Bark cells. The cerebral cortex. The connection of the cortex with the underlying parts of the brain

By the World Health Organization, viruses that cause cancer have been divided into three groups: small DNA viruses (papa viruses, adenoviruses); RNA viruses of 70-100 mmq - Rous sarcoma virus, mammalian and avian leukemia virus, viruses in mice; large DNA viruses. These include rabbit fibroma viruses, molluscum contagiosum and yaba virus.

As a rule, viruses that cause cancer cause tumor transformation, accompanied by the incorporation of the viral genome into the cell genome. Part of the viral genome in tumor cells is active and determines the synthesis of several specific antigens localized on the cell surface (specific transplant antigen) and in the nucleus (the so-called T-antigen). In tumor cells, induced. With DNA-containing viruses (adenoviruses and viruses of the papov group), synthesis of complete viral particles usually does not occur, but such synthesis can be induced by special experimental techniques. In cells of leukemias and tumors induced by RNA viruses, synthesis of complete viral particles can take place.

Small DNA viruses that cause cancer. Human and animal adenoviruses are DNA-containing viruses with a particle size of 70-75 mmq. Some types of adenoviruses (types 12 and 18) isolated from humans, as well as some adenoviruses isolated from birds and monkeys, cause tumors 1-2 months after administration to newborn Syrian hamsters and (less commonly) rats and mice. In hamster cell culture, these viruses cause tumor transformation. There is no data on the tumorigenic activity of these viruses for their natural hosts.

Papova group viruses are DNA-containing viruses with a size of about 45 mmk. These include the polyoma virus, BU-40 virus, and human, rabbit, cattle and other animal papillomaviruses.

When a mouse embryonic culture polyoma virus is infected, a productive viral infection is observed, which ends in the formation of a large number of viral particles in the cell nucleus and the destruction of most cells (cytopathogenic effect); a small proportion of surviving cells undergo tumor transformation. When the embryonic cells of the Syrian hamster are infected, productive infection is not observed, in most cells there is an abortive viral infection, in which the properties of the cells temporarily change, but after a while they return to normal. In a small part of cells, after a few months, the genome is incorporated into the cell genome and undergoes stable transformation.

RNA-containing tumor-causing viruses that cause cancer (oncornaviruses, leukoviruses) form particles 60-80 mm in diameter: the outer shell of these viruses contains lipids. The viral particle contains a number of enzymes (the so-called reverse transcriptases), which, after the virus enters the cell, can cause DNA synthesis on the viral RNA chain. Virus-specific DNA is included in the cell genome, connecting with cellular DNA. Some viruses of this group (sarcoma viruses of chickens, mice) are defective: they are not able to cause the formation of proteins that form a capsule of the viral particle. Such viruses can form infectious particles only if the cell is simultaneously infected with a helper virus that causes the synthesis of capsule components: the nucleic acid of the defective virus is then dressed in the shell of the helper virus. One and the same defective virus can “dress” in a capsule of different helper viruses. For sarcoma viruses, the helper viruses are usually leukemia viruses. In culture, viruses of this type are usually unable to cause infection, accompanied by the destruction of cells. The efficiency of cell transformation caused in culture by some RNA-containing viruses is very high: chicken sarcoma virus or murine sarcoma virus can transform 80-100% of culture cells in a short time (3-4 days).

In many cases, the viruses that cause cancer exist in a latent state and are passed on to the next generation through germ cells or through breastfeeding milk (vertical transmission). There are several groups of RNA viruses. Each group is characterized by a common group-specific antigen and antigens specific to each variant of the virus.

a) A group of leukemia viruses - avian sarcomas. This includes murine sarcoma virus and chicken leukemia viruses, various strains. The Rous sarcoma virus in chickens causes in a short time (from 1 to 3-8 weeks) tumors at the injection site in chickens. Some variants of the Rous virus cause sarcomas also when administered to newborn and adult mammals (monkeys, mice, rats, guinea pigs, hamsters), as well as when administered to some reptiles. Leukemic viruses cause different variants of leukemia in chickens (myeloblastosis, erythroblastosis).

b) A group of leukemia viruses - mouse sarcomas. The sarcoma virus (Moloney and Harvey variants) was isolated from mouse tumors and after a few days causes the proliferation of sarcomatous cells in mice, rats, and hamsters. Mouse leukemia viruses exist in many variants, differing in their pathogenicity: the Gross virus causes lymphatic leukemia, pathogenic only for newborn mice. The Moloney virus also causes lymphatic leukemia in newborn mice, but is pathogenic in adult mice. In mice infected with the vaccinia virus, it was possible to isolate a variant of the leukemia virus that causes reticulosis and hematocytoblastosis (Mazurenko virus). Several variants of leukemia viruses cause leukemia when infected in both mice and rats.

In 1908-1911 was installed viral nature of leukemia and sarcomas of chickens. In the following decades, the viral etiology of a number of lymphoid and epithelial tumors in birds and mammals was proven. It is now known that in vivo, for example, leukemia is caused by viruses in chickens, cats, cattle, mice, gibbon monkeys.

