The cerebral cortex consists of 6 layers. Structure and functions of the cerebral cortex

The cerebral cortex is the center of higher nervous (mental) activity in humans and controls the performance of a huge number of vital functions and processes. It covers the entire surface of the cerebral hemispheres and occupies about half of their volume.

The cerebral hemispheres occupy about 80% of the volume of the cranium, and consist of white matter, the basis of which consists of long myelinated axons of neurons. The outside of the hemisphere is covered by gray matter or the cerebral cortex, consisting of neurons, unmyelinated fibers and glial cells, which are also contained in the thickness of the sections of this organ.

The surface of the hemispheres is conventionally divided into several zones, the functionality of which is to control the body at the level of reflexes and instincts. It also contains the centers of higher mental activity of a person, ensuring consciousness, assimilation of received information, allowing adaptation in the environment, and through it, at the subconscious level, through the hypothalamus, the autonomic nervous system (ANS) is controlled, which controls the organs of circulation, respiration, digestion, excretion , reproduction, and metabolism.

In order to understand what the cerebral cortex is and how its work is carried out, it is necessary to study the structure at the cellular level.

Functions

The cortex occupies most of the cerebral hemispheres, and its thickness is not uniform over the entire surface. This feature is due to the large number of connecting channels with the central nervous system (CNS), which ensure the functional organization of the cerebral cortex.

This part of the brain begins to form during fetal development and is improved throughout life, by receiving and processing signals coming from the environment. Thus, it is responsible for performing the following brain functions:

connects the organs and systems of the body with each other and the environment, and also ensures an adequate response to changes;
processes incoming information from motor centers using mental and cognitive processes;
consciousness and thinking are formed in it, and intellectual work is also realized;
controls speech centers and processes that characterize the psycho-emotional state of a person.

In this case, data is received, processed, and stored thanks to a significant number of impulses passing through and generated in neurons connected by long processes or axons. The level of cell activity can be determined by the physiological and mental state of the body and described using amplitude and frequency indicators, since the nature of these signals is similar to electrical impulses, and their density depends on the area in which the psychological process occurs.

It is still unclear how the frontal part of the cerebral cortex affects the functioning of the body, but it is known that it is little susceptible to processes occurring in the external environment, therefore all experiments with the influence of electrical impulses on this part of the brain do not find a clear response in the structures . However, it is noted that people whose frontal part is damaged experience problems communicating with other individuals, cannot realize themselves in any work activity, and they are also indifferent to their appearance and outside opinions. Sometimes there are other violations in the performance of the functions of this body:

lack of concentration on everyday objects;
manifestation of creative dysfunction;
disorders of a person’s psycho-emotional state.

The surface of the cerebral cortex is divided into 4 zones, outlined by the most distinct and significant convolutions. Each part controls the basic functions of the cerebral cortex:

parietal zone - responsible for active sensitivity and musical perception;
the primary visual area is located in the occipital part;
the temporal or temporal is responsible for speech centers and the perception of sounds coming from the external environment, in addition, it is involved in the formation of emotional manifestations, such as joy, anger, pleasure and fear;
The frontal zone controls motor and mental activity, and also controls speech motor skills.

Features of the structure of the cerebral cortex

The anatomical structure of the cerebral cortex determines its characteristics and allows it to perform the functions assigned to it. The cerebral cortex has the following number of distinctive features:

neurons in its thickness are arranged in layers;
nerve centers are located in a specific place and are responsible for the activity of a certain part of the body;
the level of activity of the cortex depends on the influence of its subcortical structures;
it has connections with all underlying structures of the central nervous system;
the presence of fields of different cellular structure, which is confirmed by histological examination, while each field is responsible for performing some higher nervous activity;
the presence of specialized associative areas makes it possible to establish a cause-and-effect relationship between external stimuli and the body’s response to them;
the ability to replace damaged areas with nearby structures;
This part of the brain is capable of storing traces of neuronal excitation.

The large hemispheres of the brain consist mainly of long axons, and also contain in their thickness clusters of neurons that form the largest nuclei of the base, which are part of the extrapyramidal system.

As already mentioned, the formation of the cerebral cortex occurs during intrauterine development, and at first the cortex consists of the lower layer of cells, and already at 6 months of the child all structures and fields are formed in it. The final formation of neurons occurs by the age of 7, and the growth of their bodies is completed at 18 years.

An interesting fact is that the thickness of the cortex is not uniform over its entire length and includes a different number of layers: for example, in the area of the central gyrus it reaches its maximum size and has all 6 layers, and sections of the old and ancient cortex have 2 and 3 layers. x layer structure, respectively.

The neurons of this part of the brain are programmed to restore the damaged area through synoptic contacts, so each of the cells actively tries to restore damaged connections, which ensures the plasticity of neural cortical networks. For example, when the cerebellum is removed or dysfunctional, the neurons connecting it with the terminal section begin to grow into the cerebral cortex. In addition, the plasticity of the cortex also manifests itself under normal conditions, when the process of learning a new skill occurs or as a result of pathology, when the functions performed by the damaged area are transferred to neighboring areas of the brain or even hemispheres.

The cerebral cortex has the ability to retain traces of neuronal excitation for a long time. This feature allows you to learn, remember and respond with a certain reaction of the body to external stimuli. This is how the formation of a conditioned reflex occurs, the neural pathway of which consists of 3 series-connected apparatuses: an analyzer, a closing apparatus of conditioned reflex connections and a working device. Weakness of the closure function of the cortex and trace manifestations can be observed in children with severe mental retardation, when the formed conditioned connections between neurons are fragile and unreliable, which entails learning difficulties.

The cerebral cortex includes 11 areas consisting of 53 fields, each of which is assigned its own number in neurophysiology.

Regions and zones of the cortex

The cortex is a relatively young part of the central nervous system, developing from the terminal part of the brain. The evolutionary development of this organ occurred in stages, so it is usually divided into 4 types:

The archicortex or ancient cortex, due to the atrophy of the sense of smell, has turned into the hippocampal formation and consists of the hippocampus and its associated structures. With its help, behavior, feelings and memory are regulated.
The paleocortex, or old cortex, makes up the bulk of the olfactory area.
The neocortex or new cortex has a layer thickness of about 3-4 mm. It is a functional part and performs higher nervous activity: it processes sensory information, gives motor commands, and also forms conscious thinking and human speech.
The mesocortex is an intermediate version of the first 3 types of cortex.

Physiology of the cerebral cortex

The cerebral cortex has a complex anatomical structure and includes sensory cells, motor neurons and internerons, which have the ability to stop the signal and be excited depending on the received data. The organization of this part of the brain is built according to the columnar principle, in which the columns are divided into micromodules that have a homogeneous structure.

