Convergence and a common final path. General final path. Centers of the autonomic nervous system

Excitation convergence principle(or the principle of a common final path, Sherrington's funnel). Convergence of nerve impulses means the convergence of two or more different excitations simultaneously to one neuron.

This phenomenon was discovered by C. Sherrington. He showed that the same movement, for example, reflex flexion of a limb at the knee joint, can be caused by irritating different reflexogenic zones. In this regard, he introduced the concept of a “common final path”, or “funnel principle”, according to which streams of impulses from different neurons can converge on the same neuron (in this case, the alpha motor neurons of the spinal cord). In particular, C. Sherrington discovered the convergence of different afferents from different parts of the general receptive field (in the spinal cord and medulla oblongata) or even from different receptive fields (in the higher parts of the brain) to the same intermediate or efferent neurons. It has now been shown that convergence of excitation, as well as divergence of excitation, is a very common phenomenon in the central nervous system.

The basis for convergence (as well as for irradiation) is a certain morphological and functional structure of various parts of the brain. It is obvious that some of the convergent pathways are innate, and the other part (mainly in the cerebral cortex) is acquired as a result of learning during ontogenesis. The formation of new convergent relationships for neurons of the cerebral cortex in the process of ontogenesis is largely associated with the formation of dominant excitation foci in the cortex, which are capable of “attracting” excitation from other neurons.

Centers of the autonomic nervous system

The centers of the autonomic nervous system are located in the spinal cord, medulla oblongata, midbrain, hypothalamus, cerebellum, reticular formation and cerebral cortex. Their interaction is based on the principle of hierarchy. The conditionally designated “lower floors” of this hierarchy, having sufficient autonomy, carry out local regulation of physiological functions. Each higher level of regulation provides a higher degree of integration of vegetative functions.

1. Mesencephalic - fibers are part of the oculomotor nerve (parasympathetic)

2. Bulbar – fibers consisting of the facial, glossopharyngeal and vagus nerves (parasympathetic)

3. Thoracolumbar - nuclei of the god's horns from the 8th cervical to the 3rd lumbar segments (sympathetic)

4. Sacral - in the 2-4th segments of the sacral spinal cord (parasympathetic)

Divisions of the autonomic nervous system

Sympathetic department. The bodies of the first neurons of the sympathetic division of the ANS are located mainly in the posterior nuclei of the hypothalamus, the midbrain and medulla oblongata and in the anterior horns of the spinal cord, starting from
1st thoracic and ending with the 3rd, 4th segment of its lumbar region.

Parasympathetic department. The central neurons of the parasympathetic division of the autonomic nervous system are located mainly in the anterior parts of the hypothalamus, the midbrain and medulla oblongata, in the 2-4 segments of the sacral spinal cord.

The sympathetic nervous system is activated during stress reactions. It is characterized by a generalized effect, with sympathetic fibers innervating the vast majority of organs.

It is known that parasympathetic stimulation of some organs has an inhibitory effect, while others have an exciting effect. In most cases, the action of the parasympathetic and sympathetic systems is opposite.

Sympathetic synapse

Sympathetic synapses are formed not only in the area of numerous terminal branches of the sympathetic nerve, as in all other nerve fibers, but also at the membranes varicose veins- numerous expansions of the peripheral areas of sympathetic fibers in the area of innervated tissues. Varicosities also contain synaptic vesicles with transmitter, although in lower concentrations than the terminal endings.

The main transmitter of sympathetic synapses is norepinephrine and such synapses are called adrenergic. Receptors that bind adrenergic transmitters are called adrenoreceptors. There are two types of adrenergic receptors - alpha And beta, each of which is divided into two subtypes - 1 and 2. A small part of sympathetic synapses uses the mediator acetylcholine and such synapses are called cholinergic, and the receptors are cholinergic receptors. Cholinergic synapses of the sympathetic nervous system are found in the sweat glands. In addition to norepinephrine, adrenergic synapses contain adrenaline and dopamine, also related to catecholamines, in significantly smaller quantities, therefore the mediator substance in the form of a mixture of three compounds was previously called sympathin.

The action of postganglionic nerve fibers on the effector is ensured by the release of mediators into the synaptic cleft, which affect the postsynaptic membrane - the membrane of the cell of the working organ. Postganglionic parasympathetic fibers release acetylcholine, which binds to M-cholinergic receptors, i.e. muscari-
nopodibnym receptors (M - XP).

Parasympathetic synapse

Parasympathetic postganglionic or peripheral synapses use acetylcholine as a transmitter, which is located in the axoplasm and synaptic vesicles of presynaptic terminals in three main pools or funds. This,
Firstly, a stable, tightly bound protein pool of mediator that is not ready for release;
Secondly, mobilization, less tightly bound and suitable for release, pool;
Thirdly, a pool ready to be released spontaneously or actively allocated. At the presynaptic terminal, pools constantly move in order to replenish the active pool, and this process is also carried out by moving synaptic vesicles to the presynaptic membrane, since the mediator of the active pool is contained in those vesicles that are directly adjacent to the membrane. The release of the transmitter occurs in quanta, the spontaneous release of single quanta is replaced by active ones upon the arrival of excitation impulses that depolarize the presynaptic membrane. The process of releasing transmitter quanta, as well as in other synapses, is calcium-dependent.

Charles Sherrington published a book: The Integrative Action of the Nervous System, where he outlined the principle of organizing the effector reaction, which he called “The Principle of the Common Final Path”. The term "Sherrington's funnel" is sometimes used in the literature.

“According to his ideas, the quantitative predominance of sensory and other incoming fibers over motor fibers creates an inevitable collision of impulses in the common final path, which is a group of motor neurons and the muscles innervated by them. Thanks to this collision blocking of all influences is achieved except one, which regulates the course of the reflex reaction. The principle of a common final path, as one of the principles of coordination, applies not only to the spinal cord, but also to any other part of the central nervous system.”

