The importance of different parts of the cerebral cortex
brain.
2. Motor functions.
3. Cutaneous and proprioriceptive functions
sensitivity.
4. Auditory functions.
5. Visual functions.
6. Morphological bases of localization of functions in
cerebral cortex.
The core of the motor analyzer
The auditory analyzer core
The core of the visual analyzer
The core of the flavor analyzer
Skin Analyzer Core
7. Bioelectric activity of the brain.
8. Literature.
SIGNIFICANCE OF DIFFERENT AREAS OF LARGE BARK
HEMISPHERE OF THE BRAIN
For a long time, there has been a dispute between scientists about the location (localization) of areas of the cerebral cortex associated with various functions of the body. The most diverse and mutually opposing points of view were expressed. Some believed that each function of our body corresponds to a strictly defined point in the cerebral cortex, while others denied the presence of any centers; They attributed any reaction to the entire cortex, considering it to be completely unambiguous in a functional sense. The conditioned reflex method made it possible for I.P. Pavlov to clarify a number of unclear questions and develop a modern point of view.
In the cerebral cortex, there is no strictly fractional localization of functions. This follows from experiments on animals, when, after the destruction of certain areas of the cortex, for example, the motor analyzer, in a few days the neighboring areas take over the function of the destroyed area and the animal's movements are restored.
This ability of the cortical cells to replace the function of the lost areas is associated with the great plasticity of the cerebral cortex.
IP Pavlov believed that individual areas of the cortex have different functional significance. However, there are no strictly defined boundaries between these areas. Cells from one area move to neighboring areas.
Figure 1. Diagram of the connection between the cortex and receptors.
1 - spinal or medulla oblongata; 2 - diencephalon; 3 - cerebral cortex
In the center of these areas are clusters of the most specialized cells, the so-called analyzer nuclei, and at the periphery, less specialized cells.
In the regulation of body functions, not strictly outlined points are involved, but many nerve elements of the cortex.
Analysis and synthesis of incoming impulses and the formation of a response to them are carried out by significantly larger areas of the cortex.
Consider some areas that are predominantly of one or another meaning. A schematic location of the location of these areas is shown in Figure 1.
Motor functions. The cortical section of the motor analyzer is located mainly in the anterior central gyrus, anterior to the central (Roland) sulcus. In this area there are nerve cells, with the activity of which all movements of the body are associated.
The processes of large nerve cells located in the deep layers of the cortex descend into the medulla oblongata, where a significant part of them intersects, that is, passes to the opposite side. After the transition, they descend along the spinal cord, where the rest of them intersects. In the anterior horns of the spinal cord, they come into contact with the motor nerve cells located here. Thus, the excitation that has arisen in the cortex reaches the motor neurons of the anterior horns of the spinal cord and then flows through their fibers to the muscles. Due to the fact that in the oblong, and partially in the spinal cord, there is a transition (cross) of the motor paths to the opposite side, the excitation that arose in the left hemisphere of the brain enters the right half of the body, and impulses from the right hemisphere enter the left half of the body. That is why hemorrhage, injury or any other damage to one of the sides of the cerebral hemispheres entails a violation of the motor activity of the muscles of the opposite half of the body.
Figure 2. Diagram of individual areas of the cerebral cortex.
1 - motor area;
2 - skin area
and proprioceptive sensitivity;
3 - visual area;
4 - auditory area;
5 - gustatory area;
6 - olfactory area
In the anterior central gyrus, the centers innervating different muscle groups are located so that in the upper part of the motor region there are the centers of movement of the lower extremities, then below the center of the muscles of the trunk, even below the center of the forelimbs and, finally, below all the centers of the muscles of the head.
The centers of different muscle groups are represented differently and occupy uneven areas.
Functions of cutaneous and proprioceptive sensitivity. The area of \u200b\u200bcutaneous and proprioceptive sensitivity in humans is located mainly behind the central (Roland) sulcus in the posterior central gyrus.
Localization of this area in humans can be established by the method of electrical stimulation of the cerebral cortex during operations. Irritation of various parts of the cortex and the simultaneous questioning of the patient about the sensations that he experiences, make it possible to form a fairly clear idea of \u200b\u200bthe indicated area. The so-called muscle feeling is associated with this area. The impulses arising in the proprioceptor-receptors located in the joints, tendons and muscles mainly enter this part of the cortex.
The right hemisphere perceives impulses going along the centripetal fibers mainly from the left, and the left hemisphere mainly from the right half of the body. This explains the fact that a lesion, say, of the right hemisphere will cause a violation of the sensitivity of the predominantly left side.
Auditory functions. The auditory area is located in the temporal lobe of the cortex. When the temporal lobes are removed, complex sound perceptions are disturbed, since the ability to analyze and synthesize sound perceptions is disturbed.
Visual functions. The visual area is located in the occipital lobe of the cerebral cortex. When the occipital lobes of the brain are removed, the dog experiences loss of vision. The animal does not see, bumps into objects. Only pupillary reflexes are preserved. In humans, a violation of the visual region of one of the hemispheres causes the loss of half of the vision of each eye. If the lesion touches the visual region of the left hemisphere, then the functions of the nasal part of the retina of one eye and the temporal part of the retina of the other eye fall out.
This feature of visual impairment is due to the fact that the optic nerves partially intersect on the way to the cortex.
Morphological foundations of dynamic localization of functions in the cerebral cortex large brain (centers of the cerebral cortex).
Knowledge of the localization of functions in the cerebral cortex is of great theoretical importance, since it gives an idea of \u200b\u200bthe nervous regulation of all body processes and its adaptation to the environment. It is also of great practical importance for the diagnosis of lesions in the cerebral hemispheres.
The concept of the localization of functions in the cerebral cortex is primarily associated with the concept of the cortical center. Back in 1874, the Kiev anatomist V. A, Betz made a statement that each area of \u200b\u200bthe cortex differs in structure from other areas of the brain. This was the beginning of the doctrine of the different quality of the cerebral cortex - cytoarchitectonics (cytos - cell, architectones - system). At present, it has been possible to identify more than 50 different parts of the cortex - cortical cytoarchitectonic fields, each of which differs from others in the structure and location of nerve elements. From these fields, indicated by numbers, a special map of the human cerebral cortex is compiled.
P 
about I.P. Pavlov, the center is the brain end of the so-called analyzer. An analyzer is a nervous mechanism, the function of which is to decompose the known complexity of the external and internal world into separate elements, that is, to perform analysis. At the same time, owing to the wide connections with other analyzers, there is also a synthesis of analyzers with each other and with different activities of the organism.
Figure 3. Map of cytoarchitectonic fields of the human brain (according to the Institute of Moeg of the USSR Academy of Medical Sciences) Above - the upper lateral surface, below - the medial surface. Explanation in the text.
Currently, the entire cerebral cortex is considered as a continuous receiving surface. The cortex is a collection of the cortical ends of the analyzers. From this point of view, we will consider the topography of the cortical regions of the analyzers, that is, the most important perceiving areas of the cerebral cortex.