Opened in recent years the first viral pathogen... causing the development of human leukemia is ATLV (adult T-cell leukemia virus) Adult T-cell leukemia is an endemic disease that occurs in two regions of the world, the islands of Klushi and Shihoku in the Sea of Japan and in the Black the population of the Caribbean. Patients with this lymphoma occur sporadically and in other regions, but many of them have some kind of association with endemic areas.

This disease occurs usually in people over 50 years old, proceeds with skin lesions, hepatomegaly, splenomegaly, lymphadenopathy and has a poor prognosis ATLV or HTLV virus is exogenous to humans, differs from other known animal retroviruses, is transmitted to T cells horizontally from mother to child, from husband to wife (but not vice versa), when donating blood, is not detected in any other forms of human leukemia or lymphoma. Thus, adult T-cell leukemia is a typical infectious disease (vertical transmission of the virus through germ cells has been excluded by special studies). In endemic foci, more than 20% of practically healthy people, mainly relatives of patients, are carriers of the virus.

In other parts the globe antibodies to the virus rarely found. It is believed that 1 in 2,000 infected people will get sick. A virus indistinguishable from ATLV is found in a monkey in Africa. In addition to lymphoma (leukemia), this virus can cause AIDS, in which T-cell immunity is compromised.

Viral etiology The Epstein-Barr Virus (EBV), a member of the herpesvirus group, is also suspected of being a very likely etiological factor in Burkitt's lymphoma in relation to some other human tumors. EBV DNA is continually found in the cells of this lymphoma in endemic foci in Africa. However, Burkitt's lymphoma also occurs outside Africa, but EBV DNA is found in only a minority of these cases. Common to EBV-positive and EBV-negative tumors are characteristic rearrangements of chromosomes (translocation between chromosomes 8 and 14), which is considered as evidence of a common etiology of these tumors.

DNA of this virus is found in the genome of cells of undifferentiated nasopharyngeal carcinoma, but not in tumors of the nasopharynx of other histogenesis. In patients with these tumors, a high titer of antibodies to various components of EBV is noted, significantly exceeding these indicators in the population - EBV is widespread, and antibodies to it are found in 80-90% of healthy people. A high titer of antibodies was found in patients with lymphogranulomatosis. Suppression of immunity and activation of EBV are, according to a number of authors, the main cause of the development of lymphomas and immunoblastic sarcomas in patients with kidney transplants exposed to immunosuppressive agents; this is evidenced by the high titer of antibodies to EBV and the detection of EBV DNA in the genome of tumor cells.

There is evidence to suggest an infectious (viral) etiology cervical cancer the incidence of this cancer is higher with early onset of sexual activity with frequent change of partners; it is increased in the second wives of men, whose first wives also suffered from the same disease. On the basis of seroepidemiological data, one thinks about the role of the herpes simplex virus type II as an initiator; genital warts are also suspected.

In areas with high frequency the occurrence of viral hepatitis B the incidence of hepatocellular cancer is also increased. On the other hand, patients with this tumor are more likely to be seropositive for the hepatitis B virus than healthy individuals; but there are also seronegative cases of cancer. The obtained lines of tumor cells containing the DNA of the virus and producing its antigen. In general, the role of hepatitis B virus in the induction of hepatocellular carcinoma remains unclear.

Of human warts(verrucae vulgaris), several types of papilloma viruses have been identified, which are believed to cause only benign tumors that are not prone to malignancy. Only one of these viruses (type 5) is isolated from papillomas that develop in hereditary warty epidermodysplasia and have a tendency to malignancy.

Originally tumor-bearing viruses were considered as infectious agents that induce cells to proliferate unregulated. In contrast, L.A. Zilber (1945) developed a theory according to which the genome of a tumor-bearing virus is integrated into the genome of a normal cell, transforming it into a tumor cell, i.e., tumor-bearing viruses fundamentally differ in their action from infectious ones. In the 70s, the genes necessary for the transformation of a normal cell into a tumor cell were found in tumor-bearing RNA-containing viruses - transforming genes or oncogenes (v-onc - viral oncogenes). Subsequently, copies or analogies of oncogenes were identified in normal cells of various animals and humans (c-ops - "cellular" -cellular oncogenes), then the ability of the oncogene to integrate into the genome of the virus was proved.

Oncogenes now identified... determined their chemical structure, localization in chromosomes. Proteins have also been identified - products of the activity of these genes; each of them synthesizes its own specific protein.

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

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

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

The hemispheres reach approximately 80% of the total mass of the brain. They regulate higher mental functions, while the brain stem is lower, which are associated with the activity of internal organs.

Three main areas are distinguished on the hemispheric surface.:

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

Features of the device and activity

The cerebral cortex is divided into 4 types:

ancient - takes up just over 0.5% of the entire surface of the hemispheres;
old - 2.2%;
new - more than 95%;
average - about 1.5%.

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

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

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

Structure

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

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

The cerebral cortex consists of six cytoarchitectonic layers.