Shcherbatykh Yu.V., Turovsky Ya.A., Physiology of the central nervous system for psychologists, St. Petersburg, “Peter”, 2007, p. 105.

To explain this principle, a metaphor is often used: suppose that five trains arrive at a railway station along five tracks, but only one track leaves the station and, accordingly, only one train leaves the station per unit time...

Thus, the very principles of organization of the nervous system suggest that only some of the external influences, under conditions of their simultaneous influence on the body, will receive “access” to the muscles at the output. Some selection, selection of stimuli, discarding some of them is the law of the activity of the nervous system. Myself Charles Sherrington believed that the most important factor ensuring the choice of one of several possible influences is the strength of the influence: a strong influence, as it were, suppresses, displaces weaker ones...

In the structural organization of nerve networks, a situation occurs when several afferent terminals from other parts of the central nervous system converge on one neuron. This phenomenon is usually called convergence in neural connections. For example, about 6000 axonal collaterals of primary afferents, spinal interneurons, descending pathways from the brainstem and cortex approach one motor neuron. All these terminal endings form excitatory and inhibitory synapses on the motor neuron and form a kind of “funnel”, the narrowed part of which represents the common motor output. This funnel is an anatomical formation that determines one of the mechanisms of the coordination function of the spinal cord.

The essence of this mechanism was revealed by the English physiologist C. Sherrington, who formulated the principle of a common final path. According to C. Sherrington, the quantitative predominance of sensory and other incoming fibers over motor fibers creates an inevitable collision of impulses in the common final path, which is a group of motor neurons and the muscles innervated by them. As a result of this collision, inhibition of all possible degrees of freedom of the motor apparatus is achieved, except for one, in the direction of which a reflex reaction occurs, caused by maximum stimulation of one of the afferent inputs.

Let's consider a case with simultaneous stimulation of the receptive fields of the scratching and flexion reflexes, which are realized by identical muscle groups. Impulses coming from these receptive fields arrive at the same group of motor neurons, and here, at the bottleneck of the infundibulum, due to the integration of synaptic influences, a choice is made in favor of the flexion reflex caused by stronger pain stimulation. The principle of the common final path, as one of the principles of coordination, is valid not only for the spinal cord, it is applicable to any floor of the central nervous system, including the motor cortex.

Temporal and spatial summation. Occlusion

Convergence underlies such physiological phenomena as temporal and spatial summation. In the event that two subthreshold stimuli arriving at the neuron through the afferent input follow each other with a short time interval, the summation of EPSPs caused by these stimuli takes place, and the total EPSP reaches a threshold level sufficient to generate impulse activity. This process contributes to the amplification of weak signals arriving at the neuron and is defined as temporary summation. At the same time, synaptic activation of a neuron can occur through two separate inputs that converge on this cell. Simultaneous stimulation of these inputs by subthreshold stimuli can also lead to the summation of EPSPs arising in two spatially separated zones of the cell membrane. In this case it happens spatial summation, which, just like temporary, can cause long-term depolarization of the cell membrane and the generation of rhythmic impulse activity against the background of this depolarization.

However, a situation is also possible when, with simultaneous stimulation of two inputs, the excitation of the neuron and the corresponding reflex response will be less than the algebraic sum of the responses with separate stimulation of these inputs. With separate stimulation of two motor neuron inputs b will be excited twice: first together with the neuron A and then together with the neuron V. When two inputs are simultaneously stimulated, the neuron b will be excited only once and, accordingly, the reflex response will be less than the algebraic sum of responses with separate stimulation. This physiological phenomenon, associated with the presence of an additional common path for two inputs, is called occlusion.

As already noted, local neural networks can amplify weak signals through a positive feedback mechanism due to cyclic reverberation excitation in a chain of neurons. Another possible amplification mechanism is created by synoptic potentiation(relief) with rhythmic stimulation of presynaptic inputs. Potentiation is expressed in an increase in EPSP amplitude during (tetanic potentiation) and after (post-tetanic potentiation) rhythmic stimulation of the presynaptic axon with a fairly high frequency (100-200 impulses/s).

Braking

The coordinating function of local neural networks, in addition to strengthening, can also be expressed in weakening too intense activity of neurons due to their inhibition. Braking, as a special nervous process, it is characterized by the absence of the ability to actively spread throughout the nerve cell and can be represented in two forms - primary and secondary inhibition. Primary inhibition is caused by the presence of specific inhibitory structures and develops primarily without prior excitation. An example of primary inhibition is the so-called reciprocal inhibition of antagonist muscles, found in spinal reflex arcs. The essence of the phenomena is that if the priororeceptors of the flexor muscle are activated, then through the primary afferents they simultaneously excite the motor neuron of this flexor muscle and through the collateral of the afferent fiber - the inhibitory interneuron. Excitation of the interneuron leads to postsynaptic inhibition of the motor neuron of the antagonistic extensor muscle, on the body of which the axon of the inhibitory interneuron forms specialized inhibitory synapses. Reciprocal inhibition plays an important role in the automatic coordination of motor acts.

Inhibition by the principle of negative feedback occurs only at the output, but also at the input of the motor centers of the spinal cord. A phenomenon of this kind is described in monosynaptic connections of afferent fibers with spinal motor neurons, the inhibition of which in this situation is not associated with changes in the postsynaptic membrane. The latter circumstance made it possible to define this form of inhibition as presynaptic. It is due to the presence of intercalary inhibitory neurons, to which collaterals of afferent fibers approach. In turn, interneurons form axo-axonal synapses on afferent terminals that are presynaptic to motor neurons.

SEVENTH question.

The central nervous system distinguishes between more ancient segmental and evolutionarily younger suprasegmental parts of the nervous system. The segmental sections include the spinal cord, medulla oblongata and midbrain, sections of which regulate the functions of individual parts of the body lying at the same level. The suprasegmental sections: diencephalon, cerebellum and cerebral cortex - do not have direct connections with the organs of the body, but control their activity through the underlying segmental sections.

