PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM

Bark big brain

The highest division of the central nervous system is the cerebral cortex (cerebral cortex). It ensures the perfect organization of animal behavior based on innate and acquired functions during ontogenesis.

Morphofunctional organization

The cerebral cortex has the following morphofunctional features:

Multilayer arrangement of neurons;

Modular principle of organization;

Somatotopic localization of receptive systems;

Screenness, i.e., the distribution of external reception on the plane of the neuronal field of the cortical end of the analyzer;

Dependence of the level of activity on the influence of subcortical structures and reticular formation;

Availability of representation of all functions of the underlying structures of the central nervous system;

Cytoarchitectonic distribution into fields;

The presence in specific projection sensory and motor systems of secondary and tertiary fields with associative functions;

Availability of specialized associative areas;

Dynamic localization of functions, expressed in the possibility of compensation for the functions of lost structures;

Overlap of zones of neighboring peripheral receptive fields in the cerebral cortex;

Possibility of long-term preservation of traces of irritation;

Reciprocal functional relationship between excitatory and inhibitory states;

The ability to irradiate excitation and inhibition;

The presence of specific electrical activity.

Deep grooves divide each cerebral hemisphere into the frontal, temporal, parietal, occipital lobes and insula. The insula is located deep in the Sylvian fissure and is covered from above by parts of the frontal and parietal lobes of the brain.

The cerebral cortex is divided into ancient (archicortex), old (paleocortex) and new (neocortex). The ancient cortex, along with other functions, is related to smell and ensuring the interaction of brain systems. The old cortex includes the cingulate gyrus and hippocampus. In the neocortex, the greatest development of size and differentiation of functions is observed in humans. The thickness of the neocortex ranges from 1.5 to 4.5 mm and is maximum in the anterior central gyrus.

The functions of individual zones of the neocortex are determined by the peculiarities of its structural and functional organization, connections with other brain structures, participation in the perception, storage and reproduction of information in the organization and implementation of behavior, regulation of the functions of sensory systems and internal organs.

The peculiarities of the structural and functional organization of the cerebral cortex are due to the fact that in evolution there was a corticalization of functions, i.e., the transfer of the functions of underlying brain structures to the cerebral cortex. However, this transfer does not mean that the cortex takes over the functions of other structures. Its role comes down to the correction of possible dysfunctions of systems interacting with it, a more advanced, taking into account individual experience, analysis of signals and the organization of an optimal response to these signals, the formation in one’s own and other interested brain structures of memorable traces about the signal, its characteristics, meaning and the nature of the reaction to it. Subsequently, as automation progresses, the reaction begins to be carried out by subcortical structures.

The total area of ​​the human cerebral cortex is about 2200 cm2, the number of cortical neurons exceeds 10 billion. The cortex contains pyramidal, stellate, and fusiform neurons.

Pyramidal neurons vary in size, and their dendrites bear a large number of spines; the axon of a pyramidal neuron, as a rule, goes through the white matter to other areas of the cortex or to the structures of the central nervous system.

Stellate cells have short, well-branched dendrites and a short ascon, which provides connections between neurons within the cerebral cortex itself.

Fusiform neurons provide vertical or horizontal connections between neurons of different layers of the cortex.

The cerebral cortex has a predominantly six-layer structure

Layer I is the upper molecular layer, represented mainly by the branches of the ascending dendrites of pyramidal neurons, among which rare horizontal cells and granule cells are located; fibers of the nonspecific nuclei of the thalamus also come here, regulating the level of excitability of the cerebral cortex through the dendrites of this layer.

Layer II - external granular, consists of stellate cells that determine the duration of circulation of excitation in the cerebral cortex, i.e., related to memory.

Layer III is the outer pyramidal layer, formed from small pyramidal cells and, together with layer II, provides cortico-cortical connections of various convolutions of the brain.

Layer IV is internal granular and contains predominantly stellate cells. Specific thalamocortical pathways end here, i.e., pathways starting from the receptors of the analyzers.

Layer V is the internal pyramidal layer, a layer of large pyramids that are output neurons, their axons go to the brain stem and spinal cord.

Layer VI is a layer of polymorphic cells; most of the neurons in this layer form corticothalamic tracts.

The cellular composition of the cortex in terms of diversity of morphology, function, and forms of communication has no equal in other parts of the central nervous system. The neuronal composition and distribution of neurons into layers in different areas of the cortex are different, which made it possible to identify 53 cytoarchitectonic fields in the human brain. The division of the cerebral cortex into cytoarchitectonic fields is more clearly formed as its function improves in phylogenesis.

In higher mammals, in contrast to lower ones, secondary fields 6, 8 and 10 are well differentiated from the motor field 4, functionally ensuring high coordination and accuracy of movements; around visual field 17 are secondary visual fields 18 and 19, which are involved in analyzing the meaning of a visual stimulus (organizing visual attention, controlling eye movement). Primary auditory, somatosensory, skin and other fields also have nearby secondary and tertiary fields that provide association of the functions of this analyzer with the functions of other analyzers. All analyzers are characterized by a somatotopic principle of organizing the projection of peripheral receptive systems onto the cerebral cortex. Thus, in the sensory area of ​​the cortex of the second central gyrus there are areas representing the localization of each point on the skin surface; in the motor area of ​​the cortex, each muscle has its own topic (its own place), by irritating which one can obtain the movement of a given muscle; in the auditory area of ​​the cortex there is a topical localization of certain tones (tonotopic localization); damage to a local area of ​​the auditory area of ​​the cortex leads to hearing loss for a certain tone.

In the same way, there is a topographic distribution in the projection of retinal receptors onto the visual field of cortex 17. In the event of the death of the local zone of field 17, the image is not perceived if it falls on the part of the retina projecting onto the damaged zone of the cerebral cortex.

A special feature of cortical fields is the screen principle of their functioning. This principle lies in the fact that the receptor projects its signal not onto one cortical neuron, but onto a field of neurons, which is formed by their collaterals and connections. As a result, the signal is not focused point to point, but on many different neurons, which ensures it full analysis and the possibility of transfer to other interested structures. Thus, one fiber entering the visual cortex can activate a zone measuring 0.1 mm. This means that one axon distributes its action over more than 5,000 neurons.

Input (afferent) impulses enter the cortex from below and ascend to the stellate and pyramidal cells of the III-V layers of the cortex. From the stellate cells of layer IV, the signal goes to pyramidal neurons of layer III, and from here along associative fibers to other fields, areas of the cerebral cortex. Stellate cells of field 3 switch signals going to the cortex to layer V pyramidal neurons, from here the processed signal leaves the cortex to other brain structures.

In the cortex, input and output elements, together with stellate cells, form so-called columns - functional units of the cortex, organized in the vertical direction. The proof of this is the following: if the microelectrode is inserted perpendicularly into the cortex, then on its way it encounters neurons that respond to one type of stimulation, but if the microelectrode is inserted horizontally along the cortex, then it encounters neurons that respond to different types of stimuli.

The diameter of the column is about 500 µm and it is determined by the distribution zone of collaterals of the ascending afferent thalamocortical fiber. Adjacent columns have relationships that organize sections of many columns in the organization of a particular reaction. Excitation of one of the columns leads to inhibition of neighboring ones.

Each column can have a number of ensembles that implement any function according to the probabilistic-statistical principle. This principle lies in the fact that upon repeated stimulation, not the entire group of neurons, but part of it, participates in the reaction. Moreover, each time the part of the participating neurons may be different in composition, i.e., a group of active neurons is formed (probabilistic principle), which is statistically sufficient on average to provide the desired function (statistical principle).

As already mentioned, different areas of the cerebral cortex have different fields, determined by the nature and number of neurons, the thickness of the layers, etc. The presence of structurally different fields also implies their different functional purposes (Fig. 4.14). Indeed, the cerebral cortex is divided into sensory, motor and associative areas.

Sensory areas

The cortical ends of the analyzers have their own topography and certain afferents of the conducting systems are projected onto them. The cortical ends of the analyzers of different sensory systems overlap. In addition, in each sensory system of the cortex there are polysensory neurons that respond not only to “their” adequate stimulus, but also to signals from other sensory systems.

The cutaneous receptive system, thalamocortical pathways, project to the posterior central gyrus. There is a strict somatotopic division here. The receptive fields of the skin of the lower extremities are projected onto the upper sections of this gyrus, the torso onto the middle sections, and the arms and head onto the lower sections.

Pain and temperature sensitivity are mainly projected onto the posterior central gyrus. In the cortex of the parietal lobe (fields 5 and 7), where the sensitivity pathways also end, a more complex analysis is carried out: localization of irritation, discrimination, stereognosis.

When the cortex is damaged, the functions of the distal parts of the extremities, especially the hands, are more severely affected.

The visual system is represented in the occipital lobe of the brain: fields 17, 18, 19. The central visual pathway ends in field 17; it informs about the presence and intensity of the visual signal. In fields 18 and 19, the color, shape, size, and quality of objects are analyzed. Damage to field 19 of the cerebral cortex leads to the fact that the patient sees, but does not recognize the object (visual agnosia, and color memory is also lost).

