What is the cerebral cortex? Composition of the cerebral cortex
The cerebral cortex is the superficial layer that covers its hemispheres. It is formed predominantly by vertically oriented nerve cells and their processes, as well as bundles of afferent and efferent nerve fibers. In addition, the cortex contains neuroglial cells.
A characteristic feature of the cerebral cortex is horizontal layering, which is caused by the ordered position of nerve cells and fibers. It is worth noting that there are six layers in the cortex, which differ in the density, width, size and shape of the neurons that make them up. Due to the vertical arrangement of bundles of nerve fibers, cell bodies and processes of neurons, the cortex has vertical striations. For the functional organization of this organ, the vertical arrangement of nerve cells has enormous knowledge.
It is worth noting that cortex has a total area of approximately 2200 square centimeters, and the number of neurons in it is more than 10 billion. A significant place in the cortex is given to pyramidal neurons. They have different sizes, their dendrites have many spines: axon, stellate cells - have a short axon and short dendrites, spindle-shaped neurons - they provide horizontal or vertical connections between neurons.
- Multilayer localization of neurons.
- Somatotopic location of receptor systems.
- Modular organization.
- Screenness is the distribution on the plane of the neuronal field of external reception.
- Representation of the functions of the central nervous system structures.
- Dependence of the degree of activity on the influence of the reticular formation and subcortical structures.
- Cytoarchitectonic distribution into fields.
- The presence of secondary and tertiary fields in specific projection motor and sensory systems of the cortex with a predominance of associative functions.
- Specialized association areas of the cortex.
- The ability to preserve traces of irritation for a long time.
- Dynamic arrangement of functions, which manifests itself in the ability to compensate for the lost functions of cortical structures.
- Overlap in the cortex of areas of neighboring peripheral receptive fields.
- Reciprocal functional connection between inhibitory and excitatory states of the cortex.
- The ability to irradiate a state.
- Specific electrical activity.
The distinctive features of the organization of the cortex are influenced by the fact that in evolution there was a corticolization of the functions of the central nervous system, that is, transmission to underlying brain structures. However, this transfer does not mean that the cortex performs the functions of other structures. Its role is to correct dysfunctions of the systems that interact with it, taking into account individual experience, analyzing signals, forming the correct reaction to these signals, as well as the formation in one’s own and other interested brain structures of traces about the signal, its meaning, characteristics and reactions to it. Then, as automation progresses, the response is carried out by subcortical structures.
Layers of the cerebral cortex
Molecular layer– it is formed by fibers that are intertwined with each other, it contains few cells.
Outer granular layer– it is characterized by a dense arrangement of small neurons of different shapes. In the depths there are small pyramidal cells - they got their name due to their shape.
Outer pyramidal layer– it consists of pyramidal neurons of different sizes, with large cells located deeper.
Inner granular layer– it is characterized by a loose position of small neurons of various sizes, dense bundles of fibers pass near them.
Inner pyramidal layer– includes medium and large pyramidal neurons, their apical dendrites extend up to the molecular layer.
Spindle cell layer– spindle-shaped neurons are located here, while its deep part passes into the white matter.
Areas of the cerebral cortex
Based on the location, density and shape of neurons, the cerebral cortex is usually divided into several fields; they, to a certain extent, coincide with certain zones, which, based on clinical and physiological data, are assigned a number of functions.
Using electrophysiological methods, it was found that the cerebral cortex contains 3 types of areas in accordance with the functions performed by the cells located there. These include sensory, associative and motor areas. Thanks to the relationships between these zones, it is possible to control and coordinate voluntary and a number of involuntary forms of activity, including memory, consciousness, learning, and personality traits.
It should be noted that the functions of individual areas of the cortex, including large anterior areas, have not yet been studied. These areas, as well as some other areas of the brain, are called silent zones. This is due to the fact that in case of irritation with electric current, no reactions or sensations appear.
It is believed that these zones are responsible for a number of individual characteristics or personality. Removing these areas or cutting the pathways that lead from them to the brain was used to relieve acute agitation in patients, but this method had to be abandoned due to side effects. The consequences of this include a decrease in the level of intelligence, consciousness, creativity and logical thinking. These side effects indirectly indicate the functions performed by the prefrontal zones.
Features of neurological examination
The neurological examination focuses on movement and sensory disorders. Therefore, it is much easier to identify disturbances in the functioning of pathways and primary zones than lesions in the associative cortex. It is worth noting that there may be no neurological symptoms even in cases of extensive damage to the frontal, parietal or temporal lobe. It is important that the assessment of cognitive function be as logical and consistent as the neurological examination.
