Along with the first activating system that quickly responds to stimuli, which includes pathways, there is also a non-specific system of a slow response to external impulses, which is phylogenetically older than other brain structures and resembles a diffuse type of the nervous system. This structure is called the reticular formation (RF) and consists of more than 100 nuclei interconnected. RF extends from the nuclei of the thalamus and subthalamus to the intermediate zone of the spinal cord of the upper cervical segments.
The first descriptions of the RF were made by German morphologists: in 1861 by K. Reichert and in 1863 by O. Deiters, who introduced the term RF; a great contribution to its study was made by V.M. Bekhterev.
The neurons that make up the RF are diverse in size, structure and function; have an extensively branched dendritic tree and long axons; their processes are densely intertwined, resembling a network (lat. reticulum- mesh, formatio- education).
Properties of reticular neurons:
1. Animation(momentum multiplication) and amplification(obtaining the final great result) - is carried out due to the complex interweaving of the processes of neurons. The incoming impulse is multiplied many times, which in the ascending direction gives a sensation of even small stimuli, and in the descending direction (reticulospinal pathways) allows many NS structures to be involved in the response.
2. Pulse Generation. D. Moruzzi proved that most RF neurons constantly generate nerve discharges with a frequency of about 5-10 per second. Various afferent stimuli are summed up with this background activity of reticular neurons, causing its acceleration in some of them, and inhibition in others.
3. Polysensory. Almost all RF neurons are capable of responding to stimuli from a variety of receptors. Nevertheless, some of them respond to skin stimuli and to light, others to sound and skin stimuli, etc. Thus, complete mixing of afferent signals in reticular neurons does not occur; there is a partial internal differentiation in their connections.
4. Sensitivity to humoral factors and, especially, to pharmaceuticals. Particularly active are barbituric acid compounds, which, even in small concentrations, completely stop the activity of reticular neurons, while not affecting spinal neurons or neurons of the cerebral cortex.
In general, RF is characterized by diffuse receptive fields, a long latent period of response to peripheral stimulation, and poor reproducibility of the reaction.
Classification:
There is a topographic and functional classification of the Russian Federation.
I. Topographically the entire reticular formation can be subdivided into caudal and rostral sections.
1. Rostral nuclei (the nuclei of the midbrain and the upper part of the bridge, connected with the diencephalon) - are responsible for the state of excitation, wakefulness, alertness. Rostral nuclei have a local effect on certain areas of the cerebral cortex. The defeat of this department causes drowsiness.
2. Caudal nuclei (pons and diencephalon, connected with the nuclei of the cranial nerves and spinal cord) - perform motor, reflex and autonomic functions. Some nuclei in the process of evolution have received specialization - the vasomotor center (depressor and pressor zones), the respiratory center (expiratory and inspiratory), and the vomiting center. The caudal part of the RF has a more diffuse, generalized effect on vast areas of the brain. The defeat of this department causes insomnia.
If we consider the nuclei of the RF of each part of the brain, then the RF of the thalamus form a capsule laterally around the visual tubercles. They receive impulses from the cortex and dorsal nuclei of the thalamus. The function of the reticular nuclei of the thalamus is to filter signals going through the thalamus to the cerebral cortex; their projection onto other nuclei of the thalamus. In general, they affect all incoming sensory and cognitive information.
The midbrain RF nuclei include the tegmental nuclei: nuclei tegmentalis dorsalis and ventralis, nucleus cuneiformis. They receive impulses through fasciculus mammillo-tegmentalis (Gudden), which is part of the mammillothalamic pathway.
The RF of the bridge, formed by the near-median (paramedian) nuclei, does not have clear boundaries. These nuclei are involved in coordinated eye movement, fixed gaze, and saccadic eye movement (rapid synchronous eye movements). The pontine RF lies anterior and lateral to the medial longitudinal fasciculus, receives impulses along the nerve fibers from the superior colliculus of the quadrigemina through the pre-orsal nerve fibers and from the anterior visual fields through the frontal pontine connections.
The lateral RF is formed mainly by the nuclei of the RF of the medulla oblongata. This structure has many ganglia, interneurons around the cranial nerves that serve to modulate their associated reflexes and functions.
II. functional RF nuclei are subdivided into vertical formations:
1. Median column (raphe nuclei) - a narrow paired column of cells along the median line of the brainstem. Extend from medulla oblongata to midbrain. Dorsal raphe nuclei synthesize serotonin.
2. Medial column (bluish spot) - refers to the Russian Federation. Cells of the bluish spot synthesize norepinephrine, axons go to the areas of the cortex responsible for excitation (wakefulness).
3. Lateral column (gray matter around the aqueduct of Sylvius) - (part of the limbic system) - cells have opioid receptors, which contributes to the effect of pain relief.
RF function:
1. Regulation of consciousness by changing the activity of cortical neurons, participation in the sleep / wake cycle, arousal, attention, learning - cognitive functions
2. Providing emotional coloring to sensory stimuli (reticulolimbic connections)
3. Participation in vital autonomic reactions (vasomotor, respiratory, cough, vomiting centers)
4. Response to pain - RF conducts pain impulses to the cortex and forms descending analgesic pathways (affects the spinal cord, partially blocking the transmission of pain impulses from the spinal cord to the cortex)
5. Habituation is a process in which the brain learns to ignore minor repetitive stimuli from outside in favor of new stimuli. An example is the ability to sleep in a crowded, noisy vehicle while still being able to wake up to a car signal or a child's cry.
6. Somatomotor control - provided by the reticulospinal pathways. These pathways are responsible for muscle tone, balance, body position in space, especially when it moves.
7. Formation of integrated reactions of the body to stimuli, for example, the combined work of the speech motor apparatus, general motor activity.
RF communications
RF axons connect almost all brain structures with each other. RF is morphologically and functionally related to the spinal cord, cerebellum, limbic system, and cerebral cortex.
Part of the RF axons has a downward direction and forms the reticulospinal paths, and the other part has an ascending direction (spinoreticular paths). Circulation of impulses through closed neural circuits is also possible. Thus, there is a constant level of excitation of RF neurons, as a result of which a tone and a certain degree of readiness for the activity of various parts of the central nervous system are provided. The degree of RF excitation is regulated by the cerebral cortex.
1. Spinoreticular (spinoreticulocortical) pathways(ascending activating reticular system) - receive impulses from the axons of the ascending (sensory) pathways of general and special sensitivity. Somatovisceral fibers run as part of the spinoreticular tract (anterolateral funiculus), as well as in the propriospinal tracts and the corresponding tracts from the nucleus of the spinal trigeminal tract. Paths from all other afferent cranial nerves also come to the reticular formation, i.e. from almost all senses. Additional afferentation comes from many other parts of the brain - from the motor areas of the cortex and sensory areas of the cortex, the cerebellum, the basal ganglia, the red nucleus, from the thalamus and hypothalamus. This part of the RF is responsible for the processes of arousal, attention, wakefulness, provides emotional reactions that are important in the cognitive process. Lesions, tumors of this part of the Russian Federation cause a decrease in the level of consciousness, the activity of mental activity, in particular cognitive functions, motor activity, and chronic fatigue syndrome. Possible drowsiness, manifestations of stupor, general and speech hypokinesia, akinetic mutism, stupor, in severe cases - coma.
2. Reticulospinal pathways(descending reticular connections) - can have both a stimulating effect (responsible for muscle tone, vegetative functions, activates the ascending RF), and a depressing one (contribute to the smoothness and accuracy of voluntary movements, regulate muscle tone, body position in space, autonomic functions, reflexes) . They are provided with many efferent connections - descending to the spinal cord and ascending through nonspecific thalamic nuclei to the cerebral cortex, hypothalamus and limbic system. Most neurons form synapses with two or three dendrites of different origin; such polysensory convergence is typical for neurons of the reticular formation.