Surface molecular, in which there are not very many nerve cells. Their processes are located in itself, and they do not go beyond.
The outer granular is formed from pyramidal and stellate neurocytes. The processes come out of this layer and go to the subsequent ones.
The pyramidal cell is made up of pyramidal cells. Their axons go down, where they end or form associative fibers, and dendrites go up, into the second layer.
The inner granular is formed by stellate cells and small pyramidal cells. Dendrites go to the first layer, lateral processes branch out within their layer. Axons extend into the upper layers or into the white matter.
Ganglionic is formed by large pyramidal cells. The largest neurocytes of the cortex are located here. Dendrites are directed to the first layer or distributed in its own. Axons emerge from the cortex and begin to be fibers that connect various parts and structures of the central nervous system with each other.
Multiforme - consists of various cells. Dendrites go to the molecular layer (some only up to the fourth or fifth layers). Axons are directed to the overlying layers or emerge from the cortex as associative fibers.

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

Vertical organization

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

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

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

Horizontal organization

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

associative;
sensory (sensitive);
motor.

Scientists, when studying localized areas and their functional characteristics, used various methods: chemical or physical irritation, partial removal of brain areas, development of conditioned reflexes, registration of brain biocurrents.

Sensitive

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

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

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

Impulses traveling along the afferent fibers from the left side of the body are perceived by the right hemisphere, and from the right side - by the left (damage to the left hemisphere will cause sensory disturbance on the right side and vice versa). This is due to the fact that each postcentral gyrus is associated with an opposite part of the body.

Motor

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

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

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

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

Associative

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

The science of neuropsychology, which is at the intersection of neurobiology, psychology, psychiatry and informatics, is responsible for establishing the patterns of brain functioning, analyzing its local disorders and checking its activity.

Features of localization by fields

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

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

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

Table 1

		Matching fields
Motor
Sensitive
Visual
Olfactory
Flavoring
Reciprocating, which includes centers:	Wernicke, allowing you to perceive spoken language
	Broca - is responsible for the movement of the lingual muscles; defeat threatens complete loss of speech
	Perception of speech in writing

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

Cortex - the higher part of the central nervous system, which ensures the functioning of the body as a whole in its interaction with the environment.

brain (cerebral cortex, new cortex) is a layer of gray matter, consisting of 10-20 billion and covering the large hemispheres (Fig. 1). The gray matter of the bark makes up more than half of the total gray matter of the central nervous system. The total area of the gray matter of the bark is about 0.2 m 2, which is achieved by the tortuous folding of its surface and the presence of grooves of different depths. The thickness of the cortex in its different parts ranges from 1.3 to 4.5 mm (in the anterior central gyrus). The neurons of the cortex are located in six layers oriented parallel to its surface.

In the areas of the cortex related to, there are zones with a three-layer and five-layer arrangement of neurons in the structure of the gray matter. These areas of the phylogenetically ancient cortex occupy about 10% of the surface of the cerebral hemispheres, the remaining 90% are new cortex.

Fig. 1. Mole of the lateral surface of the cerebral cortex (according to Brodman)

The structure of the cerebral cortex

The cerebral cortex has a six-layer structure

Neurons of different layers differ in cytological characteristics and functional properties.

Molecular layer- the most superficial. It is represented by a small number of neurons and numerous branching dendrites of pyramidal neurons lying in deeper layers.

Outer granular layer formed by densely spaced numerous small neurons of various shapes. The processes of the cells of this layer form corticocortical connections.

Outer pyramidal layer consists of medium-sized pyramidal neurons, the processes of which are also involved in the formation of corticocortical connections between adjacent areas of the cortex.

Inner granular layer similar to the second layer in terms of the type of cells and the location of the fibers. In the layer there are bundles of fibers connecting different parts of the cortex.

Signals from specific nuclei of the thalamus are transmitted to the neurons of this layer. The layer is very well represented in the sensory areas of the cortex.

Inner pyramids formed by medium and large pyramidal neurons. In the motor area of the cortex, these neurons are especially large (50-100 microns) and are called giant, Betz pyramidal cells. The axons of these cells form fast-conducting (up to 120 m / s) fibers of the pyramidal tract.

Layer of polymorphic cells represented mainly by cells, the axons of which form corticothalamic pathways.

The neurons of the 2nd and 4th layers of the cortex are involved in the perception, processing of the signals coming to them from the neurons of the associative areas of the cortex. Sensory signals from the switching nuclei of the thalamus come mainly to the neurons of the 4th layer, the severity of which is greatest in the primary sensory areas of the cortex. The neurons of the 1st and other layers of the cortex receive signals from other nuclei of the thalamus, basal ganglia, and the brain stem. The neurons of the 3rd, 5th and 6th layers form efferent signals that are sent to other areas of the cortex and along the descending pathways to the lower parts of the central nervous system. In particular, layer 6 neurons form fibers that follow to the thalamus.

There are significant differences in the neuronal composition and cytological features of different parts of the cortex. Based on these differences, Brodmann divided the cortex into 53 cytoarchitectonic fields (see Fig. 1).

The location of many of these zeros, identified on the basis of histological data, coincides in topography with the location of the cortical centers, identified on the basis of their functions. Other approaches to dividing the cortex into regions are also used, for example, based on the content of certain markers in neurons, the nature of neural activity, and other criteria.