The basis of the micromodule system is made up of stellate cells and their axons, while all neurons react equally to the incoming afferent impulse and also send an efferent signal synchronously in response.

The formation of conditioned reflexes that ensure the full functioning of the body occurs due to the connection of the brain with neurons located in various parts of the body, and the cortex ensures synchronization of mental activity with the motor skills of organs and the area responsible for analyzing incoming signals.

Signal transmission in the horizontal direction occurs through transverse fibers located in the thickness of the cortex, and transmit the impulse from one column to another. Based on the principle of horizontal orientation, the cerebral cortex can be divided into the following areas:

associative;
sensory (sensitive);
motor.

When studying these zones, various methods of influencing the neurons included in its composition were used: chemical and physical stimulation, partial removal of areas, as well as the development of conditioned reflexes and registration of biocurrents.

The associative zone connects incoming sensory information with previously acquired knowledge. After processing, it generates a signal and transmits it to the motor zone. In this way, it is involved in remembering, thinking, and learning new skills. Association areas of the cerebral cortex are located in proximity to the corresponding sensory area.

The sensitive or sensory area occupies 20% of the cerebral cortex. It also consists of several components:

somatosensory, located in the parietal zone, is responsible for tactile and autonomic sensitivity;
visual;
auditory;
taste;
olfactory.

Impulses from the limbs and organs of touch on the left side of the body enter along afferent pathways to the opposite lobe of the cerebral hemispheres for subsequent processing.

Neurons of the motor zone are excited by impulses received from muscle cells and are located in the central gyrus of the frontal lobe. The mechanism of data receipt is similar to the mechanism of the sensory zone, since the motor pathways form an overlap in the medulla oblongata and follow to the opposite motor zone.

Convolutions, grooves and fissures

The cerebral cortex is formed by several layers of neurons. A characteristic feature of this part of the brain is a large number of wrinkles or convolutions, due to which its area is many times greater than the surface area of the hemispheres.

Cortical architectonic fields determine the functional structure of areas of the cerebral cortex. All of them are different in morphological characteristics and regulate different functions. In this way, 52 different fields are identified, located in certain areas. According to Brodmann, this division looks like this:

The central sulcus separates the frontal lobe from the parietal region; the precentral gyrus lies in front of it, and the posterior central gyrus lies behind it.
The lateral groove separates the parietal zone from the occipital zone. If you separate its side edges, you can see a hole inside, in the center of which there is an island.
The parieto-occipital sulcus separates the parietal lobe from the occipital lobe.

The core of the motor analyzer is located in the precentral gyrus, while the upper parts of the anterior central gyrus belong to the muscles of the lower limb, and the lower parts belong to the muscles of the oral cavity, pharynx and larynx.

The right-sided gyrus forms a connection with the motor system of the left half of the body, the left-sided one - with the right side.

The posterior central gyrus of the 1st lobe of the hemisphere contains the core of the tactile sensation analyzer and is also connected with the opposite part of the body.

Cell layers

The cerebral cortex carries out its functions through neurons located in its thickness. Moreover, the number of layers of these cells may differ depending on the area, the dimensions of which also vary in size and topography. Experts distinguish the following layers of the cerebral cortex:

The surface molecular layer is formed mainly from dendrites, with a small inclusion of neurons, the processes of which do not leave the boundaries of the layer.
The external granular consists of pyramidal and stellate neurons, the processes of which connect it with the next layer.
The pyramidal layer is formed by pyramidal neurons, the axons of which are directed downward, where they break off or form associative fibers, and their dendrites connect this layer with the previous one.
The internal granular layer is formed by stellate and small pyramidal neurons, the dendrites of which extend into the pyramidal layer, and its long fibers extend into the upper layers or descend down into the white matter of the brain.
The ganglion consists of large pyramidal neurocytes, their axons extend beyond the cortex and connect various structures and sections of the central nervous system with each other.

The multiform layer is formed by all types of neurons, and their dendrites are oriented into the molecular layer, and axons penetrate the previous layers or extend beyond the cortex and form associative fibers that form a connection between gray matter cells and the rest of the functional centers of the brain.

Video: Cerebral cortex

Cortex

brain: cortex (cerebral cortex) - the upper layer of the cerebral hemispheres, consisting primarily of nerve cells with a vertical orientation (pyramidal cells), as well as bundles of afferent (centripetal) and efferent (centrifugal) nerve fibers. In neuroanatomical terms, it is characterized by the presence of horizontal layers that differ in the width, density, shape and size of the nerve cells included in them.

The cerebral cortex is divided into a number of areas: for example, in the most common classification of cytoarchitectonic formations by K. Brodmann, 11 areas and 52 fields are identified in the human cortex. Based on phylogenetic data, a new cortex, or neocortex, is distinguished; old, or archicortex; and ancient, or paleocortex. According to functional criteria, three types of areas are distinguished: sensory zones, providing reception and analysis of afferent signals coming from specific relay nuclei of the thalamus; motor zones, which have bilateral intracortical connections with all sensory areas for the interaction of sensory and motor zones; and associative zones, which do not have direct afferent or efferent connections with the periphery, but are associated with sensory and motor zones.

Dictionary of a practical psychologist. - M.: AST, Harvest. S. Yu. Golovin. 1998.

Anatomical and physiological subsystem of the nervous system.

Specificity.

The upper layer of the cerebral hemispheres, consisting primarily of nerve cells with a vertical orientation (pyramidal cells), as well as bundles of afferent (centripetal) and efferent (centrifugal) nerve fibers. In neuroanatomical terms, it is characterized by the presence of horizontal layers that differ in the width, density, shape and size of the nerve cells included in them.

Structure.

The cerebral cortex is divided into a number of regions, for example, in the most common classification of cytoarchitectonic formations by K. Brodman, 11 regions and 52 fields are identified in the human cerebral cortex. Based on phylogenetic data, the new cortex, or neocortex, the old, or archicortex, and the ancient, or paleocortex, are distinguished. According to the functional criterion, three types of areas are distinguished: sensory areas, which provide the reception and analysis of afferent signals coming from specific relay nuclei of the thalamus, motor areas, which have bilateral intracortical connections with all sensory areas for the interaction of sensory and motor areas, and associative areas, which do not have direct afferent or efferent connections with the periphery, but associated with sensory and motor areas.

Psychological Dictionary. THEM. Kondakov. 2000.

CORTEX

(English) cerebral cortex) - superficial layer covering the cerebral hemispheres brain, formed predominantly by vertically oriented nerve cells (neurons) and their processes, as well as bundles afferent(centripetal) And efferent(centrifugal) nerve fibers. In addition, the cortex includes neuroglial cells.