The auditory system is projected in the transverse temporal gyri (Heschl's gyrus), in the depths of the posterior sections of the lateral (Sylvian) fissure (fields 41, 42, 52). It is here that the axons of the posterior colliculi and lateral geniculate bodies end.

The olfactory system projects to the region of the anterior end of the hippocampal gyrus (field 34). The bark of this area has not a six-layer, but a three-layer structure. When this area is irritated, olfactory hallucinations are noted; damage to it leads to anosmia (loss of smell).

The taste system is projected in the hippocampal gyrus adjacent to the olfactory area of ​​the cortex (field 43).

Motor areas

For the first time, Fritsch and Gitzig (1870) showed that stimulation of the anterior central gyrus of the brain (field 4) causes a motor response. At the same time, it is recognized that the motor area is an analytical one.

In the anterior central gyrus, the zones whose irritation causes movement are presented according to the somatotopic type, but upside down: in the upper parts of the gyrus - the lower limbs, in the lower - the upper.

In front of the anterior central gyrus lie premotor fields 6 and 8. They organize not isolated, but complex, coordinated, stereotypical movements. These fields also provide regulation of smooth muscle tone and plastic muscle tone through subcortical structures.

The second frontal gyrus, occipital, and superior parietal regions also take part in the implementation of motor functions.

The motor area of ​​the cortex, like no other, has a large number of connections with other analyzers, which apparently determines the presence of a significant number of polysensory neurons in it.

Associative areas

All sensory projection areas and the motor cortex occupy less than 20% of the surface of the cerebral cortex (see Fig. 4.14). The rest of the cortex constitutes the association region. Each association area of ​​the cortex is connected by powerful connections to several projection areas. It is believed that in associative areas the association of multisensory information occurs. As a result, complex elements of consciousness are formed.

Association areas of the human brain are most pronounced in the frontal, parietal and temporal lobes.

Each projection area of ​​the cortex is surrounded by association areas. Neurons in these areas are often multisensory and have greater learning abilities. Thus, in associative visual field 18, the number of neurons “learning” a conditioned reflex response to a signal is more than 60% of the number of background active neurons. For comparison: there are only 10-12% of such neurons in the projection field 17.

Damage to area 18 leads to visual agnosia. The patient sees and walks around objects, but cannot name them.

The polysensory nature of neurons in the associative area of ​​the cortex ensures their participation in the integration of sensory information, the interaction of sensory and motor areas of the cortex.

In the parietal associative area of ​​the cortex, subjective ideas about the surrounding space and our body are formed. This becomes possible due to the comparison of somatosensory, proprioceptive and visual information.

Frontal associative fields have connections with the limbic part of the brain and are involved in organizing action programs during the implementation of complex motor behavioral acts.

First and most characteristic feature the associative areas of the cortex is the multisensory nature of their neurons, and not primary, but rather processed information is received here, highlighting the biological significance of the signal. This allows you to formulate a program of targeted behavioral act.

The second feature of the associative area of ​​the cortex is the ability to undergo plastic rearrangements depending on the significance of incoming sensory information.

The third feature of the associative area of ​​the cortex is manifested in long-term storage traces of sensory influences. Destruction of the associative area of ​​the cortex leads to severe impairments in learning and memory. The speech function is associated with both sensory and motor systems. The cortical motor speech center is located in the posterior part of the third frontal gyrus (area 44), most often in the left hemisphere, and was described first by Dax (1835) and then by Broca (1861).

The auditory speech center is located in the first temporal gyrus of the left hemisphere (field 22). This center was described by Wernicke (1874). The motor and auditory speech centers are interconnected by a powerful bundle of axons.

Speech functions associated with written speech - reading, writing - are regulated by the angular gyrus of the visual cortex of the left hemisphere of the brain (field 39).

When the motor center of speech is damaged, motor aphasia develops; in this case, the patient understands speech, but cannot speak himself. If the auditory center of speech is damaged, the patient can speak, express his thoughts orally, but does not understand someone else's speech, hearing is preserved, but the patient does not recognize words. This condition is called sensory auditory aphasia. The patient often talks a lot (logorrhea), but his speech is incorrect (agrammatism), and there is a replacement of syllables and words (paraphasia).

Damage to the visual center of speech leads to the inability to read and write.

An isolated writing disorder, agraphia, also occurs in the case of dysfunction of the posterior parts of the second frontal gyrus of the left hemisphere.

In the temporal region there is field 37, which is responsible for remembering words. Patients with lesions in this field do not remember the names of objects. They resemble forgetful people who need to be prompted with the right words. The patient, having forgotten the name of an object, remembers its purpose and properties, so he describes their qualities for a long time, tells what they do with this object, but cannot name it. For example, instead of the word “tie,” the patient, looking at the tie, says: “this is something that is put on the neck and tied with a special knot so that it is beautiful when they go to visit.”

The distribution of functions across brain regions is not absolute. It has been established that almost all areas of the brain have polysensory neurons, that is, neurons that respond to various stimuli. For example, if field 17 of the visual area is damaged, its function can be performed by fields 18 and 19. In addition, different motor effects of irritation of the same motor point of the cortex are observed depending on the current motor activity.

If the operation of removing one of the zones of the cortex is carried out in early childhood, when the distribution of functions is not yet rigidly fixed, the function of the lost area is almost completely restored, i.e. in the cortex there are manifestations of mechanisms of dynamic localization of functions that make it possible to compensate for functionally and anatomically disturbed structures.

An important feature of the cerebral cortex is its ability to retain traces of excitation for a long time.

Trace processes in the spinal cord after its irritation persist for a second; in the subcortical-stem regions (in the form of complex motor-coordinating acts, dominant attitudes, emotional states) last for hours; in the cerebral cortex, trace processes can be maintained according to the feedback principle throughout life. This property gives the cortex exceptional importance in the mechanisms of associative processing and storage of information, accumulation of a knowledge base.

The preservation of traces of excitation in the cortex is manifested in fluctuations in the level of its excitability; these cycles last 3-5 minutes in the motor cortex and 5-8 minutes in the visual cortex.

The main processes occurring in the cortex are realized in two states: excitation and inhibition. These states are always reciprocal. They arise, for example, within the motor analyzer, which is always observed during movements; they can also occur between different analyzers. The inhibitory influence of one analyzer on others ensures that attention is focused on one process.

Reciprocal activity relationships are very often observed in the activity of neighboring neurons.

The relationship between excitation and inhibition in the cortex manifests itself in the form of so-called lateral inhibition. With lateral inhibition, a zone of inhibited neurons is formed around the excitation zone (simultaneous induction) and its length, as a rule, is twice as large as the excitation zone. Lateral inhibition provides contrast in perception, which in turn makes it possible to identify the perceived object.

In addition to lateral spatial inhibition, in cortical neurons, after excitation, inhibition of activity always occurs, and vice versa, after inhibition - excitation - the so-called sequential induction.

In cases where inhibition is unable to restrain the excitatory process in a certain zone, irradiation of excitation occurs throughout the cortex. Irradiation can occur from neuron to neuron, along the systems of associative fibers of layer I, and it has a very low speed - 0.5-2.0 m/s. In another case, irradiation of excitation is possible due to axon connections of pyramidal cells of the third layer of the cortex between neighboring structures, including between different analyzers. Irradiation of excitation ensures the relationship between the states of the cortical systems during the organization of conditioned reflex and other forms of behavior.

Along with the irradiation of excitation, which occurs due to impulse transmission of activity, there is irradiation of the state of inhibition throughout the cortex. The mechanism of irradiation of inhibition is the transfer of neurons into an inhibitory state under the influence of impulses coming from excited areas of the cortex, for example, from symmetrical areas of the hemispheres.

Electrical manifestations of cortical activity

Assessing the functional state of the human cerebral cortex is a difficult and still unsolved problem. One of the signs that indirectly indicates the functional state of brain structures is the registration of electrical potential fluctuations in them.

Each neuron has a membrane charge, which, when activated, decreases, and when inhibited, it often increases, i.e., hyperpolarization develops. Glia in the brain also have charge cell membranes. The dynamics of the charge of the membrane of neurons, glia, processes occurring in synapses, dendrites, axon hillock, in the axon - all these are constantly changing processes, varied in intensity and speed, the integral characteristics of which depend on the functional state of the nervous structure and ultimately determine its electrical indicators. If these indicators are recorded through microelectrodes, then they reflect the activity of a local (up to 100 μm in diameter) part of the brain and are called focal activity.

If the electrode is located in a subcortical structure, the activity recorded through it is called a subcorticogram, if the electrode is located in the cerebral cortex - a corticogram. Finally, if the electrode is located on the surface of the scalp, then the total activity of both the cortex and subcortical structures is recorded. This manifestation of activity is called an electroencephalogram (EEG) (Fig. 4.15).

All types of brain activity are dynamically subject to intensification and weakening and are accompanied by certain rhythms of electrical oscillations. In a person at rest, in the absence of external stimuli, slow rhythms of changes in the state of the cerebral cortex predominate, which is reflected on the EEG in the form of the so-called alpha rhythm, the frequency of oscillations of which is 8-13 per second, and the amplitude is approximately 50 μV.

