Functions of the human cerebral cortex briefly. cerebral cortex, areas of the cerebral cortex

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

Cortex

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

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

CORTEX

The surface covering the gray matter that forms the uppermost level of the brain. In an evolutionary sense, this is the newest nerve formation, and approximately 9-12 billion of its cells are responsible for basic sensory functions, motor coordination and control, participation in the regulation of integrative, coordinated behavior and, most importantly, for the so-called "higher mental processes"speech, thinking, problem solving, etc.

CORTEX

English cerebral cortex) - the surface layer covering the cerebral hemispheres, formed mainly by vertically oriented nerve cells (neurons) and their processes, as well as bundles of afferent (centripetal) and efferent (centrifugal) nerve fibers. In addition, the cortex includes neuroglia cells.

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

The main type of nerve cells that make up the K. m. are pyramidal cells. The body of these cells resembles a cone, from the top of which one thick and long, apical dendrite departs; heading towards the surface of the K. g. m., it becomes thinner and fan-shaped divided into thinner terminal branches. Shorter basal dendrites and an axon depart from the base of the body of the pyramidal cell, heading to the white matter, located under the K. m., or branching within the cortex. The dendrites of the pyramidal cells bear a large number of outgrowths, so-called. spines, which take part in the formation of synaptic contacts with the endings of afferent fibers that come to K. m. from other sections of the cortex and subcortical formations (see Synapses). The axons of the pyramidal cells form the main efferent pathways coming from the C. g. m. The size of the pyramidal cells varies from 5-10 microns to 120-150 microns (Betz giant cells). In addition to pyramidal neurons, stellate, fusiform, and some other types of interneurons, which are involved in the reception of afferent signals and the formation of functional interneuronal connections, are part of the cgm.

Based on the peculiarities of the distribution in the layers of the cortex of nerve cells and fibers of various sizes and shapes, the entire territory of the K. g. fields that differ in their cell structure and functional value. The classification of cytoarchitectonic formations of K. g. m., proposed by K. Brodman, who divided the entire K. g. m. of a person into 11 regions and 52 fields, is generally accepted.

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

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

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

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

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

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

Clinical neuropsychological studies show that when the posterior association areas are affected, complex shapes orientation in space, constructive activity, it is difficult to perform all intellectual operations that are carried out with the participation spatial analysis(counting, perception of complex semantic images). When defeated speech zones the ability to perceive and reproduce speech is impaired. Damage to the frontal areas of the cortex leads to the impossibility of implementing complex behavioral programs that require the selection of significant signals based on past experience and foreseeing the future. See Blocks of the brain, Cortpicalization, Brain, Nervous system, Development of the cerebral cortex, Neuro-psychological syndromes. (D. A. Farber.)

Shoshina Vera Nikolaevna

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

Articles written

Brain modern man and his complex structure is the greatest achievement of this species and its advantage, the difference from 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 inner surface 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 where 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 disorders mental development, for example, an 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 state 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 allows you 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" - greatest achievement 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 reticular formation of the brain stem occupies a central position in the medulla oblongata, pons varolii, midbrain and diencephalon.

The neurons of the reticular formation do not have direct contacts with the body's receptors. Nerve impulses, when the receptors are excited, arrive at the reticular formation along the collaterals of the autonomic and somatic fibers. nervous system.

Physiological role. The reticular formation of the brain stem has an ascending effect on the cells of the cerebral cortex and a descending effect on the motor neurons of the spinal cord. Both of these influences of the reticular formation can be activating or inhibitory.

Afferent impulses to the cerebral cortex come in two ways: specific and nonspecific. specific neural pathway necessarily passes through the visual tubercles and carries nerve impulses to certain areas of the cerebral cortex, as a result, any specific activity is carried out. For example, when the photoreceptors of the eyes are stimulated, impulses through the visual tubercles enter the occipital region of the cerebral cortex and visual sensations arise in a person.

Nonspecific neural pathway necessarily passes through the neurons of the reticular formation of the brain stem. Impulses to the reticular formation come through the collaterals of a specific nerve pathway. Due to numerous synapses on the same neuron of the reticular formation, impulses of different values ​​(light, sound, etc.) can converge (converge), while they lose their specificity. From the neurons of the reticular formation, these impulses do not arrive at any particular area of ​​the cerebral cortex, but spread like a fan through its cells, increasing their excitability and thereby facilitating the performance of a specific function.

In experiments on cats with electrodes implanted in the region of the reticular formation of the brainstem, it was shown that stimulation of its neurons causes the awakening of a sleeping animal. With the destruction of the reticular formation, the animal falls into a long sleepy state. These data indicate the important role of the reticular formation in the regulation of sleep and wakefulness. The reticular formation not only affects the cerebral cortex, but also sends inhibitory and excitatory impulses to the spinal cord to its motor neurons. Due to this, it is involved in the regulation of skeletal muscle tone.

In the spinal cord, as already mentioned, there are also neurons of the reticular formation. It is believed that they maintain a high level of activity of neurons in the spinal cord. The functional state of the reticular formation itself is regulated by the cerebral cortex.