Spinal cord. The spinal cord is the lowest and most ancient part of the central nervous system. The gray matter of the human spinal cord contains about 13.5 million nerve cells. Of these, the bulk (97%) are intermediate cells (interneurons, or interneurons), which provide complex coordination processes within the spinal cord. Among the motor neurons of the spinal cord, large cells are distinguished - alpha motor neurons and small cells - gamma motor neurons. The thickest and fastest-conducting fibers of the motor nerves depart from alpha motor neurons, causing contractions of skeletal muscle fibers. Thin fibers of gamma motor neurons do not cause muscle contraction. They approach pro-prioceptors - muscle spindles and regulate the sensitivity of these receptors, which inform the brain about the execution of movements.

Spinal cord reflexes can be divided into motor, carried out by alpha motor neurons of the anterior horns, and autonomic, carried out by efferent cells of the lateral horns. Motor neurons of the spinal cord innervate all skeletal muscles (with the exception of the facial muscles). The spinal cord carries out elementary motor reflexes: flexion and extension, rhythmic, walking, arising from irritation of the skin or proprioceptors of muscles and tendons, and also sends constant impulses to the muscles, maintaining their tension - muscle tone. Special motor neurons innervate the respiratory muscles - the intercostal muscles and the diaphragm - and provide respiratory movements. Autonomic neurons innervate all internal organs (heart, blood vessels, sweat glands, endocrine glands, digestive tract, genitourinary system) and carry out reflexes that regulate their activity.

The conductor function of the spinal cord is associated with the transmission of information received from the periphery to the overlying parts of the nervous system and with the conduction of impulses coming from the brain to the spinal cord.

Medulla oblongata and pons. The medulla oblongata and the pons are part of the brain stem. There is a large group of cranial nerves (from V to XII pairs) that innervate the skin, mucous membranes, muscles of the head and a number of internal organs (heart, lungs, liver). There are also centers for many digestive reflexes: chewing, swallowing, movements of the stomach and part of the intestines, secretion of digestive juices, as well as centers for some protective reflexes (sneezing, coughing, blinking, tearing, vomiting) and centers for water-salt and sugar metabolism. At the bottom of the IV ventricle in the medulla oblongata there is a vital respiratory center. A cardiovascular center is located in close proximity. Its large cells regulate the activity of the heart and the lumen of blood vessels.

The medulla oblongata plays an important role in the implementation of motor acts and in the regulation of skeletal muscle tone, increasing the tone of the extensor muscles. He, in particular, takes part in the implementation of postural adjustment reflexes (cervical, labyrinthine).

The ascending pathways pass through the medulla oblongata - auditory, vestibular, proprioceptive and tactile sensitivity.

Midbrain. The midbrain consists of the quadrigeminal, substantia nigra and red nuclei. In the anterior tubercles of the quadrigeminal region there are visual subcortical centers, and in the posterior ones there are auditory centers. The midbrain is involved in the regulation of eye movements and carries out the pupillary reflex (dilation of the pupils in the dark and constriction in the light).

The quadrigeminal muscles perform a number of reactions that are components of the orienting reflex. In response to sudden irritation, the head and eyes turn towards the stimulus. This reflex (according to I.P. Pavlov - the “What is this?” reflex) is necessary to prepare the body for a timely reaction to any new impact.

The substantia nigra of the midbrain is related to the chewing and swallowing reflexes, is involved in the regulation of muscle tone (especially when performing small movements with the fingers) and in the organization of friendly motor reactions.

The red nucleus of the midbrain performs motor functions: it regulates the tone of skeletal muscles, causing increased tone of the flexor muscles.

Having a significant impact on the tone of skeletal muscles, the midbrain takes part in a number of adjustment reflexes for maintaining posture (rectifying - positioning the body with the crown of the head up, etc.).

Diencephalon. The diencephalon includes the thalamus (visual thalamus) and the hypothalamus (subthalamus).

All afferent pathways (with the exception of olfactory) pass through the thalamus, which are sent to the corresponding perceptive areas of the cortex (auditory, visual, etc.). The nuclei of the thalamus are divided into specific and nonspecific. Specific ones include switching (relay) cores and associative ones. Afferent influences from all receptors of the body are transmitted through the switching nuclei of the thalamus. Associative nuclei receive impulses from switching nuclei and ensure their interaction, i.e. carry out their subcortical integration. In addition to these nuclei, the thalamus contains nonspecific nuclei that have both activating and inhibitory effects on small areas of the cortex.

Thanks to its extensive connections, the thalamus plays a vital role in the functioning of the body. Impulses coming from the thalamus to the cortex change the state of cortical neurons and regulate the rhythm of cortical activity. With the direct participation of the thalamus, the formation of conditioned reflexes and the development of motor skills, the formation of human emotions and facial expressions occur. The thalamus plays a large role in the occurrence of sensations, in particular the sensation of pain. Its activity is associated with the regulation of biorhythms in human life (daily, seasonal, etc.).

The hypothalamus is the highest subcortical center for the regulation of autonomic functions. Here are located vegetative centers that regulate metabolism in the body, ensure the maintenance of constant body temperature (in warm-blooded animals) and normal blood pressure levels, maintain water balance, and regulate the feeling of hunger and satiety. Irritation of the posterior nuclei of the hypothalamus causes increased sympathetic influences, and the anterior ones - parasympathetic effects.

Thanks to the close connection of the hypothalamus with the pituitary gland (hypothalamic-pituitary system), the activity of the endocrine glands is controlled. Autonomic and hormonal reactions, regulated by the hypothalamus, are components of human emotional and motor reactions. The structures of the hypothalamus are also associated with the regulation of states of wakefulness and sleep.

