Cortex. New cortex Structural features of the cerebral cortex

So, the area of ​​the cerebral cortex of one hemisphere of a person is about 800 - 2200 square meters. see, thickness - 1.5 × 5 mm. Most of the bark (2/3) lies deep in the furrows and is not visible from the outside. Thanks to this organization of the brain, in the process of evolution, it was possible to significantly increase the area of ​​the cortex with a limited volume of the skull. The total number of neurons in the cortex can reach 10-15 billion.

The cerebral cortex itself is heterogeneous, therefore, in accordance with phylogeny (by origin), the ancient cortex (paleocortex), the old cortex (archicortex), the intermediate (or middle) cortex (mesocortex) and the new cortex (neocortex) are distinguished.

ancient bark

Ancient bark, (or paleocortex)- this is the most simple structure of the cerebral cortex, which contains 2-3 layers of neurons. According to a number of well-known scientists such as H. Fenish, R. D. Sinelnikov and Ya. R. Sinelnikov, who indicate that the ancient cortex corresponds to the region of the brain that develops from the piriform lobe, and the components of the ancient cortex are the olfactory tubercle and the cortex surrounding it, including area of ​​the anterior perforated substance. The composition of the ancient cortex includes the following structural formations such as the prepiriform, periamygdala area of ​​the cortex, the diagonal cortex and the olfactory brain, including the olfactory bulbs, olfactory tubercle, septum pellucidum, nuclei of the septum pellucidum and fornix.

According to M. G. Prives and a number of some scientists, the olfactory brain is topographically divided into two sections, including a number of formations and convolutions.

1. peripheral section (or olfactory lobe) which includes formations lying on the basis of the brain:

olfactory bulb;

olfactory tract;

olfactory triangle (inside which is the olfactory tubercle, i.e., the top of the olfactory triangle);

internal and lateral olfactory gyrus;

internal and lateral olfactory strips (the fibers of the internal strip end in the subcallosal field of the paraterminal gyrus, the transparent septum and in the anterior perforated substance, and the fibers of the lateral strip end in the parahippocampal gyrus);

anterior perforated space, or substance;

diagonal stripe, or Broca's strip.

2. the central department includes three convolutions:

parahippocampal gyrus (hippocampal gyrus, or seahorse gyrus);

dentate gyrus;

cingulate gyrus (including its anterior part - hook).

Old and intermediate bark

Old bark (or archicortex)-- this cortex appears later than the ancient cortex and contains only three layers of neurons. It consists of the hippocampus (seahorse or ammon horn) with its base, dentate gyrus and cingulate gyrus. cerebral cortex neuron

Intermediate bark (or mesocortex)-- representing a five-layer fate of the cortex, separating the new cortex (neocortex), from the ancient cortex (paleocortex) and the old cortex (archicortex) and because of this, the middle cortex is divided into two zones:

• 1. peripaleocortical;
• 2. periarchiocortical.

According to V. M. Pokrovsky and G. A. Kuraev, the composition of the mesocortex includes the ostauvial, as well as in the entorial region, the parahippocampal gyrus bordering the old cortex and the pre-basement of the hippocampus.

According to R. D. Sinelnikov and Ya. R. Sinelnikov, the intermediate cortex includes such formations as the lower part of the insular lobe, the parahippocampal gyrus and the lower part of the limbic region of the cortex. But at the same time, it is necessary to understand that the limbic region is understood as part of the new cortex of the cerebral hemispheres, which occupies the cingulate and parahippocampal gyrus. There is also an opinion that the intermediate cortex is an incompletely differentiated zone of the cortex of the island (or visceral cortex).

Due to the ambiguity of such an interpretation of the structures related to the ancient and old crust, it has translated into the expediency of using the combined concept as the archiopaleocortex.

The structures of the archiopaleocortex have multiple connections, both among themselves and with other brain formations.

New bark

New bark (or neocortex)- phylogenetically, that is, in its origin - this is the latest formation of the brain. Due to the later evolutionary emergence and rapid development of the new cerebral cortex in its organization of complex forms of higher nervous activity and its highest hierarchical level, which is vertically coordinated with the activity of the central nervous system, making up the most features of this part of the brain. For many years, the features of the neocortex have attracted and continue to hold the attention of many researchers studying the physiology of the cerebral cortex. At present, the old ideas about the monopoly participation of the new cortex in the formation of complex forms of behavior, including conditioned reflexes, have been replaced by the idea of ​​it as the highest level of thalamocortical systems functioning in conjunction with the thalamus, limbic and other brain systems. The neocortex is involved in the mental experience of the external world - its perception and creation of its images, which persist for a more or less long time.

A feature of the structure of the new cortex is the screen principle of its organization. The main thing in this principle - the organization of neural systems - is the geometric distribution of projections of higher receptor fields on a large surface of the neuronal field of the cortex. Also for the screen organization is the characteristic organization of cells and fibers that run perpendicular to the surface or parallel to it. This orientation of cortical neurons provides opportunities for combining neurons into groupings.