A characteristic feature of the structure of the blood cell is horizontal layering, caused by the ordered arrangement of nerve cell bodies and nerve fibers. In the K. g. m. there are 6 (according to some authors, 7) layers, differing in width, density, shape and size of their constituent neurons. Due to the predominantly vertical orientation of the bodies and processes of neurons, as well as bundles of nerve fibers, the K. g. m. has vertical striations. For the functional organization of the circulatory system, the vertical, columnar arrangement of nerve cells is of great importance.

The main type of nerve cells that make up the K. g. m. are pyramidal cells. The body of these cells resembles a cone, from the apex of which one thick and long apical dendrite extends; heading towards the surface of the K. g. m., it becomes thinner and fan-shapedly divided into thinner terminal branches. Shorter basal dendrites extend from the base of the pyramidal cell body and , heading into the white matter located under the K. g. m., or branching within the cortex. The dendrites of pyramidal cells bear a large number of outgrowths, the so-called. spines, which take part in the formation of synaptic contacts with the endings of afferent fibers coming to the K. g.m. from other parts of the cortex and subcortical formations (see. ). The axons of pyramidal cells form the main efferent pathways coming from the K. g.m. The sizes of pyramidal cells vary from 5-10 microns to 120-150 microns (Betz giant cells). In addition to pyramidal neurons, the K. g. m. includes star-shaped,fusiform and some other types of interneurons involved in receiving afferent signals and forming functional interneuron connections.

Based on the characteristics of the distribution of nerve cells and fibers of different sizes and shapes in the layers of the cortex, the entire territory of the cerebral cortex is divided into a number regions(for example, occipital, frontal, temporal, etc.), and the latter - into more fractional cytoarchitectonic fields, differing in their cellular structure and functional significance. The generally accepted classification of cytoarchitectonic formations of the human hematopoietic system is proposed by K. Brodmann, who divided the entire human hemodynamic system into 11 regions and 52 fields.

Based on phylogenetic data, K. g. m. are divided into new ( neocortex), old ( archicortex) and ancient ( paleocortex). In the phylogenesis of the K. g.m., there is an absolute and relative increase in the territories of the new crust with a relative decrease in the area of the ancient and old crust. In humans, the neocortex accounts for 95.6%, while the ancient occupies 0.6%, and the old 2.2% of the total cortical territory.

Functionally, there are 3 types of areas in the cortex: sensory, motor and associative.

Sensory(or projection) cortical zones receive and analyze afferent signals along fibers coming from specific relay nuclei of the thalamus. Sensory areas are localized in certain areas of the cortex: visual located in the occipital region (fields 17, 18, 19), auditory in the upper parts of the temporal region (fields 41, 42), somatosensory, analyzing impulses coming from receptors of the skin, muscles, joints - in the area of the postcentral gyrus (fields 1, 2, 3). Olfactory sensations are associated with the function of phylogenetically older parts of the cortex (paleocortex) - the hippocampal gyrus.

Motor(motor) area - Brodmann's area 4 - is located on the precentral gyrus. The motor cortex is characterized by the presence in layer V of Betz giant pyramidal cells, the axons of which form the pyramidal tract - the main motor tract descending to the motor centers of the brain stem and spinal cord and providing cortical control of voluntary muscle contractions. The motor cortex has bilateral intracortical connections with all sensory areas, which ensures close interaction between sensory and motor areas.

Associative areas. The human cerebral cortex is characterized by the presence of a vast territory that does not have direct afferent and efferent connections with the periphery. These areas, connected through an extensive system of associative fibers with sensory and motor areas, are called associative (or tertiary) cortical areas. In the posterior parts of the cortex they are located between the parietal, occipital and temporal sensory areas, and in the anterior parts they occupy the main surface of the frontal lobes. The association cortex is either absent or poorly developed in all mammals up to primates. In humans, the posterior association cortex occupies approximately half, and the frontal areas a quarter of the entire surface of the cortex. In structure, they are distinguished by the particularly powerful development of the upper associative layers of cells in comparison with the system of afferent and efferent neurons. Their feature is also the presence of polysensory neurons - cells that perceive information from various sensory systems.

The associative cortex also contains centers associated with speech activity (see. And ). Associative areas of the cortex are considered as structures responsible for the synthesis of incoming information, and as an apparatus necessary for the transition from visual perception to abstract symbolic processes.

Clinical neuropsychological studies show that when the posterior associative areas are damaged, complex forms of orientation in space and constructive activity are disrupted, and the performance of all intellectual operations that involve spatial analysis (counting, perception of complex semantic images) becomes difficult. When speech zones are damaged, the ability to perceive and reproduce speech is impaired. Damage to the frontal cortex leads to the impossibility of implementing complex behavioral programs that require the selection of significant signals based on past experience and anticipation of the future. Cm. , , , , , . (D. A. Farber.)

Large psychological dictionary. - M.: Prime-EVROZNAK. Ed. B.G. Meshcheryakova, acad. V.P. Zinchenko. 2003 .

Cortex

A layer of gray matter covering the cerebral hemispheres of the cerebrum. The cerebral cortex is divided into four lobes: frontal, occipital, temporal and parietal. The part of the cortex that covers most of the surface of the cerebral hemispheres is called the neocortex because it formed during the final stages of human evolution. The neocortex can be divided into zones according to their functions. Different parts of the neocortex are associated with sensory and motor functions; corresponding areas of the cerebral cortex are involved in planning movements (frontal lobes) or are associated with memory and perception ().

Psychology. AND I. Dictionary reference / Transl. from English K. S. Tkachenko. - M.: FAIR PRESS. Mike Cordwell. 2000.

