Reticular formation of the brain structure and function. Q47. Reticular formation of the brainstem. Brainstem reticular formation

The reticular (reticular) formation is a cluster of neurons of various functions and sizes, connected by many nerve fibers passing in different directions and forming a network along the entire length of the brain stem, which determines its name. Neurons are located either diffusely or form nuclei.

Neurons reticular formation have long, low-branching dendrites and well-branching axons, which often form a T-shaped branch: one of the branches of the axon has a descending direction, and the other has an ascending direction.

A. Functional features of neurons of the reticular formation:

podimodalyust - the neurons of the reticular formation are characterized by polysensory convergence; they receive collaterals from several sensory pathways coming from different receptors;

tonic activity, at rest equal to 5-10 imp / s;

high sensitivity to certain blood substances (for example, adrenaline, CO2) and drugs (barbiturates, chlorpromazine, etc.);

More pronounced excitability compared to other neurons;

high lability - up to 500-1000 imp / s.

Neurons and nuclei of the reticular formation are part of the centers that regulate the functions of internal organs (blood circulation, respiration, digestion), skeletal muscle tone (see Section 5.3), and cortical activity large brain... The connections of the reticular formation with other parts of the central nervous system and reflexogenic zones are extensive: it receives impulses from various receptors of the body and parts of the central nervous system and, in turn, sends impulses to all parts of the brain. At the same time, the ascending and descending influences of the reticular formation are distinguished.

B. Descending influences of the reticular formation on the motor spinal centers. From the reticular giant cell nucleus of the medulla oblongata, there is a partially crossed lateral reticulospinal tract, the fibers of which end on the interneurons of the spinal cord. Through these interneurons, they excite the a- and y-motor neurons of the flexor muscles of the limb muscles and reciprocally inhibit the extensor muscles with the help of inhibitory interneurons.

From the caudal and oral reticular nuclei of the pons there is an uncrossed medial reticulospinal tract, the fibers of which end on the interneurons of the spinal cord. Through them, stimulation of the a- and y-motor neurons of the extensor muscles is carried out, and the flexor muscles are inhibited through the inhibitory interneurons. See fig. 5.9.

C. The upward effects of RF on the large brain can be both activating and inhibitory. The impulses of the reticular neurons of the medulla oblongata (giant cell, lateral and ventral reticular nuclei), pons (especially the caudal reticular nucleus) and midbrain arrive at the nonspecific nuclei of the thalamus, and, after switching into them, are projected into various areas of the cortex. In addition to the thalamus, ascending influences also enter the posterior hypothalamus, the striatum.

In the experiment, after transection of the brain stem between the upper and lower hillocks of the quadruple (isolated forebrain), the supply of excitation to the cerebral cortex through the most important sensory systems - visual and olfactory - was not disturbed in the animal. However, the animal behaved as if it were asleep: it had broken contact with the outside world, it did not react to light and olfactory stimuli (the sleeping brain according to Bremer). Slow-wave regular rhythms predominated on the EEG in such animals. In humans, similar rhythms occur during calm wakefulness and in a drowsy state. The same state of the brain (dormant brain) is observed when only the ascending pathways of the reticular formation are damaged.

Stimulation of the reticular formation causes the awakening of the animal [Megun G., Moruzzi J., 1949]. On the EEG, slow rhythms are replaced by high-frequency rhythms (desynchronization reaction), indicating an activated state of the cerebral cortex. Based on the data obtained, the idea was formed that the most important function of the ascending reticular formation is the regulation of the sleep / wakefulness cycle and the level of consciousness.

The inhibitory effect of the reticular formation on the large brain has been much less studied. W. Hess (1929), J. Moruzzi (1941) established that by stimulating some points of the reticular formation of the brain stem, it is possible to transfer an animal from a waking state to a sleepy one. In this case, a reaction of synchronization of EEG rhythms occurs.

BRAIN COMMUNICATION SYSTEMS

Connections between different parts of the central nervous system are carried out using nerve pathways that go in different directions and perform different functions, which is the basis for their classification. In particular, in the spinal cord, as in other parts of the central nervous system, they release ascending and descending paths(the determining factor of this classification is the direction of the pulse flow).

In addition, in the brain stem, the ascending systems are subdivided into specific and non-specific.

The ascending and descending pathways of the spinal cord are discussed in section 5.2.2.

Brain stem conduction function performed by descending and ascending paths, some of which are switched at stem centers, the other part is transient (without switching).

A. Ascending paths are part of the conductive section of the analyzers that transmit information from receptors to the projection zones of the cortex. In the brain stem, two ascending systems are distinguished: specific and nonspecific.

1. A specific ascending system constitutes the lemniscot-lamic pathway, in which the medial and lateral loops are distinguished. The medial loop is formed mainly from the axons of the neurons of the thin nucleus (Gaulle) and the wedge-shaped nucleus (Burdach), which conduct impulses from the proprioceptors. The fibers of the medial loop are switched in the ventral posterior specific nuclei of the thalamus. The medial loop enters the conduction section of the auditory analyzer, its fibers switch in the medial geniculate body of the thalamus and the lower tubercles of the quadruple. The specific conducting system includes the pathways of the visual and vestibular analyzers. Impulses through specific ascending pathways they enter the cortical end of the corresponding analyzer (visual, auditory, etc.).

2. Nonspecific (extralantic) ascending pathways switch in nonspecific (intralaminar and reticular) nuclei of the thalamus. These are mainly fibers of the lateral spinothalamic and spinoreticular tracts, which conduct temperature and pain sensitivity. The impulse from them is projected into various areas of the cortex (especially the frontal orbital cortex). A nonspecific system receives collateral fibers from a specific system, which provides a connection between these two ascending systems. A functional feature of the nonspecific system is the relatively slow conduction of excitation. The receptive fields of neurons are large, the neurons are gulimodal, associated with several types of sensitivity, the topography of the projection of the periphery in the centers is not expressed.

3. Part of the afferent impulses enters the cerebellum through other systems. The posterior spinal-cerebellar tract of Flexig and the anterior spinal-cerebellar tract of Govers pass through the brain stem into the cerebellum, conducting impulses from the receptors of muscles and ligaments, as well as the vestibulocerebellar tract, which carries information from the vestibular receptors. From the cerebellar cortex, information is transmitted to the ventral nuclei of the thalamus, then it is projected into the somatosensory, motor and premotor zones of the cerebral cortex. B. Descending pathways of the brainstem include motor pyramidal paths, starting from Betz cells of the cortex of the precentral gyrus. They innervate the motor neurons of the anterior horns of the spinal cord (corticospinal tract), motor neurons of the motor nuclei of the cranial nerves (corticobulbar tract), providing voluntary contractions of the muscles of the limbs, trunk, neck and head. Brainstem motor centers and their pathways are an essential component extrapyramidal system, the main function of which is the regulation of muscle tone, posture and balance. This system at the level of the brainstem includes the corticorubal and corticoreticular tracts, terminating at the motor centers of the trunk, from which the rubro-, reticulo- and vestibulospinal pathways go. The extrapyramidal system is a collection of nuclei of the brain stem of the extrapyramidal system. Its main elements are: striatum, pallidum, red nucleus, reticular formation.

In the brain stem, there are descending pathways that provide the motor functions of the cerebellum; these include the cortico-cerebellopontine pathway, through which impulses from the motor and other areas of the cortex enter the cerebellum. The information processed in the cerebellar cortex and its nuclei enters the motor nuclei of the trunk (red, vestibular, reticular). The tectospinal tract, which begins in the quadruple, passes through the brain stem, which provides the body's motor responses in orienting visual and auditory reflexes. All motor reactions of the body are carried out by descending systems with the help of a- and y-motor neurons of the spinal cord and neurons of the motor nuclei of the cranial nerves.

CEREBELLUM

Cerebellum located behind the cerebral hemispheres, above the medulla oblongata and the bridge. Together with the latter, it forms the hindbrain. The cerebellum contains more than half of all neurons in the central nervous system, although it makes up 10% of the mass of the brain. This indicates the great possibilities of information processing by the cerebellum. It plays an important role in the integration of motor and autonomic reactions, in particular in the coordination of voluntary and involuntary movements, maintaining balance, and regulating muscle tone.

A. Functional organization. Allocate three structures cerebellum, reflecting the evolution of its functions:

The ancient cerebellum (archycerebellum) consists of a clump and nodule (flocculonodular lobe) and the lower part of the worm; has the most pronounced connections with the vestibular system, therefore it is also called the vestibular cerebellum;

The old cerebellum (paleocerebellum) includes the upper part of the worm, the parafloccular region, the pyramids, and the uvula; receives information primarily from proprioceptors. It is also called the spinal cerebellum;

The new cerebellum (neocerebellum) consists of two hemispheres. He receives information from the cortex, mainly along the frontal-cerebellopontine pathway, from the visual and auditory receptive systems, which indicates his participation in the analysis of visual, auditory signals and the organization of reactions to them.

1. Interneuronal connections in the cortex of the cerebellar hemispheres, its afferent inputs and efferent outputs are very diverse. Piriform neurons (Purkinje cells) form the middle II (ganglionic) layer of the cortex, which is the main functional unit of the cerebellum. The structural basis is provided by numerous branching dendrites, on which there can be up to 100,000 synapses in one cell.

Purkinje cells are the only efferent neurons of the cerebellar cortex and provide its connection with the cerebral cortex, stem formations and the spinal cord. These cells directly connect its cortex with the intracerebellar and vestibular nuclei. In this regard, the functional influence of the cerebellum essentially depends on the activity of Purkinje cells.

Information to Purkinje cells (afferent inputs) comes from almost all receptors: muscle, vestibular, skin, visual, auditory; from the neurons of the base of the posterior horns of the spinal cord (along the spinal-olive path), as well as from the motor cortex of the brain, the associative cortex and the reticular formation.

The influence of certain structures of the brainstem, such as the macula and the nuclei of the suture, is transmitted to the cerebellum.

The predominant direct and indirect afferent effect on Purkinje cells is excitatory. But since Purkinje cells are inhibitory neurons ( GABA mediator), then with their help the cerebellar cortex converts excitatory signals at the input into inhibitory signals at the output. Thus, the efferent effect of the cerebellar cortex on the subsequent neural link (mainly the intracerebellar nuclei) is inhibitory. Under II the layer of the cortex (under the Purkinje cells) is a granular (III) layer consisting of grain cells, the number of which reaches 10 billion. The axons of these cells rise upward, divide in a T-shape on the surface of the cortex, forming paths of contacts with Purkinje cells. Here are the Golgi cells.