Cerebellum

Features of the structure of the cerebellum. Connections of the cerebellum with other parts of the central nervous system. The cerebellum is an unpaired formation; it is located behind the medulla oblongata and the pons, borders on the quadrigemina, is covered from above by the occipital lobes of the cerebral hemispheres, the middle part is distinguished in the cerebellum - worm and located on the sides of it two hemisphere. The surface of the cerebellum consists of gray matter called the cortex, which includes the bodies of nerve cells. Inside the cerebellum is white matter, representing the processes of these neurons.

The cerebellum has extensive connections with various parts of the central nervous system due to three pairs of legs. lower legs connect the cerebellum to the spinal cord and medulla oblongata medium- with the pons and through it with the motor area of ​​the cerebral cortex, upper with midbrain and hypothalamus.

The functions of the cerebellum were studied in animals in which the cerebellum was removed partially or completely, as well as by recording its bioelectrical activity at rest and during stimulation.

When half of the cerebellum is removed, an increase in the tone of the extensor muscles is noted, therefore, the limbs of the animal are extended, a bend of the body and a deviation of the head to the operated side are observed, sometimes rocking movements of the head. Often the movements are made in a circle in the operated direction (“manege movements”). Gradually, the marked violations are smoothed out, but some awkwardness of movements remains.

When the entire cerebellum is removed, more pronounced movement disorders occur. In the first days after the operation, the animal lies motionless with its head thrown back and elongated limbs. Gradually, the tone of the extensor muscles weakens, trembling of the muscles appears, especially the cervical ones. In the future, motor functions are partially restored. However, until the end of life, the animal remains a motor invalid: when walking, such animals spread their limbs wide, raise their paws high, i.e., they have impaired coordination of movements.

Movement disorders during the removal of the cerebellum were described by the famous Italian physiologist Luciani. The main ones are: aton and I - the disappearance or weakening of muscle tone; asthen and I - a decrease in the strength of muscle contractions. Such an animal is characterized by rapidly onset muscle fatigue; a stasis - loss of the ability to continuous tetanic contractions. In animals, trembling movements of the limbs and head are observed. The dog after removal of the cerebellum cannot immediately raise its paws, the animal makes a series of oscillatory movements with its paw before lifting it. If you put such a dog, then its body and head sway all the time from side to side.

As a result of atony, asthenia and astasia, the animal's coordination of movements is disturbed: a shaky gait, sweeping, awkward, inaccurate movements are noted. The whole complex of motor disorders in the lesion of the cerebellum is called cerebellar ataxia.

Similar disorders are observed in humans with damage to the cerebellum.

Some time after the removal of the cerebellum, as already mentioned, all movement disorders are gradually smoothed out. If the motor area of ​​the cerebral cortex is removed from such animals, then the motor disturbances increase again. Consequently, compensation (restoration) of movement disorders in case of damage to the cerebellum is carried out with the participation of the cerebral cortex, its motor area.

The studies of L. A. Orbeli showed that when the cerebellum is removed, not only a drop in muscle tone (atony), but also its incorrect distribution (dystonia) is observed. L. L. Orbeli found that the cerebellum also affects the state of the receptor apparatus, as well as autonomic processes. The cerebellum has an adaptive-trophic effect on all parts of the brain through the sympathetic nervous system, it regulates the metabolism in the brain and thereby contributes to the adaptation of the nervous system to changing conditions of existence.

Thus, the main functions of the cerebellum are the coordination of movements, the normal distribution of muscle tone, and the regulation of autonomic functions. The cerebellum realizes its influence through the nuclear formations of the middle and medulla oblongata, through the motor neurons of the spinal cord. A large role in this influence belongs to the bilateral connection of the cerebellum with the motor area of ​​the cerebral cortex and the reticular formation of the brain stem.

Structural features of the cerebral cortex.

The cerebral cortex is phylogenetically the highest and youngest part of the central nervous system.

The cerebral cortex consists of nerve cells, their processes and neuroglia. In an adult, the thickness of the cortex in most areas is about 3 mm. The area of ​​the cerebral cortex due to numerous folds and furrows is 2500 cm 2. Most areas of the cerebral cortex are characterized by a six-layer arrangement of neurons. The cerebral cortex consists of 14-17 billion cells. The cellular structures of the cerebral cortex are represented pyramidal,spindle and stellate neurons.

stellate cells perform mainly an afferent function. Pyramidal and fusiformcells are predominantly efferent neurons.

In the cerebral cortex there are highly specialized nerve cells that receive afferent impulses from certain receptors (for example, from visual, auditory, tactile, etc.). There are also neurons that are excited by nerve impulses coming from different receptors in the body. These are the so-called polysensory neurons.

The processes of the nerve cells of the cerebral cortex connect its various sections to each other or establish contacts between the cerebral cortex and the underlying sections of the central nervous system. The processes of nerve cells that connect different parts of the same hemisphere are called associative, connecting most often the same parts of the two hemispheres - commissural and providing contacts of the cerebral cortex with other parts of the central nervous system and through them with all organs and tissues of the body - conductive(centrifugal). A diagram of these paths is shown in the figure.

Scheme of the course of nerve fibers in the cerebral hemispheres.

1 - short associative fibers; 2 - long associative fibers; 3 - commissural fibers; 4 - centrifugal fibers.