See what “cerebral cortex” is in other dictionaries:

CORTEX- CEREBRAL CORTEX, the outer layer of the cerebral hemispheres covered with deep convolutions. The cortex, or “gray matter,” is the most complexly organized part of the brain; its purpose is perception of sensations, control... ... Scientific and technical encyclopedic dictionary

Cortex- the upper layer of the cerebral hemispheres, consisting primarily of nerve cells with a vertical orientation (pyramidal cells), as well as bundles of afferent, centripetal and efferent, centrifugal nerve fibers. IN … Psychological Dictionary

cortex- honey The brain is the most voluminous of the elements of the central nervous system. It consists of two lateral parts, the cerebral hemispheres connected to one another, and the underlying elements. It weighs about 1200 g. Two hemispheres of the brain... ... Universal additional practical explanatory dictionary by I. Mostitsky

Cortex- Thin (2 mm) outer shell of the cerebral hemispheres. The human cerebral cortex is the center of higher cognitive processes and sensorimotor information processing... Psychology of sensations: glossary

cortex- Cortex/ cerebral hemispheres. The superficial layer of the brain in higher vertebrates and humans... Dictionary of many expressions

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CORTEX- The surface covering the gray matter, which forms the uppermost level of the brain. In an evolutionary sense, it is the newest neural formation, and its approximately 9 12 billion cells are responsible for basic sensory functions,... ... Explanatory dictionary of psychology

cortex- see Cora... Large medical dictionary

Cerebral Cortex, Cerebral Cortex- the outer layer of the large brain, which has a complex structure, which accounts for up to 40% of the weight of the entire brain and which contains approximately 15 billion neurons (see Gray matter). The cerebral cortex is directly responsible for the psyche... ... Medical terms

cerebral cortex, cerebral cortex- (cerebral cortex) the outer layer of the large brain with a complex structure, which accounts for up to 40% of the weight of the entire brain and contains approximately 15 billion neurons (see Gray matter). The cerebral cortex directly responds... ... Explanatory dictionary of medicine

Books

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How emotions affect abstract thinking and why mathematics is incredibly accurate. How the cerebral cortex is structured, why its capabilities are limited and how emotions, complementing the work of the cortex, allow a person to make scientific discoveries, A. G. Sverdlik. Mathematics, unlike other disciplines, is universal and extremely accurate. It creates the logical structure of all natural sciences. “The incomprehensible effectiveness of mathematics”, as in its time...

Modern scientists know for certain that thanks to the functioning of the brain, such abilities as awareness of signals received from the external environment, mental activity, and memorization of thoughts are possible.

The ability of an individual to realize his own relationships with other people is directly related to the process of excitation of neural networks. Moreover, we are talking specifically about those neural networks that are located in the cortex. It represents the structural basis of consciousness and intelligence.

In this article we will look at how the cerebral cortex is structured; the areas of the cerebral cortex will be described in detail.

Neocortex

The cortex contains about fourteen billion neurons. It is thanks to them that the main zones function. The vast majority of neurons, up to ninety percent, form the neocortex. It is part of the somatic NS and its highest integrative department. The most important functions of the cerebral cortex are the perception, processing, and interpretation of information that a person receives with the help of various senses.

In addition, the neocortex controls the complex movements of the human body's muscle system. It contains centers that take part in the process of speech, memory storage, and abstract thinking. Most of the processes that occur in it form the neurophysical basis of human consciousness.

What other parts does the cerebral cortex consist of? We will consider the areas of the cerebral cortex below.

Paleocortex

It is another large and important section of the cortex. Compared to the neocortex, the paleocortex has a simpler structure. The processes that take place here are rarely reflected in consciousness. The higher vegetative centers are localized in this section of the cortex.

Connection of the cortex with other parts of the brain

It is important to consider the connection that exists between the underlying parts of the brain and the cerebral cortex, for example, with the thalamus, pons, medial pons, and basal ganglia. This connection is carried out using large bundles of fibers that form the internal capsule. Bundles of fibers are represented by wide layers, which are composed of white matter. They contain a huge number of nerve fibers. Some of these fibers provide transmission of nerve signals to the cortex. The rest of the bundles transmit nerve impulses to the nerve centers located below.

How is the cerebral cortex structured? The areas of the cerebral cortex will be presented below.

Structure of the cortex

The largest part of the brain is its cortex. Moreover, cortical zones are only one type of parts distinguished in the cortex. In addition, the cortex is divided into two hemispheres - right and left. The hemispheres are connected to each other by bundles of white matter that form the corpus callosum. Its function is to ensure coordination of the activities of both hemispheres.

Classification of cerebral cortex zones by their location

Despite the fact that the cortex has a huge number of folds, in general the location of its individual convolutions and grooves is constant. The main ones are a guideline for identifying areas of the cortex. Such zones (lobes) include occipital, temporal, frontal, parietal. Although they are classified by location, each has its own specific functions.

Auditory cortex

For example, the temporal zone is the center in which the cortical section of the hearing analyzer is located. If damage to this part of the cortex occurs, deafness may occur. In addition, Wernicke's speech center is located in the auditory zone. If it is damaged, then the person loses the ability to perceive oral speech. A person perceives it as simple noise. Also in the temporal lobe there are neural centers that belong to the vestibular apparatus. If they are damaged, the sense of balance is disrupted.

Speech areas of the cerebral cortex

Speech areas are concentrated in the frontal lobe of the cortex. The speech motor center is also located here. If damage occurs in the right hemisphere, then the person loses the ability to change the timbre and intonation of his own speech, which becomes monotonous. If damage to the speech center occurs in the left hemisphere, then articulation and the ability to articulate speech and singing disappear. What else does the cerebral cortex consist of? The areas of the cerebral cortex have different functions.

Visual zones

In the occipital lobe there is a visual zone, in which there is a center that responds to our vision as such. The perception of the world around us occurs precisely with this part of the brain, and not with the eyes. It is the occipital cortex that is responsible for vision, and damage to it can lead to partial or complete loss of vision. The visual area of the cerebral cortex is examined. What's next?

The parietal lobe also has its own specific functions. It is this zone that is responsible for the ability to analyze information that relates to tactile, temperature and pain sensitivity. If damage occurs to the parietal region, the brain's reflexes are disrupted. A person cannot recognize objects by touch.

Motor zone

Let's talk about the motor zone separately. It should be noted that this zone of the cortex does not correlate in any way with the lobes discussed above. It is part of the cortex containing direct connections to motor neurons in the spinal cord. This name is given to neurons that directly control the activity of the muscles of the body.

The main motor area of the cerebral cortex is located in a gyrus called the precentral gyrus. This gyrus is a mirror image of the sensory area in many aspects. Between them there is contralateral innervation. To put it another way, the innervation is directed to the muscles that are located on the other side of the body. The exception is the facial area, which is characterized by bilateral control of the muscles located on the jaw and lower part of the face.

Slightly below the main motor zone is an additional zone. Scientists believe that it has independent functions that are associated with the process of outputting motor impulses. The supplementary motor area has also been studied by specialists. Experiments carried out on animals show that stimulation of this zone provokes the occurrence of motor reactions. The peculiarity is that such reactions occur even if the main motor area has been isolated or completely destroyed. It is also involved in motor planning and speech motivation in the dominant hemisphere. Scientists believe that if the accessory motor is damaged, dynamic aphasia can occur. Brain reflexes suffer.