The upper (I) layer of the cerebellar cortex is molecular, consists of parallel fibers, dendritic branches and axons of layers II and III. In the lower part of the molecular layer, baskets and stellate cells are found, which ensure the interaction of Purkinje cells.

Stimulation of the upper layer of the cerebellar cortex leads to long-term (up to 200 ms) inhibition of Purkinje cell activity. The same inhibition occurs with light and sound signals. The total changes in the electrical activity of the cerebellar cortex to irritation of the sensory nerve of any muscle cause inhibition of the activity of the cortex (hyperpolarization of Purkinje cells), which occurs after 15-20 ms and lasts 20-30 ms, after which an excitation wave occurs, lasting up to 500 ms (depolarization of Purkinje cells).

Background impulse activity of neurons is recorded in the layer of Purkinje cells and the granular layer, and the frequency of generation of impulses of these cells ranges from 20 to 200 per second.

2. Subcortical system of the cerebellum includes three functionally different nuclear formations: the core of the tent, cork-shaped, spherical and toothed nuclei.

The tent nucleus receives information from the medial zone of the cerebellar cortex and is connected with the Deiters nucleus and the reticular formation of the medulla oblongata and midbrain. From here, the signals travel along the reticulospinal pathway to the motor neurons of the spinal cord.

The intermediate cerebellar cortex is projected onto the corky and spherical nuclei. From them, connections go to the midbrain to the red nucleus, then to the spinal cord along the rubrospinal path.

The dentate nucleus receives information from the lateral zone of the cerebellar cortex, it is connected with the thalamus, and through it - with the motor zone of the cerebellar cortex.

The cells of the cerebellar nuclei generate pulses much less frequently (1-3 per second) than the cells of the cerebellar cortex (Purkinje cells -20-200 pulses per second).

3. The cerebellum is connected to adjacent parts of the brain by three pairs of legs. The lower cerebellar legs connect the cerebellum with the medulla oblongata, the middle ones with the bridge, the upper ones with the midbrain. Through the pathways of the legs, the cerebellum receives afferent impulses (inputs) from other parts of the brain and sends efferent impulses (outputs) to various structures of the brain.

Through the upper legs, signals go to the thalamus, pons, red nucleus, brain stem nuclei, and the reticular formation of the midbrain. The middle pedicles of the cerebellum connect the new cerebellum to the frontal lobe of the brain. Through the lower legs of the cerebellum, signals go to the medulla oblongata, to its vestibular nuclei, olives, and the reticular formation.

Afferent impulses to the cerebellar cortex from skin receptors, muscles, articular membranes, periosteum enters the so-called spinal-cerebellar tracts: posterior (dorsal) and anterior (ventral). These pathways to the cerebellum pass through the inferior olive of the medulla oblongata. From the olive cells there are the so-called climbing fibers, which branch on the dendrites of the Purkinje cells.

The nuclei of the pons send afferent pathways to the cerebellum, forming mossy fibers that terminate in the grain cells of layer III of the cerebellar cortex. There is an afferent connection between the cerebellum and the midbrain macula using adrenergic fibers. These fibers are able to diffusely release norepinephrine into the intercellular space of the cerebellar cortex, thereby humorally changing the state of excitability of its cells.

The considered structural and functional organization of cerebellar neurons makes it possible to understand its somatic and autonomic functions.

B, Motor functions of the cerebellum consist in the regulation of muscle tone, posture and balance, coordination of the performed purposeful movement, programming purposeful movements.

1. Muscle tone and posture are regulated mainly by the ancient cerebellum (flocculonodular lobe) and partially by the old cerebellum, which are part of the medial worm zone. Receiving and processing impulses from vestibular receptors, from prioreceptors of the movement apparatus and skin receptors, from visual and auditory receptors, the cerebellum is able to assess the state of the muscles, the position of the body in space and through the nucleus of the tent, using the vestibulo-, reticulo- and rubrospinal tracts, to redistribute the muscle tone, change body posture and maintain balance. Imbalance is the most characteristic symptom of arthicerebellum lesion.

2. Coordination of the movement performed carried out by the old and new cerebellum, which is part of the intermediate (periworm) zone. The cortex of this part of the cerebellum receives impulses from proprioceptors, as well as impulses from the motor cortex, which is a program of voluntary movement. By analyzing information about the program and the execution of movement (from proprioceptors), the cerebellum is able, through its intermediate nucleus, which has outputs to the red nucleus and the motor cortex, to coordinate the posture and the targeted movement performed in space, and also to correct the direction of movement. For example, approaching the door, we raise our hand to press the bell button. In the beginning, our movement is indicative; we would also raise our hand to correct our hair, put on glasses. However, at some stage, this movement becomes only a movement towards the button, and in order for the finger to hit the button, a certain coordination of the actions of the antagonist muscles is needed, and the greater the closer the goal of the movement is. Outwardly, the movement towards the goal proceeds in a straight line, without sharp bends in the trajectory, but this external “smoothness” of movement requires a constant redistribution of the “attention” of the central regulatory apparatus from one muscle group to another. Impaired coordination of movement is the most characteristic symptom of dysfunction of the intermediate zone of the cerebellum.

3. The cerebellum is involved in the programming of movements, which is carried out by its hemispheres. The cerebellar cortex receives impulses mainly from the associative zones of the cerebral cortex through the nucleus of the pons. This information characterizes the intention of the movement. In the cortex of the new cerebellum, it is processed into a movement program, which in the form of impulses again enters through the thalamus into the premotor and motor cortex and from it through the pyramidal and extrapyramidal systems to the muscles. Control and correction of slower programmed movements are carried out by the cerebellum on the basis of reverse afferentation mainly from proprioceptors, as well as from vestibular, visual, tactile receptors.Correction of fast movements due to the short time of their execution is carried out by changing their program in the cerebellum itself, i.e. on the basis of training and previous experience. exercises, typing, playing musical instruments.

B. The motor functions of the cerebellum play an important role in the regulation of muscle tone, preservation of posture, coordination of the performed movements, in the programming of planned movements. If the cerebellum does not fulfill its regulatory function, then a person is observed disorders of motor functions. These disorders are manifested by various symptoms that are related to each other.

1. Dystopia(distonia - violation of tone) - increase or decrease in muscle tone. With damage to the cerebellum, an increase in the tone of the extensor muscles is observed. The nature of the effect on muscle tone is determined by the frequency of generation of pulses of the tent nucleus neurons. At a high frequency (30-300 pulses / s), the tone of the extensor muscles decreases, at a low frequency (2-10 pulses / s), it increases. In case of damage to the cerebellum, neurons of the vestibular nuclei and the reticular formation of the medulla oblongata are activated, which activate the motor neurons of the spinal cord. At the same time, the activity of pyramidal neurons decreases, and, consequently, their inhibitory effect on the same motor neurons of the spinal cord decreases. As a result, receiving excitatory signals from the medulla oblongata with a simultaneous decrease in inhibitory influences from the cerebral cortex, the motor neurons of the spinal cord are activated and cause hypertonicity of the extensor muscles.

2. Asthenia(astenia - weakness) - a decrease in the strength of muscle contraction, rapid muscle fatigue.

3. Astasia(astasia, from the Greek. a - not, stania - standing) - loss of the ability to prolonged muscle contraction, which makes it difficult to stand, sit.

4. Tremor(tremor - trembling) - trembling of fingers, hands, head at rest; this tremor increases with movement.

5 dysmetry(dismetria - violation of the measure) - a disorder of the uniformity of movements, expressed either in excessive or inadequate movement. The patient tries to take an object from the table and brings the hand of the object (hypermetria) or does not bring it to the object (hypometria).

6. Ataxia(ataksia, from the Greek. a - not, 1taksia - order) - impaired coordination of movements. Here, the impossibility of performing movements in the right order, in a certain sequence, is most clearly manifested. Manifestations of ataxia are also adiadochokinesis, asynergy, drunkenness - a wobbly gait. With adiadochokinesis, a person is not able to quickly rotate the palms up and down. With asynergy of muscles, he is not able to sit up from a lying position without the help of his hands. A drunken gait is characterized by the person walking with their legs wide apart, staggering from side to side.

7. Dysarthria(disartria - disorder of the organization of speech motor skills). When the cerebellum is damaged, the patient's speech becomes stretched, the words are sometimes pronounced as if in jerks (chanted speech).

The data that damage to the cerebellum leads to movement disorders that were acquired by a person as a result of training allow us to conclude that learning itself takes place with the participation of cerebellar structures, and therefore the cerebellum takes part in organizing the processes of higher nervous activity. When the cerebellum is damaged, cognitive processes are affected.

After the operation of partial removal of the cerebellum, symptoms of its damage appear, which then disappear. If, against the background of the disappearance of the cerebellar symptoms, the function of the frontal lobes of the brain is disturbed, then the cerebellar symptoms reappear. Consequently, the cortex of the frontal lobes of the brain compensates for the disorders caused by damage to the cerebellum. The mechanism of this compensation is realized through the fronto-cerebellar tract.

D. The cerebellum, due to its influence on the sensorimotor area of ​​the cortex, can change the level of tactile, temperature, and visual sensitivity.

Removal of the cerebellum leads to a weakening of the strength of the processes of excitation and inhibition, an imbalance between them, and the development of inertia. The development of conditioned motor reflexes after removal of the cerebellum is hampered, especially during the formation of a local, isolated motor reaction. In the same way, the production of conditioned food reflexes slows down, the latent period of their call increases.

5.7. INTERMEDIATE BRAIN

The diencephalon is located between the midbrain and the telencephalon, around the third ventricle of the brain. It consists of the thalamic region and the hypothalamus. The thalamic region includes the thalamus, metathalamus (geniculate bodies), and epithalamus (pineal gland). In the literature on physiology, the metathalamus is combined with the thalamus, the pineal gland is considered in the endocrine system.

Thalamus- a paired nuclear complex, which occupies mainly the dorsal part of the diencephalon. In the thalamus, up to 40 paired nuclei are distinguished, which in functional terms can be divided into the following three groups: relay, associative and nonspecific. All thalamic nuclei, to varying degrees, have three common functions: switching, integrative and modulating.