Neuroglia cells perform a number of important functions: they are a supporting tissue, participate in the metabolism of the brain, regulate blood flow inside the brain, secrete a neurosecretion that regulates the excitability of neurons in the cerebral cortex.

Functions of the cerebral cortex.

1) The cerebral cortex carries out the interaction of the organism with the environment due to unconditioned and conditioned reflexes;

2) it is the basis of the higher nervous activity (behavior) of the body;

3) due to the activity of the cerebral cortex, higher mental functions are carried out: thinking and consciousness;

4) the cerebral cortex regulates and integrates the work of all internal organs and regulates such intimate processes as metabolism.

Thus, with the appearance of the cerebral cortex, it begins to control all the processes occurring in the body, as well as all human activities, i.e., corticolization of functions occurs. IP Pavlov, characterizing the importance of the cerebral cortex, pointed out that it is the manager and distributor of all the activities of the animal and human organism.

Functional significance of various areas of the cortex brain . Localization of functions in the cerebral cortex brain . The role of individual areas of the cerebral cortex was first studied in 1870 by the German researchers Fritsch and Gitzig. They showed that stimulation of various parts of the anterior central gyrus and the frontal lobes proper causes contraction of certain muscle groups on the side opposite to the stimulation. Subsequently, the functional ambiguity of various areas of the cortex was revealed. It was found that the temporal lobes of the cerebral cortex are associated with auditory functions, the occipital lobes with visual functions, and so on. These studies led to the conclusion that different parts of the cerebral cortex are in charge of certain functions. The doctrine of the localization of functions in the cerebral cortex was created.

According to modern concepts, there are three types of zones of the cerebral cortex: primary projection zones, secondary and tertiary (associative).

Primary projection zones- these are the central sections of the analyzer cores. They contain highly differentiated and specialized nerve cells, which receive impulses from certain receptors (visual, auditory, olfactory, etc.). In these zones, a subtle analysis of afferent impulses takes place. different meanings. The defeat of these areas leads to disorders of sensory or motor functions.

Secondary zones - peripheral departments analyzer cores. Here, further processing of information takes place, connections are established between stimuli of different nature. When the secondary zones are affected, complex perceptual disorders occur.

Tertiary zones (associative) . The neurons of these zones can be excited under the influence of impulses coming from receptors of various values ​​(from hearing receptors, photoreceptors, skin receptors, etc.). These are the so-called polysensory neurons, due to which connections are established between various analyzers. Associative zones receive processed information from the primary and secondary zones of the cerebral cortex. Tertiary zones play an important role in the formation of conditioned reflexes; they provide complex forms of cognition of the surrounding reality.

Significance of different areas of the cerebral cortex . Sensory and motor areas in the cerebral cortex

Sensory areas of the cortex . (projective cortex, cortical sections of analyzers). These are zones into which sensory stimuli are projected. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways in the sensory cortex come mainly from the relay sensory nuclei of the thalamus - ventral posterior, lateral and medial. The sensory areas of the cortex are formed by the projection and associative zones of the main analyzers.

Area of ​​skin reception(the cerebral end of the skin analyzer) is represented mainly by the posterior central gyrus. The cells of this area perceive impulses from tactile, pain and temperature receptors of the skin. The projection of skin sensitivity within the posterior central gyrus is similar to that for the motor zone. The upper portions of the posterior central gyrus are associated with the receptors of the skin of the lower extremities, the middle portions with the receptors of the trunk and hands, and the lower portions with the receptors of the skin of the head and face. Irritation of this area in a person during neurosurgical operations causes sensations of touch, tingling, numbness, while pronounced pain is never observed.

Area of ​​visual reception(the cerebral end of the visual analyzer) is located in the occipital lobes of the cerebral cortex of both hemispheres. This area should be considered as a projection of the retina.

Area of ​​auditory reception(the cerebral end of the auditory analyzer) is localized in the temporal lobes of the cerebral cortex. This is where nerve impulses come from receptors in the cochlea of ​​the inner ear. If this zone is damaged, musical and verbal deafness may occur, when a person hears, but does not understand the meaning of words; Bilateral damage to the auditory region leads to complete deafness.

The area of ​​taste reception(the cerebral end of the taste analyzer) is located in the lower lobes of the central gyrus. This area receives nerve impulses from the taste buds of the oral mucosa.

Olfactory reception area(the cerebral end of the olfactory analyzer) is located in the anterior part of the piriform lobe of the cerebral cortex. This is where nerve impulses come from the olfactory receptors of the nasal mucosa.

In the cerebral cortex, several zones in charge of the function of speech(brain end of the motor speech analyzer). In the frontal region of the left hemisphere (in right-handed people) is the motor center of speech (Broca's center). With his defeat, speech is difficult or even impossible. In the temporal region is the sensory center of speech (Wernicke's center). Damage to this area leads to speech perception disorders: the patient does not understand the meaning of words, although the ability to pronounce words is preserved. In the occipital lobe of the cerebral cortex there are zones that provide the perception of written (visual) speech. With the defeat of these areas, the patient does not understand what is written.