As for the cellular composition in the neocortex, it is very diverse, the size of neurons is approximately from 8–9 µm to 150 µm. The vast majority of cells belong to two types - pramid and stellate. There are also spindle-shaped neurons in the neocortex.

In order to better consider the features of the microscopic structure of the cerebral cortex, it is necessary to turn to architectonics. Under the microscopic structure, cytoarchitectonics (cellular structure) and myeloarchitectonics (fibrous structure of the cortex) are distinguished. The beginning of the study of the architectonics of the cerebral cortex dates back to the end of the 18th century, when in 1782 Gennari first discovered the heterogeneity of the structure of the cortex in the occipital lobes of the hemispheres. In 1868, Meinert divided the diameter of the cerebral cortex into layers. In Russia, the first researcher of the cortex was V. A. Betz (1874), who discovered large pyramidal neurons in the 5th layer of the cortex in the region of the precentral gyrus, named after him. But, there is another division of the cerebral cortex - the so-called Brodmann field map. In 1903, the German anatomist, physiologist, psychologist and psychiatrist K. Brodman published a description of fifty-two cytoarchitectonic fields, which are sections of the cerebral cortex, different in their cellular structure. Each such field differs in size, shape, location of nerve cells and nerve fibers, and, of course, different fields are associated with different functions of the brain. Based on the description of these fields, a map of 52 Brodman fields was compiled

Neocortex - evolutionarily the youngest part of the cortex, occupying most of the surface of the hemispheres. Its thickness in humans is approximately 3 mm.

The cellular composition of the neocortex is very diverse, but approximately three-quarters of the neurons of the cortex are pyramidal neurons (pyramids), and therefore one of the main classifications of cortical neurons divides them into pyramidal and non-iramide (fusiform, stellate, granular, candelabra cells, Martinotti cells, etc. .). Another classification is related to the length of the axon (see section 2.4). The long-axon Golgi I cells are mainly pyramids and spindles, their axons can exit the cortex, the rest of the cells are short-axon Golgi II.

Cortical neurons also differ in the size of the cell body: the size of ultra-small neurons is 6x5 microns, the size of giant ones is more than 40 x 18. The largest neurons are the Betz pyramids, their size is 120 x 30-60 microns.

Pyramidal neurons (see Fig. 2.6, G) have the shape of a body in the form of a pyramid, the top of which is directed upwards. An apical dendrite extends from this apex and ascends into the overlying cortical layers. Basal dendrites extend from the rest of the soma. All dendrites have spines. A long axon departs from the base of the cell, forming numerous collaterals, including recurrent ones, which bend and rise upwards. Stellate cells do not have an apical dendrite; spinules on dendrites are absent in most cases. In fusiform cells, two large dendrites depart from opposite poles of the body, there are also small dendrites extending from the rest of the body. Dendrites have spines. The axon is long, slightly branching.

During embryonic development, the new cortex necessarily passes through the stage of a six-layer structure, with maturation in some areas the number of layers may decrease. The deep layers are phylogenetically older, the outer layers are younger. Each layer of the cortex is characterized by its neuronal composition and thickness, which can differ from each other in different areas of the cortex.

Let's list layers of neocortex(Fig. 9.8).

I layer - molecular- the outermost, contains a small number of neurons and mainly consists of fibers running parallel to the surface. Dendrites of neurons located in the underlying layers also rise here.

II layer - outer granular, or outer granular, - consists mainly of small pyramidal neurons and a small number of medium-sized stellate cells.

III layer - external pyramidal - the widest and thickest layer, contains mainly small and medium-sized pyramidal and stellate neurons. In the depths of the layer are large and giant pyramids.

IV layer - internal granular, or internal granular, - consists mainly of small neurons of all varieties, there are also a few large pyramids.

V layer - internal pyramidal, or ganglionic a characteristic feature of which is the presence of large and in some areas (mainly in fields 4 and 6; Fig. 9.9; subsection 9.3.4) - giant pyramidal neurons (Betz pyramids). The apical dendrites of the pyramids, as a rule, reach the first layer.

VI layer - polymorphic, or multiform, - contains predominantly spindle-shaped neurons, as well as cells of all other forms. This layer is divided into two sublayers, which a number of researchers consider as independent layers, speaking in this case of a seven-layer bark.

Rice. 9.8.

a- Neurons are stained as a whole; b- only the bodies of neurons are painted; in- painted

only processes of neurons

Main functions each layer is also different. Layers I and II carry out connections between neurons of different layers of the cortex. Callosal and associative fibers mainly come from the pyramids of layer III and come to layer II. The main afferent fibers entering the cortex from the thalamus terminate on layer IV neurons. Layer V is mainly associated with the system of descending projection fibers. The axons of the pyramids of this layer form the main efferent pathways of the cerebral cortex.

