At present, the division of the cortex into sensory, motor and associative (non-specific) zones (areas) is accepted.
Motor. There are primary and secondary motor areas. The primary contains neurons responsible for the movement of the muscles of the face, trunk and limbs. Irritation of the primary motor zone causes contractions of the muscles of the opposite side of the body. With the defeat of this zone, the ability to fine coordinated movements is lost, especially with the fingers. The secondary motor zone is associated with the planning and coordination of voluntary movements. Here, the readiness potential is regenerated about 1 second before the start of the movement.
The sensory zone consists of primary and secondary. In the primary sensory zone, a spatial topographic representation of body parts is formed. The secondary sensory area consists of neurons responsible for the action of several stimuli. Sensory zones are localized mainly in the parietal lobe of the GM. Here there is a projection of skin sensitivity, pain, temperature, tactile receptors. The primary visual area is located in the occipital lobe.
Associative. Includes the talo-temporal, talo-frontal, and talo-temporal lobes.
Sensory area of the cerebral cortex.
Sensory zones- These are the functional areas of the cerebral cortex, which, through the ascending nerve pathways, receive sensory information from most of the body's receptors. They occupy separate areas of the cortex associated with certain types of sensations. The sizes of these zones correlate with the number of receptors in the corresponding sensory system.
Primary sensory areas and primary motor areas (projection areas);
Secondary sensory areas and secondary motor areas (associative unimodal areas);
Tertiary zones (associative multimodal zones);
Primary sensory and motor areas occupy less than 10% of the surface of the cerebral cortex and provide the simplest sensory and motor functions.
Somatosensory cortex- an area of the cerebral cortex that is responsible for the regulation of certain sensory systems. The first somatosensory zone is located on the postcentral gyrus immediately behind the deep central sulcus. The second somatosensory zone is located on the upper wall of the lateral groove separating the parietal and temporal lobes. Thermoreceptive and nociceptive (pain) neurons were found in these zones. First zone(I) fairly well studied. Almost all areas of the body surface are represented here. As a result of systematic studies, a fairly accurate picture of the representations of the body in this area of the cerebral cortex has been obtained. in literary and scientific sources such a representation was called the “somatosensory homunculus” (for details, see unit 3). The somatosensory cortex of these zones, taking into account the six-layer structure, is organized in the form of functional units - columns of neurons (diameter 0.2 - 0.5 mm), which are endowed with two specific properties: limited horizontal distribution of afferent neurons and vertical orientation of pyramidal cell dendrites. Neurons of one column are excited by receptors of only one type, i.e. specific receptor endings. The processing of information in columns and between them is carried out hierarchically. The efferent connections of the first zone transmit processed information to the motor cortex (the regulation of movements is provided by feedback), the parietal-associative zone (the integration of visual and tactile information is provided) and to the thalamus, the nuclei of the posterior column, the spinal cord (the efferent regulation of the flow of afferent information is provided). The first zone functionally provides accurate tactile discrimination and conscious perception of stimuli on the surface of the body. Second zone(II) is less studied and takes up much less space. Phylogenetically, the second zone is older than the first and is involved in almost all somatosensory processes. The receptive fields of the neural columns of the second zone are located on both sides of the body, and their projections are symmetrical. This zone coordinates the actions of sensory and motor information, for example, when touching objects with both hands.
Subsequently, the efforts of physiologists turned out to be aimed at finding "critical" areas of the brain, the destruction of which led to a violation of the reflex activity of one or another organ. Gradually, an idea was formed about the rigid anatomical localization of "reflex arcs", and, accordingly, the reflex itself began to be thought of as a mechanism for the operation of only the lower parts of the brain (spinal centers).
At the same time, the question of the localization of functions in the higher parts of the brain was being developed. Ideas about the localization of elements of mental activity in the brain arose long ago. In almost every era, one or more
Other hypotheses of representation in the brain of higher mental functions and consciousness in general.
Austrian physician and anatomist Franz Joseph Gall(1758-1828) compiled a detailed description of anatomy and physiology nervous system man, equipped with a beautiful atlas.
: A whole generation of researchers have been based on these data. Gall's anatomical discoveries include the following: identification of the main differences between the gray and white matter of the brain; determination of the origin of nerves in the gray matter; definitive proof of decussation of the pyramidal tracts and optic nerves; establishment of differences between "convergent" (according to modern terminology "associative") and "divergent" ("projective") fibers (1808); the first clear description of the commissures of the brain; proof of the beginning of the cranial nerves in the medulla oblongata (1808), etc. Gall was one of the first to give a decisive role to the cerebral cortex in the functional activity of the brain. Thus, he believed that the folding of the cerebral surface is an excellent solution by nature and evolution of an important task: to ensure the maximum increase in the surface area of the brain while maintaining its volume more or less constant. Gall introduced the term "arc", familiar to every physiologist, and described its clear division into three parts.
However, Gall's name is mostly known in connection with his rather dubious (and sometimes scandalous!) doctrine of the localization of higher mental functions in the brain. Attaching great importance to the correspondence of function and structure, Gall as early as 1790 made an application for the introduction of a new science into the arsenal of knowledge - phrenology(from the Greek phren - soul, mind, heart), which also received a different name - psychomorphology, or narrow localizationism. As a doctor, Gall observed patients with various disorders of brain activity and noticed that the specificity of the disease largely depends on which part of the brain substance is damaged. This led him to the idea that each mental function corresponds to a specific part of the brain. Seeing the infinite variety of characters and individual mental qualities of people, Gall suggested that the strengthening (or greater predominance) of any character trait or mental function in a person’s behavior also entails the predominant development of a certain area of the cerebral cortex where this function is represented. Thus, the thesis was put forward: the function makes the structure. As a result of the growth of this hypertrophied area of the cortex ("brain cones"), pressure on the bones of the skull increases, which, in turn, causes the appearance of an external cranial tubercle above the corresponding area of \u200b\u200bthe brain. In case of underdevelopment of the function, vice versa.
On the surface of the skull there will be a noticeable depression ("fossa"). Using the method of "cranioscopy" created by Gall - the study of the relief of the skull with the help of palpation - and detailed "topographic" maps of the surface of the brain, which indicated the places of localization of all abilities (considered innate), Gall and his followers made a diagnosis, i.e. made a conclusion about character and inclinations of a person, about his mental and moral qualities. Were 2 allocated? areas of the brain where certain abilities of the individual are localized (moreover, 19 of them were recognized as common to humans and animals, and 8 as purely human). In addition to the "bumps" responsible for the implementation of physiological functions, there were those that testified to visual and auditory memory, orientation in space, a sense of time, the instinct of procreation; such personal qualities. as courage, ambition, piety, wit, secrecy, amorousness, caution, self-esteem, refinement, hope, curiosity, malleability of education, pride, independence, diligence, aggressiveness, fidelity, love of life, love of animals.
Gall's erroneous and pseudoscientific ideas (which, however, were extremely popular in their time) contained a rational grain: the recognition of the closest connection between the manifestations of mental functions and the activity of the cerebral cortex. The problem of finding differentiated "think tanks" and drawing attention to the functions of the brain was put on the agenda. Gall can truly be considered the founder of "brain localization". Of course, for the further progress of psychophysiology, the formulation of such a problem was more promising than the ancient search for the location of the "common sensory area".
The solution of the question of the localization of functions in the cerebral cortex was facilitated by data accumulating in clinical practice and in experiments on animals. German physician, anatomist and physicist Julius Robert Mayer(1814-1878), who practiced for a long time in Parisian clinics, and also served as a ship's doctor, observed in patients with craniocerebral injuries the dependence of a violation (or complete loss) of a particular function on damage to a certain part of the brain. This allowed him to suggest that memory is localized in the cerebral cortex (it should be noted that T. Willis came to a similar conclusion back in the 17th century), imagination and judgments in the white matter of the brain, apperception and will in the basal ganglia. A kind of "integral organ" of behavior and the psyche is, according to Mayer, the corpus callosum and the cerebellum.
Over time, the clinical study of the consequences of brain damage was supplemented by laboratory studies. artificial extirpation method(from Latin ex (s) tirpatio - removal with a root), which allows you to partially or completely destroy (remove) parts of the brain of animals to determine their functional role in brain activity. AT early XIX in. carried out mainly acute experiments on animals (frogs, birds), later, with the development of asepsis methods, chronic experiments began to be carried out, which made it possible to observe the behavior of animals for a more or less long time after the operation. Removal of various parts of the brain (including the cerebral cortex) in mammals (cats, dogs, monkeys) made it possible to elucidate the structural and functional basis of complex behavioral reactions.
It turned out that the deprivation of animals of the higher parts of the brain (birds - the forebrain, mammals - the cerebral cortex) in general did not cause a violation of the main functions: respiration, digestion, excretion, blood circulation, metabolism and energy. Animals retained the ability to move, to respond to certain external influences. Consequently, the regulation of these physiological manifestations of vital activity occurs at the underlying (compared to the cerebral cortex) levels of the brain. However, when the higher parts of the brain were removed, profound changes in the behavior of animals occurred: they became practically blind and deaf, “stupid”; they lost previously acquired skills and could not develop new ones, could not adequately navigate in the environment, did not distinguish and could not differentiate objects in the surrounding space. In a word, animals became "living automata" with monotonous and rather primitive ways of responding.