AT parietal cortex brain ends of the analyzers were not found in the cerebral hemispheres, it is referred to the associative zones. Among the nerve cells of the parietal region, a large number of polysensory neurons were found, which contribute to the establishment of connections between various analyzers and play an important role in the formation of reflex arcs of conditioned reflexes.

motor areas of the cortex The idea of ​​the role of the motor cortex is twofold. On the one hand, it has been shown that electrical stimulation of certain cortical zones in animals causes limb movement. opposite side body, which indicated that the cortex is directly involved in the implementation of motor functions. At the same time, it is recognized that the motor area is an analyzer, i.e. represents the cortical section of the motor analyzer.

The brain section of the motor analyzer is represented by the anterior central gyrus and the parts of the frontal region located near it. When it is irritated, various contractions of the skeletal muscles occur on the opposite side. Correspondence between certain zones of the anterior central gyrus and skeletal muscles has been established. In the upper parts of this zone, the muscles of the legs are projected, in the middle - the torso, in the lower - the head.

Of particular interest is the frontal region itself, which reaches its greatest development in humans. With the defeat of the frontal areas in a person, complex motor functions are disturbed that ensure labor activity and speech, as well as adaptive, behavioral reactions of the body.

Any functional area of ​​the cerebral cortex is in both anatomical and functional contact with other areas of the cerebral cortex, with subcortical nuclei, with formations of the diencephalon and reticular formation, which ensures the perfection of their functions.

1. Structural and functional features of the CNS in the antenatal period.

In the fetus, the number of CNS neurons reaches a maximum by the 20-24th week and remains in the postnatal period without a sharp decrease until old age. Neurons are small in size and the total area of ​​the synaptic membrane.

Axons develop before dendrites, processes of neurons intensively grow and branch. There is an increase in the length, diameter and myelination of axons towards the end of the antenatal period.

Phylogenetically old pathways are myelinated earlier than phylogenetically new ones; for example, vestibulospinal tracts from the 4th month of intrauterine development, rubrospinal tracts from the 5th-8th month, pyramidal tracts after birth.

Na- and K-channels are evenly distributed in the membrane of myelin and non-myelin fibers.

Excitability, conductivity, lability of nerve fibers is much lower than in adults.

The synthesis of most mediators begins during fetal development. Gamma-aminobutyric acid in the antenatal period is an excitatory mediator and, through the Ca2 mechanism, has morphogenic effects - it accelerates the growth of axons and dendrites, synaptogenesis, and the expression of pithoreceptors.

By the time of birth, the process of differentiation of neurons in the nuclei of the medulla oblongata and midbrain, the bridge, ends.

There is structural and functional immaturity of glial cells.

2. Features of the CNS in the neonatal period.

> The degree of myelination of nerve fibers increases, their number is 1/3 of the level of an adult organism (for example, the rubrospinal path is fully myelinated).

> The permeability of cell membranes for ions decreases. Neurons have a lower MP amplitude - about 50 mV (in adults, about 70 mV).

> There are fewer synapses on neurons than in adults, the neuron membrane has receptors for synthesized mediators (acetylcholine, GAM K, serotonin, norepinephrine to dopamine). The content of mediators in the neurons of the brain of newborns is low and amounts to 10-50% of mediators in adults.

> The development of the spiny apparatus of neurons and axospinous synapses is noted; EPSP and IPSP have a longer duration and lower amplitude than in adults. The number of inhibitory synapses on neurons is less than in adults.

> Increased excitability of cortical neurons.

> Disappears (more precisely, sharply decreases) mitotic activity and the possibility of regeneration of neurons. Proliferation and functional maturation of gliocytes continues.

Z. Features of the central nervous system in infancy.

CNS maturation progresses rapidly. The most intense myelination of CNS neurons occurs at the end of the first year after birth (for example, myelination of the nerve fibers of the cerebellar hemispheres is completed by 6 months).

The rate of conduction of excitation along axons increases.

There is a decrease in the duration of AP of neurons, the absolute and relative refractory phases are shortened (the duration of absolute refractoriness is 5–8 ms, relative 40–60 ms in early postnatal ontogenesis, in adults, respectively, 0.5–2.0 and 2–10 ms).

The blood supply to the brain in children is relatively greater than in adults.

4. Features of the development of the central nervous system in other age periods.

1) Structural and functional changes in nerve fibers:

An increase in the diameters of axial cylinders (by 4-9 years). Myelination in all peripheral nerve fibers is close to completion by 9 years, and pyramidal tracts are completed by 4 years;

The ion channels are concentrated in the region of nodes of Ranvier, the distance between the nodes increases. Continuous conduction of excitation is replaced by saltatory, the speed of its conduction after 5-9 years is almost the same as the speed in adults (50-70 m/s);

There is a low lability of nerve fibers in children of the first years of life; with age, it increases (in children 5-9 years old it approaches the norm for adults - 300-1,000 impulses).

2) Structural and functional changes in synapses:

Significant maturation of nerve endings (neuromuscular synapses) occurs by 7-8 years;

The terminal ramifications of the axon and the total area of ​​its endings increase.

Profile material for students of the pediatric faculty

1. Development of the brain in the postnatal period.

In the postnatal period, the leading role in the development of the brain is played by flows of afferent impulses through various sensory systems (the role of an information-enriched external environment). The absence of these external signals, especially during critical periods, can lead to slow maturation, underdevelopment of function, or even its absence.

