Shoshina Vera Nikolaevna

Therapist, education: Northern Medical University. Work experience 10 years.

Articles written

The brain of modern man and its complex structure is the greatest achievement of this species and its advantage, unlike other representatives of the living world.

The cerebral cortex is a very thin layer of gray matter that does not exceed 4.5 mm. It is located on the surface and sides of the cerebral hemispheres, covering them from above and along the periphery.

Anatomy of the cortex or cortex, complex. Each site performs its function and is of great importance in the implementation of nervous activity. This site can be considered the highest achievement of the physiological development of mankind.

Structure and blood supply

The cerebral cortex is a layer of gray matter cells that makes up approximately 44% of the total volume of the hemisphere. The area of ​​the cortex of an average person is about 2200 square centimeters. Structural features in the form of alternating furrows and convolutions are designed to maximize the size of the cortex and at the same time fit compactly within the cranium.

Interestingly, the pattern of convolutions and furrows is as individual as the prints of papillary lines on a person's fingers. Each individual is individual in pattern and.

The cortex of the hemispheres from the following surfaces:

1. Upper lateral. It adjoins the inner side of the bones of the skull (vault).
2. Lower. Its anterior and middle sections are located on the inner surface of the base of the skull, and the posterior ones rest on the cerebellum.
3. medial. It is directed to the longitudinal fissure of the brain.

The most protruding places are called poles - frontal, occipital and temporal.

The cerebral cortex is symmetrically divided into lobes:

• frontal;
• temporal;
• parietal;
• occipital;
• islet.

In the structure, the following layers of the human cerebral cortex are distinguished:

• molecular;
• external granular;
• layer of pyramidal neurons;
• internal granular;
• ganglionic, internal pyramidal or Betz cell layer;
• a layer of multiformate, polymorphic, or spindle-shaped cells.

Each layer is not a separate independent formation, but represents a single, well-functioning system.

Functional areas

Neurostimulation revealed that the cortex is divided into the following sections of the cerebral cortex:

1. Sensory (sensitive, projection). They receive incoming signals from receptors located in various organs and tissues.
2. Motor, outgoing signals sent to effectors.
3. Associative, processing and storing information. They evaluate previously obtained data (experience) and issue an answer based on them.

The structural and functional organization of the cerebral cortex includes the following elements:

• visual, located in the occipital lobe;
• auditory, occupying the temporal lobe and part of the parietal;
• vestibular is less studied and is still a problem for researchers;
• olfactory is on the bottom;
• taste is located in the temporal regions of the brain;
• the somatosensory cortex appears in the form of two areas - I and II, located in the parietal lobe.

Such a complex structure of the cortex suggests that the slightest violation will lead to consequences that affect many functions of the body and cause pathologies of varying intensity, depending on the depth of the lesion and the location of the site.

How is the cortex connected to other parts of the brain?

All areas of the human cortex do not exist in isolation, they are interconnected and form inextricable bilateral chains with deeper brain structures.

The most important and significant is the connection between the cortex and the thalamus. When the skull is injured, the damage is much more significant if the thalamus is also injured along with the cortex. Injuries to the cortex alone are found to be much smaller and have less significant consequences for the body.

Almost all connections from different parts of the cortex pass through the thalamus, which gives reason to combine these parts of the brain into the thalamocortical system. Interruption of connections between the thalamus and the cortex leads to the loss of functions of the corresponding part of the cortex.

Pathways from sensory organs and receptors to the cortes also run through the thalamus, with the exception of some olfactory pathways.

Interesting facts about the cerebral cortex

The human brain is a unique creation of nature, which the owners themselves, that is, people, have not yet learned to fully understand. It is not entirely fair to compare it with a computer, because now even the most modern and powerful computers cannot cope with the volume of tasks performed by the brain within a second.

We are accustomed to not paying attention to the usual functions of the brain associated with the maintenance of our daily life, but even the smallest failure occurred in this process, we would immediately feel it "in our own skin".

“Little gray cells,” as the unforgettable Hercule Poirot said, or from the point of view of science, the cerebral cortex is an organ that still remains a mystery to scientists. We found out a lot, for example, we know that the size of the brain does not affect the level of intelligence in any way, because the recognized genius - Albert Einstein - had a brain that was below average, about 1230 grams. At the same time, there are beings that have brains of a similar structure and even larger size, but have not yet reached the level of human development.

A striking example is the charismatic and intelligent dolphins. Some people believe that once in the deepest antiquity the tree of life split into two branches. Our ancestors went one way, and dolphins went the other way, that is, we may have had common ancestors with them.

A feature of the cerebral cortex is its indispensability. Although the brain is able to adapt to injury and even partially or completely restore its functionality, if part of the cortex is lost, the lost functions are not restored. Moreover, scientists were able to conclude that this part largely determines the personality of a person.

With an injury to the frontal lobe or the presence of a tumor here, after the operation and removal of the destroyed part of the cortex, the patient changes radically. That is, the changes concern not only his behavior, but also the personality as a whole. There have been cases when a good kind person turned into a real monster.

Based on this, some psychologists and criminologists have concluded that intrauterine damage to the cerebral cortex, especially its frontal lobe, leads to the birth of children with antisocial behavior, with sociopathic tendencies. These kids have a high chance of becoming a criminal and even a maniac.