A. Switching nuclei of the thalamus(relay, specific) are divided into sensory and non-sensory.

1. The main function sensory nuclei is the switching of the streams of afferent impulses into the sensory zones of the cerebral cortex. Along with this, transcoding and information processing takes place. The main sensory nuclei are as follows.

Ventral posterior nuclei are the main relay for switching the somatosensory afferent system. They switch tactile, proprioceptive, gustatory, visceral, partly temperature and pain sensitivity. In these nuclei there is a topographic projection of the periphery, therefore, electrical stimulation of the ventral posterior nuclei causes parasthesias (false sensations) in different parts of the body, sometimes a violation of the "body scheme" (distorted perception of body parts).

Lateral geniculate body acts as a relay for switching visual impulses to the occipital cortex, where it is used to form visual sensations. In addition to the cortical projection, part of the visual impulses is directed to the upper hillocks of the quadruple. This information is used to regulate eye movement in the visual orientation reflex.

The medial geniculate body is a relay for switching auditory impulses to the temporal cortex of the posterior part of the sylvian sulcus (Heschl gyrus, or transverse temporal gyrus).

2.K non-sensory switching nuclei of the thalamus include the anterior and ventral nuclei. They switch non-sensory impulses into the cortex that enter the thalamus from different parts of the brain. V front ventral, medial and dorsal kernels impulses come from the hypothalamus. The anterior thalamic nuclei are considered part of the limbic system and are sometimes referred to as the "thalamic limbic nuclei".

Ventral nuclei participate in the regulation of movement, thus performing a motor function. In them, impulse is switched from the basal ganglia, the dentate nucleus of the cerebellum, the red nucleus of the midbrain, which is then projected into the motor and premotor cortex.

Along with the cortical projections of the switching nuclei, each of them receives descending cortical fibers from the same projection zone, which creates the structural basis for the mutually regulating relationship between the thalamus and the cortex.

B. Associative nuclei of the thalamus include cushion nuclei, mediodorsal nucleus, and lateral nuclei. Fibers to these nuclei come not from the conductive pathways of the analyzers, but from other nuclei of the thalamus. Efferent outputs from these nuclei are directed mainly to the associative fields of the cortex. In turn, the cerebral cortex sends fibers to the associative nuclei, regulating their function. The main function of these nuclei is the integrative function, which is expressed in the unification of the activity of both the thalamic nuclei and various zones of the associative cortex of the cerebral hemispheres.

Pillow receives the main entrances from the geniculate bodies and nonspecific nuclei of the thalamus. Efferent pathways from it go to the temporal-parietal-occipital zones of the cortex involved in gnostic (recognition of objects, phenomena), speech and visual functions (for example, in the integration of words with the visual image), as well as in the perception of the "body scheme".

V lateral nuclei visual and auditory impulses come from the geniculate bodies and somatosensory impulses from the ventral nucleus. The integrated sensory information from these sources is further projected into the associative parietal cortex and used in its function of gnosis, praxis, and the formation of a "body scheme".

Mediodorsal nucleus receives impulses from the hypothalamus, amygdala, hippocampus, thalamic nuclei, central gray matter of the trunk. The projection of this nucleus extends to the associative frontal and limbic cortex. It is involved in the formation of emotional and behavioral motor activity, as well as, possibly, in the formation of memory.

C. Nonspecific nuclei constitute an evolutionarily more ancient part of the thalamus, its nuclei contain predominantly small, multifaceted neurons and are functionally considered as a derivative of the reticular formation of the brainstem. The nonspecific nuclei receive impulses from other nuclei of the thalamus along the tracts that conduct mainly pain and temperature sensitivity. Part of impulses along collaterals from all specific sensory systems... In addition, impulses from the motor centers of the trunk (red nucleus, black matter), cerebellar nuclei, basal ganglia and hippocampus, as well as from the cerebral cortex, especially the frontal lobes, come to the nonspecific nuclei. Nonspecific nuclei have efferent outputs to other thalamic nuclei, the cerebral cortex both directly and through the reticular nuclei, as well as descending pathways to other structures of the brain stem, i.e., these nuclei, like other parts of the reticular formation, have ascending and descending influence.

The nonspecific nuclei of the thalamus act as an integrating mediator between the brainstem and cerebellum, on the one hand, and the neocortex, limbic system, and basal ganglia, on the other, uniting them into a single functional complex. The nonspecific thalamus has a predominantly modulating effect on the cerebral cortex. The destruction of nonspecific nuclei does not cause gross disorders of emotions, perception, sleep and wakefulness, the formation of conditioned reflexes, but only violates the fine regulation of behavior.

The hypothalamus is the ventral part of the diencephalon; macroscopically, it includes the preoptic region and the optic nerve intersection, the gray tubercle and funnel, and the mastoid bodies. In the hypothalamus, up to 48 paired nuclei are isolated, which are subdivided by different authors into 3-5 groups.

The hypothalamus is a multifunctional system with broad regulating and integrating influences. However, the most important functions of the hypothalamus are difficult to relate to its individual nuclei. Typically, a single kernel has several functions. In this regard, the physiology of the hypothalamus is usually considered in the aspect of the functional specificity of its various areas and zones. The hypothalamus is the most important center for the integration of autonomic functions, regulation of the endocrine system, heat balance of the body, the cycle "wakefulness - sleep" and other biorhythms; its role is great in the organization of behavior (food, sexual, aggressive-defensive), aimed at the realization of biological needs, in the manifestation of motivations and emotions.

BASAL GANGLES

The nasal ganglia are located at the base of the cerebral hemispheres and include three paired formations: the pallidus, phylogenetically later, the formation is the striatum, and the youngest part is the fence. The globus pallidus consists of an outer and an inner segment; the striatum includes the caudate and the shell.

A. Functional connections of the basal ganglia. Afferent impulses in the basal ganglia it enters mainly the striatum mainly from three sources: 1) from all areas of the cortex directly and through the thalamus; 2) from black matter; 3) from nonspecific thalamic nuclei.

Among efferent connections of the basal ganglia, three outputs can be noted:

From the striatum, the paths go to the pallid ball. From the globus pallidus begins the most important efferent tract of the basal ganglia into the thalamus, into its relay ventral nuclei, from which the excitatory pathway goes to the motor cortex;

Part of the efferent fibers from the pallidus and striatum follows to the centers of the brain stem (reticular formation, red nucleus and further to the spinal cord), as well as through the inferior olive to the cerebellum;

From the striatum, the inhibitory pathways go to the substantia nigra and, after switching, to the nuclei of the thalamus.

The basal ganglia are an intermediate link (switching station) connecting the associative and partly sensory cortex with the motor cortex. Let's consider the functions of individual structures of the basal ganglia.

B. Functions of the striatum. 1. The striatum has a twofold effect on the pallidum - exciting and inhibitory with a predominance of the latter, which is carried out mainly through thin inhibitory fibers (mediator GABA).

2. The striatum has inhibitory influence(a mediator of GABA) on the neurons of the substantia nigra, which in turn exert modulating influence(mediator dopamine) on corticostriatal communication channels.

3. Effects on the cerebral cortex: irritation of the striatum causes synchronization of the EEG - the appearance of high-amplitude rhythms in it, characteristic of the phase of slow sleep. The destruction of the striatum decreases the sleep time in the wake-sleep cycle.

4. Striatal stimulation through chronically implanted electrodes, it causes relatively simple motor reactions: turning the head and body to the side opposite to irritation, sometimes bending the limb on the opposite side. Stimulation of some zones of the striatum causes a delay in the current behavioral activity - motor, orientation, food. The animal seems to "freeze" in one position. At the same time, slow high-amplitude rhythms develop on the EEG. Irritation of some points of the striatum leads to suppression of the sensation of pain.

When the striatal system is damaged, a hypotonic-hyperkinetic syndrome occurs, which is due to a deficiency of the inhibitory effect of the striatum on the underlying motor centers, as a result of which muscle hypotension and excessive involuntary movements (hyperkinesis) develop. Hyperkinesis - automatic excessive movements involving individual parts of the body, limbs. They arise involuntarily, disappear in sleep, and intensify with voluntary movements and excitement.

Certain types of hyperkinesis are associated with damage to certain structures of the striatal system. With the defeat of the oral part of the striatum, violent movements occur in the muscles of the face and neck, with damage to the middle part, in the muscles of the trunk and arms. Lesion in the caudal striatum causes hyperkinesis in the legs. The specific symptoms of striatum lesions are very diverse.

Athetosis - slow, worm-like, pretentious movements in the distal extremities (in the hands and feet). Can be observed in the muscles of the face: protruding lips, twisting of the mouth, grimacing, tongue clicking. Usually athetosis is associated with damage to large cells of the striatal system. Its characteristic feature is the formation of transient contractures (zraztia gloIN $), which give the hand and fingers a peculiar position. In children, bilateral, double athetosis is often observed with subcortical degenerations. Hemiatetosis is much less common.

Hemiballism - sweeping throwing movements in the limbs, most often in the hands in the form of a "bird's wing" flap. Violent movements with hemiballism are made with great force, it is difficult to stop them. The occurrence of hemiballism is associated with a lesion of the submilky nucleus (Lewis body), located under the optic hillock.

The variety of functions performed by different parts of the reticular formation is presented in the table below.

a) Motion program generators... Cranial nerve movement programs include the following:
Concomitant (parallel) eye movements, locally controlled by motor nodes (gaze centers) in the midbrain and pons, which have a connection with the nuclei of the motor nerves of the eyes.
Rhythmic chewing movements controlled by the supratrieminal premotor nucleus of the pons.
Swallowing, gagging, coughing, yawning and sneezing control the individual premotor nuclei of the medulla oblongata, which are connected with the corresponding cranial nerves and the respiratory center.

The salivary nuclei are referred to as the small-cell reticular formation of the pons and the medulla oblongata. Preganglionic parasympathetic fibers depart from them to the facial and glossopharyngeal nerves.

Reticular formation (RF).
(A) Departments. (B) Groups of aminergic and cholinergic cells.

1. Motion program generators... From experiments on animals it has long been established that the generators of the movement programs of lower vertebrates and lower mammals are located in the gray matter of the spinal cord, connecting with the help of nerves to each of the four limbs. These generators in the spinal cord are electrical neural networks that sequentially deliver signals to flexor and extensor muscle groups. The generative activity of the spinal cord obeys commands from the higher centers, the motor region of the midbrain (DOSM).