First of all, let us consider the cortical ends of the analyzers that perceive irritations from the internal environment of the body.
1. The nucleus of the motor analyzer, ie, the analyzer of proprioceptive (kinesthetic) stimulation emanating from bones, joints, skeletal muscles and their tendons, is located in the precentral gyrus (fields 4 and 6) and lobulus paracentralis. Motor conditioned reflexes are closed here. IP Pavlov explains the motor paralysis that occurs when the motor zone is damaged not by damage to motor efferent neurons, but by a violation of the motor analyzer nucleus, as a result of which the cortex does not perceive kinesthetic stimuli and movements become impossible. The cells of the motor analyzer nucleus are embedded in the middle layers of the motor cortex. In its deep layers (V, partly VI) there are giant pyramidal cells, which are efferent neurons, which I.P. Pavlov considers as intercalary neurons connecting the cerebral cortex with the subcortical nuclei, nuclei of the cranial nerves and the anterior horns of the spinal cord, i.e. with motor neurons. In the precentral gyrus, the human body, as well as in the posterior gyrus, is projected upside down. In this case, the right motor region is connected with the left half of the body and vice versa, because the pyramidal pathways starting from it intersect partly in the oblong, and partly in the spinal cord. The muscles of the trunk, larynx, pharynx are influenced by both hemispheres. In addition to the precentral gyrus, proprioceptive impulses (muscular-articular sensitivity) also come to the cortex of the postcentral gyrus.
2. The nucleus of the motor analyzer, related to the combined rotation of the head and eyes in the opposite direction, is placed in the middle frontal gyrus, in the premotor region (field 8). Such a turn also occurs upon stimulation of the field 17, located in the occipital lobe in the vicinity of the nucleus of the visual analyzer. Since, when the muscles of the eye contract, not only impulses from the receptors of these muscles, but also impulses from the receptors of these muscles (visual analyzer, field 77) always arrive in the cerebral cortex (motor analyzer, field 8), then various visual stimuli are always combined with different positions eye, set by the contraction of the muscles of the eyeball.
3. The nucleus of the motor analyzer, through which the synthesis of purposeful complex professional, labor and sports movements occurs, is placed in the left (in right-handed) lower parietal lobe, in the gyrus supramarginalis (deep layers of field 40). These coordinated movements, formed according to the principle of temporary connections and developed by the practice of individual life, are carried out through the connection of the gyrus supramarginalis with the precentral gyrus. When field 40 is damaged, the ability to move in general remains, but there is an inability to perform purposeful movements, to act - apraxia (praxia - action, practice).
4. The nucleus of the analyzer of the position and movement of the head - the static analyzer (vestibular apparatus) in the cerebral cortex has not yet been precisely localized. There is reason to believe that the vestibular apparatus is projected in the same area of \u200b\u200bthe cortex as the cochlea, that is, in the temporal lobe. So, with the defeat of fields 21 and 20, lying in the area of \u200b\u200bthe middle and lower temporal gyri, ataxia is observed, that is, a disorder of balance, swaying of the body when standing. This analyzer, which plays a decisive role in man's upright posture, is of particular importance for the work of pilots in jet aircraft, since the sensitivity of the vestibular apparatus on an aircraft is significantly reduced.
5. The nucleus of the analyzer of impulses coming from the viscera and vessels is located in the lower parts of the anterior and posterior central gyri. Centripetal impulses from the viscera, vessels, involuntary muscles and glands of the skin enter this section of the cortex, from where centrifugal paths depart to the subcortical vegetative centers.
In the premotor area (fields 6 and 8), the unification of vegetative functions takes place.
Nerve impulses from the external environment of the body enter the cortical ends of the analyzers of the external world.
1. The nucleus of the auditory analyzer lies in the middle part of the superior temporal gyrus, on the surface facing the insula - fields 41, 42, 52, where the cochlea is projected. The damage leads to deafness.
2. The nucleus of the visual analyzer is located in the occipital lobe - fields 18, 19. On the inner surface of the occipital lobe, along the edges of the sulcus Icarmus, the visual path ends in field 77. The retina of the eye is projected here. When the nucleus of the visual analyzer is damaged, blindness occurs. Above field 17, field 18 is located, with the defeat of which vision is preserved and only visual memory is lost. Even higher is the field, when it is defeated, the orientation in the unfamiliar environment is lost.
3. The nucleus of the gustatory analyzer, according to some data, is located in the inferior postcentral gyrus, close to the centers of the muscles of the mouth and tongue, according to others, in the immediate vicinity of the cortical end of the olfactory analyzer, which explains the close connection of olfactory and gustatory senses. It has been established that a taste disorder occurs when field 43 is affected.
The analyzers of smell, taste and hearing of each hemisphere are connected to the receptors of the corresponding organs of both sides of the body.
4. The core of the skin analyzer (tactile, pain and temperature sensitivity) is located in the postcentral gyrus (fields 7, 2, 3) and in the neuperior parietal region (fields 5 and 7).
A particular type of skin sensitivity - recognition of objects by touch - stereognosia (stereos - spatial, gnosis - knowledge) is connected with a section of the upper parietal lobe cortex (field 7) crosswise: the left hemisphere corresponds to the right hand, the right to the left hand. When the surface layers of field 7 are damaged, the ability to recognize objects by touch is lost, with the eyes closed.
Bioelectric activity of the brain.
Abstraction of brain biopotentials - electroencephalography - gives an idea of \u200b\u200bthe level of physiological activity of the brain. In addition to the method of electroencephalography-recording of bioelectric potentials, the method of encephaloscopy-registration of fluctuations in the brightness of the glow of many points of the brain (from 50 to 200) is used.
The electroencephalogram is an integrative spatio-temporal indicator of spontaneous electrical activity in the brain. It distinguishes between the amplitude (range) of oscillations in microvolts and the frequency of oscillations in hertz. In accordance with this, four types of waves are distinguished in the electroencephalogram: -, -, - and -rhythms. The -rhythm is characterized by frequencies in the range of 8-15 Hz, with an oscillation amplitude of 50-100 μV. It is recorded only in humans and higher apes in a state of wakefulness, with closed eyes and in the absence of external stimuli. Visual stimuli inhibit the -rhythm.
Some people with a vivid visual imagination may not have the -rhythm at all.
An active brain is characterized by (-rhythm. These are electrical waves with an amplitude of 5 to 30 μV and a frequency of 15 to 100 Hz. It is well recorded in the frontal and central regions of the brain. The -rhythm appears during sleep. It is also observed with negative emotions, painful conditions The frequency of the-rhythm potentials is from 4 to 8 Hz, the amplitude is from 100 to 150 μV During sleep, the -rhythm also appears - slow (with a frequency of 0.5-3.5 Hz), high-amplitude (up to 300 μV ) fluctuations in the electrical activity of the brain.