The critical period in postnatal development is characterized by intense morphological and functional maturation of the brain and the peak of the formation of NEW connections between neurons.

The general regularity of the development of the human brain is the heterochrony of maturation: fvlogetically older sections develop earlier than younger ones.

The medulla oblongata of a newborn is functionally more developed than other departments: ALMOST all of its centers are active - respiration, regulation of the heart and blood vessels, sucking, swallowing, coughing, sneezing, the chewing center begins to function somewhat later In the regulation of muscle tone, the activity of the vestibular nuclei is reduced (reduced extensor tone) By the age of 6, these Centers complete the differentiation of neurons, myelination of fibers, and the coordination activity of the Centers improves.

The midbrain in newborns is functionally less mature. For example, the orienting reflex and the activity of the centers that control the movement of the eyes and THEM are carried out in infancy. The function of the Substance Black as part of the striopallidary system reaches perfection by the age of 7.

The cerebellum in a newborn is structurally and functionally underdeveloped during infancy, its increased growth and differentiation of neurons occurs, and the connections of the cerebellum with other motor centers increase. Functional maturation of the cerebellum generally begins at age 7 and is completed by age 16.

Maturation of the diencephalon includes the development of sensory nuclei of the thalamus and centers of the hypothalamus

The function of the sensory nuclei of the thalamus is already carried out in the Newborn, which allows the Child to distinguish between taste, temperature, tactile and pain sensations. The functions of the nonspecific nuclei of the thalamus and the ascending activating reticular formation of the brain stem in the first months of life are poorly developed, which leads to a short time of his wakefulness during the day. The nuclei of the thalamus finally develop functionally by the age of 14.

The centers of the hypothalamus in a newborn are poorly developed, which leads to imperfection in the processes of thermoregulation, regulation of water-electrolyte and other types of metabolism, and the need-motivational sphere. Most of the hypothalamic centers are functionally mature by 4 years. The most late (by the age of 16) the sexual hypothalamic centers begin to function.

By the time of birth, the basal nuclei have a different degree of functional activity. The phylogenetically older structure, the globus pallidus, is functionally well developed, while the function of the striatum manifests itself by the end of 1 year. In this regard, the movements of newborns and infants are generalized, poorly coordinated. As the striopalidar system develops, the child performs more and more precise and coordinated movements, creates motor programs of voluntary movements. Structural and functional maturation of the basal nuclei is completed by the age of 7.

The cerebral cortex in early ontogenesis matures later in structural and functional terms. The motor and sensory cortex develops the earliest, the maturation of which ends at the 3rd year of life (auditory and visual cortex somewhat later). The critical period in the development of the associative cortex begins at the age of 7 years and continues until the pubertal period. At the same time, cortical-subcortical interconnections are intensively formed. The cerebral cortex ensures the corticalization of body functions, the regulation of voluntary movements, the creation of motor stereotypes for the implementation, and higher psychophysiological processes. The maturation and implementation of the functions of the cerebral cortex are described in detail in specialized materials for students of the pediatric faculty in topic 11, v. 3, topics 1-8.

The hematoliquor and blood-brain barriers in the postnatal period have a number of features.

In the early postnatal period, large veins are formed in the choroid plexuses of the ventricles of the brain, which can deposit a significant amount of blood 14, thereby participating in the regulation of intracranial pressure.

30.07.2013

Formed by neurons, it is a layer of gray matter that covers the cerebral hemispheres. Its thickness is 1.5 - 4.5 mm, the area in an adult is 1700 - 2200 cm 2. Myelinated fibers, forming the white matter of the telencephalon, connect the cortex with the rest departments of the . Approximately 95 percent of the surface of the hemispheres is the neocortex, or neocortex, which is phylogenetically considered the most late education brain. Archiocortex (old cortex) and paleocortex (ancient cortex) have a more primitive structure, they are characterized by a fuzzy division into layers (weak stratification).

The structure of the bark.

The neocortex is made up of six layers of cells: the molecular lamina, the outer granular lamina, the outer pyramidal lamina, the inner granular and pyramidal laminae, and the lamina multiforme. Each layer is distinguished by the presence of nerve cells of a certain size and shape.

The first layer is the molecular plate, which is formed by a small number of horizontally oriented cells. Contains branching dendrites of pyramidal neurons of the underlying layers.

The second layer is the outer granular plate, consisting of the bodies of stellate neurons and pyramidal cells. This also includes a network of thin nerve fibers.

The third layer - the outer pyramidal plate consists of the bodies of pyramidal neurons and processes that do not form long pathways.

The fourth layer - the inner granular plate is formed by densely spaced stellate neurons. They are adjacent to thalamocortical fibers. This layer includes bundles of myelin fibers.

The fifth layer - the inner pyramidal plate is formed mainly by large Betz pyramidal cells.

The sixth layer is a multiform plate, consisting of a large number small polymorphic cells. This layer smoothly passes into the white matter of the cerebral hemispheres.

Furrows cortex each of the hemispheres is divided into four lobes.

The central sulcus begins on the inner surface, descends down the hemisphere and separates the frontal lobe from the parietal. The lateral groove originates from the lower surface of the hemisphere, rises obliquely to the top and ends in the middle of the upper lateral surface. The parietal-occipital sulcus is localized in the back of the hemisphere.