DOSM includes the leg-bridge nucleus, adjacent to the superior cerebellar peduncle in the place of its passage in the region of the upper edge of the fourth ventricle and junction with the midbrain. Descending fibers depart from these nuclei as part of the central tegmental pathway to the oral and caudal nuclei of the pons, formed by motor neurons that innervate the extensor muscles, and to the large cell neurons of the medulla oblongata, which control neurons that innervate the flexor muscles.

The main mechanism of rehabilitation for spinal cord injuries is the activation of spinal motor reflexes in patients who have suffered injuries with partial or complete rupture of the spinal cord. It is now well known that even after a complete rupture at the level of the cervical or thoracic spine, it is possible to activate lumbosacral movement programs by prolonged electrical stimulation of the dura mater at the level of the lumbar segments. Stimulation largely activates the dorsal root fibers, triggering impulses at the base of the anterior horn.

Surface electromyography (EMG) from flexor and extensor muscles showed consistent excitation of neurons in flexor and extensor muscles, although this program did not correspond to normal. For the formation of a normal program, the rupture must be incomplete with the preservation of a part of the descending paths from the leg-bridge nucleus.

The creation of true stepping movements with a complete rupture is possible if the patient is placed on a treadmill with simultaneous stimulation of the dura mater, mainly due to the generator receiving additional sensitive and proprioceptive impulses. Muscle strength and walking speed will build up over several weeks, but not enough to walk without using a walker.

Modern research is aimed at improving the ability to "create a bridge" with supraspinal motor fibers by cleansing tissue debris at the site of rupture and replacing these tissues with a composition that physically and chemically stimulates axonal regeneration.

2. Higher Centers for Urinary Control are described in the following article on the site.

General scheme of movement control.

b) Breathing control... The respiratory cycle is largely regulated by the dorsal and ventral respiratory nuclei, located in the upper part of the medulla oblongata on each side of the midline. The dorsal respiratory nucleus is located in the mid-lateral nucleus of the solitary tract. The ventral nucleus is located behind the double nucleus (hence the name - the posterior double nucleus). It is responsible for exhaling; Since this process normally occurs passively, the activity of neurons during normal respiration is relatively low, but it increases significantly under exertion. The third, medial parabrachial nucleus, adjacent to the macula macula, is likely to play a role in the breathing mechanism that occurs in the waking state.

Parabrachial nucleus, formed by many subgroups of neurons, together with the above-described aminergic and cholinergic systems, is involved in maintaining a state of wakefulness by activating the cerebral cortex. Stimulation of this nucleus by the amygdala in anxiety disorders results in characteristic hyperventilation.

Dorsal respiratory nucleus controls the inhalation process. Fibers depart from it to motor neurons on the opposite side of the spinal cord, which innervate the diaphragm, intercostal and auxiliary respiratory muscles. The nucleus receives ascending excitatory impulses from the chemoreceptors of the chemosensitive region of the medulla oblongata and the carotid sinus.

Ventral respiratory nucleus responsible for exhalation. When breathing calmly, it works as a neural circuit, participating in reciprocal inhibition of the inspiratory center by means of GABAergic (γ-aminobutyric acid) intercalary neurons. With forced breathing, it activates the cells of the anterior horn, which innervate the abdominal muscles, which are responsible for the collapse of the lungs.

1. Chemosensitive region of the medulla oblongata... The choroid plexus of the fourth ventricle produces cerebrospinal fluid (CSF) passing through the lateral aperture (Lushka) of the fourth ventricle. The cells of the lateral reticular formation on the surface of the medulla oblongata in this area are extremely sensitive to the concentration of hydrogen ions (H +) in the washing CSF. In fact, this chemosensitive region of the medulla oblongata analyzes the partial pressure of carbon dioxide (pCO 2) in the CSF, which corresponds to the pCO 2 of the blood supplying the brain. Any increase in the concentration of H + ions leads to stimulation of the dorsal respiratory nucleus by direct synaptic communication (several other chemosensitive nuclei are located in the medulla oblongata).

2. Carotid sinus chemoreceptors... The carotid sinus, the size of a pinhead, is adjacent to the trunk of the internal carotid artery and receives a branch from this artery that branches out inside. The blood flow through the carotid sinus is so intense that the arteriovenous oxygen partial pressure (pO 2) changes by less than 1%. Chemoreceptors are glomerular cells innervated by branches of the sinus nerve (branch IX of the cranial nerve). Carotid chemoreceptors respond to both a decrease in pO 2 and an increase in pCO 2 and provide reflex regulation of blood gas levels by changing the respiratory rate.

The chemoreceptors of the aortic glomus (under the aortic arch) in humans are relatively underdeveloped.

Respiratory center. All slices are shown from below and from the back.
(A) - enlarged cut (B).
(A) Inhibitory interaction between the dorsal and ventral respiratory nuclei (DSP, VDN).
To the chemosensitive area (CCR) of the medulla oblongata, the fibers from which are directed to the DNF, there are capillaries of the choroid that produce cerebrospinal fluid (CSF) (B).
As part of the glossopharyngeal nerve (IX), chemosensitive fibers pass from the carotid sinus to the DNF.
(C) Excitation of the motor neurons of the diaphragm carries out the opposite DFN.
(D) For forced expiration, the VDJ of the opposite side excites the neurons of the muscles of the anterior abdominal wall.

v) Control of the cardiovascular system... Cardiac output and peripheral vascular resistance regulate the nervous and endocrine systems. Due to the widespread occurrence of essential arterial hypertension in late middle age, most studies in this area are aimed at studying the mechanisms of cardiovascular regulation.

The ascending fibers that signal high blood pressure start from stretch receptors (numerous free nerve endings) in the wall of the carotid sinus and the aortic arch. These ascending fibers, known as baroreceptors, travel to the medially located cells of the solitary tract nucleus that form the baroreceptor center. Ascending fibers from the carotid sinus pass through the glossopharyngeal nerve; fibers from the aortic arch are part of the vagus nerve. Baroreceptor nerves are referred to as "buffer nerves", since their action is to correct any deviations in blood pressure from the norm.

Cardiac output and peripheral vascular resistance depend on the activity of the sympathetic and parasympathetic nervous systems. Two main baroreceptor reflexes - parasympathetic and sympathetic - help to normalize high blood pressure.

:
(A) Upper medulla oblongata.
(B) Segments of the spinal cord from T1 to L3.
(B) The posterior wall of the heart. Baroreceptor reflex (left):
1. Stretch receptors in the carotid sinus excite the fibers of the sinus branch of the glossopharyngeal nerve. ICA-internal carotid artery.
2. Baroreceptor neurons of the nucleus of the solitary pathway respond by firing the heart-inhibiting (cardio-inhibiting) neurons of the dorsal (motor) nucleus of the vagus nerve (DN-X).
3. Preganglionic parasympathetic cholinergic fibers of the vagus nerve form synapses with cells of intramural ganglia in the posterior wall of the heart.
4. Postgangionic parasympathetic cholinergic fibers inhibit the pacemaker activity of the sinoatrial node, thereby reducing the heart rate.
Barosympathetic reflex (right):
1 Afferent fibers of the stretch receptors of the carotid sinus excite the medial baroreceptor neurons of the nucleus of the solitary pathway.
2. Baroreceptor neurons respond by firing inhibitory neurons of the depressor center in the central reticular nucleus of the medulla oblongata.
3. Inhibition of adrenergic and noradrenergic neurons of the pressor center of the lateral reticular nucleus (anterior ventrolateral part of the medulla oblongata) occurs.
4. Reduced tonic excitation of neurons in the lateral horns of the spinal cord.
5 and 6. Pre- and postganglionic inhibition of sympathetic innervation of arteriole tone occurs, which, in turn, leads to a decrease in peripheral vascular resistance.

G) Sleep and wakefulness... With electroencephalography (EEG), characteristic patterns of the electrical activity of cortical neurons can be observed in different states of consciousness. The normal state of wakefulness is characterized by high-frequency, low-amplitude waves. Falling asleep is accompanied by low-frequency high-amplitude waves, a higher wave amplitude is due to the synchronized activity of a larger number of neurons. This type of sleep is called slow-wave (synchronized) sleep or He-REM sleep (REM-rapid eye movement). It lasts about 60 minutes, and then goes into desynchronized sleep, in which the sequences on the EEG resemble those in the waking state. Only during this period do dreams and rapid eye movements occur (hence the more commonly used term - REM sleep). During a normal night's sleep, several cycles of REM sleep and non-REM sleep follow each other, described in a separate article on the website.

The alternation of sleep and wakefulness cycles is a reflection of two neural networks in the brain, one operating in the waking state and the other in the sleep state. These networks are opposed to each other as a "switch" between sleep and wakefulness (which makes it possible to switch between networks quickly and completely). A similar pattern works when changing from REM sleep to slow-wave sleep. Normally, sleep is controlled using physiological systems (the contribution of the homeostasis system is a change in the level of cell metabolism), circadian rhythms (the suprachiasmal nucleus is the main biological clock that is synchronized with information from environment, exposure to light on the retina and melatonin produced by the pineal gland and control the sleep-wake cycle and other physiological functions) and allostatic stress (food intake and physical activity).

These factors change slowly, and without a rapid change in the state of the switching mechanism, the transition from wakefulness to sleep would also be slow and uncomfortable.

3. Stimulation of awakening, or activating systems(caudal midbrain and rostral pons). Two main pathways are responsible for the activation of the cerebral cortex:

Cholinergic neurons (of the pons and laterodorsal tegmental nuclei) approach the thalamus (switching nuclei and reticular nucleus) and inhibit those GABAergic neurons of the thalamus, whose task is to prevent the transmission of sensitive information to the cerebral cortex.

Monoaminergic neurons are located in the macula macula, the dorsal and median nuclei of the suture (serotonergic), the parabrachial nucleus (glutamatergic), the periaqueductal gray matter (OBCV, dopaminergic) and in the serotus-mastoid nucleus (histaminergic). The axons of neurons in each of these areas are directed to the basal regions of the forebrain (the basal nucleus of Meinert and the unnamed substance), and from there to the cerebral cortex.