In experiments with partial removal of areas of the cerebral cortex, it was found that the brain is functionally heterogeneous and the destruction of one area or another leads to a violation of a certain physiological function. So, it turned out that the occipital areas of the cortex are associated with visual function, the temporal - with auditory, the area of the sigmoid gyrus - with motor function as well as skin and muscle sensitivity. Moreover, this differentiation of functions in individual regions of the higher parts of the brain is being improved in the course of the evolutionary development of animals.
The strategy of scientific research in the study of brain functions led to the fact that, in addition to the method of extirpation, scientists began to use the method of artificial stimulation of certain areas of the brain using electrical stimulation, which also made it possible to evaluate the functional role of the most important parts of the brain. Data generated by these methods laboratory research, as well as the results of clinical observations, outlined one of the main directions of psychophysiology of the 19th century. - determination of the localization of nerve centers responsible for higher mental functions and behavior of the organism as a whole. So. in 1861, the French scientist, anthropologist and surgeon Paul Broca (1824-1880), on the basis of clinical facts, strongly opposed the physiological equivalence of the cerebral cortex. During the autopsy of the corpses of patients suffering from a speech disorder in the form of motor aphasia (the patients understood someone else's speech, but they themselves could not speak), he found changes in the posterior part of the lower (third) frontal gyrus of the left hemisphere or in the white matter under this area of the cortex. Thus, as a result of these observations, Broca established the position of the motor (motor) center of speech, later named after him. In 1874, the German psychiatrist and neurologist K? Wernicke (1848-1905) described the sensory center of speech (today bearing his name) in the posterior third of the first temporal gyrus of the left hemisphere. The defeat of this center leads to the loss of the ability to understand human speech(sensory aphasia). Even earlier, in 1863, using the method of electrical stimulation of certain areas of the cortex (the precentral gyrus, the precentral region, the anterior part of the pericentral lobule, the posterior parts of the upper and middle frontal gyri), the German researchers Gustav Fritsch and Eduard Gitzig established motor centers (motor cortical fields), the irritation of which caused certain contractions of the skeletal muscles, "and the destruction led to profound disorders of motor behavior. In 4874, the Kyiv anatomist and physician Vladimir Alekseevich Betz (1834-1894) discovered efferent nerve cells of the motor centers - giant pyramidal cells of the V layer cortex, named after him Betz cells German researcher Hermann Munch (student of I. Müller and E. Dubois-Reymond) discovered not only the motor cortical fields, using the method of extirpation, he found the centers of sensory perceptions He managed to show that the center of vision is located in the posterior lobe of the brain, c the center of hearing is in the temporal lobe. Removal of the occipital lobe of the brain led to the loss of the animals' ability to see (with complete preservation of the visual apparatus). Already in
early 20th century eminent Austrian neurologist Konstantin Economo(1876-1931) the centers of swallowing and chewing were established in the so-called black matter of the brain (1902), the centers that control sleep - in the midbrain (1917). Running a little ahead, we say that Economo gave an excellent description of the structure of the cerebral cortex an adult and in 1925 refined the cytoarchitectonic map of the cortical fields of the brain, putting 109 fields on it.
However, it should be noted that in the XIX century. serious arguments were put forward against the position of narrow localizationists, according to whose views motor and sensory functions are confined to different areas of the cerebral cortex. Thus, a theory of the equivalence of sections of the cortex arose, asserting the idea of the equal importance of cortical formations for the implementation of any activity of the body, - equipotentialism. In this regard, the phrenological views of Gall, one of the most vehement supporters of localizationism, were criticized by the French physiologist Marie Jean Pierre Flourance(1794-1867). Back in 1822, he pointed out the presence of a respiratory center in the medulla oblongata (which he called the "vital knot"); linked coordination of movements with the activity of the cerebellum, vision - with the quadrigemina; I saw the main function of the spinal cord in conducting excitation along the nerves. However, despite such seemingly localizationist views, Flurence believed that the basic mental processes (including intellect and will) underlying the purposeful behavior of a person are carried out as a result of the activity of the brain as a holistic formation and therefore a holistic behavioral function. cannot be confined to any particular anatomical entity. Flourance spent most of his experiments on pigeons and chickens, removing parts of their brains and observing changes in the behavior of birds. Usually, after some time after the operation, the behavior of birds was restored regardless of which areas of the brain were damaged, so Flurance concluded that the degree of violation of various forms of behavior is determined primarily by how much brain tissue was removed during the operation. Having improved the technique of operations, he was the first to be able to completely remove the hemispheres of the forebrain from animals and save their life for further observations.
Based on the experiments, Flurance came to the conclusion that the forebrain hemispheres play a decisive role in the implementation of a behavioral act. Their complete removal leads to the loss of all "intelligent" functions. Moreover, especially severe behavioral disorders were observed in chickens after the destruction of the gray matter of the surface of the cerebral hemispheres - the so-called corticoid plate, an analogue of the cerebral cortex of mammals. Flourance suggested that this area of the brain is the seat of the soul, or "controlling spirit", and therefore acts as a whole, having a homogeneous and equivalent mass (similar, for example, to the tissue structure of the liver). Despite the somewhat fantastic ideas of the equipotentialists, one should note the progressive element in their views. First, complex psychophysiological functions were recognized as the result of the combined activity of brain formations. Secondly, the idea of a high dynamic plasticity of the brain, expressed in the interchangeability of its parts, was put forward.
- Gall managed to quite accurately determine the "center of speech", but "officially" it was discovered by the French researcher Paul Broca (1861).
- In 1842 Mayer, working on the definition of the mechanical equivalent of heat, came to a generalized law of conservation of energy.
- Unlike his predecessors, who endowed the nerve with the ability to feel (ie, recognizing a certain mental quality behind it), Hall considered the nerve ending (in the sense organ) to be an "apsychic" formation.
This question is extremely important theoretically and especially practically. Hippocrates already knew that brain injuries lead to paralysis and convulsions on the opposite side of the body, and sometimes are accompanied by loss of speech.
In 1861, the French anatomist and surgeon Broca, on autopsy of the corpses of several patients suffering from a speech disorder in the form of motor aphasia, discovered profound changes in the pars opercularis of the third frontal gyrus of the left hemisphere or in the white matter under this area of the cortex. Based on his observations, Broca established in the cerebral cortex the motor center of speech, later named after him.
The English neuropathologist Jackson (1864) spoke in favor of the functional specialization of individual sections of the hemispheres on the basis of clinical data. Somewhat later (1870), the German researchers Fritsch and Gitzig proved the existence of special areas in the dog's cerebral cortex, the stimulation of which is weak. electric shock accompanied by contraction of individual muscle groups. This discovery caused a large number of experiments, basically confirming the existence of certain motor and sensory areas in the cerebral cortex of higher animals and humans.
On the issue of localization (representation) of function in the cerebral cortex, two diametrically opposed points of view competed with each other: localizationists and antilocalizationists (equipotentialists).
Localizationists were supporters of narrow localization of various functions, both simple and complex.
The anti-localizationists took a completely different view. They denied any localization of functions in the brain. The whole bark for them was equivalent and homogeneous. All its structures, they believed, have the same possibilities for performing various functions (equipotential).
The problem of localization can be correctly resolved only with a dialectical approach to it, which takes into account both the integral activity of the entire brain and the different physiological significance of its individual parts. It was in this way that IP Pavlov approached the problem of localization. In favor of the localization of functions in the cortex, numerous experiments by IP Pavlov and his colleagues with the extirpation of certain areas of the brain convincingly speak. Resection of the occipital lobes of the cerebral hemispheres (centers of vision) in a dog causes enormous damage to the conditioned reflexes developed in it to visual signals and leaves intact all conditioned reflexes to sound, tactile, olfactory and other stimuli. On the contrary, resection of the temporal lobes (hearing centers) leads to the disappearance conditioned reflexes on sound signals and does not affect the reflexes associated with optical signals, etc. Against equipotentialism, in favor of the representation of the function in certain areas of the cerebral hemispheres, the latest data from electroencephalography also speak. Irritation of a certain area of the body leads to the appearance of reactive (evoked) potentials in the cortex in the "center" of this area.
IP Pavlov was a staunch supporter of localization of functions in the cerebral cortex, but only relative and dynamic localization. The relativity of localization is manifested in the fact that each section of the cerebral cortex, being the carrier of a certain special function, the "center" of this function, responsible for it, participates in many other functions of the cortex, but not as the main link, not in the role of the "center ”, but on a par with many other areas.
The functional plasticity of the cortex, its ability to restore the lost function by establishing new combinations speak not only of the relativity of the localization of functions, but also of its dynamism.
The basis of any more or less complex function is the coordinated activity of many areas of the cerebral cortex, but each of these areas participates in this function in its own way.