This type of examination focuses on the fixed connections between function and structure. For example, with damage to the striate cortex or optic tract, contralateral homonymous hemianopsia always occurs. If the sciatic nerve is affected, the Achilles reflex is not observed.
At first it was assumed that the functions of the associative cortex act in a similar way. There was an opinion that there were centers for memory, perception of space, and understanding of words, so with the help of special tests it was possible to determine the location of the lesion. Later, ideas emerged regarding distributed neural systems and functional specialization within them. These ideas indicate that distributed systems—complex neural circuits that include cortical and subcortical formations—are responsible for complex behavioral and cognitive functions.
Therefore, the following conclusions can be drawn:
- Complex functions, for example, memory or speech, suffer if any structure included in the corresponding distributed system is damaged.
- If a structure belongs simultaneously to a number of distributed systems, its defeat becomes the cause of disruption of several functions.
- If the preserved links take over the functions of the affected area, then the dysfunction may be temporary or minimal.
- The individual structures that make up a distributed system are responsible for different aspects of the function provided by that system, but it is worth noting that this specialization is relative.
That is, damage to any structure of this distributed system will lead to disruption of the same function, while the clinical manifestations will be different.
The cerebral cortex is a complex organ that performs many important functions. Malfunctions in its operation can lead to quite serious consequences for the body, so in case of any violations, you must promptly seek help from a competent specialist.
30.07.2013
Formed by neurons, it is a layer of gray matter that covers the cerebral hemispheres. Its thickness is 1.5 - 4.5 mm, the area of an adult is 1700 - 2200 cm 2. Myelinated fibers forming the white matter of the telencephalon connect the cortex with the rest departments of the Moscow . Approximately 95 percent of the surface of the hemispheres is neocortex, or neocortex, which is phylogenetically considered the most recent formation of the brain. The archiocortex (old cortex) and paleocortex (ancient cortex) have a more primitive structure, they are characterized by a fuzzy division into layers (weak stratification).
The structure of the cortex.
The neocortex is formed by six layers of cells: the molecular lamina, the outer granular lamina, the outer pyramidal lamina, the internal granular and pyramidal lamina, and the multiforme lamina. Each layer is distinguished by the presence of nerve cells of a certain size and shape.
The first layer is a molecular plate, which is formed by a small number of horizontally oriented cells. Contains branching dendrites of pyramidal neurons of the underlying layers.
The second layer is the outer granular plate, consisting of the bodies of stellate neurons and pyramidal cells. This also includes a network of thin nerve fibers.
The third layer, the outer pyramidal plate, consists of the bodies of pyramidal neurons and processes that do not form long pathways.
The fourth layer, the internal granular plate, is formed by densely spaced stellate neurons. Thalamocortical fibers are adjacent to them. This layer includes bundles of myelin fibers.
The fifth layer, the inner pyramidal plate, is formed mainly by large pyramidal Betz cells.
The sixth layer is a multiform plate, consisting of a large number of small polymorphic cells. This layer smoothly passes into the white matter of the cerebral hemispheres.
Furrows cortex Each hemisphere is divided into four lobes.
The central sulcus begins on the inner surface, descends down the hemisphere and separates the frontal lobe from the parietal lobe. The lateral groove originates from the lower surface of the hemisphere, rises obliquely to the top and ends in the middle of the superolateral surface. The parieto-occipital sulcus is localized in the posterior part of the hemisphere.
Frontal lobe.
The frontal lobe has the following structural elements: frontal pole, precentral gyrus, superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus, pars tegmental, triangular and orbital. The precentral gyrus is the center of all motor acts: from elementary functions to complex complex actions. The richer and more differentiated the action, the larger the area a given center occupies. Intellectual activity is controlled by the lateral sections. The medial and orbital surfaces are responsible for emotional behavior and autonomic activity.
Parietal lobe.
Within its boundaries there are the postcentral gyrus, intraparietal sulcus, paracentral lobule, superior and inferior parietal lobules, supramarginal and angular gyri. Somatic sensitive cortex located in the postcentral gyrus; a significant feature of the arrangement of functions here is somatotopic division. The entire remaining parietal lobe is occupied by the association cortex. It is responsible for recognizing somatic sensitivity and its relationship with various forms of sensory information.
Occipital lobe.
It is the smallest in size and includes the semilunar and calcarine sulci, the cingulate gyrus and a wedge-shaped area. The cortical center of vision is located here. Thanks to which a person can perceive visual images, recognize and evaluate them.
Temporal lobe.
On the lateral surface, three temporal gyri can be distinguished: superior, middle and inferior, as well as several transverse and two occipitotemporal gyri. Here, in addition, there is the hippocampal gyrus, which is considered the center of taste and smell. The transverse temporal gyrus is a zone that controls auditory perception and interpretation of sounds.