Peptidergic (orexin) and glutamatergic neurons of the lateral hypothalamus, as well as cholinergic and GABAergic neurons of the basal forebrain ganglia also send fibers to the cerebral cortex.

Lecture 6.

The reticular formation is a complex of neurons in the brain stem and partly in the spinal cord, which has extensive connections with various nerve centers, the cerebral cortex and among themselves. The reticular formation is represented by scattered cells in the lining of the brainstem and in the spinal cord.

A number of cells of the reticular formation in the brainstem are vital centers:

1. respiratory (center of inhalation and exhalation) - in the medulla oblongata;

2. vasomotor - in the medulla oblongata;

3. the center of gaze coordination (the nucleus of Kakhal and Darkshevich) - in the midbrain;

4. the center of thermoregulation - in the diencephalon;

5. the center of hunger and satiety is in the diencephalon.
The reticular formation performs the following functions:

Providing segmental reflexes: scattered cells are
intercalary neurons of the spinal cord and brainstem
(swallowing reflex);

Maintaining the tone of skeletal muscles: cells of the nuclei of the reticular formation send tonic impulses to the motor nuclei of the cranial nerves and the motor nuclei of the anterior horns of the spinal cord;

Ensuring the tonic activity of the nuclei of the brain stem and
cortex of the hemispheres, which is necessary for further carrying out and
analysis of nerve impulses;

Correction during conduction of nerve impulses: due to reticular formation, impulses can either be significantly increased or significantly weakened depending on the condition nervous system;

Active influence on the higher centers of the cerebral cortex, which
leads to either a decrease in the tone of the cortex, apathy and the onset of sleep,
either to increase efficiency, euphoria;

Participation in the regulation of cardiac activity, respiration, vascular tone,
secretion of glands and other autonomic functions (centers of the brain stem);

Participation in the regulation of sleep and wakefulness: blue spot, suture nuclei -
are projected onto the diamond-shaped fossa;

Providing a combined rotation of the head and eyes: the Cajal nucleus and
Darkshevich.

The main descending tract of the reticular formation is the reticulospinal, which runs along the trunk to the neurons of the motor nuclei of the anterior horns of the spinal cord and motor nuclei of the cranial nerves, as well as to the intercalary neurons of the autonomic nervous system.

Thalamo-cortical fibers go from the reticular nuclei of the visual hillock to various areas of the cerebral cortex: they end in all layers of the cerebral cortex, activating the cortex necessary for the perception of specific stimuli.

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Functions of the reticular formation

Reticular formation the brain stem is considered as one of the important integrative devices of the brain.
The integrative functions of the reticular formation proper include:

1. control over the states of sleep and wakefulness
2. muscle (phase and tonic) control
3. processing information signals from the environment and the internal environment of the body, which come through different channels

The reticular formation unites various parts of the brain stem (the reticular formation of the medulla oblongata, pons varoli and midbrain). Functionally, the reticular formation of different parts of the brain has a lot in common, so it is advisable to consider it as a single structure. The reticular formation is a diffuse accumulation of cells of different types and sizes, which are separated by many fibers. In addition, about 40 nuclei and pidyaders are isolated in the middle of the reticular formation.

Reticular formation of the brain: structure and function

The neurons of the reticular formation have widely branched dendrites and elongated axons, some of which divide in a T-shape (one process is directed downward, forming the reticular-spinal path, and the second - to the upper parts of the brain).

A large number of afferent pathways from other brain structures converge in the reticular formation: from the cerebral cortex - collaterals of the cortico-spinal (pyramidal) pathways, from the cerebellum and other structures, as well as collateral fibers that approach through the brain stem, fibers of sensory systems (visual, auditory, etc.). All of them end in synapses on the neurons of the reticular formation. So, thanks to this organization, the reticular formation is adapted to uniting influences from various brain structures and is able to influence them, that is, to perform integrative functions in the activity of the central nervous system, determining to a large extent the overall level of its activity.

Properties of reticular neurons. The neurons of the reticular formation are capable of sustained background impulse activity. Most of them constantly generate discharges with a frequency of 5-10 Hz. The reason for this constant background activity of reticular neurons is: firstly, the massive convergence of various afferent influences (from receptors of the skin, muscle, visceral, eyes, ears, etc.), as well as influences from the cerebellum, cerebral cortex, vestibular nuclei and others. brain structures on the same reticular neuron. At the same time, excitement often arises in response to this. Secondly, the activity of the reticular neuron can be changed by humoral factors (adrenaline, acetylcholine, CO2 tension in the blood, hypoxia, etc.) .. These continuous impulses and chemicals contained in the blood support the depolarization of the membranes of reticular neurons, their ability to sustain impulse activity. In this regard, the reticular formation also has a constant tonic effect on other brain structures.

A characteristic feature of the reticular formation is also the high sensitivity of its neurons to various physiologically active substances. Due to this, the activity of reticular neurons can be relatively easily blocked by pharmacological drugs that bind to the cytoreceptors of the membranes of these neurons. Compounds of barbituric acid (barbiturates), chlorpromazine and others are especially active in this respect. medications, which are widely used in medical practice.

The nature of the nonspecific influences of the reticular formation. The reticular formation of the brain stem is involved in the regulation of the autonomic functions of the body. However, back in 1946, the American neurophysiologist N. W. Megoun and his colleagues discovered that the reticular formation is directly related to the regulation of somatic reflex activity. It has been proven that the reticular formation has a diffuse nonspecific, descending and ascending influence on other brain structures.

Downward influence. When the reticular formation of the hindbrain is irritated (especially the giant cell nucleus of the medulla oblongata and the reticular nucleus of the pons, where the reticulospinal pathway begins), all spinal motor centers (flexion and extensor) are inhibited. This inhibition is very deep and prolonged. This situation in natural conditions can be observed during deep sleep.
Along with diffuse inhibitory influences, when certain areas of the reticular formation are irritated, a diffuse effect is revealed, which facilitates the activity of the spinal motor system.

The reticular formation plays an important role in the regulation of the activity of muscle spindles, changing the frequency of discharges delivered by gamma-efferent fibers to the muscles. Thus, the reverse impulse in them is modulated.

Rising influence. Research N. W. Megoun, G. Moruzzi (1949) showed that irritation of the reticular formation (posterior, midbrain and diencephalon) affects the activity of the higher parts of the brain, in particular the cerebral cortex, providing its transition to an active state. This position is confirmed by the data of numerous experimental studies and clinical observations. So, if the animal is in a state of sleep, then direct stimulation of the reticular formation (especially the pons of varoli) through the electrodes inserted into these structures causes a behavioral reaction of awakening of the animal. In this case, a characteristic image appears on the EEG - a change in the alpha rhythm by the beta rhythm, i.e. the reaction of desynchronization or activation is recorded. This reaction is not limited to a certain area of ​​the cerebral cortex, but covers its large arrays, i.e. is generalized. When the reticular formation is destroyed or its ascending connections with the cerebral cortex are turned off, the animal falls into a dream-like state, does not respond to light and olfactory stimuli, and does not actually come into contact with the outside world. That is, the terminal brain ceases to function actively.

Thus, the reticular formation of the brainstem performs the functions of the ascending activating system of the brain, which maintains the excitability of neurons in the cerebral cortex at a high level.

In addition to the reticular formation of the brain stem, the ascending activating system of the brain also includes nonspecific nuclei of the thalamus, the posterior hypothalamus, and limbic structures. As an important integrative center, the reticular formation, in turn, is part of the more global integration systems of the brain, which include the hypothalamic-limbic and neocortical structures. It is in interaction with them that purposeful behavior is formed, aimed at adapting the organism to the changing conditions of the external and internal environment.

One of the main manifestations of damage to the reticular structures in humans is loss of consciousness. It happens with craniocerebral trauma, cerebrovascular accident, tumors and infectious processes in the brain stem. The duration of the state of fainting depends on the nature and severity of dysfunctions of the reticular activating system and ranges from a few seconds to many months. Dysfunction of ascending reticular influences is also manifested by loss of vigor, constant pathological drowsiness or frequent bouts of falling asleep (paroxysmal hypersomia), restless night sleep. There are also violations (more often an increase) of muscle tone, various vegetative changes, emotional and mental disorders, etc.
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Topic 13. Reticular formation.

The term reticular formation was proposed in 1865 by the German scientist O. Deiters. By this term, Deiters meant cells scattered in the brain stem, surrounded by many fibers going in different directions. It is the network-like arrangement of the fibers connecting nerve cells with each other that served as the basis for the proposed name.

At present, morphologists and physiologists have accumulated rich material on the structure and functions of the reticular formation. Determined that structural elements reticular formations are localized in a number of brain formations, starting with the intermediate zone of the cervical segments of the spinal cord (plate VII), and ending with some structures of the diencephalon (intralaminar nuclei, thalamic reticular nucleus). The reticular formation consists of a significant number of nerve cells (it contains almost 9/10 of the cells of the entire brain stem). Common features the structure of the reticular structures - the presence of special reticular neurons and the distinctive nature of the connections.

Rice. 1. Neuron of the reticular formation. Sagittal section of the rat brain stem.

Figure A shows only one neuron of the reticular formation. It can be seen that the axon is divided into caudal and rostral segments, of great length, with many collaterals. B. Collaterali. Sagittal section of the lower part of the rat brainstem showing the connections of the collaterals of the large descending tract (pyramidal tract) with reticular neurons. Collaterals of the ascending pathways (sensory pathways), which are absent in the figure, are connected to reticular neurons in the same way (according to Sheibel M.E. and Sheibel A.B.)

Along with numerous separately lying neurons, different in shape and size, there are nuclei in the reticular formation of the brain. Scattered neurons of the reticular formation primarily play an important role in providing segmental reflexes that are closed at the level of the brain stem. They act as intercalary neurons in the implementation of such reflex acts as blinking, corneal reflex, etc.

The significance of many nuclei of the reticular formation has been clarified. So, the nuclei located in the medulla oblongata have connections with the autonomic nuclei of the vagus and glossopharyngeal nerves, the sympathetic nuclei of the spinal cord, they are involved in the regulation of cardiac activity, respiration, vascular tone, glandular secretion, etc.