The basis of modern ideas about the "systemic localization of functions" is the teaching of I. P. Pavlov about the dynamic stereotype. Thus, the higher mental functions (speech, writing, reading, counting, gnosis, praxis) have a complex organization. They are never carried out by some isolated centers, but are always processes "placed in a complex system of zones of the cerebral cortex" (AR Luria, 1969). These "functional systems" are mobile; in other words, the system of means by which this or that task can be solved changes, which, of course, does not reduce the importance for them of the well-studied “fixed” cortical areas of Broca, Wernicke, and others.
The centers of the cerebral cortex of a person are divided into symmetrical, presented in both hemispheres, and asymmetric, present in only one hemisphere. The latter include the centers of speech and functions associated with the act of speech (writing, reading, etc.), which exist only in one hemisphere: in the left - in right-handers, in the right - in left-handers.
Modern ideas about the structural and functional organization of the cerebral cortex come from the classical Pavlovian concept of analyzers, refined and supplemented by subsequent studies. There are three types of cortical fields (G. I. Polyakov, 1969). The primary fields (analyzer cores) correspond to the architectonic zones of the cortex, where sensory pathways end (projection zones). Secondary fields (peripheral sections of the analyzer nuclei) are located around the primary fields. These zones are connected with receptors indirectly, in them a more detailed processing of incoming signals takes place. Tertiary, or associative, fields are located in zones of mutual overlap of the cortical systems of analyzers and occupy more than half of the entire surface of the cortex in humans. In these zones, inter-analyzer connections are established that provide a generalized form of a generalized action (V. M. Smirnov, 1972). The defeat of these zones is accompanied by violations of gnosis, praxis, speech, purposeful behavior.
The cerebral cortex is the evolutionarily youngest formation that has reached the largest values in humans in relation to the rest of the brain mass. In humans, the mass of the cerebral cortex is on average 78% of the total mass of the brain. The cerebral cortex is extremely important in the regulation of the vital activity of the organism, the implementation of complex forms of behavior and in the development of neuropsychic functions. These functions are provided not only by the entire mass of the cortical substance, but also by the unlimited possibilities of associative connections between the cells of the cortex and subcortical formations, which creates conditions for the most complex analysis and synthesis of incoming information, for the development of forms of learning that are inaccessible to animals.
Speaking about the leading role of the cerebral cortex in neurophysiological processes, one should not forget that this higher department can function normally only in close cooperation with subcortical formations. The contrast between the cortex and the underlying parts of the brain is largely schematic and conditional. In recent years, ideas have been developed about the vertical organization of the functions of the nervous system, about circular cortical-subcortical connections.
The cells of the cortical substance are specialized to a much lesser extent than the nuclei of the subcortical formations. It follows that the compensatory capabilities of the cortex are very high - the functions of the affected cells can be taken over by other neurons; the defeat of fairly significant areas of the cortical substance can be clinically very blurred (the so-called clinical silent zones). The absence of a narrow specialization of cortical neurons creates the conditions for the emergence of a wide variety of interneuronal connections, the formation of complex "ensembles" of neurons that regulate various functions. This is the most important basis for the ability to learn. The theoretically possible number of connections between the 14 billion cells of the cerebral cortex is so great that during a person's life a significant part of them remains unused. This once again confirms the unlimited possibilities of human learning.
Despite the well-known nonspecificity of cortical cells, certain groups of them are anatomically and functionally more closely related to certain specialized parts of the nervous system. The morphological and functional ambiguity of different parts of the cortex allows us to speak of cortical centers of vision, hearing, touch, etc., which have a certain localization. In the works of researchers of the 19th century, this principle of localization was taken to an extreme: attempts were made to identify centers of will, thinking, the ability to understand art, etc. At present, it would be wrong to speak of the cortical center as a strictly limited group of cells. It should be noted that the specialization of nerve links is formed in the process of life.
According to I.P. Pavlov, the brain center, or the cortical section of the analyzer, consists of a “core” and “scattered elements”. The "nucleus" is a relatively morphologically homogeneous group of cells with an accurate projection of receptor fields. "Scattered elements" are located in a circle or at a certain distance from the "core": they carry out a more elementary and less differentiated analysis and synthesis of incoming information.
Of the 6 layers of cortical cells, the upper layers are most developed in humans in comparison with similar layers in animals and are formed in ontogenesis much later than the lower layers. The lower layers of the cortex have connections with peripheral receptors (layer IV) and with muscles (layer V) and are called “primary”, or “projection”, cortical zones due to their direct connection with the peripheral parts of the analyzer. Above the "primary" zones, systems of "secondary" zones (layers II and III) are built up, in which associative connections with other parts of the cortex predominate, therefore they are also called projection-associative.
In the cortical representations of the analyzers, thus, two groups of cell zones are revealed. Such a structure is found in the occipital zone, where the visual pathways are projected, in the temporal, where the auditory pathways end, in the posterior central gyrus - the cortical section of the sensitive analyzer, in the anterior central gyrus - the cortical motor center. The anatomical heterogeneity of the "primary" and "secondary" zones is accompanied by physiological differences. Experiments with stimulation of the cortex showed that excitation of the primary zones of the sensory regions leads to the emergence of elementary sensations. For example, irritation of the occipital regions causes a sensation of flashing points of light, dashes, etc. When the secondary zones are irritated, more complex phenomena arise: the subject sees variously designed objects - people, birds, etc. It can be assumed that it is in the secondary zones that operations are carried out gnosis and partly praxis.
In addition, tertiary zones are distinguished in the cortical substance, or zones of overlap of the cortical representations of individual analyzers. In humans, they occupy a very significant place and are located primarily in the parietal-temporal-occipital region and in the frontal zone. Tertiary zones enter into extensive connections with cortical analyzers and thereby ensure the development of complex, integrative reactions, among which meaningful actions occupy the first place in humans. In the tertiary zones, therefore, operations of planning and control take place, requiring the complex participation of different parts of the brain.
In early childhood, the functional zones of the cortex overlap each other, their boundaries are diffuse, and only in the process of practical activity does a constant concentration of functional zones occur in outlined centers separated from each other. In the clinic, in adult patients, very constant symptom complexes are observed when certain areas of the cortical substance and the nerve pathways associated with them are affected.
In childhood, due to incomplete differentiation of functional areas, focal lesions of the cerebral cortex may not have a clear clinical manifestation, which should be remembered when assessing the severity and boundaries of brain damage in children.
Functionally, the main integrative levels of cortical activity can be distinguished.
The first signaling system is associated with the activities of individual analyzers and carries out the primary stages of gnosis and praxis, i.e., the integration of signals coming through the channels of individual analyzers and the formation of response actions, taking into account the state of the external and internal environment, as well as past experience. This first level includes visual perception objects with a concentration of attention on certain of its details, arbitrary movements with active amplification or inhibition of them.
More difficult functional level cortical activity combines systems of various analyzers, includes a second signaling systems)", unites the systems of various analyzers, making it possible to perceive the surroundings meaningfully, to relate to the surrounding world "with knowledge and understanding." This level of integration is closely related to speech activity, and understanding of speech (speech gnosis) and the use of speech as a means of addressing and thinking (speech praxis) are not only interrelated, but also due to various neurophysiological mechanisms, which is of great clinical importance.
Highest level integration is formed in a person in the process of his maturation as a social being, in the process of mastering the skills and knowledge that society has.
The third stage of cortical activity plays the role of a kind of dispatcher of complex processes of higher nervous activity. It ensures the purposefulness of certain acts, creating conditions for their best implementation. This is achieved by "filtering" signals that currently have highest value, from secondary signals, the implementation of probabilistic forecasting of the future and the formation of promising tasks.
Of course, complex cortical activity could not be carried out without the participation of the information storage system. Therefore, memory mechanisms are one of the most important components of this activity. In these mechanisms, not only the functions of fixing information (memorization) are essential, but also the functions of obtaining the necessary information from memory “stores” (recollection), as well as the functions of transferring information flows from RAM blocks (what is needed at the moment) to blocks of long-term memory and vice versa. Otherwise, the assimilation of the new would be impossible, since the old skills and knowledge would interfere with this.
Recent neurophysiological studies have made it possible to establish which functions are predominantly characteristic of certain sections of the cerebral cortex. Even in the last century, it was known that the occipital region of the cortex is closely connected with the visual analyzer, the temporal region with the auditory (Geshl's convolutions), the taste analyzer, the anterior central gyrus with the motor, the posterior central gyrus with the musculoskeletal analyzer. It can be conditionally considered that these departments are associated with the first type, cortical activity and provide the simplest forms of gnosis and praxis.
In the formation of more complex gnostic-practical functions, the cortical regions lying in the parietal-temporal-occipital region take an active part. The defeat of these areas leads to more complex forms of disorders. The gnostic speech center of Wernicke is located in the temporal lobe of the left hemisphere. The motor center of speech is located somewhat anterior to the lower third of the anterior central gyrus (Broc's center). In addition to the centers of oral speech, there are sensory and motor centers of written speech and a number of other formations, one way or another connected with speech. The parietal-temporal-occipital region, where the paths coming from various analyzers are closed, is of great importance for the formation of higher mental functions. The well-known neurophysiologist and neurosurgeon W. Penfield called this area the interpretive cortex. In this area, there are also formations that take part in the mechanisms of memory.