In most cortical fields, all six layers are equally well expressed. Such a bark is called homotypic. However, in some fields, the severity of the layers may change during development. This bark is called heterotypic. It is of two types:

granular (zeros 3, 17, 41; Fig. 9.9), in which the number of neurons in the outer (II) and especially in the inner (IV) granular layers is greatly increased, as a result of which the IV layer is divided into three sublayers. Such a cortex is characteristic of primary sensory areas (see below);

Agranular (fields 4 and 6, or motor and premotor cortex; Fig. 9.9), in which, on the contrary, there is a very narrow II layer and practically no IV, but very wide pyramidal layers, especially the inner one (V).

By origin, the cerebral cortex is divided into ancient (pleocortex), old (archecortex) and new (neocortex). The ancient cortex includes structures associated with the analysis of olfactory stimuli, it includes olfactory bulbs, tracts and tubercles. The old cortex includes the cingulate cortex, the hippocampal cortex, the dentate gyrus, and the amygdala. The ancient and old cortex forms the olfactory brain. In addition to the sense of smell, the olfactory brain provides reactions of alertness and attention, takes part in the regulation of vegetative functions, plays a role in the formation of sexual, nutritional, defensive instinctive behavior, and provides emotions.

All other structures of the cortex belong to the neocortex, which occupies about 96% of the total area of ​​the entire cortex.

The arrangement of nerve cells in the cortex is designated by the term "cytoarchitectonics". And conductive fibers - "myeloarchitectonics".

The neocortex is composed of 6 cell layers, differing in cell composition, neural connections and functions. In the areas of the ancient cortex and the old cortex, only 2-3 layers of cells are revealed. Neurons in the upper four layers of the neocortex primarily process information from other parts of the nervous system. The main centrifugal layer is the 5th layer. The axons of its cells form the main descending pathways of the cerebral cortex, they carry signals that control the work of the stem structures and the spinal cord.

1 layer - the outermost, molecular. It contains mainly nerve fibers of deeper located neurons. In addition, it contains a small number of small cells. The fibers of the molecular layer form connections between different areas of the cortex

Layer 2 - outer granular. It contains a large number of small multipolar neurons. In this layer, part of the ascending dendrites from the third layer ends.

3rd layer - outer pyramidal. It is the widest, contains mainly medium and less often small and large pyramidal neurons. Dendrites of neurons from this layer are sent to the second layer.

4 layer - internal granular. It consists of a large number of small granular, as well as medium and large stellate cells. They are divided into two sublayers: 4a and 4b.

Layer 5 - ganglionic, or internal pyramidal. It is characterized by the presence of large pyramidal neurons. Their upwardly directed dendrites reach the molecular layer, and the basal and collateral axons are distributed in the fifth layer.

6th layer - polymorphic. It contains, along with cells of other forms, spindle-shaped neurons. The shapes of other cells are very diverse: they have a triangular, pyramidal, oval and polygonal shape.

Topic 14

Physiology of the brain

PartV

New cerebral cortex

The new cortex (neocortex) is a layer of gray matter with a total area of ​​1500-2200 cm 2, covering the large hemispheres of the telencephalon. It makes up about 40% of the mass of the brain. There are about 14 billion neurons and about 140 billion glial cells in the cortex. The cerebral cortex is phylogenetically the youngest nervous structure. In humans, it carries out the highest regulation of body functions and psychophysiological processes that provide various forms of behavior.

Structural and functional characteristics of the cortex. The cerebral cortex consists of six horizontal layers, located in the direction from the surface to the depth.

molecular layer has very few cells, but a large number of branching dendrites of pyramidal cells forming a plexus parallel to the surface. On these dendrites, afferent fibers form synapses, coming from the associative and nonspecific nuclei of the thalamus.

Outer granular layer composed mainly of stellate and partially small pyramidal cells. The fibers of the cells of this layer are located mainly along the surface of the cortex, forming corticocortical connections.

Outer pyramidal layer consists mainly of pyramidal cells of medium size. The axons of these cells, like the granular cells of layer II, form corticocortical associative connections.

Inner granular layer in terms of the nature of the cells and the arrangement of their fibers, it is similar to the outer granular layer. On the neurons of this layer, synaptic endings form afferent fibers coming from the neurons of the specific nuclei of the thalamus and, consequently, from the receptors of sensory systems.

Inner pyramidal layer It is formed by medium and large pyramidal cells, with Betz's giant pyramidal cells located in the motor cortex. The axons of these cells form efferent corticospinal and corticobulbar motor pathways.

Layer of polymorphic cells It is formed mainly by spindle-shaped cells, the axons of which form the corticothalamic pathways.

▓ Afferent and efferent connections of the cortex. In layers I and IV, the perception and processing of signals entering the cortex occurs. Neurons of II and III layers carry out corticocortical associative connections. The efferent pathways leaving the cortex are formed mainly in the V-VI layers. A more detailed division of the cortex into different fields was carried out on the basis of cytoarchitectonic features (the shape and location of neurons) by K. Brodman, who identified 11 areas, including 52 fields, many of which are characterized by functional and neurochemical features. According to Brodman, the frontal area includes 8, 9, 10, 11, 12, 44, 45, 46, 47 fields. The precentral region includes fields 4 and 6, and the postcentral region includes fields 1, 2, 3, and 43. The parietal region includes fields 5, 7, 39, 40, and the occipital region 17 18 19. The temporal region consists of a very large number of cytoarchitectonic fields: 20, 21, 22, 36, 37, 38, 41, 42, 52.

