The solution of many problems on Earth and beyond requires the creation of artificial, completely or almost completely closed trophic systems, or even

small biospheres. In such systems, with the participation of organisms of various species organized in trophic chains, the circulation of substances must occur, as a rule, to maintain the life of large and small communities of people or animals. The formation of artificial closed trophic systems and artificial microbiospheres is of direct practical importance in the exploration of outer space, the world ocean, etc.

The problem of creating closed trophic systems, especially necessary for long-term space flights, has long been of concern to researchers and thinkers. On this occasion, many fundamental ideas have been developed. Important, though in some cases unrealistic, demands have been made on such human-designed systems. The point is that trophic systems must be highly productive, reliable, must have high rates and completeness of deactivation of toxic components. It is clear that it is extremely difficult to implement such a system. Indeed, doubts have been expressed about the possibility of constructing a safe and secure ecosystem (review: Odum, 1986). Nevertheless, one should try at least to determine the maximum capacity of the trophic system, figuratively speaking, to find out what a small island suitable for life of Robinson Crusoe should be like if it is covered with a transparent but impenetrable cap.

An example is the recently developed model of the artificial biosphere (biosphere II), which is a stable closed system and is necessary for life in various areas of outer space, including the Moon and Mars (review: Allen, Nelson, 1986). It should simulate the conditions of life on Earth, for which one should have a good knowledge of the natural technologies of our planet. In addition, such a biosphere must contain engineering, biological, energy, information open systems, living systems that accumulate free energy, etc. Like the biosphere, an artificial biosphere must include real water, air, rocks, earth, vegetation, and etc. It should model the jungle, desert, savanna, ocean, swamps, intensive agriculture, etc., reminiscent of the homeland of man (Fig. 1.8). In this case, the optimal ratio of the artificial ocean and the land surface should be

lyat not 70:30, as on Earth, but 15:85. However, the ocean in the artificial biosphere should be at least 10 times more efficient than the real one.

Recently, the same researchers (Allen, Nelson, 1986) presented a description of a model complex of connected artificial biospheres designed for the long life of 64-80 people on Mars. Each of these 4 biospheres, located radially in relation to the so-called technical center, serves as a living space for 6-10 people. The technical center houses a reserve ocean to mitigate the environment and maintain a closed system as a whole. There are also biological, transportation, mining, and task forces, as well as a hospital for visitors from Earth, the Moon, or other parts of Mars.

The specific problems of power in space during long flights are beyond the scope of this book. Nevertheless, it should be said that during long-term flights in a spacecraft, a microcosm is created, isolated from the environment familiar to humans for a long, and in some cases, for an indefinitely long time. The features of this microcosm, and in particular the features of its trophism, largely determine the existence of the system as a whole. In all likelihood, one of the most important steps in the biotic cycle is the degradation of waste products. The importance of degradation processes is often underestimated. In particular, when discussing the problem of food resources, a person is traditionally considered as the highest and final link in the trophic chain (reviews: Odum, 1986; Biotechnology..., 1989, etc.). Meanwhile, such a formulation of the problem has already led to the formation of serious environmental defects, since the ecological system can be stable only with a combination of effective input and output of substances. Examples of this are very numerous. One of them is a dramatic episode in Australia, where the destruction of the vegetation cover by the droppings of sheep and cows occurred due to the absence of dung beetles.

In all cases, the problems of degradation of vital products and elimination of the most weakened members of the population are extremely important. The recently developed point of view was unexpectedly confirmed. When modeling a long interplanetary flight of a crew of 10, California researchers found that the gyre

substances is significantly improved if two goats are introduced into a system that includes a person, plants, algae, bacteria, etc. Improvement in this system of circulation of substances is achieved to some extent due to the appearance of milk in the diet and, consequently, additional high-grade food components (including proteins), but to a much greater extent due to the acceleration of the processes of degradation of plant residues in the gastrointestinal tract of goats. Understanding the trophic system as dynamic cycles, rather than chains or pyramids with initial and final links, apparently, will contribute not only to a more correct reflection of reality, but also to more reasonable actions, at least reducing the harmful impact on the environment.

In all likelihood, when creating artificial biospheres, many interesting phenomena can also be discovered in the future, since we still do not know all the ways to form a minimal, but already satisfactory trophic cycle. There are a number of indications that in a small group of people, the bacterial population of the gastrointestinal tract may be unstable. Over time, she will become poorer, especially if any therapeutic interventions using antibiotics are used. Therefore, to restore the intestinal microflora of space crews, it would be highly advisable to have some bank of bacteria. In addition, mutations of plants and bacteria entering the trophic cycle cannot be ruled out during long-term space flights. This can lead to serious violations of the properties of the respective organisms and their biological role. These circumstances must be taken into account, since, in all likelihood, the trophic system (artificial microtrophosphere) of a spacecraft must not only be sufficiently modern, but also flexible, which can ensure its certain changes. In this regard, the optimistic prediction that already in the 21st century attracts attention. millions of people will be able to live in space settlements (O "Neill, 1977) (see also ch. 5).