CHM pathologies and their diagnostics

All violations of the structure and functioning of the brain and its cortex can be divided into congenital and acquired. Some of these lesions are incompatible with life, for example, anencephaly - the complete absence of the brain and acrania - the absence of cranial bones.

Other diseases leave a chance for survival, but are accompanied by mental disorders, such as encephalocele, in which part of the brain tissue and its membranes protrude outward through a hole in the skull. The same group also includes an underdeveloped small brain, accompanied by various forms of mental retardation (oligophrenia, idiocy) and physical development.

A rarer variant of the pathology is macrocephaly, that is, an increase in the brain. Pathology is manifested by mental retardation and convulsions. With it, the increase in the brain can be partial, that is, asymmetric hypertrophy.

Pathologies in which the cerebral cortex is affected are represented by the following diseases:

1. Holoprosencephaly is a condition in which the hemispheres are not separated and there is no full division into lobes. Children with such a disease are born dead or die on the first day after birth.
2. Agyria is the underdevelopment of the gyri, in which the functions of the cortex are impaired. Atrophy is accompanied by multiple disorders and leads to the death of the infant during the first 12 months of life.
3. Pachygyria is a condition in which the primary gyri are enlarged to the detriment of the others. At the same time, the furrows are short and straightened, the structure of the cortex and subcortical structures is disturbed.
4. Micropolygyria, in which the brain is covered with small convolutions, and the cortex does not have 6 normal layers, but only 4. The condition is diffuse and local. Immaturity leads to the development of plegia and muscle paresis, epilepsy, which develops in the first year, mental retardation.
5. Focal cortical dysplasia is accompanied by the presence in the temporal and frontal lobes of pathological areas with huge neurons and abnormal ones. Incorrect cell structure leads to increased excitability and seizures, accompanied by specific movements.
6. Heterotopia is an accumulation of nerve cells that, in the process of development, did not reach their place in the cortex. A solitary condition may appear after the age of ten, large accumulations cause seizures such as epileptic seizures and mental retardation.

Acquired diseases are mainly the consequences of serious inflammations, injuries, and also appear after the development or removal of a tumor - benign or malignant. Under such conditions, as a rule, the impulse emanating from the cortex to the corresponding organs is interrupted.

The most dangerous is the so-called prefrontal syndrome. This area is actually a projection of all human organs, therefore damage to the frontal lobe leads to memory, speech, movements, thinking, as well as partial or complete deformation and a change in the patient's personality.

A number of pathologies accompanied by external changes or deviations in behavior are easy to diagnose, others require more careful study, and removed tumors are subjected to histological examination to rule out a malignant nature.

Alarming indications for the procedure are the presence of congenital pathologies or diseases in the family, fetal hypoxia during pregnancy, asphyxia during childbirth, and birth trauma.

Methods for diagnosing congenital abnormalities

Modern medicine helps prevent the birth of children with severe malformations of the cerebral cortex. For this, screening is performed in the first trimester of pregnancy, which makes it possible to identify pathologies in the structure and development of the brain at the earliest stages.

In a baby born with suspected pathology, neurosonography is performed through the "fontanelle", and older children and adults are examined by conducting. This method allows not only to detect a defect, but also to visualize its size, shape and location.

If there were hereditary problems in the family related to the structure and functioning of the cortex and the entire brain, a genetic consultation and specific examinations and analyzes are required.

The famous "gray cells" are the greatest achievement of evolution and the highest good for man. Damage can be caused not only by hereditary diseases and injuries, but also by acquired pathologies provoked by the person himself. Doctors urge you to take care of your health, give up bad habits, allow your body and brain to rest and not let your mind be lazy. Loads are useful not only for muscles and joints - they do not allow nerve cells to grow old and fail. The one who studies, works and loads his brain, suffers less from wear and tear and later comes to the loss of mental abilities.

The cerebral cortex is the center of higher nervous (mental) human activity and controls the implementation 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 are composed of white matter, the basis of which consists of long myelinated axons of neurons. Outside, the hemisphere is covered with gray matter or the cerebral cortex, consisting of neurons, non-myelinated fibers and glial cells, which are also contained in the thickness of the departments of this organ.

The surface of the hemispheres is conditionally divided into several zones, the functionality of which is to control the body at the level of reflexes and instincts. Also, it contains centers of higher mental activity of a person, providing consciousness, assimilation of the information received, allowing to adapt to the environment, and through it, at the subconscious level, the autonomic nervous system (ANS) is controlled by the hypothalamus, which controls the organs of blood 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 required 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 improves throughout life, by receiving and processing signals from the environment. Thus, it is responsible for the following functions of the brain:

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

At the same time, data is received, processed, and stored due to a significant number of impulses that pass through and are formed 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 not very susceptible to processes occurring in the external environment, therefore, all experiments with the impact 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 in communicating with other individuals, cannot realize themselves in any work activity, and they are indifferent to their appearance and third-party opinions. Sometimes there are other violations in the implementation of the functions of this body:

• lack of concentration on household items;
• manifestation of creative dysfunction;
• violations of the psycho-emotional state of a person.

The surface of the cerebral cortex is divided into 4 zones, outlined by the most clear and significant convolutions. Each of the parts at the same time controls the main functions of the cerebral cortex:

1. parietal zone - responsible for active sensitivity and musical perception;
2. in the back of the head is the primary visual area;
3. the temporal or temporal is responsible for the 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;
4. 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 features 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 the performance of any higher nervous activity;
• the presence of specialized associative areas makes it possible to establish a causal 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 able to store traces of excitation of neurons.