Fig.1. Cytoarchitectonic fields of the human cerebral cortex (according to K. Brodman): a - the outer surface of the hemisphere; b - the inner surface of the hemisphere.

Histological data show that the elementary neural circuits involved in information processing are located perpendicular to the surface of the cortex. In the motor and various areas of the sensory cortex, there are neuronal columns with a diameter of 0.5-1.0 mm, which represent a functional association of neurons. Neighboring neuronal columns can partially overlap, as well as interact with each other by the mechanism of lateral inhibition and carry out self-regulation by the type of recurrent inhibition.

In phylogenesis, the role of the cerebral cortex in the analysis and regulation of body functions and the subordination of the underlying parts of the central nervous system increases. This process is called corticolization functions.

The feature localization problem has three concepts:

The principle of narrow localizationism - all functions are placed in one, separately taken structure.

The concept of equipotentialism - different cortical structures are functionally equivalent.

The principle of multifunctionality of cortical fields. The property of multifunctionality allows this structure to be included in the provision of various forms of activity, while realizing the main, genetically inherent function. The degree of multifunctionality of different cortical structures is not the same: for example, in the fields of the associative cortex it is higher than in the primary sensory fields, and in the cortical structures it is higher than in the stem ones. The multifunctionality is based on the multichannel input of afferent excitation into the cerebral cortex, the overlap of afferent excitations, especially at the thalamic and cortical levels, the modulating effect of various structures (nonspecific thalamus, basal ganglia) on cortical functions, the interaction of cortical-subcortical and intercortical pathways for conducting excitation.

One of the largest options for the functional division of the new cerebral cortex is the allocation of sensory, associative and motor areas in it.

Sensory areas of the cerebral cortex. Sensory areas of the cortex are areas into which sensory stimuli are projected. The sensory areas of the cortex are otherwise called: the projection cortex or the cortical sections of the analyzers. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways to the sensory cortex come predominantly from specific sensory nuclei of the thalamus (ventral, posterior lateral, and medial). The sensory cortex has well-defined layers II and IV and is called granular .

Areas of the sensory cortex, irritation or destruction of which causes clear and permanent changes in the sensitivity of the body, are called primary sensory areas . They consist mainly of monomodal neurons and form sensations of the same quality. Primary sensory areas usually have a clear spatial (topographic) representation of body parts, their receptor fields. Around the primary sensory areas are less localized secondary sensory areas , whose polymodal neurons respond to the action of several stimuli.

╠ The most important sensory area is the parietal cortex of the postcentral gyrus and the corresponding part of the paracentral lobule on the medial surface of the hemispheres (fields 1-3), which is referred to as the primary somatosensory area (S I). Here there is a projection of skin sensitivity of the opposite side of the body from tactile, pain, temperature receptors, interoceptive sensitivity and sensitivity of the musculoskeletal system from muscle, articular and tendon receptors. The projection of body parts in this area is characterized by the fact that the projection of the head and upper parts of the body is located in the inferolateral areas of the postcentral gyrus, the projection of the lower half of the trunk and legs is in the upper medial zones of the gyrus, the projection of the lower part of the lower leg and feet is in the cortex of the paracentral lobule on the medial surface of the hemispheres . At the same time, the projection of the most sensitive areas (tongue, lips, larynx, fingers) has relatively large zones compared to other parts of the body (see Fig. 2). It is assumed that the projection of taste sensitivity is also located in the zone of tactile sensitivity of the tongue.

In addition to S I, a smaller secondary somatosensory area is isolated (S II). It is located on the upper wall of the lateral furrow, on the border of its intersection with the central furrow. The functions of S II are poorly understood. It is known that the localization of the body surface in it is less clear, the impulse comes here both from the opposite side of the body and from the "own" side, suggesting its participation in the sensory and motor coordination of the two sides of the body.

╠ Another primary sensory area is the auditory cortex (fields 41, 42), which is located deep in the lateral sulcus (the cortex of the transverse temporal gyri of Heschl). In this zone, in response to irritation of the auditory receptors of the organ of Corti, sound sensations are formed that change in volume, tone, and other qualities. Here it has a clear topical projection: in different parts of the cortex, different parts of the organ of Corti are represented. The projection cortex of the temporal lobe also includes the center of the vestibular analyzer in the superior and middle temporal gyri (fields 20 and 21). The processed sensory information is used to form the "body map" and regulate the functions of the cerebellum (temporocerebellar tract).

Fig.2. Diagram of the sensory and motor homunculi. Section of the hemispheres in the frontal plane: a - projection of general sensitivity in the cortex of the postcentral gyrus; b - projection of the motor system in the cortex of the precentral gyrus.