The role of the blue spot and suture nuclei in the regulation of sleep and wakefulness has been established. Blue spot, is located in the upper lateral part of the rhomboid fossa. The neurons of this nucleus produce a biologically active substance - norepinephrine, which has an activating effect on the neurons of the overlying parts of the brain. The activity of neurons in the blue spot is especially high during wakefulness; during deep sleep, it fades out almost completely. Seam core are located along the median line of the medulla oblongata. The neurons of these nuclei produce serotonin, which causes the processes of diffuse inhibition and the state of sleep.

Cajal kernels and Darkshevich, related to the reticular formation of the midbrain, have connections with the nuclei of the III, IV, VI, VIII and XI pairs of cranial nerves. They coordinate the work of these nerve centers, which is very important for ensuring the combined rotation of the head and eyes. The reticular formation of the brainstem is important in maintaining skeletal muscle tone by sending tonic impulses to the motor neurons of the motor nuclei of the cranial nerves and the motor nuclei of the anterior horns of the spinal cord. In the process of evolution from the reticular formation, such independent formations as a red nucleus and black matter emerged.

According to structural and functional criteria, the reticular formation is divided into 3 zones:

1. Median, located along the midline;

2. Medial, occupying the medial sections of the trunk;

3. Lateral, the neurons of which lie near the sensory formations.

Median zone is represented by suture elements, consisting of nuclei, whose neurons synthesize a mediator - serotonin. The suture nucleus system takes part in the organization of aggressive and sexual behavior, in the regulation of sleep.

Medial (axial) zone consists of small neurons that do not branch.

What is the reticular formation

The zone contains a large number of cores. There are also large multipolar neurons with a large number of densely branching dendrites. They form ascending nerve fibers into the cerebral cortex and descending nerve fibers into the spinal cord. The ascending communication pathways of the medial zone have an activating effect (directly or indirectly through the thalamus) on the new cortex. Descending paths have an inhibitory effect.

Lateral zone- it includes reticular formations located in the brain stem near sensory systems, as well as reticular neurons lying inside sensory formations. The main component of this zone is a group of nuclei that are adjacent to the nucleus of the trigeminal nerve. All nuclei of the lateral zone (with the exception of the reticular lateral nucleus of the medulla oblongata) consist of small and medium-sized neurons and lack large elements. In this zone, the ascending and descending pathways are located, providing a connection of sensory formations with the medial zone of the reticular formation and the motor nuclei of the trunk. This part of the reticular formation is younger and possibly more progressive; its development is associated with a decrease in the volume of the axial reticular formation in the course of evolutionary development. Thus, the lateral zone is a collection of elementary integrative units formed near and within specific sensory systems.

Rice. 2. The nuclei of the reticular formation (RF)(after: Niuwenhuys et al, 1978).

1-6 - median zone of the RF: 1-4- core of the suture (1 - pale, 2 - dark, 3 - large, 4- bridge), 5 - upper central, 6 - dorsal core of the suture, 7-13 - medial zone of RF : 7 - reticular paramedian, 8 - giant cell, 9 - reticular nucleus of the pons tegmental, 10, 11 - caudal (10) and oral (11) nuclei of the pons, 12 - dorsal tegmental nucleus (Goodden), 13 - wedge-shaped nucleus, 14 - I5 -lateral zone of the RF: 14 - central reticular nucleus of the medulla oblongata, 15 - lateral reticular nucleus, 16, 17 - medial (16) and lateral (17) parabrachial nuclei, 18, 19 - compact (18) and scattered (19) parts of the pedunculus -pontic core.

Due to the descending influences, the reticular formation also exerts a tonic effect on the motor neurons of the spinal cord, which in turn increases the tone of the skeletal muscles, and improves the afferent feedback system. As a result, any motor act is performed much more efficiently, it provides more precise control over movement, but excessive excitation of the cells of the reticular formation can lead to muscle tremors.

The centers of sleep and wakefulness are located in the nuclei of the reticular formation, and the stimulation of these or those centers leads either to the onset of sleep or to awakening. The use of sleeping pills is based on this. The reticular formation contains neurons that respond to painful stimuli from muscles or internal organs. It also houses special neurons that provide a quick response to sudden, undefined signals.

The reticular formation is closely connected with the cerebral cortex, due to this, a functional connection is formed between the external parts of the central nervous system and the brain stem. The reticular formation plays an important role both in the integration of sensory information and in the control over the activity of all effector neurons (motor and autonomic). It is also of paramount importance for the activation of the cerebral cortex to maintain consciousness.

It should be noted that the cerebral cortex, and in turn, sends cortical-reticular pathways impulses to the reticular formation. These impulses arise mainly in the cortex of the frontal lobe and pass through the pyramidal pathways. The cortical-reticular connections have either an inhibitory or a stimulating effect on the reticular formation of the brainstem; they correct the passage of impulses along the efferent pathways (selection of efferent information).

Thus, there is a two-way connection between the reticular formation and the cerebral cortex, which provides self-regulation in the activity of the nervous system. The functional state of the reticular formation determines the tone of the muscles, the work of internal organs, mood, concentration of attention, memory, etc. In general, the reticular formation creates and maintains conditions for the implementation of complex reflex activity with the participation of the cerebral cortex.

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IV. Reticular formation

Reticular formation- an extended structure in the brain stem is an important integrative area of ​​the nonspecific system. The first descriptions of the reticular formation (RF) of the brainstem were made by German morphologists: in 1861 by K. Reichert (Reichert K., 1811-1883) and in 1863 by O. Deiters (Deiters O., 1834-1863); among domestic researchers, a great contribution to its study was made by V.M. Bekhterev. RF is a set of nerve cells and their processes located in the tectum of all levels of the trunk between the nuclei of the cranial nerves, olives, passing here afferent and efferent pathways (Figure 17). Some medial structures of the diencephalon, including the medial nuclei of the thalamus, are sometimes referred to as the reticular formation.

RF cells are different in shape and size, axon length, are located mainly diffusely, in places they form clusters - nuclei, which provide the integration of impulses coming from nearby cranial nuclei or penetrating here through collaterals from afferent and efferent pathways passing through the trunk. Among the connections of the reticular formation of the brain stem, the most important can be considered the cortical-reticular, spinal-reticular pathways, the connections between the RF of the stem with the formations of the diencephalon and the striopallidal system, the cerebellar-reticular pathways. The processes of the RF cells form afferent and efferent connections between the nuclei of the cranial nerves contained in the trunk tectum and the projection pathways that are part of the trunk lining. Through collaterals from the afferent pathways passing through the brain stem, the RF receives "recharging" impulses and performs the functions of a battery and an energy generator. It should also be noted that the RF is highly sensitive to humoral factors, including hormones, drugs, the molecules of which reach it in a hematogenous way.

Fig. 17. Reticular formation.

The neurons of the reticular formation are assembled into nuclei that perform specific functions and send processes to most areas of the cerebral cortex. Distinguish between the ascending reticular system (left), which causes the activation of the cortex, and the descending reticular system (right), mainly regulating postural tone (maintaining posture) due to the inhibitory and facilitating effect on the motor pathways descending from the motor cortex to the spinal cord.

The ascending activating system includes the nuclei of the reticular formation, located mainly at the level of the midbrain, to which collaterals from the ascending sensory systems approach. Nerve impulses arising in these nuclei along polysynaptic pathways, passing through the intralaminar nuclei of the thalamus, subthalamic nuclei to the cerebral cortex, exert an activating effect on it. The ascending influences of the nonspecific activating reticular system are of great importance in the regulation of the tone of the cerebral cortex, as well as in the regulation of the processes of sleep and wakefulness.

In cases of damage to the activating structures of the reticular formation, as well as in violation of its connections with the cerebral cortex, a decrease in the level of consciousness, mental activity, in particular cognitive functions, and motor activity occurs. Possible manifestations of stunnedness, general and speech hypokinesia, akinetic mutism, stupor, coma, vegetative state.

Within the Russian Federation, there are separate territories that have received elements of specialization in the process of evolution - the vasomotor center (its depressor and pressor zones), the respiratory center (expiratory and inspiratory), and the vomiting center. RF contains structures that affect somatopsychovegetative integration... RF ensures the maintenance of vital reflex functions - respiration and cardiovascular activity, takes part in the formation of such complex motor acts as coughing, sneezing, chewing, vomiting, combined work of the speech motor apparatus, general motor activity.

The downward effects of RF on the spinal cord affect primarily the state of muscle tone and can be activating or lowering muscle tone, which is important for the formation of motor acts. Usually, the activation or inhibition of the upward and downward influences of the RF is carried out in parallel. So, during sleep, which is characterized by inhibition of ascending activating influences, inhibition of descending nonspecific projections occurs, which is manifested, in particular, by a decrease in muscle tone.

FunctionsRF not yet fully understood. It is believed to be involved in a number of processes:

- regulation of excitability of the cortex: the level of awareness of stimuli and reactions, the sleep-wake rhythm (ascending activating reticular system);

- imparting affective-emotional coloring to sensory stimuli, especially painful ones, due to the transmission of afferent information to the limbic system;

- motor regulation of functions, including vital reflexes (blood circulation, breathing, swallowing, coughing and sneezing), in which different afferent and efferent systems must be mutually coordinated;

- participation in the regulation of posture and purposeful movements as an important component of the motor centers of the brain stem.

V. Cerebellum

Cerebellum located under a duplicate dura mater known as outline of the cerebellum, which divides the cranial cavity into two unequal spaces - supratentorial and subtentorial. V subtentorial space, the bottom of which is the posterior cranial fossa, in addition to the cerebellum, is the brain stem. The volume of the cerebellum averages 162 cm3. Its weight varies within 136-169 g.

The cerebellum is located above the bridge and the medulla oblongata. Together with the superior and inferior cerebral sails, it constitutes the roof of the IV ventricle of the brain, the bottom of which is the so-called rhomboid fossa. Above the cerebellum are the occipital lobes of the large brain, separated from it by the tentorium of the cerebellum.

In the cerebellum, there are two hemispheres... Between them in the sagittal plane above the IV ventricle of the brain is the phylogenetically most ancient part of the cerebellum - its worm... The vermis and cerebellar hemispheres are fragmented into lobules by deep transverse grooves.

The cerebellum is composed of gray and white matter. The gray matter forms the cerebellar cortex and the paired nuclei located in its depth (Figure 18). The largest of them are jagged kernels- located in the hemispheres. In the central part of the worm there are tent cores, between them and the jagged nuclei are spherical and corky nuclei.

