbs. Gradually, the tone of the extensor muscles weakens, trembling of the muscles appears, especially the cervical ones. In the future, motor functions are partially restored. However, until the end of life, the animal remains a motor invalid: when walking, such animals spread their limbs wide, raise their paws high, i.e., they have impaired coordination of movements.

Movement disorders during the removal of the cerebellum were described by the famous Italian physiologist Luciani. The main ones are: aton and I - the disappearance or weakening of muscle tone; asthen and I - a decrease in the strength of muscle contractions. Such an animal is characterized by rapidly onset muscle fatigue; a stasis - loss of the ability to continuous tetanic contractions. In animals, trembling movements of the limbs and head are observed. The dog after removal of the cerebellum cannot immediately raise its paws, the animal makes a series of oscillatory movements with its paw before lifting it. If you put such a dog, then its body and head sway all the time from side to side.

As a result of atony, asthenia and astasia, the animal's coordination of movements is disturbed: a shaky gait, sweeping, awkward, inaccurate movements are noted. The whole complex of motor disorders in the lesion of the cerebellum is called cerebellar ataxia.

Similar disorders are observed in humans with damage to the cerebellum.

Some time after the removal of the cerebellum, as already mentioned, all movement disorders are gradually smoothed out. If the motor area of ​​the cerebral cortex is removed from such animals, then the motor disturbances increase again. Consequently, compensation (restoration) of movement disorders in case of damage to the cerebellum is carried out with the participation of the cerebral cortex, its motor area.

The studies of L. A. Orbeli showed that when the cerebellum is removed, not only a drop in muscle tone (atony), but also its incorrect distribution (dystonia) is observed. L. L. Orbeli found that the cerebellum also affects the state of the receptor apparatus, as well as autonomic processes. The cerebellum has an adaptive-trophic effect on all parts of the brain through the sympathetic nervous system, it regulates the metabolism in the brain and thereby contributes to the adaptation of the nervous system to changing conditions of existence.

Thus, the main functions of the cerebellum are the coordination of movements, the normal distribution of muscle tone, and the regulation of autonomic functions. The cerebellum realizes its influence through the nuclear formations of the middle and medulla oblongata, through the motor neurons of the spinal cord. A large role in this influence belongs to the bilateral connection of the cerebellum with the motor area of ​​the cerebral cortex and the reticular formation of the brain stem.

Structural features of the cerebral cortex.

The cerebral cortex is phylogenetically the highest and youngest part of the central nervous system.

The cerebral cortex consists of nerve cells, their processes and neuroglia. In an adult, the thickness of the cortex in most areas is about 3 mm. The area of ​​the cerebral cortex due to numerous folds and furrows is 2500 cm 2. Most areas of the cerebral cortex are characterized by a six-layer arrangement of neurons. The cerebral cortex consists of 14-17 billion cells. The cellular structures of the cerebral cortex are represented pyramidal,spindle and stellate neurons.

stellate cells perform mainly an afferent function. Pyramidal and fusiformcells are predominantly efferent neurons.

In the cerebral cortex there are highly specialized nerve cells that receive afferent impulses from certain receptors (for example, from visual, auditory, tactile, etc.). There are also neurons that are excited by nerve impulses coming from different receptors in the body. These are the so-called polysensory neurons.

The processes of the nerve cells of the cerebral cortex connect its various sections to each other or establish contacts between the cerebral cortex and the underlying sections of the central nervous system. The processes of nerve cells that connect different parts of the same hemisphere are called associative, connecting most often the same parts of the two hemispheres - commissural and providing contacts of the cerebral cortex with other parts of the central nervous system and through them with all organs and tissues of the body - conductive(centrifugal). A diagram of these paths is shown in the figure.

Scheme of the course of nerve fibers in the cerebral hemispheres.

1 - short associative fibers; 2 - long associative fibers; 3 - commissural fibers; 4 - centrifugal fibers.

Neuroglia cells perform a number of important functions: they are a supporting tissue, participate in the metabolism of the brain, regulate blood flow inside the brain, secrete a neurosecretion that regulates the excitability of neurons in the cerebral cortex.