Limbic complex.
Unites a group of structures that are located in the marginal zone of the cerebral cortex and the visual thalamus of the diencephalon. It's limbic cortex, dentate gyrus, amygdala, septal complex, mammillary bodies, anterior nuclei, olfactory bulbs, bundles of connective myelin fibers. The main function of this complex is the control of emotions, behavior and stimuli, as well as memory functions.
Basic dysfunctions of the cortex.
Main disorders to which cortex, divided into focal and diffuse. The most common focal ones are:
Aphasia is a disorder or complete loss of speech function;
Anomia is the inability to name various objects;
Dysarthria is a disorder of articulation;
Prosody is a violation of the rhythm of speech and the placement of stress;
Apraxia is the inability to perform habitual movements;
Agnosia is the loss of the ability to recognize objects using sight or touch;
Amnesia is a memory disorder that is expressed by a slight or complete inability to reproduce information received by a person in the past.
Diffuse disorders include: stupor, stupor, coma, delirium and dementia.
The cortex works in conjunction with other structures. This part of the organ has certain features associated with its specific activity. The main basic function of the cortex is to analyze information received from the organs and store the received data, as well as their transmission to other parts of the body. The cerebral cortex communicates with information receptors, which act as receivers of signals entering the brain.
Among the receptors there are sensory organs, as well as organs and tissues that carry out commands, which, in turn, are transmitted from the cortex.
For example, visual information coming from is sent along nerves through the cortex to the occipital zone, which is responsible for vision. If the image is not static, it is analyzed in the parietal zone, in which the direction of movement of the observed objects is determined. The parietal lobes are also involved in the formation of articulate speech and a person’s perception of his location in space. The frontal lobes of the cerebral cortex are responsible for the higher psyches involved in the formation of personality, character, abilities, behavioral skills, creative inclinations, etc.
Lesions of the cerebral cortex
When one or another part of the cerebral cortex is damaged, disturbances occur in the perception and functioning of certain sensory organs.
With lesions of the frontal lobe of the brain, mental disorders occur, which most often manifest themselves in serious impairment of attention, apathy, weakened memory, sloppiness and a feeling of constant euphoria. A person loses some personal qualities and develops serious behavioral deviations. Frontal ataxia often occurs, which affects standing or walking, difficulty moving, problems with accuracy, and the occurrence of hit-and-miss phenomena. The phenomenon of grasping may also occur, which consists of obsessively grasping objects surrounding a person. Some scientists associate the appearance of epileptic seizures precisely after injury to the frontal lobe.
When the frontal lobe is damaged, a person’s mental abilities are significantly impaired.
With lesions of the parietal lobe, memory disorders are observed. For example, astereognosis may occur, which manifests itself in the inability to recognize an object by touch when closing the eyes. Apraxia often appears, manifested in a violation of the formation of a sequence of events and the building of a logical chain for performing a motor task. Alexia is characterized by the inability to read. Acalculia is an impairment of the ability to process numbers. There may also be impaired perception of one's own body in space and an inability to understand logical structures.
The affected temporal lobes are responsible for hearing and perception disorders. With lesions of the temporal lobe, the perception of oral speech is impaired, attacks of dizziness, hallucinations and seizures, mental disorders and excessive irritation begin. Injuries to the occipital lobe cause visual hallucinations and disturbances, the inability to recognize objects when looking at them, and distorted perception of the shape of an object. Sometimes photoms appear - flashes of light that occur when the inner part of the occipital lobe is irritated.
CORTEX (cortex brain) - all surfaces of the cerebral hemispheres, covered with a cloak (pallium) formed by gray matter. Together with other departments of the c. n. With. the cortex is involved in the regulation and coordination of all functions of the body, 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 actual old cortex and paleocortex - the ancient cortex) is a phylogenetically more ancient formation than the new cortex (neocortex), which appeared during the development of the cerebral hemispheres (see Architectonics of the cerebral cortex, Brain).