A person’s transition to active activity leads to a change in the alpha rhythm to a faster beta rhythm, which has an oscillation frequency of 14-30 per second, the amplitude of which is 25 μV.

The transition from a state of rest to a state of focused attention or to sleep is accompanied by the development of a slower theta rhythm (4-8 vibrations per second) or delta rhythm (0.5-3.5 vibrations per second). The amplitude of slow rhythms is 100-300 μV (see Fig. 4.15).

When, against a background of rest or another state, the brain is presented with a new, rapidly increasing stimulus, so-called evoked potentials (EPs) are recorded on the EEG. They represent a synchronous reaction of many neurons in a given cortical area.

The latent period and amplitude of the EP depend on the intensity of the applied stimulation. The components of the EP, the number and nature of its fluctuations depend on the adequacy of the stimulus relative to the EP recording zone.

EP may consist of a primary response or of a primary and a secondary response. Primary responses are biphasic, positive-negative oscillations. They are recorded in the primary zones of the analyzer’s cortex and only with a stimulus adequate for the given analyzer. For example, visual stimulation for the primary visual cortex (field 17) is adequate (Fig. 4.16). Primary responses are characterized by a short latent period (LP), two-phase oscillation: first positive, then negative. The primary response is formed due to short-term synchronization of the activity of nearby neurons.

Secondary responses are more variable in latency, duration, and amplitude than primary ones. As a rule, secondary responses more often occur to signals that have a certain semantic meaning, to stimuli that are adequate for a given analyzer; they are well formed with training.

Interhemispheric relationships

The relationship of the cerebral hemispheres is defined as a function that ensures the specialization of the hemispheres, facilitating the implementation of regulatory processes, increasing the reliability of controlling the activities of organs, organ systems and the body as a whole.

The role of relationships between the cerebral hemispheres is most clearly manifested in the analysis of functional interhemispheric asymmetry.

Asymmetry in the functions of the hemispheres was first discovered in the 19th century, when attention was paid to the different consequences of damage to the left and right half of the brain.

In 1836, Mark Dax spoke at a meeting of the medical society in Montpellier (France) with a short report on patients suffering from loss of speech - a condition known to specialists as aphasia. Dax noticed a connection between the loss of speech and the damaged side of the brain. In his observations, more than 40 patients with aphasia showed signs of damage to the left hemisphere. The scientist was unable to detect a single case of aphasia with damage to only the right hemisphere. Summarizing these observations, Dax made the following conclusion: each half of the brain controls its own specific functions; speech is controlled by the left hemisphere.

His report was not successful. Some time after the death of Dax Broca, during a post-mortem examination of the brains of patients suffering from loss of speech and unilateral paralysis, in both cases clearly identified foci of damage that involved parts of the left frontal lobe. This area has since become known as Broca's area; it was defined by him as an area in the posterior parts of the inferior frontal gyrus.

Having analyzed the connection between preference for one of the two hands and speech, he suggested that speech and greater dexterity in the movements of the right hand are associated with the superiority of the left hemisphere in right-handed people.

Ten years after Broca's observations were published, the concept now known as hemispheric dominance had become the dominant view of the relationship between the two hemispheres of the brain.

In 1864, the English neurologist John Jackson wrote: “Not so long ago, it was rarely doubted that the two hemispheres were the same, both physically and functionally, but now, thanks to the research of Dax, Broca and others, it has become clear that the damage one hemisphere can cause a person to completely lose speech, the previous point of view has become untenable.”

D. Jackson put forward the idea of ​​a “leading” hemisphere, which can be considered as a predecessor to the concept of hemispheric dominance. “The two hemispheres cannot simply duplicate each other,” he wrote, “if damage to only one of them can lead to loss of speech. For these processes (speech), above which there is nothing, there must certainly be a leading party.” Jackson further concluded "that in most people the dominant side of the brain is the left side of the so-called will, and that the right side is automatic."

By 1870, other researchers began to realize that many types of speech disorders could be caused by damage to the left hemisphere. K. Wernicke found that patients with damage to the posterior part of the temporal lobe of the left hemisphere often experienced difficulties in understanding speech.

Some patients with damage to the left rather than the right hemisphere had difficulty reading and writing. It was also believed that left hemisphere also controls “purposeful movements.”

The totality of these data became the basis for the idea of ​​the relationship between the two hemispheres. One hemisphere (usually the left in right-handed people) was considered to be leading for speech and other higher functions, the other (right), or “secondary,” was considered to be under the control of the “dominant” left.

The speech asymmetry of the cerebral hemispheres, which was the first to be identified, predetermined the idea of ​​the equipotentiality of the cerebral hemispheres of children before the appearance of speech. It is believed that brain asymmetry develops during the maturation of the corpus callosum.

The concept of hemispheric dominance, according to which in all gnostic and intellectual functions the left hemisphere is dominant in “right-handed people”, and the right hemisphere is “deaf and dumb”, has existed for almost a century. However, evidence gradually accumulated that the idea of ​​the right hemisphere as secondary, dependent, does not correspond to reality. Thus, patients with disorders of the left hemisphere of the brain perform worse on tests for the perception of shapes and assessment of spatial relationships than healthy people. Neurologically healthy subjects who speak two languages ​​(English and Yiddish) better identify English words, presented in the right visual field, and Yiddish words in the left. It was concluded that this kind of asymmetry is related to reading skills: English words are read from left to right, and Yiddish words are read from right to left.

Almost simultaneously with the spread of the concept of hemispheric dominance, evidence began to appear indicating that the right, or secondary, hemisphere also has its own special abilities. Thus, Jackson made the statement that the ability to form visual images is localized in the posterior lobes of the right brain.

Damage to the left hemisphere tends to result in poor performance on verbal ability tests. At the same time, patients with damage to the right hemisphere typically performed poorly on nonverbal tests that included manipulating geometric shapes, assembling puzzles, filling in missing parts of pictures or figures, and other tasks involving the assessment of shape, distance, and spatial relationships.

It was found that damage to the right hemisphere was often accompanied by profound disturbances in orientation and consciousness. Such patients have poor spatial orientation and are unable to find their way to the house in which they have lived for many years. Damage to the right hemisphere has also been associated with certain types agnosia, i.e. disturbances in the recognition or perception of familiar information, depth perception and spatial relationships. One of the most interesting forms of agnosia is facial agnosia. A patient with such agnosia is not able to recognize a familiar face, and sometimes cannot distinguish people from each other at all. Recognition of other situations and objects, for example, may not be impaired. Additional information indicating a specialization of the right hemisphere was obtained from observations of patients suffering from severe speech disorders, who, however, often retain the ability to sing. In addition, clinical reports have suggested that damage to the right side of the brain can lead to loss of musical abilities without affecting speech. This disorder, called amusia, was most often seen in professional musicians who had suffered a stroke or other brain damage.

After neurosurgeons performed a series of commissurotomy operations and psychological studies were performed on these patients, it became clear that the right hemisphere has its own higher gnostic functions.

There is an idea that interhemispheric asymmetry depends critically on the functional level of information processing. In this case, decisive importance is attached not to the nature of the stimulus, but to the features of the gnostic task facing the observer. It is generally accepted that the right hemisphere is specialized in processing information at the figurative functional level, the left - at the categorical level. The use of this approach allows us to remove a number of intractable contradictions. Thus, the advantage of the left hemisphere, discovered when reading musical notes and finger signs, is explained by the fact that these processes occur at the categorical level of information processing. Comparing words without them linguistic analysis It is more successfully carried out when they are addressed to the right hemisphere, since to solve these problems it is sufficient to process information at the figurative functional level.

Interhemispheric asymmetry depends on the functional level of information processing: the left hemisphere has the ability to process information at both semantic and perceptual functional levels, the capabilities of the right hemisphere are limited to the perceptual level.

In cases of lateral presentation of information, three methods of interhemispheric interactions can be distinguished, manifested in the processes of visual recognition.

1. Parallel activities. Each hemisphere processes information using its own mechanisms.

2. Election activities. Information is processed in the “competent” hemisphere.

3. Cooperative activity. Both hemispheres are involved in information processing, consistently playing a leading role at certain stages of this process.

The main factor determining the participation of one or another hemisphere in the processes of recognition of incomplete images is what elements the image lacks, namely, what is the degree of significance of the elements missing in the image. If image details were removed without taking into account the degree of their significance, identification was more difficult in patients with lesions of the structures of the right hemisphere. This gives grounds to consider the right hemisphere to be the leading one in recognizing such images. If a relatively small but highly significant area was removed from the image, then recognition was disrupted primarily when the structures of the left hemisphere were damaged, which indicates the predominant participation of the left hemisphere in the recognition of such images.

In the right hemisphere, a more complete assessment of visual stimuli is carried out, while in the left, their most significant, significant features are assessed.

When a significant number of details of the image to be identified are removed, the likelihood that the most informative, significant parts of it will not be distorted or deleted is small, and therefore the left hemisphere recognition strategy is significantly limited. In such cases, the strategy characteristic of the right hemisphere, based on the use of all information contained in the image, is more adequate.