Functions of the cerebral cortex.

1) The cerebral cortex carries out the interaction of the organism with the environment due to unconditioned and conditioned reflexes;

2) it is the basis of the higher nervous activity (behavior) of the body;

3) due to the activity of the cerebral cortex, higher mental functions are carried out: thinking and consciousness;

4) the cerebral cortex regulates and integrates the work of all internal organs and regulates such intimate processes as metabolism.

Thus, with the advent of the cerebral cortex, it begins to control all the processes occurring in the body, as well as all human activities, i.e., corticolization of functions occurs. IP Pavlov, characterizing the importance of the cerebral cortex, pointed out that it is the manager and distributor of all the activities of the animal and human organism.

Functional significance of various areas of the cortex brain . Localization of functions in the cerebral cortex brain . The role of individual areas of the cerebral cortex was first studied in 1870 by the German researchers Fritsch and Gitzig. They showed that stimulation of various parts of the anterior central gyrus and the frontal lobes proper causes contraction of certain muscle groups on the side opposite to the stimulation. Subsequently, the functional ambiguity of various areas of the cortex was revealed. It was found that the temporal lobes of the cerebral cortex are associated with auditory functions, the occipital lobes with visual functions, and so on. These studies led to the conclusion that different parts of the cerebral cortex are in charge of certain functions. The doctrine of the localization of functions in the cerebral cortex was created.

According to modern concepts, there are three types of zones of the cerebral cortex: primary projection zones, secondary and tertiary (associative).

Primary projection zones- these are the central sections of the analyzer cores. They contain highly differentiated and specialized nerve cells, which receive impulses from certain receptors (visual, auditory, olfactory, etc.). In these zones, a subtle analysis of afferent impulses of various meanings takes place. The defeat of these areas leads to disorders of sensory or motor functions.

Secondary zones- peripheral parts of the analyzer nuclei. Here, further processing of information takes place, connections are established between stimuli of different nature. When the secondary zones are affected, complex perceptual disorders occur.

Tertiary zones (associative) . The neurons of these zones can be excited under the influence of impulses coming from receptors of various values ​​(from hearing receptors, photoreceptors, skin receptors, etc.). These are the so-called polysensory neurons, due to which connections are established between various analyzers. Associative zones receive processed information from the primary and secondary zones of the cerebral cortex. Tertiary zones play an important role in the formation of conditioned reflexes; they provide complex forms of cognition of the surrounding reality.

Significance of different areas of the cerebral cortex . Sensory and motor areas in the cerebral cortex

Sensory areas of the cortex . (projective cortex, cortical sections of analyzers). These are zones into which sensory stimuli are projected. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways in the sensory cortex come mainly from the relay sensory nuclei of the thalamus - ventral posterior, lateral and medial. The sensory areas of the cortex are formed by the projection and associative zones of the main analyzers.

Area of ​​skin reception(the cerebral end of the skin analyzer) is represented mainly by the posterior central gyrus. The cells of this area perceive impulses from tactile, pain and temperature receptors of the skin. The projection of skin sensitivity within the posterior central gyrus is similar to that for the motor zone. The upper portions of the posterior central gyrus are associated with the receptors of the skin of the lower extremities, the middle portions with the receptors of the trunk and hands, and the lower portions with the receptors of the skin of the head and face. Irritation of this area in a person during neurosurgical operations causes sensations of touch, tingling, numbness, while pronounced pain is never observed.

Area of ​​visual reception(the cerebral end of the visual analyzer) is located in the occipital lobes of the cerebral cortex of both hemispheres. This area should be considered as a projection of the retina.

Area of ​​auditory reception(the cerebral end of the auditory analyzer) is localized in the temporal lobes of the cerebral cortex. This is where nerve impulses come from receptors in the cochlea of ​​the inner ear. If this zone is damaged, musical and verbal deafness may occur, when a person hears, but does not understand the meaning of words; Bilateral damage to the auditory region leads to complete deafness.