Rice. 18.Nucleus of the cerebellum.

1 - toothed core; 2 - corky core; 3 - the core of the tent; 4 - spherical nucleus.

Rice. 19 . Sagittal section of the cerebellum and brainstem.

1 - cerebellum; 2 - "tree of life"; 3 - forebrain sail; 4 - plate of the quadruple; 5 - aqueduct of the brain; 6 - the leg of the brain; 7 - bridge; 8 - IV ventricle, its choroid plexus and tent; 9 - medulla oblongata.

Due to the fact that the cortex covers the entire surface of the cerebellum and penetrates into the depth of its furrows, on a sagittal section of the cerebellum, its tissue has a leaf pattern, the veins of which are formed by a white matter (Figure 19), which makes up the so-called tree of life of the cerebellum... At the base of the tree of life there is a wedge-shaped notch, which is the upper part of the cavity of the IV ventricle; the edges of this recess form his tent. The roof of the tent is the cerebellar worm, and its anterior and posterior walls are thin medulla plates known as the anterior and posterior cerebral sails.

The impulses enter the cerebellar cortex through mossy and creeping fibers penetrating into it from the white matter, which make up the afferent pathways of the cerebellum. Functions of the reticular formation Through mossy fibers, impulses from the spinal cord, vestibular nuclei and pons nuclei are transmitted to the cells of the granular layer of the cortex. The axons of these cells, together with creeping fibers passing through the granular layer in transit and carrying impulses from the inferior olives to the cerebellum, reach the superficial, molecular layer of the cerebellum. Here, the axons of the cells of the granular layer and the creeping fibers divide in a T-shape, and in the molecular layer their branches take a direction longitudinal to the surface of the cerebellum. The impulses that have reached the molecular layer of the cortex, having passed through the synaptic contacts, fall on the branching dendrites of Purkinje cells located here. Then they follow the dendrites of Purkinje cells to their bodies located at the border of the molecular and granular layers. Then, along the axons of the same cells crossing the granular layer, they penetrate into the depth of the white matter. The axons of Purkinje cells end in the nuclei of the cerebellum. Mainly in the dentate nucleus. Efferent impulses coming from the cerebellum along the axons of the cells that make up its nucleus and participating in the formation of the cerebellar peduncles leave the cerebellum.

The cerebellum has three pairs of legs: lower, middle and upper. The lower leg connects it with the medulla oblongata, the middle - with the bridge, the upper - with the midbrain. The legs of the brain make up the pathways that carry impulses to and from the cerebellum.

The cerebellar worm provides stabilization of the body's center of gravity, its balance, stability, regulation of the tone of reciprocal muscle groups, mainly the neck and trunk, and the emergence of physiological cerebellar synergies that stabilize the balance of the body.

To successfully maintain body balance, the cerebellum constantly receives information passing along the spinocerebellar pathways from the proprioceptors of various parts of the body, as well as from the vestibular nuclei, inferior olives, the reticular formation and other formations involved in controlling the position of body parts in space. Most of the afferent pathways leading to the cerebellum pass through the lower cerebellar pedicle, some of them are located in the superior cerebellar pedicle.

Through its middle legs, the cerebellum receives impulses from the cerebral cortex. These impulses pass through cortical-cerebellopontine pathways.

Some of the impulses that have arisen in the cerebral cortex reach the opposite hemisphere of the cerebellum, bringing information not about the produced, but only about the planned active movement. Having received such information, the cerebellum instantly sends out impulses that correct voluntary movements, mainly, by extinguishing inertia and the most rational regulation of reciprocal muscle tone — muscle agonists and antagonists. As a result, a kind of eimetry is created, making voluntary movements clear, refined, devoid of inappropriate components.

The pathways that leave the cerebellum are composed of the axons of the cells, the bodies of which form its nuclei. . Most efferent pathways, including pathways from the dentate nuclei, leave the cerebellum through its upper leg. At the level of the lower tubercles of the quadruple, the efferent cerebellar pathways cross (intersection of the upper cerebellar legs of Werneking). After crossing each one of them reaches the red nuclei of the opposite side of the midbrain. In the red nuclei, cerebellar impulses switch to the next neuron and then move along the axons of cells whose bodies are embedded in the red nuclei. These axons are formed in red-nuclear-spinal pathways which shortly after exits from red kernels undergo a cross (tire cross or Trout cross), after which they descend into the spinal cord. In the spinal cord, the red-nuclear spinal pathways are located in the lateral cords; their constituent fibers end at the cells of the anterior horns of the spinal cord.

From the nuclei of the cerebellar vermis, efferent pathways go mainly through the lower cerebellar pedicle to the reticular formation of the brain stem and the vestibular nuclei. From here, along the reticulospinal and vestibulospinal pathways passing along the anterior cords of the spinal cord, they also reach the cells of the anterior horns. Part of the impulses coming from the cerebellum, passing through the vestibular nuclei, enters the medial longitudinal bundle, reaches the nuclei III, IV and VI of the cranial nerves that provide the movement of the eyeballs, and affects their function.

Thus:

1. Each half of the cerebellum receives impulses mainly a) from the homolateral half of the body, b) from the opposite hemisphere of the brain, which has cortico-spinal connections with the same half of the body.

2. From each half of the cerebellum, efferent impulses are directed to the cells of the anterior horns of the homolateral half of the spinal cord and to the nuclei of the cranial nerves that provide movement of the eyeballs.

This nature of the cerebellar connections makes it possible to understand why, when one half of the cerebellum is affected, cerebellar disorders occur mainly in the same, i.e. homolateral, half of the body. This is especially pronounced when the cerebellar hemispheres are affected.

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Reticular formation

The term "reticular formation" (English ret - network) was first introduced by Deiters more than 100 years ago. The reticular formation (RF) is located in the central part of the brain stem, entering the rostral end into the thalamus, and the caudal end into the spinal cord. Due to the presence of network connections with almost all structures of the central nervous system, it is called the reticular, or network, formation.

RF neurons of various shapes and sizes have long dendrites and a short axon, although there are giant neurons with long axons that form, for example, the rubrospinal and reticulospinal tracts. Up to 40,000 synapses can end on one nerve cell, which indicates wide interneuronal connections within the RF. It singled out a number of nuclei and nuclear groups that differ both structurally and the functions they perform.

The reticular formation forms numerous afferent pathways: spinoreticular, cerebelloreticular, cortical-subcortical-reticular (from the cortex, basal ganglia, hypothalamus), from the structures of each level of the brainstem (from the midbrain, pons, medulla oblongata), and efferent reticulospinal, reticulocortical-subcortical, reticulocerebellar, as well as pathways to other structures of the brain stem.

The reticular formation has a generalized, tonic, activating effect on the anterior parts of the brain and the cerebral cortex (ascending activating system of the RF) and descending, controlling the activity of the spinal cord (descending reticulospinal system), which can be both facilitating on many body functions and brake. One of the types of inhibitory effect of RF on the reflex activity of the spinal cord is Sechenov's inhibition, which consists in the inhibition of spinal reflexes when the thalamic reticular formation is stimulated by a salt crystal.

G. Magun showed that local electrical stimulation of the giant cell nucleus of the RF medulla oblongata causes inhibition of the flexion and extensor reflexes of the spinal cord, and prolonged TPSP and postsynaptic inhibition by the type of hyperpolarization occur on the motor neuron.

The inhibitory effects on flexion reflexes are mainly exerted by the medial reticular formation of the medulla oblongata, and the facilitating ones - by the lateral zones of the RF pons.

The reticular formation takes part in the implementation of many functions of the body. Thus, RF controls motor activity, postural tone and phasic movements.

In 1944 in the United States during the epidemic of poliomyelitis, a disease that interferes with physical activity, the main structural changes were found in the reticular formation. This led the American scientist G. Magun to the idea of ​​the participation of the Russian Federation in motor activity. Its main structures responsible for this type of activity are the Deiters nucleus of the medulla oblongata and the red nucleus of the midbrain. Deiters' nucleus maintains the tone of the alpha and gamma motor neurons of the spinal cord, which innervate the extensor muscles, and inhibits the alpha and gamma motor neurons of the flexor muscles. The red nucleus, on the other hand, tones up the alpha and gamma motor neurons of the flexor muscles and inhibits the alpha and gamma neurons of the extensor muscles. The red nucleus has an inhibitory effect on the Deiters nucleus, maintaining a uniform tone of the extensor muscles. Damage or transection of the brain between the middle and the oblong one leads to the removal of the inhibitory effects from the red nucleus on the Deiters nucleus, and therefore on the tone of the extensor muscles, which begins to prevail over the tone of the flexor muscles and decerebration rigidity or increased muscle tone occurs, manifested in strong tensile resistance. Such an animal has a characteristic body posture: the head is thrown back, the front and hind limbs are extended. Put on its feet, it falls down at the slightest jolt, since there is no fine regulation of body posture.

Irritation of the reticular formation causes tremors, spastic tone.

RF of the midbrain plays a role in coordinating the contractions of the eye muscles. Having received information from the upper tubercles of the quadruple, cerebellum, vestibular nuclei, visual areas of the cerebral cortex, the RF integrates it, which leads to reflex changes in the work of the oculomotor apparatus, especially in the case of a sudden appearance of moving objects, changes in the position of the head and eyes.

The reticular formation regulates autonomic functions, in the implementation of which the so-called starting neurons of the RF participate, which trigger the excitation process within a certain group of neurons responsible for respiratory and vasomotor functions. In the RF of the medulla oblongata, there are two nuclei, one of them is responsible for inhalation, the other for exhalation. Their activity is controlled by the pneumotaxic center of the Russian Federation of the Varoliev Bridge. By irritating these parts of the RF, various respiratory acts can be reproduced.

The vasomotor center is located in the rhomboid fossa of the bottom of the fourth ventricle, which is part of the RF. With electrical stimulation of certain points of the pons and the medulla oblongata, vasomotor reactions occur.

The reticular formation is connected with all parts of the cerebral cortex with the help of a diffuse nonspecific projection afferent system, which, unlike the specific one, conducts excitation that has arisen on the periphery to the cerebral cortex slowly through sequentially connected multi-neuronal systems.

Reticular formation

RF has an activating upward influence on the cerebral cortex. Irritation of the RF causes an "awakening reaction", and on the electroencephalogram - desynchronization of the alpha rhythm and an orientation reflex.