Frontal lobe.

The frontal lobe has the following structural elements: frontal pole, precentral gyrus, superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus, operculum, triangular and orbital parts. The precentral gyrus is the center of all motor acts: starting from elementary functions and ending with complex complex actions. The richer and more differentiated the action, the larger the zone occupied by the given center. Intellectual activity is controlled by the lateral divisions. The medial and orbital surfaces are responsible for emotional behavior and autonomic activity.

Parietal lobe.

Within its limits, the postcentral gyrus, intraparietal sulcus, paracentral lobule, superior and inferior parietal lobules, supramarginal and angular gyrus are distinguished. Somatic sensitive cortex is located in the postcentral gyrus, an essential feature of the location of functions here is the somatotopic dissection. The entire remaining parietal lobe is occupied by the associative cortex. It is responsible for the recognition of somatic sensitivity and its relationship with various forms of sensory information.

Occipital lobe.

It is the smallest in size and includes the lunate and spur sulci, the cingulate gyrus and the wedge-shaped area. Here is the cortical center of vision. Thanks to this, a person can perceive visual images, recognize and evaluate them.

The temporal share.

On the lateral surface, three temporal gyri can be distinguished: superior, middle, and inferior, as well as several transverse and two occipitotemporal gyri. Here, in addition, is the gyrus of the hippocampus, which is considered the center of taste and smell. The transverse temporal gyrus is a zone that controls auditory perception and interpretation of sounds.

limbic complex.

It unites a group of structures that are located in the marginal zone of the cerebral cortex and the visual mound of the diencephalon. It's limbic cortex, dentate gyrus, amygdala, septal complex, mastoid bodies, anterior nuclei, olfactory bulbs, bundles of connective myelin fibers. The main function of this complex is the control of emotions, behavior and stimuli, as well as memory functions.

The main violations of the functions of the cortex.

The main disorders to which cortex, divided into focal and diffuse. Of the focal, the most common are:

Aphasia - a disorder or complete loss of speech function;

Anomia - the inability to name various objects;

Dysarthria - articulation disorder;

Prosody - violation of the rhythm of speech and placement of stresses;

Apraxia - inability to perform habitual movements;

Agnosia - the loss of the ability to recognize objects with the help of sight or touch;

Amnesia is a memory impairment, which is expressed by a slight or complete inability to reproduce information received by a person in the past.

Diffuse disorders include: stunning, stupor, coma, delirium, and dementia.

Cortex - the highest department 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 bark) is a layer of gray matter, consisting of 10-20 billion and covering the large hemispheres (Fig. 1). The gray matter of the cortex makes up more than half of the total gray matter of the CNS. The total area of ​​the gray matter of the cortex is about 0.2 m 2, which is achieved by the sinuous folding of its surface and the presence of furrows 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 arranged 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 the new cortex.

Rice. 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 features 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 pyramidal neurons of medium size, 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 cell type and fiber arrangement. In the layer there are bundles of fibers that connect various parts of the cortex.

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

Inner pyramidal layers 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, pyramidal Betz cells. The axons of these cells form fast-conducting (up to 120 m/s) fibers of the pyramidal tract.

Layer of polymorphic cells It is represented mainly by cells whose axons form corticothalamic pathways.

Neurons of the 2nd and 4th layers of the cortex are involved in the perception, processing of 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, the basal ganglia, and the brain stem. Neurons of the 3rd, 5th and 6th layers form efferent signals sent to other areas of the cortex and downstream to the underlying parts of the CNS. In particular, the neurons of the 6th layer form fibers that follow to the thalamus.

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

The location of many of these fields, 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, according to the nature of neuronal activity, and other criteria.

The white matter of the cerebral hemispheres is made up of nerve fibers. Allocate association fibers, subdivided into arcuate fibers, but to which signals are transmitted between neurons of adjacent gyri and long longitudinal bundles of fibers that deliver signals to neurons of more distant parts 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 the 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. There is also a special kind of local neuronal circuits in the cortex, formed nearby located neurons. These neural structures are called functional cortical columns. Neuronal 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 when the recording electrode is slowly moved in the cortex in a perpendicular direction. If we register the electrical activity of neurons located in horizontal plane cortex, then there is an increase in their activity when irritated by various receptive fields.

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. The neurons of adjacent columns are connected to each other by processes through 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.

Efficiency of perception, processing and use of information by the cortex for regulation physiological processes also provided 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 (projective) area of ​​the cortex, not any, but topographically outlined areas of the receptive field of the surface of the body, 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 scheme, when receptive fields of a specific area of ​​the body surface are presented at a certain point in the cortex. Efferent neurons are represented in a strict topographical way in the primary motor cortex, the activation of which causes the contraction of certain muscles of the body.

The fields of the cortex are also inherent screen operating principle. 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 field of neurons connected by processes. The functional cells of this field (screen) are columns of neurons.

The cerebral cortex, being formed at the later stages of the evolutionary development of higher organisms, to a certain extent subordinated to itself all the underlying parts of the CNS 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 the neurons of the reticular formation of the brain stem and signals from the receptive fields of the sensory systems of the body.