Classification according to the structure and functions of the cerebral cortex

Physiological experiments and clinical trials, which were carried out at the end of the nineteenth century, made it possible to establish the boundaries between the areas to which different receptor surfaces are projected. Among them are sensory organs that are directed to the outside world (skin sensitivity, hearing, vision), receptors embedded directly in the organs of movement (motor or kinetic analyzers).

Cortical areas in which various analyzers are located can be classified according to structure and function. So, there are three of them. These include: primary, secondary, tertiary zones of the cerebral cortex. The development of the embryo involves the formation of only primary zones, characterized by simple cytoarchitecture. Next comes the development of secondary ones, tertiary ones develop last. Tertiary zones are characterized by the most complex structure. Let's look at each of them in a little more detail.

Central fields

Over many years of clinical research, scientists have managed to accumulate significant experience. Observations made it possible to establish, for example, that damage to various fields, within the cortical sections of different analyzers, can have a far different impact on the overall clinical picture. If we consider all these fields, then among them we can single out one that occupies a central position in the nuclear zone. This field is called central or primary. It is located simultaneously in the visual zone, in the kinesthetic zone, and in the auditory zone. Damage to the primary field entails very serious consequences. A person cannot perceive and carry out the most subtle differentiation of stimuli that affect the corresponding analyzers. How else are areas of the cerebral cortex classified?

Primary zones

In the primary zones there is a complex of neurons that is most predisposed to providing bilateral connections between the cortical and subcortical zones. It is this complex that connects the cerebral cortex with various sensory organs in the most direct and shortest way. In this regard, these zones have the ability to identify stimuli in a very detailed manner.

An important common feature of the functional and structural organization of the primary areas is that they all have a clear somatic projection. This means that individual peripheral points, for example, skin surfaces, retina, skeletal muscles, cochleae of the inner ear, have their own projection into strictly limited, corresponding points, which are located in the primary zones of the cortex of the corresponding analyzers. In this regard, they were given the name projection zones of the cerebral cortex.

Secondary zones

In another way, these zones are called peripheral. This name was not given to them by chance. They are located in the peripheral parts of the cortex. Secondary zones differ from the central (primary) zones in their neural organization, physiological manifestations and architectural features.

Let's try to figure out what effects occur if the secondary zones are affected by an electrical stimulus or if they are damaged. The effects that arise mainly concern the most complex types of processes in the psyche. In the event that damage occurs to the secondary zones, the elementary sensations remain relatively intact. Basically, there are disturbances in the ability to correctly reflect mutual relationships and entire complexes of elements that make up the various objects that we perceive. For example, if the secondary zones of the visual and auditory cortex are damaged, then the emergence of auditory and visual hallucinations can be observed, which unfold in a certain temporal and spatial sequence.

Secondary areas are of significant importance in the implementation of mutual connections between stimuli, which are allocated with the help of primary areas of the cortex. In addition, they play a significant role in the integration of functions that are carried out by the nuclear fields of different analyzers as a result of combining into complex complexes of receptions.

Thus, secondary zones are of particular importance for the implementation of mental processes in more complex forms that require coordination and which are associated with a detailed analysis of the relationships between objective stimuli. During this process, specific connections are established, which are called associative. Afferent impulses entering the cortex from receptors of various external sensory organs reach secondary fields through many additional switches in the association nucleus of the thalamus, which is also called the thalamus optic. Afferent impulses going to the primary zones, in contrast to impulses going to the secondary zones, reach them via a shorter route. It is implemented through a relay core in the visual thalamus.

We figured out what the cerebral cortex is responsible for.

What is the thalamus?

Fibers from the thalamic nuclei reach each lobe of the cerebral hemispheres. The thalamus is a visual thalamus located in the central part of the forebrain; it consists of a large number of nuclei, each of which transmits impulses to certain areas of the cortex.

All signals that enter the cortex (with the exception of olfactory signals) pass through the relay and integrative nuclei of the visual thalamus. From the nuclei of the thalamus, fibers are directed to sensory areas. The taste and somatosensory zones are located in the parietal lobe, the auditory sensory zone is in the temporal lobe, and the visual zone is in the occipital lobe.

Impulses to them come, respectively, from the ventro-basal complexes, medial and lateral nuclei. Motor areas are connected to the ventral and ventrolateral nuclei of the thalamus.

EEG desynchronization

What happens if a person who is in a state of complete rest is exposed to a very strong stimulus? Naturally, a person will fully concentrate on this stimulus. The transition of mental activity, which occurs from a state of rest to a state of activity, is reflected on the EEG by the beta rhythm, which replaces the alpha rhythm. Fluctuations become more frequent. This transition is called EEG desynchronization; it appears as a result of sensory stimulation entering the cortex from nonspecific nuclei located in the thalamus.

Activating reticular system

The diffuse nervous system consists of nonspecific nuclei. This system is located in the medial sections of the thalamus. It is the anterior part of the activating reticular system, which regulates the excitability of the cortex. A variety of sensory signals can activate this system. Sensory signals can be both visual and olfactory, somatosensory, vestibular, auditory. The activating reticular system is a channel that transmits signal data to the superficial layer of the cortex through nonspecific nuclei located in the thalamus. Excitation of the ARS is necessary for a person to be able to maintain a state of wakefulness. If disturbances occur in this system, comatose sleep-like states may occur.

Tertiary zones

There are functional relationships between the analyzers of the cerebral cortex, which have an even more complex structure than that described above. During the growth process, the fields of the analyzers overlap each other. Such overlap zones that form at the ends of the analyzers are called tertiary zones. They are the most complex types of combining the activities of the auditory, visual, and skin-kinesthetic analyzers. Tertiary zones are located outside the boundaries of the analyzers’ own zones. In this regard, their damage does not have a pronounced effect.

Tertiary zones are special cortical areas in which scattered elements of different analyzers are collected. They occupy a very vast territory, which is divided into regions.

The upper parietal region integrates the movements of the whole body with the visual analyzer and forms a body diagram. The inferior parietal region combines generalized forms of signaling that are associated with differentiated object and speech actions.

No less important is the temporo-parietal-occipital region. She is responsible for the complex integration of auditory and visual analyzers with oral and written speech.

It is worth noting that, compared to the first two zones, the tertiary zones are characterized by the most complex interaction chains.

If we rely on all the material presented above, we can conclude that the primary, secondary, and tertiary zones of the human cortex are highly specialized. Separately, it is worth emphasizing the fact that all three cortical zones that we considered, in a normally functioning brain, together with systems of connections and subcortical formations, function as a single differentiated whole.

We examined in detail the zones and sections of the cerebral cortex.