Securing the brain below the RF causes a picture of wakefulness, above - sleep. RF regulates the sleep-wake cycle.

The reticular formation affects the sensory systems of the brain: hearing acuity, vision, olfactory sensations. Thus, RF damage and barbituric anesthesia lead to an increase in sensory impulses, which are normally under the inhibitory, regulatory influence of RF. Perception of various sensations when focusing on some other sensation, habituation to repetitive stimuli is also explained by reticular influences.

In the reticular formation of the medulla oblongata, midbrain and thalamus, there are neurons that respond to painful stimuli from muscles and internal organs, thus creating a feeling of dull pain.

Reticular formation the brain stem is considered as one of the important integrative devices of the brain.
The integrative functions of the reticular formation proper include:

1. control over the states of sleep and wakefulness
2. muscle (phase and tonic) control
3. processing information signals from the environment and the internal environment of the body, which come through different channels

The reticular formation unites various parts of the brain stem (the reticular formation of the medulla oblongata, pons varoli and midbrain). Functionally, the reticular formation of different parts of the brain has a lot in common, so it is advisable to consider it as a single structure. The reticular formation is a diffuse accumulation of cells of different types and sizes, which are separated by many fibers. In addition, about 40 nuclei and pidyaders are isolated in the middle of the reticular formation. The neurons of the reticular formation have widely branched dendrites and elongated axons, some of which divide in a T-shape (one process is directed downward, forming the reticular-spinal path, and the second - to the upper parts of the brain).

A large number of afferent pathways from other brain structures converge in the reticular formation: from the cerebral cortex - collaterals of the cortico-spinal (pyramidal) pathways, from the cerebellum and other structures, as well as collateral fibers that approach through the brain stem, fibers of sensory systems (visual, auditory, etc.). All of them end in synapses on the neurons of the reticular formation. So, thanks to this organization, the reticular formation is adapted to uniting influences from various brain structures and is able to influence them, that is, to perform integrative functions in the activity of the central nervous system, determining to a large extent the overall level of its activity.

Properties of reticular neurons. The neurons of the reticular formation are capable of sustained background impulse activity. Most of them constantly generate discharges with a frequency of 5-10 Hz. The reason for this constant background activity of reticular neurons is: firstly, the massive convergence of various afferent influences (from receptors of the skin, muscle, visceral, eyes, ears, etc.), as well as influences from the cerebellum, cerebral cortex, vestibular nuclei and others. brain structures on the same reticular neuron. At the same time, excitement often arises in response to this. Secondly, the activity of the reticular neuron can be changed by humoral factors (adrenaline, acetylcholine, CO2 tension in the blood, hypoxia, etc.) .. These continuous impulses and chemicals contained in the blood support the depolarization of the membranes of reticular neurons, their ability to sustain impulse activity. In this regard, the reticular formation also has a constant tonic effect on other brain structures.

A characteristic feature of the reticular formation is also the high sensitivity of its neurons to various physiologically active substances. Due to this, the activity of reticular neurons can be relatively easily blocked by pharmacological drugs that bind to the cytoreceptors of the membranes of these neurons. Especially active in this respect are compounds of barbituric acid (barbiturates), chlorpromazine and other drugs that are widely used in medical practice.

The nature of the nonspecific influences of the reticular formation. The reticular formation of the brain stem is involved in the regulation of the autonomic functions of the body. However, back in 1946, the American neurophysiologist N. W. Megoun and his colleagues discovered that the reticular formation is directly related to the regulation of somatic reflex activity. It has been proven that the reticular formation has a diffuse nonspecific, descending and ascending influence on other brain structures.

Downward influence. When the reticular formation of the hindbrain is irritated (especially the giant cell nucleus of the medulla oblongata and the reticular nucleus of the pons, where the reticulospinal pathway begins), all spinal motor centers (flexion and extensor) are inhibited. This inhibition is very deep and prolonged. This situation in natural conditions can be observed during deep sleep.
Along with diffuse inhibitory influences, when certain areas of the reticular formation are irritated, a diffuse effect is revealed, which facilitates the activity of the spinal motor system.

The reticular formation plays an important role in the regulation of the activity of muscle spindles, changing the frequency of discharges delivered by gamma-efferent fibers to the muscles. Thus, the reverse impulse in them is modulated.

Rising influence. Research N. W. Megoun, G. Moruzzi (1949) showed that irritation of the reticular formation (posterior, midbrain and diencephalon) affects the activity of the higher parts of the brain, in particular the cerebral cortex, providing its transition to an active state. This position is confirmed by the data of numerous experimental studies and clinical observations. So, if the animal is in a state of sleep, then direct stimulation of the reticular formation (especially the pons of varoli) through the electrodes inserted into these structures causes a behavioral reaction of awakening of the animal. In this case, a characteristic image appears on the EEG - a change in the alpha rhythm by the beta rhythm, i.e. the reaction of desynchronization or activation is recorded. This reaction is not limited to a certain area of ​​the cerebral cortex, but covers its large arrays, i.e. is generalized. When the reticular formation is destroyed or its ascending connections with the cerebral cortex are turned off, the animal falls into a dream-like state, does not respond to light and olfactory stimuli, and does not actually come into contact with the outside world. That is, the terminal brain ceases to function actively.

Thus, the reticular formation of the brainstem performs the functions of the ascending activating system of the brain, which maintains the excitability of neurons in the cerebral cortex at a high level.

In addition to the reticular formation of the brainstem, the ascending activating system of the brain also includes nonspecific nuclei of the thalamus, posterior hypothalamus, limbic structure. As an important integrative center, the reticular formation, in turn, is part of the more global integration systems of the brain, which include the hypothalamic-limbic and neocortical structures. It is in interaction with them that purposeful behavior is formed, aimed at adapting the organism to the changing conditions of the external and internal environment.

One of the main manifestations of damage to the reticular structures in humans is loss of consciousness. It happens when there is a violation of cerebral circulation, tumors and infectious processes in the brain stem. The duration of the state of fainting depends on the nature and severity of dysfunctions of the reticular activating system and ranges from a few seconds to many months. Dysfunction of ascending reticular influences is also manifested by loss of vigor, constant pathological drowsiness or frequent bouts of falling asleep (paroxysmal hypersomia), restless night sleep. There are also violations (more often an increase) of muscle tone, various vegetative changes, emotional and mental disorders, etc.

Reticular formation (from Latin 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 hillocks). Neuron s , components of R. f., various in size, structure and length 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 cerebral cortex. In the area of ​​R. f. the interaction of both ascending - afferent and descending - efferent impulses coming into it is carried out. Circulation of impulses through closed neural circuits is also possible. Thus, there is a constant level of excitation of the neurons of the R. f., 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 ensured. R.'s degree of excitement f. is regulated by the cerebral cortex (See. The cerebral cortex).

Downward influences. In R. f. distinguish between 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 areas of the brain stem and spinal reflexes was first noted in 1862 by I.M.Sechenov. In 1944-46 the American neurophysiologist H. Magone and his co-workers showed that irritation of various parts of the R. f. medulla oblongata has a facilitating or inhibitory effect on the motor responses of the spinal cord. Electrical irritation of the medial part of R. f. the 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, this effect is often observed with a lower threshold of irritation. Some manifestations of the inhibiting influences of R. f. medulla oblongata correspond to the picture of central inhibition described by Sechenov (see Sechenov inhibition). Irritation of the lateral area of ​​R. f. medulla oblongata along the periphery of the region that has inhibitory effects, accompanied by a facilitating effect on the motor activity of the spinal cord. The area of ​​R. f., Exerting facilitating effects on the spinal cord, is not limited to the medulla oblongata, but extends anteriorly, capturing the area of ​​the pons and midbrain. R. f. can act on various formations of the spinal cord, for example, on alpha-motoneurons, which innervate the main (extrafusal) fibers of muscles involved in voluntary movements. An increase in the latent periods of responses of motoneurons upon stimulation of the inhibitory divisions of R. f. suggests that the inhibitory effects of the 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 disclosed by the Swedish neurophysiologist R. Granit, who showed that R. f. 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) exert 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, studying the bioelectric activity of the brain, found that the irritation of the R. f. the brain stem changes the slow synchronous high-voltage oscillations characteristic of sleep to the low-amplitude high-frequency activity characteristic of wakefulness. Changes in the electrical activity of the cerebral cortex are accompanied in animals by external manifestations of awakening. R. f. is closely connected anatomically with classical pathways, and its excitation is carried out using extero- and interoceptive afferent (sensory) systems. On this basis, a number of authors consider 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 action of chemical preparations on the reactions carried out with the participation of R. f., Allowed P.K. to formulate the position on the specificity of the ascending influences of R. f. on 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). Introduced into the body, narcotic drugs induce inhibition of the neurons of the P. 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. f. in the regulation of some autonomic functions. The cerebral cortex, experiencing tonic activating influences from the R. f., Can actively change the functional state of the reticular formations (change the rate of excitation in it, affect 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 organism. R.'s research f. with the use of pharmacological agents, they open up the possibilities of drug treatment of a number of diseases of the central nervous system, they 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., Zanketti A., Brainstem reticular formation, 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 PK, Biology and neurophysiology of a conditioned reflex, M., 1968; Granite 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 "Reticular formation" is in other dictionaries:

- (formatio reticularis; lat.reticulum network; synonym for 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 occupy 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

The 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 trunk of the spinal cord. 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, oblong, midbrain and pons of varoli and forming a single function. complex. Phylogenetically ancient motor system. control. Well developed for everyone ... ... Biological encyclopedic dictionary

Reticular formation- (lat. rete network, formatio formation, formation, composition) a network-like neural structure, consisting of more than 50 nuclei and an extensive network of neurons with complex and branched axonal and dendritic processes. Title suggested ... ... Encyclopedic Dictionary of Psychology and Pedagogy

A set of structures located in the spinal cord, medulla oblongata and midbrain and the pons varoli 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 collection of small but numerous nuclei located in the central parts of the brain stem. The neurons of the reticular formation have strongly branching processes going in different directions, resembling under a microscope ... Glossary of terms and concepts in human anatomy

Reticular formation- (from Lat. reticulum mesh) a nervous structure located along the entire brain stem and consisting of cells, the processes of which branch out in large 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; Latin reticulum mesh; synonym for 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

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