In the implementation of the adaptive-trophic functions of the sympathetic nervous system, catecholamines are of particular importance. It is they who can quickly and intensively influence metabolic processes, changing the level of glucose in the blood, stimulating the breakdown of glycogen and fats, increase the efficiency of the heart, ensure the redistribution of blood in different areas, increase the excitation of the nervous system, and contribute to the emergence of emotional reactions.

It is known that neurogenic atrophy of the muscle occurs shortly after denervation.

It may seem that the nervous system exerts its influence on the metabolism of an organ purely through the transmission of excitation.

However, in neurogenic atrophy it is not enough to compensate for the inactivity of the muscle by electrical stimulation, which cannot stop the process of atrophy, although it does cause muscle contraction.

Consequently, it is impossible to reduce the trophic process only to activity and inactivity. Very interesting in denervation changes are axoplasmic shifts.

It turns out that the larger the peripheral end of the cut nerve, the later degenerative changes develop in the denervation muscle. Apparently, in this case, the main role is played by the amount of axoplasm remaining in contact with the muscle after nervectomy.

During the regeneration of a nerve fiber, the difference between trophic function and readiness for excitation is clearly visible: even a few days before the possibility of impulse transmission, an increase in muscle tone and a number of other properties is observed. Consequently, the mediator released during impulse transmission can hardly be considered a trophic substance, although the role of a spontaneously released mediator or another yet unexplored substance in this process cannot be ruled out.

With denervation, the metabolic differences between the slow (tonic) and fast (phasic) types of muscle fibers or groups largely disappear. When reinnervated, they are restored again.

However, if the reinnervating fibers are cross-replaced, then metabolic restructuring and a change in the initial specialization of the muscle occur - the tonic becomes phasic, and vice versa. These rearrangements are independent of the frequency of efferent impulses; the main role is played by specific trophic factors.

It has been repeatedly postulated and is now widely recognized that the role of neurotransmitters, including ACh, is not limited to purely mediator influence, but also consists in changing the vital processes of the innervated organs. Although chemoreactive (in this case, cholinoreactive) biochemical systems are considered to be channels for the transmission of regulatory signals, the specific mechanisms for the existence of influences remain poorly understood.

Now the position has been formulated that the mediator of the nerve impulse, poisoning the effector organ, is included in the mechanism of energy supply for the work of this organ, and in the process of plastic compensation of material costs in it.

The very fact of the presence of many pharmacological substances that can change cholinergic transmission, as well as the polyvalence of the synaptic apparatus, lead to the conclusion that at present the possibilities for directed action on the body through cholinergic structures are used only to a small extent [Denisenko P. P., 1980] .

In this regard, it is of interest to observe numerous changes in carbohydrate, protein, water, and electrolyte metabolism during activation of choline-reactive systems [Speransky AA, 1937]; there are also data indicating a positive effect of therapy with ACh injections for skin diseases, in particular eczema, malignant brain tumors, and cerebral atherosclerosis.

Interesting and important ideas about the depletion of cholinergic processes in chronic alcoholism, data on the antiviral effect of the acetylcholine - erythrocyte cholinesterase system, and the participation of the cholinergic system in the formation of germ cells.

Thus, although there has recently been great interest in this problem, we do not have accurate data on the nature and methods of the trophic influence of the sympathetic nervous system.

"Physiology of the autonomic nervous system",
HELL. Nozdrachev

Popular section articles

Adaptive-trophic function of the sympathetic nervous system

The classical scheme proposed by J. Langley for the distribution of sympathetic innervation provided for its effect only on smooth muscles and glands. However, sympathetic impulses can also affect skeletal muscles. If, by stimulating the motor nerve, the frog muscle is brought to fatigue (Fig. 5.16), and then at the same time the sympathetic trunk is irritated, then the performance of the tired muscle increases - phenomenon of Orbeli-Ginetsinsky. By itself, stimulation of sympathetic fibers does not cause muscle contraction, but changes the state of muscle tissue, increases its susceptibility to impulses transmitted through somatic fibers. Such an increase in muscle performance is the result of the stimulating effect of metabolic processes in the muscle: oxygen consumption increases, the content of ATP, creatine phosphate, and glycogen increases. It is believed that the place of application of this influence is the neuromuscular synapse.

