Trophic function of a neuron. Trophic function of motor nerve fibers and their endings Trophic function of nerve cells
One of the divisions of the central nervous system, called the autonomic one, consists of several parts. One of them is the sympathetic nervous system, and its morphological characteristics make it possible to roughly divide it into several sections. Another department of the autonomic nervous system is the parasympathetic nervous system. In this article we will look at what trophic function is.
About the nervous system
In the life of absolutely any living organism, a number of important functions are performed by the nervous system. Therefore, its significance is very great. The nervous system itself is quite complex and includes different sections and has several subtypes. Each of them performs a number of specific functions specific to each department. An interesting fact is that the very concept of the sympathetic nervous system was first used in 1732. At the very beginning, this term was used to designate the entire autonomic nervous system as a whole. However, as medicine developed and scientific knowledge accumulated, it became clear that the sympathetic nervous system conceals a wider range of functions. That is why this concept began to be used in relation to only one of the departments of the autonomic nervous system. The trophic function of the nervous system will be presented below.
Sympathetic NS
If we dwell on specific values, it will become clear that the sympathetic nervous system is characterized by quite interesting functions - it is responsible for the process of consuming the body’s resources, and also mobilizes its internal forces when emergency situations arise. If the need arises, the sympathetic system significantly increases the expenditure of energy resources in order for the body to continue normal functioning and perform certain tasks. In the case when a conversation arises that the human body has hidden capabilities, this is precisely the process that is implied. A person’s condition directly depends on how well the sympathetic system copes with its tasks.
Parasympathetic NS
However, such conditions cause great stress for the body, and in this state it cannot function normally for a long time. Here the parasympathetic system is of great importance, which comes into play and allows you to restore and accumulate the body’s resources, which, in turn, allows you not to limit its capabilities. allow the human body to conduct normal life activities in various conditions. They are closely interconnected and complement each other. But what does the trophic function of the NS mean? More on this later.
Anatomical device
The sympathetic nervous system has a rather complex and branched structure. Its central part is located in the spinal cord, and the peripheral part connects various nerve nodes and nerve endings of the body. All nerve endings of the sympathetic system are connected into plexuses and concentrated in the innervated tissues.
The peripheral part of the system is formed by a variety of sensitive efferent neurons that have specific processes. These processes are distant from the spinal cord and are located mainly in the prevertebral and paravertebral nodes.
Functions of the sympathetic system
As noted, activation of the sympathetic system occurs when the body finds itself in a stressful situation. Some sources call it the reactive sympathetic nervous system. This name is due to the fact that it presupposes the occurrence of a certain reaction of the body to external influences. This is its trophic function.
When a stressful situation occurs, the adrenal glands immediately begin to secrete adrenaline. It is the main substance that allows a person to react better and faster in response to stress. A similar situation can occur during physical activity. The adrenaline rush allows you to cope better with it. Adrenaline enhances the action of the sympathetic system, and it, in turn, provides resources for increased energy consumption. The secretion of adrenaline itself is not an energy resource, but only helps stimulate human organs and senses.
Main function
The main function of the sympathetic nervous system is the adaptation-trophic function.
Let's look at it in more detail.
Biological scientists have been convinced for quite a long time that exclusively the somatic nervous system provides regulation of the activity of skeletal muscles. This belief was only shaken at the beginning of the 20th century.
It is a well-known fact: with prolonged work, contractions become fatigued, gradually fade away, and they may stop altogether. Muscle performance tends to recover after a short rest. For a long time, the reasons for this phenomenon were unknown.
In 1927, Orbeli L.A. experimentally established the following: if you bring the frog’s leg to a complete cessation of movement, that is, to fatigue, through prolonged exposure to the motor nerve, and then, without stopping motor stimulation, begin to simultaneously irritate the nerve of the sympathetic system, the function of the limb will be quickly restored. It turns out that connecting the influence on the sympathetic system changes the functionality of the muscle that is tired. Fatigue is eliminated and performance is restored. This is the trophic function of nerve cells.