Morphologically, K. g. m. is formed by nerve cells (see), their processes and neuroglia (see), which has a supporting-trophic function. In primates and humans, the cortex contains approx. 10 billion neurocytes (neurons). Depending on their shape, pyramidal and stellate neurocytes are distinguished, which are characterized by great diversity. The axons of pyramidal neurocytes are directed into the subcortical white matter, and their apical dendrites are directed into the outer layer of the cortex. Stellate 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 they, following horizontally, form a dense plexus with the apices of the apical dendrites of pyramidal neurocytes. Along the surface of the dendrites there are kidney-shaped projections, or spines, which represent the area of axodendritic synapses (see). The cell body membrane is the region of axosomatic synapses. Each area of the cortex has many input (afferent) and output (efferent) fibers. Efferent fibers go to other areas of the K. g. m., to subcortical formations or to the motor centers of the spinal cord (see). Afferent fibers enter the cortex from cells of 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 cortex has a more complex structure and occupies (in humans) approx. 96% of the entire surface of the K. g. m. Therefore, when they talk about the K. g. m., they usually mean the new cortex, which is divided into the frontal, temporal, occipital and parietal lobes. These lobes are divided into regions 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 sulci). Nissl-stained sections show a layered structure of the cortex, which depends on the grouping of neurocytes at its different levels (layers). It is customary to distinguish 6 layers in the bark. 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 fact, in many parts of the cortex there is a gradual and uniform transition between layers. Cells of all layers, located on the same perpendicular to the surface of the cortex, are closely connected with each other and with the 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 the horizontal plane, the neighboring one - in the vertical, etc.
Similar complexes of neocortical cells have a horizontal orientation. It is assumed that, for example, small-cell layer II and IV consist mainly of receptive cells and are “entrances” to the cortex, large-cell layer V is the “exit” from the cortex to the subcortical structures, and middle-cell layer III is associative and connects with each other. different zones of the cortex.
Thus, we can distinguish several types of direct and feedback connections between the cellular elements of the cortex and subcortical formations: vertical bundles of fibers that carry information from the subcortical structures to the cortex and back; intracortical (horizontal) bundles of associative fibers passing at various levels of the cortex and white matter.
The variability and originality of the structure of neurocytes indicate the extreme complexity of intracortical switching apparatuses and methods of connections between neurocytes. This structural feature of the K. g. m. should be considered as a morphol, the equivalent of its extreme reactivity and functionality, plasticity, providing it with higher nervous functions.
The increase in the mass of cortical tissue occurred in a limited space of the skull, so the surface of the cortex, smooth in lower mammals, was transformed into convolutions and grooves in higher mammals and humans (Fig. 1). It was with the development of the cortex that already in the last century scientists associated such aspects of brain activity as memory (q.v.), intelligence, consciousness (q.v.), thinking (q.v.), 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 Hitzig (G. Fritsch, E. Hitzig, 1870) showed that electrical stimulation of certain areas of the anterior section of the canine muscle causes contraction of certain groups of skeletal muscles. Many scientists believed that when the brain is irritated, the “centers” of voluntary movements and motor memory are activated. However, even C. Sherrington preferred to avoid the functional interpretation of this phenomenon and limited himself to only the statement that the area of the cortex, irritation of the cut causes a contraction of muscle groups, is intimately connected with the spinal cord.
The directions of experimental research of K. g.m. of the end of the last century were almost always associated with problems of wedge, neurology. On this basis, experiments were begun with partial or complete decortication of the brain (see). Goltz (F. L. Goltz, 1892) was the first to perform complete decortication in a dog. The decorticated dog turned out to be viable, but many of its most important functions were severely impaired - vision, hearing, orientation in space, coordination of movements, etc. Before I. P. Pavlov discovered the phenomenon of the conditioned reflex (see), the interpretation of experiments with both complete and partial extirpations of the cortex suffered from the lack of an objective criterion for their assessment. The introduction of the conditioned reflex method into the practice of experiments with extirpations opened a new era in the study of the structural and functional organization of blood cells.
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 the coronary gland is the “organ” of conditioned reflexes. However, further research showed the possibility of developing conditioned reflexes in decorticated animals. It was found that conditioned reflexes are not disturbed by vertical transections of various areas of the cerebral cortex 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 extirpation method for studying the significance of K. g.m. in the organization of behavior prompted the development of methods for reversible, functional, shutdown 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 of the K. g. m. (rats, mice).
Another way to function, turn off the K.G.M. is its cooling. The method developed by N. Yu. Belenkov et al. (1969), is that in accordance with the shape of the surface of the cortical areas planned for switching off, capsules are made that are implanted above the dura mater; During the experiment, a cooled liquid is passed through the capsule, as a result of which the temperature of the cortex under the capsule decreases to 22-20°. Removal of biopotentials using microelectrodes shows that at this temperature the impulse activity of neurons stops. The method of cold decortication, used in chronic experiments on animals, demonstrated the effect of emergency shutdown of the neocortex. It turned out that such a shutdown stops the implementation of previously developed conditioned reflexes. Thus, it was shown that the K. g. m. is a necessary structure for the manifestation of a conditioned reflex in the intact brain. Consequently, the observed facts of the development of conditioned reflexes in surgically decorticated animals are the result of compensatory changes that occur in the time interval from the moment of surgery to the beginning of the study of the animal in the chronic experiment. Compensatory phenomena also occur in the case of functional shutdowns of the neocortex. Just like cold shutdown, acute shutdown of the neocortex in rats by spreading depression dramatically disrupts conditioned reflex activity.