In addition to the considered types of electrical activity, an E-wave (a wave of expectation of a stimulus) and spindle-shaped rhythms are recorded in a person. Waves of anticipation are recorded when performing conscious, expected actions. It precedes the appearance of the expected stimulus in all cases, even with its repeated repetition. Apparently, it can be considered as an electroencephalographic correlate of an action acceptor, which ensures the anticipation of the results of an action before its completion. Subjective readiness to respond to the action of a stimulus in a strictly defined way is achieved by a psychological attitude (D. N. Uznadze). Spindle-shaped rhythms of variable amplitude, with a frequency of 14 to 22 Hz, appear during sleep. Various forms of life activity lead to a significant change in the rhythms of bioelectrical activity of the brain.
With mental work, the -rhythm increases, while the -rhythm disappears. With muscular work of a static nature, desynchronization of the electrical activity of the brain is observed. Fast oscillations with low amplitude appear. During dynamic operation, ne-. The periods of desynchronized and synchronized activity are observed, respectively, during the moments of work and rest.
The formation of a conditioned reflex is accompanied by desynchronization of brain wave activity.
Desynchronization of waves occurs during the transition from sleep to wakefulness. In this case, the spindle-shaped rhythms of sleep are replaced
-rhythm, the electrical activity of the reticular formation increases. Synchronization (identical in phase and wave direction)
characteristic of the inhibitory process. It is most pronounced when the reticular formation of the brain stem is turned off. Electroencephalogram waves, according to most researchers, are the result of the summation of inhibitory and excitatory postsynaptic potentials. The electrical activity of the brain is not a simple reflection of metabolic processes in the nervous tissue. It was established, in particular, that in the impulse activity of individual clusters of nerve cells, signs of acoustic and semantic codes are found.
In addition to specific nuclei of the thalamus, associative nuclei arise and develop, which have connections with the neocortex and determine the development of the telencephalon. The third source of afferent influences on the cerebral cortex is the hypothalamus, which plays the role of the highest regulatory center of autonomic functions. In mammals, phylogenetically more ancient parts of the anterior hypothalamus are associated with ...
The formation of conditioned reflexes becomes difficult, memory processes are disturbed, the selectivity of reactions is lost and their immoderate increase is noted. The large brain consists of almost identical halves - the right and left hemispheres, which are connected by the corpus callosum. Commissural fibers connect symmetrical areas of the cortex. However, the cortex of the right and left hemispheres is not symmetrical not only externally, but also ...
The approach to assessing the mechanisms of work of the higher parts of the brain using conditioned reflexes was so successful that it allowed Pavlov to create a new branch of physiology - "Physiology of higher nervous activity", the science of the mechanisms of work of the cerebral hemispheres. UNCONDITIONAL AND CONDITIONAL REFLEXES The behavior of animals and humans is a complex system of interrelated ...
- 1) at the beginning of the 19th century. F. Gall suggested that the substrate for various psychic "abilities" (honesty, frugality, love, etc.))) are small areas of n. shopping mall KBPs that grow with the development of these abilities. Gall believed that various abilities have a clear localization in the GM and that they can be determined by the protrusions on the skull, where the corresponding to the given ability is supposedly growing. shopping mall and begins to bulge, while forming a tubercle on the skull.
- 2) In the 40s of the XIX century. Gall is opposed by Flurance, who, on the basis of experiments with extirpation (removal) of parts of the GM, puts forward a provision on the equipotentiality (from the Latin equus - "equal") of the functions of the KBP. In his opinion, GM is a homogeneous mass that functions as a single integral organ.
- 3) The French scientist P. Broca laid the foundation of the modern doctrine of the localization of functions in the KBP, who in 1861 identified the motor center of speech. Subsequently, the German psychiatrist K. Wernicke in 1873 discovered the center of verbal deafness (impaired understanding of speech).
Since the 70s. The study of clinical observations has shown that the defeat of limited areas of the CBD leads to a predominant loss of quite specific mental functions. This gave grounds to single out individual areas in the PCB, which began to be considered as nerve centers responsible for certain mental functions.
Summarizing the observations carried out on the wounded with brain damage during the First World War, in 1934 the German psychiatrist K. Kleist drew up the so-called localization map, in which even the most complex mental functions were correlated with limited areas of the PCD. But the approach of direct localization of complex mental functions in certain areas of the CPD is untenable. Analysis of the facts of clinical observations showed that violations of such complex mental processes, like speech, writing, reading, counting, can occur with completely different lesions of the PCD. The defeat of limited areas of the cerebral cortex, as a rule, leads to disruption of a whole group of mental processes.
4) a new trend has emerged, which considers mental processes as a function of the entire GM as a whole ("anti-localizationism"), but is untenable.
Through the works of I. M. Sechenov, and then I. P. Pavlov, the doctrine of the reflex foundations of mental processes and the reflex laws of the KBP operation, it led to a radical revision of the concept of "function" - began to be considered as a set of complex temporary connections. The foundations were laid for new concepts of dynamic localization of functions in KBP.
Summing up, we can highlight the main provisions of the theory of systemic dynamic localization of higher mental functions:
- - each mental function is a complex functional system and is provided by the brain as a whole. At the same time, various brain structures make their own specific contribution to the implementation of this function;
- - various elements of the functional system can be located in areas of the brain that are quite distant from each other and, if necessary, replace each other;
- - when a certain part of the brain is damaged, a "primary" defect occurs - a violation of a certain physiological principle of work inherent in a given brain structure;
- - as a result of the defeat of a common link included in different functional systems, "secondary" defects may arise.
Currently, the theory of systemic dynamic localization of higher mental functions is the main theory explaining the relationship between the psyche and the brain.
Histological and physiological studies have shown that KBP is a highly differentiated apparatus. Different areas of the cerebral cortex have a different structure. The neurons of the cortex are often so specialized that among them one can distinguish those that respond only to very special stimuli or to very special signs. A number of sensory centers are located in the cerebral cortex.
Localization is firmly established in the so-called "projection" zones - cortical fields directly connected by their own paths with the underlying parts of the NS and the periphery. The functions of KBP are more complex, phylogenetically younger, and cannot be narrowly localized; very extensive areas of the cortex, and even the entire cortex as a whole, are involved in the implementation of complex functions. At the same time, within the KBP, there are areas, the lesion of which causes varying degrees, for example, speech disorders, disorders of gnosia and praxia, the topodiagnostic value of which is also significant.
