Why is the top layer of the brain called the cortex. Functions and structure of the cerebral cortex

12.10.2019

The brain is a mysterious organ that is constantly being studied by scientists and remains not fully explored. The structural system is not simple and is a combination of neuronal cells that are grouped into separate sections. The cerebral cortex is present in most animals and mammals, but it is in the human body that it has received greater development. This was facilitated by labor activity.

Why is the brain called gray matter or gray matter? It is grayish, but it has white, red and black colors. The gray substance represents different types of cells, and the white substance represents nervous matter. Red is blood vessels, and black is melanin pigment, which is responsible for the color of hair and skin.

The structure of the brain

The main body is divided into five main parts. The first part is oblong. It is an extension of the spinal cord, which controls communication with the activities of the body and is composed of a gray and white substance. The second, middle, includes four hillocks, of which two are responsible for auditory, and two for visual function. The third, posterior, includes the bridge and the cerebellum or cerebellum. Fourth, buffer hypothalamus and thalamus. Fifth, final, which forms two hemispheres.

The surface consists of grooves and brains covered with a shell. This department makes up 80% of the total weight of a person. Also, the brain can be divided into three parts cerebellum, stem and hemispheres. It is covered with three layers that protect and nourish the main organ. This is an arachnoid layer in which the cerebral fluid circulates, soft contains blood vessels, hard close to the brain and protects it from damage.

Brain Functions

Brain activity includes the basic functions of gray matter. These are sensory, visual, auditory, olfactory, tactile reactions and motor functions. However, all the main control centers are located in the oblong part, where the activities of the cardiovascular system, protective reactions and muscle activity are coordinated.

The motor pathways of the oblong organ create a crossing with a transition to the opposite side. This leads to the fact that receptors are first formed in the right region, after which impulses arrive in the left region. Speech is performed in the cerebral hemispheres. The posterior section is responsible for the vestibular apparatus.

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

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

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

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

Three main regions are distinguished on the hemispheric surface:

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

Features of the device and activities

The cerebral cortex is divided into 4 types:

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

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

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

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

Structure

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

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

The cerebral cortex consists of six cytoarchitectonic layers.

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

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

Vertical organization

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

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

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

Horizontal organization

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

associative;
sensory (sensitive);
motor.

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

sensitive

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

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

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

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

Motor

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

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

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

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

Associative

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

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

Features of localization by fields

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

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

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

Table 1

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

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

The cerebral cortex is present in the structure of the body of many creatures, but in humans it has reached its perfection. Scientists say that this became possible thanks to the age-old labor activity that accompanies us all the time. Unlike animals, birds or fish, a person is constantly developing his abilities and this improves his brain activity, including the functions of the cerebral cortex.

But, let's approach this gradually, first considering the structure of the crust, which is undoubtedly very exciting.

The internal structure of the cerebral cortex

The cerebral cortex has over 15 billion nerve cells and fibers. Each of them has a different shape, and form several unique layers responsible for certain functions. For example, the functionality of the cells of the second and third layers lies in the transformation of excitation and the correct redirection to certain parts of the brain. And, for example, centrifugal impulses represent the performance of the fifth layer. Let's take a closer look at each layer.

The numbering of the layers of the brain starts from the surface and goes deeper:

The molecular layer has a fundamental difference in its low level of cells. Their very limited number, consisting of nerve fibers are closely interconnected with each other.
The granular layer is otherwise called the outer layer. This is due to the presence of an inner layer.
The pyramidal level is named after its structure, because it has a pyramidal structure of neurons of various sizes.
The granular layer No. 2 is called the inner layer.
Pyramidal level No. 2 is similar to the third level. Its composition is the neurons of the pyramidal image having an average and big size. They penetrate to the molecular level because it contains apical dendrites.
The sixth layer is fusiform cells, which have the second name "fusiform", which systematically pass into the white matter of the brain.

If we consider these levels in more depth, it turns out that the cerebral cortex takes on the projections of each level of excitation that occur in different parts of the central nervous system and are called "underlying". They, in turn, are transported to the brain through the nervous pathways of the human body.

Presentation: "Localization of higher mental functions in the cerebral cortex"

Thus, the cerebral cortex is the organ of the higher nervous activity of a person, and regulates absolutely everything. nervous processes occurring in the body.

And this happens due to the peculiarities of its structure, and it is divided into three zones: associative, motor and sensory.

Modern understanding of the structure of the cerebral cortex

It is worth noting that there is a somewhat different idea of its structure. According to him, there are three zones that distinguish from each other not only the structure, but also its functional purpose.

The primary zone (motor), in which its specialized and highly differentiated nerve cells are located, receives impulses from auditory, visual and other receptors. This is a very important area, the defeat of which can lead to serious disorders of motor and sensory function.
The secondary (sensory) zone is responsible for the information processing functions. In addition, its structure consists of the peripheral sections of the analyzer nuclei, which establish the correct connections between stimuli. Her defeat threatens a person with a serious disorder of perception.
The associative, or tertiary zone, its structure allows it to be excited by impulses coming from the receptors of the skin, hearing, etc. It forms conditioned reflexes person, helping to cognize the surrounding reality.