A comparative assessment of the effects of complete and partial decortication in various animal species showed that monkeys tolerate these operations more severely than cats and dogs. The degree of dysfunction during extirpation of the same cortical zones is different in animals at different stages of evolutionary development. For example, removal of the temporal regions in cats and dogs impairs hearing function less than in monkeys. Similarly, after removal of the occipital cortex, vision is affected more in monkeys than in cats and dogs. Based on these data, the idea of corticolization of functions in the process of evolution of c. n. p., according to Krom, phylogenetically earlier links of the nervous system move to a lower level of the hierarchy. At the same time, K. g.m. plastically rearranges the functioning of these phylogenetically older structures in accordance with the influence of the environment.
Cortical projections of the afferent systems of the brain are specialized terminal stations of the pathways from the sensory organs. From the K. g. m. to the motor neurons of the spinal cord as part of the pyramidal tract there are efferent pathways. They originate primarily 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. Posterior to the central sulcus is the somatosensory area K. g. m. - the posterior central gyrus. Individual areas of skeletal muscle are corticolized to varying degrees. The lower limbs and trunk are represented least differentiated in the anterior central gyrus; a large area is occupied by the muscles of the hand. An even larger area corresponds to the muscles of the face, tongue and larynx. In the posterior central gyrus, afferent projections of body parts are represented in the same ratio as in the anterior central gyrus. We can say 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 nonspecific, areas that receive information from receptors that perceive stimuli of various modalities, and from all projection zones. The phylogenetic development of K. 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, 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. n. d.
In primates and humans, the frontal (prefrontal) region reaches the greatest development. This is phylogenetically the youngest structure, directly related to the highest mental functions. However, attempts to project these functions onto individual areas of the frontal cortex are unsuccessful. Obviously, any part of the frontal cortex can be involved in the implementation of any of the functions. The effects observed when various parts of this area are destroyed are relatively short-lived or often completely absent (see Lobectomy).
The association of individual structures of the blood muscle with certain functions, considered as a problem of localization of functions, remains to this day 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 brain. With the help of microelectrode research methods (see), it was possible to register in various areas of the brain the activity of specific neurocytes that respond to stimuli of a certain sensory modality. Superficial removal of bioelectric potentials reveals the distribution of primary evoked potentials over significant areas of the brain, outside the corresponding projection zones and cytoarchitectonic fields. These facts, along with the multi-functionality of disturbances when any sensory area is removed or its reversible shutdown, indicate multiple representation of functions in the circulatory system. Motor functions are also distributed over large areas of the circulatory system. Thus, neurocytes, the processes of which form a pyramidal tract, are located not only in the motor areas, but also beyond them. In addition to sensory and motor cells, in the K. g. m. there are also intermediate cells, or interneurocytes, which make up the bulk of the K. g. m. and concentrated hl. arr. in associative areas. Multimodal excitations converge on interneurocytes.
Experimental data indicate, therefore, the relativity of the localization of functions in the K. g.m., the absence of cortical “centers” reserved for one or another function. The least differentiated in functional terms are the associative areas, which have especially pronounced properties of plasticity and interchangeability. This, however, does not imply that the associative regions are equipotential. The principle of equipotentiality of the cortex (equivalence of its structures), expressed by K. S. Lashley in 1933 based on the results of extirpations of the poorly differentiated rat cortex, in general 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 quantum mechanics.
The solution to the problem of the structural and functional organization of the K. g. m. is in many ways difficult to identify the localization of symptoms of extirpations and stimulation of certain cortical zones with the localization of the functions of the K. g. m. This question concerns the methodological aspects of neurophysiology, experiment, since from a dialectical point From our point of view, any structural and functional unit in the form in which it appears in each given study is a fragment, one of the aspects of the existence of the whole, a product of the integration of brain structures and connections. For example, the position that the function of motor speech is “localized” in the inferior 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 caused by stimulation of the rostral thalamus, which sends afferent impulses to the left hemisphere. Phrases caused by such stimulation have nothing to do with voluntary speech and are not adequate to the situation. This highly integrated stimulation effect suggests 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 irritation 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 connection between the cortex and subcortical formations. Therefore, cortical mechanisms cannot be opposed to the work of subcortical structures, but specific cases of their interaction must be considered.