Instead of representing the KBP as, to a certain extent, an isolated superstructure over other floors of the NS with narrowly localized, surface-connected (associative) and periphery (projection) areas, I.P. Pavlov created the doctrine of the functional unity of neurons belonging to different departments nervous system - from receptors on the periphery to the cerebral cortex - the doctrine of analyzers. What we call the center is the higher, cortical, section of the analyzer. Each analyzer is associated with specific areas of the cerebral cortex
3) The doctrine of the localization of functions in the cerebral cortex developed in the interaction of two opposite concepts - anti-localizationism, or equiponticalism (Flurance, Lashley), which denies the localization of functions in the cortex, and a narrow localization psychomorphologism, which tried in its extreme versions (Gall ) localize in limited areas of the brain even such mental qualities as honesty, secrecy, love for parents. Of great importance was the discovery by Fritsch and Gitzig in 1870 of areas of the cortex, the irritation of which caused a motor effect. Other researchers have also described areas of the cortex associated with skin sensitivity, vision, and hearing. Clinicians-neurologists and psychiatrists also testify to the violation of complex mental processes in focal brain lesions. The foundations of the modern view of the localization of functions in the brain were laid by Pavlov in his theory of analyzers and the theory of dynamic localization of functions. According to Pavlov, an analyzer is a complex, functionally unified neural ensemble that serves to decompose (analyze) external or internal stimuli into separate elements. It starts with a receptor at the periphery and ends in the cerebral cortex. Cortical centers are the cortical sections of the analyzers. Pavlov showed that the cortical representation is not limited to the projection zone of the corresponding conductors, going far beyond its limits, and that the cortical zones of various analyzers overlap each other. The result of Pavlov's research was the doctrine of the dynamic localization of functions, suggesting the possibility of the participation of the same nervous structures in the provision of various functions. Localization of functions means the formation of complex dynamic structures or combination centers, consisting of a mosaic of excited and inhibited far-removed points of the nervous system, united in common work according to the nature of the required end result... The doctrine of the dynamic localization of functions received its further development in the works of Anokhin, who created the concept of a functional system as a circle of certain physiological manifestations associated with the performance of a certain function. The functional system includes, each time, in different combinations, various central and peripheral structures: cortical and deep nerve centers, pathways, peripheral nerves, executive organs. The same structures can be included in a variety of functional systems, which expresses the dynamism of the localization of functions. IP Pavlov believed that individual areas of the cortex have different functional significance. However, there are no strictly defined boundaries between these areas. Cells from one area move to neighboring areas. In the center of these areas are clusters of the most specialized cells, the so-called analyzer nuclei, and at the periphery, less specialized cells. In the regulation of body functions, not strictly outlined points are involved, but many nerve elements of the cortex. Analysis and synthesis of incoming impulses and the formation of a response to them are carried out by significantly larger areas of the cortex. According to Pavlov, the center is the brain end of the so-called analyzer. An analyzer is a neural mechanism whose function is to decompose the known complexity of external and inner peace into separate elements, that is, to make an analysis. At the same time, owing to the broad connections with other analyzers, the synthesizing of analyzers with each other and with different activities of the organism takes place here.
Motor zones of the cortex... Movement occurs when the cortex is irritated in the area of \u200b\u200bthe precentral gyrus. The zone that controls the movements of the hand, tongue, and facial muscles is especially large.
Sensory areas of the cortex: somatic (skin) human sensitivity, feelings of touch, pressure, cold and heat are projected into the postcentral gyrus. In the upper part there is a projection of the skin sensitivity of the legs and trunk, below - the arms and even lower - the head. Proprioceptive sensitivity (muscular sense) is projected into the postcentral and precentral gyrus . Visual zone the cortex is located in the occipital lobe. Auditory zone the cortex is located in the temporal lobes of the cerebral hemispheres. Olfactory zone the cortex is located at the base of the brain. Projection taste analyzer , localized in the region of the mouth and tongue of the postcentral gyrus .
Associative zones of the cortex. The neurons of these areas are not connected either with the sensory organs or with the muscles, they carry out a connection between different areas of the cortex, integrating, combining all impulses entering the cortex into integral acts of learning (reading, speech, writing), logical thinking, memory and providing the possibility of an appropriate response behavior. These areas include the frontal and parietal lobes of the cerebral cortex, which receive information from the associative nuclei of the thalamus.
Lateral ventricles (right and left) are the cavities of the telencephalon, lie below the level of the corpus callosum in both hemispheres and communicate through the interventricular openings with the third ventricle. They are irregular shape and consist of anterior, posterior and lower horns and a central part connecting them.
Topic 17. Basal nuclei
The basal nuclei of the telencephalon are accumulations of gray matter within the hemispheres. These include striatum (striatum)consisting of tailed and lenticular nuclei interconnected. The lenticular core is divided into two parts: located outside shell and lying inside pallidus... The caudate nucleus and shells combine to form neostriatum... They are subcortical motor centers. Outside the lenticular nucleus, there is a thin plate of gray matter - a fence. In the anterior part of the temporal lobe lies amygdala... Between the basal nuclei and the thalamus there are layers of white matter, the inner, outer and outermost capsules. Pathways pass through the inner capsule.
Topic 1. Limbic system
In the endbrain are the formations that make up the limbic system: the cingulate gyrus, hippocampus, mammary bodies, anterior thalamus, amygdala, fornix, transparent septum, hypothalamus. They are involved in maintaining the constancy of the internal environment of the body, the regulation of the autonomic function and the formation of emotions and motivations. This system is otherwise called the "visceral brain". This is where information comes from internal organs... When the limbic cortex is irritated, vegetative functions change: blood pressure, respiration, movements of the digestive tract, tone of the uterus and bladder.
Topic 19. Fluids of the central nervous system: circulatory and cerebrospinal fluid systems.The blood-brain barrier.
Blood supplythe brain is carried out by the left and right internal carotid and branches of the vertebral arteries. Based on the brain, arterial circle (Wilisian circle), which provides favorable conditions for the blood circulation of the brain. From the arterial circle to the hemispheres are the left and right anterior, middle and posterior cerebral arteries. Blood from the capillaries is collected in the venous vessels and from the brain flows into the sinuses of the dura mater.
The cerebrospinal fluid system.The brain and spinal cord are washed by cerebrospinal fluid (CSF), which protects the brain from mechanical damage, maintains intracranial pressure, and takes part in the transport of substances from the blood to the brain tissues. From the lateral ventricles, cerebrospinal fluid flows through the Monroe opening into the third ventricle, and then through the aqueduct into the fourth ventricle. From it, the cerebrospinal fluid passes into the spinal canal and into the subarachnoid space.
Blood-brain barrier... Between neurons and blood in the brain, there is a so-called blood-brain barrier, which ensures the selective flow of substances from the blood to the nerve cells. This barrier has a protective function, as it ensures the constancy of the cerebrospinal fluid. It consists of astrocytes, capillary endothelial cells, epithelial cells of the vascular plexus of the brain.
Seminar Topics
1. Role of the spinal and cranial nerves in sensory perception
2. The role of the telencephalon in the perception of signals from the external and internal environment
3. The main stages of the evolution of the central nervous system and ontogenesis of the nervous system
4. Brain Diseases
5. Aging brain
Self-study assignments
1. Draw a frontal section of the spinal cord with all the notation you know.
2. Draw a sagittal section of the brain showing all of its sections.
3. Draw a sagittal section of the spinal cord and brain, showing all the cavities in the brain.
4. Draw a sagittal section of the brain showing all the structures you know.
Questions for self-control
1. Give the definitions of the basic concepts of the anatomy of the central nervous system:
Nervous system concept;
Central and peripheral nervous system;
Somatic and autonomic nervous system;
Axes and planes in anatomy.