Difficulties in implementing the left-hemisphere strategy under these conditions are further aggravated by the fact that the left hemisphere has insufficient “abilities” for accurately assessing individual image elements. This is also evidenced by studies according to which the assessment of the length and orientation of lines, the curvature of arcs, and the size of angles is impaired primarily with lesions of the right hemisphere.

A different picture is observed in cases where most of the image is removed, but its most significant, informative section is preserved. In such situations, a more adequate method of identification is based on the analysis of the most significant fragments of the image - a strategy used by the left hemisphere.

In the process of recognizing incomplete images, structures of both the right and left hemispheres are involved, and the degree of participation of each of them depends on the characteristics of the presented images, and primarily on whether the image contains the most significant informative elements. In the presence of these elements, the predominant role belongs to the left hemisphere; when they are removed, the right hemisphere plays a predominant role in the recognition process.

How many nerve cells are there in our brain? One hundred billion. The number is widely known, but no one knows where it came from. In any case, according to Suzana Herculano-Houzel from the Federal University of Rio de Janeiro (Brazil), when she tried to find out from fellow neuroscientists the origin of these “hundred billions”, no one could give her a clear answer . And then she decided to count the brain neurons herself.

Manually going through all the neurons of the human brain seems even less possible than counting the number of stars in the sky, hairs in a beard and poppy seeds in a bag of poppies. You can't do it without the help of a fairytale assistant. Nevertheless, there are scientific approaches that allow solving this problem with varying degrees of accuracy.

The work could be done using the standard method: take a small piece of the brain and count the number of neurons in it, and then increase the result in proportion to the size of the whole brain - based on the fact that the neurons are distributed more or less evenly.

But the researchers chose a different method. They took the entire brain and carefully dissolved the cell membranes, creating a soup of broken cells in which the cell nuclei floated. The density of the kernels in any portion of this soup was exactly the same. After which the number of neuron nuclei, relatively speaking, in a teaspoon of the resulting mixture was calculated. In this case, of course, the nuclei of service, glial cells that are not involved in conducting the nerve signal were not taken into account.

For their work, scientists used the brains of four men aged 50, 51, 54 and 71 years old. None of them suffered from neurological diseases (they all bequeathed their brains to science). As it turns out, our average brain has about 86 billion neurons—14 billion fewer than thought. If this difference does not seem so significant to someone, let us specifically clarify that the human brain has “lost weight” by the number of nerve cells that make up the entire brain of a baboon and half of the brain of a gorilla. Size matters here!

However, there are different opinions regarding the correspondence between brain size and the degree of development of the body. It is known that, in addition to the number of neurons, their organization, methods of connections between nerve cells, the number of such connections, as well as the ability of the neurons themselves to enter into various contacts with each other play an important role. A small number of interneuron connections can negate the advantage of many nerve cells.

Some researchers believe that the size of the brain generally corresponds only to the size of the body, that the brain grows only to make a larger body easier to control. Others, on the contrary, believe that the enlargement of the human brain is associated precisely with the emergence of higher mental functions and the development of social life.

Nervous system. Lecture 2.

Bark cerebrum (cortex cerebri) is a continuous layer of gray matter on the surface cerebral hemispheres 2-5 mm thick. It is located not only on the convolutions, but continues into all furrows, as a result of which its area is relatively large and amounts to 2200 cm 2 in an adult. The mass of the bark is 581 g, its volume is about 560 cm 3. In this case, the main volume of the cortex is composed of white matter (450 cm 3, weight - 470 g). The cell body mass of cortical neurons is only about 21 g (20 cm3).

The size of cortical nerve cells varies widely from 8-9 mk up to 150 mk. In the human cerebral cortex there are up to 15 billion nerve cells, of which 6 billion are small cells. The vast majority of cortical neurons belong to two types: pyramidal neurons and stellate neurons. These cells are located in the cortex in certain layers.

In the human brain there are several phylogenetically distinguished different types bark:

The ancient cortex - paleocortex (0.6%) - has virtually no layering (1-2 layers), is localized in the area of ​​the olfactory triangles, forms a covering of the septum pellucidum and surrounds the amygdala nucleus.

The old cortex - archicortex (2.2%) - has 2-3 layers, represented by the gray matter of the dentate gyrus, the gray matter of the hippocampus, and the medullary striae on the corpus callosum.

Transitional cortex - mesocortex (1.6%) - area of ​​the vaulted gyrus.

The new cortex - neocortex (95.6%) - is well structured and has 6 layers.

In higher vertebrates there are predominantly six more or less clearly defined layers. But each of these layers, except the first, can be divided into two or even three sublayers.

First layer, the so-called zonal or molecular plate, consists mainly of plexuses of apical dendrites of pyramidal neurons, the cell bodies of which are located in other layers of the cortex. There are very few nerve cells in the first layer. It contains horizontal cells, the axons and dendrites of which are also located horizontally in the same layer.

Second layer, the so-called external granular or outer granular plate, includes a mass of small cells belonging to small pyramidal, so-called interneurons, and stellate neurons, and small pyramidal cells dominate in the second layer.

The third layer is the outer pyramidal plate contains medium-sized pyramidal cells

Fourth layer, the so-called internal granular or internal granular plate, consists mainly of small stellate cells, but it also contains small and medium-sized pyramids.

The fifth layer is the inner pyramidal plate contains giant pyramidal cells or Betz cells.

Sixth layer – multiform plate contain mainly medium-sized pyramidal cells and small numbers of small pyramidal and stellate cells.

The first three layers are the youngest; they provide connection between different sections of the cortex. The fourth layer is most developed in the areas where afferent information arrives (sensitive centers, especially the postcentral gyrus). The fifth layer is expressed in the motor areas of the cortex: precentral gyrus, pericentral lobule, supramarginal gyrus.

Each pyramidal neuron has a pyramidal cell and many dendrites. The axon of a pyramidal neuron emerges from a small hillock at the base of the cell. In small, so-called intercalary or intermediate pyramidal neurons, the axons, branching in a horizontal or vertical direction, end immediately, without leaving the cortex. Axons of middle and great pyramids give off many collaterals in the cortex, and the main trunks go into the subcortical white matter. Some of them return from the subcortical substance to the cortex of a given hemisphere, or, passing through the corpus callosum, end in the cortex of the other hemisphere. They serve to unite different parts of the cerebral cortex. Therefore, such pyramidal neurons are called associative. Other axons are directed to the subcortical formations and further to various parts of the brain and spinal cord. These pyramids are called projection. In connection with the phylogenetic development of mammals, the number of pyramidal cells increases greatly.

The width of the entire cortex, the number of cells and the width of each layer of cells in the frontal section, as well as the cellular composition, i.e., the size, shape, and arrangement of cells in each section of the cortex vary extremely. These variations occupy certain, clearly demarcated territories. In the large mammalian brain there are 11 clearly visible large cortical fields.

Based on histological and physiological studies, each such field was divided into several independent sections. More significant differentiation of the cortex is observed in higher mammals - monkeys. It is especially great in humans.

The beginning of such research was laid by the Kyiv scientist Vladimir Alekseevich Bets, who in 1874 published the article “Two centers in the cerebral cortex,” in which he described the motor zone in the precentral gyrus and the sensitive zone in the postcentral gyrus.

In 1909, German neurologist Korbinian Brodmann published maps of cytoarchitectonic fields cerebral cortex. Brodmann was the first to create maps of the cortex. Subsequently, O. Vogt and C. Vogt (1919-1920), taking into account the fiber structure, described 150 myeloarchitectonic areas in the cerebral cortex. At the Brain Institute of the USSR Academy of Medical Sciences, I. N. Filippov and S. A. Sarkisov created maps of the cerebral cortex, including 47 cytoarchitectonic fields.

Data from experimental studies indicate that when certain areas of the cerebral cortex are destroyed or removed in animals, certain functions are disrupted. These facts are confirmed by clinical observations of sick people with tumor lesions or injuries to certain areas of the cerebral cortex. All this allowed us to conclude that in the cerebral cortex there are centers that regulate the performance of certain functions. Morphological confirmation of physiological and clinical data was the doctrine of the different quality of the structure of the cerebral cortex in its various parts - cyto- and myeloarchitectonics of the cortex. It has been established that neurons are not located diffusely in the cortex, but are grouped into ensembles.

The use of modern microelectrode methods to study the functions of cortical neurons has significantly expanded the understanding of the processing of sensory information in the neocortex and the structural organization of the cortex. In 1957, American researcher V. Mountcastle, analyzing the responses of cells in the somatosensory (sensorimotor) cortex of a cat to stimuli of various modalities, discovered the following interesting fact. When the microelectrode was immersed perpendicular to the surface of the somatosensory cortex, all cells it encountered responded equally to a stimulus, for example, to a light touch on the skin or to movement in a joint. If the electrode was immersed at an angle to the surface of the cortex, then along its path came neurons with different sensory modalities, alternating with a certain periodicity.