3. Reticulo-reticular connections.
Ticket 15
1. Forms (fragments) of afferent synthesis: Dominant motivation; situational afferentation; Starting afferentation. The role of the reticular formation.
2. Fast and slow muscle fibers.
Question 1
AFFERENT SYNTHESIS- (connection, compilation) - the process of comparing, selecting and synthesizing numerous and different functional value the afferentations caused by various influences on an organism occurring in c. n. s., on the basis of which the purpose of the action is formed.
A. s. according to Anokhin's theory of the functional system, it is the first, universal, stage of any purposeful behavioral act (see Functional systems).
A. s. includes processing of 4 main types of afferent excitations.
1. Motivational excitation reflects the dominant need of the organism, which arises under the influence of metabolic, hormonal, and in humans - social factors. Motivation plays a decisive role in shaping the purpose of the action. Specifically increasing the reactivity of cortical neurons with the help of exploratory reaction, motivational arousal contributes to the processing and active selection of sensory information necessary for the construction of goal-directed behavior.
2. Situational afferentation is the impact on the body of the totality of external factors that make up a specific environment, against the background of which adaptive activity develops. Situational afferentation is formed not only by constant components of the situation, but also by a number of successive afferent influences on the organism. Feature situational afferentation lies in the fact that it gives specificity to the future behavioral response, providing its adaptive value only in a given situation.
The role of situational afferentation is most clearly manifested in experiments with conditioned reflexes. In these cases, the animal responds to the same conditioned stimulus with a conditioned defensive reaction in one experimental chamber and a conditioned food reaction in the other (or in the same experimental chamber in the morning the animal responds with a food reaction, and in the evening with a defensive one).
At the stage of afferent synthesis, the questions “what to do?”, “how to do?”, “when to do?” are solved.
Starting afferentation
It is a special stimulus that actually triggers a behavioral response. The significance of the starting stimulus lies in the fact that it is intended to indicate the moment of the onset of a behavioral response.
Goal-directed behavior can begin without an explicit trigger stimulus. Examples of such reactions are regularly occurring physiological functions (eating, sleeping, defecation, urination, etc.), timed to coincide with certain periods of the day.
Afferent synthesis is carried out on the basis of the following neurophysiological mechanisms:
1) mechanisms of ascending activating influences of subcortical formations on the cerebral cortex. First of all, these are the activating influences of the hypothalamus to the frontal cortex, through the anterior nuclei of the thalamus, which reflects motivational excitations. Other limbic systems act similarly. Second in activating value are the reticular structures of the midbrain and pons, which provide an appropriate level of wakefulness.
2) mechanisms of convergence of excitations different quality on the neurons of the cortex and subcortical structures of the brain. In particular, multisensory convergence from surfaces (visual, tactile, auditory, temperature, etc.); multibiological convergence associated with certain conditions (hunger, pain, etc.), etc.;
3) integration of motivational, situational and triggering afferentations on the neurons of the cerebral cortex;
4) the mechanisms of formation of the dominant, due to which the current activity is suppressed and the newly formed behavioral reaction is retained.
The role of the reticular formation
The reticular formation is characterized by relatively low excitability. The effects of her irritation appear after a long latent period, she reacts slowly and remains active for a long time after the cessation of irritation (long aftereffect). The reticular formation facilitates or suppresses phasic movements and tension of skeletal muscles caused by motor neurons of the spinal cord, as well as movements caused from the cerebral cortex. The reticular formation of the midbrain and diencephalon facilitates the reflex movements of animals; irritation of the diencephalon inhibits the motor reflexes of the spinal cord.
The lateral sections of the reticular formation of the pons and midbrain facilitate, and its middle sections in the medulla oblongata inhibit motor reflexes. Relief and inhibition also depend on the intensity and duration of stimulation of the reticular formation. By gamma neurons, it regulates the functions of muscle spindles, and therefore feedback from skeletal muscles. It also changes the excitability of the ascending afferent pathways of the spinal cord, which can reduce or stop postsynaptic inhibition. Tonic influences of the reticular formation cause EPSP or IPSP in the motor neurons of the spinal cord. It also changes the transmission of impulses in the brain stem and, simultaneously with the effect on the skeletal muscles, causes vasomotor, respiratory, pupillary and other reactions.
The reticular formation has an adaptive-trophic effect on the cerebral cortex, subcortical formations of the diencephalon, cerebellum and spinal cord. There are mutual influences of these parts of the nervous system, both excitatory and inhibitory. She participates in physiological processes sleep and awakening, as well as in emotions, in the reaction of tension (“stress”), etc. Irritation of the reticular formation causes the awakening of sleeping animals, and its destruction and switching off causes deep sleep in awake animals. The mutual influences of the reticular formation and the cerebral cortex were studied. The participation of the reticular formation in the formation and course of conditioned reflexes was established.
By sympathetic fibers, the reticular formation regulates the excitability and performance of skeletal muscles, functional state nervous system and sensory organs, exerting an adaptive-trophic effect on them. The regulation of posture reflexes and motor reflexes that move the body is carried out along efferent gamma fibers innervating proprioceptors.
The reticular formation regulates autonomic functions, the activity of internal organs. It affects the formation of hormones in the pituitary gland and other endocrine glands and hormones and mediators are concentrated in it.
Afferent fibers enter it through the sympathetic and vagus nerves. Part of the cells of the reticular formation of the midbrain and varolneval bridge is excited by adrenaline and norepinephrine (adrenergic systems), and the other part, located in the diencephalon, slightly above the midbrain, is excited by acetylcholine and its derivatives (cholinoreactive systems). The adrenoreactive systems of the midbrain and pons facilitate the onset of motor reflexes, and the adrenoreactive systems of the medulla oblongata inhibit spinal reflexes. Adrenaline also stimulates cholinergic systems. It is assumed that the action of acetylcholine and its derivatives is less limited than the action of adrenaline, and covers many areas of the brain. The action of acetylcholine on the reticular formation is opposite to its peripheral effect on the internal organs. The reticular formation of the middle and medulla oblongata excites carbon dioxide.
Hormones and mediators act on the function of the cerebral hemispheres both directly and through the reticular formation. Thus, the reticular formation of the brain stem is the subcortical center of the autonomic nervous system.
Question 2.
RETICULAR FORMATION [formatio reticularis(PNA, JNA, BNA); syn.: reticular substance, reticular formation] - a set of structures located in the central parts of the spinal cord and brain stem. The Reticular Formation is characterized by the presence of a large number of nerve fibers passing in various directions, and therefore given education Under a microscope, it looks like a mesh. This was the basis for Deiters (O. F. C. Deiters) to call it a mesh formation.
Morphology
At the end of the 19th - beginning of the 20th century. were described the outer section of the Reticular Formation of the medulla oblongata, consisting mainly of gray matter (formatio reticularis grisea), the internal section, consisting mainly of white matter (formatio reticularis alba), the lateral section (substantia reticularis lateralis), as well as individual nuclei of the Reticular Formation. The first systematic description of the nuclei of the Reticular Formation of the brain stem was given in 1909 by H. Jacobsohn.
The atlas of Messen and Olszewski (Meessen, J. Olszewski, 1949) describes 32 nuclei of the rhomboid brain of the rabbit. In his work of 1954, Olshevsky describes 22 nuclei of R. f. medulla oblongata, pons and midbrain in humans.
The study of the structure of individual nuclei of the Reticular Formation and their constituent neurons, as well as the connections of the Reticular Formation served as the basis for the division of R. f. into zones, parts or columns.