Presentation: "Cerebral cortex"

Main functions

What is the difference between human and animal cerebral cortex? The fact that its purpose is to generalize all departments and control work. These functions provide billions of neurons with a diverse structure. These include such types as intercalary, afferent and efferent. Therefore, it will be relevant to consider each of these types in more detail.

The intercalated view of neurons has, at first glance, mutually exclusive functions, namely, inhibition and excitation.

The afferent type of neurons is responsible for impulses, or rather for their transmission. Efferent, in turn, provide a specific area of human activity and refer to the periphery.

Of course, this is medical terminology and it is worth digressing from it, concretizing the functionality of the human cerebral cortex on a simple in native language. So, the cerebral cortex is responsible for the following functions:

The ability to correctly establish a connection between internal organs and tissues. And what's more, it makes it perfect. This possibility is based on conditional and unconditioned reflexes human body.
Organization of the relationship between the human body and the environment. In addition, it controls the functionality of organs, corrects their work and is responsible for the metabolism in the human body.
100% responsible for ensuring that the thinking processes are correct.
And the final, but no less important function is the highest level of nervous activity.

Having become acquainted with these functions, we come to understand that, which allowed each person and the whole family as a whole, to learn to control the processes that occur in the body.

Presentation: "Structural and functional characteristics of the sensory cortex"

Academician Pavlov, in his multiple studies, has repeatedly pointed out that it is the cortex that is both the manager and the distributor of human and animal activity.

But, it is also worth noting that the cerebral cortex has ambiguous functions. This is mainly manifested in the work of the central gyrus and the frontal lobes, which are responsible for muscle contraction on the side completely opposite to this irritation.

In addition, its different parts are responsible for different functions. For example, the occipital lobes are for visual, and the temporal lobes are for auditory functions:

To be more specific, the occipital lobe of the cortex is actually a projection of the retina, which is responsible for its visual functions. If any violations occur in it, a person may lose orientation in an unfamiliar environment and even complete, irreversible blindness.
The temporal lobe is an area of auditory reception that receives impulses from the cochlea of the inner ear, that is, is responsible for its auditory functions. Damage to this part of the cortex threatens a person with complete or partial deafness, which is accompanied by a complete misunderstanding of words.
The lower lobe of the central gyrus is responsible for brain analyzers or, in other words, taste reception. She receives impulses from the oral mucosa and her defeat threatens to lose all taste sensations.
And finally, the anterior part of the cerebral cortex, in which the piriform lobe is located, is responsible for olfactory reception, that is, the function of the nose. Impulses come into it from the nasal mucosa, if it is affected, then the person will lose his sense of smell.

It is not worth reminding once again that a person is at the highest stage of development.

This confirms the structure of a particularly developed frontal region, which is responsible for labor activity and speech. It is also important in the process of formation of human behavioral reactions and its adaptive functions.

There are many studies, including the work of the famous academician Pavlov, who worked with dogs, studying the structure and functioning of the cerebral cortex. All of them prove the advantages of man over animals, precisely due to its special structure.

True, we should not forget that all parts are in close contact with each other and depend on the work of each of its components, so that the perfection of a person is the key to the work of the brain as a whole.

From this article, the reader has already understood that the human brain is complex and still poorly understood. However, it is the perfect device. By the way, few people know that the power of processing processes in the brain is so high that next to it the most powerful computer in the world is powerless.

Here are some more interesting facts that scientists have published after a series of tests and studies:

2017 was marked by an experiment in which a hyper-powerful PC tried to simulate only 1 second of brain activity. The test took about 40 minutes. The result of the experiment - the computer did not cope with the task.
Memory human brain holds n-number bt, which is expressed by 8432 zeros. Approximately it is 1000 Tb. If on an example, then the historical information for the last 9 centuries is stored in the national British archive and its volume is only 70 Tb. Feel how significant the difference between these numbers is.
The human brain contains 100 thousand kilometers of blood vessels, 100 billion neurons (a figure equal to the number of stars in our entire galaxy). In addition, there are one hundred trillion neural connections in the brain that are responsible for the formation of memories. Thus, when you learn something new, the structure of the brain changes.
During awakening, the brain accumulates an electric field with a power of 23 W - this is enough to light Ilyich's lamp.
By weight, the brain consists of 2% of the total mass, but it uses approximately 16% of the energy in the body and more than 17% of the oxygen in the blood.
Another interesting fact that the brain consists of 75% water, and the structure is somewhat similar to Tofu cheese. And 60% of the brain is fat. In view of this, for the correct functioning of the brain, a healthy and proper nutrition. Eat fish every day olive oil, seeds or nuts - and your brain will work long and clear.
Some scientists, after conducting a series of studies, noticed that when dieting, the brain begins to “eat” itself. And low oxygen levels for five minutes can lead to irreversible consequences.
Surprisingly, a human being is not able to tickle himself, because. the brain tunes in to external stimuli and in order not to miss these signals, the actions of the person himself are slightly ignored.
Forgetfulness is natural process. That is, the elimination of unnecessary data allows the CNS to be flexible. And the effect of alcoholic beverages on memory is explained by the fact that alcohol slows down the processes.
The brain's response to alcoholic beverages is six minutes.

