How does the cortex work? Cerebral cortex areas

It is now known for certain that the higher functions of the nervous system, such as the ability to comprehend signals received from the external environment, to mental activity, to memorization and thinking, are largely due to the way the cortex functions. The areas of the cerebral cortex will be considered in this article.

The fact that a person is aware of his relationships with other people is connected with the excitation of neural networks. We are talking about those who are in the bark. It is the structural basis of intelligence and consciousness.

Neocortex

About 14 billion neurons have a cortex of the brain. The areas of the cerebral cortex, which will be discussed below, function thanks to them. The bulk of the neurons (about 90%) form the neocortex. It refers to the somatic nervous system, being its highest integrative department. The most important function of the neocortex is the processing and interpretation of information obtained with the help of the sense organs (visual, somatosensory, taste, auditory). It is also important that he controls precisely the complex muscular movements. There are centers in the neocortex that participate in the processes of speech, abstract thinking, and memory storage. The bulk of the processes occurring in it is the neurophysiological basis of our consciousness.

Paleocortex

Paleocortex is another large and important department that has a cortex of the brain. The areas of the cerebral cortex related to it are also very important. This part has a simpler structure than the neocortex. The processes taking place here are not always reflected in consciousness. The paleocortex contains the highest vegetative centers.

Correlation of the cortex with the underlying parts of the brain

It should be noted the relationship of the cortex of the cerebral hemispheres with the underlying parts of our brain (thalamus, basal nuclei, bridge and middle brain). It is carried out by means of large bundles of fibers that form an inner capsule. These bundles of fibers are wide layers of white matter. They contain a lot of nerve fibers (millions). Some of these fibers (axons of neurons of the thalamus) provide transmission to the cortex of nerve signals. The other part, namely the axons of the cortical neurons, serves to transfer them to the nerve centers located below.

Structure of the cerebral cortex

Do you know which department of the brain is the largest? Some of you probably guessed what was being said. This is the cortex of the brain. The areas of the cerebral cortex are just one type of parts that stand out in it. So, it is divided into the right and left hemispheres. They are connected to each other by beams of white matter, which forms a corpus callosum. The main function of the corpus callosum is to ensure the coordination of the activity of the two hemispheres.

Cerebral cortex areas by location

Although there are a lot of folds in the cerebral cortex, on the whole the arrangement of the most important furrows and gyri is characterized by constancy. Therefore, the main of them serve as a reference point for the division of cortical areas. Its outer surface is divided into 4 parts by three furrows. These shares (zones) - temporal, occipital, parietal and frontal. Although they are allocated by location, each of them has its own specific functions.

The temporal zone of the cerebral cortex is the center where the cortical layer of the auditory analyzer is located. In case of damage, deafness occurs. The auditory zone of the cerebral cortex, in addition, has the center of Wernicke's speech. In case of damage, the ability to understand spoken language is lost. It starts to be perceived as noise. In addition, in the temporal lobe there are neural centers related to the vestibular apparatus. The sense of balance is violated in case of damage.

The zones of speech of the cerebral cortex are concentrated in the frontal lobe. It is here that the motor center is located. If it is damaged in the right hemisphere , the ability to change intonation and the timbre of speech will be lost. It becomes monotonous. If the damage relates to the left hemisphere, where there are also speech zones of the cerebral cortex, the articulation disappears. The ability to sing and articulate speech also disappears.

The visual area of the cerebral cortex corresponds to the occipital lobe. Here is the department, which is responsible for our vision as such. The surrounding world, we perceive it is the brain, not the eyes. For the vision is just the occipital part. Therefore, if it is damaged, full or partial blindness develops.

The dark share also has its own specific functions. She is responsible for analyzing information related to general sensitivity: tactile, temperature, pain. In case of damage, the ability to recognize objects to the touch, as well as some other abilities, is lost.

Motor zone

I would like to talk about her separately. The fact is that the motor zone of the cerebral cortex does not correlate with the proportions, which we described above. It is a part of the cortex that contains descending direct connections to the spinal cord, more precisely, to its motoneurons. The so-called neurons, which directly control the work of muscles.