The white matter of the cerebral hemispheres is formed by nerve fibers. Allocate associative fibers, subdivided into arcuate fibers, but which signals are transmitted between neurons of adjacent convolutions and long longitudinal bundles of fibers that deliver signals to neurons in more distant sections of the hemisphere of the same name.

Commissural fibers - transverse fibers that transmit signals between neurons of the left and right hemispheres.

Projection fibers - conduct signals between neurons of the cortex and other parts of the brain.

The listed types of fibers are involved in the creation of neural circuits and networks, the neurons of which are located at considerable distances from each other. The cortex also contains a special kind of local neural circuits formed by adjacent neurons. These neural structures are called functional cortical columns. Neural columns are formed by groups of neurons located one above the other perpendicular to the surface of the cortex. The belonging of neurons to the same column can be determined by the increase in their electrical activity in response to stimulation of the same receptive field. Such activity is recorded with a slow movement of the recording electrode in the cortex in the perpendicular direction. If the electrical activity of neurons located in the horizontal plane of the cortex is recorded, then an increase in their activity is noted when various receptive fields are stimulated.

The diameter of the functional column is up to 1 mm. The neurons of one functional column receive signals from the same afferent thalamocortical fiber. Neurons of adjacent columns are connected to each other by processes, with the help of which they exchange information. The presence of such interconnected functional columns in the cortex increases the reliability of perception and analysis of information coming to the cortex.

The efficiency of perception, processing and use of information by the cortex for the regulation of physiological processes is also ensured somatotopic principle of organization sensory and motor fields of the cortex. The essence of such an organization lies in the fact that in a certain (projection) area of the cortex, not any, but topographically delineated areas of the receptive field of the body surface, muscles, joints or internal organs are represented. So, for example, in the somatosensory cortex, the surface of the human body is projected in the form of a diagram, when at a certain point of the cortex the receptive fields of a specific area of the body surface are presented. In a strict topographic manner, efferent neurons are represented in the primary motor cortex, the activation of which causes the contraction of certain muscles of the body.

Bark fields also have on-screen principle of operation. In this case, the receptor neuron sends a signal not to a single neuron or to a single point of the cortical center, but to a network or zero of neurons connected by processes. The functional cells of this field (screen) are the columns of neurons.

The cerebral cortex, forming at the later stages of the evolutionary development of higher organisms, to a certain extent subordinated to itself all the lower parts of the central nervous system and is able to correct their functions. At the same time, the functional activity of the cerebral cortex is determined by the influx of signals to it from neurons of the reticular formation of the brain stem and signals from the receptive fields of the body's sensory systems.

Functional areas of the cerebral cortex

On a functional basis, sensory, associative and motor areas are distinguished in the cortex.

Sensory (sensitive, projection) areas of the cortex

They consist of zones containing neurons, the activation of which by afferent impulses from sensory receptors or direct action of stimuli causes the appearance of specific sensations. These zones are found in the occipital (fields 17-19), parietal (zero 1-3) and temporal (fields 21-22, 41-42) areas of the cortex.

In the sensory zones of the cortex, central projection fields are distinguished, providing a slushy, clear perception of sensations of certain modalities (light, sound, touch, heat, cold) and secondary projection zeros. The function of the latter is to provide an understanding of the connection of the primary sensation with other objects and phenomena of the surrounding world.

The zones of representation of receptive fields in the sensory zones of the cortex overlap to a large extent. The peculiarity of the nerve centers in the area of the secondary projection fields of the cortex is their plasticity, which is manifested by the possibility of restructuring specialization and restoring functions after damage to any of the centers. These compensatory capabilities of the nerve centers are especially pronounced in childhood. At the same time, damage to the central projection fields after suffering a disease is accompanied by a gross violation of the functions of sensitivity and often the impossibility of its recovery.

Visual cortex

The primary visual cortex (VI, field 17) is located on both sides of the spur sulcus on the medial surface of the occipital lobe of the brain. In accordance with the identification of alternating white and dark stripes on unstained sections of the visual cortex, it is also called the striate (striped) cortex. The neurons of the lateral geniculate body send visual signals to the neurons of the primary visual cortex, which receive signals from the ganglion cells of the retina. The visual cortex of each hemisphere receives visual signals from the ipsilateral and contralateral halves of the retina of both eyes and their delivery to the neurons of the cortex is organized according to the somatotopic principle. The neurons that receive visual signals from photoreceptors are topographically located in the visual cortex, similar to receptors in the retina. In this case, the area of the macular retina has a relatively larger area of representation in the cortex than other areas of the retina.

The neurons of the primary visual cortex are responsible for visual perception, which, based on the analysis of input signals, is manifested by their ability to detect a visual stimulus, to determine its specific shape and orientation in space. In a simplified way, one can represent the sensory function of the visual cortex in solving a problem and answering the question of what a visual object is.

In the analysis of other qualities of visual signals (for example, location in space, movement, connection with other events, etc.), neurons of fields 18 and 19 of the extrastriatal cortex, located but adjacent to zero 17, take part. areas of the cortex, will be transferred for further analysis and use of vision to perform other brain functions in the associative areas of the cortex and other parts of the brain.