The large hemispheres of the brain consist mainly of long axons, and also contains clusters of neurons in its thickness, forming the largest nuclei of the base, which are part of the extrapyramidal system.

As already mentioned, the formation of the cerebral cortex occurs even 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 of age.

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

The neurons of this part of the brain are programmed to repair the damaged area through synoptic contacts, thus each of the cells actively tries to repair the damaged connections, which ensures the plasticity of neural cortical networks. For example, when the cerebellum is removed or dysfunction, the neurons that connect it with the final section begin to grow into the cerebral cortex. In addition, cortical plasticity also manifests itself under normal conditions, when a new skill is being learned or as a result of pathology, when the functions performed by the damaged area are transferred to neighboring parts of the brain or even the hemisphere.

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 takes place, the nervous path of which consists of 3 devices connected in series: an analyzer, a closing apparatus of conditioned reflex connections and a working device. Weakness of the closing function of the cortex and trace manifestations can be observed in children with severe mental retardation, when the conditioned connections formed between neurons are fragile and unreliable, which leads to learning difficulties.

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

Areas and zones of the cortex

The cortex is a relatively young part of the CNS, developed from the terminal part of the brain. The evolutionary formation of this organ occurred in stages, so it is usually divided into 4 types:

1. The archicortex or ancient cortex, due to atrophy of the sense of smell, has turned into a hippocampal formation and consists of the hippocampus and its associated structures. It regulates behavior, feelings and memory.
2. The paleocortex, or old cortex, makes up the bulk of the olfactory zone.
3. The neocortex or neocortex is about 3-4 mm thick. It is a functional part and performs higher nervous activity: it processes sensory information, gives motor commands, and it also forms conscious thinking and speech of a person.
4. The mesocortex is an intermediate variant 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 that 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 on a columnar principle, in which the columns are made into micromodules that have a homogeneous structure.

The system of micromodules is based on stellate cells and their axons, while all neurons respond in the same way to an 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 the synchronization of mental activity with the motility of organs and the area responsible for the analysis of incoming signals.

Signal transmission in the horizontal direction occurs through transverse fibers located in the thickness of the cortex, and transmit an impulse from one column to another. According to 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 irritation, partial removal of areas, as well as the development of conditioned reflexes and registration of biocurrents.

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

The sensitive or sensory zone 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 tactile organs on the left side of the body are sent along afferent pathways to the opposite lobe of the cerebral hemispheres for further processing.

The 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 input mechanism is similar to that of the sensory area, as the motor pathways form an overlap in the medulla oblongata and follow to the opposite motor area.

Crinkles furrows 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 sections of the cerebral cortex. All of them are different in morphological features and regulate different functions. Thus, 52 different fields are allocated, located in certain areas. According to Brodman, this division looks like this:

1. 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.
2. The lateral furrow separates the parietal zone from the occipital zone. If you spread its lateral edges, then inside you can see a hole, in the center of which there is an island.
3. 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 apparatus of the left half of the body, the left-sided - with the right side.

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

Cell layers

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

1. The surface molecular layer is formed mainly from dendrites, with a small interspersed with neurons, the processes of which do not leave the layer boundary.
2. The outer granular consists of pyramidal and stellate neurons, the processes of which connect it with the next layer.
3. The pyramidal one is formed by pyramidal neurons, the axons of which are directed downward, where they break or form associative fibers, and their dendrites connect this layer with the previous one.
4. The inner granular layer is formed by stellate and small pyramidal neurons, the dendrites of which go into the pyramidal layer, and its long fibers go into the upper layers or go down into the white matter of the brain.
5. Ganglionic consists of large pyramidal neurocytes, their axons extend beyond the cortex and connect various structures and departments of the central nervous system with each other.

The multiform layer is formed by all types of neurons, and their dendrites are oriented to the molecular layer, and the axons penetrate the previous layers or go 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

The cerebral cortex is represented by a uniform layer of gray matter 1.3-4.5 mm thick, consisting of more than 14 billion nerve cells. Due to the folding of the bark, its surface reaches large sizes - about 2200 cm 2.

The thickness of the cortex consists of six layers of cells, which are distinguished by special staining and examination under a microscope. The cells of the layers are different in shape and size. From them, processes extend into the depths of the brain.

It was found that different areas - fields of the cerebral cortex differ in structure and function. Such fields (also called zones, or centers) are distinguished from 50 to 200. There are no strict boundaries between the zones of the cerebral cortex. They constitute an apparatus that provides reception, processing of incoming signals and response to incoming signals.

In the posterior central gyrus, behind the central sulcus, is located zone of skin and joint-muscular sensitivity. Here, signals are perceived and analyzed that occur when touching our body, when it is exposed to cold or heat, or pain effects.

In contrast to this zone - in the anterior central gyrus, in front of the central sulcus, is located motor zone. It revealed areas that provide movement of the lower extremities, muscles of the trunk, arms, head. When this zone is irritated by an electric current, contractions of the corresponding muscle groups occur. Wounds or other damage to the cortex of the motor zone entail paralysis of the muscles of the body.