The cerebral cortex is the outer layer of nervous tissue in the brain of humans and other mammalian species. The cerebral cortex is divided by a longitudinal fissure (lat. Fissura longitudinalis) into two large parts, which are called the cerebral hemispheres or hemispheres - right and left. Both hemispheres are connected below by the corpus callosum (lat. Corpus callosum). The cerebral cortex plays a key role in the performance of brain functions such as memory, attention, perception, thinking, speech, consciousness.

In large mammals, the cerebral cortex is collected in the mesenteries, giving a larger surface area in the same volume of the skull. The ripples are called convolutions, and between them lie furrows and deeper ones - cracks.

Two-thirds of the human brain is hidden in grooves and fissures.

The cerebral cortex has a thickness of 2 to 4 mm.

The cortex is formed by gray matter, which consists mainly of cell bodies, mainly astrocytes, and capillaries. Therefore, even visually, the cortical tissue differs from the white matter, which lies deeper and consists mainly of white myelin fibers - the axons of neurons.

The outer part of the cortex, the so-called neocortex (lat. Neocortex), the most evolutionarily young part of the cortex in mammals, has up to six cell layers. Neurons of different layers are interconnected in cortical mini-columns. Various areas of the cortex, known as Brodmann's areas, differ from each other in cytoarchitectonics (histological structure) and functional role in sensitivity, thinking, consciousness and cognition.

Development

The cerebral cortex develops from the embryonic ectoderm, namely, from the anterior part of the neural plate. The neural plate folds and forms the neural tube. The ventricular system arises from the cavity inside the neural tube, and neurons and glia arise from the epithelial cells of its walls. From the frontal part of the neural plate, the forebrain, the cerebral hemispheres and then the cortex are formed

The growth zone of cortical neurons, the so-called “S” zone, is located next to the ventricular system of the brain. This zone contains progenitor cells that later in the process of differentiation become glial cells and neurons. Glial fibers, formed in the first divisions of precursor cells, are radially oriented, span the thickness of the cortex from the ventricular zone to the pia mater (lat. Pia mater) and form “rails” for the migration of neurons outward from the ventricular zone. These daughter nerve cells become pyramidal cells of the cortex. The development process is clearly regulated in time and is guided by hundreds of genes and energy regulation mechanisms. During development, the layer-by-layer structure of the cortex is also formed.

Cortical development between 26 and 39 weeks (human embryo)

Cell layers

Each of the cell layers has a characteristic density of nerve cells and connections with other areas. There are direct connections between different areas of the cortex and indirect connections, for example, through the thalamus. One typical pattern of cortical lamination is the strip of Gennari in the primary visual cortex. This strand is visually whiter than the tissue, visible to the naked eye at the base of the calcarine groove (lat. Sulcus calcarinus) in the occipital lobe (lat. Lobus occipitalis). The stria Gennari consists of axons that carry visual information from the thalamus to the fourth layer of the visual cortex.

Staining columns of cells and their axons allowed neuroanatomists at the beginning of the twentieth century. make a detailed description of the layer-by-layer structure of the cortex in different species. After the work of Corbinian Brodmann (1909), neurons in the cortex were grouped into six main layers - from the outer ones, adjacent to the pia mater; to the internal ones, bordering the white matter:

Layer I, the molecular layer, contains a few scattered neurons and consists primarily of vertically (apically) oriented dendrites of pyramidal neurons and horizontally oriented axons and glial cells. During development, this layer contains Cajal-Retzius cells and subpial cells (cells located immediately under the granular layer. Spinous astrocytes are also sometimes found here. The apical tufts of dendrites are considered to be of great importance for reciprocal connections (“feedback”) in the cerebral cortex, and are involved in the functions of associative learning and attention.
Layer II, the outer granular layer, contains small pyramidal neurons and numerous stellate neurons (whose dendrites extend from different sides of the cell body, forming a star shape).
Layer III, the outer pyramidal layer, contains predominantly small and medium pyramidal and nonpyramidal neurons with vertically oriented intracortical ones (those within the cortex). Cell layers I to III are the main targets of intrapulmonary afferents, and layer III is the main source of cortico-cortical connections.
Layer IV, the internal granular layer, contains various types of pyramidal and stellate neurons and serves as the main target of thalamocortical (thalamus to cortex) afferents.
Layer V, the inner pyramidal layer, contains large pyramidal neurons, the axons of which leave the cortex and project to subcortical structures (such as the basal ganglia. In the primary motor cortex, this layer contains Betz cells, the axons of which extend through the internal capsule, brainstem and spinal cord and form the corticospinal pathway, which controls voluntary movements.
Layer VI, the polymorphic or multiforme layer, contains few pyramidal neurons and many polymorphic neurons; Efferent fibers from this layer go to the thalamus, establishing a reverse (reciprocal) connection between the thalamus and the cortex.

The outer surface of the brain, on which the areas are designated, is supplied with blood by cerebral arteries. The area indicated in blue corresponds to the anterior cerebral artery. The portion of the posterior cerebral artery is indicated in yellow

The cortical layers are not simply stacked one on one. There are characteristic connections between the different layers and the cell types within them that permeate the entire thickness of the cortex. The basic functional unit of the cortex is considered to be the cortical minicolumn (a vertical column of neurons in the cerebral cortex that runs through its layers. The minicolumn includes from 80 to 120 neurons in all areas of the brain except the primary visual cortex of primates).

Areas of the cortex without the fourth (internal granular) layer are called agranular; those with a rudimentary granular layer are called disgranular. The speed of information processing within each layer is different. So in II and III it is slow, with a frequency (2 Hz), while in layer V the oscillation frequency is much faster - 10-15 Hz.

Cortical zones

Anatomically, the cortex can be divided into four parts, which have names corresponding to the names of the skull bones that cover:

Frontal lobe (brain), (lat. Lobus frontalis)
Temporal lobe (lat. Lobus temporalis)
Parietal lobe, (lat. Lobus parietalis)
Occipital lobe, (lat. Lobus occipitalis)

Taking into account the features of the laminar (layer-by-layer) structure, the cortex is divided into neocortex and alocortex:

Neocortex (lat. Neocortex, other names - isocortex, lat. Isocortex and neopallium, lat. Neopallium) is part of the mature cerebral cortex with six cellular layers. The exemplar neocortical areas are Brodmann Area 4, also known as primary motor cortex, primary visual cortex, or Brodmann Area 17. The neocortex is divided into two types: isocortex (the true neocortex, examples of which Brodmann Areas 24, 25, and 32 are only discussed) and prosocortex, which is represented, in particular, by Brodmann area 24, Brodmann area 25 and Brodmann area 32
Alocortex (lat. Allocortex) - part of the cortex with the number of cell layers less than six, is also divided into two parts: paleocortex (lat. Paleocortex) with three layers, archicortex (lat. Archicortex) of four to five, and the adjacent perialocortex (lat. periallocortex). Examples of areas with such a layered structure are the olfactory cortex: the vaulted gyrus (lat. Gyrus fornicatus) with the hook (lat. Uncus), the hippocampus (lat. Hippocampus) and structures close to it.