Auditory cortex

Located in the lateral groove of the temporal lobe in the area of the Heschl gyrus (AI, fields 41-42). The neurons of the primary auditory cortex receive signals from the neurons of the medial geniculate bodies. The fibers of the auditory tract, which conduct sound signals to the auditory cortex, are organized tonotopically, and this allows the neurons of the cortex to receive signals from certain auditory receptor cells of the organ of Corti. The auditory cortex regulates the sensitivity of the auditory cells.

In the primary auditory cortex, sound sensations are formed and an analysis of individual qualities of sounds is carried out, which makes it possible to answer the question of what the perceived sound is. The primary auditory cortex plays an important role in the analysis of short sounds, intervals between sound signals, rhythm, sound sequence. A more complex analysis of sounds is carried out in the associative areas of the cortex adjacent to the primary auditory. Based on the interaction of neurons in these areas of the cortex, binaural hearing is carried out, the characteristics of pitch, timbre, sound volume, the belonging of the sound are determined, and the idea of a three-dimensional sound space is formed.

Vestibular cortex

Located in the superior and middle temporal gyri (fields 21-22). Its neurons receive signals from neurons of the vestibular nuclei of the brain stem, connected by afferent connections with the receptors of the semicircular canals of the vestibular apparatus. In the vestibular cortex, a sensation is formed about the position of the body in space and the acceleration of movements. The vestibular cortex interacts with the cerebellum (through the temporocerebellar pathway), participates in the regulation of body balance, and the adaptation of posture to the implementation of targeted movements. Based on the interaction of this area with the somatosensory and associative areas of the cortex, awareness of the body scheme occurs.

Olfactory cortex

Located in the region of the upper part of the temporal lobe (hook, zero 34, 28). The cortex includes a number of nuclei and belongs to the structures of the limbic system. Its neurons are located in three layers and receive afferent signals from the mitral cells of the olfactory bulb, connected by afferent connections with the olfactory receptor neurons. In the olfactory cortex, a primary qualitative analysis of smells is carried out and a subjective sense of smell, its intensity, and belonging is formed. Damage to the cortex leads to a decrease in the sense of smell or to the development of anosmia - loss of smell. When this area is artificially irritated, sensations of various odors appear, such as hallucinations.

Taste bark

Located in the lower part of the somatosensory gyrus, immediately anterior to the projection area of the face (field 43). Its neurons receive afferent signals from relay neurons in the thalamus, which are associated with neurons in the nucleus of the solitary tract of the medulla oblongata. The neurons of this nucleus receive signals directly from sensory neurons that form synapses on the cells of taste buds. In the gustatory cortex, a primary analysis of the taste qualities of bitter, salty, sour, sweet is carried out, and on the basis of their summation, a subjective sensation of taste, its intensity, and belonging is formed.

The signals of smell and taste reach the neurons in the anterior part of the insular cortex, where, on the basis of their integration, a new, more complex quality of sensations is formed, which determines our attitude to the sources of smell or taste (for example, to food).

Somatosensory cortex

Occupies the area of the postcentral gyrus (SI, fields 1-3), including the paracentral lobule on the medial side of the hemispheres (Fig. 9.14). The somatosensory region receives sensory signals from thalamic neurons connected by spinothalamic pathways with skin receptors (tactile, temperature, pain sensitivity), proprioceptors (muscle spindles, bursae, tendons) and interoreceptors (internal organs).

Fig. 9.14. The most important centers and areas of the cerebral cortex

Due to the intersection of afferent pathways, signaling from the right side of the body arrives in the somatosensory zone of the left hemisphere, respectively, to the right hemisphere - from the left side of the body. In this sensory area of the cortex, all parts of the body are somatotopically represented, but the most important receptive zones of the fingers, lips, skin of the face, tongue, and larynx occupy relatively larger areas than the projections of such body surfaces as the back, front of the body, and legs.

The location of the representation of the sensitivity of body parts along the postcentral gyrus is often called the "inverted homunculus", since the projection of the head and neck is in the lower part of the postcentral gyrus, and the projection of the caudal trunk and legs is in the upper part. In this case, the sensitivity of the legs and feet is projected onto the cortex of the paracentral lobule of the medial surface of the hemispheres. Within the primary somatosensory cortex, there is a certain specialization of neurons. For example, neurons of field 3 receive mainly signals from muscle spindles and mechanoreceptors of the skin, field 2 - from receptors of joints.

The cortex of the postcentral gyrus is referred to as the primary somatosensory region (SI). Its neurons send processed signals to neurons in the secondary somatosensory cortex (SII). It is located posterior to the postcentral gyrus in the parietal cortex (fields 5 and 7) and belongs to the associative cortex. SII neurons do not receive direct afferent signals from thalamic neurons. They are associated with SI neurons and neurons in other areas of the cerebral cortex. This makes it possible to carry out here an integral assessment of signals entering the cortex along the spinothalamic pathway with signals coming from other (visual, auditory, vestibular, etc.) sensory systems. The most important function of these fields of the parietal cortex is the perception of space and the transformation of sensory signals into motor coordinates. In the parietal cortex, the desire (intention, urge) to carry out a motor action is formed, which is the basis for starting planning for the upcoming motor activity in it.