In the temporal lobe is auditory zone. Impulses arising in the receptors of the cochlea of ​​the inner ear are received here and analyzed here. Irritations of parts of the auditory zone cause sensations of sounds, and when they are affected by the disease, hearing is lost.

visual area located in the cortex of the occipital lobes of the hemispheres. When it is irritated by an electric current during brain surgery, a person experiences sensations of flashes of light and darkness. If it is affected by any disease, it worsens and vision is lost.

Near the lateral furrow is located taste zone, where the sensations of taste are analyzed and formed based on the signals that occur in the receptors of the tongue. Olfactory the zone is located in the so-called olfactory brain, at the base of the hemispheres. When these areas are irritated during surgical operations or during inflammation, people smell or taste any substances.

Purely speech zone does not exist. It is represented in the cortex of the temporal lobe, the lower frontal gyrus on the left, and in areas of the parietal lobe. Their illnesses are accompanied by speech disorders.

First and second signal systems

The role of the cerebral cortex in the improvement of the first signaling system and the development of the second is invaluable. These concepts were developed by I.P. Pavlov. The signal system as a whole is understood as the totality of the processes of the nervous system that carry out the perception, processing of information and the body's response. It connects the body with the outside world.

First signal system

The first signal system determines the perception of sensory-specific images through the senses. It is the basis for the formation of conditioned reflexes. This system exists in both animals and humans.

In the higher nervous activity of man, a superstructure has developed in the form of a second signaling system. It is peculiar only to man and is manifested by verbal communication, speech, concepts. With the advent of this signal system, abstract thinking became possible, the generalization of the countless signals of the first signal system. According to I.P. Pavlov, words have turned into “signals of signals”.

Second signal system

The emergence of the second signaling system became possible due to the complex labor relations between people, since this system is a means of communication, collective labor. Verbal communication does not develop outside of society. The second signaling system gave rise to abstract (abstract) thinking, writing, reading, counting.

Words are also perceived by animals, but completely different from people. They perceive them as sounds, and not their semantic meaning, like people. Therefore, animals do not have a second signaling system. Both human signaling systems are interconnected. They organize human behavior in the broadest sense of the word. Moreover, the second changed the first signaling system, since the reactions of the first began to largely depend on the social environment. A person has become able to control his unconditioned reflexes, instincts, i.e. first signal system.

Functions of the cerebral cortex

Acquaintance with the most important physiological functions of the cerebral cortex indicates its extraordinary importance in life. The cortex, together with the subcortical formations closest to it, is a department of the central nervous system of animals and humans.

The functions of the cerebral cortex are the implementation of complex reflex reactions that form the basis of the higher nervous activity (behavior) of a person. It is no coincidence that she received the greatest development from him. The exceptional properties of the cortex are consciousness (thinking, memory), the second signal system (speech), high organization of work and life in general.

The human is a surface layer that covers the cerebral hemisphere and is mainly formed by vertically oriented nerve cells (the so-called neurons), as well as their processes and efferent (centrifugal), afferent bundles (centripetal) and nerve fibers.

In addition, the basis of the composition of the cortex, in addition, includes cells, as well as neuroglia.

A very significant feature of the structure is the horizontal dense layering, which is primarily due to the whole ordered arrangement of each body of nerve cells and fibers. There are 6 main layers, which mainly differ in their own width, the overall density of its location, the size and shape of all the constituent external neurons.

Predominantly, precisely because of the vertical orientation of their processes, these bundles of all the various nerve fibers, as well as the bodies of neurons, which have a vertical striation. And for the full-fledged functional organization of the human cerebral cortex, the column-like, vertical location of absolutely all internal nerve cells on the surface of the cerebral cortex zone is of great importance here.

The main type of all the main nerve cells that are part of the cerebral cortex are special pyramidal cells. The body of these cells resembles an ordinary cone, from the height of which one long and thick, apical dendrite begins to depart. An axon and shorter basal dendrites also depart from the base of the body of this pyramidal cell, heading into a full-fledged white matter, which is located directly under the cerebral cortex, or branching in the cortex.

All the dendrites of the cells of the pyramid carry a fairly large number of spines, outgrowths, which take the most active part in the full formation of synaptic contacts at the end of afferent fibers that come to the cerebral cortex from other subcortical formations and sections of the cortex. The axons of these cells are able to form efferent main pathways that go directly from the C.G.M. The sizes of all pyramidal cells can vary from 5 to 150 microns (150 are giant cells named after Betz). In addition to pyramidal neurons, K.G.M. the composition includes some spindle-shaped and stellate types of interneurons that are involved in receiving incoming afferent signals, as well as the formation of interneuronal functional connections.

Features of the cerebral cortex

Based on various phylogenesis data, the cerebral cortex is divided into ancient (paleocortex), old (archicortex), and new (neocortex). In the phylogeny of K.G.M. there is a relative ubiquitous increase in the territory of the new surface of the crust, with a slight decrease in the area of ​​the old and ancient.

Functionally, the areas of the cerebral cortex are divided into 3 types: associative, motor and sensory. In addition, the cerebral cortex is also responsible for the corresponding areas.

What is the cerebral cortex responsible for?