╠ Another primary projection area of ​​the new cortex is located in the occipital cortex - the primary visual area (cortex of the sphenoid gyrus and lingular lobule, field 17). Here it has a topical representation of retinal receptors, and each point of the retina corresponds to its own area of ​​the visual cortex, while the zone of the macula has a large zone of representation. In connection with the incomplete decussation of the visual pathways, the same halves of the retina are projected into the visual region of each hemisphere. The presence in each hemisphere of the projection of the retina of both eyes is the basis of binocular vision. Irritation of the cortex of the 17th field leads to the appearance of light sensations. Near field 17 is the cortex of the secondary visual area (fields 18 and 19). The neurons of these zones are polymodal and respond not only to light, but also to tactile and auditory stimuli. In this visual area, a synthesis of various types of sensitivity occurs and more complex visual images and their identification arise. Irritation of these fields causes visual hallucinations, obsessive sensations, eye movements.

The main part of the information about the environment and the internal environment of the body, received in the sensory cortex, is transmitted for further processing to the associative cortex.

Association areas of the cortex. Associative areas of the cortex include areas of the new cortex located near the sensory and motor areas, but not directly performing sensory and motor functions. The boundaries of these areas are not clearly marked, the uncertainty is mainly associated with the secondary projection zones, the functional properties of which are transitional between the properties of the primary projection and associative zones. In humans, the association cortex makes up 70% of the neocortex.

The main physiological feature of the neurons of the associative cortex is polymodality: they respond to several stimuli with almost the same strength. Polymodality (polysensory) neurons of the associative cortex is created due, firstly, to the presence of corticocortical connections with different projection zones, and secondly, due to the main afferent input from the associative nuclei of the thalamus, in which complex processing of information from various sensory pathways has already taken place. As a result, the associative cortex is a powerful apparatus for the convergence of various sensory excitations, which makes it possible to perform complex processing of information about the external and internal environment of the body and use it to implement higher psychophysiological functions. In the associative cortex, there are three associative systems of the brain: thalamo-temporal, thalamo-frontal, and thalamo-temporal.

╠ thalamotenal system represented by the associative zones of the parietal cortex (fields 5, 7, 40), which receive the main afferent inputs from the posterior group of the associative nuclei of the thalamus (lateral posterior nucleus and pillow). The parietal association cortex has efferent outputs to the nuclei of the thalamus and hypothalamus, the motor cortex, and the nuclei of the extrapyramidal system. The main functions of the thalamo-temporal system are gnosis, the formation of a "body schema" and praxis. Under gnosis understand the function of various types of recognition: shapes, sizes, meanings of objects, understanding of speech, knowledge of processes, patterns. Gnostic functions include the evaluation of spatial relationships. In the parietal cortex, a center of stereognosis is isolated, located behind the middle sections of the postcentral gyrus (fields 7, 40, partially 39) and providing the ability to recognize objects by touch. A variant of the gnostic function is the formation in the mind of a three-dimensional model of the body (“body scheme”), the center of which is located in field 7 of the parietal cortex. Under praxis understand purposeful action, its center is located in the supramarginal gyrus (fields 39 and 40 of the dominant hemisphere). This center ensures the storage and implementation of the program of motorized automated acts.

╠ Thalamolobic system represented by associative zones of the frontal cortex (fields 9-14), which have the main afferent input from the associative mediodorsal nucleus of the thalamus. The main function of the frontal associative cortex is the formation of goal-directed behavior programs, especially in a new environment for a person. The implementation of this general function is based on other functions of the thalamo-frontal system: 1) the formation of the dominant motivation that provides the direction of human behavior. This function is based on the close bilateral connections of the pubic cortex with the limbic system and the role of the latter in the regulation of higher human emotions associated with its social activity and creativity .; 2) providing probabilistic forecasting, which is expressed by a change in behavior in response to changes in the environment and the dominant motivation; 3) self-control of actions by constantly comparing the result of an action with the original intentions, which is associated with the creation of a foresight apparatus (acceptor of the result of an action).

When the prefrontal cortex, where the connections between the frontal lobe and the thalamus intersect, is damaged, a person becomes rude, tactless, unreliable, he has a tendency to repeat any motor acts, although the situation has already changed and other actions must be performed.

╠ thalamotemporal system not studied enough. But if we talk about the temporal cortex, then it should be noted that some associative centers, such as stereognosis and praxis, also include sections of the temporal cortex (field 39). In the temporal cortex, the auditory center of Wernicke's speech is located, located in the posterior sections of the superior temporal gyrus (fields 22, 37, 42 of the left dominant hemisphere). This center provides speech gnosis - recognition and storage of oral speech, both one's own and someone else's. In the middle part of the superior temporal gyrus (field 22) there is a center for recognizing musical sounds and their combinations. On the border of the temporal, parietal and occipital lobes (field 39) there is a center for reading written speech, which provides recognition and storage of images of written speech.

Motor areas of the cortex. The motor cortex is divided into primary and secondary motor areas.