It has also been found that stimulation of sympathetic fibers can significantly alter the excitability of receptors and even the functional properties of the CNS. For example, when the sympathetic fibers of the tongue are stimulated,

taste sensitivity, with irritation of the sympathetic nerves, an increase in the reflex excitability of the spinal cord is observed, the functions of the medulla oblongata and midbrain change. Characteristically, with varying degrees of excitation, the sympathetic nervous system exerts the same type of influence on organs and tissues. Removal of the cranial cervical sympathetic nodes in animals leads to a decrease in the magnitude of conditioned reflexes, their chaotic course, and the predominance of inhibitory processes in the cerebral cortex.

These facts were generalized by L. A. Orbeli in the theory adaptive-trophic function sympathetic nervous system, according to which sympathetic influences are not accompanied by a directly visible action, but significantly change the functional reactivity or adaptive properties of tissues.

The sympathetic nervous system activates the activity of the nervous system as a whole, activates the protective functions of the body, such as immune processes, barrier mechanisms, blood coagulation, thermoregulation processes. Her excitation is an indispensable condition for any stressful conditions, it serves as the first link in launching a complex chain of hormonal reactions.

Particularly vividly, the participation of the sympathetic nervous system is found in the formation of human emotional reactions, regardless of the cause that caused them.

So, joy is accompanied by tachycardia, vasodilation of the skin, fear - by slowing the heart rate, narrowing of the skin vessels, sweating, changes in intestinal motility, anger - by dilated pupils.

Consequently, in the process of evolutionary development, the sympathetic nervous system has become a special tool for mobilizing all the resources (intellectual, energy, etc.) of the organism as a whole in cases where the very existence of the individual is threatened.

This position of the sympathetic nervous system in the body is based on an extensive system of its connections, which allows, through the multiplication of impulses in numerous para- and prevertebral ganglia, to instantly cause generalized reactions in almost all organs and systems. A significant addition is the release into the blood from the adrenal glands and chromaffin tissue of the "fluid of the sympathetic nervous system" - adrenaline And norepinephrine.

In the manifestation of its excitatory action, the sympathetic nervous system leads to a change in the homeostatic constants of the body, which is expressed in an increase in blood pressure, the release of blood from blood depots, the entry of enzymes and glucose into the blood, an increase in tissue metabolism, a decrease in urination, inhibition of the function of the digestive tract, etc. Maintaining the constancy of these indicators falls entirely on the parasympathetic and metasympathetic parts.

Consequently, in the sphere of control of the sympathetic nervous system, there are mainly processes associated with the expenditure of energy in the body, parasympathetic and metasympathetic - with its cumulation.

Significance of the sympathetic nervous system convincingly demonstrated in experiments with its surgical, chemical or immune removal. Complete extirpation of sympathetic trunks in cats, i.e., total sympathectomy, is not accompanied by significant disorders of visceral functions. Blood pressure is almost within normal limits, except for a slight insufficiency that occurs due to the shutdown of the reflexogenic zones; in close to normal limits, the function of the alimentary canal unfolds, reproductive functions continue to remain possible: fertilization, pregnancy, childbirth. Nevertheless, sympathectomized animals are unable to exercise physical effort, with great difficulty recover from bleeding, appetite disorders, shock, hypoglycemia, and also poorly tolerate cold and overheating. In sympathectomized animals, there are no manifestations of characteristic protective reactions and indicators of aggressiveness: tachycardia, dilated pupils, increased blood flow to the somatic muscles.

Has a number of advantages immunosympathectomy. While not having a significant effect on the physical development and general behavioral reactions of animals, this method, at the same time, makes it possible to obtain a unique model for studying the function of the autonomic nervous system in chronic conditions. A certain advantage is that the introduction of the nerve growth factor under conditions of atrophy of the sympathetic nervous system makes it possible to obtain hypertrophy of the sympathetic nervous system in the same animals, thus creating a double control that is rare under experimental conditions.

After transection of the sympathetic fibers and their degeneration, the innervated organs may atrophy to some extent. However, a few weeks after denervation, their increased sensitivity to mediators and mediator-type substances occurs. This effect is clearly seen in the pupil of the animal after removal of the cranial cervical sympathetic ganglion. Usually, after the operation, pupil constriction occurs as a result of the predominance of parasympathetic tone. After a certain time, its value approaches the initial value, and in conditions of emotional stress it even increases sharply.

This fact is explained by the occurrence sensitization (hypersensitivity) denervated muscle to adrenaline and norepinephrine released from the adrenal glands into the bloodstream during emotions. This phenomenon is probably based on a change in the ability of denervated cell membranes to bind calcium and change conductivity.