Nonspecific brain system. The nonspecific system occupies the middle part of the brain stem. It does not involve the analysis of any specific sensitivity or the execution of specific reflex reactions. Impulses into this system enter through lateral branches from all specific pathways, resulting in their extensive interaction.

A nonspecific system is characterized by the arrangement of neurons in the form of a diffuse network, the abundance and diversity of their processes. In this regard, it received the name reticular formation, or reticular formation.

There are two types of influence of a nonspecific system on the work of other nerve centers - activating and inhibitory. Both types of these influences can be ascending (to overlying centers) and descending (to underlying centers). They serve to regulate the functional state of the brain, the level of wakefulness and the regulation of postural-tonic and phasic reactions of skeletal muscles.

Cerebellum. The cerebellum is a suprasegmental formation that does not have direct connections with the executive apparatus. The cerebellum consists of an unpaired formation - the vermis and paired hemispheres. The main neurons of the cerebellar cortex are numerous Purkin cells. Thanks to extensive connections (up to 200,000 synapses terminate on each cell), they integrate a wide variety of sensory influences, primarily proprioceptive, tactile and vestibular. The representation of various peripheral receptors in the cerebellar cortex has a soma-totopic organization (from the Greek somatos - body, topos - place), i.e. reflects the order of their location in the human body. In addition, this order of arrangement corresponds to the same order of arrangement of the representation of body parts in the cerebral cortex, which facilitates the exchange of information between the cortex and the cerebellum and ensures their joint activity in controlling human behavior. The correct geometric organization of cerebellar neurons determines its importance in timing and clearly maintaining the tempo of cyclic movements.

The main function of the cerebellum is the regulation of postural-tonic reactions and coordination of motor activity.

According to anatomical features (connections of the cerebellar cortex with its nuclei) and functional significance, the cerebellum is divided into three longitudinal zones: the internal, or medial, cortex of the vermis, the function of which is to regulate the tone of skeletal muscles, maintain posture and balance of the body; intermediate - the middle part of the cortex of the cerebellar hemispheres, the function of which is the coordination of postural reactions with movements, as well as error correction; the lateral, or lateral, cortex of the cerebellar hemispheres, which, together with the diencephalon and the cerebral cortex, is involved in programming fast ballistic movements (throws, strikes, jumps, etc.).

Basal ganglia. The basal nuclei include the striatal nucleus, consisting of the caudate nucleus and putamen, and the pallid nucleus, and currently also include the amygdala (related to the autonomic centers of the limbic system) and the substantia nigra of the midbrain.

Afferent influences come to the basal ganglia from body receptors through the thalamus and from all areas of the cerebral cortex. They enter the striatum. Efferent influences from it are directed to the pallid nucleus and further to the stem centers of the extrapyramidal system, as well as through the thalamus back to the cortex.

The basal ganglia are involved in the formation of conditioned reflexes and the implementation of complex unconditioned reflexes (defensive, food-procuring, etc.). They provide the necessary body position during physical work, as well as the flow of automatic rhythmic movements (ancient automatisms).

The nucleus pallidus performs the main motor function, and the striatum regulates its activity. Currently, the importance of the caudate nucleus in the control of complex mental processes - attention, memory, error detection - has been revealed.

EIGHTH question.

In higher mammals - animals and humans - the leading part of the central nervous system is the cerebral cortex.

Cortical neurons. The cortex is a layer of gray matter 2-3 mm thick, containing on average about 14 billion nerve cells. It is characterized by an abundance of interneuron connections.

The main types of cortical cells are stellate and pyramidal neurons. Stellate neurons associated with the processes of perception of irritations and the unification of the activities of various pyramidal neurons. Pyramidal neurons carry out the efferent function of the cortex (mainly through the pyramidal tract) and intracortical processes of interaction between neurons remote from each other. The largest pyramidal cells - the giant pyramids of Betz - are located in the anterior central gyrus (motor zone of the cortex).

The functional unit of the cortex is a vertical column of interconnected neurons. Vertically elongated large pyramidal cells with neurons located above and below them form functional associations of neurons. All neurons of the vertical column respond to the same afferent stimulation (from the same receptors) with the same reaction and jointly form the efferent responses of pyramidal neurons.

Diagram of a cortical functional unit - a vertical column of neurons

1,2 - pyramidal neurons; 3, 4 - recurrent axonal collaterals; 5 – efferent output; 6, 7 - afferent inputs; 8 – interneuron

As needed, vertical columns can be combined into larger formations, providing combined reactions. Functional significance of various cortical fields. Based on the structural features and functional significance of individual cortical areas, the entire cortex is divided into three main groups of fields - primary, secondary and tertiary.

Primary fields are associated with sensory organs and organs of movement on the periphery. They provide sensations. These include, for example, the field of pain and musculo-articular sensitivity in the posterior central gyrus of the cortex, the visual field in the occipital region, the auditory field in the temporal region and the motor field in the anterior central gyrus. The primary fields contain highly specialized determinant cells, or detectors, that selectively respond only to certain stimuli.

Primary, secondary and tertiary fields of the cerebral cortex

On A: large dots are primary fields, medium ones are secondary fields, small ones (gray background) are tertiary fields. In B: primary (projection) fields of the cerebral cortex

For example, in the visual cortex there are detector neurons that are excited only when the light is turned on or off, sensitive only to a certain intensity, to specific intervals of light exposure, to a certain wavelength, etc.

When the primary fields of the cortex are destroyed, so-called cortical blindness, cortical deafness, etc. occur. Secondary fields are located next to the primary ones. In them, comprehension and recognition of sound, light and other signals occur, and complex forms of generalized perception arise. When secondary fields are damaged, the ability to see objects and hear sounds is retained, but the person does not recognize them and does not remember the meaning.