There is also a “transitional” (between the alocortex and neocortex) cortex, which is called paralimbic, where cell layers 2,3 and 4 merge. This zone contains the proisocortex (from the neocortex) and the perialocortex (from the alocortex).

Cortex. (according to Poirier fr. Poirier.). Livooruch - groups of cells, on the right - fibers.

Paul Brodmann

Different areas of the cortex are involved in performing different functions. This difference can be seen and recorded in various ways - by comparing lesions in certain areas, comparing patterns of electrical activity, using neuroimaging techniques, studying cellular structure. Based on these differences, researchers classify cortical areas.

The most famous and cited for a century is the classification created in 1905-1909 by the German researcher Corbinian Brodmann. He divided the cerebral cortex into 51 regions based on the cytoarchitecture of neurons, which he studied in the cerebral cortex using Nissl staining of cells. Brodmann published his maps of cortical areas in humans, apes, and other species in 1909.

Brodmann's fields have been actively and in detail discussed, debated, clarified, and renamed for almost a century and remain the most widely known and frequently cited structures of the cytoarchitectonic organization of the human cerebral cortex.

Many of the Brodmann fields, initially defined solely by their neuronal organization, were later associated by correlation with various cortical functions. For example, Fields 3, 1 & 2 are the primary somatosensory cortex; area 4 is the primary motor cortex; field 17 is primary visual cortex, and fields 41 and 42 are more correlated with primary auditory cortex. Determining the correspondence of processes of Higher nervous activity to areas of the cerebral cortex and linking them to specific Brodmann fields is carried out using neurophysiological studies, functional magnetic resonance imaging and other techniques (as this was, for example, done with linking Broca's areas of speech and language to Brodmann fields 44 and 45). However, functional imaging can only approximately determine the localization of brain activation in Brodmann's fields. And to accurately determine their boundaries in each individual brain, a histological examination is needed.

Some of the important Brodmann fields. Where: Primary somatosensory cortex - primary somatosensory cortex Primary motor cortex - primary motor (motor) cortex; Wernicke’s area - Wernicke’s area; Primary visual area - primary visual area; Primary auditory cortex - primary auditory cortex; Broca's area - Broca's area.

Bark thickness

In mammalian species with large brain sizes (in absolute terms, not just relative to body size), the cortex tends to be thicker. The range, however, is not very large. Small mammals such as shrews have a neocortex thickness of approximately 0.5 mm; and species with the largest brains, such as humans and cetaceans, are 2.3-2.8 mm thick. There is a roughly logarithmic relationship between brain weight and cortical thickness.

Magnetic resonance imaging (MRI) of the brain makes it possible to measure intravital cortical thickness and correlate it with body size. The thickness of different areas varies, but in general, the sensory (sensitive) areas of the cortex are thinner than the motor (motor) areas. One study showed the dependence of cortical thickness on intelligence level. Another study showed greater cortical thickness in migraine sufferers. However, other studies show the absence of such a connection.

Convolutions, grooves and fissures

Together, these three elements - Convolutions, sulci and fissures - create a large surface area of the brain of humans and other mammals. When looking at the human brain, it is noticeable that two-thirds of the surface is hidden in grooves. Both grooves and fissures are depressions in the cortex, but they vary in size. The sulcus is a shallow groove that surrounds the gyri. The fissure is a large groove that divides the brain into parts, as well as into two hemispheres, such as the medial longitudinal fissure. However, this distinction is not always clear-cut. For example, the lateral fissure is also known as the lateral fissure and as the "Sylvian fissure" and the "central fissure", also known as the Central fissure and as the "Rolandic fissure".

This is very important in conditions where the size of the brain is limited by the internal size of the skull. An increase in the surface of the cerebral cortex using a system of convolutions and sulci increases the number of cells that are involved in the performance of brain functions such as memory, attention, perception, thinking, speech, consciousness.

Blood supply

The supply of arterial blood to the brain and cortex, in particular, occurs through two arterial basins - the internal carotid and vertebral arteries. The terminal section of the internal carotid artery branches into branches - the anterior cerebral and middle cerebral arteries. In the lower (basal) parts of the brain, arteries form a circle of Willis, due to which arterial blood is redistributed between the arterial basins.

Middle cerebral artery

The middle cerebral artery (lat. A. Cerebri media) is the largest branch of the internal carotid artery. Poor circulation in it can lead to the development of ischemic stroke and middle cerebral artery syndrome with the following symptoms:

Paralysis, plegia or paresis of the opposite muscles of the face and arms
Loss of sensory sensitivity in the opposite muscles of the face and arm
Damage to the dominant hemisphere (often left) of the brain and the development of Broca's aphasia or Wernicke's aphasia
Damage to the non-dominant hemisphere (often the right) of the brain leads to unilateral spatial agnosia on the remote affected side
Infarctions in the area of the middle cerebral artery lead to déviation conjuguée, when the pupils of the eyes move towards the side of the brain lesion.

Anterior cerebral artery

The anterior cerebral artery is a smaller branch of the internal carotid artery. Having reached the medial surface of the cerebral hemispheres, the anterior cerebral artery goes to the occipital lobe. It supplies the medial areas of the hemispheres to the level of the parieto-occipital sulcus, the area of the superior frontal gyrus, the area of the parietal lobe, as well as areas of the lower medial sections of the orbital gyri. Symptoms of her defeat:

Paresis of the leg or hemiparesis with a predominant lesion of the leg on the opposite side.
Blockage of the paracentral branches leads to monoparesis of the foot, reminiscent of peripheral paresis. Urinary retention or incontinence may occur. Reflexes of oral automatism and grasping phenomena, pathological foot bending reflexes appear: Rossolimo, Bekhterev, Zhukovsky. Changes in mental state occur due to damage to the frontal lobe: decreased criticism, memory, unmotivated behavior.