2. What is the basic structural unit of the nervous system?
3. What are the main structural elements nerve cell.
4. Give the classification of nerve cell processes.
5. List the sizes and shapes of neurons. Tell us about the application of microscopic techniques.
6. Tell us about the nucleus of the nerve cell.
7. What are the main structural elements of neuroplasm?
8. Tell us about the nerve cell sheath.
9. What are the main building blocks of a synapse?
10. What is the role of neurotransmitters in the nervous system?
11. What are the main types of glia in the nervous system?
12. What is the role of the myelin sheath of the nerve fiber for conducting nerve impulses?
13. Name the types of the nervous system in phylogenesis.
14. List the structural features of the reticular nervous system.
15. List the structural features of the nodal nervous system.
16. List the structural features of the tubular nervous system.
17. Expand the principle of bilateral symmetry in the structure of the nervous system.
18. Expand the principle of cephalization in the development of the nervous system.
19. Describe the structure of the nervous system of coelenterates.
20. What is the structure of the nervous system of annelids?
21. What is the structure of the nervous system of molluscs?
22. What is the structure of the nervous system of insects?
23. What is the structure of the vertebrate nervous system?
24. Give comparative characteristics the structure of the nervous system of lower and higher vertebrates.
25. Describe the formation of the neural tube from the ectoderm.
26. Describe the stage of the three brain bubbles.
27. Describe the stage of the five brain bubbles.
28. The main divisions of the central nervous system in a newborn.
29. The reflex principle of the structure of the nervous system.
30. What is the general structure of the spinal cord?
31. Describe the segments of the spinal cord.
32. What is the purpose of the anterior and posterior roots of the spinal cord?
33. Segmental apparatus of the spinal cord. What is the organization of the spinal reflex?
34. What is the structure of the gray matter of the spinal cord?
35. What is the structure of the white matter of the spinal cord?
36. Describe the commissural and suprasegmental apparatus of the spinal cord.
37. What is the role of the ascending pathways of the spinal cord in the central nervous system?
38. What is the role of the descending pathways of the spinal cord in the central nervous system?
39. What are spinal nodes?
40. What are the consequences of spinal cord injury?
41. Describe the development of the spinal cord in ontogenesis.
42. What are the structural features of the main membranes of the central nervous system?
43. Describe the reflex principle of the organization of the central nervous system.
44. What are the main parts of the diamond-shaped brain.
45. Describe the dorsal surface of the medulla oblongata.
46. \u200b\u200bDescribe the ventral surface of the medulla oblongata.
47. What are the functions of the main nuclei of the medulla oblongata?
48. What are the functions of the respiratory and vasomotor centers of the medulla oblongata?
49. What is the general structure of the fourth ventricle, the cavity of the rhomboid brain?
50. Name the features of the structure and function of the cranial nerves.
51. List the characteristics of the sensory, motor and autonomic nuclei of the cranial nerves.
52. What is the purpose of the bulbar parasympathetic center of the brain?
53. What are the consequences of bulbar disorders?
54. What is the general structure of the bridge?
55. List the nuclei of the cranial nerves lying at the level of the bridge.
56. What reflexes in the central nervous system correspond to the auditory, vestibular nuclei of the pons?
57. Tell us about the ascending and descending paths of the bridge.
58. What are the functions of the lateral and medial lemniscal pathways?
59. What is the purpose of the reticular formation of the brainstem in the CNS?
60. What is the role of the blue spot in the organization of brain functions. What is the noradrenergic system of the brain?
61. What is the role of the suture nuclei in the central nervous system. What is the serotonergic system of the brain?
62. What is the general structure of the cerebellum. What are its functions in the central nervous system?
63. List the evolutionary formations of the cerebellum.
64. What are the connections of the cerebellum with other parts of the central nervous system. Front, middle and hind peduncles of the cerebellum?
65. Cerebellar cortex. The tree of life of the cerebellum.
66. Describe the cellular structure of the cerebellar cortex.
67. What is the role of the subcortical nuclei of the cerebellum in the central nervous system?
68. What are the consequences of cerebellar disorders?
69. What is the role of the cerebellum in the organization of movements?
70. What are the main functions in the central nervous system of the midbrain. What is the sylvian plumbing.
71. What is the structure of the midbrain roof. Anterior and posterior tubercles of the quadruple and their purpose?
72. What is the purpose of the main cores of the tire?
73. What is the purpose of the mesencephalic parasympathetic center?
74. What is a near-water gray matter for? Expand the features of the organization of the pain system in the central nervous system.
75. What are the red nuclei of the midbrain. What is the definition of decerebration stiffness?
76. Black nucleus and ventral tegmental area. What is the role of the dopaminergic system of the brain in the central nervous system?
77. Descending and ascending pathways of the midbrain. Pyramidal and extrapyramidal systems of the central nervous system.
78. What is the structure and purpose of the legs of the brain?
79. What is the purpose of the dorsal and ventral midbrain chiasm?
80. Describe the general structure of the diencephalon and its main functions. What is the location of the third ventricle?
81. What are the main parts of the thalamic brain.
82. Describe the structure and function of the thalamus.
83. Describe the structure and function of the supra-thalamic area.
84. Describe the structure and function of the zathalamic area.
85. What is the role of the hypothalamus in organizing the functions of the central nervous system?
86. Neurohumoral brain function. Epiphysis and pituitary gland, their location and purpose.
87. What is the role of the Peipets circle in the organization of adaptive behavior.
88. The hippocampus, its structure and function.
89. The cingulate cortex, its structure and functions.
90. Almond-shaped complex, its cost and functions.
91. Emotional and motivational sphere and its brain supply.
92. What are the systems of "reward" and "punishment" of the brain? Self-irritation reaction.
93. Neurochemical organization of the brain's reinforcing systems.
94. What are the consequences of damage to individual formations of the limbic system? Animal studies.
95. Describe the general structure of the telencephalon. What is its role in providing adaptive behavior in humans and animals?