Effect on muscle fibers
Scientists have found that the nerves of the sympathetic system have a strong influence on muscle fibers, in particular on their ability to conduct electrical currents, as well as on the level of excitability of the motor nerve. When exposed to sympathetic innervation, a change occurs in the composition and quantity of chemical compounds contained in the muscle and playing an important role in the implementation of its activity. Such compounds include lactic acid, glycogen, creatine, and phosphates. In accordance with these data, it became possible to conclude that the sympathetic system stimulates the occurrence of certain physicochemical changes in skeletal muscles and has a regulatory effect on the sensitivity of the muscle to emerging motor impulses that come through the fibers of the somatic system. It is the sympathetic system that adapts muscle tissue to perform loads that may arise under various circumstances. It was believed that the work of a tired muscle is enhanced by the influence of the sympathetic nerve due to increased blood flow. However, the experiments conducted did not confirm this opinion. This is how trophic work
Through special studies, it was possible to establish that direct sympathetic excitability is absent in vertebrate organisms. Thus, the influence of a sympathetic nature on skeletal muscles occurs only through the diffusion of a mediator or other substances that are released by the vasomotor terminals of the sympathetic system. This conclusion can be easily confirmed with a simple experiment. If a muscle is placed in a solution or its vessels are perfused, and then the effect on the sympathetic nerve is started, then substances of unknown nature are observed in the solution or in the perfusate. If these substances are introduced into other muscles, they cause an effect of a sympathetic nature.
This mechanism is also confirmed by the large latent period and its significant duration before the effect occurs. The appearance of the adaptive-trophic function does not require a long time in those organs that are endowed with direct sympathetic irritability, for example, the heart and other internal organs.
Supporting facts
Facts proving neurotrophic regulation by the sympathetic system were obtained from various studies on skeletal muscle tissue. Research included functional overload, denervation, regeneration, and cross-connection of nerves that are connected to different types of muscle fibers. As a result of the research, it was concluded that the trophic function is performed by metabolic processes that maintain normal muscle structure and provide its needs during specific loads. These also help restore the necessary resources after the muscle has stopped working. The operation of such processes is determined by a number of biological regulatory substances. There is evidence that for a trophic action to occur, it is necessary to transport the necessary substances from the cell body to the executive organ.
For example, catecholamines take part in a process such as the implementation of trophic function. The level of energy substrates in the blood increases, which leads to a rapid and intense effect on metabolic processes.
Conclusion
It is known that sensitive ones also exhibit an adaptive-trophic effect. Scientists have found that the endings of sensory fibers contain various types of neuroactive substances, such as neuropeptides. The most common are P-neuropeptides, as well as peptides that are associated with the calcitonin gene. Such peptides, after being released from nerve endings, are capable of exerting a trophic effect on the surrounding tissues.
In a broad biological sense, trophism (from the Greek trophe - nutrition, food) is understood as the process of providing a cell, tissue, or organ with everything necessary for normal life and maintaining a genetically determined functioning program. The necessary plastic and energy materials are delivered to cellular structures by blood through the microcirculatory network of vessels. The mechanisms for regulating metabolic processes are diverse. They depend on the number and functionality of receptors - protein macromolecules built into the surface membrane. In a complex, multicellular organism, all processes occurring in each cell are strictly coordinated with each other. This coordination is ensured by the secretion of biologically active substances by some cells (a group of cells), their reception by other cells and the subsequent activation of intracellular signaling. Such biologically active numerous (more than 100) regulatory substances include neurotransmitters, hormones, prostaglandins, interleukins, antigens, immunoglobulins, other stimulants and their antagonists.
The disturbance of trophism is called dystrophy, and the functional and structural changes that dynamically develop in a cell, organ, tissue are called the dystrophic process. The causes that initiate dystrophy can be of various origins. Intracellular mechanisms for triggering pathologically altered signaling are standard. They begin with a violation of consistency in the course of chemical reactions, changes in functional and metabolic activity in the cell. Therefore, degenerative processes in the cell began to be classified as typical intracellular processes.
Not the only, but the most important role in the development of dystrophic processes belongs to the nervous system and the neurotransmitters it produces.
The importance of the nervous factor in dystrophic phenomena was first shown by Magendie (1824). After cutting the trigeminal nerve in a rabbit, he discovered changes in the structure of the tissues of the eye, nasal cavity and mouth. The eye became dry and motionless, clouding of the cornea rapidly progressed, turning into ulcerations; ulcerative keratitis could be accompanied by perforation and complete destruction of the eye. Based on the experimental data obtained, the idea of trophic nerves and neurogenic dystrophies arose, which was developed in the works of I. P. Pavlov and his numerous scientific school. The advanced position about the trophic influence of the nervous system on metabolism in tissues remains relevant at the present time. Disorders of nervous trophism can manifest themselves not only as gross structural changes, but also as functional disorders caused by changes in metabolism.