Particular importance is attached to the frontal area. According to modern concepts, it is this section of the cerebral cortex that takes an active part in the organization of purposeful activity, in long-term planning and purposefulness, that is, it belongs to the third type of cortical functions.
The main centers of the cerebral cortex. Frontal lobe. The motor analyzer is located in the anterior central gyrus and paracentral lobule (fields 4, 6 and 6a according to Brodmann). In the middle layers there is an analyzer of kinesthetic stimuli coming from skeletal muscles, tendons, joints and bones. In the V and partly VI layer there are Betz's giant pyramidal cells, the fibers of which form the pyramidal pathway. The anterior central gyrus has a certain somatotopic projection and is associated with the opposite half of the body. In the upper sections of the gyrus, the muscles of the lower extremities are projected, in the lower - of the face. The trunk, larynx, pharynx are presented in both hemispheres (Fig. 55).
The center of rotation of the eyes and head in the opposite direction is located in the middle frontal gyrus in the premotor region (fields 8, 9). The work of this center is closely connected with the system of the posterior longitudinal bundle, the vestibular nuclei, formations of the striopallidar system involved in the regulation of torsion, as well as with the cortical section of the visual analyzer (field 17).
In the posterior sections of the superior frontal gyrus, a center is present that gives rise to the fronto-cerebellopontine pathway (field 8). This area of the cerebral cortex is involved in ensuring the coordination of movements associated with bipedalism, maintaining balance while standing, sitting, and regulates the work of the opposite hemisphere of the cerebellum.
The motor center of speech (the center of speech praxis) is located in the back of the inferior frontal gyrus - Broca's gyrus (field 44). The center provides analysis of kinesthetic impulses from the muscles of the speech motor apparatus, storage and implementation of "images" of speech automatisms, the formation of oral speech, is closely related to the location posterior to it by the lower section of the anterior central gyrus (the projection zone of the lips, tongue and larynx) and to the anterior musical motor center.
The musical motor center (field 45) provides a certain tonality, modulation of speech, as well as the ability to compose musical phrases and sing.
The center of written speech is localized in the posterior part of the middle frontal gyrus in close proximity to the projection cortical zone of the hand (field 6). The center provides automatism of writing and is functionally connected with Broca's center.
Parietal lobe. The center of the skin analyzer is located in the posterior central gyrus of fields 1, 2, 3 and the cortex of the upper parietal region (fields 5 and 7). Tactile, pain, temperature sensitivity of the opposite half of the body is projected in the posterior central gyrus. In the upper sections, the sensitivity of the leg is projected, in the lower sections - the sensitivity of the face. Boxes 5 and 7 represent elements of deep sensitivity. Behind the middle sections of the posterior central gyrus is the center of stereognosis (fields 7.40 and partly 39), which provides the ability to recognize objects by touch.
Behind the upper sections of the posterior central gyrus, there is a center that provides the ability to recognize one's own body, its parts, their proportions and mutual position (field 7).
The center of praxis is localized in the lower parietal lobule on the left, supramarginal gyrus (fields 40 and 39). The center ensures the storage and implementation of images of motor automatisms (praxis functions).
In the lower parts of the anterior and posterior central gyri is the center of the analyzer of interoceptive impulses internal organs and vessels. The center has close ties with subcortical vegetative formations.
The temporal share. The center of the auditory analyzer is located in the middle part of the superior temporal gyrus, on the surface facing the insula (Geshl's gyrus, fields 41, 42, 52). These formations provide the projection of the cochlea, as well as the storage and recognition of auditory images.
The center of the vestibular analyzer (fields 20 and 21) is located in the lower sections of the outer surface of the temporal lobe, is projective, is in close connection with the lower basal sections of the temporal lobes, giving rise to the occipital-temporal cortical-pontocerebellar tract.
Rice. 55. Scheme of localization of functions in the cerebral cortex (A - D). I - projection motor zone; II - the center of turning the eyes and head in the opposite direction; III - projection zone of sensitivity; IV - projection visual zone; projection gnostic zones: V - hearing; VI - smell, VII - taste, VIII - gnostic zone of the body scheme; IX - zone of stereognosis; X - gnostic visual zone; XI - Gnostic reading zone; XII - Gnostic speech zone; XIII - praxis zone; XIV - praxic speech zone; XV - praxic zone of writing; XVI - zone of control over the function of the cerebellum.
The center of the olfactory analyzer is located in the phylogenetically most ancient part of the cerebral cortex - in the hook and the ammon horn (field 11a, e) and provides the projection function, as well as the storage and recognition of olfactory images.
The center of the taste analyzer is located in the immediate vicinity of the center of the olfactory analyzer, i.e., in the hook and ammon horn, but, in addition, in the lowest part of the posterior central gyrus (field 43), as well as in the insula. Like the olfactory analyzer, the center provides a projection function, storage and recognition of taste patterns.
The acoustic-gnostic sensory center of speech (Wernicke's center) is localized in the posterior sections of the superior temporal gyrus on the left, in the depth of the lateral sulcus (field 42, as well as fields 22 and 37). The center provides recognition and storage of sound images of oral speech, both one's own and someone else's.
In the immediate vicinity of Wernicke's center (the middle third of the superior temporal gyrus - field 22) there is a center that provides recognition of musical sounds and melodies.
Occipital lobe. The center of the visual analyzer is located in the occipital lobe (fields 17, 18, 19). Field 17 is a projection visual zone, fields 18 and 19 provide storage and recognition of visual images, visual orientation in an unusual environment.
On the border of the temporal, occipital and parietal lobes is the center of the analyzer of written speech (field 39), which is closely connected with the Wernicke's center of the temporal lobe, with the center of the visual analyzer of the occipital lobe, and also with the centers of the parietal lobe. The Reading Center provides recognition and storage of images of written speech.
Data on the localization of functions were obtained either as a result of stimulation of various sections of the cortex in the experiment, or as a result of an analysis of disturbances resulting from damage to certain areas of the cortex. Both of these approaches can only indicate the participation of certain cortical zones in certain mechanisms, but do not at all mean their strict specialization, unambiguous connection with strictly defined functions.
In the neurological clinic, in addition to signs of damage to areas of the cerebral cortex, there are symptoms of irritation of its individual areas. In addition, phenomena of delayed or impaired development of cortical functions are observed in childhood, which largely modifies the "classic" symptoms. The existence of different functional types of cortical activity causes different symptoms of cortical lesions. Analysis of these symptoms allows us to identify the nature of the lesion and its localization.
Depending on the types of cortical activity, it is possible to distinguish among cortical lesions violations of gnosis and praxis at different levels of integration; speech disorders due to their practical importance; disorders of regulation of purposefulness, purposefulness of neurophysiological functions. With each type of disorder, the mechanisms of memory involved in this functional system can also be disturbed. In addition, more total memory impairments are possible. In addition to relatively local cortical symptoms, more diffuse symptoms are also observed in the clinic, manifested primarily in intellectual insufficiency and behavioral disorders. Both of these disorders are of particular importance in child psychiatry, although in fact many variants of such disorders can be considered borderline between neurology, psychiatry and pediatrics.
The study of cortical functions in childhood has a number of differences from the study of other parts of the nervous system. It is important to establish contact with the child, to maintain a relaxed tone of conversation with him. Since many of the diagnostic tasks presented to the child are very complex, it is necessary to strive so that he not only understands the task, but also becomes interested in it. Sometimes, when examining excessively distracted, motor-disinhibited, or mentally retarded children, much patience and ingenuity must be applied in order to identify the existing deviations. In many cases, the analysis of the child's cortical functions is aided by reports from parents about his behavior at home, at school, and school characteristics.
In the study of cortical functions, a psychological experiment is of great importance, the essence of which is the presentation of standardized purposeful tasks. Separate psychological techniques make it possible to evaluate certain aspects of mental activity in isolation, others more comprehensively. These include the so-called personality tests.
Gnosis and its disorders. Gnosis literally means recognition. Our orientation in the surrounding world is connected with the recognition of the shape, size, spatial correlation of objects and, finally, with the understanding of their meaning, which is contained in the name of the object. This stock of information about the surrounding world is made up of the analysis and synthesis of sensory impulse flows and is deposited in memory systems. The receptor apparatus and the transmission of sensory impulses are preserved in the case of lesions of higher gnostic mechanisms, but the interpretation of these impulses, the comparison of the received data with the images stored in the memory, are violated. As a result, a disorder of gnosis arises - agnosia, the essence of which is that while the perception of objects is preserved, the feeling of their “familiarity” is lost and the world, previously so familiar in detail, becomes alien, incomprehensible, devoid of meaning.
But gnosis cannot be imagined as a simple juxtaposition, recognition of an image. Gnosis is a process of continuous renewal, clarification, concretization of the image stored in the memory matrix, under the influence of its re-comparison with the received information.
total agnosia, in which there is complete disorientation, occurs infrequently. Significantly more often, gnosis is disturbed in any one analyzer system, and, depending on the degree of damage, the severity of agnosia is different.