96. What are the main functions of the striatum.
97. Evolutionary formations of the striatum.
98. Caudate nucleus, its location and purpose. Nigrostriatal system of the brain.
99. Ventral striatum, its structure and functions. Mesolimbic system of the brain.
100. General structure of the cerebral hemispheres (lobes, grooves, convolutions).
101. Dorso-lateral surface of the cerebral cortex.
102. Medial and basal surfaces of the cerebral cortex.
103. What is the role of interhemispheric asymmetry in the organization of adaptive behavior. Corpus callosum.
104. Cytoarchitectonics of the cerebral cortex (layers of the cortex and Brodmann's fields).
105. Evolutionary formations of the cerebral cortex (new cortex, old cortex, ancient cortex) and their functions.
106. Projection and associative areas of the cerebral cortex and their purpose.
107. Speech-sensory and speech-motor centers of the cerebral cortex.
108. Sensomotor cortex, its localization. Human body projections in the sensorimotor cortex.
109. Visual, auditory, olfactory, gustatory cortical projections.
110. Fundamentals of topical diagnostics in case of damage to areas of the cerebral cortex.
111. Frontal and parietal cortex and their role in providing the adaptive activity of the brain.
Lecture 12. LOCALIZATION OF FUNCTIONS IN THE LARGE HEMISPHERE CORRECT Cortical zones. Projection cortical zones: primary and secondary. Motor (motor) zones of the cerebral cortex. Tertiary cortical zones.
Loss of functions, observed with damage to various parts of the cortex (inner surface). 1 - olfactory disorders (with unilateral damage are not observed); 2 - visual disturbances (hemianopsia); 3 - sensitivity disorders; 4 - central paralysis or paresis. The data of experimental studies on the destruction or removal of certain sections of the cortex and clinical observations indicate the confinement of functions to the activity of certain sections of the cortex. The area of \u200b\u200bthe cerebral cortex that has some specific function is called the cortical area. Distinguish between projection, associative cortical zones and motor (motor).
The projected cortex is the cortical representation of the analyzer. The neurons of the projection zones receive signals of the same modality (visual, auditory, etc.). There are: - primary projection zones; - secondary projection zones, providing an integrative function of perception. In the zone of one or another analyzer, tertiary fields, or associative zones are also distinguished.
The primary projection fields of the cortex receive information mediated through the smallest number of switchings in the subcortex (thalamus, diencephalon). In these fields, the surface of peripheral receptors is projected. Nerve fibers enter the cerebral cortex mainly from the thalamus (these are afferent inputs).
The projection zones of the analyzer systems occupy outer surface the cortex of the posterior parts of the brain. This includes the visual (occipital), auditory (temporal), and general sensory (parietal) areas of the cortex. The cortical section also includes the representation of gustatory, olfactory, visceral sensitivity
Primary sensory areas (Brodmann's fields): visual - 17, auditory - 41 and somatosensory - 1, 2, 3 (collectively they are called the sensory cortex), motor (4) and premotor (6) cortex
Primary sensory areas (Brodmann's fields): visual - 17, auditory - 41 and somatosensory - 1, 2, 3 (collectively they are called the sensory cortex), motor (4) and premotor (6) cortex Each field of the cerebral cortex is characterized by a special composition neurons, their location and connections between them. The fields of the sensory cortex, in which the primary processing of information from the sensory organs occurs, differ sharply from the primary motor cortex, which is responsible for the formation of commands for voluntary muscle movements.
The motor cortex is dominated by neurons, shaped like pyramids, and the sensory cortex is represented mainly by neurons, the shape of the bodies of which resembles grains, or granules, which is why they are called granular. The structure of the cerebral cortex I. molecular II. outer granular III. outer pyramidal IV. internal granular V. ganglion (giant pyramids) VI. polymorphic
The neurons of the primary projection zones of the cortex are generally of the highest specificity. So, for example, neurons of the visual areas selectively respond to shades of color, direction of movement, the nature of lines, etc. However, in the primary zones of individual areas of the cortex there are also multimodal type neurons that react to several types of stimuli and neurons, the reaction of which reflects the effect of nonspecific ( limbicoreticular) systems.
In the primary fields, the projection afferent fibers end. So, fields 1 and 3, occupying the medial and lateral surface of the posterior central gyrus, are the primary projection fields of skin sensitivity of the body surface.
The functional organization of the projection zones in the cortex is based on the principle of topical localization. Periphery sensing elements located next to each other (for example, skin areas) are also projected on the cortical surface next to each other.
In the medial part, the lower limbs are represented, and the projections of the receptor fields of the skin surface of the head are located at the lowest on the lateral part of the gyrus. In this case, areas of the body surface richly supplied with receptors (fingers, lips, tongue) are projected onto a larger area of \u200b\u200bthe cortex than areas with fewer receptors (thigh, back, shoulder).
Fields 17-19, located in the occipital lobe, are the visual center of the cortex, the 17th field, which occupies the occipital pole itself, is primary. The adjacent 18th and 19th fields function as secondary fields and receive inputs from the 17th field.
The temporal lobes contain auditory projection fields (41, 42). Next to them, on the border of the temporal, occipital and parietal lobes, there are 37th, 39th and 40th, characteristic only for the human cerebral cortex. Most people have a speech center in these fields of the left hemisphere, which is responsible for the perception of spoken and written speech.
Secondary projection fields, receiving information from the primary ones, are located next to them. For the neurons of these fields, the perception of complex signs of stimuli is characteristic, however, the specificity corresponding to the neurons of the primary zones is preserved. The complication of the detector properties of the neurons of the secondary zones can occur through the convergence of the neurons of the primary zones on them. In the secondary zones (18th and 19th Brodmann fields), detectors of more complex contour elements appear: edges of limited line length, angles with different orientations, etc.
Motor (motor) zones of the cerebral cortex are areas of the motor cortex, the neurons of which cause a motor act. The motor areas of the cortex are located in the precentral gyrus of the frontal lobe (in front of the projection zones of skin sensitivity). This part of the cortex is occupied by fields 4 and 6. From the V layer of these fields, the pyramidal path begins, ending on the motor neurons of the spinal cord.
Premotor zone (field 6) The premotor cortex is located in front of the motor zone, it is responsible for muscle tone and carries out coordinated movements of the head and trunk. The main efferent exits from the cortex are the axons of the pyramids of the V layer. These are efferent, motor neurons involved in the regulation of motor functions.
Tertiary or interanalyzer zones (associative) Prefrontal zone (fields 9, 10, 45, 46, 47, 11), parietotemporal (fields 39, 40) Afferent and efferent projection zones of the cortex occupy a relatively small area of \u200b\u200bit. Most of the surface of the cortex is occupied by tertiary or inter-analytic zones, called associative. They receive polymodal inputs from the sensory areas of the cortex and thalamic associative nuclei and have outputs to the motor areas of the cortex. Associative zones provide the integration of sensory inputs and play an essential role in mental activity (learning, thinking).
Functions of different zones of the neocortex: 5 3 7 6 4 1 2 Memory, needs Behavior trigger 1. Occipital lobe - visual cortex. 2. The temporal lobe is the auditory cortex. 3. The anterior part of the parietal lobe - pain, skin and muscle sensitivity. 4. Inside the lateral furrow (insular lobe) - vestibular sensitivity and taste. 5. The posterior part of the frontal lobe is the motor cortex. 6. The posterior part of the parietal and temporal lobes - the associative parietal cortex: unites signal streams from different sensory systems, speech centers, centers of thought. 7. The anterior part of the frontal lobe - the associative frontal cortex: taking into account sensory signals, signals from the centers of needs, memory and thinking, makes decisions about launching behavioral programs ("center of will and initiative").