The neurodystrophic process, therefore, is caused by the loss or weakening of the influence of neurons on the metabolic activity and structure of the cellular elements of organs and tissues. At the same time, the latter have a certain influence on the state of the neuron itself. Neurons and the cellular elements innervated by them form a regional trophic circuit, within which a mutual exchange of information occurs. Signal molecules released by nerve fibers are perceived by recipient cells, which, in turn, influence the corresponding neuron by humoral factors. Signaling molecules acting within the trophic circuit are called trophogens. Disorders of the relationships between the components of the trophic circuit can be the result of an excess or deficiency of mediators (acetylcholine, norepinephrine), disruption or complete cessation of the axoplasmic current (movement along the axons of fluid with proteins, enzymes, electrolytes dissolved in it), going in both directions, which leads to ultimately to dystrophies of neurogenic origin.
The trophic function is inherent in all nerves - somatic (motor and sensitive) and autonomic (sympathetic and parasympathetic). At the same time, specialized nerve structures have been discovered that take part in the metabolism of cells, tissues, and organs. Thus, I.P. Pavlov identified a strengthening nerve of the heart, which increases the strength of myocardial contractions and does not change its rhythm. The Orbeli-Ginetzinsky phenomenon is described, the essence of which is that the frog gastrocnemius muscle, tired by electrical stimuli, began to respond again with a full contraction after irritation of the sympathetic fibers. These and subsequent experiments proved the adaptive-trophic role of the sympathetic nervous system on the myocardium, skeletal muscles, receptors, activity of the spinal cord, medulla oblongata, thalamic region, and cerebral cortex. Specific innervation is also inherent in the parasympathetic division of the autonomic nervous system. It is believed that somatic functional nerves contain trophic fibers that are involved in the regulation of organ metabolism and adaptation to changing needs.
Neurogenic dystrophies arise as a result of damage to peripheral nerves or disturbances in the activity of nerve centers.
In experiments, transection of the sciatic nerve leads in experimental animals (rat, cat, rabbit) to atrophy of the innervated muscle group and the appearance of trophic ulcers on the foot. Spontaneous mechanical injury of the femoral nerve in dogs first leads to abrasions and abrasions, and then to the development of neurotrophic ulcers that cannot be treated. In horses, sprains and ruptures of the sciatic nerve, which sometimes occur while overcoming obstacles, are accompanied by relatively rapid muscle atrophy. Transection of the tibial, peroneal and median nerves in animals of this species leads to muscle atrophy and detachment of the hoof horn.
The participation of central formations in the trophic function of the nervous system has become known since the time of C. Bernard (1867), who performed a “sugar injection” into the area of the bottom of the fourth cerebral ventricle. Experiments showed that irritation of the interstitial medulla, the area of the gray tubercle, led to the appearance of trophic ulcers on the mucous membrane of the oral cavity and other parts of the gastrointestinal tract. Damage to the premotor and motor areas of the cerebral cortex caused disruption of metabolic processes and tissue structure in the form of chronically non-healing ulcers and long-term non-healing bone fractures. The most important area of the brain is the hypothalamus, where nuclei are concentrated that influence metabolic processes through the autonomic nerves and the endocrine system. Evidence has been obtained of the participation of its higher parts, the cerebral cortex, in the trophic function of the nervous system. It has been established that, based on the principle of conditioned reflexes, the development of severe dystrophic disorders is possible.
According to modern concepts, thanks to numerous interneuron connections, the nervous system is a trophic network through which exogenous (toxins, viruses) and endogenous (pathotrophogens) harmful factors that can cause metabolic and structural-functional disorders in organs are distributed.
5. Sympathetic nervous system. Central and peripheral divisions of the sympathetic nervous system.
6. Sympathetic trunk. Cervical and thoracic sections of the sympathetic trunk.
7. Lumbar and sacral (pelvic) sections of the sympathetic trunk.
8. Parasympathetic nervous system. The central part (division) of the parasympathetic nervous system.
9. Peripheral division of the parasympathetic nervous system.
10. Innervation of the eye. Innervation of the eyeball.
11. Innervation of the glands. Innervation of the lacrimal and salivary glands.
12. Innervation of the heart. Innervation of the heart muscle. Innervation of the myocardium.
13. Innervation of the lungs. Innervation of the bronchi.
14. Innervation of the gastrointestinal tract (intestine to the sigmoid colon). Innervation of the pancreas. Innervation of the liver.