Comparative anatomical, morphological and ontogenetic study of R. t. allowed V. V. Amunts (1966, 1976, 1980) to group the nuclei of R. f. into 3 sections: external, internal and middle - and highlight the transition zones between reticular and specific, as well as between various reticular structures.
Characteristics of the neural structure of R. t. was made by Scheibel and Scheibel (A. B. Scheibel, M. E. Scheibel, 1962), G. P. Zhukova (1977), T. A. Leontovich (1978), Mannen (H. Mannen, 1966, 1975), Valverde (F Valverde, 1961), N. S. Kositsyn (1976) and others.
Nerve connections R. t. were studied mainly by methods of degeneration. R.'s fibers f. divided into radial, directed ventrally, concentric fibers, crossing in the area middle line, and fibers are longitudinal, grouped into bundles. These bundles make up both afferent and efferent pathways. Relationship data R.f. summarized in the works of Brodal (1957), Rossi and Zanchetti (G. F. Rossi, A. Zanchetti, 1957).
Physiology
In the region of the brain stem there are anatomical formations, the excitation of which has a generalized tonic effect on the anterior parts of the brain (see). This group of anatomical formations is called the ascending activating system of the reticular formation (Fig. 1). She plays an important role in maintaining the waking state, as well as in the mechanisms of formation of integral, and in particular conditioned reflex reactions of the body. Along with the ascending activating system, descending reticulospinal systems are also distinguished, which have a controlling effect on the reflex activity of the spinal cord. The activity of both ascending and descending systems is supported by a continuous influx of afferent impulses entering R. t. along collateral fibers from sensory pathways. An important role in maintenance of activity of reticular mechanisms is played by humoral irritants, in relation to to-the Crimea R. f. has a high sensitivity, which ensures its participation in the regulation of a number of vegetative functions. Along with it R. f. is the site of selective action of many pharmacological agents, which is widely used in the treatment of a number of diseases of c. n. with., and also causes a new approach to the study of such important problems of medicine as, for example, the problem of pain and anesthesia. In the area of R. f. there is an extensive spatial coincidence and interaction of impulses coming from various peripheral receptor formations with excitations coming from the cerebellum and the cerebral cortex. Due to the large number of cortico-reticular connections, the cerebral cortex has a controlling effect on the activity of reticular mechanisms, regulating the level of their activity.
Reticulospinal ratios. The influence of the brain stem on the motor activity of the spinal cord was first demonstrated by I. M. Sechenov in 1862 (see Sechenov's inhibition). He showed that when the brain stem is irritated, both inhibition and facilitation of reflex reactions can be observed. However, the mechanism and structures mediating these influences remained unclear. In 1944, X. Megun, using direct electrical stimulation of the brain stem, showed that stimulation of certain areas of the bulbar R. f. leads to a complete stop of movements caused both by reflex and by irritation of the motor areas of the cerebral cortex. This inhibition was general and extended to all muscle groups, regardless of their topographic relationships and physiological function. X. Megun suggested that the controlling influence of R. f. is carried out at the level of the spinal cord, and not at the level of the cerebral cortex. This assumption was confirmed by him in experiments on decerebrated animals.
Concerning the mechanism of reticulospinal influences there is no consensus. While some researchers believe that R. t. can affect directly the motor neurons of the spinal cord, others suggest that these influences are transmitted to motor neurons through some intermediate neurons, the role of which can be played by intercalary neurons involved in the closure of segmental spinal reflex arcs.
Reticulocortical relationships and the problem of the ascending activating effect of reticular mechanisms on the cerebral cortex. It is a known fact that the main symptoms in the defeat of certain parts of the brain stem are a general decrease in the activity of the patient, weakness, drowsiness. Experiments have shown that such phenomena can develop when the animal's subcortical-stem parts of the brain are destroyed. These data served as a basis for a number of P1 researchers to believe that in the region of the brain stem there are centers that are in charge of the general activity of the body, centers of sleep and wakefulness (see Centers of the nervous system). This assumption was justified by the fact that direct stimulation of certain parts of the brain stem could cause sleep in the experimental animal or wake it from this state. However, genuine progress in this problem became possible only after electrophysiological methods, in particular electroencephalography, became increasingly widely used for brain research (see). Studies by V. V. Pravdich-Neminsky (1925) showed that external stimuli cause characteristic changes in the EEG, which consist in the change of slow high-amplitude and low-frequency oscillations characteristic of the state of rest, with fast low-amplitude and high-frequency oscillations. Such EEG changes are observed in humans or animals during the transition from sleep to wakefulness. In this regard, this type of reaction is called "EEG activation reaction", or "awakening reaction".
The development of experimental research methods made it possible to develop methods for subtle stimulation and destruction of individual subcortical structures using electrodes inserted with great accuracy at the points necessary for the experimenter (see Stereotaxic method). This allowed J. Mo-ruzzi and X. Megun in 1949 to approach the solution of the question of which brain structures are responsible for the occurrence of the “awakening reaction”. To solve this problem, J. Moruzzi and X. Megun conducted a series of experiments, during which they found that when certain points of the brain stem are irritated in animals, a change in slow synchronous high-voltage oscillations characteristic of sleep is observed to low-amplitude high-frequency activity. These EEG changes were diffuse, i.e., were observed throughout the cerebral cortex, but were better expressed in the hemisphere of the same name in relation to the area of stimulation. Changes in the electrical activity of the cortex of large polungaria were accompanied by external signs of awakening.
Further studies have shown that similar phenomena can be observed during stimulation of various departments of R. t. brain stem - from the medulla oblongata to the diencephalon. In the area of the medulla oblongata (see), the excitable zone coincides with those areas of R. f., to-rye, according to X. Megan and R. Rhines, also have a downward effect on the activity of the spinal cord. At the level of the bridge (see. Bridge of the brain) and the midbrain (see), this zone is located in the region of the tire, and at the level of the diencephalon (see), it captures the subthalamic nucleus and the posterior hypothalamus (see), reaching the medial thalamic nuclei. These structures of a brain trunk also make the ascending activating reticular system, a cut is an anatomic substrate a number of the ascending short-axon reticular ways. X. Megun and J. Moruzzi came to the conclusion that the EEG changes observed by them were not the result of antidromic conduction of impulses to the cerebral cortex along the known cortico-fugal pathways. Nor could these changes be explained by conduction of excitation to the cortex along the known classical sensory (lemniscal) pathways, since even after the transection of these pathways, stimulation of the structures of the medulla oblongata continued to cause distinct EEG changes.
The ideas of J. Moruzzi and X. Meguna about the activating system R. f. of the brain stem have been further developed and confirmed in the work performed in laboratories in many countries of the world. The main conclusions of J. Moruzzi and X. Meguna were confirmed and the topography of the structures related to the ascending activating reticular system of the brain stem was clarified.
Electrophysiological experiments carried out using microelectrode technology have shown that impulses from various peripheral sources and the cortex can converge to the same neuron of the Reticular Formation. big brain. It is the interaction between these impulses that apparently determines the variety of observed effects from external stimuli.
The works of Dell (R. Dell) and his school show that an important role in maintaining the activity of R. t. belongs to humoral factors, in particular adrenaline. It was found that the activating effect of adrenaline on the cerebral cortex is carried out through R. t. midbrain and pons (Fig. 2). After transection of the brainstem anterior to the midbrain, the administration of adrenaline no longer elicited a "wake-up response." Thus, the rostral parts of the brain stem have hypersensitivity to adrenaline. Moreover, the studies of Vogt (M. Vogt, 4954) and P. K. Anokhin (1956) in the rostral parts of the brain stem revealed the presence of a large number of elements containing adrenaline and norepinephrine. IP Anokhina (1956) found that chlorpromazine, which has the ability to block alpha-adrenergic receptors, prevents the development of EEG activation during painful stimuli. It gives the basis to assume that the activating influence of R. f. on the cerebral cortex during painful stimuli is carried out due to the involvement in the activity of a-adrenergic receptors of the rostral parts of the brain stem.