The integration of different sensory signals is associated with the formation of different sensations addressed to different parts of the body. These sensations are used both for the formation of mental and other responses, examples of which can be movements with the simultaneous participation of the muscles of both sides of the body (for example, moving, feeling with both hands, grabbing, unidirectional movement with both hands). The functioning of this area is necessary for recognizing objects by touch and determining the spatial location of these objects.

The normal function of the somatosensory areas of the cortex is an important condition for the formation of such sensations as heat, cold, pain and their addressing to a specific part of the body.

Damage to neurons in the area of the primary somatosensory cortex leads to a decrease in various types of sensitivity on the opposite side of the body, and local damage to a loss of sensitivity in a certain part of the body. The discriminatory sensitivity of the skin is especially vulnerable when the neurons of the primary somatosensory cortex are damaged, and the least painful one. Damage to neurons in the secondary somatosensory area of the cortex may be accompanied by impaired ability to recognize objects by touch (tactile agnosia) and skills in using objects (apraxia).

Motor areas of the cortex

About 130 years ago, researchers, applying point stimuli to the cerebral cortex with an electric current, found that exposure to the surface of the anterior central gyrus causes muscle contraction on the opposite side of the body. So the presence of one of the motor areas of the cerebral cortex was discovered. Subsequently, it turned out that several areas of the cerebral cortex and its other structures are related to the organization of movements, and in the areas of the motor cortex there are not only motor neurons, but also neurons that perform other functions.

Primary motor cortex

Primary motor cortex located in the anterior central gyrus (MI, field 4). Its neurons receive the main afferent signals from neurons of the somatosensory cortex - fields 1, 2, 5, premotor cortex and thalamus. In addition, cerebellar neurons send signals to the MI via the ventrolateral thalamus.

The efferent fibers of the pyramidal pathway begin from the pyramidal neurons Ml. Some of the fibers of this pathway follow to the motor neurons of the cranial nerve nuclei of the brain stem (corticobulbar tract), some - to the neurons of the stem motor nuclei (red nucleus, nuclei of the reticular formation, stem nuclei associated with the cerebellum) and some - to the inter- and motor neurons of the spinal cord. brain (corticospinal tract).

There is a somatotopic organization of the arrangement of neurons in MI, which control the contraction of various muscle groups of the body. The neurons that control the muscles of the legs and trunk are located in the upper portions of the gyrus and occupy a relatively small area, while the control muscles of the hands, especially the fingers, face, tongue, and pharynx, are located in the lower portions and occupy a large area. Thus, in the primary motor cortex, a relatively large area is occupied by those neural groups that control muscles that carry out various, precise, small, finely regulated movements.

Since many Ml neurons increase electrical activity immediately before the onset of voluntary contractions, the primary motor cortex is assigned a leading role in controlling the activity of the motor nuclei of the trunk and motor neurons of the spinal cord and initiating voluntary, purposeful movements. Damage to the Ml field leads to muscle paresis and the impossibility of performing fine voluntary movements.

Secondary motor cortex

Includes areas of the premotor and accessory motor cortex (MII, field 6). Premotor cortex located in field 6, on the lateral surface of the brain, anterior to the primary motor cortex. Its neurons receive afferent signals through the thalamus from the occipital, somatosensory, parietal associative, prefrontal regions of the cortex and cerebellum. Signals processed in it are sent by neurons of the cortex along efferent fibers to the motor cortex MI, a small number to the spinal cord and more to the red nuclei, nuclei of the reticular formation, basal ganglia and cerebellum. The premotor cortex plays a major role in programming and organizing vision-controlled movements. The bark is involved in the organization of posture and auxiliary movements for actions carried out by the distal muscles of the limbs. Damage to the proximal cortex often causes a tendency to re-execute the initiated movement (perseveration), even if the movement performed has reached the goal.

In the lower part of the premotor cortex of the left frontal lobe, immediately anterior to the area of the primary motor cortex, which contains the neurons that control the muscles of the face, is located speech area, or the motor center of Broca's speech. Violation of its function is accompanied by impaired speech articulation, or motor aphasia.

Additional motor cortex is located in the upper part of field 6. Its neurons receive afferent signals from the somatosensory, parietal and prefrontal regions of the cerebral cortex. Signals processed in it are sent by neurons of the cortex through efferent fibers to the primary motor cortex MI, spinal cord, and stem motor nuclei. The activity of neurons in the additional motor cortex increases earlier than neurons in the MI cortex, mainly due to the implementation of complex movements. At the same time, the increase in neural activity in the additional motor cortex is not associated with movements as such; for this, it is enough to mentally imagine a model of the upcoming complex movements. The additional motor cortex takes part in the formation of the program of the forthcoming complex movements and in the organization of motor responses to the specificity of sensory stimuli.