15. Innervation of the sigmoid colon. Innervation of the rectum. Innervation of the bladder.
16. Innervation of blood vessels. Innervation of blood vessels.
17. Unity of the autonomic and central nervous systems. Zones Zakharyin - Geda.
Above, a fundamental qualitative difference was noted in the structure, development and function of non-striated (smooth) and striated (skeletal) muscles. Skeletal muscles are involved in the body's response to external influences and respond to changes in the environment with quick and appropriate movements. Smooth muscles, embedded in the viscera and blood vessels, work slowly but rhythmically, ensuring the flow of life processes in the body. These functional differences are associated with differences in innervation: skeletal muscles receive motor impulses from the animal, somatic part of the nervous system, smooth muscles - from the autonomic one.
Autonomic nervous system controls the activities of all organs involved in the implementation of plant functions of the body (nutrition, respiration, excretion, reproduction, circulation of fluids), and also carries out trophic innervation (I. P. Pavlov).
Trophic function of the autonomic nervous system determines the nutrition of tissues and organs in relation to the function they perform in certain environmental conditions ( adaptive-trophic function).
It is known that changes in the state of higher nervous activity affect the function of internal organs and, conversely, changes in the internal environment of the body affect the functional state of the central nervous system. Autonomic nervous system strengthens or weakens function specifically working organs. This regulation is tonic in nature, so the autonomic nervous system changes the tone of the organ. Since the same nerve fiber is capable of acting only in one direction and cannot simultaneously increase and decrease tone, accordingly, the autonomic nervous system is divided into two sections, or parts: sympathetic and parasympathetic - pars sympathica and pars parasympathica.
Sympathetic department in its main functions it is trophic. It enhances oxidative processes, consumption of nutrients, increased breathing, increased heart activity, and increased oxygen supply to the muscles.
The role of the parasympathetic department protective: constriction of the pupil in strong light, inhibition of cardiac activity, emptying of the abdominal organs.
Comparing distribution area sympathetic and parasympathetic innervation, it is possible, firstly, to detect the predominant importance of one particular vegetative department. The bladder, for example, receives mainly parasympathetic innervation, and transection of the sympathetic nerves does not significantly change its function; Only the sweat glands, hair muscles of the skin, spleen, and adrenal glands receive sympathetic innervation. Secondly, in organs with dual autonomic innervation, interaction between the sympathetic and parasympathetic nerves is observed in the form of a certain antagonism. Thus, irritation of the sympathetic nerves causes dilation of the pupil, constriction of blood vessels, acceleration of heart contractions, inhibition of intestinal motility; irritation parasympathetic nerves leads to constriction of the pupil, dilation of blood vessels, slowing of the heartbeat, and increased peristalsis.
However, the so-called antagonism of the sympathetic and parasympathetic parts should not be understood statically, as a opposition between their functions. These parts interact, the relationship between them changes dynamically at different phases of the function of a particular organ; they can act both antagonistically and synergistically.
Antagonism and synergism- two sides of a single process. The normal functions of our body are ensured by the coordinated action of these two parts of the autonomic nervous system. This coordination and regulation of functions is carried out by the cerebral cortex. The reticular formation is also involved in this regulation.
Autonomy of the autonomic nervous system is not absolute and manifests itself only in local reactions of short reflex arcs. Therefore, the term proposed by PNA “ autonomic nervous system" is not accurate, which explains the preservation of the old, more correct and logical term " autonomic nervous system». Division of the autonomic nervous system on the sympathetic and parasympathetic departments is carried out mainly on the basis of physiological and pharmacological data, but there are also morphological differences due to the structure and development of these parts of the nervous system.
Educational video of the anatomy of the autonomic nervous system (ANS)
Along with the function of transmitting impulses causing muscle contractions, nerve fibers and their endings also provide trophic impact on the muscle, i.e. they participate in the regulation of its metabolism. It is well known that muscle denervation by cutting the motor roots of the spinal cord leads to gradually developing atrophy of muscle fibers. Special studies show that this atrophy is not only the result of inactivity of a muscle that has lost motor innervation.