In what ways is the influence of reticular mechanisms on the cerebral cortex carried out? X. Megun and J. Moruzzi (1949) suggested that one of the ways through which R. f. affects the cerebral cortex, is a group of medial nuclei of the thalamus (see), which is the so-called. nonspecific projection thalamocortical system. This system includes (in a cat) the nucleus reticularis, n. ventralis anterior, n. centralis medialis, n. lateralis, n. medialis, n. centrum medianum, n. parafascicularis and other nuclei of the intralaminar complex (intralamellar nuclei of the thalamus, T.). When the nonspecific nuclei of the thalamus are stimulated, generalized changes in the electrical activity of the cerebral cortex are observed, regardless of which of the nuclei is irritated; the nuclei of this system have a large number of connections between themselves, due to which, when excited, this system reacts as a single system.
To studying of functional ratios between the ascending activating system R. t. the brain stem and the nonspecific projection (diffuse) thalamic system have been the subject of a large number of works. Many researchers simply combine these systems into one, given their close morphological unity. However, J. Moruzzi (1958) believes that there are no sufficient grounds for such an association and it is more expedient to attribute the nonspecific thalamic system to the “spheres of influence” of R. f., especially since there are experimental data indicating reciprocal relationships between these formations. Detailed studying of the ways connecting R. f. brain stem with nonspecific nuclei of the thalamus, Peips held (J. W. Papez, 1956). According to him, there are three such ways: reticular-thalamic, passing from R. t. medulla oblongata to the centromedial nucleus of the thalamus, as well as to the posteromedial and parafascicular nuclei. Sensory pathways (lemniscal system) pass along the lateral side of this path, from which collaterals extend to the cores of the tegmentum. From the nuclei of the tire, the tegmental-thalamic path begins, ending in the central median nucleus (centrum medianum) and adjacent cells. The most lateral in location is the tectothalamic pathway, ending in the border nucleus of the thalamus. Through these pathways, the non-specific projection thalamic system becomes a link between the ascending reticular activating system of the brain stem and the cerebral cortex.
Recognition of the existence of two afferent systems (specific and nonspecific), which have different forms, methods and spheres of influence, led to the need to study the characteristics of the termination of the fibers of both of these systems in the cerebral cortex. It has been shown that the nerve fibers of these systems have endings in the cortex that differ in shape and distribution in different cortical layers. Specific afferent fibers terminate mainly in the 4th layer of the cortex, nonspecific fibers - in all layers of the cortex. Specific fibers terminate mainly on the cell body, non-specific - on its dendrites. Axodendritic endings of nonspecific fibers can create a change in the excitability of cortical neurons, facilitating or hindering synaptic transmission (see Synapse). These influences are diffuse and changeable. The axosomatic endings of specific fibers provide fast and localized responses. The interaction of both these systems, according to Chang (H. T. Chang, 1952), determines the final reaction of cortical neurons.
It should be noted that if in the 50s and 60s. 20th century the view prevailed, according to Krom R. f. was considered as diffusely organized-barking, providing a "non-specific" ascending and descending influence, then in the 70s. this view has been reconsidered.
One of the first researchers who indicated that the activating influences of R. t. always have a certain biological "sign", was P. K. Anokhin (1958). The reason for the radical revision of views was the progress of both physiological and morphological research methods. The latter, first of all, include the improvement of the technique of histofluorescent analysis, which made it possible to identify neurons containing monoamines (norepinephrine, serotonin, and dopamine) in the brain stem and to show the nature of the branching of the fibers of these neurons. It was noted that the noradrenal and serotonin systems contain typical reticular neurons. These data forced to reconsider a morphological dogma, according to a cut all ways to a cerebral cortex are switched in a thalamus. It was found that mesencephalic serotonergic and norepinephrine neurons ascend directly from R.'s nuclei f. into the cerebral cortex. In this regard, the question arose about the neurochemical basis of the cortical "awakening reaction".
A significant contribution to the physiology of the Reticular Formation was made by the use of microelectrode research methods (see). It was shown that one of the important mechanisms of activating reticulothalamic and reticulo-cortical influences is the suppression of inhibitory interneurons, i.e. "inhibition of inhibition."
New data were obtained in the process of studying reticulomotor coordination, i.e., in identifying local groups of cells that are specifically associated with the control of certain forms of motor activity, in particular, in the identification of neurons that regulate eye movements, neurons that control the mechanisms of posture and locomotion, and etc.
Opening in a number of structures R. f. high concentrations of the so-called. opiate receptors, indicated a connection with the organization of pain sensitivity. These structures include the nuclei of the median suture, as well as the central gray matter around the Sylvian aqueduct, etc.
Detection of functional specialization of various departments of R. t. led to a reassessment of the relationship to R. f. as a "non-specific system". In the USA the special international symposium was organized and held, materials to-rogo are published in the monograph "Revision of views on a reticular formation: specific function of nonspecific system" (1980).
However, it should be noted that studies that summarize information about R. f. do not cancel the view on R. f. as a system that works in functional unity with the analyzer systems and exerts tonic influences on the lower and higher departments of c. n. With.
It must be taken into account that long before the appearance of the first studies devoted to R. f., I. M. Sechenov showed that structures that control the activity of the spinal cord are located in the region of the brain stem. IP Pavlov also attached great importance to subcortical formations in maintaining the activity of the cerebral cortex. He spoke of the "blind power" of the subcortex, of the subcortex as "the source of energy for the cortex." Establishment of an important role of reticular mechanisms in activity of c. n. With. is a concretization of the theoretical ideas of these brilliant Russian scientists.
Pathology of the reticular formation
Violation of R.'s function f. develops owing to defeat of its kernels, localized, hl. arr., in the area of the medulla oblongata, bridge and midbrain, as well as afferent and efferent connections at various levels.
The pathology of the integrative functions of R. f., as shown by A. M. Wein (1974), Eliasson (S. G. Eliasson, 1978), can manifest itself in the form of movement disorders (see), disturbances of consciousness (see), sleep (see. ), autonomic dysfunction.
Movement disorders are caused by a violation of the phasic and tonic control of the striated muscles, which is normally carried out through the interaction of activating and inhibitory influences of R. f. transmitted to alpha and gamma motor neurons of the spinal cord (see) through the reticulospinal and vestibulospinal pathways.
Pathology R. f. brain stem, as well as its afferent and efferent connections, can be accompanied by both an increase in muscle tone and tendon reflexes, and their decrease. Muscular hypertension and increased tendon reflexes arise due to the predominance of the activating influences of the reticular formation on the a- and y-motoneurons of the spinal cord, which is observed when the giant cell reticular nucleus is damaged at the level of the medulla oblongata or pons, its afferent connections with the cerebral cortex and caudate nucleus, as well as in the pathology of efferent pathways to the motor neurons of the spinal cord.
Diffuse defeat of R. f. at the level of the brain stem, it can lead to a sharp decrease in muscle tone and tendon reflexes due to the absence of activating effects on the a- and 7-motor neurons of the spinal cord.
Motor disorders in the pathology of R. t. concern not only the striated muscles of the trunk and limbs, but also the muscles innervated by the cranial (cranial, T.) nerves.