In addition, it is important to note that the entire cerebral cortex, in addition to all of the above, is responsible for everything. As part of the zones of the cerebral cortex, these are neurons of various structures, including stellate, small and large pyramidal, basket, fusiform and others. In a functional relationship, all main neurons are divided into the following types:

1. Intercalary neurons (fusiform, small pyramidal and others). Interneurons also have subdivisions and can be both inhibitory and excitatory (small and large basket neurons, neurons with cystic neurons and candelabra-shaped axons)
2. Afferent (these are the so-called stellate cells) - which receive impulses from all specific pathways, as well as various specific sensations. It is these cells that transmit impulses directly to the efferent and intercalary neurons. Groups of polysensory neurons, respectively, receive different impulses from the optic tubercles of the associative nuclei
3. Efferent neurons (they are called large pyramidal cells) - impulses from these cells go to the so-called periphery, where they provide a certain type of activity

Neurons, as well as processes on the surface of the cerebral cortex, are also arranged in six layers. Neurons that perform the same reflex functions are located strictly one above the other. Thus, individual columns are considered to be the main structural unit of the surface of the cerebral cortex. And the most pronounced connection between the third, fourth and fifth stage of the layers of K.G.M.

Pads of the cerebral cortex

The following factors can also be considered proof of the presence of columns in the cerebral cortex:
With the introduction of various microelectrodes into the K.G.M. an impulse is recorded (registered) strictly perpendicularly under the full impact of a similar reflex reaction. And when the electrodes are inserted in a strictly horizontal direction, characteristic impulses are recorded for various reflex reactions. Basically, the diameter of one column is 500 µm. All adjacent columns are tightly connected in all functional respects, and are also often located with each other in close reciprocal relationships (some inhibit, others excite).

When stimuli act on the response, many columns are also involved and a perfect synthesis and analysis of stimuli occurs - this is the screening principle.

Since the cerebral cortex grows in the periphery, then all the superficial layers of the cerebral cortex are fully related to all signal systems. These superficial layers consist of a very large number of nerve cells (about 15 billion) and, together with their processes, with the help of which the possibility of such unlimited closing functions, wide associations is created - this is the essence of all the activity of the signaling second system. But with all this, the second s.s. works with other systems.

Attention!

CORTEX (cortexencephali) - all surfaces of the cerebral hemispheres, covered with a cloak (pallium), formed by gray matter. Together with other departments of c. n. With. the bark is involved in the regulation and coordination of all body functions, plays an extremely important role in mental, or higher nervous activity (see).

In accordance with the stages of evolutionary development of c. n. With. the bark is divided into old and new. The old cortex (archicortex - the old cortex itself and paleocortex - the ancient cortex) is a phylogenetically older formation than the new cortex (neocortex), which appeared during the development of the cerebral hemispheres (see Architectonics of the cerebral cortex, Brain).

Morphologically, K. m. is formed by nerve cells (see), their processes and neuroglia (see), which has a support-trophic function. In primates and humans in the cortex, there are approx. 10 billion neurocytes (neurons). Depending on the shape, pyramidal and stellate neurocytes are distinguished, which are characterized by great diversity. The axons of pyramidal neurocytes are sent to the subcortical white matter, and their apical dendrites - to the outer layer of the cortex. Star-shaped neurocytes have only intracortical axons. Dendrites and axons of stellate neurocytes branch abundantly near the cell bodies; some of the axons approach the outer layer of the cortex, where, following horizontally, they form a dense plexus with the tops of the apical dendrites of pyramidal neurocytes. Along the surface of the dendrites there are reniform outgrowths, or spines, which represent the region of axodendritic synapses (see). The cell body membrane is the area of ​​axosomatic synapses. In each area of ​​the cortex there are many input (afferent) and output (efferent) fibers. Efferent fibers go to other areas K. of m, to subcrustal educations or to the motive centers of a spinal cord (see). Afferent fibers enter the cortex from the cells of the subcortical structures.

The ancient cortex in humans and higher mammals consists of a single cell layer, poorly differentiated from the underlying subcortical structures. Actually the old bark consists of 2-3 layers.

The new bark has a more complex structure and takes (in humans) approx. 96% of the entire surface of K. g. m. Therefore, when they talk about K. g. m., they usually mean a new bark, which is divided into the frontal, temporal, occipital and parietal lobes. These lobes are divided into areas and cytoarchitectonic fields (see Architectonics of the cerebral cortex).

The thickness of the cortex in primates and humans varies from 1.5 mm (on the surface of the gyri) to 3-5 mm (in the depth of the furrows). On the sections painted across Nissl, the layered structure of bark is visible, a cut depends on grouping of neurocytes at its different levels (layers). In the bark, it is customary to distinguish 6 layers. The first layer is poor in cell bodies; the second and third - contain small, medium and large pyramidal neurocytes; the fourth layer is the zone of stellate neurocytes; the fifth layer contains giant pyramidal neurocytes (giant pyramidal cells); the sixth layer is characterized by the presence of multiform neurocytes. However, the six-layer organization of the cortex is not absolute, since in reality in many parts of the cortex there is a gradual and uniform transition between layers. The cells of all layers, located on the same perpendicular with respect to the surface of the cortex, are closely connected with each other and with subcortical formations. Such a complex is called a column of cells. Each such column is responsible for the perception of predominantly one type of sensitivity. For example, one of the columns of the cortical representation of the visual analyzer perceives the movement of an object in a horizontal plane, the neighboring one - in a vertical one, etc.