Development of the autonomic nervous system.

The smooth muscles of invertebrates are regulated by the ganglionic-reticular nervous system, which, in addition to this special function, also regulates metabolism. The adaptation of the metabolic rate to the changing function of organs is called adaptation (adaptare - adjust), and the corresponding function of the nervous system - adaptive-trophic(L. A. Orbeli). Adaptive-trophic function is the most general and very ancient function of the nervous system that existed in the primitive ancestors of the vertebrates. In the further course of evolution, the movement apparatus (development of the hard skeleton and skeletal muscles) and the sense organs, i.e., the organs of animal life, progressed most of all. Therefore, that part of the nervous system that was associated with them, i.e., the animal part of the nervous system, underwent the most dramatic changes and acquired new features, in particular: isolation of fibers with the help of myelin sheaths, greater excitation speed (100-120 m/s). On the contrary, the organs of plant life have undergone a slower and less progressive evolution, so that the part of the nervous system associated with them has retained the most general function -adaptive-trophic. This part of the nervous system is autonomic nervous system A.

Along with some specialization, she retained a series of ancient primitive traits: the absence of myelin sheaths in most nerve fibers (non-myelinated fibers), a lower speed of excitation conduction (0.3 - 10 m / s), as well as a lower concentration and centralization of effector neurons that remained scattered on the periphery, as part of ganglia, nerves and plexuses. At the same time, the effector neuron turned out to be located near the working organ or even in its thickness.

Such peripheral location of the effector neuron determined the main morphological feature of the autonomic nervous system - the two-neuronality of the efferent peripheral pathway, consisting of intercalary and effector neurons.

With the advent of the trunk brain (in non-cranial ones), the adaptation impulses arising in it go along the intercalary neurons, which have a higher excitation rate; adaptation is carried out by involuntary muscles and glands, to which effector neurons, which are characterized by slow conduction, are suitable. This contradiction is resolved in the process of evolution due to the development of special nerve nodes in which contacts are established between intercalary neurons and effector neurons, and one intercalary neuron enters into connection with many effector neurons (approximately 1:32). This achieves the switching of impulses from myelinated fibers, which have a high speed of conduction of irritations, to non-myelinated ones, which have a low speed.

autonomic part of the nervous system

As a result, the entire efferent peripheral pathway of the autonomic nervous system is divided into two parts - pre-nodal and post-nodal, and the nodes themselves become transformers of excitation rates from fast to slow.

In lower fish, when the brain is formed, centers develop in it that unite the activity of the organs that produce the internal environment of the body.

Since, in addition to smooth muscles, skeletal (striated) muscles also take part in this activity, there is a need to coordinate the work of smooth and striated muscles. For example, the gill covers are set in motion by skeletal muscles, and in humans, both the smooth muscles of the bronchi and the skeletal muscles of the chest participate in the act of breathing. Such coordination is carried out by a special reflex apparatus developing in the hindbrain in the form of the vagus nerve system (the bulbar section of the parasympathetic part of the autonomic nervous system).

IN central nervous system other formations arise, which, like the vagus nerve, perform the function of coordinating the joint activity of the skeletal muscles, which have a fast excitation speed, and smooth muscles and glands, which have a slow speed. This includes that part of the oculomotor nerve that, with the help of striated and non-striated muscles of the eye, performs the standard setting of pupil width, accommodation and convergence, according to the strength of illumination and the distance to the object under consideration, according to the same principles as the photographer does (mesencephalic division of the parasympathetic part of the autonomic nervous system) . This includes that part of the sacral nerves (I-IV), which carry out the standard function of the pelvic organs (bladder and rectum) - emptying, in which each involuntary muscles of these organs participate, as well as the voluntary muscles of the pelvis and abdominal press - the sacral section of the parasympathetic parts of the autonomic nervous system.

IN midbrain and diencephalon a central adaptive apparatus developed in the form of gray matter around the aqueduct and the gray mound (hypothalamus).

Finally, centers arose in the cerebral cortex that unite the higher animal and vegetative functions.

Development of the autonomic nervous system V ontogenesis (embryogenesis) goes differently than phylogeny.

autonomic nervous system arises from a common source with the animal part - the neuroectoderm, which proves the unity of the entire nervous system.

Sympathoblasts are evicted from the common rudiment of the nervous system, which accumulate in certain places, forming first nodes of the sympathetic trunk, and then intermediate nodes, as well as nerve plexuses. The processes of the cells of the sympathetic trunk, uniting into bundles, form rami communicantes grisei.