Visual agnosia occur with damage to the occipital cortex. The patient sees the object, but does not recognize it. There may be various options here. In some cases, the patient correctly describes the external properties of the object (color, shape, size), but cannot recognize the object. For example, the patient describes an apple as “something round, pink”, not recognizing an apple in an apple. But if you give the patient this object in his hands, then he will recognize it when he feels it. There are times when the patient does not recognize familiar faces. Some patients with a similar disorder are forced to remember people according to some other signs (clothing, mole, etc.). In other cases, the patient with agnosia recognizes an object, names its properties and function, but cannot remember what it is called. These cases belong to the group of speech disorders.
In some forms of visual agnosia, spatial orientation and visual memory are disturbed. In practice, even when an object is not recognized, one can speak of violations of the mechanisms of memory, since the perceived object cannot be compared with its image in the gnostic matrix. But there are also cases when, upon repeated presentation of an object, the patient says that he has already seen it, although he still cannot recognize it. In case of violations of spatial orientation, the patient not only does not recognize faces, houses, etc. familiar to him before, but can also walk many times in the same place without suspecting it.
Often, with visual agnosia, recognition of letters and numbers also suffers, and there is a loss of the ability to read. An isolated type of this disorder will be analyzed in the analysis of speech function.
A set of objects is used to study visual gnosis. Presenting them to the subject, they are asked to identify, describe them. appearance, compare which items are larger, which are smaller. A set of pictures is also used, color, monochrome and contour. Evaluate not only the recognition of objects, faces, but also plots. Along the way, you can also check visual memory: present several pictures, then mix them with previously unseen ones and ask the child to choose familiar pictures. At the same time, work time, perseverance, and fatigue are also taken into account.
It should be borne in mind that children recognize contour pictures worse than color and plain ones. Understanding the plot is related to the age of the child and the degree mental development. At the same time, classical agnosias in children are rare due to incomplete differentiation of cortical centers.
auditory agnosia. Occur when the temporal lobe is damaged in the region of the Geshl gyrus. The patient cannot recognize previously familiar sounds: the ticking of a clock, the ringing of a bell, the sound of pouring water. There may be violations of recognition of musical melodies - amusia. In some cases, the definition of the direction of sound is violated. In some types of auditory agnosia, the patient is unable to distinguish the frequency of sounds, such as metronome beats.
Sensitive agnosias are caused by impaired recognition of tactile, pain, temperature, proprioceptive images or their combinations. They occur when the parietal region is affected. This includes astereognosis, body schema disorders. In some variants of astereognosis, the patient not only cannot determine the object by touch, but is also unable to determine the shape of the object, the feature of its surface. Sensitive agnosia also includes anosognosia, in which the patient is not aware of his defect, such as paralysis. Phantom sensations can be attributed to violations of sensitive gnosis.
When examining children, it should be borne in mind that Small child can not always correctly show parts of his body; the same applies to patients suffering from dementia. In such cases, of course, it is not necessary to speak of a disorder of the body scheme.
Taste and olfactory agnosia are rare. In addition, the recognition of odors is very individual, largely due to personal experience person.
Praxis and its disorders. Praxis is understood as purposeful action. A person learns in the process of life a lot of special motor acts. Many of these skills, being formed with the participation of higher cortical mechanisms, are automated and become the same inalienable human ability as simple movements. But when the cortical mechanisms involved in the implementation of these acts are damaged, peculiar motor disorders arise - apraxia, in which there are no paralysis, no violations of tone or coordination, and even simple voluntary movements are possible, but more complex, purely human motor acts are violated. The patient suddenly finds himself unable to perform such seemingly simple actions as shaking hands, fastening buttons, combing his hair, lighting a match, etc. Apraxia occurs primarily with damage to the parietal-temporal-occipital region of the dominant hemisphere. In this case, both halves of the body are affected. Apraxia can also occur with damage to the subdominant right hemisphere (in right-handed people) and the corpus callosum, which connects both hemispheres. In this case, apraxia is determined only on the left. With apraxia, the plan of action suffers, that is, the compilation of a continuous chain of motor automatisms. Here it is appropriate to quote the words of K. Marx: “Human action differs from the work of the“ best bee ”in that, before building, a person has already built in his head. At the end of the labor process, a result is obtained that already before the start of this process was ideal, that is, in the mind of the worker.
Due to the violation of the action plan, when trying to complete the task, the patient makes many unnecessary movements. In some cases, parapraxia is observed when an action is performed that only remotely resembles this task. Sometimes there are also perseverations, i.e., getting stuck on any actions. For example, the patient is asked to make an alluring hand movement. After completing this task, they offer to wag a finger, but the patient still performs the first action.
In some cases, with apraxia, ordinary, everyday activities are preserved, but professional skills are lost (for example, the ability to use a planer, screwdriver, etc.).
According to clinical manifestations, several types of apraxia are distinguished: motor, ideational and constructive.
motor apraxia. The patient cannot perform actions on assignment and even on imitation. He is asked to cut the paper with scissors, lace up his shoe, line the paper with a pencil and ruler, etc., but the patient, although he understands the task, cannot complete it, showing complete helplessness. Even if you show how it is done, the patient still cannot repeat the movement. In some cases, it may not be possible to carry out such simple actions like crouching, twisting, clapping.
ideational apraxia. The patient cannot perform actions on the task with real and imaginary objects (for example, show how they comb their hair, stir sugar in a glass, etc.), at the same time, imitation actions are preserved. In some cases, the patient can automatically, without hesitation, perform certain actions. For example, purposefully, he cannot fasten a button, but performs this action automatically.
constructive apraxia. The patient can perform various actions by imitation and by verbal order, but is unable to create a qualitatively new motor act, to put together a whole from parts, for example, to make a certain figure out of matches, to put together a pyramid, etc.
Some variants of apraxia are associated with impaired gnosis. The patient does not recognize the object or his body scheme is disturbed, so he is not able to perform tasks or performs them uncertainly and not quite correctly.
To study praxis, a number of tasks are offered (sit down, wag a finger, comb your hair, etc.). They also present tasks for actions with imaginary objects (they ask to show how they eat, how they call on the phone, how they cut firewood, etc.). Evaluate how the patient can imitate the actions shown.
Special psychological techniques are also used to study gnosis and praxis. Among them, an important place is occupied by Segen boards with recesses of various shapes, in which you need to put figures corresponding to the recesses. This method also allows assessing the degree of mental development. The Koss method is also used: a set of cubes of different colors. From these cubes you need to add a pattern corresponding to the one shown in the picture. Older children are also offered a Link cube: you need to add a cube from 27 differently colored cubes so that all its sides are the same color. The patient is shown the assembled cube, then they destroy it and ask them to fold it again.
In these methods, it is of great importance how the child performs the task: whether he acts according to the trial and error method or according to a certain plan.
Rice. 56. Scheme of connections between speech centers and regulation of speech activity.
1 - the center of the letter; 2 - Broca's center; 3 - center of praxis; 4 - center of proprioceptive gnosis; 5 - reading center; 6 - Wernicke's center; 7 - the center of auditory gnosis; 8 - the center of visual gnosis.
It is important to remember that praxis is formed as the child matures, so young children cannot yet perform such simple actions as combing their hair, fastening buttons, etc. Apraxia in their classic form, like agnosia, occurs mainly in adults.
Speech and its disorders. AT the visual, auditory, motor and kinesthetic analyzers take part in the implementation of the speech function, as well as writing and reading. Great importance have the preservation of the innervation of the muscles of the tongue, larynx, soft palate, the state of the paranasal sinuses and the oral cavity, which play the role of resonator cavities. In addition, coordination of breathing and pronunciation of sounds is important.
For normal speech activity, the coordinated functioning of the entire brain and other parts of the nervous system is necessary. Speech mechanisms have a complex and multi-stage organization (Fig. 56).
Speech is the most important function of a person, therefore, cortical speech zones located in the dominant hemisphere (Brock and Wernicke centers), motor, kinetic, auditory and visual areas, as well as conducting afferent and efferent pathways related to the pyramidal and extrapyramidal systems take part in its implementation. , analyzers of sensitivity, hearing, vision, bulbar parts of the brain, visual, oculomotor, facial, auditory, glossopharyngeal, vagus and hypoglossal nerves.
Complexity, versatility speech mechanisms causes a variety of speech disorders. When the innervation of the speech apparatus is disturbed, dysarthria- violation of articulation, which may be due to central or peripheral paralysis of the speech motor apparatus, damage to the cerebellum, striopallidar system.
There are also dyslalia- phonetically incorrect pronunciation of individual sounds. Dyslalia can be functional and speech therapy classes removed quite successfully. Under alalia understand speech delay. Usually to VA At the age of 18, the child begins to speak, but sometimes this happens much later, although the child understands well the speech addressed to him. The delay in speech development also affects mental development, since speech is the most important means of information for the child. However, there are also cases of alalia associated with dementia. The child lags behind in mental development, and therefore his speech is not formed. These different cases of alalia need to be differentiated as they have a different prognosis.
With the development of the speech function in the dominant hemisphere (for right-handers, in the left, for left-handers, in the right), gnostic and practical speech centers are formed, and subsequently - centers of writing and reading.