Since neurons in the secondary motor cortex send many axons to the MI field, it is considered a higher structure in the hierarchy of motor centers of the organization of movements, standing above the motor centers of the MI motor cortex. The nerve centers of the secondary motor cortex can influence the activity of motor neurons in the spinal cord in two ways: directly through the corticospinal pathway and through the MI field. Therefore, they are sometimes called supra-motor fields, whose function is to instruct the centers of the MI field.

It is known from clinical observations that maintaining the normal function of the secondary motor cortex is important for the implementation of precise hand movements, and especially for the performance of rhythmic movements. So, for example, if they are damaged, the pianist ceases to feel the rhythm and to maintain the interval. The ability to carry out opposite hand movements is impaired (manipulation with both hands).

With simultaneous damage to the MI and MII motor zones of the cortex, the ability for fine coordinated movements is lost. Point irritations in these areas of the motor zone are accompanied by the activation not of individual muscles, but of a whole group of muscles that cause directional movement in the joints. These observations gave rise to the conclusion that the motor cortex contains not so much muscles as movements.

Prefrontal cortex

Located in the area of field 8. Its neurons receive the main afferent signals from the occipital visual, parietal associative cortex, upper hillocks of the quadruple. The processed signals are transmitted along the efferent fibers to the premotor cortex, the superior hillocks of the quadruple, and the brainstem motor centers. The cortex plays a decisive role in organizing eye-controlled movements and is directly involved in the initiation and control of eye and head movements.

The mechanisms that implement the transformation of the concept of movement into a specific motor program, into bursts of impulses sent to specific muscle groups, remain insufficiently understood. It is believed that the concept of movement is formed due to the functions of the associative and other areas of the cortex that interact with many structures of the brain.

Information about the intention of movement is transmitted to the motor areas of the frontal cortex. The motor cortex through the descending pathways activates systems that ensure the development and use of new motor programs or the use of old ones, already worked out in practice and stored in memory. The basal ganglia and cerebellum are part of these systems (see their functions above). The movement programs developed with the participation of the cerebellum and basal ganglia are transmitted through the thalamus to the motor zones and, above all, to the primary motor cortex. This area directly initiates the execution of movements, connecting certain muscles to it and providing a sequence of alternating their contraction and relaxation. The commands of the cortex are transmitted to the motor centers of the brainstem, spinal motor neurons and motor neurons of the cranial nerve nuclei. In the implementation of movements, motor neurons play the role of the final path through which motor commands are transmitted directly to the muscles. The features of signal transmission from the cortex to the motor centers of the trunk and spinal cord are described in the chapter on the central nervous system (brain stem, spinal cord).

Associative areas of the cortex

In humans, the associative areas of the cortex occupy about 50% of the area of the entire cerebral cortex. They are located in the areas between the sensory and motor areas of the cortex. Associative areas do not have clear boundaries with secondary sensory areas, both in morphological and functional features. The parietal, temporal and frontal associative areas of the cerebral cortex are distinguished.

Parietal associative area of the cortex. Located in fields 5 and 7 of the superior and inferior parietal lobes of the brain. The area is bordered in front by the somatosensory cortex, in the back - by the visual and auditory cortex. The neurons of the parietal associative region can receive and activate their visual, sound, tactile, proprioceptive, pain, signals from the memory apparatus and other signals. Some neurons are polysensory and can increase their activity when they receive somatosensory and visual signals. However, the degree of increase in the activity of neurons in the associative cortex to the receipt of afferent signals depends on the current motivation, the subject's attention, and information retrieved from memory. It remains insignificant if the signal coming from the sensory regions of the brain is indifferent for the subject, and it increases significantly if it coincided with the existing motivation and attracted his attention. For example, when a monkey is presented with a banana, the activity of neurons in the associative parietal cortex remains low if the animal is full, and vice versa, the activity increases sharply in hungry animals that like bananas.

The neurons of the parietal associative cortex are connected by efferent connections with the neurons of the prefrontal, premotor, motor regions of the frontal lobe and cingulate gyrus. Based on experimental and clinical observations, it is generally accepted that one of the functions of the cortex of field 5 is the use of somatosensory information for the implementation of purposeful voluntary movements and manipulation of objects. The function of the cortex of field 7 is the integration of visual and somatosensory signals to coordinate eye movements and visually guided hand movements.

Violation of these functions of the parietal associative cortex when its connections with the frontal lobe cortex are damaged or a disease of the frontal lobe itself, explains the symptoms of the consequences of diseases localized in the parietal associative cortex. They can be manifested by difficulty in understanding the semantic content of signals (agnosia), an example of which is the loss of the ability to recognize the shape and spatial location of an object. The processes of transformation of sensory signals into adequate motor actions may be disrupted. In the latter case, the patient loses the skills of practical use of well-known instruments and objects (apraxia), and he may develop the inability to carry out visually guided movements (for example, the movement of the hand in the direction of the object).

Frontal associative area of the cortex. It is located in the prefrontal cortex, which is part of the frontal lobe cortex located anterior to fields 6 and 8. Neurons in the frontal associative cortex receive processed sensory signals via afferent connections from neurons in the cortex of the occipital, parietal, temporal lobes of the brain and from neurons in the cingulate gyrus. The frontal associative cortex receives signals about the current motivational and emotional states from the nuclei of the thalamus, limbic and other structures of the brain. In addition, the frontal cortex can operate with abstract, virtual signals. The associative frontal cortex sends efferent signals back to the brain structures from which they were received, to the motor areas of the frontal cortex, the caudate nucleus of the basal ganglia and the hypothalamus.