Similarly, it develops part of the autonomic nervous system in the head area. The rudiments of parasympathetic nodes are evicted from the medulla oblongata or ganglionic plate and migrate long distance along the branches of the trigeminal, vagus and other nerves, settling along their course or forming intramural ganglia.

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Adaptive-trophic function of the ANS

The most important functional task of the ANS is the regulation of the vital processes of the organs of the body, the coordination and adaptation of their functioning to the general needs and requirements of the body in environmental conditions.

Adaptive-trophic functions of the sympathetic nervous system

The expression of this function is the regulation of metabolism, excitability and other aspects of the activity of organs and the central nervous system itself. In this case, the work of tissues, organs and systems is controlled by other types of influences - starting and correcting.

starting influences, are used if the functioning of the executive body is not constant, but occurs only with the arrival of impulses to it along the fibers of the autonomic nervous system. If the organ has automatism and its function is carried out continuously, then the autonomic nervous system, through its influences, can strengthen or weaken its activity, depending on the need - it is a corrective influence. Starting influences can be supplemented by corrective ones.

All structures and systems of the body are innervated by fibers of the ANS. Many of them have double, and the genital visceral organs even triple (sympathetic, parasympathetic and metasympathetic) innervation. The study of the role of each of them is usually carried out using electrical stimulation, surgical or pharmacological exclusion, chemical stimulation, etc.

Thus, a strong irritation of sympathetic fibers causes an increase in heart rate, an increase in the force of contraction of the heart, relaxation of the muscles of the bronchi, a decrease in motor activity of the stomach and intestines, relaxation of the gallbladder, contraction of sphincters and other effects. Irritation of the vagus nerve is characterized by the opposite effect. These observations formed the basis for the idea of ​​the existence of an "antagonistic" relationship between the sympathetic and parasympathetic parts of the autonomic nervous system.

The idea of ​​“balancing” sympathetic influences by parasympathetic influences is contradicted by a number of factors: for example, salivation is stimulated by rarefaction of fibers of a sympathetic and parasympathetic nature, so that a coordinated reaction is manifested here, which is necessary for digestion; a number of organs and tissues are supplied only with either sympathetic or parasympathetic fibers. These organs include many blood vessels, the spleen, the adrenal medulla, some exocrine glands, the sense organs, and the central nervous system.

Along with the function of transmitting impulses that cause muscle contractions, nerve fibers and their endings also have a trophic effect on the muscle, that is, they participate in the regulation of its metabolism. It is well known that denervation of the muscle, which develops with degeneration of the motor nerve, leads to atrophy of the muscle fibers, which manifests itself in the fact that the amount of sarcoplasm decreases first, and then the diameter of the muscle fibers; later, the destruction of myofibrils occurs. Special studies have shown that this atrophy is not the result of only the inactivity of a muscle that has lost motor activity. Muscle inactivity can also be caused by tendotomy, i.e., transection of the tendon. However, if we compare the muscle after tendotomy and after denervation, we can see that in the latter case qualitatively different changes in its properties develop in the muscle, which are not detected during tendotomy. This is most clearly manifested in changes in the sensitivity of the muscle to acetylcholine. In normal and tendotomized muscle, only the postsynaptic membrane is sensitive to acetylcholine, in which chemo-excitable ion channels equipped with cholinergic receptors are concentrated. Denervation leads to the fact that the same channels appear in extrasynaptic areas of the muscle fiber. As a result, the sensitivity of the denervated muscle to acetylcholine increases dramatically. The indicated hypersensitivity to acetylcholine is not formed if, with the help of certain chemical reagents, protein synthesis in muscle fibers is inhibited. Reinnervation of the muscle due to the regeneration of nerve fibers leads to the disappearance of cholinergic channels in the region of the extra-postsynaptic membrane. These data indicate that nerve fibers regulate the synthesis of proteins that form chemo-excitable cholinergic receptor channels.

In the denervated muscle, the activity of a number of enzymes also drops sharply, in particular ATPase, which plays an important role in the process of releasing the energy contained in the phosphate bonds of ATP. At the same time, during denervation, the processes of protein breakdown are significantly enhanced. This leads to a gradual decrease in the mass of muscle tissue characteristic of atrophy.

All degenerative changes in a denervated muscle begin the sooner the motor nerve is cut at a shorter distance from the muscle. This suggests that certain substances ("trophic agents") produced in nerve cells move along the nerve fibers from the proximal to the distal regions and are released by the nerve endings. The larger the segment of the nerve remains connected to the muscle, the longer it receives substances important for its metabolism. The movement of these substances is carried out due to the movement of the neuroplasm, the speed of which is 1-2 mm / h.