Posterior cerebral artery

A paired vessel that supplies blood to the posterior parts of the brain (occipital lobe). Has an anastomosis with the middle cerebral artery. Its lesions lead to:

Homonymous (or upper quadrant) hemianopsia (loss of part of the visual field)
Metamorphopsia (impaired visual perception of the size or shape of objects and space) and visual agnosia,
Alexia,
Sensory aphasia,
Transient (transient) amnesia;
Tubular vision
Cortical blindness (while maintaining reaction to light),
Prosopagnosia,
Disorientation in space
Loss of topographic memory
Acquired achromatopsia - deficiency of color vision
Korsakoff's syndrome (impaired working memory)
Emotional and affective disorders

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 in the later stages of the 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. Thanks to bilateral connections with the underlying parts of the nervous system, the cortex can participate in the regulation and coordination of all body functions. In humans, the cortex makes up on average 44% of the volume of the entire hemisphere as a whole. Its surface reaches 1468-1670 cm2.

Structure of the cortex . A characteristic feature of the structure of the cortex is the oriented, horizontal-vertical distribution of its constituent nerve cells across layers and columns; Thus, the cortical structure is characterized by a spatially ordered arrangement of functioning units and connections between them. The space between the bodies and processes of cortical nerve cells is filled with neuroglia and a 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. Stellate 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 branches. Stellate cells play the role of perceiving and synchronizing elements capable of coordinating (simultaneously inhibiting or exciting) spatially close groups of pyramidal neurons. The cortical neuron is characterized by a complex submicroscopic structure. Cortical areas of different topography differ in the density of cells, their size and other characteristics of the layer-by-layer and columnar structure. All these indicators determine the architecture of the cortex, or its cytoarchitectonics. The largest divisions 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%, old 2.2%, ancient 0.6%, interstitial 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; interstitial formations - transitional structures between the fields of the old and new cortex, as well as the ancient and new cortex - from 4-5 layers of cells. The neocortex is divided into the following areas: precentral, postcentral, temporal, inferior parietal, superior parietal, temporo-parietal-occipital, occipital, insular and limbic. In turn, areas are divided into subareas and fields. The main type of direct and feedback connections of the new cortex are vertical bundles of fibers that bring information from subcortical structures to the cortex and send it from the cortex to these 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 beams are most characteristic of layers I and III of the cortex, and in some fields for layer V.

Horizontal bundles ensure the exchange of information 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 above-mentioned distribution of nerve cells and their connections across layers and columns. Convergence (convergence) of impulses from various sensory organs is possible on cortical neurons. According to modern concepts, such a convergence of heterogeneous excitations is a neurophysiological mechanism of integrative activity of the brain, that is, analysis and synthesis of the body’s response activity. It is also significant that the neurons are combined into complexes, apparently realizing the results of the convergence of excitations on 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 at one perpendicular to the surface of the cortex. The cells in the column are closely connected to each other 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 reacts to the movement of the limb in the joint. In the visual analyzer, the functions of perceiving visual images are also distributed across columns. For example, one of the columns perceives the movement of an object in the horizontal plane, the adjacent one in the vertical plane, etc.

The second complex of cells of the neocortex - the layer - is oriented in the horizontal plane. It is believed that small cell layers II and IV consist mainly of perceptive elements and are “entrances” to the cortex. Large cell layer V is the exit from the cortex to the subcortex, and the middle cell layer III is associative, connecting different 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 zones of the cortex associated with the perception of information from a specific sensory 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, areas) 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 cortical zones and the activity of subcortical structures. Cortical territories differ sharply in their functions. Most of the ancient cortex is included in the olfactory analyzer system. The old and interstitial cortex, being closely related to the ancient cortex both by systems of connections and evolutionarily, are not directly related to smell. They are part of the system responsible for the regulation of vegetative reactions and emotional states. The new cortex is a set of final links of various perceptive (sensory) systems (cortical ends of analyzers).

It is customary to distinguish projection, or primary, and secondary fields, as well as tertiary fields, or associative zones, in the zone of a particular analyzer. Primary fields receive information mediated through the smallest number of switches in the subcortex (in the thalamus, or thalamus, of the diencephalon). The surface of peripheral receptors is, as it were, projected onto these fields. In the light of modern data, projection zones cannot be considered as devices that perceive point-to-point stimulation. In these zones, the perception of certain parameters of objects occurs, i.e., images are created (integrated), since these areas of the brain respond to certain changes in objects, their shape, orientation, speed of movement, etc.

Cortical structures play a primary role in learning in animals and humans. However, the formation of some simple conditioned reflexes, mainly from internal organs, can be ensured by subcortical mechanisms. These reflexes can also form at lower levels of development, when there is no cortex yet. Complex conditioned reflexes that underlie integral acts of behavior 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 also directly related to memory mechanisms. Electrical stimulation of certain areas of the cortex (for example, the temporal cortex) evokes complex patterns of memories in people.

A characteristic feature of the activity of the cortex is 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 occurring 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 different types can be distinguished by the frequency of potentials (alpha, beta, delta and theta rhythms). The EEG undergoes characteristic changes in many physiological and pathological conditions (various phases of sleep, tumors, 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 pyramidal cells. The rhythmic activity of the cortex is influenced by influences coming from the senses. Thus, a flash of light, a click or a touch on the skin causes the so-called in the corresponding areas. a primary response consisting of a series of positive waves (downward deflection of the electron beam on the oscilloscope screen) and a negative wave (upward deflection of the beam). These waves reflect the activity of the structures of a given area of the cortex and change in its different layers.

Phylogeny and ontogeny of the cortex . The cortex is a product of long-term evolutionary development, during which the ancient cortex first appears, arising in connection with the development of the olfactory analyzer in fish. With the emergence of animals from water onto land, the so-called. a mantle-shaped part of the cortex, completely separate 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 associated with the improvement and interaction of various perceptive and motor systems. In amphibians, the cortex is represented by an ancient and rudiment of the old cortex; in reptiles, the ancient and old cortex is well developed and the rudiment of a new cortex appears. The greatest development the new cortex reaches mammals, and among them 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 grooves and convolutions. Improvement of the cortex The 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 higher stages of evolution leads to disruption of the vital functions of the body. The association zones undergo the greatest changes and increase during the evolution of the neocortex, while the primary sensory fields decrease in relative size. The growth of the new cortex leads to the displacement of the old and ancient cortex onto the lower and middle surfaces of the brain.

The cortical plate appears relatively early in the process of intrauterine development of a person - at the 2nd month. The lower layers of the cortex (VI-VII) are distinguished first, then the higher 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 turning points 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. By the last period, the cytoarchitecture of the cortex is fully formed, although the cell bodies of neurons continue to increase until 18 years of age. 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 great diversity in the timing of maturation of cortical structures in different individuals, which coincides with the diversity of timing of maturation of the functional characteristics of the cortex. Thus, individual (ontogeny) and historical (phylogeny) development of the cortex is characterized by similar patterns.

On the topic : structure of the cerebral cortex

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