Based on these experimental facts, W. Mountcastle came to the conclusion that the somatosensory cortex is organized in elementary functional units - columns oriented perpendicular to the surface. The diameter of such a column is about 500 μm determined by the horizontal distribution of the terminals of the afferent thalamocortical fiber and the vertical orientation of the dendrites pyramidal cells. According to Mountcastle, the column is elementary block of the sensorimotor cortex, where local processing of information from receptors of one modality is carried out. This hypothesis of the columnar organization of the neocortex has become widespread and has given impetus to further research in this area in our country and abroad.

According to modern concepts, each functional column of the sensorimotor cortex consists of several morphological micromodules, combining five to six nest-like neurons. This module includes several pyramidal cells, the apical dendrites of which are as close as possible and form a dendritic bundle; within this beam are possible electrotonic connections, which ensure, in all likelihood, the synchronous operation of the entire association.

Adjacent to the group of vertically oriented pyramidal cells are stellate cells, with which thalamocortical fibers coming to the micromodule contact. Some of the stellate cells that perform an inhibitory function have long axons extending horizontally. Axons of pyramidal cells form recurrent collaterals, which can provide both facilitatory influences within a micromodule and inhibitory interactions between micromodules, contacting inhibitory interneurons. Several structural micromodules, united by horizontal branching of the terminals of specific thalamocortical afferents, axons of the terminals and processes of stellate cells form a column (or macromodule), the diameter of which reaches 500-1000 µm. Each column is characterized by functional unity, which is manifested in the fact that the neurons of the column respond to a stimulus of one modality.

Subsequently, the principle of columnar organization was confirmed in the study of other projection zones of the cortex.

I.P. Pavlov considered the cerebral cortex as a continuous perceptive surface, as a collection of cortical ends of analyzers. He showed that the cortical end of the analyzers is not some strictly defined zone. The cerebral cortex is divided into a nucleus and scattered elements. The nucleus is the place where the nerve cells of the cortex are concentrated, constituting the exact projection of all the elements of a certain peripheral receptor, where higher analysis, synthesis and integration of functions. Scattered elements can be located both along the periphery of the nucleus and at a considerable distance from it. They carry out simpler analysis and synthesis. The presence of scattered elements during the destruction of the core partly makes it possible to compensate for the impaired function. The areas occupied by scattered elements of various analyzers can be layered on top of each other and overlap each other. Thus, the cerebral cortex can be schematically imagined as a set of nuclei of various analyzers, between which there are scattered elements belonging to different (adjacent) analyzers. The above allows us to talk about dynamic localization of functions in the cerebral cortex (I.P. Pavlov).

Let us consider the position of some cortical ends of various analyzers (nuclei) in relation to the gyri and lobes of the cerebral hemispheres in humans in accordance with cytoarchitectonic maps.

1. In the cortex of the postcentral gyrus and superior parietal lobule lie nerve cells that form the core of the cortical analyzer of the general sensitivity(temperature, pain, tactile) and proprioceptive. Sensory pathways leading to the cerebral cortex intersect either at the level of different segments of the spinal cord (pathways of pain, temperature sensitivity, touch and pressure), or at the level of the medulla oblongata (pathways of proprioceptive sensitivity of the cortical direction). As a result, the postcentral gyri of each hemisphere are connected to the opposite half of the body. In the postcentral gyrus, all the receptor fields of various parts of the human body are projected in such a way that the cortical ends of the sensitivity analyzer of the lower torso and lower extremities are located most highly, and the receptor fields of the upper parts of the body and head and upper extremities are projected most low (closer to the lateral sulcus).

2. Core motor The analyzer is located mainly in the so-called motor cortex, which includes the precentral gyrus and paracentral lobule on the medial surface of the hemisphere. In the 5th layer of the cortex of the precentral gyrus lie pyramidal neurons (Betz cells), which I.P. Pavlov classified as intercalary and noted that these cells, with their processes, are connected with the subcortical nuclei, motor cells of the nuclei of the cranial and spinal nerves. Moreover, in the upper parts of the precentral gyrus and in the paracentral lobule there are cells, impulses from which are sent to the muscles of the lowermost parts of the trunk and lower extremities. In the lower part of the precentral gyrus there are motor centers that regulate the activity of the facial muscles.

Thus, all areas of the human body are projected “upside down” in the precentral gyrus. Due to the fact that the pyramidal tracts, originating from gigantopyramidal cells, intersect either at the level of the brain stem (corticonuclear fibers), at the border with the spinal cord, or in segments of the spinal cord (corticospinal tract), the motor areas of each hemispheres are connected to the skeletal muscles of the opposite side of the body. If the muscles of the limbs are connected in isolation to one of the hemispheres, the muscles of the trunk, larynx and pharynx are connected to the motor areas of both hemispheres.

Motor I.P. Pavlov also called the area of ​​the cerebral cortex the receptor area, since proprioceptive (kinetic stimuli perceived by receptors embedded in skeletal muscles, tendons, fascia and joint capsules).

3. Analyzer core providing the function combined rotation of the head and eyes in the opposite direction, is located in the posterior parts of the middle frontal gyrus, in the so-called premotor zone.

4. In the region of the inferior parietal lobule, in the supramarginal gyrus, there is the nucleus of the motor analyzer, the functional significance of which is to implement synthesis everyone purposeful, professional, labor and sports movements. This core is asymmetrical. For right-handers it is in the left, and for left-handers- only in the right hemisphere. The ability to coordinate these complex purposeful movements is acquired by the individual throughout life as a result of practical activity and accumulation of experience. Purposeful movements occur due to the formation of temporary connections between cells located in the precentral and supramarginal gyri. Damage to the field does not cause paralysis, but only leads to the loss of the ability to produce complex coordinated purposeful movements - apraxia (praxis - practice).

5. In the cortex of the superior parietal lobule there is the nucleus of the skin analyzer of one of the particular types of sensitivity, which has an inherent function recognizing objects by touch,- streognosia. The cortical end of this analyzer is located in the right hemisphere. Damage to the superficial layers of the cortex in this section is accompanied by a loss of the function of recognizing objects by touch, although other types of general sensitivity are preserved.

6. In the depths of the lateral sulcus, on the surface of the middle part of the superior temporal gyrus facing the insula (where the transverse temporal gyri, or Heschl’s gyri, are visible), there is a nucleus auditory analyzer. The nerve cells that make up the core of the auditory analyzer of each hemisphere are approached by pathways from receptors on both the left and right sides. In this regard, unilateral damage to this nucleus does not cause a complete loss of the ability to perceive sounds. Bilateral damage is accompanied by cortical deafness.

7. Core visual The analyzer is located in the occipital lobe of the cerebral hemisphere in the circumference of the calcarine sulcus. The nucleus of the visual analyzer of the right hemisphere is connected by pathways to the lateral half of the retina of the right eye and the medial half of the retina of the left eye. In the cortex of the occipital lobe of the left hemisphere, the receptors of the lateral half of the retina of the left eye and the medial half of the retina of the right eye are projected, respectively. As with the auditory analyzer nucleus, only bilateral damage to the visual analyzer nuclei leads to complete cortical blindness. Damage to the field located slightly above the nucleus of the visual analyzer is accompanied by loss of visual memory, but no loss of vision is noted. Even higher is a section of the cortex, the defeat of which is accompanied by a loss of the ability to navigate in an unfamiliar environment.

8. On the lower surface of the temporal lobe of the cerebral hemisphere, in the area of ​​the uncus and partly in the area of ​​the hippocampus there is a nucleus olfactory analyzer. From a phylogenetic point of view, these areas belong to the most ancient parts of the cerebral cortex. The senses of smell and taste are closely interrelated, which is explained by the close location of the nuclei of the olfactory and gustatory analyzers. It was also noted (V.M. Bekhterev) that taste perception is impaired when the cortex of the lowest parts of the postcentral gyrus is damaged. The nuclei of the taste and olfactory analyzers of both hemispheres are connected with receptors on both the left and right sides of the body.

The described cortical ends of some analyzers are not present in the cerebral cortex only humans, but also animals. They are specialized in the perception, analysis and synthesis of signals coming from the external and internal environment, constituting, as defined by I.P. Pavlov, the first signal system of reality.

Second signaling system exists only in humans and is determined by the development of speech. Speech, and with it consciousness, are phylogenetically the youngest functions of the brain. In this regard, the cortical ends of the analyzers are the least localized. Speech and thinking functions are performed with the participation of the entire cortex. However, in the cerebral cortex it is possible to distinguish certain areas that are characterized by strictly defined speech functions. Yes, analyzers motor speech(oral and written) are located next to the motor area of ​​the cortex, more precisely, in those parts of the frontal lobe cortex that are adjacent to the precentral gyrus.

Analyzers visual and auditory perception speech signals are located next to the vision and hearing analyzers. It should be pointed out that speech analyzers in right-handers are localized in the left hemisphere, and in left-handers - mainly in the right.

Let us consider the position of some of the speech analyzers in the cerebral cortex.