Other a wedge, the syndrome observed at R.'s pathology f., the disturbance of consciousness up to emergence of a coma is. Coma (see) is characterized by complete loss of consciousness, lack of response to external stimuli, slow synchronized EEG rhythm. The coma is based on the blockade of the ascending activating R. f., responsible for the processes of wakefulness, activation of attention to various sensory stimuli. Functional or structural disturbances of the ascending activating system at any level, including the oral brainstem, septum pellucidum, hypothalamus, thalamus, and thalamocortical connections, can lead to disorders of consciousness. Coma states most often develop in the pathology of the brain stem and midbrain or in processes leading to their dislocation. But another mechanism of coma is also possible, with Krom it is based on the pathology of the cerebral cortex and the violation of the descending influences of the cortex on R. f., as a result of which the functional state of R. f changes for the second time.
For R.'s defeat f. in the area of \u200b\u200bthe tire of the bridge and the midbrain, pseudocoma syndrome, or akinetic mutism, is characteristic. The syndrome of akinetic mutism is characterized by the loss of the ability to adequately respond to external stimuli with intact consciousness or its mild impairment. At the same time, the patient's speech is disturbed (see), active movements, he does not remember the events occurring in a given period of time. Pupillary reactions, tendon and periosteal reflexes do not change. Strong pain and sound stimuli cause a motor response. The syndrome is based on a violation of the ascending activating system and its connections with the limbic structures of the brain (see Limbic system), which leads to a lack of urges to act, difficulty in integrating motor functions, and memory impairment (see).
A frequent symptom of R.'s defeat f. and its links is a sleep disorder. Sleep pathology (see) is caused either by a violation of the functional reciprocal relationship between the ascending activating system and the hypnogenic synchronizing zones responsible for the generation of sleep, or by the dysfunction of the hypnogenic zones themselves, located ch. arr. within the limbic-reticular complex.
Sleep disorders can be in the form of increased drowsiness (hypersomnia) and a variety of nighttime sleep disorders (insomnia). Hypersomnia may be due to hypofunction of the ascending activating system or hyperfunction of one of the systems of sleep regulation mechanisms. Hypersomnic states observed in organic lesions of the mesencephalic-diencephalic region of the brain are the result of a disruption in the functioning of the activating system R. t. Insomnias characterized by insomnia, difficulty falling asleep, frequent waking up, shortening of the duration of nocturnal sleep may be due to a relatively increased functional activity of the ascending activating system, as well as impaired functioning of individual somnogenic brain regions responsible for the generation of REM and non-REM sleep phases. Such hypnogenic zones are located in the caudal part of the brain stem (the so-called synchronizing system of J. Moruzzi), in the nuclei of the median suture, and in the hypothalamus. With their pathology, disorganization of individual phases of sleep is observed. Violation of the cyclic organization of sleep without gross changes in individual phases is characteristic of the pathology of integrating apparatuses that regulate the activation of synchronizing and desynchronizing mechanisms of sleep. These include individual structures of the limbic-reticular complex (hypothalamus, thalamus, basal nuclei of the telencephalon), as well as the activating thalamocortical system.
At disturbance of R.'s function f. brain stem syndrome can be observed vegetative-vascular dystonia. According to A. M. Wayne et al. (1981), vegetative-vascular disorders are observed in most patients with pathology of the brain stem. Vegetative disorders are represented by cardiovascular, vasomotor and respiratory disorders, to-rye may have a sympathetic-adrenal or parasympathetic orientation (see Neurocirculatory dystonia). At the heart of the vegetative disturbances arising at R.'s defeat f. brain stem, lies not only dysfunction of specific vegetative centers (vasomotor, respiratory), but also a violation of the integral integrative function necessary to ensure appropriate adaptive behavior. Therefore, the respiratory, cardiovascular and vasomotor disorders observed in R.'s pathology f. brain stem, accompanied by changes in muscle tone, motility and secretion of internal organs, endocrine disorders, mood changes, memory loss. There is a certain dependence a wedge, displays of vegetative and vascular dystonia from the area of defeat of R. f. brain stem. In violation of the upper parts of the trunk, vegetative disorders are sympathetic, may be accompanied by mild neuroendocrine disorders. In patients with damage to the caudal parts of the trunk, a parasympathetic direction of the tone of the autonomic nervous system is detected, and vestibular disorders are often observed. It is caused by existence of communications R. f. with nuclei of the vagus nerve and vestibular nuclei.
Studying of physiology and pathophysiology R. t. allowed to significantly deepen the understanding of the mechanisms of development of many diseases of the nervous system. Pathology of the ascending activating system R. t. underlies disorders of consciousness and coma (in acute disorders of cerebral circulation, craniocerebral trauma, tumors, encephalitis, metabolic disorders). Blockade of activating influences on the cerebral cortex can be caused either directly by the lesion itself, localized in the brain stem, midbrain, or hypothalamus, or by edema, leading to compression, dislocation, and secondary metabolic disorders in this area.
In comatose states caused by a metabolic disorder (eg, hypoglycemia) or drug intoxication (barbiturates, tranquilizers, adrenolytic agents), there is a direct suppression of the neurons of the activating reticular system or blockade of adrenergic receptors of synapses.
An increase in the functional activity of the wakefulness system, manifested by sleep pathology in the form of insomnia, is characteristic of neuroses. At patients with neurosises (see) the syndrome of a vegetative and vascular dystonia, the emotional frustration characteristic of dysfunction of a limbiko-reticular complex are often observed also.
Pathology R. f. plays a role in the development of parkinsonism syndrome (see). Among typical morphological changes at this disease often find the death of neurons R. f., providing a condition of wakefulness. Increased drowsiness and akinesia in parkinsonism depend not only on the primary lesion of the R. f.
Pathology of descending influences R. t. plays a role in the formation of central paralysis and paresis, extrapyramidal rigidity, myoclonus.
Refinement of the function of R. f. and clarification of its role in development patol. violations became possible on the basis of extensive experimental and clinical studies. For studying of function R. f. apply the method of implantation of electrodes with the determination of the activity of cell populations, electroencephalographic analysis, morphological studies using electron microscopy (see), methods of histochemistry (see) and biochemistry (see), including the study of the neurochemistry of mediators (see). In a wedge, practice the polygraphic methods of a research including at the same time an electroencephalography (see), electrooculography (see), electromyography (see), electrocardiography (see) are widely used, by means of to-rykh it is possible to differentially determine the level of damage to the nervous system, functional the state of the ascending and descending systems R. t. and to identify the features of their response to the use of various pharmacological agents.
Treatment
There is a wide arsenal of the pharmacological preparations influencing R.'s function f. and its connections with other formations of the brain. Barbiturates have a selective effect on the activating reticular system, which block ascending impulses to the cerebral cortex. This mechanism underlies their narcotic and anticonvulsant effects. Bromine preparations, phenothiazine preparations (chlorpromazine, etc.), some tranquilizers (chlordiazepoxide, diazepam, oxazepam, nitrazepam) have a direct inhibitory effect on the ascending activating system, which is associated with their calming, anticonvulsant and mild hypnotic effect. The ascending reticular system is activated by adrenergic mediators (adrenaline, noradrenaline), their precursor L-DOPA, as well as indirect adrenomimetics (caffeine, nialamide, imizin, amitriptyline, phenamine, meridil, sydnocarb, etc.). These funds are used in the complex therapy of patients in a coma, with increased drowsiness, depression, asthenia. Cholinergic synapses of the reticular formation are blocked by central cholinomimetics (scopolamine, amizil, metalisyl), which leads to a decrease in the parasympathetic influences of R. f. brain stem to internal organs. A decrease in the flow of sympathetic impulses to the periphery can be achieved by using sympatholytic agents (reserpine, methyldopa), which disrupt the formation of catecholamines and activate the inhibitory structures of R. f. There are agents that have a selective effect on the serotonergic structures of R.f. (L-tryptophan, diseryl). These drugs are used in the clinic to normalize sleep. The effect of inhibition of reticular cells of the caudal brain stem by drugs such as Lioresal, midokalam, diazepam is used in the treatment of patients with increased muscle tone.