Sensory (left) and motor (right) representation of various parts of the body in the cerebral cortex

Tertiary fields are developed only in humans. These are associative areas of the cortex, providing higher forms of analysis and synthesis and forming purposeful human behavioral activity. Tertiary fields are found in the posterior half of the cortex - between the parietal, occipital and temporal regions - and in the anterior half - in the anterior parts of the frontal regions. Their role is especially great in organizing the coordinated work of both hemispheres. Tertiary fields mature in humans later than other cortical fields and degrade earlier than others during the aging of the body.

The function of the posterior tertiary fields (mainly the inferior parietal areas of the cortex) is to receive, process and store information. They form an idea of the body diagram and the spatial diagram, providing spatial orientation of movements. The anterior tertiary fields (frontal areas) perform the general regulation of complex forms of human behavior, forming intentions and plans, programs of voluntary movements and control over their implementation. The development of tertiary fields in humans is associated with the function of speech. Thinking (inner speech) is possible only with the joint activity of various sensory systems, the integration of information from which occurs in tertiary fields. With congenital underdevelopment of the tertiary fields, a person is not able to master speech (pronounces only meaningless sounds) and even the simplest motor skills (cannot dress, use tools, etc.).

Pair activity and hemispheric dominance. Information processing is carried out as a result of paired activity of both hemispheres of the brain. However, as a rule, one of the hemispheres is leading - dominant. In most people with a dominant right hand (right-handed people), the left hemisphere is dominant, and the right hemisphere is subordinate (subdominant).

The left hemisphere, compared to the right, has a finer neural structure, a greater richness of neuronal connections, a more concentrated representation of functions and better blood supply conditions. In the left dominant hemisphere there is a motor speech center (Broca's center), which provides speech activity, and a sensory speech center, which carries out the understanding of words. The left hemisphere is specialized in fine sensorimotor control of hand movements.

Functional asymmetry found in humans in relation to not only motor functions (motor asymmetry), but also sensory (sensory asymmetry). As a rule, a person has a “dominant eye” and a “dominant ear,” the signals from which are dominant in perception. However, the problem of functional asymmetry is quite complex. For example, a right-handed person may have a dominant left eye or left ear. In each hemisphere, the functions of not only the opposite, but also the side of the body of the same name can be represented. As a result of this, it is possible to replace one hemisphere with another in case of damage, and also creates a structural basis for the variable dominance of the hemispheres in controlling movements.

Specialization of the hemispheres also manifests itself in relation to mental functions (mental asymmetry). The left hemisphere is characterized by analytical processes, sequential processing of information, including through speech, abstract thinking, assessment of temporal relationships, anticipation of future events, and successful solution of verbal and logical problems. In the right hemisphere, information is processed holistically, synthetically (without breaking down into details), taking into account past experience and the absence of speech, and substantive thinking predominates. These features make it possible to associate the perception of spatial features and the solution of visuospatial problems with the right hemisphere.

Electrical activity of the cerebral cortex. Changes in the functional state of the cortex are reflected in the recording of its electrical activity - an electroencephalogram (EEG). Modern electroencephalographs amplify brain potentials by 2-3 million times and make it possible to study EEG from many points of the cortex simultaneously, i.e. study system processes.

There are certain frequency ranges called EEG rhythms; in a state of relative rest, the alpha rhythm is most often recorded (8-13 oscillations per 1 s); in a state of active attention - beta rhythm (14 oscillations per 1 s and higher); when falling asleep, in some emotional states - theta rhythm (4-7 oscillations per 1 s); during deep sleep, loss of consciousness, anesthesia - delta rhythm (1-3 vibrations per 1 s).

Electroencephalogram of the occipital (a - e) and motor (f - h) areas of the human cerebral cortex in various conditions and during muscle work:

a - active state, eyes open (beta rhythm); b - rest, eyes closed (alpha rhythm); c - drowsiness (theta rhythm); g - falling asleep; d - deep sleep (delta rhythm); e - unusual or hard work - asynchronous frequent activity (desynchronization phenomenon); g -cyclic movements - slow potentials at the pace of movement (“marked rhythms” of the EEG); h - execution of a mastered movement - appearance of alpha rhythm

In addition to background activity, the EEG distinguishes individual potentials associated with certain events: evoked potentials that arise in response to external stimuli (auditory, visual, etc.); potentials reflecting brain processes during the preparation, implementation and completion of individual motor acts - “wave of anticipation”, or conditioned negative wave: premotor, motor, final potentials, etc. In addition, ultra-slow oscillations lasting from several seconds to tens of minutes are recorded (the so-called “omega potentials”, etc.), which reflect the biochemical processes of regulation of functions and mental activity.

NINTH question.

The limbic system is understood as a number of cortical and subcortical structures, the functions of which are associated with the organization of motivational and emotional reactions, memory and learning processes.

The cortical sections of the limbic system, representing its highest section, are located on the lower and inner surfaces of the cerebral hemispheres (parts of the frontal cortex, cingulate gyrus, or limbic cortex, hippocampus, etc.). The subcortical structures of the limbic system include the hypothalamus, some nuclei of the thalamus, midbrain and reticular formation. Between all these formations there are close direct and feedback connections, forming the so-called limbic ring.

The limbic system is involved in a wide variety of manifestations of the body’s activity: in the regulation of eating and drinking behavior, the sleep-wake cycle, in the processes of forming a memory trace (deposition and retrieval from memory), in the development of aggressive-defensive reactions, ensuring the selective nature of behavior. It forms positive and negative emotions with all their motor and hormonal components. A study of various parts of the limbic system has revealed the presence of centers of pleasure, which form positive emotions, and displeasure, which form negative emotions. Isolated irritation of such points in the deep structures of the human brain caused the appearance of feelings of “causeless joy,” “pointless melancholy,” and “unaccountable fear.”

TENTH question.

All functions of the body can be conditionally divided into somatic, or animal (animal), associated with the perception of external information and muscle activity, and vegetative (plant), associated with the activity of internal organs: the processes of respiration, blood circulation, digestion, excretion, metabolism, growth and reproduction.