With electrical stimulation of individual cortical areas, the activity of the cardiovascular system, respiratory system, and gastrointestinal tract changes. tract and other visceral systems. K. M. Bykov also substantiated the influence of K. g. m. on internal organs by the possibility of the formation of visceral conditioned reflexes, which, along with vegetative shifts during various emotions, was 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 by the cortex of the activity of subcortical structures that are directly related to the regulation of the internal environment of the body.
A significant role is played by the connections of K. g. m. with the hypothalamus (see).
The level of activity of K. g. m. is mainly determined by ascending influences from the reticular formation (see) of the brain stem, which is controlled by corticofugal influences. The effect of the latter is dynamic in nature and is a consequence of the current afferent synthesis (see). Studies using electroencephalography (see), in particular corticography (i.e., the removal of biopotentials directly from the K. g.m.), would seem to confirm the hypothesis about 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 electroencephalography technique in understanding 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 the K. g.m. and the manifestation of the conditioned reflex depends on the level of distant synchronization of biopotentials removed from spatially distant points of the K. g.m. An increase in the level of spatial synchronization is observed with mental stress (Fig. 5). In this state, areas of synchronization are not concentrated in certain areas of the cortex, but are distributed over its entire area. Correlation relationships cover points throughout the frontal cortex, but at the same time, increased synchrony is also recorded in the precentral gyrus, in the parietal region, and in other areas of the brain muscle.
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 circulatory system. 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 hemisphere was specialized to perform certain functions. In most people, the left hemisphere is dominant, providing speech function and control of the action of the right hand. The right hemisphere is specialized for the perception of shape and space. At the same time, the functional differentiation of the hemispheres is not absolute. However, extensive damage to the left temporal lobe is usually accompanied by sensory and motor speech impairments. It is obvious that lateralization is based on innate mechanisms. However, the potential capabilities of the right hemisphere in organizing speech function can manifest themselves 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 different integrative mechanisms over time. It is possible that cortical specialization counteracts the incompatibility of various functional systems (see), facilitates decision-making about the goal and method of action. The integrative activity of the brain is not limited, i.e., to external (summative) integrity, understood as the interaction of the activities of independent elements (whether neurocytes or entire brain formations). Using the example of the development of lateralization, one can see how this holistic, integrative activity of the brain itself becomes a prerequisite for differentiating the properties of its individual elements, endowing them with functionality and specificity. Consequently, the functional contribution of each individual structure of the brain cannot, in principle, 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 damage, to a greater or lesser extent, usually accompany brain pathology (see) and are part of its symptoms. Usually patol, the processes affect not only K. g. m., but also the white matter of the hemispheres. Therefore, the pathology of K. g.m. is usually understood as its predominant lesion (diffuse or local, without a strict boundary between these concepts). The most extensive and intense lesion of the K. g. m. is accompanied by the disappearance of mental activity, a complex of both diffuse and local symptoms (see Apallic syndrome). Along with neurol, symptoms of damage to the motor and sensory spheres, symptoms of damage to various analyzers in children are a delay in speech development and even the complete impossibility of mental development. In K. g.m., changes in cytoarchitectonics are observed in the form of disruption of layering, up to its complete disappearance, foci of loss of neurocytes with their replacement by glial growths, heterotopia of neurocytes, pathology of the synaptic apparatus and other pathomorphological changes. Lesions of K. g. m. are observed with various congenital anomalies of the brain in the form of anencephaly, microgyria, microcephaly, with various forms of oligophrenia (see), as well as with a variety of infections and intoxications with damage to the nervous system, with traumatic brain injuries, with hereditary and degenerative brain diseases, cerebrovascular accidents, etc.
Studying the EEG when localizing patol, a focus in K. g. m. more often reveals the predominance of focal slow waves, which are considered as a correlate of protective inhibition (W. Walter, 1966). Weak expression of slow waves in the area of the patol lesion is a useful diagnostic sign in the preoperative assessment of the condition of patients. As studies by N.P. Bekhtereva (1974), conducted jointly with neurosurgeons, showed, the absence of slow waves in the area of pathol, the focus is an unfavorable prognostic sign of the consequences of surgical intervention. To assess patol, the state of K. g.m., a test for the interaction of the EEG in the zone of focal lesion with evoked activity in response to positive and differentiating conditioned stimuli is also used. The bioelectric effect of such 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. Factor of structural integration in brain activity, Usp. Physiol, Sciences, vol. 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 M. N. Spatial organization of brain processes, M., 1972, bibliogr.; Luria A. R. Higher human cortical functions and their disorders in local brain lesions, 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, Leningrad, 1964, bibliogr.; Polyakov G.I. Fundamentals of the taxonomy of neurons in the human neocortex, M., 1973, bibliogr.; Cytoarchitecture of the human cerebral cortex, ed. S. A. Sarkisova et al., p. 187, 203, M., 1949; Schade 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., u. 25, p. 277, 1974, bibliogr.; S h o 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.