Separate large associative areas are located next to the corresponding sensory areas. Some associative zones perform only a limited specialized function and are associated with other associative centers capable of subjecting information to further processing. For example, the sound associative zone analyzes sounds by categorizing them and then transmits signals to more specialized zones, such as the speech associative zone, where the meaning of the words heard is perceived.
The associative fields of the parietal lobe combine information from the somatosensory cortex (from the skin, muscles, tendons, and joints with respect to body position and movements) with visual and auditory information from the visual and auditory cortex of the occipital and temporal lobes. This combined information helps to have an accurate picture of your own body while moving around in the surrounding space.
Wernicke's area and Broca's area are two areas of the brain involved in the process of reproducing and understanding information related to speech. Both areas are located along the Sylvian groove (the lateral groove of the cerebral hemispheres). Aphasia is a complete or partial loss of speech due to local brain lesions.
Localization of functions in the cerebral cortex
General characteristics.In certain areas of the cerebral cortex, mainly neurons are concentrated that perceive one type of stimulus: the occipital region - light, the temporal lobe - sound, etc. However, after removing the classic projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved. According to the theory of IP Pavlov in the cerebral cortex there is a "nucleus" of the analyzer (cortical end) and "scattered" neurons throughout the cortex. Modern concept localization of functions is based on the principle of multifunctionality (but not equivalence) of cortical fields. The property of multifunctionality allows one or another cortical structure to be included in the provision of various forms of activity, while realizing the main, genetically inherent function of it (OS Adrianov). The degree of multifunctionality of various cortical structures is not the same. It is higher in the fields of the associative cortex. Multifunctionality is based on the multichannel flow of afferent excitation into the cerebral cortex, overlapping of afferent excitations, especially at the thalamic and cortical levels, the modulating effect of various structures, for example, nonspecific thalamic nuclei, basal ganglia on cortical functions, the interaction of cortical-subcortical and intercortical pathways of excitation. With the help of microelectrode technology, it was possible to register in various areas of the cerebral cortex the activity of specific neurons responding to stimuli of only one type of stimulus (only to light, only to sound, etc.), i.e., there is multiple representation of functions in the cerebral cortex ...
Currently, the division of the cortex into sensory, motor and associative (nonspecific) zones (areas) is accepted.
Sensory areas of the cortex.Sensory information enters the projection cortex, cortical parts of the analyzers (I.P. Pavlov). These zones are located mainly in the parietal, temporal and occipital lobes. The ascending pathways into the sensory cortex come mainly from relay sensory nuclei in the thalamus.
Primary sensory zones - these are areas of the sensory cortex, irritation or destruction of which causes clear and constant changes in the sensitivity of the organism (the nucleus of the analyzers according to I.P. Pavlov). They consist of monomodal neurons and form sensations of the same quality. In primary sensory zones, there is usually a clear spatial (topographic) representation of body parts and their receptor fields.
The primary projection zones of the cortex consist mainly of neurons of the 4th afferent layer, which are characterized by a clear topical organization. A significant proportion of these neurons have the highest specificity. So, for example, the neurons of the visual areas selectively respond to certain signs of visual stimuli: some to shades of color, others to the direction of movement, and still others to the nature of the lines (edge, strip, slope of the line), etc. However, it should be noted that the primary zones of individual areas of the cortex also include multimodal neurons that respond to several types of stimuli. In addition, there are also neurons, the response of which reflects the impact of non-specific (limbic-reticular, or modulating) systems.
Secondary sensory areas are located around the primary sensory zones, are less localized, their neurons respond to the action of several stimuli, i.e. they are polymodal.
Localization of sensory zones. The most important sensory area is parietal lobepostcentral gyrus and the corresponding part of the paracentral lobule on the medial surface of the hemispheres. This zone is designated as somatosensory areaI. There is a projection of the skin sensitivity on the opposite side of the body from tactile, pain, temperature receptors, interoceptive sensitivity and sensitivity of the musculoskeletal system - from muscle, articular, tendon receptors (Fig. 2).
Figure: 2. Diagram of the sensory and motor homunculi
(according to W. Penfield, T. Rasmussen). Frontal plane section of the hemispheres:
and- projection of the general sensitivity in the cortex of the postcentral gyrus; b- projection of the motor system in the cortex of the precentral gyrus
In addition to the somatosensory region I, there are somatosensory areaII smaller, located at the border of the intersection of the central groove with the upper edge temporal lobe,deep in the lateral groove. The accuracy of localization of body parts is less pronounced here. A well-studied primary projection area is auditory cortex(fields 41, 42), which is located in the depth of the lateral groove (cortex of the transverse temporal gyri of Heschl). The projection cortex of the temporal lobe also includes the center of the vestibular analyzer in the superior and middle temporal gyri.
AT occipital lobelocated primary visual area(bark of part of the wedge-shaped gyrus and lingular lobule, field 17). Here there is a topical representation of retinal receptors. Each point of the retina corresponds to its own section of the visual cortex, while the area of \u200b\u200bthe macula has a relatively large area of \u200b\u200brepresentation. Due to the incomplete intersection of the visual pathways, the retina halves of the same name are projected into the visual area of \u200b\u200beach hemisphere. The presence in each hemisphere of the projection of the retina of both eyes is the basis of binocular vision. Bark is located near field 17 secondary visual area(fields 18 and 19). The neurons of these zones are polymodal and respond not only to light, but also to tactile and auditory stimuli. In this visual area, a synthesis of various types of sensitivity occurs, more complex visual images and their identification appear.
In the secondary zones, the leading are the 2nd and 3rd layers of neurons, for which the bulk of information about the environment and the internal environment of the body, which has entered the sensory cortex, is transmitted for its further processing to the associative cortex, after which it is initiated (if necessary) behavioral reaction with the obligatory participation of the motor cortex.
Motor zones of the cortex.There are primary and secondary motor zones.
AT primary motor zone (precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and limbs. It has a clear topographic projection of the muscles of the body (see Fig. 2). The main regularity of topographic representation is that the regulation of muscle activity, providing the most accurate and varied movements (speech, writing, facial expressions), requires the participation of large areas of the motor cortex. Irritation of the primary motor cortex causes contraction of the muscles on the opposite side of the body (for the muscles of the head, contraction can be bilateral). With the defeat of this cortical zone, the ability to fine coordinated movements of the limbs, especially the fingers, is lost.
Secondary motor area (field 6) is located both on the lateral surface of the hemispheres, in front of the precentral gyrus (premotor cortex), and on the medial surface corresponding to the cortex of the superior frontal gyrus (additional motor area). Functionally, the secondary motor cortex is of paramount importance in relation to the primary motor cortex, realizing higher motor functions associated with the planning and coordination of voluntary movements. Here, a slowly increasing negative readiness potential,arising approximately 1 s before the start of the movement. The cortex of field 6 receives the bulk of impulses from the basal ganglia and cerebellum, and participates in the recoding of information about the plan of complex movements.