An important role in the implementation of the trophic influences of the nerve is played by acetylcholine, which is secreted by the nerve endings both at rest and especially during excitation. There are reasons to believe that acetylcholine and its cleavage products by cholinesterase - choline and acetic acid - are involved in muscle metabolism, exerting an activating effect on certain enzyme systems. Thus, when acetylcholine is injected into the denervated rabbit muscle, the breakdown of adenosine triphosphate, creatine phosphate, and glycogen sharply increases during tetanus caused by direct electrical stimulation of this muscle.

Substances that have a specific effect on the synthesis of muscle fiber proteins are released from the nerve endings. This is evidenced by experiments with cross-linking of motor nerves innervating fast and slow skeletal muscles. With such stitching, the peripheral segments of the nerves and their endings in the muscle degenerate, and along their paths new fibers grow into the muscle from the central segments of the nerves. Shortly after these fibers form motor endings, a distinct restructuring of the functional properties of the muscles occurs. Muscles that were previously fast now become slow, and those that were slow become fast. With such a rearrangement, the activity of the ATPase of their contractile protein myosin changes: in the former fast muscles, it sharply decreases, and in slow ones it increases. Accordingly, in the first, the rate of ATP decay increases, and in the second, it decreases. The properties of the ion channels of the cell membrane also change.

The fibers of the sympathetic nervous system also have a trophic effect on the skeletal muscle, the endings of which release norepinephrine.

FEATURES OF NEURO-MUSCULAR EXCITATION TRANSMISSION IN SMOOTH MUSCLES

The mechanism of transmission of excitation from the motor nerve fiber to smooth muscle fibers is in principle similar to the mechanism of neuromuscular transmission in skeletal muscles. The differences concern only the chemical nature of the mediator and the features of the summation of postsynaptic potentials.

In all skeletal muscles, the excitatory mediator is acetylcholine. In smooth muscles, the transmission of excitation in the nerve endings is carried out with the help of various mediators. So, for the smooth muscles of the gastrointestinal tract, the excitatory mediator is acetylcholine, and for the smooth muscles of the blood vessels, noradrenaline.

The portion of the mediator released by the nerve ending in response to a single nerve impulse is in most cases insufficient for critical depolarization of the smooth muscle cell membrane. Critical depolarization occurs only when several consecutive impulses arrive at the nerve ending. Then single excitatory postsynaptic potentials are summed up (Fig. 57) and at the moment when their sum reaches the threshold value, an action potential arises.

In skeletal muscle fiber, the repetition rate of action potentials corresponds to the frequency of rhythmic stimulation of the motor nerve. In contrast, in smooth muscles, this correspondence is already violated at frequencies of 7–15 pulses/s. If the stimulation frequency exceeds 50 pulses/s, pessimal inhibition occurs.

Inhibitory synapses in smooth muscles. Irritation of some nerve fibers innervating smooth muscles can cause their inhibition, rather than excitation. Nerve impulses arriving at certain nerve endings release an inhibitory neurotransmitter.

Acting on the postsynaptic membrane, the inhibitory neurotransmitter interacts with chemo-excitable channels that are predominantly permeable to K + ions. The outflow of potassium through these channels causes hyperpolarization of the postsynaptic membrane, manifesting itself in the form of an "inhibitory postsynaptic potential", similar to that observed in the inhibitory synapses of neurons in the CNS.

With rhythmic stimulation of inhibitory nerve fibers, inhibitory postsynaptic potentials are summed up with each other, and this summation is most effective in the frequency range of 5-25 pulses / s (Fig. 58).

If the stimulation of the inhibitory nerve somewhat precedes the stimulation of the activating nerve, then the excitatory postsynaptic potential caused by the

the latter is weakened and may not be sufficient for critical depolarization of the membrane. Irritation of the inhibitory nerve against the background of spontaneous muscle activity inhibits the generation of action potentials and, consequently, leads to the cessation of its contractions.

The role of the inhibitory mediator in smooth muscles excited by acetylcholine (for example, intestines, bronchi) is performed by norepinephrine. On the contrary, in the muscle cells of the bladder sphincter and some other smooth muscles, for which the excitatory mediator is norepinephrine, the inhibitory mediator is acetylcholine. The latter has an inhibitory effect on the cells of the pacemaker of the heart.

In skeletal muscles, neuromuscular transmission, carried out with the help of acetylcholine, is blocked by curare drugs that have a high affinity for cholinergic receptors. In smooth muscles, the cholinergic receptor has a different chemical structure than in skeletal muscles, so it is blocked not by curare preparations, but by atropine.