N. Yu. Belenkov.
Cortex
brain: cortex (cerebral cortex) - 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 the width, density, shape and size of the nerve cells included in them.
The cerebral cortex is divided into a number of areas: for example, in the most common classification of cytoarchitectonic formations by K. Brodmann, 11 areas and 52 fields are identified in the human cortex. Based on phylogenetic data, a new cortex, or neocortex, is distinguished; old, or archicortex; and ancient, or paleocortex. According to functional criteria, three types of areas are distinguished: sensory zones, providing reception and analysis of afferent signals coming from specific relay nuclei of the thalamus; motor zones, which have bilateral intracortical connections with all sensory areas for the interaction of sensory and motor zones; and associative zones, which do not have direct afferent or efferent connections with the periphery, but are associated with sensory and motor zones.
Dictionary of a practical psychologist. - M.: AST, Harvest. S. Yu. Golovin. 1998.
Anatomical and physiological subsystem of the nervous system.
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 the width, density, shape and size of the nerve cells included in them.Structure.
The cerebral cortex is divided into a number of regions, for example, in the most common classification of cytoarchitectonic formations by K. Brodman, 11 regions and 52 fields are identified in the human cerebral cortex. Based on phylogenetic data, the new cortex, or neocortex, the old, or archicortex, and the ancient, or paleocortex, are distinguished. According to the functional criterion, three types of areas are distinguished: sensory areas, which provide the reception and analysis of afferent signals coming from specific relay nuclei of the thalamus, motor areas, which have bilateral intracortical connections with all sensory areas for the interaction of sensory and motor areas, and associative areas, which do not have direct afferent or efferent connections with the periphery, but associated with sensory and motor areas. Psychological Dictionary
CORTEX
. THEM. Kondakov. 2000. (English) cerebral cortex ) - superficial layer covering the cerebral hemispheres brain , formed predominantly by vertically oriented nerve cells (neurons) and their processes, as well as bundles(afferent centripetal ) And(efferent centrifugal
) nerve fibers. In addition, the cortex includes neuroglial cells.
A characteristic feature of the structure of the blood cell is horizontal layering, caused by the ordered arrangement of nerve cell bodies and nerve fibers. In the K. g. m. there are 6 (according to some authors, 7) layers, differing in width, 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, the K. g. m. has vertical striations. For the functional organization of the circulatory system, the vertical, columnar arrangement of nerve cells is of great importance. The main type of nerve cells that make up the K. g. m. are. The body of these cells resembles a cone, from the apex of which one thick and long apical dendrite extends; heading towards the surface of the K. g. m., it becomes thinner and fan-shapedly divided into thinner terminal branches. Shorter basal dendrites extend from the base of the pyramidal cell body and , heading into the white matter located under the K. g. 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 coming to the K. g.m. from other parts of the cortex and subcortical formations (see. ). The axons of pyramidal cells form the main efferent pathways coming from the K. g.m. The sizes of pyramidal cells vary from 5-10 microns to 120-150 microns (Betz giant cells). In addition to pyramidal neurons, the K. g. m. includes star-shaped,fusiform and some other types of interneurons involved in receiving afferent signals and forming functional interneuron connections.
Based on the characteristics of the distribution of nerve cells and fibers of different sizes and shapes in the layers of the cortex, the entire territory of the cerebral cortex is divided into a number regions(for example, occipital, frontal, temporal, etc.), and the latter - into more fractional cytoarchitectonic fields, differing in their cellular structure and functional significance. The generally accepted classification of cytoarchitectonic formations of the human hematopoietic system is proposed by K. Brodmann, who divided the entire human hemodynamic system into 11 regions and 52 fields.
Based on phylogenetic data, K. g. m. are divided into new ( neocortex), old ( archicortex) and ancient ( paleocortex). In the phylogenesis of the K. g.m., 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 crust. In humans, the neocortex accounts for 95.6%, while the ancient occupies 0.6%, and the old 2.2% of the total 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 areas are localized in certain areas of the cortex: visual located in the occipital region (fields 17, 18, 19), auditory in the upper parts of the temporal region (fields 41, 42), somatosensory, analyzing impulses coming from receptors of the skin, muscles, joints - in the area 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.
Motor(motor) area - Brodmann's area 4 - is located on the precentral gyrus. The motor cortex is characterized by the presence in layer V of Betz giant 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.