Irritation of the cortex of field 6 causes complex coordinated movements, for example, turning the head, eyes and trunk in the opposite direction, friendly contractions of the flexors or extensors on the opposite side. The premotor cortex contains the motor centers associated with human social functions: the center of written speech in the posterior part of the middle frontal gyrus (field 6), Broca's motor speech center in the posterior part of the inferior frontal gyrus (field 44), providing speech praxis, as well as the musical motor center (field 45), providing the tonality of speech, the ability to sing. The neurons of the motor cortex receive afferent inputs through the thalamus from muscle, articular and cutaneous receptors, from the basal ganglia and cerebellum. The main efferent outlet of the motor cortex to the stem and spinal motor centers is the pyramidal cells of layer V. The main lobes of the cerebral cortex are shown in Fig. 3.
Figure: 3. The four main lobes of the cerebral cortex (frontal, temporal, parietal and occipital); side view. They contain the primary motor and sensory areas, motor and sensory areas of a higher order (second, third, etc.) and the associative (non-specific) cortex.
Associative areas of the cortex(nonspecific, intersensory, inter-analytic cortex) include areas of the neocortex that are located around the projection areas and next to the motor areas, but do not directly perform sensory or motor functions, therefore they cannot be attributed primarily to sensory or motor functions, the neurons of these areas have large learning ability. The boundaries of these areas are not clearly marked. The associative cortex is phylogenetically the youngest part of the neocortex, which has received the greatest development in primates and humans. In humans, it makes up about 50% of the entire cortex or 70% of the neocortex. The term "associative cortex" arose in connection with the existing idea that these zones, due to the cortico-cortical connections passing through them, connect the motor zones and at the same time serve as a substrate for higher mental functions. The main associative cortex zonesare: the parieto-temporo-occipital, prefrontal cortex of the frontal lobes and the limbic associative zone.
The neurons of the associative cortex are polysensory (polymodal): they usually respond not to one (like the neurons of the primary sensory zones), but to several stimuli, that is, the same neuron can be excited by stimulation of auditory, visual, skin and other receptors. The polysensory nature of neurons in the associative cortex is created by cortical-cortical connections with different projection zones, connections with the associative nuclei of the thalamus. As a result, the associative cortex is a kind of collector of various sensory excitations and is involved in the integration of sensory information and in ensuring the interaction of sensory and motor areas of the cortex.
The associative areas occupy the 2nd and 3rd cellular layers of the associative cortex, where powerful unimodal, multi-modal and nonspecific afferent streams meet. The work of these parts of the cerebral cortex is necessary not only for the successful synthesis and differentiation (selective discrimination) of stimuli perceived by a person, but also for the transition to the level of their symbolization, that is, for operating with the meanings of words and using them for abstract thinking, for the synthetic nature of perception.
Since 1949, D. Hebb's hypothesis has become widely known, postulating the coincidence of presynaptic activity with the discharge of a postsynaptic neuron as a condition for synaptic modification, since not all synapse activity leads to excitation of a postsynaptic neuron. Based on the hypothesis of D. Hebb, it can be assumed that individual neurons of the associative zones of the cortex are connected by various pathways and form cellular ensembles that distinguish "patterns", i.e. corresponding to unitary forms of perception. These connections, as D. Hebb noted, are so well developed that it is enough to activate one neuron, as the whole ensemble is excited.
The apparatus that plays the role of a regulator of the level of wakefulness, as well as selectively modulates and actualizes the priority of a particular function, is the modulating system of the brain, which is often called the limbic-reticular complex, or the ascending activating system. The limbic and nonspecific brain systems with activating and inactivating structures belong to the nervous formations of this apparatus. Among the activating formations, the reticular formation of the midbrain, the posterior hypothalamus, the blue spot in the lower parts of the brain stem are primarily distinguished. Inactivating structures include the preoptic region of the hypothalamus, the nucleus of the suture in the brainstem, and the frontal cortex.
At present, according to thalamocortical projections, it is proposed to distinguish three main associative systems of the brain: thalamophenous, thalamophobic and thalamotemporal.
Thalamo-parietal system represented by the associative zones of the parietal cortex, receiving the main afferent inputs from the posterior group of the associative nuclei of the thalamus. The parietal associative cortex has efferent outputs to the nuclei of the thalamus and hypothalamus, to the motor cortex and the nucleus of the extrapyramidal system. The main functions of the thalamotemic system are gnosis and praxis. Under gnosis understand the function of various types of recognition: shapes, sizes, meanings of objects, understanding of speech, cognition of processes, patterns, etc. Gnostic functions include the assessment of spatial relationships, for example, the mutual arrangement of objects. In the parietal cortex, the center of stereognosis is distinguished, which provides the ability to recognize objects by touch. A variant of the gnostic function is the formation in the mind of a three-dimensional model of the body ("body schema"). Under praxis understand purposeful action. The praxis center is located in the supracortical gyrus of the left hemisphere; it provides storage and implementation of the program of motorized automated acts.
Thalamophobic system represented by the associative zones of the frontal cortex, which have the main afferent input from the associative mediodorsal nucleus of the thalamus and other subcortical nuclei. The main role of the frontal associative cortex is reduced to the initiation of the basic systemic mechanisms of the formation of functional systems of purposeful behavioral acts (P.K. Anokhin). The prefrontal area plays a major role in developing a strategy of behavior.The violation of this function is especially noticeable when it is necessary to quickly change the action and when some time passes between the formulation of the problem and the beginning of its solution, i.e. stimuli have time to accumulate, requiring the correct inclusion in a holistic behavioral response.
Thalamotemporal system. Some associative centers, for example, stereognosis, praxis, also include areas of the temporal cortex. In the temporal cortex is the auditory center of Wernicke's speech, located in the posterior parts of the superior temporal gyrus of the left hemisphere. This center provides speech gnosis: recognition and storage of oral speech, both one's own and someone else's. In the middle part of the superior temporal gyrus is the center for the recognition of musical sounds and their combinations. On the border of the temporal, parietal and occipital lobes there is a reading center, which provides recognition and storage of images.
An essential role in the formation of behavioral acts is played by the biological quality of an unconditioned reaction, namely, its importance for the preservation of life. In the process of evolution, this meaning was fixed in two opposite emotional states - positive and negative, which in humans form the basis of his subjective experiences - pleasure and displeasure, joy and sadness. In all cases, purposeful behavior is built in accordance with the emotional state that arose under the action of the stimulus. During behavioral reactions of a negative nature, the tension of the vegetative components, especially the cardiovascular system, in some cases, especially in continuous so-called conflict situations, can reach great strength, which causes a violation of their regulatory mechanisms (autonomic neuroses).
In this part of the book, the main general issues of the analytic-synthetic activity of the brain are considered, which will allow us to move in the subsequent chapters to an exposition of particular issues of the physiology of sensory systems and higher nervous activity.
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