The activation of the intellect allows the production of additional brain tissue that compensates for those that are sick. In view of this, it is recommended to engage in development, which in the future will save you from a weak mind and various mental disorders.

Engage in new activities - this is best for brain development. For example, communication with people who are superior to you in one or another intellectual field is a powerful tool for developing your intellect.

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

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

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

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

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

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

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

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

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

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

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

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

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

On the topic : the structure of the cerebral cortex

Prepared

The cortex is the most complex highly differentiated section of the CNS. It is divided morphologically into 6 layers, which differ in the content of neurons and the position of nerve variables. 3 types of neurons - pyramidal, stellate (astrocytes), spindle-shaped, which are interconnected.

The main role in the afferent function and excitation switching processes belongs to astrocytes. They have short but highly branched axons that do not extend beyond the gray matter. Shorter and more branching dendrites. They participate in the processes of perception, irritation and unification of the activity of pyramidal neurons.

Bark layers:

Molecular (zonal)

outer granular

Small and medium pyramids

Internal grainy

Ganglionic (layer of the great pyramids)

Layer of polymorphic cells

Pyramidal neurons carry out the efferent function of the cortex and connect the neurons of the cortical regions remote from each other. The pyramidal neurons include Betz's pyramids (giant pyramidal), they are located in the anterior central gyrus. The longest processes of axons are at the pyramids of Betz. A characteristic feature of pyramidal cells is their perpendicular orientation. The axon goes down, and the dendrites go up.

On each of the neurons, there can be from 2 to 5 thousand synaptic contacts. This suggests that the control cells are under a great influence of other neurons in other zones, which makes it possible to coordinate the motor response in response to the external environment.

Fusiform cells are characteristic of layers 2 and 4. In humans, these layers are most widely expressed. They perform an associative function, connect the cortical zones with each other when solving various problems.

The structural organizing unit is the cortical column - a vertical interconnected module, all cells of which are functionally interconnected and form a common receptor field. It has multiple inputs and multiple outputs. Columns that have similar functions are combined into macro columns.

CBP develops immediately after birth, and until the age of 18 there is an increase in the number of elementary bonds in the CBP.

The size of the cells contained in the cortex, the thickness of the layers, their interconnection determine the cytoarchitectonics of the cortex.

Broadman and Fog.

The cytoarchitectonic field is a section of the cortex that is different from others, but similar inside. Each field has its own specifics. Currently, 52 main fields are distinguished, but some of the fields are absent in humans. In a person, areas are distinguished that have corresponding fields.

The bark bears the imprint of phylogenetic development. It is divided into 4 main types, which differ from each other in the differentiation of neuronal layers: paleocortex - an ancient cortex related to olfactory functions: olfactory bulb, olfactory tract, olfactory groove; archeocortex - old cortex, includes areas of the medial surface around the corpus callosum: cingulate gyrus, hippocampus, amygdala; mesocortex - intermediate cortex: outer-lower surface of the island; The neocortex is a new cortex, only in mammals, 85% of the entire cortex of the IBC lies on the convexital and lateral surfaces.

The paleocortex and archeocortex are the limbic system.

The connections of the cortex with subcortical formations are carried out by several types of pathways:

Associative fibers - only within 1 hemisphere, connect neighboring gyrus in the form of arcuate bundles, or neighboring lobes. their purpose is to ensure the holistic work of one hemisphere in the analysis and synthesis of multimodal excitations.

Projection fibers - connect peripheral receptors with KGM. They have different entrances, as a rule, they cross, they all switch in the thalamus. The task is to transmit a monomodal impulse to the corresponding primary zone of the cortex.

Integrative-starting fibers (integrative pathways) - start from the motor zones. These are descending efferent paths, they have crosshairs at different levels, the zone of application is muscle commands.

Commissural fibers - provide a holistic joint work of 2 hemispheres. They are located in the corpus callosum, optic chiasm, thalamus and at the level of 4-cholomium. The main task is to connect equivalent convolutions of different hemispheres.

Limbico-reticular fibers - connect the energy-regulating zones of the medulla oblongata with the CBP. The task is to maintain a general active / passive background of the brain.

2 body control systems: reticular formation and limbic system. These systems are modulating - amplify / attenuate impulses. This block has several levels of response: physiological, psychological, behavioral.