Correction of syndromic disorders R. t. is a part of complex therapy of diseases of a nervous system, in a cut the leading place should be given to etiological and pathogenetic treatment.
Bibliography: Amunts VV Development of the reticular formation of the brainstem in the ontogeny of the lower monkey compared to man, Arkh. anat., hist. and Embryol., v. 71, c. 7, p. 25, 1976, bibliogr.; Anokhin PK The value of the reticular formation for various forms of higher nervous activity, Fiziol. magazine USSR, vol. 43, no. 11, p. 1072.1957; about N e, Nodal questions of the theory of functional system, M., 1980; Brod and l A. Reticular formation of the brain stem, trans. from English, M., 1960, bibliography; Bein A. M. Lectures on the neurology of nonspecific brain systems, M., 1974; Wayne A. M. and With about l about in e in and A. D. Limbiko-reticular complex and vegetative regulation, M., 1973, bibliogr.; Wayne A. M., With about l about in e in and A. D. and Kolosova O. A. Vegetovascular dystonia, M., 1981, bibliogr.; D em and N H. N., Kogan A. B. and M about and-seeva N. I. Neurophysiology and neurochemistry of a dream, L., 1978; Zhukova G. P. Neuronal structure and interneuronal connections of the brain stem and spinal cord, M., 1977, bibliogr.; Kositsyn N. S. Microstructure of dendrites and axodendritic connections in the central nervous system, M., 1976; M e g at N G. Waking brain, the lane with English. from English, M., 1961; Reticular formation of the brain, ed. G. G. Jasper et al., trans. from English, M., 1962; Rossi D. F. and Ts and N to e t-t and A. Reticular formation of a brain stem, the lane with English, t. from English, M., 1960, bibliography; Svyadoshch A. M. Neurosis, M., 1982; Structure and function of the reticular formation and its place in the system of analyzers, ed. S. A. Sarkisova. Moscow, 1959. Handbook of clinical neurology, ed. by P. J. Vinken a. G. W. Bruyn, v. 1, Amsterdam a. o., 1975; Meessen H. u. Olszewski J. Cytoarchitektonischer Atlas des Rautenhirns des Kaninchens, Basel - N. Y., 1949; M o r u z z i G. a. M a- g o u n H. W. Brain stem reticular formation and activation of E E G, Electroen-ceph. clin. Neurophysiol., v. 1, p. 455, 1949; Neurological pathophysiology, ed. by S. G. Eliasson a. o., N. Y., 1978; O 1 s-zewski J. The cytoarchitecture of the human reticular formation, in: Brain mechanisms and consciousness, ed. by E. D. Adrian a. o., p. 54, Oxford, 1954, bibliogr.; Purpura D. P., Me Murtry J. G. a. Maekawa K. Synaptic events in ventrolateral thalamic neurons during suppression of recruitfing responses by brain stem reticular stimulation, Brain Res., v. 1, p. 63, 1966; R a-mon in Cajal S. Histologie du sys-teme nerveux de l'homme et des vertebres, t. 1-2, Madrid, 1952-1955; The reticular formation revised, ed. by J. A. Hobson a. M. A. B. Brazier, N. Y., 1980, bibliogr.
V. V. Amunts, V. G. Skrebitsky, V. N. Shelikhov; L. O. Badalyan (neur.).
Reticular formation (from lat. reticulum - mesh, formatio - education)
reticular formation, a set of nerve structures located in the central parts of the brain stem (medulla oblongata and midbrain, visual tubercles). Neuron s ,
components of R. f., are diverse in size, structure and length of axons ;
their fibers are densely intertwined. The term R. f.", introduced by the German scientist O. Deiters, reflects only its morphological features. R. f. morphologically and functionally connected with the spinal cord, cerebellum (See Cerebellum), limbic system (See Limbic system) and the cerebral cortex. In the area of R. f. the interaction of both ascending - afferent, and descending - efferent impulses entering it is carried out. Circulation of impulses through closed neural circuits is also possible. Thus, there is a constant level of excitation of R. f. neurons, as a result of which the tone and a certain degree of readiness for the activity of various parts of the central nervous system are provided. Degree of excitation R. f. regulated by the cerebral cortex (See. Cerebral cortex).
Downward Influences. In R. f. distinguish areas that have inhibitory and facilitating effects on the motor responses of the spinal cord (See Spinal cord) ( rice. 1
). The relationship between stimulation of various regions of the brainstem and spinal reflexes was first noted in 1862 by IM Sechenov. In 1944-46, the American neurophysiologist H. Magone and his co-workers showed that stimulation of various areas of R. f. medulla oblongata has a facilitating or inhibitory effect on the motor reactions of the spinal cord. Electrical stimulation of the medial part of R. t. medulla oblongata in anesthetized and decerebrated cats and monkeys is accompanied by a complete cessation of movements caused both reflexively and by stimulation of the motor areas of the cerebral cortex. All inhibitory effects are bilateral, but on the side of irritation, such an effect is often observed at a lower threshold of irritation. Some manifestations of inhibitory influences R. t. medulla oblongata correspond to the picture of central inhibition described by Sechenov (see Sechenov's inhibition). Irritation of the lateral region R. t. medulla oblongata along the periphery of the area that has inhibitory effects, is accompanied by a facilitating effect on the motor activity of the spinal cord. The area of R. f., which has facilitating effects on the spinal cord, is not limited to the medulla oblongata, but extends anteriorly, capturing the region of the pons and midbrain. R. f. can affect various formations of the spinal cord, for example, alpha motor neurons that innervate the main (extrafusal) muscle fibers involved in voluntary movements. An increase in the latent periods of responses of motor neurons during stimulation of the inhibitory sections of R. t. suggests that the inhibitory effects of reticular structures on the motor responses of the spinal cord are carried out with the help of intercalary neurons, possibly Renshaw cells. The mechanism of influence of R. f. on muscle tone revealed by the Swedish neurophysiologist R. Granit, who showed that R. t. also affects the activity of gamma motor neurons, the axons of which go to the so-called intrafusal muscle fibers, playing an important role in the regulation of posture and phase movements of the body. Rising influences. Various departments of R. f. (from the diencephalon to the medulla oblongata) have excitatory generalized effects on the cerebral cortex, that is, they involve all areas of the cerebral cortex in the process of excitation ( rice. 2
). In 1949, the Italian physiologist J. Moruzzi and Magone, investigating the bioelectrical activity of the brain, found that stimulation of R. f. brainstem changes slow synchronous high-voltage oscillations characteristic of sleep to low-amplitude high-frequency activity characteristic of wakefulness. A change in the electrical activity of the cerebral cortex is accompanied in animals by external manifestations of awakening. R. f. is closely connected anatomically with the classical conduction pathways, and its excitation is carried out with the help of extero- and interoceptive afferent (sensitive) systems. On this basis, a number of authors attribute R. f. to the nonspecific afferent system of the brain. However, the use of various pharmacological substances in the study of the function of R. f., the discovery of the selective effect of chemicals on reactions carried out with the participation of R. f., allowed P. K. Anokhin to
to formulate a position on the specificity of the ascending influences of R. f. to the cerebral cortex. The activating influences of R. f. always have a certain biological significance and are characterized by selective sensitivity to various pharmacological substances (Anokhin, 1959, 1968). Drugs introduced into the body cause inhibition of the neurons of R. f., thereby blocking its ascending activating influences on the cerebral cortex. An important role in maintaining the activity of R. f., sensitive to various circulating in the blood chemicals, belongs to humoral factors: catecholamines, carbon dioxide, cholinergic substances, etc. This ensures the inclusion of R. t. in the regulation of some autonomic functions. The cerebral cortex, experiencing tonic activating influences from R. f., can actively change the functional state of reticular formations (change the rate of excitation in it, influence the functioning of individual neurons), i.e., control, according to I. P. Pavlov , the "blind force" of the subcortex. The discovery of the properties of R. f., its relationship with other subcortical structures and areas of the cerebral cortex made it possible to clarify the neurophysiological mechanisms of pain, sleep, wakefulness, active attention, the formation of integral conditioned reflex reactions, and the development of various motivational and emotional states of the body. R.'s research f. with the use of pharmacological agents, they open up the possibility of medical treatment of a number of diseases of the central nervous system, determine a new approach to such important problems of medicine as anesthesia, etc. Lit.: Brodal A., Reticular formation of the brain stem, lane, from English, M., 1960; Rossi J. F., Tsanchetti A., Reticular formation of the brainstem, trans. from English, M., 1960; Reticular formation of the brain, trans. from English, M., 1962; Magun, G., The Waking Brain, trans. from English, 2nd ed., M., 1965; Anokhin P.K., Biology and neurophysiology conditioned reflex, M., 1968; Granit R., Fundamentals of regulation of movements, trans. from English, M., 1973; Moruzzi G., Magoun H. W., Brain stem reticular formation and activation of EEG, in Electroencephalography and clinical neurophysiology, v. 1, Boston, 1949 V. G. ZILOV Big soviet encyclopedia. - M.: Soviet Encyclopedia.