Cortical speech disorders are variants of agnosia and apraxia. There are expressive (motor) and impressive (sensory) speech. Cortical impairment of motor speech is speech apraxia, sensory speech - speech agnosia. In some cases, the recall of the necessary words is disturbed, i.e., memory mechanisms suffer. Speech agnosias and apraxias are called aphasias.
It should be remembered that speech disorders can be the result of general apraxia (apraxia of the trunk, limbs) or oral apraxia, in which the patient loses the ability to open his mouth, puff out his cheeks, stick out his tongue. These cases do not apply to aphasias; speech apraxia here occurs a second time as a manifestation of general praxic disorders.
Speech disorders in childhood, depending on the causes of their occurrence, can be divided into the following groups:
I. Speech disorders associated with organic damage to the central nervous system. Depending on the level of damage to the speech system, they are divided into:
1) aphasia - the disintegration of all components of speech as a result of damage to the cortical speech zones;
2) alalia - systemic underdevelopment of speech due to lesions of the cortical speech zones in the pre-speech period;
3) dysarthria - a violation of the sound-producing side of speech as a result of a violation of the innervation of the speech muscles.
Depending on the localization of the lesion, several forms of dysarthria are distinguished.
II. Speech disorders associated with functional changes
central nervous system:
1) stuttering;
2) mutism and deafness.
III. Speech disorders associated with defects in the structure of the articulatory apparatus (mechanical dyslalia, rhinolalia).
IV. Delays in speech development of various origins (with prematurity, somatic weakness, pedagogical neglect, etc.).
Sensory aphasia(Wernicke's aphasia), or verbal "deafness", occurs when the left temporal region is affected (middle and posterior sections of the superior temporal gyrus). A. R. Luria distinguishes two forms of sensory aphasia: acoustic-gnostic and acoustic-mnestic.
The basis of the defect acoustic-gnostic form constitutes a violation of auditory gnosis. The patient does not differentiate by ear phonemes similar in sound in the absence of deafness (phonemic analysis is considered), as a result of which the understanding of the meaning of individual words and sentences is distorted and disrupted. The severity of these disorders may vary. In the most severe cases, the addressed speech is not perceived at all and seems to be a speech in a foreign language. This form occurs when the posterior part of the upper temporal gyrus of the left hemisphere is damaged - Brodmann's field 22.
In the cerebral cortex there is an analysis of all stimuli that come from the external and internal environment. The largest number of afferent impulses comes to the cells of the 3rd and 4th layers of the cerebral cortex. In the cerebral cortex there are centers that regulate the performance of certain functions. IP Pavlov considered the cerebral cortex as a set of cortical ends of analyzers. The term "analyzer" refers to a complex set of anatomical structures, which consists of a peripheral receptor (perceiving) apparatus, conductors of nerve impulses and a center. In the process of evolution, functions are localized in the cerebral cortex. The cortical end of the analyzers is not a strictly defined zone. In the cerebral cortex, the "core" of the sensory system and "scattered elements" are distinguished. The nucleus is the location of the largest number of cortical neurons, in which all the structures of the peripheral receptor are precisely projected. Scattered elements are located near the nucleus and at different distances from it. If the highest analysis and synthesis is carried out in the nucleus, then it is simpler in the scattered elements. In this case, the zones of "scattered elements" of various analyzers do not have clear boundaries and are layered on top of each other.
Functional characteristics of the cortical zones of the frontal lobe. In the region of the precentral gyrus of the frontal lobe is the cortical nucleus of the motor analyzer. This area is also called the sensorimotor cortex. Here comes part of the afferent fibers from the thalamus, carrying proprioceptive information from the muscles and joints of the body (Fig. 8.7). Descending pathways to the brainstem and spinal cord also begin here, providing the possibility of conscious regulation of movements (pyramidal pathways). The defeat of this area of the cortex leads to paralysis of the opposite half of the body.
Rice. 8.7. Somatotopic distribution in the precentral gyrus
The center of writing lies in the posterior third of the middle frontal gyrus. This zone of the cortex gives projections to the nuclei of the oculomotor cranial nerves, and also communicates with the center of vision in the occipital lobe and the control center of the muscles of the arms and neck in the precentral gyrus with the help of cortical-cortical connections. The defeat of this center leads to impaired writing skills under visual control (agraphia).
In the zone of the inferior frontal gyrus, there is a speech motor center (Broc's center). It has a pronounced functional asymmetry. When it is destroyed in the right hemisphere, the ability to regulate timbre and intonation is lost, speech becomes monotonous. With the destruction of the speech-motor center on the left, speech articulation is irreversibly disturbed, up to the loss of the ability to articulate speech (aphasia) and singing (amusia). With partial violations, agrammatism can be observed - the inability to correctly build phrases.
In the region of the anterior and middle thirds of the superior, middle, and partially inferior frontal gyri, there is an extensive anterior associative cortical zone that programs complex forms of behavior (planning various forms of activity, decision-making, analysis of the results obtained, volitional reinforcement of activity, correction of the motivational hierarchy).
The region of the frontal pole and the medial frontal gyrus is associated with the regulation of the activity of the emotive areas of the brain that are part of the limbic system and is related to the control of psycho-emotional states. Violations in this area of the brain can lead to changes in what is commonly called the “personality structure” and affect the character of a person, his value orientations, and intellectual activity.
The orbital region contains the centers of the olfactory analyzer and is closely connected in anatomical and functional terms with the limbic system of the brain.
Functional characteristics of the cortical zones of the parietal lobe. The cortical center of the analyzer is located in the postcentral gyrus and superior parietal lobule. general sensitivity(pain, temperature and tactile), or somatosensory cortex. The representation of various parts of the body in it, as well as in the precentral gyrus, is built according to the somatotopic principle. This principle assumes that body parts are projected onto the surface of the furrow in the same topographical relationship that they have in the human body. However, representation different parts body in the cerebral cortex varies significantly. Those areas (hand, head, especially tongue and lips) that are associated with complex movements such as writing, speech, etc. have the greatest representation. Cortical disorders in this area lead to partial or complete anesthesia (loss of sensitivity).
Damage to the cortex in the region of the superior parietal lobule leads to a decrease in pain sensitivity and a violation of stereognosis - recognition of objects by touch without the help of vision.
In the lower parietal lobe in the region of the supramarginal gyrus, there is a center of praxia, which regulates the ability to carry out complexly coordinated actions that form the basis of labor processes and require special training. It also gives rise to a significant number of descending fibers that follow as part of the paths that control conscious movements (pyramidal paths). This area of the parietal cortex interacts closely with the cortex of the frontal lobe and with all sensory areas of the posterior half of the brain with the help of cortical-cortical connections.
The visual (optical) center of speech is located in the angular gyrus of the parietal lobe. Its damage leads to the inability to understand the readable text (alexia).
Functional characteristics of the cortical zones of the occipital lobe. In the region of the spur groove is the cortical center of the visual analyzer. Its damage leads to blindness. In case of disturbances in the areas of the cortex adjacent to the spur groove in the region of the occipital pole on the medial and lateral surfaces of the lobe, there may be a loss of visual memory, the ability to navigate in an unfamiliar environment, functions associated with binocular vision are impaired (the ability to assess the shape of objects with the help of vision, the distance to them , to correctly measure movements in space under visual control, etc.).
Functional characteristics of the cortical zones of the temporal lobe. In the region of the superior temporal gyrus, in the depths of the lateral sulcus, is the cortical center of the auditory analyzer. Its damage leads to deafness.
In the posterior third of the superior temporal gyrus lies the auditory speech center (Wernicke's center). Injuries in this area lead to the inability to understand spoken language: it is perceived as noise (sensory aphasia).
In the region of the middle and inferior temporal gyri, there is a cortical representation of the vestibular analyzer. Damage to this area leads to imbalance when standing and a decrease in the sensitivity of the vestibular apparatus.
Functional characteristics of the cortical zones of the insular lobe.
Information concerning the functions of the insular lobe is contradictory and insufficient. There is evidence that the cortex of the anterior part of the insula is related to the analysis of olfactory and gustatory sensations, and the back part is related to the processing of somatosensory information and auditory perception of speech.
Functional characteristics of the limbic system. limbic system- a set of a number of brain structures, including the cingulate gyrus, isthmus, dentate and parahippocampal gyrus, etc. Participates in the regulation of the functions of internal organs, smell, instinctive behavior, emotions, memory, sleep, wakefulness, etc.
The cingulate and parahippocampal gyrus are directly related to the limbic system of the brain (Figures 8.8 and 8.9). It controls the complex of vegetative and behavioral psycho-emotional reactions to external environmental influences. In the parahippocampal gyrus and hook, there is a cortical representation of the gustatory and olfactory analyzers. At the same time, the hippocampus plays an important role in learning: the mechanisms of short-term and long-term memory are associated with it.
Rice. 8.8. Medial surface of the brain
Basal (subcortical central) nuclei - accumulations of gray matter, forming separately lying nuclei, which lie closer to the base of the brain. These include the striatum, which makes up the predominant mass of the hemispheres in lower vertebrates; fence and amygdala (Fig. 8.10).