Functional organization of the autonomic nervous system. The autonomic nervous system is a collection of efferent nerve cells of the spinal cord and brain, as well as cells of special nodes (ganglia) that innervate internal organs. Stimulation of various body receptors can cause changes in both somatic and autonomic functions, since the afferent and central parts of these reflex arcs are common. They differ only in their efferent sections. A characteristic feature of the efferent pathways included in the reflex arcs of autonomic reflexes is their two-neuron structure (one neuron is located in the central nervous system, the other in the ganglia or in the innervated organ).

The autonomic nervous system is divided into two divisions - sympathetic and parasympathetic.

The efferent pathways of the sympathetic nervous system begin in the thoracic and lumbar parts of the spinal cord from the neurons of its lateral horns. The transfer of excitation from prenodal sympathetic fibers to postnodal ones occurs with the participation of the mediator acetylcholine, and from postnodal fibers to innervated organs - with the participation of the mediator norepinephrine. The exception is the fibers that innervate the sweat glands and dilate the vessels of skeletal muscles, where excitation is transmitted using acetylcholine.

The efferent pathways of the parasympathetic nervous system begin in the brain - from some nuclei of the midbrain and medulla oblongata - and in the spinal cord - from neurons of the sacral region. The conduction of excitation at the synapses of the parasympathetic pathway occurs with the participation of the mediator acetylcholine. The second neuron is located in or near the innervated organ.

The highest regulator of autonomic functions is the hypothalamus, which acts together with the reticular formation and limbic system, under the control of the cerebral cortex. In addition, neurons located in the organs themselves or in the sympathetic ganglia can carry out their own reflex reactions without the participation of the central nervous system - “peripheral reflexes”.

Functions of the sympathetic nervous system. With the participation of the sympathetic nervous system, many important reflexes occur in the body, aimed at ensuring its active state, including its motor activity. These include reflexes of bronchi dilatation, increased heart rate, release of stored blood from the liver and spleen, breakdown of glycogen into glucose in the liver (mobilization of carbohydrate energy sources), increased activity of the endocrine glands and sweat glands. The sympathetic nervous system reduces the activity of a number of internal organs: as a result of vasoconstriction in the kidneys, the processes of urine formation are reduced, the secretory and motor activity of the gastrointestinal tract organs is inhibited; the act of urination is prevented - the muscles of the bladder wall relax and its sphincter contracts.

Increased activity of the body is accompanied by a sympathetic reflex of pupil dilation. The trophic influence of sympathetic nerves on skeletal muscles, which improves their metabolism and relieves fatigue, is of great importance for the motor activity of the body.

Autonomic nervous system

The sympathetic department of the nervous system not only increases the level of functioning of the body, but also mobilizes its hidden functional reserves, activates brain activity, increases protective reactions (immune reactions, barrier mechanisms, etc.), and triggers hormonal reactions. The sympathetic nervous system is of particular importance during the development of stressful conditions, in the most difficult conditions of life. The role of sympathetic influences in the processes of adaptation (adaptation) of the body to hard work in various environmental conditions is important. This function is called adaptation-trophic.

Functions of the parasympathetic nervous system. The parasympathetic nervous system constricts the bronchi, slows down and weakens heart contractions, replenishes energy resources (synthesis of glycogen in the liver and enhances digestion processes), enhances the processes of urine formation in the kidneys and ensures the act of urination (contraction of the bladder muscles and relaxation of its sphincter), etc. The parasympathetic nervous system has predominantly triggering effects: constriction of the pupils, bronchi, activation of the digestive glands, etc.

The activity of the parasympathetic department of the autonomic nervous system is aimed at the ongoing regulation of the functional state, at maintaining the constancy of the internal environment - homeostasis. The parasympathetic department ensures the restoration of various physiological indicators, sharply changed after intense muscular work, and the replenishment of expended energy resources. The mediator of the parasympathetic system - acetylcholine, reducing the sensitivity of adrenergic receptors to the action of adrenaline and norepinephrine, has a certain anti-stress effect.

Autonomic reflexes. Through the autonomic sympathetic and parasympathetic pathways, the central nervous system carries out some autonomic reflexes, starting from various receptors of the external and internal environment: viscero-visceral (from internal organs to internal organs - for example, the respiratory-cardiac reflex); dermo-visceral (from the skin - changes in the activity of internal organs when irritating active points of the skin, for example, acupuncture, acupressure); from the receptors of the eyeball - Ansher's eye-heart reflex (decrease in heartbeat when pressing on the eyeballs - parasympathetic effect); motor-visceral, etc. They are used to assess the functional state of the body, and especially the state of the autonomic nervous system. They are used to judge the strengthening of the influence of its sympathetic or parasympathetic department.

In the structural organization of nerve networks, a situation occurs when several afferent terminals from other parts of the central nervous system converge on one neuron. This phenomenon is commonly called convergence in neural connections. For example, about 6000 axon collaterals of primary afferents, spinal interneurons, descending pathways from the brainstem and cortex approach one motor neuron. All these terminal endings form excitatory and inhibitory synapses on the motor neuron and form a kind of “funnel”, the narrowed part of which represents the general motor output. This funnel is an anatomical formation that determines one of the mechanisms of the coordination function of the spinal cord

The essence of this mechanism was revealed by the English physiologist C. Sherrington, who formulated the principle of a common final path. According to C. Sherrington, the quantitative predominance of sensory and other incoming fibers over motor fibers creates an inevitable collision of impulses in the common final path, which is a group of motor neurons and the muscles innervated by them. As a result of this collision, inhibition of all possible degrees of freedom of the motor apparatus is achieved, except for one, in the direction of which a reflex reaction occurs, caused by maximum stimulation of one of the afferent inputs.