1969-1978
.
See what the "Reticular formation" is in other dictionaries:
- (formatio reticularis; lat. reticulum network; synonymous with reticular substance) a complex of cellular and nuclear formations that occupy a central position in the brain stem and in the upper spinal cord. A large number of nerve fibers ... Wikipedia
Reticular formation- A complex network of neurons and cell nuclei that occupies the central part of the brain stem. Often referred to as the "reticular activation system" because of the role it plays in the activation process. Modern research allows ... ... Great Psychological Encyclopedia
A set of structures in the central parts of the brain that regulate the level of excitability and tone below and overlying parts of the central nervous system, including the cerebral cortex ... Big Encyclopedic Dictionary
RETICULAR FORMATION, a complex mechanism of the CENTRAL NERVOUS SYSTEM of vertebrates, located in the spinal cord stem. Consists of interconnected clusters of nerve cell bodies (gray matter) and is believed to affect many physiological... ... Scientific and technical encyclopedic dictionary
- (formatio reticularis), a set of nerve structures located in the spinal, medulla oblongata, midbrain and pons and forming a single funkt. complex. Phylogenetically ancient engine system. control. Well developed in all ... ... Biological encyclopedic dictionary
Reticular formation- (Latin rete network, formatio formation, education, compilation) a network-like nervous structure, consisting of more than 50 nuclei and an extensive network of neurons with complex and branched axonal and dendritic processes. Name suggested... Encyclopedic Dictionary of Psychology and Pedagogy
A set of structures located in the spinal, medulla oblongata and midbrain and the pons and forming a single functional complex. It has an activating and inhibitory effect on various parts of the central nervous system, increasing ... ... encyclopedic Dictionary
reticular formation- (formatio reticularis) a set of small but numerous nuclei located in the central parts of the brain stem. Neurons of the reticular formation have strongly branching processes going in different directions, resembling under a microscope ... Glossary of terms and concepts on human anatomy
Reticular formation- (from lat. reticulum mesh) a nervous structure located along the entire brain stem and consisting of cells whose processes branch out in vast areas of the cerebral cortex. The function of the reticular formation is to activate the cerebral cortex ... ... Human psychology: glossary of terms
I Reticular formation (formatio reticularis; lat. reticulum mesh; synonymous with reticular substance) is a complex of cellular and nuclear formations that occupy a central position in the brain stem and in the upper spinal cord. Big… … Medical Encyclopedia
Books
- network society. Necessity and possible construction strategies. Network (reticular) socio-economic formation: quasi-socialist principles and meritocracy. Issue No. 133, Oleskin A.V. This book is devoted to the prospects for the use of decentralized cooperative network structures (networks) in various areas of human society, with special attention to their applications in…
Summary: the biological basis of attention is the orienting reflex.
I.P. Pavlov described the orienting reflex as an unconditioned reflex, serving as the basis involuntary attention. The very processes of attention in its system are explained, first of all, due to the interaction of excitation and inhibition occurring in the cerebral cortex of the brain. When a person is attentive to something, this means that a focus of excitation appears in his cerebral cortex. At the same time, all other parts of the brain are in a state of inhibition. Therefore, a person who is focused on one thing may not notice anything else at that moment. But these ideas about brain relationships are too abstract. To be convinced of this, it is worth comparing this approach with the approach of A.R. Luria.
The teachings of A.R. Luria. In the teachings of A.R. Luria on the cerebral localization of higher mental functions of a person, a structural-functional model of the brain is given, in which each higher mental function is performed due to the joint work of three brain blocks (Luria A.R. Fundamentals of neuropsychology. M., 1973). The first block (a block regulating the level of general and selective brain activation) is formed by non-specific structures of the reticular formation of the brain stem, structures of the midbrain, diencephalic parts of the brain stem, limbic system, mediobasal parts of the cortex of the frontal and temporal lobes of the brain. The second block (the block for receiving, processing and storing modal-specific information) is formed by the main analyzer systems (visual, auditory, skin-kinesthetic), the cortical zones of which are located in the posterior sections of the cerebral hemispheres. The third block (the block of programming, regulation and control over the course of the mental function, which ensures the formation of motives for activity and control over the results of activity through a large number of bilateral connections with cortical and subcortical structures) is formed by the motor, premotor and prefrontal sections of the cerebral cortex. At the same time, the sequence of work of these structures is important: at the first stage, there is an incentive to activity, the basis of which is, among other things, the activation of the reticular formation.
The role of the reticular formation. The ability to be alert, sometimes reacting to a very slight change in environment, is provided by networks of nerve pathways located in the cerebral hemispheres connecting the reticular formation (a set of brain structures that regulate the level of excitability) with different parts of the cerebral cortex. Nerve impulses traveling through this network arise along with signals from the sense organs and excite the cortex, bringing it into a state of readiness to respond to future irritations expected in the future. Thus, the reticular formation with its ascending and descending fibers, together with the sense organs, causes the appearance of an orienting (or orienting-exploratory) reflex, being the primary physiological basis attention.
Back in 1935, F. Bremer compared electroencephalograms with two types of brainstem transection: a) at the level of the cervical vertebrae (a drug called "encephale isole" - the lower sections of the trunk) and b) at the level of the bridge (the drug "cerveau isole" - upper parts of the trunk). In the first case, the recordings of bioelectrical activity did not differ from the EEG of normal animals, while in the second case, slow waves of large amplitude, characteristic of the state of sleep, were constantly present in the EEG. In preparations called "cerveau isole", only visual and olfactory afferent stimuli reach the cortex, since the signals transmitted by other cranial nerves (in particular, auditory and trigeminal) are cut. From this, F. Bremer concluded that when the central nervous system loses most of the stimulation emanating from the outside world, sleep occurs; accordingly, maintaining the state of wakefulness is the result of the activating effect exerted by sensations. As D. Lindsley later showed, in these cases the signals caused by sensory stimuli continue to reach the cortex, but the electrical responses of the cortex to these signals become only short-lived and do not cause permanent changes. This showed that for the emergence of persistent excitation processes that characterize the state of wakefulness, one influx of sensory impulses is not enough, a supporting influence of the activating reticular system is necessary.