The main motor zone of the cerebral cortex is located in the precentral gyrus. In many of its aspects this gyrus is a mirror image of another zone, sensory. There is a contralateral innervation. In other words, innervation occurs in relation to the muscles located on the opposite side of the body. An exception is the facial area, in which the bilateral control of the muscles of the jaw and lower part of the face.

Another additional motor area of the cerebral cortex is located in the area below the main zone. Scientists believe that it has independent functions associated with the output of motor impulses. This motor zone of the cerebral cortex was also studied by scientists. In experiments on animals, it was found that its stimulation leads to motor reactions. And this happens even in the event that the main motor zone of the cerebral cortex was destroyed before it. In the dominant hemisphere, it is involved in the motivation of speech and in the planning of movements. Scientists believe that its damage leads to dynamic aphasia.

Cerebral cortex zones by function and structure

As a result of clinical observations and physiological experiments carried out in the second half of the 19th century, the boundaries of the areas into which various receptor surfaces were projected were established. Among the latter, the sense organs directed toward the external world (skin sensitivity, hearing, vision) and those that are incorporated in the organs of motion (the kinetic or motor analyzer) are distinguished as sensory organs .

The occipital region is the zone of the visual analyzer (fields 17 to 19), the upper temporal region of the auditory analyzer (fields 22, 41 and 42), the postcentral region of the skin-kinesthetic analyzer (fields 1, 2 and 3).

Cortical representatives of various analyzers in terms of functions and structure are divided into the following 3 zones of the cerebral cortex: primary, secondary and tertiary. In the early period, during the development of the embryo, the primary ones are laid, which are characterized by simple cytoarchitecture. In the last turn develop tertiary. They have the most complex structure. Intermediate position from this point of view is occupied by the secondary zones of the hemispheres of the cerebral cortex. We suggest that you take a closer look at the functions and structure of each of them, as well as their relationship to the brain regions below, in particular, to the thalamus.

Central fields

Scientists have accumulated considerable experience in clinical research over many years of study. As a result of observations it was established, in particular, that the damage to certain fields in the cortical representatives of the analyzers affects the overall clinical picture is far from being equivalent. Among the remaining fields in this respect one is allocated, which in the nuclear zone occupies a central position. It is called primary, or central. He is the field at number 17 in the visual zone, in the auditory - at number 41, and in the kinesthetic - 3. Their damage leads to very serious consequences. The ability to perceive or carry out the most subtle differentiation of the stimuli of the corresponding analyzers is lost.

Primary zones

In the primary zone, the most developed complex of neurons, which is adapted to provide cortical-subcortical two-way connections. He connects the cortex with one or another sense organ in the shortest and most direct way. Because of this, the primary zones of the cerebral cortex can adequately isolate the stimuli.

An important common feature of the functional and structural organization of these areas is that they all have a clear somatotypic projection. This means that individual points of the periphery (the retina of the eye, the skin surface, the cochlea of the inner ear, the skeletal musculature) are projected into the corresponding, strictly delineated points located in the primary cortex of the corresponding analyzer. For this reason, they began to be called projection.

Secondary zones

Otherwise they are called peripheral, and this is not accidental. They are located in the nuclear sections of the cortex, in their peripheral regions. Secondary zones differ from primary, or central, in physiological manifestations, neuronal organization and features of architectonics.

What effects are observed when they are electrically irritated or affected? These effects relate mainly to more complex types of mental processes. If the secondary zones are affected, the elementary sensations are relatively preserved. Mostly, the ability to correctly reflect mutual relationships and whole complexes of composite elements of various objects that we perceive is upset. If the secondary zones of the auditory and visual cortex are irritated, then auditory and visual hallucinations are observed, unfolded in a certain sequence (temporal and spatial).

These regions are very important for the realization of the interconnection of stimuli, the isolation of which occurs with the help of primary zones. In addition, they play a significant role in integrating the functions of the nuclear fields of various analyzers when combining receptions into complex complexes.