Question 56

DOMINANT(from lat. dominans, gender dominantis - dominant) (physiol.), the predominant (dominant) system of interconnected nerve centers, temporarily determining the nature of the body's response to any external. or internal irritants. Basic The provisions of the doctrine of D., as the general principle of the work of nerve centers, were formulated by A. A. Ukhtomsky in 1911-1923. He put forward the idea of a “dominant central constellation” that creates the body’s latent readiness to determine. activity while simultaneously inhibiting extraneous reflex acts. D. arises on the basis of dominant motivational arousal. In this regard, food, sexual, defensive, and other types of D are distinguished. For example, in male frogs in the spring, due to an increase in the concentration of sex hormones in the blood, a strong “hug reflex* and irritation of the surface of their body is observed at this time instead of in order to cause correspondence. defensive, reflex, increases tension in the flexor muscles of the forelimbs. D. serves as a vector of behavior in physiol. the basis of a number of complex mental phenomena. Biological encyclopedic dictionary. Ch. ed. M.S. Gilyarov. M.: Sov. encyclopedia, 1986.

Question 57

What is the importance of the reticular formation in the perception of information?

A person understands the world with the help of information (signals), which he receives, processes, and with the help of which he makes decisions and forms behavior. The perception of information is associated with the reticular formation.

The reticular formation and the cerebral cortex are closely connected. There is a connection between them: cortex-reticular formation-cortex.

All impulses coming from the sense organs are transmitted to the cerebral cortex, and from it to the reticular formation, where excitation accumulates. If necessary (intense physical work, control work, etc.), the reticular formation transmits excitation to the cerebral cortex and activates it. It is often compared to a central switch that turns energy on or off. This kind of “powerhouse” of the brain operates at full capacity when a person is actively working, thinking, or overwhelmed by emotions. The reticular formation receives information from all sensory organs, internal and other organs, evaluates it and selectively (only what is needed) transmits it to the limbic system and the cerebral cortex. It regulates the level of excitability and tone of various parts of the nervous system, including the cerebral cortex, plays an important role in the processes of consciousness, memory, perception, thinking, sleep, wakefulness, autonomic functions, purposeful movements, as well as in the mechanisms of formation of integral reactions of the body.

So, the reticular formation functions as a kind of filter that allows sensory systems important for the body to activate the cerebral cortex, but does not allow signals that are familiar to it or signals that are often repeated. It is an “information indicator” that determines the importance of information entering the brain. Thanks to this ability, the reticular formation protects the brain from excess information. However, the function of the reticular formation itself is under the control of the cerebral hemispheres.

Question 58

amino-specific brain systems
Neurons whose mediators are monoamines (serotonin, norepinephrine and dopamine) are involved in uniting various brain structures into a single functional formation. The bodies of these neurons are located predominantly in the structures of the brain stem, and the processes extend to almost all parts of the central nervous system, starting from the spinal cord and to the cerebral cortex.
The bodies of serotonergic neurons are located in the midline of the brain stem, starting from the medulla oblongata to the lower parts of the midbrain. The processes of these neurons reach almost all parts of the diencephalon, forebrain, they are also found in the cerebellum and spinal cord. Three types of receptors have been found for serotonin (M, B, T). In most brain structures, excitation of serotonergic neurons causes inhibition of varying degrees of severity: reflexes of the spinal cord and medulla oblongata are inhibited, the transmission of excitation through the nuclei of the thalamus is suppressed, and the activity of neurons in the reticular formation and cerebral cortex is suppressed. Thanks to its numerous connections with various structures of the brain, the serotonergic system is involved in the formation of memory, regulation of sleep and wakefulness, motor activity, sexual behavior, expression of an aggressive state, thermoregulation, and pain reception.
The bodies of noradrenergic neurons are located in separate groups in the medulla oblongata and the pons, and there are especially many of them in the locus coeruleus. The locus coeruleus is connected to almost all areas of the brain: with various structures of the midbrain, thalamus and such parts of the anterior brain as the amygdala, hippocampus, cingulate gyrus and neocortex. There are four types of adrenergic receptors in the central nervous system: a1, a2, P1, P2. a-receptors are concentrated mainly in the cortex, hypothalamus, and hippocampus. β-receptors are found in the cortex, striatum and hippocampus. But the location, as well as the functional purpose, of these receptors is significantly different. Thus, α1 receptors are located on the presynaptic membrane and, obviously, provide regulation of the release of norepinephrine, i.e. have a modulating effect. In contrast, P1 receptors are localized on the postsynaptic membrane, and through them norepinephrine exerts its influence on neurons. a2-, P2-receptors are found on the terminals of serotonergic neurons, where they modulate the release of this mediator, as well as on neuroglial cells.
Excitation of noradrenergic structures is accompanied by inhibition of the activity of various neurons, including serotonergic ones, inhibition, or vice versa, facilitation of the transmission of afferent information at different levels of the central nervous system.
The bodies of the dopaminergic system lie in the ventral parts of the midbrain, they are especially numerous in the substantia nigra. Their processes go both to the basal motor nuclei (striopalidal system), and to the limbic system, hypothalamus, and frontal lobe of the cerebral cortex. Because of this, the dopaminergic system is involved in the regulation of movements, the formation of the sensation of pain, positive and negative emotions. There are two types of dopamine receptors, upon interaction with which dopamine “triggers” various intracellular intermediaries: B1 receptors are associated with adenylate lazo (an enzyme that stimulates the formation of cAMP), and B2 receptors are not associated with this enzyme.
In recent years, the participation of monoaminergic brain systems in the occurrence of human mental illnesses has been widely studied. It is possible that diseases such as schizophrenia and cyclothymia are based on disturbances in the activity of monoaminergic systems. Many drugs that have a positive therapeutic effect affect the exchange of catecholamines in the corresponding centers of the brain.