Functional areas of the cerebral cortex

According to the 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 exposure to stimuli causes the appearance of specific sensations. These zones are present in the occipital (fields 17-19), parietal (zeros 1-3) and temporal (fields 21-22, 41-42) areas of the cortex.

AT sensory areas the cortex highlights central projection fields that provide a subtle, clear perception of sensations of certain modalities (light, sound, touch, heat, cold) and secondary projection fields. 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 areas of representation of receptive fields in the sensory areas of the cortex largely overlap. A feature of the nerve centers in the area of ​​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 restoration.

visual cortex

The primary visual cortex (VI, field 17) is located on both sides of the spur groove 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 (striated) 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 flow to the neurons of the cortex is organized according to the somatotopic principle. Neurons that receive visual signals from photoreceptors are topographically located in the visual cortex, similar to receptors in the retina. At the same time, the area of ​​the macula of the retina has a relatively large zone 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, determine it specific form and orientation in space. In a simplified way, it is possible to imagine the sensory function of the visual cortex in solving a problem and answering the question of what constitutes a visual object.

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 extrastriate cortex, located adjacent to zero 17, take part. Information about the signals received by the sensory visual zones 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

It is located in the lateral sulcus of the temporal lobe in the region 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 pathways that conduct sound signals to the auditory cortex are organized tonotopically, and this allows cortical neurons to receive signals from certain auditory receptor cells in the organ of Corti. The auditory cortex regulates the sensitivity of auditory cells.

In the primary auditory cortex, sound sensations are formed and the individual qualities of sounds are analyzed to answer the question of what the perceived sound is. Primary auditory cortex plays important role in analysis short sounds, intervals between sound signals, rhythm, sound sequence. More complex analysis sounds are 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, sound belonging are determined, and an idea of ​​a three-dimensional sound space is formed.

vestibular cortex

It is located in the upper and middle temporal gyri (fields 21-22). Its neurons receive signals from the 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 feeling is formed about the position of the body in space and the acceleration of movements. The vestibular cortex interacts with the cerebellum (through the temporo-pontocerebellar pathway), participates in the regulation of body balance, the adaptation of the posture to the implementation of purposeful movements. Based on the interaction of this area with the somatosensory and associative areas of the cortex, awareness of the body schema occurs.

Olfactory cortex

It is located in the region of the upper part of the temporal lobe (hook, zeros 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 olfactory receptor neurons. In the olfactory cortex, primary qualitative analysis odors and a subjective sensation of smell, its intensity, 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. With artificial stimulation of this area, there are sensations of various smells like hallucinations.

taste bark

It is located in the lower part of the somatosensory gyrus, directly anterior to the face projection area (field 43). Its neurons receive afferent signals from relay neurons of 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 the taste buds. Primary analysis is carried out in the taste cortex palatability bitter, salty, sour, sweet, and on the basis of their summation, a subjective sensation of taste, its intensity, belonging is formed.

Smell and taste signals reach the neurons of the anterior insular cortex, where, based on their integration, a new, more complex quality of sensations is formed that determines our relationship to sources of smell or taste (for example, to food).

Somatosensory cortex

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

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

Due to the intersection of afferent pathways, signaling comes to the somatosensory zone of the left hemisphere from the right side of the body, 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 part of the 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, field 3 neurons receive mainly signals from muscle spindles and mechanoreceptors of the skin, field 2 - from joint receptors.

The postcentral gyrus cortex is referred to as the primary somatosensory area (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 association 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 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 these fields of the parietal cortex is the perception of space and the transformation of sensory signals into motor coordinates. In the parietal cortex, a desire (intention, impulse) to carry out a motor action is formed, which is the basis for the beginning of planning for the upcoming motor activity in it.

The integration of various sensory signals is associated with the formation of various sensations addressed to different parts of the body. These sensations are used both to form 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, grasping, 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 important condition the formation of such sensations as heat, cold, pain and their addressing to a certain part of the body.

Damage to neurons in the area of ​​the primary somatosensory cortex leads to a decrease various kinds sensation on the opposite side of the body, and local damage - to loss of sensation in a certain part of the body. Discriminatory sensitivity of the skin is especially vulnerable when the neurons of the primary somatosensory cortex are damaged, and the least sensitive is pain. 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 stimulation to the cerebral cortex with an electric current, discovered that the impact on the surface of the anterior central gyrus causes contraction of the muscles of the opposite side of the body. Thus, 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 the 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.

Efferent fibers of the pyramidal pathway begin from the pyramidal neurons Ml. Some of the fibers of this pathway follow the motor neurons of the nuclei of the cranial nerves of the brainstem (corticobulbar tract), some - to the neurons of the stem motor nuclei (the 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 location of neurons in MI that control the contraction of different muscle groups of the body. The neurons that control the muscles of the legs and trunk are located in the upper parts of the gyrus and occupy relatively small area, and the controlling muscles of the hands, especially the fingers, face, tongue and pharynx are located in the lower regions and occupy a large area. Thus, in the primary motor cortex, a relatively large area is occupied by those neural groups that control the 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 the leading role in controlling the activity of the motor nuclei of the trunk and spinal cord motoneurons and initiating voluntary, purposeful movements. Damage to the Ml field leads to muscle paresis and the impossibility of fine voluntary movements.

secondary motor cortex

Includes areas of the premotor and supplementary 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 areas of the cortex and cerebellum. The signals processed in it are sent by the neurons of the cortex along the efferent fibers to the motor cortex MI, a small number - to the spinal cord and a larger number - to the red nuclei, the nuclei of the reticular formation, the basal ganglia and the cerebellum. The premotor cortex plays a major role in the programming and organization of movements under the control of vision. The cortex is involved in the organization of posture and auxiliary movements for the actions carried out by the distal muscles of the limbs. Damage to the visual cortex often causes a tendency to re-execute the initiated movement (perseveration), even if the completed movement has reached the goal.