The area of ​​taste reception(the cerebral end of the taste analyzer) is located in the lower lobes of the central gyrus. This area receives nerve impulses from the taste buds of the oral mucosa.

Olfactory reception area(the cerebral end of the olfactory analyzer) is located in the anterior part of the piriform lobe of the cerebral cortex. This is where nerve impulses come from the olfactory receptors of the nasal mucosa.

In the cerebral cortex, several zones in charge of the function of speech(brain end of the motor speech analyzer). In the frontal region of the left hemisphere (in right-handed people) is the motor center of speech (Broca's center). With his defeat, speech is difficult or even impossible. In the temporal region is the sensory center of speech (Wernicke's center). Damage to this area leads to speech perception disorders: the patient does not understand the meaning of words, although the ability to pronounce words is preserved. In the occipital lobe of the cerebral cortex there are zones that provide the perception of written (visual) speech. With the defeat of these areas, the patient does not understand what is written.

AT parietal cortex brain ends of the analyzers were not found in the cerebral hemispheres, it is referred to the associative zones. Among the nerve cells of the parietal region, a large number of polysensory neurons were found, which contribute to the establishment of connections between various analyzers and play an important role in the formation of reflex arcs of conditioned reflexes.

motor areas of the cortex The idea of ​​the role of the motor cortex is twofold. On the one hand, it was shown that electrical stimulation of certain cortical zones in animals causes the movement of the limbs of the opposite side of the body, which indicated that the cortex is directly involved in the implementation of motor functions. At the same time, it is recognized that the motor area is an analyzer, i.e. represents the cortical section of the motor analyzer.

The brain section of the motor analyzer is represented by the anterior central gyrus and the parts of the frontal region located near it. When it is irritated, various contractions of the skeletal muscles occur on the opposite side. Correspondence between certain zones of the anterior central gyrus and skeletal muscles has been established. In the upper parts of this zone, the muscles of the legs are projected, in the middle - the torso, in the lower - the head.

Of particular interest is the frontal region itself, which reaches its greatest development in humans. With the defeat of the frontal areas in a person, complex motor functions are disturbed that ensure labor activity and speech, as well as adaptive, behavioral reactions of the body.

Any functional area of ​​the cerebral cortex is in both anatomical and functional contact with other areas of the cerebral cortex, with subcortical nuclei, with formations of the diencephalon and reticular formation, which ensures the perfection of their functions.

1. Structural and functional features of the CNS in the antenatal period.

In the fetus, the number of CNS neurons reaches a maximum by the 20-24th week and remains in the postnatal period without a sharp decrease until old age. Neurons are small in size and the total area of ​​the synaptic membrane.

Axons develop before dendrites, processes of neurons intensively grow and branch. There is an increase in the length, diameter and myelination of axons towards the end of the antenatal period.

Phylogenetically old pathways are myelinated earlier than phylogenetically new ones; for example, vestibulospinal tracts from the 4th month of intrauterine development, rubrospinal tracts from the 5th-8th month, pyramidal tracts after birth.

Na- and K-channels are evenly distributed in the membrane of myelin and non-myelin fibers.

Excitability, conductivity, lability of nerve fibers is much lower than in adults.

The synthesis of most mediators begins during fetal development. Gamma-aminobutyric acid in the antenatal period is an excitatory mediator and, through the Ca2 mechanism, has morphogenic effects - it accelerates the growth of axons and dendrites, synaptogenesis, and the expression of pithoreceptors.

By the time of birth, the process of differentiation of neurons in the nuclei of the medulla oblongata and midbrain, the bridge, ends.

There is structural and functional immaturity of glial cells.

2. Features of the CNS in the neonatal period.

> The degree of myelination of nerve fibers increases, their number is 1/3 of the level of an adult organism (for example, the rubrospinal path is fully myelinated).

> The permeability of cell membranes for ions decreases. Neurons have a lower MP amplitude - about 50 mV (in adults, about 70 mV).

> There are fewer synapses on neurons than in adults, the neuron membrane has receptors for synthesized mediators (acetylcholine, GAM K, serotonin, norepinephrine to dopamine). The content of mediators in the neurons of the brain of newborns is low and amounts to 10-50% of mediators in adults.