This area of the cortex plays a primary role in the formation of the higher mental functions of a person. It provides the formation of target attitudes and programs of conscious behavioral reactions, recognition and semantic assessment of objects and phenomena, understanding of speech, logical thinking. After extensive damage to the frontal cortex, patients may develop apathy, a decrease in the emotional background, a critical attitude towards their own actions and the actions of others, complacency, a violation of the ability to use past experience to change behavior. Patient behavior can become unpredictable and inadequate.

The temporal associative area of the cortex. Located in fields 20, 21, 22. Cortex neurons receive sensory signals from neurons of the auditory, extrastriatal visual and prefrontal cortex, hippocampus and amygdala.

After a bilateral disease of the temporal associative areas with the involvement of the hippocampus in the pathological process or connections with it, patients may develop pronounced memory impairments, emotional behavior, inability to concentrate (absent-mindedness). In some people, if the lower temporal region is damaged, where the center of face recognition is supposedly located, visual agnosia may develop - the inability to recognize the faces of familiar people, objects, while maintaining vision.

On the border of the temporal, visual and parietal areas of the cortex in the lower parietal and posterior parts of the temporal lobe, there is an associative section of the cortex, called the sensory center of speech, or Wernicke's center. After its damage, a violation of the function of understanding speech develops, while the speech-motor function is preserved.

The neurons of the cortex are located in delimited layers, which are denoted by Roman numerals. (cm. )

Each layer is characterized by the predominance of any one type of cells. Six main layers are distinguished in the cerebral cortex:

molecular;
outer granular;
outer pyramidal;
internal granular;
ganglionic (inner pyramidal, layer of nodular cells);
layer of polymorphic cells (multiforme).

Molecular layer

Stellate small cells that carry out local integration of the activity of efferent neurons.

Here come afferent thalamocortical fibers from the nonspecific nuclei of the thalamus, which regulate the level of excitability of cortical neurons.

Contains Cajal cells. A feature of these cells is the departure from them of a large number of small branching dendrites, which provide interneuronal connections with the entire layer of the cerebral cortex.

Outer granular layer

Small neurons of various shapes, which have synaptic connections with neurons in the molecular layer throughout the entire diameter of the cortex.

It consists of stellate and small pyramidal cells, the axons of which end in layers 3, 5 and 6, i.e. participates in the connection of various layers of the cortex.

The outer pyramidal one performs mainly associative functions.

Some of the processes of these cells reach the first layer, participating in the formation of the tangential sublayer, others are immersed in the white matter of the cerebral hemispheres, therefore, layer III is sometimes referred to as tertiary associative.

Functionally, layers II and III of the cortex unite neurons, the processes of which provide cortical-cortical associative connections.

This layer has two sub-layers. External - consists of smaller cells that communicate with neighboring areas of the cortex, especially well developed in the visual cortex. The inner sublayer contains larger cells that are involved in the formation of commissural connections (connections between two hemispheres).

Inner granular layer

In layer IV, a tangential layer of nerve fibers is also formed. Therefore, sometimes this layer is referred to as secondary projection-associative.

The inner granular layer is the place where the bulk of the projection afferent fibers ends.

Includes granular cells, stellate and small pyramids. Their apical dendrites rise into the 1st layer of the cortex, and the basal ones (from the base of the cell) into the 6th layer of the cortex, i.e. participate in the implementation of intercortical communication.

Ganglionic layer

Ganglionic voluntary motor pathways are formed (projection efferent fibers.

Formed by giant Betz pyramidal cells. The axons of these cells are projected and communicate with the nuclei of the brain and spinal cord.

Layer of polymorphic cells

The axons of these cells are part of the pathways of the cerebral cortex.

It contains cells of various shapes, but mostly fusiform. Their axons go up, but mostly down and form associative and projection pathways that pass into the white matter of the brain.

Associative zones

connect newly arriving sensory information with previously received and stored in memory blocks, due to which new stimuli are "recognized",
information from some receptors is compared with sensory information from other receptors,
participate in the processes of memorization, learning and thinking.

The white matter of the cerebral cortex is represented by three groups of nerve fibers:

Afferent- or sensitive - carry information from the whole organism to the cerebral cortex.

Efferent- or executive - carry information about the necessary actions to each cell of the body.

Associative fibers carry out communication between all cells of the cerebral cortex.

Histological structure of the cerebral cortex even harder. The same uniform surface of gray matter that covers the hemispheres consists of more than 60 different types of nerve cells. These cells can be divided into two types: pyramidal and non-pyramidal.

Pyramidal neurons- cells found only in the cerebral cortex. Their main function is integration (communication) within the cortex itself and the formation of efferent pathways.

Non-pyramidal cells are located in all parts of the cerebral cortex. Their main function is the perception of afferent signals from the whole organism. After receiving information, they process it, differentiate it and send it to pyramidal neurons.