Question 59

Limbic system.
The limbic system (synonym: limbic complex, visceral brain, rhinencephalon, timencephalon) is a complex of structures of the midbrain, diencephalon and telencephalon involved in the organization of visceral, motivational and emotional reactions of the body.
The main part of the structures of the limbic system consists of brain formations related to the ancient, old and new cortex, located mainly on the medial surface of the cerebral hemispheres, as well as numerous subcortical structures that are closely connected with them.
At the initial stage of development of vertebrates, the limbic system provided all the most important reactions of the body (food, orientation, sexual, etc.), which are formed on the basis of the most ancient distant sense - smell. It was the sense of smell that acted as an integrating factor of many integral functions of the body and united the structures of the telencephalon, diencephalon and midbrain into a single morphofunctional complex. A number of structures of the limbic system form closed systems based on ascending and descending pathways.
Morphologically, the limbic system in higher mammals includes areas of the old cortex (cingulate, or limbic, gyrus, hippocampus), some formations of the new cortex (temporal and frontal regions, intermediate frontotemporal zone), subcortical structures (globus pallidus, caudate nucleus, putamen, amygdala body, septum, hypothalamus, reticular formation of the midbrain, nonspecific nuclei of the thalamus).
The structures of the limbic system are involved in the regulation of the most important biological needs related to the production of energy and plastic materials, maintaining water and salt balance, optimizing body temperature, etc.
It has been experimentally proven that the emotional behavior of an animal when certain areas of the limbic system are stimulated is manifested mainly by reactions of aggression (anger), escape (fear), or mixed forms of behavior are observed, for example defensive reactions. Emotions, unlike motivations, arise in response to sudden changes in the environment and serve as a tactical task of behavior. Therefore, they are fleeting and optional. Long-term unmotivated changes in emotional behavior may be a consequence of organic pathology or the action of certain neuroleptics. In various parts of the limbic system, “pleasure” and “dissatisfaction” centers are open, united in the “reward” and “punishment” systems. When the “punishment” system is stimulated, animals behave in the same way as when they are afraid or in pain, and when the “reward” system is stimulated, they strive to restore the irritation and carry it out on their own if given the opportunity. Reward effects are not directly related to the regulation of biological motivations or inhibition of negative emotions and most likely represent a nonspecific mechanism of positive reinforcement, the activity of which is perceived as pleasure or reward. This general nonspecific positive reinforcement system is connected to various motivational mechanisms and ensures the direction of behavior based on the “better - worse” principle.
Visceral reactions when affecting the limbic system, as a rule, are a specific component of the corresponding type of behavior. Thus, when the hunger center is stimulated in the lateral parts of the hypothalamus, abundant salivation, increased motility and secretory activity of the gastrointestinal tract are observed, when sexual reactions are provoked - erection, ejaculation, etc., and in general, against the background of various types of motivational and emotional behavior, changes in breathing, heart rate and blood pressure, secretion of ACTH, catecholamines, other hormones and mediators,
To explain the principles of the integrative activity of the limbic system, an idea has been put forward about the cyclical nature of the movement of excitation processes through a closed network of structures, including the hippocampus, mammillary bodies, fornix of the brain, anterior nuclei of the thalamus, cingulate gyrus - the so-called Peipsi circle. Then the cycle is restored. This “transit” principle of organizing the functions of the limbic system is confirmed by a number of facts. For example, food reactions can be evoked by stimulating the lateral nucleus of the hypothalamus, the lateral preoptic area and some other structures. Nevertheless, despite the multiplicity of localization of functions, it was possible to establish key, or pacemaker, mechanisms turning them off leads to complete loss of the function.
Currently, the problem of consolidating structures into a specific functional system is being solved from the perspective of neurochemistry. It has been shown that many formations of the limbic system contain cells and terminals that secrete several types of biologically active substances. Among them, the most studied are monoaminergic neurons, which form three systems: dopaminergic, noradrenergic and serotonergic. The neurochemical relationship of individual structures of the limbic system largely determines the degree of their participation in a particular type of behavior. The activity of the reward system is ensured by noradrenergic and dopaminergic mechanisms; blockade of the corresponding cellular receptors by drugs from a number of phenothiazines or bugarophenones is accompanied by emotional and motor retardation, and with excessive doses - depression and motor disorders close to parkinsonism syndrome. In the regulation of sleep and wakefulness, next to monoaminergic mechanisms, GABAergic and neuromodulatory mechanisms are involved, specifically responding to gamma-aminobutyric acid (GABA) and delta-sleep peptide. The key role in pain mechanisms is played by the endogenous opiate system and morphine-like substances - endorphins and enkephalins.
Dysfunction of the limbic system manifests itself in various diseases (brain trauma, intoxication, neuroinfections, vascular pathology, endogenous psychoses, neuroses) and can be extremely diverse in clinical picture. Depending on the location and extent of the lesion, these disorders may be related to motivation, emotions, autonomic functions and can be combined in different proportions. Low thresholds of convulsive activity of the limbic system predetermine various forms of epilepsy: large and small forms of convulsive seizures, automatisms, changes in consciousness (depersonalization and derealization), autonomic paroxysms, which are preceded or accompanied by various forms of mood changes in combination with olfactory, gustatory and auditory hallucinations.

30. Centers of the autonomic nervous system

Mesencephalic - fibers are part of the oculomotor nerve (parasympathetic)

Bulbar – fibers of the facial, glossopharyngeal and vagus nerves (parasympathetic)

Thoracolumbar - nuclei of the god's horns from the 8th cervical to the 3rd lumbar segments (sympathetic)

Sacral – in the 2-4 segments of the sacral spinal cord (parasympathetic)

31. Divisions of the autonomic nervous system

Sympathetic department. The bodies of the first neurons of the sympathetic division of the ANS are located mainly in the posterior nuclei of the hypothalamus, the midbrain and medulla oblongata, and in the anterior horns of the spinal cord, starting from the 1st thoracic region and ending with the 3rd and 4th segment of its lumbar region.

The sympathetic nervous system is activated during stress reactions. It is characterized by a generalized effect, with sympathetic fibers innervating the vast majority of organs.