In those smooth muscles in which norepinephrine serves as a mediator, chemo-excitable channels are equipped with adrenoreceptors. There are two main types of adrenergic receptors: a-adrenergic receptors. and (b -adrenergic receptors, which are blocked by various chemical compounds - adrenoblockers.

CONCLUSION

Excitable tissues, in addition to nervous and muscular, also include glandular tissue, but the mechanisms of excitation of the cells of the glands of external secretion are somewhat different from those of the nervous and muscular ones.

As shown by microelectrode studies, the membrane of secretory cells at rest is polarized, and its outer surface is positively charged, and the inner one is negatively charged. The potential difference is 30-40 mV. When the secretory nerves innervating the gland are stimulated, it is not depolarization that occurs, but hyperpolarization of the membrane and the potential difference reaches 50-60 mV. It is believed that this is due to the injection of C1 ~ and other negative ions into the cell. Under the influence of electrostatic forces, positive ions then begin to enter the cell, which leads to an increase in osmotic pressure, water entering the cell, an increase in hydrostatic pressure, and swelling of the cell. As a result, secretion is released from the cell into the lumen of the gland.

The release of a secret can be stimulated not only by nervous, but also by chemical (humoral) influences. Here, as elsewhere in the body, the regulation of functions is carried out in two ways - nervous and humoral.

A nerve impulse is the fastest way to transmit information in the body. Therefore, in the course of evolution, in those cases when a high rate of reactions was necessary, when the very existence of an organism depended on the speed of response reactions, this method of signal transmission became the main one.

In the region of nerve endings, in the synaptic clefts, a nerve impulse usually causes the release of a neurotransmitter and thus the interaction between cells remains essentially chemical. In this case, instead of the slow spread of a chemical substance with a fluid flow (with moving blood, lymph, tissue fluid, etc.), a signal to release a biologically active substance (mediator) in the region of nerve endings (on the spot) propagates at a high speed in the nervous system. All this dramatically increased the speed of the body's responses, while retaining essentially the principle of chemical interaction between cells. At the same time, in a number of cases, when an even faster and, moreover, always unambiguous reaction is necessary for cellular interaction, intercellular signal transmission is ensured by direct electrical interaction of cells. This type of connection is observed, for example, in the interaction of myocardial cells, as well as some electrical synapses of the central nervous system, called epapses.

Intercellular connections are reduced not only to electrical interactions or the influence of mediators. The chemical relationship between cells is more complex. Cells of organs and tissues produce a number of specific chemicals that act on other cells and cause not only the switching on and off (or strengthening or weakening) of the function, but also a change in the intensity of metabolism and the processes of synthesis of specific proteins by the cell. The mechanisms of all these reflex influences and intercellular interactions are discussed in detail in the second section of the textbook.

trophism of the neuron. Inside the neuron is a jelly-like substance - neuroplasm. The bodies of nerve cells perform a trophic function in relation to the processes, that is, they regulate their metabolism. Trophic influence on the effector cells of the body with the help of chemicals of the nerve cells themselves. The nutritional function of glia was suggested by Golgi, based on the structural relationships between nerve and glial cells and the relationship of the latter with brain capillaries. The processes of protoplasmic astrocytes (vascular pedicles) are in close contact with the basement membrane of the capillaries, covering up to 80% of their surface. The trophic function of glial cells is carried out either by a single astrocyte (vascular stalk on the capillary and other processes on the neuron), or through the astrocyte-oligodendrocyte-neuron system. It has also been shown that glial cells take part in the formation of the blood-brain barrier, which, as is known, ensures the selective transfer of substances from the blood to the nervous tissue. However, it should be noted that the essential role of glial cells in the functioning of the blood-brain barrier is not recognized by all researchers. 27. Concepts of reactivity and activity in considering the functioning of a neuron.

Reactivity paradigm: A neuron, like an individual, responds to a stimulus. From the standpoint of the traditional paradigm of reactivity, an individual's behavior is a response to a stimulus. The reaction is based on the conduction of excitation along the reflex arc: from receptors through the central structures to the executive organs. In this case, the neuron turns out to be an element included in the reflex arc, and its function is to ensure the conduction of excitation. Then it is quite logical to consider the determination of the activity of this element as follows: the response to a stimulus that has acted on a certain part of the surface of a nerve cell can spread further along the cell and act as a stimulus on other nerve cells. Within the framework of the reactivity paradigm, consideration of the neuron is quite methodologically consistent: the neuron, like the body, responds to stimuli. The impulse that the neuron receives from other cells acts as a stimulus, and the impulse of this neuron following the synaptic influx acts as a reaction. Activity paradigm: a neuron, like an individual, achieves a “result” by obtaining the necessary metabolites from its microenvironment.