> The development of the spiny apparatus of neurons and axospinous synapses is noted; EPSP and IPSP have a longer duration and lower amplitude than in adults. The number of inhibitory synapses on neurons is less than in adults.

> Increased excitability of cortical neurons.

> Disappears (more precisely, sharply decreases) mitotic activity and the possibility of regeneration of neurons. Proliferation and functional maturation of gliocytes continues.

Z. Features of the central nervous system in infancy.

CNS maturation progresses rapidly. The most intense myelination of CNS neurons occurs at the end of the first year after birth (for example, myelination of the nerve fibers of the cerebellar hemispheres is completed by 6 months).

The rate of conduction of excitation along axons increases.

There is a decrease in the duration of AP of neurons, the absolute and relative refractory phases are shortened (the duration of absolute refractoriness is 5-8 ms, relative 40-60 ms in early postnatal ontogenesis, in adults, respectively, 0.5-2.0 and 2-10 ms).

The blood supply to the brain in children is relatively greater than in adults.

4. Features of the development of the central nervous system in other age periods.

1) Structural and functional changes in nerve fibers:

An increase in the diameters of axial cylinders (by 4-9 years). Myelination in all peripheral nerve fibers is close to completion by 9 years, and pyramidal tracts are completed by 4 years;

The ion channels are concentrated in the region of nodes of Ranvier, the distance between the nodes increases. Continuous conduction of excitation is replaced by saltatory, the speed of its conduction after 5-9 years is almost the same as the speed in adults (50-70 m/s);

There is a low lability of nerve fibers in children of the first years of life; with age, it increases (in children 5-9 years old it approaches the norm for adults - 300-1,000 impulses).

2) Structural and functional changes in synapses:

Significant maturation of nerve endings (neuromuscular synapses) occurs by 7-8 years;

The terminal ramifications of the axon and the total area of ​​its endings increase.

Profile material for students of the pediatric faculty

1. Development of the brain in the postnatal period.

In the postnatal period, the leading role in the development of the brain is played by the flows of afferent impulses through various sensory systems (the role of an information-enriched external environment). The absence of these external signals, especially during critical periods, can lead to slow maturation, underdevelopment of function, or even its absence.

The critical period in postnatal development is characterized by intense morphological and functional maturation of the brain and the peak of the formation of NEW connections between neurons.

The general regularity of the development of the human brain is the heterochrony of maturation: fvlogetically older sections develop earlier than younger ones.

The medulla oblongata of a newborn is functionally more developed than other departments: ALMOST all of its centers are active - respiration, regulation of the heart and blood vessels, sucking, swallowing, coughing, sneezing, the chewing center begins to function somewhat later In the regulation of muscle tone, the activity of the vestibular nuclei is reduced (reduced extensor tone) By the age of 6, these Centers complete the differentiation of neurons, myelination of fibers, and the coordination activity of the Centers improves.

The midbrain in newborns is functionally less mature. For example, the orienting reflex and the activity of the centers that control the movement of the eyes and THEM are carried out in infancy. The function of the Substance Black as part of the striopallidary system reaches perfection by the age of 7.

The cerebellum in a newborn is structurally and functionally underdeveloped during infancy, its increased growth and differentiation of neurons occurs, and the connections of the cerebellum with other motor centers increase. Functional maturation of the cerebellum generally begins at age 7 and is completed by age 16.

Maturation of the diencephalon includes the development of sensory nuclei of the thalamus and centers of the hypothalamus

The function of the sensory nuclei of the thalamus is already carried out in the Newborn, which allows the Child to distinguish between taste, temperature, tactile and pain sensations. The functions of the nonspecific nuclei of the thalamus and the ascending activating reticular formation of the brain stem in the first months of life are poorly developed, which leads to a short time of his wakefulness during the day. The nuclei of the thalamus finally develop functionally by the age of 14.