1. The motor analyzer of written speech is located in the posterior part of the middle frontal gyrus. The activity of this analyzer is closely connected with the analyzer of purposeful movements, which ensures the formation of the learned hand and eye movements necessary for writing. If damaged, the ability to perform fine movements, usually carried out under the control of vision and necessary for drawing letters, words and other signs, is lost (agraphia).

2. Motor analyzer core speech articulation(speech motor analyzer) is located in the posterior parts of the inferior frontal gyrus (Broca's center). Damage to the cortex in this area leads to motor aphasia, i.e. loss of the ability to pronounce words (aphasia). This aphasia is not associated with loss of the ability to contract muscles involved in speech production. Moreover, if this field is damaged, the ability to pronounce sounds or sing is not lost.

3. In the central parts of the inferior frontal gyrus there is the core of the speech analyzer associated with singing. His defeat is accompanied by vocal amusia - the inability to compose and reproduce musical phrases and agrammatism, when the ability to compose meaningful sentences from individual words is lost. The speech of such people consists of a set of words that are not connected in semantic meaning.

4. Core auditory speech analyzer closely related to
cortical center of the auditory analyzer and is located in the posterior regions
superior temporal gyrus, on its surface facing to the side
lateral sulcus of the cerebral hemisphere. Damage to the nucleus does not impair the auditory perception of sounds in general, but the ability to understand words and speech is lost (verbal deafness, or sensory aphasia). The function of this core is that a person not only hears and understands the speech of another person, but also controls his own.

5. In the middle third of the superior temporal gyrus there is a nucleus of the cortical analyzer, the defeat of which is accompanied by the onset of musical deafness, when musical phrases are perceived as a meaningless set of various noises. This cortical end of the auditory analyzer belongs to the centers of the second signaling system, perceiving the verbal designation of objects, actions, phenomena, i.e. signal-sensing signals.

6. In direct connection with the core of the visual analyzer there is a core visual analyzer of written speech(field 39), located in the angular gyrus of the inferior parietal lobule. Damage to this nucleus leads to loss of the ability to perceive written text and read (dyslexia).

The human frontal cortex is associated with social origins. Its neurons form two-way connections with all other areas of the cortex. As a result of the damage, disturbances in social behavior, rudeness, disloyalty, decreased sense of purpose, and apathy are formed. After the lobotomy there is a complete lack of initiative and social activity.

The asymmetry of the functions of the right and left hemispheres is very pronounced. The left hemisphere provides logic, abstract thinking, dominates in relation to speech functions (reading, writing, counting), and complex voluntary movements. Right hemisphere– emotionality, creative thinking, non-speech functions of recognition of complex visual and auditory images, tactile perception, perception of space, shape, direction, intuitive thinking.

(cortex cerebri) - gray matter located on the surface of the cerebral hemispheres and consisting of nerve cells (neurons), neuroglia, interneuron connections of the cortex, as well as blood vessels. The cerebral cortex contains the central (cortical) sections of the analyzers and plays a leading role in higher nervous activity person.

ANATOMY
The area of ​​the cerebral cortex of one human hemisphere is about 800 cm2, thickness - 1.5-5 mm. The number of neurons in the cortex reaches more than 10 billion Kb. m. has a layered structure, contains pyramidal nerve cells and a large number of neurons with short processes. There are ancient, old and new cortex (paleo-, archi-, and neocortex). The neocortex occupies 95.6% of the surface of the cerebral hemispheres. Most of the new cortex has 6 layers, or plates (homotypic cortex): molecular, outer granular, outer pyramidal, internal granular, inner pyramidal, polymorphic. The degree of development of the plates and their cellular composition are not the same in different parts of the hemisphere; On this basis, an idea is built about the architectonics or cytoarchitectonics of the cerebral cortex, in which 52 cytoarchitectonic fields are distinguished.

The nerve fibers of the cortex are divided into radial, located perpendicular to its surface, and tangential, running parallel to the surface of the cortex; the latter form white stripes in the molecular, outer and inner granular and inner pyramidal plates. Along with the horizontal division into plates, cortical columns are distinguished, which are vertically located rows of neurons passing through all layers of the cortex. Accordingly, interneuron connections of the cerebral cortex are organized both horizontally and vertically.

The grooves and convolutions of the cerebral cortex increase its surface without increasing the volume of the hemispheres. Their formation begins in the 5th month of fetal development and ends after birth. The location of the grooves and convolutions varies individually. On the superolateral surface of the hemisphere there are large furrows- central (sulcus centralis), separating the frontal and parietal lobes, and lateral (sulcus lat.), separating the temporal lobe from the frontal and parietal. On the surface of the frontal lobe, anterior to the central sulcus, there is a precentral sulcus (sulcus precentralis), and between it and the central sulcus there is a precentral gyrus (gyrus precentralis).

Here in the V layer of the cortex lie large pyramidal neurons (Betz cells), giving rise to the pyramidal system. From the precentral sulcus, the superior and inferior frontal sulci (suici frontales sup. et inf.) extend forward, delimiting the superior, middle and inferior frontal gyri (gyri frontales sup., med. et inf.). In the parietal lobe, posterior to the central sulcus, there is a postcentral sulcus (sulcus postcentralis). Between the central and postcentral sulci is the postcentral gyrus (gyros postcentralis). From the postcentral sulcus, the intraparietal sulcus (sulcus intraparietalis) goes back, separating the superior and inferior parietal lobules (lobuli parietales sup. et inf.). The superior and inferior temporal sulci (suici temporales sup. et inf.) run along the temporal lobe, delimiting the superior, middle and inferior temporal gyri (gyri temporales sup., med. et inf.). Parts of the frontal, parietal and temporal lobes adjacent to the lateral sulcus cover the insular lobe located in the depths of this sulcus, forming its operculum. The occipital lobe on the superolateral surface of the hemisphere has no noticeable anatomical boundaries; the transverse occipital groove (sulcus occipitalis transversus) is most pronounced on it.

On the medial surface of the hemisphere, above the corpus callosum, the corpus callosum groove (sulcus corporis callosi) is visible, and the cingulate groove (sulcus cinguli) runs above it.

Between both grooves there is the cingulate gyrus (gyris cinguli), which narrows posterior to the corpus callosum and continues into the parahippocampal gyrus (gyrus parahippocampalis), which belongs to the temporal lobe. The cingulate and parahippocampal gyri are part of the limbic lobe, which belongs to the central division of the autonomic nervous system. Above the cingulate sulcus is the medial frontal gyrus (gyrus frontalis med.), and posterior to the latter lies the paracentral lobule (lobulus paracentralis). The parietal lobe is separated from the occipital lobe by the deep parieto-occipital sulcus (sulcus parietooccipitalis). Below the occipital lobe runs the calcarine groove (sulcus calcarinus). Between the parieto-occipital and curtain sulci there is a wedge (cuneus). Down from the calcarine groove is the lingual gyrus (gyrus lingualis). On the lower surface of the temporal lobe, the occipitotemporal sulcus (sulcus occipitotemporalis) is distinguished, which separates the medial and lateral occipitotemporal gyrus (gyri occipitotemporales med. et lat.). On the lower surface of the frontal lobe there is an olfactory groove (sulcus olfactorius), on which the olfactory bulb and olfactory tract lie. More lateral are the orbital sulci and gyri (suici et gyri orbitales).

Blood supply to the cerebral cortex is carried out by cortical arteries arising from the anterior, middle and posterior cerebral arteries, as well as branches of the medullary arteries. In the cortex, the arteries have a straight course and form continuous capillary networks in its various layers. There are no anastomoses between precapillary arterioles. Venous blood from the capillary networks enters the cortical and medullary veins, which flow into the superficial veins of the cerebrum.

PHYSIOLOGY
The functional activity of the cerebral cortex is considered in close connection with the activity of other brain structures. Along with the mechanisms of functioning of the cerebral cortex common to the nervous system, it has specific features related to its architectonics. The cytoarchitectural features of the neocortex make it possible to identify a number of areas (frontal, temporal, post- and precentral, parietal, occipital) that are associated with the implementation of certain psychosomatic functions (corticolization functions). A map of the localization of each sensory and motor function in the cerebral cortex is the basis for the topical diagnosis of many neurological diseases. The localization of functions is largely determined by the morphological connections of specific cortical fields within each region with certain peripheral receptors or effectors. Such morphological connections make it possible to divide the main functions of the cerebral cortex into sensory and motor.

Afferent impulses from peripheral receptors reach the sensory areas of the cerebral cortex through specific nuclei of the thalamus. In each hemisphere of the brain, primary zones of representation are distinguished different types sensitivity. The primary somatosensory area is located in the postcentral gyrus just posterior to the central sulcus. The entire receptor surface of the skin of the human body is projected onto the postcentral gyrus. The largest surface of the gyrus is occupied by receptors of the hands, vocal apparatus and face, a smaller part is occupied by receptors of the trunk, thigh and lower leg. Damage to areas of the somatosensory area leads to loss of fine sensitivity of that part of the body that is represented in the damaged area of ​​the cortex. This is due to the fact that the location of each neuron in the somatosensory cortex clearly corresponds to the localization of its receptive field on the surface of the body, opposite to the postcentral gyrus. The interaction between neurons occurs mainly within vertical columns (columns) located perpendicular to the surface of the cortex and covering all six of its layers. Within each column, the localization of irritation on the body surface is determined, as well as the location and strength of two simultaneously applied irritants are distinguished (discrimination). Many columns determine the quality of the stimulus: sharpness, roughness, temperature. The cerebral cortex also has a secondary somatosensory area located at the lateral end of the postcentral gyrus. It receives signals from both the same (ipsilateral) and the opposite (contralateral) surface of the body and carries out bilateral sensorimotor coordination of activity (for example, palpating with both hands).