╠ In the primary motor cortex(precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and limbs. It has a clear topographic projection of the muscles of the body. At the same time, the projections of the muscles of the lower extremities and the trunk are located in the upper parts of the precentral gyrus and occupy a relatively small area, and the projection of the muscles of the upper extremities, face and tongue are located in the lower parts of the gyrus and occupy a large area (see Fig. 2). The main pattern of topographic representation is that the regulation of the activity of muscles that provide the most accurate and diverse movements (speech, writing, facial expressions) requires the participation of large areas of the motor cortex. Motor reactions to irritation of the primary motor cortex are carried out with a minimum threshold (high excitability), and are represented by elementary contractions of the muscles of the opposite side of the body (for the muscles of the head, the contraction can be bilateral). With the defeat of this area of ​​​​the cortex, the ability to fine coordinated movements of the hands, especially fingers, is lost.

╠ secondary motor cortex(field 6) is located on the lateral surface of the hemispheres, in front of the precentral gyrus (premotor cortex). It performs higher motor functions associated with the planning and coordination of voluntary movements. The cortex of field 6 receives the main part of the efferent impulses of the basal nuclei and the cerebellum and is involved in recoding information about the program of complex movements. Irritation of the cortex of field 6 causes more complex coordinated movements, for example, turning the head, eyes and torso in the opposite direction, friendly contractions of the flexor muscles or extensor muscles on the opposite side. The premotor cortex contains motor centers associated with human social functions: the center of written speech in the posterior part of the middle frontal gyrus (field 6), the center of Broca's motor leak in the posterior part of the inferior frontal gyrus (field 44), which provides speech praxis, as well as musical motor center (field 45), which determines the tone of speech, the ability to sing.

▓ Afferent and efferent connections of the motor cortex. In the motor cortex, a layer containing Betz's giant pyramidal cells is better expressed than in other areas of the cortex. Motor cortex neurons receive afferent inputs through the thalamus from muscle, joint, and skin receptors, as well as from the basal ganglia and the cerebellum. The main efferent output of the motor cortex to the stem and spinal motor centers is formed by the pyramidal cells of layer V. Pyramidal and associated intercalary neurons are located vertically with respect to the surface of the cortex and form neural motor columns. Pyramidal neurons of the motor column can excite or inhibit the motor neurons of the stem and spinal centers. Neighboring columns functionally overlap, and pyramidal neurons that regulate the activity of one muscle are usually located not in one, but in several columns.

The main efferent connections of the motor cortex are carried out through the pyramidal and extrapyramidal pathways, which start from the Betz giant pyramidal cells and smaller pyramidal cells of the V layer of the cortex of the precentral gyrus (60% of fibers), premotor cortex (20% of fibers) and postcentral gyrus (20% of fibers) . Large pyramidal cells have fast-conducting axons and a background impulse activity of about 5 Hz, which increases to 20-30 Hz during movement. These cells innervate large (high-threshold) ά-motoneurons in the motor centers of the brainstem and spinal cord that regulate physical movements. Thin slow-conducting myelinated axons depart from small pyramidal cells. These cells have a background activity of about 15 Hz, which increases or decreases during movement. They innervate small (low-threshold) ά-motor neurons in the stem and spinal motor centers that regulate muscle tone.

pyramid paths consist of 1 million fibers of the corticospinal tract, which originate from the cortex of the upper and middle third of the precentral gyrus, and 20 million fibers of the corticobulbar tract, which originate from the cortex of the lower third of the precentral gyrus. The fibers of the pyramidal tract terminate on the ά-motoneurons of the motor nuclei III-VII and IX-XII of the cranial nerves (corticobulbar tract) or on the spinal motor centers (corticospinal tract). Arbitrary simple movements and complex purposeful motor programs, for example, professional skills, are carried out through the motor cortex and pyramidal pathways, the formation of which begins in the basal ganglia and cerebellum and ends in the secondary motor cortex. Most of the fibers of the pyramidal tracts cross, however, a small part of the fibers remain uncrossed, which helps to compensate for impaired movement functions in unilateral lesions. Through the pyramidal pathways, the premotor cortex also performs its functions: motor skills of writing, turning the head, eyes and torso in the opposite direction, as well as speech (Broca's motor speech center, field 44). In the regulation of writing and especially oral speech, there is a pronounced asymmetry of the cerebral hemispheres: in 95% of right-handers and 70% of left-handers, oral speech is controlled by the left hemisphere.

To the cortical extrapyramidal tracts include corticorubral and corticoreticular pathways, starting approximately from those zones that give rise to pyramidal pathways. The fibers of the corticorubral pathway terminate on the neurons of the red nuclei of the midbrain, from which the rubrospinal pathways continue. The fibers of the corticoreticular pathways terminate on the neurons of the medial nuclei of the reticular formation of the pons (the medial reticulospinal pathways originate from them) and on the neurons of the reticular giant cell nuclei of the medulla oblongata, from which the lateral reticulospinal pathways originate. Through these pathways, the regulation of tone and posture is carried out, which provide precise targeted movements. Cortical extrapyramidal pathways are a component of the extrapyramidal system of the brain, which includes the cerebellum, basal ganglia, and motor centers of the brainstem. The extrapyramidal system regulates tone, balance posture, and the performance of learned motor acts, such as walking, running, speech, and writing. Since the corticopyramidal pathways give their numerous collaterals to the structures of the extrapyramidal system, both systems work in a functional unity.