These ideas about the processes of general activation were further developed in the works of G. Moruzzi and G. Magun (Moruzzi G., Magoun H.W. Brain stem reticular formation and activation of the EEG // EEG and Clinical Neurophysiology. 1949, 1 - “Reticular formation of the brain stem and activation response in the EEG). They conducted experiments based on electrical stimulation of the brain, which revealed the functions of a non-specific system of the brain - the reticular formation of the brain stem, which, along with the limbic system, is referred to as "modulating" systems of the brain. The main function of these systems is the regulation of the functional states of the body. The researchers did not turn off, but irritated the ascending reticular formation with electrodes implanted in it, showed that such stimulation of the reticular formation leads to the awakening of the animal, and further intensification of these stimuli leads to the appearance of pronounced effective reactions of the animal. It turned out that when she was irritated electric shock, an activation reaction occurs, and when this structure is removed, coma occurs. These structures are actually responsible for maintaining the state of wakefulness, and the degree of their activity itself depends in part on sensory influences. However, contrary to what Bremer suggested, the activating influence of sensory is not in the form of direct activation of the cerebral cortex by specific signals; it affects primarily the reticular formation, the activity of which, in turn, regulates the functional state of the cortex, motor and vegetative centers. It was found that the cortical sleep of Bremer's "cerveau isole" preparations was caused not by the cutting of specific sensory pathways to the cortex, but by the elimination of the influence exerted on it by the reticular formation.
Also in the experiments of D. Lindsley, it was found that irritation of the stem nuclei of the ascending activating reticular formation significantly lowers the sensitivity thresholds (in other words, exacerbate sensitivity) of the animal and allows subtle differentiations (for example, differentiation of the image of a cone from the image of a triangle), which were previously inaccessible to the animal .
Neuroanatomy of the reticular formation. Initially, it was believed that the nonspecific brain system that performs the task of diffuse and generalized activation of the cerebral cortex included only reticular formations of the brain stem. It is now accepted that the ascending non-specific activating system takes place from the medulla oblongata to the visual tubercle (thalamus).
The reticular (from the Latin word reticulum - mesh) formation consists of numerous groups of neurons that do not have clear boundaries. Such an accumulation of nerve cells, according to its principle of organization, resembles the nerve networks of intestinal cavities. Their long and highly branching processes form networks around the gray matter of the spinal cord and in the dorsal part of the brainstem. It was first described in the middle of the 19th century, and O. Deiters gave the name to this structure. In the reticular formation of the brain stem, more than 100 nuclei are isolated, which, from the spinal cord to the diencephalon, are combined into three main groups. 1) The median group of nuclei is concentrated around the midline, mainly in the region of the suture of the bridge and the medulla oblongata (nucleus of the suture), which are formed by the fibers of the sensory pathways coming from the spinal cord, the nuclei of the trigeminal nerve and forming a decussation along the midline. 2) The medial group of nuclei is located on the sides of the previous one: it includes the medial large cell nucleus, the bluish place, neurons of the central gray matter of the midbrain, etc. 3) The lateral group of nuclei is located lateral to the medial and includes the lateral reticular nucleus, parabrachial nuclei, etc.
The neurons of the reticular formation have different sizes: in the median and medial nuclei there are large nerve cells that form long afferent and efferent pathways, and in the lateral nuclei there are medium and small neurons, which are mainly associative neurons.
Most neurons of the reticular formation use peptides (enkephalins, neurotensin, etc.) as a transmitter of a nerve impulse, but monoamines are also widely represented. The raphe nuclei contain serotonergic neurons, and the bluish locus contains noradrenergic ones.
Connections of the reticular formation are divided into afferent and efferent. Afferent fibers end on its neurons: from the spinal cord, following along the branches of all sensory pathways, as well as along the spinoreticular tract, from the nuclei of the cranial nerves as part of the collaterals of the nuclear-cortical, auditory and visual pathways, from the cerebellum as part of the cerebellar-reticular pathway, from the nuclei of the thalamus, subthalamus and hypothalamus, the striatum, structures of the limbic system, various parts of the cerebral cortex, including along the branches of the cortical-spinal and cortical-nuclear tracts. Neurons of the reticular formation have long thin efferent processes, divided into ascending and descending branches, which are directed to various parts of the brain and spinal cord: motor neurons of the anterior horns of the spinal cord and motor nuclei of the cranial nerves of the brain stem as part of the reticulonuclear and reticulo-cerebellar pathways, cerebellum, red nucleus, substantia nigra and nuclei of the spinal cord roof plate, reticular nuclei of the thalamus, nuclei of the hypothalamus, indirectly, through the nuclei of the diencephalon to the striatum, limbic system and neocortex.
With the help of the reticular formation, the motor and autonomic nuclei of the brain stem are combined into functional centers, regulating many complex forms of behavior: circulatory, respiratory, coughing, swallowing, vomiting, etc. The reticular formation provides: 1) Maintaining the state of wakefulness. By increasing or decreasing the flow of sensory information to the cerebral cortex and subcortical structures, the reticular formation plays the role of a regulator of the level of consciousness (sleep/wake cycle). By regulating the mediator exchange of neurons of the reticular formation or by modulating the activity of their receptors with the help of certain medicines, you can activate the activity of the cerebral cortex, or vice versa - to achieve sleep. For example, caffeine contained in coffee or tea stimulates the nerve cells of the reticular formation. On the contrary, among psychotropic drugs (from the Greek psyche - soul + tropos - direction) there are so-called neuroleptics, which, by blocking the reticular formation of the brain and reducing the speed of excitation, act in a calming way (suppress delirium, hallucinations, fear, aggressiveness, psychomotor agitation ). 2) Control of reflex activity by stimulating or inhibiting the motor neurons of the anterior horns of the gray matter of the spinal cord and the motor nuclei of the cranial nerves of the brain stem. 3) Combining a group of neurons from different parts of the brain and spinal cord, which makes it possible to perform complex reflex acts: swallowing, chewing, coughing, vomiting, etc. 4) Ensuring autonomic regulation by coordinating efferent and afferent signals in the corresponding centers of the brain stem. Thus, the vasomotor and respiratory centers combine groups of neurons responsible for the regulation of respiration and blood circulation. 5) Participation in the emotional perception of sensitive signals by increasing or decreasing the flow of afferent impulses to the limbic system.
The selective nature of the course of mental processes, which is characteristic of attention, is provided only by the waking state of the cortex with an optimal level of excitability. This wakeful level is achieved due to the work of the mechanisms of connection of the upper trunk with the cerebral cortex and, above all, with the work of the ascending activating reticular formation. It is this ascending activating reticular formation that conveys to the cortex, keeping it in a state of wakefulness, impulses associated with the body's metabolic processes, drives, with exteroreceptors that bring information from the outside world. First, this flow goes to the upper sections of the trunk and the nucleus of the thalamus, and then to the cerebral cortex.
Ensuring the optimal tone and waking state of the cortex is carried out, however, not only by the ascending activating reticular formation. The apparatus of the descending system is also closely connected with it, the fibers of which begin in the cerebral cortex (primarily in the medial and mediobasal sections of the frontal and temporal lobes) and go both to the nuclei of the brainstem and to the motor nuclei of the spinal cord. The work of the descending reticular formation is very important because with its help those forms of excitation that initially arise in the cerebral cortex and are the product of higher forms conscious human activity with its complex cognitive processes and complex programs of life-formed actions.
The interaction of both constituent parts activating reticular system and provides the most complex forms of self-regulation of active states of the brain, changing them under the influence of both elementary (biological) and complex (social in origin) forms of stimulation.