Another primary sensory projection zone is the inner surface of the occipital region, in which visual signals are analyzed. In humans, fields 17, 18 and 19 of the visual cortex provide not only identification of a visual stimulus, but also association visual perception with other types of sensitivity. The visual cortex has a strict retinotopic organization, in which the point localization of photoreceptors in the retina corresponds to the location of neurons in the visual fields. Depending on the complexity of the image on the retina, excitable neurons in the visual cortex are divided into three types: 1) neurons with simple receptive fields that respond, for example, to stimuli in the form of the difference between light and dark stripes; 2) neurons with complex receptive fields, excited when a differentiated stimulus acts on the retina (for example, a dark stripe strictly oriented on a light background); 3) neurons with highly complex fields that respond to differentiated stimuli with many parameters (for example, on a light background, a dark strip of a certain size and shape, strictly oriented and moving in space). Neurons of the visual cortex are also grouped into columns, each of which performs an integrative function. The integrative functions of the visual cortex include not only mechanisms for analyzing light stimuli, but also the formation of a visual image based on the mechanisms of color perception, binocular vision and regulation of eye movement.

The auditory zone of the cerebral cortex (fields 41 and 42) occupies the dorsolateral parts of the temporal lobe. The auditory cortex also has a representation various parts snails Individual cortical neurons have maximum sensitivity to a specific sound frequency (characteristic frequency). As in the visual cortex, in the auditory cortex, the tonotopic organization of neurons is integrated with the mechanisms of binaural sound perception, which ensure the determination of the position of the sound source in space.

Other sensory functions, such as taste, smell, and balance, are less corticolized or associated with ancient and old cortical structures. Limbic structures, to a greater extent than neocortical structures, are involved in cortico-visceral relationships and play a primary role in regulating the activity of internal organs.

The motor functions of the cerebral cortex are associated with the primary motor motor area, localized in the precentral gyrus, premotor and secondary motor area. The primary motor area provides contraction of individual muscles. It is formed by a set of vertical neuronal columns, each of which excites or inhibits one group of motor neurons innervating a separate muscle. Large areas of the motor cortex regulate contractions of the muscles of the fingers, lips and tongue, which carry out numerous and very subtle movements (for example, speaking or playing the piano). The muscles of the back, abdomen and lower extremities, involved in maintaining posture and performing less subtle movements, correspond to only a small area of ​​the motor cortex. The motor cortex gives rise to the pyramidal or corticospinal tract, which directly regulates the activity of spinal cord motor neurons when performing precise movements.

The associative areas of the cerebral cortex (frontal, temporal, occipito-parietal) provide both inter-analyzer interaction and complex integration of excitations in the process of organizing goal-directed behavior. for example, the parietal region is involved in organizing visual tracking of a moving stimulus. The parietal and temporal zones of the cortex are also involved in the formation of the act of speech and in the perception of the shape and location of the body in space. The frontal lobes in humans are the structural basis for the implementation of higher mental functions, which are manifested in the formation personal qualities, creative processes and desires. The construction of goal-directed behavior based on anticipation is sharply disrupted when the frontal parts of the cerebral cortex are damaged.

The neurophysiological basis of integrative processes in the cerebral cortex is the mechanism of convergence of excitations to individual neurons. In the structures of the brain, including the cerebral cortex, multisensory convergence is most pronounced, characterized by the meeting and interaction on a single nerve cell of two or more heterogeneous afferent excitations of different sensory modalities. At the same time, other types of convergence characteristic only of it appear in the cerebral cortex. During the formation of conditioned reactions, sensory-biological convergence takes place, when excitations arising from the action of conditioned and unconditioned stimuli converge to a separate cortical neuron. Ascending excitations from subcortical structures can converge to the neurons of the cerebral cortex during food, pain, sexual and other motivations. In the projection areas of the cerebral cortex, afferent-efferent convergence can be observed when an individual neuron receives afferent excitation from peripheral receptors and efferent excitation along the collaterals of the axons of pyramidal cells.

The neurophysiological basis that unites the neurons of the cerebral cortex is not only intracortical connections, but also the mechanisms of cortical-subcortical relationships. On the one hand, they develop due to ascending activating influences from subcortical structures, on the other, due to descending influences of the cortex on subcortical structures with recurrent generalization of excitations. Unity of functioning of the right and left hemispheres of K. b. m. is provided by commissural fibers entering the corpus callosum. When it is damaged or cut, each hemisphere begins to independently carry out its specific functions. In most healthy people, the left hemisphere dominates, providing interpretation and formation of oral and written language and control of actions right hand. The right hemisphere provides spatial and temporal relationships, and is also involved in musical and artistic creativity. The degree of severity of interhemispheric asymmetry can be detected based on EEG analysis (see Electroencephalography)

The activity of the cerebral cortex is associated with such higher functions of the nervous system as sleep and wakefulness, memory and learning, thinking and awareness of perceived signals from environment.

PATHOLOGY
Damage to the cerebral cortex occurs in cases of cerebral circulation disorders, for example, ischemic and hemorrhagic strokes, thrombosis of the venous system of the brain, inflammatory intracranial processes: encephalitis, meningitis, arachnoiditis (see Meninges), brain abscesses, brain tumors, traumatic brain injury. In these cases, not only the cortex, but also the subcortical white matter, and often the deep structures of the brain (basal ganglia, hypothalamus, etc.) are often affected. Relatively selective damage to the cerebral cortex is observed in some hereditary degenerative diseases of the central nervous system, for example, in Pick's disease, Alzheimer's disease, etc. Intravital brain imaging with X-ray axial computed tomography has made it possible to identify a group of brain diseases accompanied by brain atrophy and destruction of cortical neurons. These include many hereditary diseases of the metabolism of lipids, amino acids, vitamins, nucleic acids, as well as progressive systemic degeneration of the brain with an unclear primary biochemical defect, slow neuroinfections, post-traumatic and vascular encephalopathies. In childhood, in addition, lesions of the cerebral cortex occur with various malformations of the brain, for example, microcephaly, anencephaly, microgyria, and hydrocephalus.

The abundance of causes of pathology determines the diversity of the pathological picture of the lesion: from the complete absence of the cortex in case of malformations of the brain, its destruction in injuries, strokes, to subtle changes in the cytoarchitectonics of the cortex, disruption of its layering, proliferation of glia, changes in the synaptic apparatus, dendritic tree, the presence of diapedetic hemorrhages and inflammatory infiltrates, perivascular and pericellular edema, etc.

The most extensive damage to the cerebral cortex is accompanied by the disappearance of mental activity and a complex of diffuse and local symptoms. Local damage to the projection cortical zones of individual analyzers leads to the development of paresis and paralysis, central loss of vision, hearing, and sensitivity. Damage to the secondary associative fields of the cortex is accompanied by the occurrence of apraxia, agnosia, damage to speech zones - disorders of speech, writing and reading (aphasia, alalia, agraphia, alexia, etc.).

In the topical diagnosis of lesions of the cerebral cortex, it is important to distinguish between symptom complexes of pathology of the frontal, parietal, occipital and temporal lobes.

Damage to the frontal lobe in the region of the anterior central gyrus is manifested by monoplegia, hemiplegia, and insufficiency of central innervation of the facial and hypoglossal nerves. Irritation of this area causes partial seizures involving the upper or lower limb on the side opposite the lesion (so-called motor Jacksonian epilepsy). Damage to the posterior sections of the middle frontal gyrus (cortical center of gaze) leads to paralysis or paresis of gaze with a forced rotation of both eyes towards the pathological focus, and irritation of this area is accompanied by a convulsive gaze with rotation of the eyes in the opposite direction. Damage to the posterior parts of the inferior frontal gyrus (Broca's area) leads to the appearance of motor aphasia, often in combination with agraphia. Motor aphasia, like other speech disorders, occurs when the dominant (left in right-handed people) hemisphere of the brain is damaged. Hemiataxia on the side opposite to the lesion (damage to the superior frontal gyrus), symptoms of oral automatism, and grasping reflexes (which are physiological in early childhood) are also observed. For lesions of the frontal lobe, peculiar mental disorders (“frontal psyche”) are typical, manifested by a loss of purposefulness of mental processes, the ability to long-term planning actions, apathy, weakness of will, loss of initiative; there is euphoria, a tendency to make shallow jokes, and sloppiness; behavior becomes inadequate to the situation and surrounding conditions.