Assessing in general terms the role of various structures of the brain and spinal cord in the regulation of complex directional movements, it can be noted that the impulse (motivation) to move is created in the limbic system, the idea of ​​movement is created in the associative cortex of the cerebral hemispheres, the programs of movements are created in the basal ganglia, cerebellum and premotor cortex, and the execution of complex movements occurs through the motor cortex, motor centers of the brainstem and spinal cord.

Interhemispheric relationships. Interhemispheric relationships in humans manifest themselves in two forms - functional asymmetry of the cerebral hemispheres and their joint activity.

╠ Functional asymmetry of the hemispheres is the most important psychophysiological property of the human brain. Allocate mental, sensory and motor interhemispheric functional asymmetries of the brain. In the study of psychophysiological functions, it was shown that in speech the verbal information channel is controlled by the left hemisphere, and the non-verbal channel (voice, intonation) is controlled by the right. Abstract thinking and consciousness are associated mainly with the left hemisphere. During the development of the conditioned reflex, the right hemisphere dominates in the initial phase, and during the strengthening of the reflex, the left hemisphere dominates. The right hemisphere processes information simultaneously, synthetically, according to the principle of deduction, the spatial and relative features of an object are better perceived. The left hemisphere processes information sequentially, analytically, by the principle of induction, perceives the absolute features of the object and temporal relationships better. In the emotional sphere, the right hemisphere causes predominantly negative emotions, controls the manifestations of strong emotions, in general it is more “emotional”. The left hemisphere causes mainly positive emotions, controls the manifestation of weaker emotions.

In the sensory realm, the role of the right and left hemispheres is best manifested in visual perception. The right hemisphere perceives the visual image holistically, immediately in all details, it is easier to solve the problem of distinguishing objects and identifying visual images of objects, which is difficult to describe in words, creates the prerequisites for concrete-sensory thinking. The left hemisphere evaluates the visual image dissected, analytically, with each feature being analyzed separately. Familiar objects are more easily recognized and tasks of similarity of objects are solved, visual images are devoid of specific details and have a high degree of abstraction; prerequisites for logical thinking are created.

Motor asymmetry is expressed primarily in right-left handedness, which is controlled by the motor cortex of the opposite hemisphere. The asymmetry of other muscle groups is individual, not specific.

Fig.3. Asymmetry of the cerebral hemispheres.

╠ Pairing in the activity of the cerebral hemispheres is provided by the presence of the commissural system (corpus callosum, anterior and posterior, hippocampal and habenular commissures, interthalamic fusion), which anatomically connect the two hemispheres of the brain. In other words, both hemispheres are connected not only by horizontal connections, but also by vertical ones. The main facts obtained with the help of electrophysiological techniques showed that excitation from the area of ​​stimulation of one hemisphere is transmitted through the commissural system not only to the symmetrical area of ​​the other hemisphere, but also to asymmetrical areas of the cortex. The study of the method of conditioned reflexes showed that in the process of developing a reflex, a “transfer” of a temporary connection to the other hemisphere occurs. Elementary forms of interaction between the two hemispheres can be carried out through the quadrigemina and the reticular formation of the trunk.

Brain at the base the latest anatomical... influences bark big hemispheres on the bark cerebellum. Lower reflex centers of the spinal brain and stem parts head brain ...

Man is the only species on earth that is capable, in addition to satisfying the needs dictated by instincts, to carry out emotional, creative and mental activity. The uniqueness of people lies in the presence of vast, highly developed and complexly constructed areas of the brain, which have a generalized name neocortex. Therefore, in the study of man, as a species at the upper stage of evolution, the main directions are questions about the structure and functions of this part of the central nervous system.

General information

Neocortex (new cortex, isocortex or lat. Neocortex) is a region of the cerebral cortex, occupying about 96% of the surface of the hemispheres and having a thickness of 1.5 - 4 mm, which are responsible for the perception of the surrounding world, motor skills, thinking and speech.

The neocortex is made up of three main types of neurons - pyramidal, stellate, and fusiform. The first, the most numerous group, which makes up about 70-80% of the total amount in the brain. The proportion of stellate neurons is at the level of 15-25%, and spindle-shaped - about 5%.

The structure of the neocortex is almost homogeneous and consists of 6 horizontal layers and vertical columns of the cortex. The layers of the new cortex have the following structure:

1. Molecular, consisting of fibers and a small number of small stellate neurons. The fibers form a tangential plexus.
2. Outer granular, formed by small neurons of various shapes, which are associated with the molecular layer over all areas. At the very end of the layer are small pyramidal cells.
3. External pyramidal, consisting of small, medium and large pyramidal neurons. The processes of these cells can be associated with both layer 1 and white matter.
4. Internal granular, which consists mainly of stellate cells. This layer is characterized by a non-dense arrangement of neurons in it.
5. Internal pyramidal, formed by medium and large pyramidal cells, the processes of which are connected with all other layers.
6. Polymorphic, which is based on spindle-shaped neurons connected by processes with the 5th layer and white matter.