28. Standard ranges of the background electroencephalogram.

EEG is a method of recording the electrical activity (biopotentials) of the brain through intact integuments of the head (intact method), which makes it possible to judge its physiological maturity, functional state, the presence of focal lesions, cerebral disorders and their nature.

(Recording of biopotentials directly from the naked brain is called electrocorticography, ECoG, and is usually performed during neurosurgical operations).

The first scientist to demonstrate the possibility of such recording of the electrical activity of the human brain was Hans Berger (1929-1938).

The main concepts on which the EEG characterization is based are:

Average oscillation frequency

Maximum amplitude

The total background EEG of the cortex and subcortical formations of the brain of animals, varying depending on the level of phylogenetic development and reflecting the cytoarchitectonic and functional features of brain structures, also consists of slow oscillations of different frequencies.

One of the main characteristics of the EEG is the frequency. However, due to the limited perceptual capabilities of a person in the visual analysis of the EEG used in clinical electroencephalography, a number of frequencies cannot be accurately characterized by the operator, since the human eye highlights only some of the main frequency bands that are clearly present in the EEG. In accordance with the capabilities of manual analysis, a classification of EEG frequencies was introduced into some main ranges, which were assigned the names of the letters of the Greek alphabet:

alpha - 8-13 Hz,

beta - 14-40 Hz,

theta - 4-6 Hz,

delta - 0.5-3 Hz,

gamma - above 40 Hz, etc.).

In a healthy adult with closed eyes, the main alpha rhythm. This is the so-called synchronized EEG.

When the eyes are open or when signals from other senses are received, a blockade occurs alpha rhythm and appear beta waves. This is called EEG desynchronization.

Theta waves and delta waves normally, they are not detected in awake adults, they appear only during sleep.

On the contrary, the EEG of adolescents and children is characterized by slower and more irregular delta waves even in the waking state.

Depending on the frequency range, but also on the amplitude, waveform, topography and type of reaction, EEG rhythms are distinguished, which are also denoted by Greek letters. For example, alpha rhythm, beta rhythm, gamma rhythm, delta rhythm, theta rhythm, kappa rhythm, mu rhythm, sigma rhythm etc. It is believed that each such “rhythm” corresponds to a certain state of the brain and is associated with certain cerebral mechanisms.

The study of trophic relationships between the autonomic nervous system and the tissue innervated by it is one of the most complex issues. Of the currently available evidence for trophic function, most is purely circumstantial.

It is still not clear whether all neurons of the autonomic nervous system have a trophic function, or whether this is the prerogative of only the sympathetic part, and whether they are solely responsible for mechanisms related to triggering activity, i.e., various mediators, or other, still unknown biologically active substances?

It is well known that in the process of prolonged work the muscle gets tired, as a result of which its work decreases and may finally stop completely.

It is also known that after more or less rest, the working capacity of tired muscles is restored. What “relieves” muscle fatigue, and does the sympathetic nervous system have anything to do with this?

L. A. Orbeli (1927) found that if the motor nerves are irritated and the muscles of the frog’s limbs are brought to considerable fatigue, then it quickly disappears and the limb again acquires the ability to work for a relatively long time, if stimulation of the sympathetic trunk of this frog is added to the irritation of the motor nerve. same limbs.

Thus, the inclusion in the work of the sympathetic nerve, which changes the functional state of the tired muscle, eliminates the fatigue that has arisen and makes the muscle workable again. In the adaptive-trophic action of the sympathetic nervous system, L. A. Orbeli singled out two interrelated aspects. The first is adaptive. It defines the functional parameters of the working body. The second ensures the maintenance of these parameters through physicochemical changes in the level of tissue metabolism.

The state of sympathetic innervation has a significant impact on the content in the muscle of a number of chemicals that play an important role in its activity: lactic, acids, glycogen, creatinine.

The sympathetic fiber also affects the ability of muscle tissue to conduct electricity, significantly affects the excitability of the motor nerve, etc.

Based on all these data, it was concluded that the sympathetic nervous system, without causing any structural changes in the muscle, at the same time adapts the muscle, changing its physical and chemical properties, and makes it more or less sensitive to those impulses that come to it. along motor fibers. This makes her work more tailored to the needs of the moment.

It was suggested that the increased work of a tired skeletal muscle under the influence of irritation of the sympathetic nerve approaching it occurs due to contractions of blood vessels and, accordingly, the entry of new portions of blood into the capillaries, but this assumption was not confirmed in subsequent studies.

It turned out that this phenomenon can be reproduced not only on a bloodless muscle, but also on a muscle whose vessels are filled with vaseline oil.

"Physiology of the autonomic nervous system",
HELL. Nozdrachev