Similar cell complexes of the neocortex have a horizontal orientation. It is assumed that, for example, small cell layers II and IV consist mainly of receptive cells and are “entrances” to the cortex, large cell layer V is an “exit” from the cortex to subcortical structures, and middle cell layer III is associative, connects different areas of the cortex.

Thus, several types of direct and feedback connections between the cellular elements of the cortex and subcortical formations can be distinguished: vertical bundles of fibers that carry information from subcortical structures to the cortex and back; intracortical (horizontal) bundles of associative fibers passing at different levels of the cortex and white matter.

The variability and originality of the structure of neurocytes indicate the extreme complexity of the apparatus of intracortical switching and the methods of connections between neurocytes. This feature of the structure of K. g. m should be considered as morfol, the equivalent of its extreme reactivity and funkts, plasticity, providing it with higher nervous functions.

An increase in the mass of the cortical tissue occurred in a limited space of the skull; therefore, the surface of the cortex, which was smooth in lower mammals, was transformed into convolutions and furrows in higher mammals and humans (Fig. 1). It was with the development of the cortex already in the last century that scientists associated such aspects of brain activity as memory (see), intelligence, consciousness (see), thinking (see), etc.

I. P. Pavlov defined 1870 as the year "from which scientific fruitful work on the study of the cerebral hemispheres begins." This year, Fritsch and Gitzig (G. Fritsch, E. Hitzig, 1870) showed that electrical stimulation of certain areas of the anterior section of the CT of dogs causes a contraction of certain groups of skeletal muscles. Many scientists believed that when stimulated by K. m., the “centers” of voluntary movements and motor memory are activated. However still Ch. Sherrington preferred to avoid funkts, interpretations of this phenomenon and was limited only by the statement that the area of ​​bark, irritation a cut causes reduction of muscle groups, is intimately connected with a spinal cord.

Directions of experimental researches K. of m of the end of the last century were almost always connected with problems a wedge, neurology. On this basis, experiments were started with partial or complete decortication of the brain (see). The first complete decortication in a dog was made by Goltz (F. L. Goltz, 1892). The decorticated dog turned out to be viable, but many of its most important functions were sharply impaired - vision, hearing, orientation in space, coordination of movements, etc. Prior to the discovery by I. P. Pavlov of the phenomenon of a conditioned reflex (see) partial extirpations of the cortex suffered from the absence of an objective criterion for their evaluation. The introduction of the conditioned reflex method into the practice of experimenting with extirpations opened up a new era in studies of the structural and functional organization of CG m.

Simultaneously with the discovery of the conditioned reflex, the question arose about its material structure. Since the first attempts to develop a conditioned reflex in decorticated dogs failed, I. P. Pavlov came to the conclusion that C. g. m. is an "organ" of conditioned reflexes. However, further studies showed the possibility of developing conditioned reflexes in decorticated animals. It was found that conditioned reflexes are not disturbed during vertical cuts of various areas of the K. g. m. and their separation from subcortical formations. These facts, along with electrophysiological data, gave reason to consider the conditioned reflex as a result of the formation of a multichannel connection between various cortical and subcortical structures. The shortcomings of the method of extirpation for studying the significance of C. g. m in the organization of behavior prompted the development of methods for reversible, functional, exclusion of the cortex. Buresh and Bureshova (J. Bures, O. Buresova, 1962) applied the phenomenon of the so-called. spreading depression by applying potassium chloride or other irritants to one or another part of the cortex. Since depression does not spread through the furrows, this method can only be used on animals with a smooth surface K. g. m. (rats, mice).

Other way funkts, switching off K. m. - its cooling. The method developed by N. Yu. Belenkov et al. (1969) consists in the fact that, in accordance with the shape of the surface of the cortical areas scheduled for shutdown, capsules are made that are implanted over the dura mater; during the experiment, a cooled liquid is passed through the capsule, as a result of which the temperature of the cortex under the capsule decreases to 22–20°C. The assignment of biopotentials with the help of microelectrodes shows that at such a temperature, the impulse activity of neurons stops. The cold decortication method used in hron, experiments on animals demonstrated the effect of an emergency shutdown of the new cortex. It turned out that such a switch-off stops the implementation of previously developed conditioned reflexes. Thus, it was shown that K. g. m. is a necessary structure for the manifestation of a conditioned reflex in an intact brain. Consequently, the observed facts of the development of conditioned reflexes in surgically decorticated animals are the result of compensatory rearrangements occurring in the time interval from the moment of operation to the beginning of the study of the animal in hron, experiment. The compensatory phenomena take place and in case funkts, switching-offs of a new bark. Just like cold shutdown, acute shutdown of the neocortex in rats with the help of spreading depression sharply disrupts conditioned reflex activity.

A comparative evaluation of the effects of complete and partial decortication in various animal species showed that monkeys endure these operations more difficult than cats and dogs. The degree of dysfunction during extirpation of the same areas of the cortex is different in animals at different stages of evolutionary development. For example, the removal of temporal regions in cats and dogs impairs hearing less than in monkeys. Similarly, vision after removal of the occipital lobe of the cortex is affected to a greater extent in monkeys than in cats and dogs. On the basis of these data there was an idea of ​​corticolization of functions in the course of evolution of c. n. N of page, according to Krom phylogenetically earlier links of a nervous system pass to lower level of hierarchy. At the same time, K. g. m. plastically rebuilds the functioning of these phylogenetically older structures in accordance with the influence of the environment.