Associative 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 parts of the cortex they are located between the parietal, occipital and temporal sensory areas, and in the anterior parts they occupy the main surface of the frontal lobes. The association cortex is either absent or poorly developed in all mammals up to primates. In humans, the posterior association cortex occupies approximately half, and the frontal regions, a quarter of the entire surface of the cortex. In structure, they are distinguished by the 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.
The associative cortex also contains centers associated with speech activity (see. And ). 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 when the posterior associative areas are damaged, complex forms of orientation in space and constructive activity are disrupted, and the performance of all intellectual operations that involve spatial analysis (counting, perception of complex semantic images) becomes difficult. When speech zones are damaged, the ability to perceive and reproduce speech is impaired. Damage to the frontal cortex leads to the impossibility of implementing complex behavioral programs that require the selection of significant signals based on past experience and anticipation of the future. Cm. , , , , , . (D. A. Farber.)
Large psychological dictionary. - M.: Prime-EVROZNAK. Ed. B.G. Meshcheryakova, acad. V.P. Zinchenko. 2003 .
Cortex
A 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 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; corresponding areas of the cerebral cortex are involved in planning movements (frontal lobes) or are associated with memory and perception ().
Psychology. AND I. Dictionary reference / Transl. from English K. S. Tkachenko. - M.: FAIR PRESS. Mike Cordwell. 2000.
See what “cerebral cortex” is in other dictionaries:
CORTEX- CEREBRAL CORTEX, the outer layer of the cerebral hemispheres covered with deep convolutions. The cortex, or “gray matter,” is the most complexly organized part of the brain; its purpose is perception of sensations, control... ... Scientific and technical encyclopedic dictionary
Cortex- 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 … The cerebral cortex is divided into a number of regions, for example, in the most common classification of cytoarchitectonic formations by K. Brodman, 11 regions and 52 fields are identified in the human cerebral cortex. Based on phylogenetic data, the new cortex, or neocortex, the old, or archicortex, and the ancient, or paleocortex, are distinguished. According to the functional criterion, three types of areas are distinguished: sensory areas, which provide the reception and analysis of afferent signals coming from specific relay nuclei of the thalamus, motor areas, which have bilateral intracortical connections with all sensory areas for the interaction of sensory and motor areas, and associative areas, which do not have direct afferent or efferent connections with the periphery, but associated with sensory and motor areas.
cortex- honey The brain is the most voluminous of the elements of the central nervous system. It consists of two lateral parts, the cerebral hemispheres connected to one another, and the underlying elements. It weighs about 1200 g. Two hemispheres of the brain... ... Universal additional practical explanatory dictionary by I. Mostitsky
Cortex- Thin (2 mm) outer shell of the cerebral hemispheres. The human cerebral cortex is the center of higher cognitive processes and sensorimotor information processing... Psychology of sensations: glossary
cortex- Cortex/ cerebral hemispheres. The superficial layer of the brain in higher vertebrates and humans... Dictionary of many expressions
Cortex- Central nervous system (CNS) I. Cervical nerves. II. Thoracic nerves. III. Lumbar nerves. IV. Sacral nerves. V. Coccygeal nerves. / 1. Brain. 2. Diencephalon. 3. Midbrain. 4. Bridge. 5. Cerebellum. 6. Medulla oblongata. 7.… …Wikipedia
CORTEX- The surface covering the gray matter, which forms the uppermost level of the brain. In an evolutionary sense, it is the newest neural formation, and its approximately 9 12 billion cells are responsible for basic sensory functions,... ... Explanatory dictionary of psychology
cortex- see Cora... Large medical dictionary
Cerebral Cortex, Cerebral Cortex- the outer layer of the large brain, which has a complex structure, which accounts for up to 40% of the weight of the entire brain and which contains approximately 15 billion neurons (see Gray matter). The cerebral cortex is directly responsible for the psyche... ... Medical terms
cerebral cortex, cerebral cortex- (cerebral cortex) the outer layer of the large brain with a complex structure, which accounts for up to 40% of the weight of the entire brain and contains approximately 15 billion neurons (see Gray matter). The cerebral cortex directly responds... ... Explanatory dictionary of medicine
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- How emotions affect abstract thinking and why mathematics is incredibly accurate. How the cerebral cortex is structured, why its capabilities are limited and how emotions, complementing the work of the cortex, allow a person to make scientific discoveries, A. G. Sverdlik. Mathematics, unlike other disciplines, is universal and extremely accurate. It creates the logical structure of all natural sciences. “The incomprehensible effectiveness of mathematics”, as in its time...
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