The centers of the hypothalamus in a newborn are poorly developed, which leads to imperfection in the processes of thermoregulation, regulation of water-electrolyte and other types of metabolism, and the need-motivational sphere. Most of the hypothalamic centers are functionally mature by 4 years. The most late (by the age of 16) the sexual hypothalamic centers begin to function.

By the time of birth, the basal nuclei have a different degree of functional activity. The phylogenetically older structure, the globus pallidus, is functionally well developed, while the function of the striatum manifests itself by the end of 1 year. In this regard, the movements of newborns and infants are generalized, poorly coordinated. As the striopalidar system develops, the child performs more and more precise and coordinated movements, creates motor programs of voluntary movements. Structural and functional maturation of the basal nuclei is completed by the age of 7.

The cerebral cortex in early ontogenesis matures later in structural and functional terms. The motor and sensory cortex develops the earliest, the maturation of which ends at the 3rd year of life (auditory and visual cortex somewhat later). The critical period in the development of the associative cortex begins at the age of 7 years and continues until the pubertal period. At the same time, cortical-subcortical interconnections are intensively formed. The cerebral cortex ensures the corticalization of body functions, the regulation of voluntary movements, the creation of motor stereotypes for the implementation, and higher psychophysiological processes. The maturation and implementation of the functions of the cerebral cortex are described in detail in specialized materials for students of the pediatric faculty in topic 11, v. 3, topics 1-8.

The hematoliquor and blood-brain barriers in the postnatal period have a number of features.

In the early postnatal period, large veins are formed in the choroid plexuses of the ventricles of the brain, which can deposit a significant amount of blood 14, thereby participating in the regulation of intracranial pressure.

The cerebral cortex , a layer of gray matter 1-5 mm thick, covering the cerebral hemispheres of mammals and humans. This part of the brain, which developed in the later stages of the evolution of the animal world, plays an extremely important role in the implementation of mental, or higher nervous activity, although this activity is the result of the work of the brain as a whole. Due to bilateral connections with the underlying parts of the nervous system, the cortex can participate in the regulation and coordination of all body functions. In humans, the cortex makes up an average of 44% of the volume of the entire hemisphere as a whole. Its surface reaches 1468-1670 cm2.

The structure of the bark . A characteristic feature of the structure of the cortex is the oriented, horizontal-vertical distribution of its constituent nerve cells in layers and columns; thus, the cortical structure is distinguished by a spatially ordered arrangement of functioning units and connections between them. The space between the bodies and processes of the nerve cells of the cortex is filled with neuroglia and the vascular network (capillaries). Cortical neurons are divided into 3 main types: pyramidal (80-90% of all cortical cells), stellate and fusiform. The main functional element of the cortex is the afferent-efferent (i.e., perceiving centripetal and sending centrifugal stimuli) long-axon pyramidal neuron. Stellar cells are distinguished by weak development of dendrites and powerful development of axons, which do not extend beyond the diameter of the cortex and cover groups of pyramidal cells with their branchings. Stellar cells act as receptive and synchronizing elements capable of coordinating (simultaneously inhibiting or exciting) spatially close groups of pyramidal neurons. A cortical neuron is characterized by a complex submicroscopic structure. Topographically different areas of the cortex differ in the density of the cells, their size, and other characteristics of the layered and columnar structure. All these indicators determine the architecture of the cortex, or its cytoarchitectonics. The largest divisions of the territory of the cortex are the ancient (paleocortex), old (archicortex), new (neocortex) and interstitial cortex. The surface of the new cortex in humans occupies 95.6%, the old 2.2%, the ancient 0.6%, the intermediate 1.6%.