Cortical projections of afferent systems K. of m represent specialized terminal stations of ways from sensory organs. Efferent pathways go from K. m. to the motor neurons of the spinal cord as part of the pyramidal tract. They originate mainly from the motor area of ​​the cortex, which in primates and humans is represented by the anterior central gyrus, located anterior to the central sulcus. Behind the central sulcus is the somatosensory area K. m. - the posterior central gyrus. Individual parts of the skeletal muscles are corticolized to varying degrees. The least differentiated in the anterior central gyrus are the lower limbs and the trunk, a large area is occupied by the representation of the muscles of the hand. An even larger area corresponds to the musculature of the face, tongue and larynx. In the posterior central gyrus, in the same ratio as in the anterior central gyrus, afferent projections of body parts are presented. It can be said that the organism is, as it were, projected into these convolutions in the form of an abstract "homunculus", which is characterized by an extreme preponderance in favor of the anterior segments of the body (Fig. 2 and 3).

In addition, the cortex includes associative, or non-specific, areas that receive information from receptors that perceive irritations of various modalities, and from all projection zones. The phylogenetic development of C. g. m. is characterized primarily by the growth of associative zones (Fig. 4) and their separation from projection zones. In lower mammals (rodents), almost the entire cortex consists of projection zones alone, which simultaneously perform associative functions. In humans, the projection zones occupy only a small part of the cortex; everything else is reserved for associative zones. It is assumed that associative zones play a particularly important role in the implementation of complex forms in c. n. d.

In primates and humans, the frontal (prefrontal) region reaches the greatest development. It is phylogenetically the youngest structure directly related to the highest mental functions. However, attempts to project these functions to separate areas of the frontal cortex have not been successful. Obviously, any part of the frontal cortex can be included in the implementation of any of the functions. The effects observed during the destruction of various parts of this area are relatively short-lived or often completely absent (see Lobectomy).

The confinement of separate structures of K. of m to certain functions, considered as a problem of localization of functions, remains till now one of the most difficult problems of neurology. Noting that in animals, after the removal of the classical projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved, I. P. Pavlov hypothesized the existence of a "core" of the analyzer and its elements, "scattered" throughout the C. g. With the help microelectrode research methods (see) it was succeeded to register activity of the specific neurocytes responding to incentives of a certain touch modality in various areas K. of m. Superficial assignment of bioelectric potentials reveals distribution of primary evoked potentials on the considerable areas K. of m - outside of the corresponding projection zones and cytoarchitectonic fields. These facts, along with the polyfunctionality of disturbances upon removal of any sensory area or its reversible shutdown, indicate a multiple representation of functions in C.g.m. Motor functions are also distributed over large areas of C.g.m. tract, are located not only in the motor areas, but also beyond them. In addition to sensory and motor cells, in K. m. there are also intermediate cells, or interneurocytes, which make up the bulk of K. g. m. and concentrated ch. arr. in association areas. Multimodal excitations converge on interneurocytes.

Experimental data indicate, thus, the relativity of the localization of functions in C. g. m., the absence of cortical "centers" reserved for one or another function. The least differentiated in funkts, the relation are the associative areas possessing especially expressed properties of plasticity and interchangeability. However, it does not follow from this that associative regions are equipotential. The principle of equipotentiality of the cortex (the equivalence of its structures), expressed by Lashley (K. S. Lashley) in 1933 on the basis of the results of extirpations of a poorly differentiated rat cortex, as a whole cannot be extended to the organization of cortical activity in higher animals and humans. I. P. Pavlov contrasted the principle of equipotentiality with the concept of dynamic localization of functions in C.G.M.

The solution to the problem of the structural and functional organization of C. g. m. is largely hampered by the identification of the localization of symptoms of extirpations and stimulations of certain cortical zones with the localization of the functions of K. g. m. This question already concerns the methodological aspects of neurophysiol, experiment, since from a dialectical point From the point of view of any structural-functional unit in the form in which it appears in each given study, it is a fragment, one of the aspects of the existence of the whole, a product of the integration of structures and connections of the brain. For example, the position that the function of motor speech is "localized" in the lower frontal gyrus of the left hemisphere is based on the results of damage to this structure. At the same time, electrical stimulation of this "center" of speech never causes an act of articulation. It turns out, however, that the utterance of entire phrases can be induced by stimulation of the rostral thalamus, which sends afferent impulses to the left hemisphere. Phrases caused by such stimulation have nothing to do with arbitrary speech and are not adequate to the situation. This highly integrated stimulation effect indicates that ascending afferent impulses are transformed into a neuronal code effective for the higher coordination mechanism of motor speech. In the same way, complexly coordinated movements caused by stimulation of the motor area of ​​the cortex are organized not by those structures that are directly exposed to irritation, but by neighboring or spinal and extrapyramidal systems excited along descending pathways. These data show that there is a close relationship between the cortex and subcortical formations. Therefore, it is impossible to oppose cortical mechanisms to the work of subcortical structures, but it is necessary to consider specific cases of their interaction.