Rice. 8.9. limbic system
Rice. 8.10. Basal ganglia
The striatum consists of the caudate and lenticular nuclei. The gray matter of the caudate and lenticular nuclei alternates with layers of white matter, which led to the common name for this group of subcortical nuclei - the striatum.
The caudate nucleus is located laterally and above the thalamus, being separated from it by a terminal strip. The caudate nucleus has a head, body and tail. The lentiform nucleus is located lateral to the caudate. A layer of white matter - the inner capsule, separates the lenticular nucleus from the caudate and from the thalamus. In the lenticular nucleus, a pale ball (medially) and a shell (laterally) are distinguished. The outer capsule (a narrow strip of white matter) separates the shell from the fence.
The caudate nucleus, putamen and globus pallidus control complexly coordinated automated movements of the body, control and maintain the tone of skeletal muscles, and are also the highest center of regulation of such vegetative functions as heat production and carbohydrate metabolism in the muscles of the body. With damage to the shell and pale ball, slow stereotyped movements (athetosis) can be observed.
The nuclei of the striatum belong to the extrapyramidal system involved in the control of movements, the regulation of muscle tone.
The fence is a vertical plate of gray matter, the lower part of which continues into the substance of the anterior perforated plate at the base of the brain. The fence is located in the white matter of the hemisphere lateral to the lenticular nucleus and has numerous connections with the cerebral cortex.
The amygdala lies in the white matter of the temporal lobe of the hemisphere, 1.5–2 cm posterior to its temporal pole, through the nuclei it has connections with the cerebral cortex, with the structures of the olfactory system, with the hypothalamus and the nuclei of the brain stem that control the autonomic functions of the body. Its destruction leads to aggressive behavior or an apathetic, lethargic state. Through its connections to the hypothalamus, the amygdala influences the endocrine system as well as reproductive behavior.
The white matter of the hemisphere includes the internal capsule and fibers passing through the commissures of the brain (corpus callosum, anterior commissure, commissure of the fornix) and heading to the cortex and basal ganglia, the fornix, as well as systems of fibers connecting areas of the cortex and subcortical centers within one half of the brain (hemispheres).
I and II lateral ventricles. The cavities of the cerebral hemispheres are the lateral ventricles (I and II), located in the thickness of the white matter under the corpus callosum. Each ventricle consists of four parts: the anterior horn lies in the frontal, the central part - in the parietal, the posterior horn - in the occipital and the lower horn - in the temporal lobe (Fig. 8.11).
The anterior horns of both ventricles are separated from each other by two plates of a transparent septum. The central part of the lateral ventricle curves from above around the thalamus, forms an arc and passes backwards - into the posterior horn, downwards into the lower horn. The choroid plexus protrudes into the central part and the lower horn of the lateral ventricle, which, through the interventricular foramen, connects to the choroid plexus of the third ventricle.
Rice. 8.11. Ventricles of the brain:
1 - left hemisphere of the brain, 2 - lateral ventricles, 3 - third ventricle, 4 - aqueduct of the midbrain, 5 - fourth ventricle, 6 - cerebellum, 7 - entrance to the central canal of the spinal cord, 8 - spinal cord
The ventricular system includes paired C-shaped cavities - the lateral ventricles with their anterior, inferior and posterior horns, extending respectively into the frontal lobes, into the temporal lobes and into the occipital lobes of the cerebral hemispheres. About 70% of all cerebrospinal fluid is secreted by the choroid plexus of the walls of the lateral ventricles.
From the lateral ventricles, fluid passes through the interventricular openings into the slit-like cavity of the third ventricle, located in the sagittal plane of the brain and dividing the thalamus and hypothalamus into two symmetrical halves. The cavity of the third ventricle is connected by a narrow canal - the aqueduct of the midbrain (Sylvian aqueduct) with the cavity of the fourth ventricle. The fourth ventricle communicates with the subarachnoid spaces of the brain and spinal cord through several channels (apertures).
diencephalon
The diencephalon is located under the corpus callosum and consists of the thalamus, epithalamus, metathalamus, and hypothalamus (Fig. 8.12, see Fig. 7.2).
thalamus(optic tubercle) - paired, ovoid, formed mainly by gray matter. The thalamus is the subcortical center of all kinds of sensitivity. The medial surface of the right and left thalamus, facing each other, form the side walls of the cavity of the diencephalon - the third ventricle, they are interconnected by interthalamic fusion. The thalamus contains gray matter, which is made up of clusters of neurons that form the nuclei of the thalamus. The nuclei are separated by thin layers of white matter. About 40 nuclei of the thalamus were studied. The main nuclei are anterior, medial, posterior.
Rice. 8.12. Departments of the brain
Epithalamus includes the pineal gland, the leashes, and the triangles of the leashes. The pineal body, or pineal gland, which is an endocrine gland, is, as it were, suspended on two leashes, interconnected by adhesions and connected to the thalamus by means of triangles of leashes. The triangles of the leashes contain nuclei related to the olfactory analyzer. In an adult, the average length of the epiphysis is ~ 0.64 cm, and the weight is ~ 0.1 g. Metathalamus formed by paired medial and lateral geniculate bodies, lying behind each thalamus. The medial geniculate body is located behind the pillow of the thalamus, it is, along with the lower hillocks of the plate of the roof of the midbrain (the quadrigemina), the subcortical center of the auditory analyzer. Lateral - located down from the pillow, it, together with the upper mounds of the roof plate, is the subcortical center of the visual analyzer. Nuclei cranked bodies associated with the cortical centers of the visual and auditory analyzers.
Hypothalamus, which is the ventral part of the diencephalon, is located anterior to the legs of the brain and includes a number of structures that have a different origin - the anterior visual part (optic chiasm, optic tract, gray tubercle, funnel, neurohypophysis) is formed from the telencephalon; from the intermediate - the olfactory part (mastoid bodies and the actual subthalamic region - the hypothalamus) (Fig. 8.13).
Figure 8.13. Basal ganglia and diencephalon
The hypothalamus is the center of regulation of endocrine functions, it combines the nervous and endocrine regulatory mechanisms into a common neuroendocrine system, coordinates the nervous and hormonal mechanisms of regulation of the functions of internal organs. In the hypothalamus there are neurons of the usual type and neurosecretory cells. The hypothalamus forms a single functional complex with the pituitary gland, in which the former plays a regulatory and the latter an effector role.
There are more than 30 pairs of nuclei in the hypothalamus. Large neurosecretory cells of the supraoptic and paraventricular nuclei of the anterior hypothalamic region produce neurosecretions of a peptide nature.
The medial hypothalamus contains neurons that perceive all changes that occur in the blood and cerebrospinal fluid (temperature, composition, hormone levels, etc.). The medial hypothalamus is also connected to the lateral hypothalamus. The latter does not have nuclei, but has bilateral connections with the overlying and underlying parts of the brain. The medial hypothalamus is the link between the nervous and endocrine systems. In recent years, enkephalins and endorphins (peptides) with a morphine-like effect have been isolated from the hypothalamus. It is believed that they are involved in the regulation of behavior and vegetative processes.
Anterior to the posterior perforated substance are two small spherical mastoid bodies formed by a gray substance covered with a thin layer of white. The nuclei of the mastoid bodies are the subcortical centers of the olfactory analyzer. Anterior to the mastoid bodies is a gray tubercle, which is bounded in front by the optic chiasm and optic tract, it is a thin plate of gray matter at the bottom of the third ventricle, which is extended downward and anteriorly and forms a funnel. Its end goes to pituitary - an endocrine gland located in the pituitary fossa of the Turkish saddle. The nuclei of the autonomic nervous system lie in the gray hillock. They also influence a person's emotional reactions.
The part of the diencephalon, located below the thalamus and separated from it by the hypothalamic groove, constitutes the hypothalamus itself. Here the tires of the legs of the brain continue, here the red nuclei and the black substance of the midbrain end.
III ventricle. The cavity of the diencephalon III ventricle It is a narrow, slit-like space located in the sagittal plane, bounded laterally by the medial surfaces of the thalamus, below by the hypothalamus, in front by the columns of the fornix, the anterior commissure and the terminal plate, behind the epithalamic (posterior) commissure, and above by the vault, over which the corpus callosum is located. The upper wall itself is formed by the vascular base of the third ventricle, in which its choroid plexus lies.
The cavity of the third ventricle posteriorly passes into the aqueduct of the midbrain, and in front on the sides through the interventricular openings communicates with the lateral ventricles.
midbrain
midbrain - the smallest part of the brain, lying between the diencephalon and the bridge (Fig. 8.14 and 8.15). The area above the aqueduct is called the roof of the midbrain, and there are four bulges on it - the plate of the quadrigemina with the upper and lower hillocks. From here exit the paths of visual and auditory reflexes heading to the spinal cord.