If we imagine the cerebral cortex as a single cover (cloak) covering the surface of the hemispheres, then the main central part of it will be the new cortex, while the ancient, old and intermediate will take place on the periphery, i.e. along the edges of this cloak. The ancient cortex in humans and higher mammals consists of a single cell layer, indistinctly separated from the underlying subcortical nuclei; the old bark is completely separated from the latter and is represented by 2-3 layers; the new cortex consists, as a rule, of 6-7 layers of cells; intermediate formations - transitional structures between the fields of the old and new crust, as well as the ancient and new crust - from 4-5 layers of cells. The neocortex is subdivided into the following regions: precentral, postcentral, temporal, inferoparietal, superior parietal, temporoparietal-occipital, occipital, insular, and limbic. In turn, the areas are divided into sub-areas and fields. The main type of direct and feedback connections of the new cortex are vertical bundles of fibers that bring information from the subcortical structures to the cortex and send it from the cortex to the same subcortical formations. Along with vertical connections, there are intracortical - horizontal - bundles of associative fibers passing at various levels of the cortex and in the white matter under the cortex. Horizontal bundles are most characteristic of layers I and III of the cortex, and in some fields for layer V.

Horizontal bundles provide information exchange both between fields located on adjacent gyri and between distant areas of the cortex (for example, frontal and occipital).

Functional features of the cortex are determined by the distribution of nerve cells and their connections in layers and columns mentioned above. Convergence (convergence) of impulses from various sense organs is possible on cortical neurons. According to modern concepts, such a convergence of heterogeneous excitations is a neurophysiological mechanism of the integrative activity of the brain, i.e., analysis and synthesis of the body's response activity. It is also essential that the neurons are combined into complexes, apparently realizing the results of the convergence of excitations to individual neurons. One of the main morpho-functional units of the cortex is a complex called a column of cells, which passes through all the cortical layers and consists of cells located on one perpendicular to the surface of the cortex. The cells in the column are closely interconnected and receive a common afferent branch from the subcortex. Each column of cells is responsible for the perception of predominantly one type of sensitivity. For example, if at the cortical end of the skin analyzer one of the columns reacts to touching the skin, then the other - to the movement of the limb in the joint. In the visual analyzer, the functions of perception of visual images are also distributed in columns. For example, one of the columns perceives the movement of an object in a horizontal plane, the neighboring one - in a vertical one, etc.

The second complex of cells of the new cortex - the layer - is oriented in the horizontal plane. It is believed that the small cell layers II and IV consist mainly of receptive elements and are "entrances" to the cortex. The large cell layer V is the exit from the cortex to the subcortex, and the middle cell layer III is associative, connecting various cortical zones.

The localization of functions in the cortex is characterized by dynamism due to the fact that, on the one hand, there are strictly localized and spatially delimited cortical zones associated with the perception of information from a particular sense organ, and on the other hand, the cortex is a single apparatus in which individual structures are closely connected and if necessary, they can be interchanged (the so-called plasticity of cortical functions). In addition, at any given moment, cortical structures (neurons, fields, regions) can form coordinated complexes, the composition of which changes depending on specific and nonspecific stimuli that determine the distribution of inhibition and excitation in the cortex. Finally, there is a close interdependence between the functional state of the cortical zones and the activity of the subcortical structures. Territories of the crust differ sharply in their functions. Most of the ancient cortex is included in the olfactory analyzer system. The old and intermediate cortex, being closely related to the ancient cortex both by systems of connections and evolutionarily, are not directly related to the sense of smell. They are part of the system that controls the regulation of vegetative reactions and emotional states. New cortex - a set of final links of various perceiving (sensory) systems (cortical ends of analyzers).

It is customary to single out projection, or primary, and secondary, fields, as well as tertiary fields, or associative zones, in the zone of one or another analyzer. Primary fields receive information mediated through the smallest number of switches in the subcortex (in the optic tubercle, or thalamus, diencephalon). On these fields, the surface of peripheral receptors is, as it were, projected. In the light of modern data, projection zones cannot be considered as devices that perceive “point to point” irritations. In these zones, certain parameters of objects are perceived, i.e., images are created (integrated), since these parts of the brain respond to certain changes in objects, to their shape, orientation, speed of movement, etc.

Cortical structures play a primary role in the learning of animals and humans. However, the formation of some simple conditioned reflexes, mainly from the internal organs, can be provided by subcortical mechanisms. These reflexes can also form at lower levels of development, when there is no cortex yet. Complex conditioned reflexes underlying integral behavioral acts require the preservation of cortical structures and the participation of not only the primary zones of the cortical ends of the analyzers, but also the associative - tertiary zones. Cortical structures are directly related to the mechanisms of memory. Electrical stimulation of certain areas of the cortex (for example, the temporal one) evokes complex pictures of memories in people.