With electrical stimulation of individual cortical areas, the activity of the cardiovascular system, the respiratory apparatus, went. - kish. a path and other visceral systems. K. M. Bykov also substantiated the influence of C. m. on the internal organs by the possibility of the formation of visceral conditioned reflexes, which, along with vegetative shifts with various emotions, was put by him as the basis for the concept of the existence of cortico-visceral relations. The problem of cortico-visceral relations is solved in terms of studying the modulation of the activity of subcortical structures by the cortex, which are directly related to the regulation of the internal environment of the body.

An essential role is played by communications K. of m with a hypothalamus (see).

The level of activity of K. of m is mainly determined by ascending influences from the reticular formation (see) of the brain stem, which is controlled by cortico-fugal influences. The effect of the last has dynamic character and is a consequence of the current afferent synthesis (see). Studies with the help of electroencephalography (see), in particular corticography (i.e., the assignment of biopotentials directly from K. g. m.), It would seem that they confirmed the hypothesis of the closure of the temporary connection between the foci of excitations arising in the cortical projections of the signal and unconditioned stimuli in the process of formation of a conditioned reflex. However, it turned out that as the behavioral manifestations of the conditioned reflex become stronger, the electrographic signs of the conditioned connection disappear. This crisis of the technique of electroencephalography in the knowledge of the mechanism of the conditioned reflex was overcome in the studies of M. N. Livanov et al. (1972). They showed that the spread of excitation along C. g. m. and the manifestation of a conditioned reflex depend on the level of distant synchronization of biopotentials taken from spatially remote points of C. g. m. An increase in the level of spatial synchronization is observed with mental stress (Fig. 5). In this state, synchronization areas are not concentrated in certain areas of the cortex, but are distributed over its entire area. Correlation relations cover points of the entire frontal cortex, but at the same time, increased synchrony is also recorded in the precentral gyrus, in the parietal region, and in other parts of the C. g. m.

The brain consists of two symmetrical parts (hemispheres) interconnected by commissures consisting of nerve fibers. Both hemispheres of the brain are united by the largest commissure - the corpus callosum (see). Its fibers connect identical points K. g. m. The corpus callosum ensures the unity of the functioning of both hemispheres. When it is cut, each hemisphere begins to function independently of one another.

In the process of evolution, the human brain acquired the property of lateralization, or asymmetry (see). Each of its hemispheres specialized to perform certain functions. In most people, the left hemisphere is dominant, providing the function of speech and control over the action of the right hand. The right hemisphere is specialized for the perception of form and space. At the same time funkts, differentiation of hemispheres is not absolute. However, extensive damage to the left temporal lobe is usually accompanied by sensory and motor speech disorders. Obviously, lateralization is based on innate mechanisms. However, the potential of the right hemisphere in organizing the function of speech can manifest itself when the left hemisphere is damaged in newborns.

There are reasons to consider lateralization as an adaptive mechanism that developed as a result of the complication of brain functions at the highest stage of its development. Lateralization prevents the interference of various integrative mechanisms in time. It is possible that cortical specialization counteracts the incompatibility of various functional systems (see), facilitates decision-making about the purpose and mode of action. The integrative activity of the brain is not limited, therefore, to the external (summative) integrity, understood as the interaction of the activities of independent elements (be it neurocytes or whole brain formations). Using the example of the development of lateralization, one can see how this integral, integrative activity of the brain itself becomes a prerequisite for the differentiation of the properties of its individual elements, endowing them with functionality and specificity. Consequently, the funkts, the contribution of each individual structure of the C. g. m., in principle, cannot be assessed in isolation from the dynamics of the integrative properties of the whole brain.

Pathology

The cerebral cortex is rarely affected in isolation. Signs of its defeat to a greater or lesser extent usually accompany the pathology of the brain (see) and are part of its symptoms. Usually patol, not only K. of m, but also white matter of hemispheres is surprised by processes. Therefore, pathology K. of m is usually understood as its primary lesion (diffuse or local, without a strict boundary between these concepts). The most extensive and intense lesion of K. m. is accompanied by the disappearance of mental activity, a complex of both diffuse and local symptoms (see Apallic syndrome). Along with nevrol, symptoms of damage to the motor and sensitive spheres, symptoms of damage to various analyzers in children is a delay in the development of speech and even the complete impossibility of the formation of the psyche. In this case, changes in cytoarchitectonics are observed in the form of a violation of layering, up to its complete disappearance, foci of loss of neurocytes with their replacement by growths of glia, heterotopia of neurocytes, pathology of the synaptic apparatus and other pathomorphol changes. Lesions of K. m. hereditary and degenerative diseases of the brain, disorders of cerebral circulation, etc.

Studying of EEG at localization patol, the center in K. of m reveals dominance of focal slow waves which are considered as a correlate of guarding braking more often (U. Walter, 1966). Weak expressiveness of slow waves in the field patol, the center is a useful diagnostic sign in a preoperative assessment of a condition of patients. As N. P. Bekhtereva's (1974) researches which are carried out jointly with neurosurgeons showed, absence of slow waves in the field patol, the center is an adverse prognostic sign of consequences of surgical intervention. For an assessment patol, K.'s state of m also the test for interaction of EEG in a zone of focal defeat with the caused activity is used in response to positive and differentiating conditional irritants. The bioelectric effect of such an interaction can be both an increase in focal slow waves, and a weakening of their severity or an increase in frequent oscillations such as pointed beta waves.

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H. Yu. Belenkov.