The legs of the brain are white rounded strands emerging from the bridge and heading forward to the cerebral hemispheres. From the groove on the medial surface of each leg comes the oculomotor nerve (III pair of cranial nerves). Each leg consists of a tire and a base, the border between them is a black substance. The color depends on the abundance of melanin in its nerve cells. Substance nigra refers to the extrapyramidal system, which is involved in maintaining muscle tone and automatically regulates muscle function. The base of the stalk is formed by nerve fibers running from the cerebral cortex to the spinal cord and medulla oblongata and the pons. The covering of the legs of the brain contains mainly ascending fibers heading to the thalamus, among which the nuclei lie. The largest are the red nuclei, from which the motor red-nuclear-spinal path begins. In addition, the reticular formation and the nucleus of the dorsal longitudinal bundle (intermediate nucleus) are located in the tegmentum.
Hind brain
The pons located ventrally and the cerebellum lying behind the pons belong to the hindbrain.
Rice. 8.14. Schematic representation of a longitudinal section of the brain
Rice. 8.15. Cross section through the midbrain at the level of the superior colliculi (cut plane shown in Figure 8.14)
Bridge it looks like a transversely thickened roller, from the lateral side of which the middle cerebellar legs extend to the right and left. The posterior surface of the bridge, covered by the cerebellum, participates in the formation of the rhomboid fossa, the anterior (adjacent to the base of the skull) borders on medulla oblongata below and the legs of the brain above (see Fig. 8.15). It is transversely striated due to the transverse direction of the fibers that go from the own nuclei of the bridge to the middle cerebellar peduncles. On the front surface of the bridge middle line the basilar sulcus is located longitudinally, in which the artery of the same name passes.
The bridge consists of many nerve fibers that form pathways, among which are cell clusters - nuclei. The pathways of the anterior part connect the cerebral cortex with the spinal cord and with the cortex of the cerebellar hemispheres. In the back of the bridge (tire) there are ascending pathways and partially descending, there is a reticular formation, the nuclei of V, VI, VII, VIII pairs of cranial nerves. On the border between both parts of the bridge lies a trapezoid body formed by nuclei and transversely running fibers of the auditory analyzer pathway.
Cerebellum plays a major role in maintaining body balance and coordination of movements. The cerebellum reaches its greatest development in humans in connection with upright walking and the adaptation of the hand to work. In this regard, the hemispheres (new part) of the cerebellum are highly developed in humans.
In the cerebellum, two hemispheres and an unpaired median phylogenetically old part - the worm (Fig. 8.16) are distinguished.
Rice. 8.16. Cerebellum: top and bottom view
The surfaces of the hemispheres and the vermis are separated by transverse parallel grooves, between which are located narrow long leaves of the cerebellum. In the cerebellum, the anterior, posterior, and flocculent-nodular lobes are distinguished, separated by deeper fissures.
The cerebellum consists of gray and white matter. The white matter, penetrating between the gray, branches, as it were, forming on the median section the figure of a branching tree - the "tree of life" of the cerebellum.
The cerebellar cortex consists of gray matter 1–2.5 mm thick. In addition, in the thickness of the white matter there are accumulations of gray - paired nuclei: a jagged nucleus, a corky, a spherical and a tent nucleus. Afferent and efferent fibers connecting the cerebellum with other departments form three pairs of cerebellar peduncles: the lower ones go to the medulla oblongata, the middle ones go to the pons, and the upper ones go to the quadrigemina.
By the time of birth, the cerebellum is less developed than the telencephalon (especially the hemispheres), but in the first year of life it develops faster than other parts of the brain. A pronounced increase in the cerebellum is noted between the 5th and 11th months of life, when the child learns to sit and walk.
Medulla is a direct continuation of the spinal cord. Its lower boundary is considered to be the exit point of the roots of the 1st cervical spinal nerve or the intersection of the pyramids, the upper one is the posterior edge of the bridge, its length is about 25 mm, the shape approaches a truncated cone, turned base up.
The anterior surface is divided by the anterior median fissure, on the sides of which there are pyramids formed by pyramidal pathways, partially crossing (crossing the pyramids) in the depth of the described fissure on the border with the spinal cord. Fibers of the pyramidal pathways connect the cerebral cortex with the nuclei of the cranial nerves and the anterior horns of the spinal cord. On the side of the pyramid, on each side, there is an olive, separated from the pyramid by the anterior lateral groove.
The posterior surface of the medulla oblongata is divided by the posterior median sulcus, on the sides of it there are continuations of the posterior cords of the spinal cord, which diverge upward, passing into the lower cerebellar peduncles.
The medulla oblongata is built of white and gray matter, the latter is represented by the nuclei of the IX-XII pairs of cranial nerves, olives, centers of respiration and circulation, and the reticular formation. White matter is formed by long and short fibers that make up the corresponding pathways.
Reticular formation is a collection of cells, cell clusters and nerve fibers located in the brainstem (medulla oblongata, pons and midbrain) and forming a network. The reticular formation is connected with all sense organs, motor and sensitive areas of the cerebral cortex, the thalamus and hypothalamus, and the spinal cord. It regulates the level of excitability and tone of various parts of the central nervous system, including the cerebral cortex, is involved in the regulation of the level of consciousness, emotions, sleep and wakefulness, autonomic functions, purposeful movements.
IV ventricle- this is the cavity of the rhomboid brain, from top to bottom it continues into the central canal of the spinal cord. The bottom of the IV ventricle, due to its shape, is called the rhomboid fossa (Fig. 8.17). It is formed by the posterior surfaces of the medulla oblongata and the pons, the upper sides of the fossa are the upper, and the lower sides are the lower cerebellar peduncles.
Rice. 8.17. brain stem; back view. The cerebellum is removed, the rhomboid fossa is open
The median sulcus divides the bottom of the fossa into two symmetrical halves, on both sides of the sulcus, medial elevations are visible, expanding in the middle of the fossa into the right and left facial tubercles, where they lie: the nucleus of the VI pair of cranial nerves (abducens nerve), deeper and more lateral - the nucleus of the VII pair ( facial nerve), and downwards the medial eminence passes into the triangle of the hypoglossal nerve, lateral to which is the triangle of the vagus nerve. In triangles, in the thickness of the substance of the brain, the nuclei of the nerves of the same name lie. The upper corner of the rhomboid fossa communicates with the aqueduct of the midbrain. The lateral sections of the rhomboid fossa are called the vestibular fields, where the auditory and vestibular nuclei of the vestibulocochlear nerve (VIII pair of cranial nerves) lie. Transverse cerebral stripes extend from the auditory nuclei to the median sulcus, which are located on the border between the medulla oblongata and the pons and are fibers of the auditory analyzer pathway. In the thickness of the rhomboid fossa lie the nuclei of the V, VI, VII, VIII, IX, X, XI and XII pairs of cranial nerves.
Blood supply to the brain
Blood enters the brain through two paired arteries: the internal carotid and vertebral. In the cranial cavity, both vertebral arteries merge, together forming the main (basal) artery. At the base of the brain, the main artery merges with two carotid arteries, forming a single arterial ring (Fig. 8.18). This cascading mechanism of blood supply to the brain guarantees sufficient blood flow if any of the arteries fail.
Rice. 8.19. Arteries at the base of the brain and the circle of Willis (the right hemisphere of the cerebellum and the right temporal lobe are removed); The circle of Willis is shown as a dotted line.
Three vessels depart from the arterial ring: the anterior, posterior and middle cerebral arteries that feed the cerebral hemispheres. These arteries run along the surface of the brain, and from them, blood is delivered deep into the brain by smaller arteries.
The system of carotid arteries is called the carotid pool, which provides 2/3 of the needs of the brain in arterial blood and supplies blood to the anterior and middle sections of the brain.
The system of arteries "vertebral - main" is called the vertebrobasilar basin, which provides 1/3 of the needs of the brain and delivers blood to the posterior sections.
The outflow of venous blood occurs mainly through the superficial and deep cerebral veins and venous sinuses (Fig. 8.19). Ultimately, blood is sent to the internal jugular vein, which exits the skull through the jugular foramen, located at the base of the skull, lateral to the foramen magnum.
Shells of the brain
The membranes of the brain protect it from mechanical damage and from the penetration of infections and toxic substances (Fig. 8.20).
Rice. 8.19. Veins and venous sinuses of the brain
Fig.8.20. Coronal section through skull meninges and brain
The first layer that protects the brain is called the pia mater. It closely adjoins the brain, goes into all the grooves and cavities (ventricles) that are present in the thickness of the brain itself. The ventricles of the brain are filled with a fluid called cerebrospinal fluid or cerebrospinal fluid. The dura mater is directly adjacent to the bones of the skull. Between the soft and hard shell is the arachnoid (arachnoid) shell. Between the arachnoid and soft shells there is a space (subarachnoid or subarachnoid space) filled with cerebrospinal fluid. Above the furrows of the brain, the arachnoid membrane is thrown over, forming a bridge, and the soft one merges with them. Due to this, cavities called cisterns are formed between the two shells. The cisterns contain cerebrospinal fluid. These tanks protect the brain from mechanical injury, acting as "airbags".
Nerve cells and blood vessels are surrounded by neuroglia - special cell formations that perform protective, supporting and metabolic functions, providing reactive properties of the nervous tissue and participating in the formation of scars, in inflammation reactions, etc.
When the brain is damaged, the mechanism of plasticity is activated, when the preserved structures of the brain take on the functions of the affected areas.