A characteristic feature of the activity of the cortex is its spontaneous electrical activity, recorded in the form of an electroencephalogram (EEG). In general, the cortex and its neurons have rhythmic activity, which reflects the biochemical and biophysical processes taking place in them. This activity has a varied amplitude and frequency (from 1 to 60 Hz) and changes under the influence of various factors.

The rhythmic activity of the cortex is irregular, but it is possible to distinguish several different types of it (alpha, beta, delta, and theta rhythms) by the frequency of potentials. The EEG undergoes characteristic changes in many physiological and pathological conditions (different phases of sleep, tumors, seizures, etc.). The rhythm, i.e. frequency, and amplitude of the bioelectric potentials of the cortex are set by subcortical structures that synchronize the work of groups of cortical neurons, which creates the conditions for their coordinated discharges. This rhythm is associated with the apical (apical) dendrites of the pyramidal cells. The rhythmic activity of the cortex is superimposed by influences coming from the sense organs. So, a flash of light, a click or a touch on the skin causes the so-called. the primary response, consisting of a series of positive waves (the downward deflection of the electron beam on the oscilloscope screen) and a negative wave (the upward deflection of the beam). These waves reflect the activity of the structures of a given area of ​​the cortex and change in its various layers.

Phylogeny and ontogeny of the cortex . The bark is the product of a long evolutionary development, during which the ancient bark first appears, arising in connection with the development of the olfactory analyzer in fish. With the release of animals from the water to land, the so-called. a cloak-like part of the cortex, completely separated from the subcortex, which consists of old and new cortex. The formation of these structures in the process of adaptation to the complex and diverse conditions of terrestrial existence is connected (by the improvement and interaction of various perceiving and motor systems. In amphibians, the cortex is represented by the ancient and the rudiment of the old cortex, in reptiles the ancient and old cortex are well developed and the rudiment of the new cortex appears. The greatest development the new cortex reaches in mammals, and among them in primates (monkeys and humans), proboscis (elephants) and cetaceans (dolphins, whales).Due to the uneven growth of individual structures of the new cortex, its surface becomes folded, covered with furrows and convolutions.Improvement of the cortex telencephalon in mammals is inextricably linked with the evolution of all parts of the central nervous system.This process is accompanied by an intensive growth of direct and feedback connections connecting cortical and subcortical structures.Thus, at higher stages of evolution, the functions of subcortical formations begin to be controlled by cortical structures. This phenomenon is called corticolization of functions. As a result of corticolization, the brain stem forms a single complex with the cortical structures, and damage to the cortex at the higher stages of evolution leads to a violation of the vital functions of the body. Associative zones undergo the greatest changes and increase during the evolution of the neocortex, while the primary, sensory fields decrease in relative magnitude. The growth of the new cortex leads to the displacement of the old and ancient on the lower and median surfaces of the brain.

The cortical plate appears in the process of intrauterine development of a person relatively early - on the 2nd month. First of all, the lower layers of the cortex stand out (VI-VII), then the more highly located ones (V, IV, III and II;) By 6 months, the embryo already has all the cytoarchitectonic fields of the cortex characteristic of an adult. After birth, three critical stages can be distinguished in the growth of the cortex: at the 2-3rd month of life, at 2.5-3 years and at 7 years. By the last term, the cytoarchitectonics of the cortex is fully formed, although the bodies of neurons continue to increase up to 18 years. The cortical zones of the analyzers complete their development earlier, and the degree of their increase is less than that of the secondary and tertiary zones. There is a great diversity in the timing of maturation of cortical structures in different individuals, which coincides with the diversity of the timing of maturation of the functional features of the cortex. Thus, the individual (ontogeny) and historical (phylogenesis) development of the cortex is characterized by similar patterns.

On the topic : the structure of the cerebral cortex

Prepared