Secondary zones, therefore, are important for the realization of more complex forms of mental processes that require coordination and are associated with a careful analysis of the relationships of objective stimuli, as well as with orientation in time and in the surrounding space. At the same time, connections are established, called associations. The afferent impulses, which from the receptors of various surface sensory organs are directed to the cortex, reach these fields through a variety of additional switching operations in the associational nuclei of the thalamus (visual hillock). Unlike them, the afferent impulses that follow in the primary zones reach them in a shorter way through the relay-core of the visual hillock.

What is the thalamus

Fibers from thalamic nuclei (one or several) fit each part of the hemispheres of our brain. The visual hillock, or thalamus, is in the forebrain, in its central region. It consists of a set of nuclei, each of which transmits an impulse to a strictly defined section of the cortex.

All signals coming to it (except for olfactory ones) pass through the relay and integrative nuclei of the thalamus. Then the fibers go from them to the sensory zones (in the parietal lobe - to the taste and somatosensory, in the temporal - to the auditory in the occipital - to the visual). Pulses come from the ventro-basal complex, the medial and lateral nuclei, respectively. As for the motor cortical areas, they have a connection with the ventrolateral and anterior ventral thalamus nuclei.

Desynchronization of EEG

What happens if a person who is in a state of rest suddenly presents a strong stimulus? Of course, he immediately pricked up and concentrated his attention on this stimulus. The transition of mental activity, carried out from rest to the state of activity, corresponds to the replacement of the alpha-rhythm of the EEG by the beta-rhythm, as well as to other fluctuations, more frequent. This transition, called desynchronization of the EEG, appears as a result of sensory excitations coming from the nonspecific nuclei of the thalamus in the cortex.

Activating reticular system

Nonspecific nuclei form a diffuse nerve network, located in the thalamus, in its medial parts. This front section of the APC (activating the reticular system), which regulates the excitability of the cortex. Various sensor signals can activate the APC. They can be visual, vestibular, somatosensory, olfactory and auditory. APC is the channel through which these signals are transmitted to the surface layers of the cortex through nonspecific nuclei located in the thalamus. Excitation of APC plays an important role. It is necessary to maintain a wakeful state. In experimental animals, in which this system was destroyed, a comatose, dreamlike state was observed.

Tertiary zones

The functional relationships that are traced between the analyzers are even more complex than described above. Morphologically, their further complication is expressed in the fact that in the process of growth along the hemisphere surface of nuclear fields of analyzers, these zones overlap. At the cortical ends of the analyzers, "overlap zones" are formed, that is, tertiary zones. These formations refer to the most complex types of combining the activity of the skin-kinesthetic, auditory and visual analyzers. Tertiary zones are located beyond the boundaries of their own nuclear fields. Therefore, their irritation and damage does not lead to pronounced fallout phenomena. Also, no significant effects are observed with respect to the specific functions of the analyzer.

Tertiary zones are special areas of the cortex. They can be called a collection of "scattered" elements of various analyzers. That is, they are elements that by themselves are no longer capable of producing any complicated syntheses or analyzes of stimuli. The territory they occupy is quite extensive. It splits into a number of areas. Briefly describe them.

The upper parietal region is important for integrating the movements of the whole body with visual analyzers, as well as for shaping the body scheme. As for the lower parietal, it refers to the unification of abstract and generalized forms of signaling associated with complex and subtly differentiated verbal and objective actions, the performance of which is controlled by sight.

The area of the temporo-parietal-occipital region is also very important. It is responsible for the complex types of integration of the visual and auditory analyzers with written and oral speech.

Note that the tertiary zones have the most complex chains of communication in comparison with the primary and secondary ones. Bilateral relations are observed in them with a complex of thalamus nuclei, which in turn are connected with relay-nuclei by means of a long chain of internal bonds that are present directly in the thalamus.

On the basis of the foregoing, it is clear that in the human of the zone the primary, secondary and tertiary regions are cortical areas that are highly specialized. Especially it is necessary to emphasize that the 3 groups of cortical zones described above, in a normally functioning brain, together with systems of connections and switching between themselves, as well as with subcortical formations function as one complex differentiated whole.