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

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

Since the neurons of the secondary motor cortex send many axons to the MI field, it is considered to be more in the hierarchy of motor centers for organizing movements. high structure standing above the motor centers of the motor cortex MI. 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 supramotor fields, whose function is to instruct the centers of the MI field.

From clinical observations, it is known 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 maintain the interval. The ability to perform opposite hand movements (manipulation with both hands) is impaired.

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

prefrontal cortex

It is located in the region of field 8. Its neurons receive the main afferent signals from the occipital visual, parietal associative cortex, superior colliculi of the quadrigemina. The processed signals are transmitted via efferent fibers to the premotor cortex, superior colliculus, and stem motor centers. The cortex plays a decisive role in the organization of movements under the control of vision and is directly involved in the initiation and control of eye and head movements.

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

Information about the intention of movement is transmitted to the motor areas of the frontal cortex. The motor cortex, through descending pathways, activates systems that ensure the development and use of new motor programs or the use of old ones that have already been worked out in practice and stored in memory. An integral part of these systems are the basal ganglia and the cerebellum (see their functions above). Movement programs developed with the participation of the cerebellum and basal ganglia are transmitted through the thalamus to the motor areas 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 changes in their contraction and relaxation. Cortical commands are transmitted to the motor centers of the brain stem, spinal motor neurons and motor neurons of the cranial nerve nuclei. Motor neurons in the implementation of movements play a role final path through which motor commands are transmitted directly to the muscles. Features of signal transmission from the cortex to the motor centers of the stem and spinal cord are described in the chapter on the central nervous system (brain stem, spinal cord).

Association 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 sensory and motor areas bark. Associative areas do not have clear boundaries with secondary sensory areas, both in terms of morphological and functional features. Allocate parietal, temporal and frontal associative areas of the cerebral cortex.

Parietal association area of ​​the cortex. It is located in fields 5 and 7 of the upper and lower parietal lobes of the brain. The region borders anteriorly on the somatosensory cortex, posteriorly on the visual and auditory cortex. Visual, sound, tactile, proprioceptive, pain, signals from the memory apparatus and other signals can enter and activate the neurons of the parietal associative area. 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 in response to afferent signals depends on the current motivation, the attention of the subject, and information retrieved from memory. It remains insignificant if the signal coming from the sensory areas of the brain is indifferent to the subject, and 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, activity increases sharply in hungry animals that like bananas.

The neurons of the parietal association cortex are connected by efferent connections with the neurons of the prefrontal, premotor, motor areas of the frontal lobe and cingulate gyrus. Based on experimental and clinical observations, it is generally accepted that one of the functions of the field 5 cortex is the use of somatosensory information for the implementation of purposeful voluntary movements and manipulation of objects. The function of the field 7 cortex 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 in case of damage to its connections with the cortex of the frontal lobe or a disease of the frontal lobe itself, explains the symptoms of the consequences of diseases localized in the region of the parietal associative cortex. They can be manifested by difficulty in understanding the semantic content of signals (agnosia), an example of which may be 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 disturbed. In the latter case, the patient loses skills practical use familiar tools and objects (apraxia), and may develop an inability to make visually guided movements (eg, moving a hand towards an object).

Frontal association area of ​​the cortex. It is located in the prefrontal cortex, which is part of the cortex of the frontal lobe, localized anterior to fields 6 and 8. The neurons of the frontal association cortex receive processed sensory signals via afferent connections from the neurons of the cortex of the occipital, parietal, temporal lobes of the brain and from the neurons of the cingulate gyrus. The frontal association cortex receives signals about the current motivational and emotional states from the nuclei of the thalamus, limbic and other brain structures. 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 higher mental functions person. It provides the formation of target settings and programs of conscious behavioral reactions, recognition and semantic evaluation of objects and phenomena, understanding of speech, logical thinking. After extensive damage to the frontal cortex, patients may develop apathy, decreased emotional background, a critical attitude towards one's own actions and the actions of others, complacency, a violation of the possibility of using past experience to change behavior. The behavior of patients can become unpredictable and inadequate.

Temporal association area of ​​the cortex. It is located in fields 20, 21, 22. Cortical neurons receive sensory signals from neurons in the auditory, extrastriate visual and prefrontal cortex, hippocampus and amygdala.

After a bilateral disease of the temporal association areas with involvement of the hippocampus or connections with it in the pathological process, patients may develop severe memory impairment, emotional behavior, inability to concentrate (absent-mindedness). Some people with damage to the lower temporal region, where the center of face recognition is supposedly located, may develop visual agnosia - 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 part of the temporal lobe, there is an associative area of ​​the cortex, called 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.