In addition, the new cortex is divided into regions, which in turn are subdivided into Brodmann fields. The following areas are distinguished:

1. Occipital (17,18 and 19 fields).
2. Upper parietal (5 and 7).
3. Lower parietal (39 and 40).
4. Postcentral (1, 2, 3 and 43).
5. Precentral (4 and 6).
6. Frontal (5, 9, 10, 11, 12, 32, 44, 45, 46 and 47).
7. Temporal (20, 21, 22, 37, 41 and 42).
8. Limbic (23, 24, 25 and 31).
9. Islet (13 and 14).

Cortex columns are a group of neurons that are perpendicular to the cerebral cortex. Within a small column, all cells perform the same task. But a hypercolumn, consisting of 50-100 minicolumns, can have either one or many functions.

neocortex functions

The new cortex is responsible for the performance of higher nervous functions (thinking, speech, processing information from the senses, creativity, etc.). Clinical trials have shown that each area of ​​the cerebral cortex is responsible for strictly defined functions. For example, human speech is controlled by the left frontal gyrus. However, if any of the areas is damaged, the neighboring one can take over its function, although this requires a long period of time. Conventionally, there are three main groups of functions that the neocortex performs - sensory, motor and associative.

touch

This group includes a set of functions by which a person is able to perceive information from the senses.

Each feeling is analyzed by a separate area, but signals from others are also taken into account.

Signals from the skin are processed by the posterior central gyrus. Moreover, information from the lower extremities enters the upper part of the gyrus, from the body - to the middle, from the head and hands - to the lower. At the same time, only pain and temperature sensations are processed by the posterior central gyrus. The sense of touch is controlled by the upper parietal region.

Vision is controlled by the occipital region. Information is received in field 17, and in fields 18 and 19 it is processed, that is, color, size, shape and other parameters are analyzed.

Hearing is processed in the temporal region.

Charm and taste sensations are controlled by the hippocampal gyrus, which, unlike the general structure of the neocortex, has only 3 horizontal layers.

It should be noted that in addition to the zones of direct reception of information from the senses, there are secondary ones next to them, in which the ratio of the received images with those stored in memory takes place. With damage to these areas of the brain, a person completely loses the ability to recognize incoming data.

Motor

This group includes the functions of the new cortex, with the help of which any movement of the human limbs is carried out. Motor skills are controlled and controlled by the precentral region. The lower limbs depend on the upper parts of the central gyrus, and the upper limbs depend on the lower ones. In addition to the precentral, the frontal, occipital and upper parietal regions are involved in the movement. An important feature of the performance of motor functions is that they cannot be performed without constant connections with sensory areas.

Associative

This group of neocortical functions is responsible for such complex elements of consciousness as thinking, planning, emotional control, memory, empathy, and many others.

Associative functions are performed by the frontal, temporal and parietal regions.

In these parts of the brain, a reaction is formed to the data coming from the sense organs and command signals are sent to the motor and sensory zones.

To receive and control, all sensory and motor areas of the cerebral cortex are surrounded by associative fields, in which the analysis of the received information takes place. But at the same time, it should be taken into account that the data coming into these fields are already initially processed in sensory and motor areas. For example, if there is a malfunction in the work of such a section in the visual area, a person sees and understands that there is an object, but cannot name it and, accordingly, make a decision about his further behavior.

In addition, the frontal lobe of the cortex is very tightly connected to the limbic system, which allows it to control and manage emotional messages and reflexes. This enables a person to take place as a person.

The performance of associative functions in the neocortex is possible due to the fact that the neurons of this part of the central nervous system are able to retain traces of excitation according to the feedback principle, they can persist for a long time (from several years to a lifetime). This ability is a memory, with the help of which associative links of the received information are built.

The role of the neocortex in emotions and stereogenesis

Emotions in humans initially appear in the limbic system of the brain. But in this case, they are represented by primitive concepts, which, getting into the new cortex, are processed with the help of an associative function. As a result, a person can operate with emotions at a higher level, which makes it possible to introduce such concepts as joy, sadness, love, anger, etc.

Also, the neocortex has the ability to dampen strong bursts of emotion in the limbic system by sending calming signals to areas of high neuronal arousal. This leads to the fact that in a person the dominant role in behavior is played by the mind, and not by instinctive reflexes.

Differences from the old bark

The old cortex (archicortex) is an earlier emerging area of ​​the cerebral cortex than the neocortex. But in the process of evolution, the new crust became more developed and extensive. In this regard, the archicortex ceased to play a dominant role and became one of the constituent parts.

If we compare the old and the functions performed, then the first one is assigned the role of fulfilling innate reflexes and motivation, and the second - managing emotions and actions at a higher level.

In addition, the neocortex is much larger than the old cortex. So the first occupies about 96% of the total surface of the hemispheres, and the size of the second - no more than 3%. This ratio shows that the archicortex cannot perform higher nervous functions.