Damage to the parietal lobe in the region of the posterior central gyrus leads to mono- or hemianesthesia, sensitive (associated with a violation of deep sensitivity) hemiataxia on the side opposite to the pathological focus. Irritation of this area causes sensory Jacksonian attacks with partial numbness, burning, and the appearance of paresthesia on the opposite side of the body. Astereognosis, disturbance of the body diagram (autotopagnosia, pseudopoly- or pseudoamelia), anosognosia (denial of one's own functional defect), apraxia, and less commonly acalculia, alexia are also observed.

Damage to the occipital lobe is manifested by visual disturbances in the form of homonymous quadrant hemianopia, central scotoma, distortion of the shape of visible objects (metamorphopsia) or their size (macro- or micropsia), the appearance of visual illusions or visual hallucinations; visual agnosia, decreased visual memory and orientation are determined. Less commonly, hemiataxia is observed on the opposite side due to a violation of the occipital-pontine-cerebellar system.

Damage to the temporal lobe is accompanied by auditory agnosia, sensory aphasia (involvement of Wernicke's center), homonymous quadrant hemianopsia (damage to optic radiation), hemiataxia (disturbance of temporo-pontine-cerebellar connections). When the temporal lobe is irritated, auditory, gustatory and olfactory hallucinations, attacks of dizziness, short-term memory impairment, twilight states, and complex psychomotor automatisms occur. The complex of these disorders often occurs paroxysmally and is combined with complex autonomic disorders, sometimes with seizures (temporal lobe epilepsy).

Topical diagnosis of lesions of the cerebral cortex is based primarily on the results of clinical studies. Along with a neurological examination of the patient great importance has neuropsychological and pathopsychological studies using special samples and tests. Neuropsychological examination technique developed by A.R. Luria, includes special tests to identify disorders of praxis (kinesthetic, dynamic, visuospatial and constructive), gnosis (visual, auditory, tactile, etc.), speech function (impressive, expressive and nominative), memory (auditory, visual), thinking, as well as functions of interhemispheric interaction. The normal structure of higher mental functions is not immediately formed in the process of ontogenesis, therefore, what is a deviation from the norm or pathology in an adult, in a child can be a manifestation of only a certain stage of development of the central nervous system. Differentiated neuropsychological examination schemes are used with special sets of samples and tests for the main age periods of childhood, starting from early age and up to preschool. To study thinking, special personality tests have been developed with a total quantitative assessment their results. These include the method of calculating the “intelligence quotient”, etc. A high-quality neuropsychological examination of the patient allows high degree accurately determine the topic of functional deficit of the cerebral cortex.

To identify a structural or functional defect in the cerebral cortex, along with classical electroencephalography, methods of spectral frequency analysis of EEG with computer mapping are used functional activity cerebral cortex, as well as the technique of evoked somatosensory, visual and auditory cortical potentials, which make it possible to qualitatively and quantitatively study and visualize on the display screen functional deficiency or irritation of certain areas of the cortex. A method for recording electromagnetic potentials of the brain is also used - magnetoencephalography, as well as magnetoencephalographic mapping of the brain. Visualization of structural defects in the cerebral cortex is provided by x-ray axial computed tomography, magnetic resonance imaging, and in young children and newborns - ultrasound neurosonography through an open large fontanel.

Medicine and veterinary medicine

Pyramidal neurons. Large cells, perikarya 10-130 microns in size. The cell has an apical dendrite, which is directed towards the molecular layer; lateral processes – dendrites; a long axon comes from the base - it will be a motor nerve fiber (the beginning of the formation of the pyramidal tract).

Lecture on histology No. 13

Central nervous system. Cerebral cortex. Cytoarchitecture of the layers of the cerebral cortex. Neuronal composition. Characteristics of pyramidal neurons. Module structural and functional unit of the cerebral cortex. Cerebellum. Structure and neural composition of the cerebellar cortex.

Source of development of gray and white matter brain

Develops from the mantle or mantle zone of the neural tube gray matter

Marginal veil white matter

Components gray matter of the brain (neocortex)

6 layers:

1. Molecular is formed mainly by processes of cells below the underlying layers, but there are single neurons that are called horizontal.
2. External granular present star-shaped neurons and not numerous pyramidal neurons.
3. Outer pyramidal (pyramidal) the widest layer, contained pyramidal neurons.
4. Internal granular fine star-shaped neurons carry out intra-cortical connections (do not enter the white matter).
5. Internal pyramidal (ganglionic) is represented by large pyramidal neurons or Betts cells.
6. Polymorphic cell forms are varied, the cells are small, their axons extend into the white matter.

Stellate neurons.Perikarya have a round or triangular shape, a diameter of 4-8 microns; the axon and dendrites of these cells participate in intracortical connections.

Pyramidal neurons.Large cells, perikarya 10-130 microns in size. The cell has an apical dendrite, which is directed towards the molecular layer; lateral processes dendrites; a long axon comes from the base and will be a motor nerve fiber (the beginning of the formation of the pyramidal tract). Collaterals come from the axon: they go to neighboring cells, or rise up and interact with the overlying layers.

general characteristics cortical neurons:

All neurons of the cerebral cortex are multipolar. By function, layers 1-4: associative (intercalary), 5-6 motor.

Structural and functional unit of the brain: module

Module (in the cerebral cortex up to 3 million) a vertical column with a diameter of 300 microns, perpendicular to the surface of the cortex and passing through the entire thickness of the cortex.

In the center of the module:

• One corticocarticular nerve fiber is a nerve fiber within the cortex; coming either from pyramidal neurons of the same hemisphere (associative-intercalary) or from the opposite hemisphere (commissural).
• Two thalamocortical fibers (affirent-sensitive fibers), coming from the thalamus opticus and running in 4 layers; then an efferent nerve fiber is formed, formed by the axons of Best cells.

Cytoarchitectureareas of the cortex that differ from each other in the structure and location of cells.

Myeloarchitectureareas of the cortex that differ from each other in the characteristics of the arrangement of fibers.

Fields various areas of the cortex that differ from each other: cyto, myeloarchitecture and functional significance.

Types of bark:

1. Granular sensitive center, in which layers 2 and 4 are well developed; they terminate the (afferent) sensory nerve fibers coming from the organs of smell, hearing, and vision.
2. Agranular motor center, in which layers 3, 5 and 6 are developed.

A reliable morphological equivalent of intelligence is the number of synapses of associative neurons (layers 1-4), normally 10 thousand.

Cerebellum

Source of development of the cerebellum hindbrain

Functions: coordinates movement and balance

The cerebellum has a large number of convolutions, in the preparation in the form of a branched tree.

The gyri are separated by grooves. Each gyrus contains: a narrow plate of white matter, completely covered with gray matter (cortex). Clusters of neurons lie deep in the white matter of the cerebellum.: cerebellar nuclei.

The gray matter or cerebellar cortex has three layers:

1. External Molecular is represented by multipolar associative (intercalary) neurons. There are 2 types of cells:

• Basket neurons are located in the lower third of the molecular layer, cells of irregular shape and small sizes. The axon of the cell synapses with the perikareon of the Purkenje cell, where it branches and forms a plexus in the form of a basket. Dendrites in the molecular layer.
• Stellate (large and small) are localized to the outside of the molecular layer (surface of the cortex).Large stellate neurons:the axon synapses with the perikarya of Purkenje cells and takes part in the formation of the basket. Dendrites in the molecular layer.Small stellate neurons: The axon synapses with the dendrites of Purkenje cells.

1. Middle Ganglionic - represented by one layer, the bodies of multipolar motor neurons or Purkinje cells. These are large pear-shaped cells from the perikaryon (body) with 2-3 dendrites extending into the molecular layer. The axon arises from the cell body and passes through the granular layer into the white matter, where it ends at the cerebellar nuclei. Purkinje cell axons are the only efferent (motor) nerve fibers emerging from the cerebellar cortex. Closer to the cell body, collaterals depart from the axon, which go to the ganglion layer and the deep parts of the molecular layer, where they synapse with the bodies and dendritesneighboring Purkinje cells.
2. Internal Granular all cells are polar and associative contains two types of cells:

1-Cells-Grains small cells, perikaryons have a diameter of 4-6 microns, dendrites: short 3-4 pieces, directed towards the white matter, reminiscent of bird's feet. The axon ascends into the molecular layer, where it divides in a T-shape.

2-Large stellate: with long axons and short axons Golgi cells of the second type. The large cells of the body are localized immediately under the ganglion layer. The axon synapses with rosettes of mossy fibers before they synapse with the dendrites of granule cells. Dendrites rise into the molecular layer.

Afferent (sensitive) nerve fibers:

1. Mossy fibers The terminal of a mossy nerve fiber is called a rosette. The mossy fiber rosettes synapse with the dendrites of the granule cells, forming the cerebellar glomeruli.
2. Climbing or liana-shaped fibers come from the white matter, pass through the granular layers and synapse either with the perikaryon of the Purkinje cell or with the dendrites of these cells.

Axons of granule cells synapse with dendrites:

• Cell molecular layer
• Purkenje cells
• Golgi cell type II

The inhibitory system of the cerebellum includes:

• Cells of the molecular layer
• Golgi cells type 2
• Excitatory synapses:
• Mossy fibers
• Liana fibers

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