Muscle inactivity can also be caused by tendotomy, i.e. cutting the tendon. However, if you compare the muscle after tendotomy and after denervation, you can see that in the latter case, qualitatively different changes in its properties develop in the muscle that are not detected during tendotomy. Thus, denervated muscle fibers acquire high sensitivity to acetylcholine throughout their entire length, while in normal or tendotomized muscle only the area of the postsynaptic membrane has high sensitivity to acetylcholine.
In denervated muscle, the activity of a number of enzymes and, in particular, the activity of adenosine triphosphatase, which plays an important role in the process of releasing energy contained in the phosphate bonds of adenosine triphosphoric acid, sharply decreases. At the same time, during denervation, the processes of protein breakdown are significantly enhanced, which leads to a gradual decrease in muscle tissue characteristic of atrophy. A comprehensive study of metabolism in denervated muscle allowed S. E. Severin to come to the conclusion that the cessation of the trophic influences of the nerve leads to the fact that metabolic processes in the muscle begin to proceed randomly and uncoordinated.
The specific mechanism by which motor nerve fibers and their endings have a regulatory effect on metabolism has not yet been clarified. There is reason to believe that the mediator released in the nerve endings - acetylcholine - and the products of its cleavage by cholipesterase - choline and acetic acid - interfere with muscle metabolism, exerting an activating effect on certain enzyme systems. Thus, the experiments of V. M. Vasilevsky showed that the introduction of acetylcholine into the denervated muscle of a rabbit sharply increases the breakdown of adenosine triphosphate, creatine phosphate and glycogen during tetanus caused by direct electrical stimulation of this muscle.
In this regard, we note that acetylcholine is secreted by nerve endings not only during excitement, but also at rest. The only difference is that at rest, small amounts of acetylcholine are released into the synaptic cleft, while iodine, under the influence of a nerve impulse, releases large portions of this transmitter.
The release of acetylcholine at rest is associated with the fact that individual vesicles in the nerve ending “mature” and rupture from time to time. The small amounts of acetylcholine released during this process cause depolarization of the postsynaptic membrane, which is manifested by the appearance of so-called miniature potentials. These miniature potentials have an amplitude of about 0.5 mV, which is about 50 times smaller than the amplitude of the end plate potential. Their frequency is about 1 per second.
It can be assumed that the formation of acetylcholine and, possibly, some other, not yet studied substances by nerve endings at rest and during excitement is an important mechanism of the trophic effect of the nerve on the muscle.
Fibers of the sympathetic nervous system, in the endings of which adrenaline-like substances are formed, have a special trophic effect on skeletal muscle.
In biology, for a long time, the prevailing belief was that the nervous regulation of skeletal muscle activity is provided exclusively by the somatic nervous system. This idea, firmly established in the minds of researchers, was shaken only in the first third of the 20th century.
It is well known that with prolonged work a muscle becomes tired: its contractions gradually weaken and may finally stop completely. Then, after some rest, the muscle's performance is restored. The causes and material basis of this phenomenon remained unknown.
In 1927 L.A. Obreli found that if by prolonged stimulation of the motor nerve the frog's leg is brought to the point of fatigue (cessation of movements), and then, continuing motor stimulation, the sympathetic nerve is simultaneously irritated, then the limb quickly resumes its work. Consequently, the connection of the sympathetic influence changed the functional state of the tired muscle, eliminated fatigue and restored its performance.
It was found that sympathetic nerves influence the ability of muscle fibers to conduct electrical current and the excitability of the motor nerve. Under the influence of sympathetic innervation, the content in the muscle of a number of chemical compounds that play an important role in its activity changes: lactic acid, glycogen, creatine, phosphates. Based on these data, it was concluded that the sympathetic nervous system causes certain physicochemical changes in skeletal muscle tissue, regulates its sensitivity to motor impulses coming through somatic fibers, and adapts it to perform loads that arise in each specific situation. It was suggested that the increased work of a tired muscle under the influence of the sympathetic nerve fiber entering it occurs due to an increase in blood flow. However, experimental testing did not confirm this opinion.
Special studies have established that in all vertebrates there is no direct sympathetic innervation of skeletal muscle tissue. Consequently, sympathetic influences on skeletal muscles can only be achieved through the diffusion of the mediator and, apparently, other substances secreted by the vasomotor sympathetic terminals. The validity of this conclusion is confirmed by a simple experiment. If, during stimulation of the sympathetic nerve, a muscle is placed in a solution or its vessels are perfused, then substances (of unknown nature) appear in the washing solution and perfusate, which, when introduced into other muscles, cause the effect of sympathetic irritation.
The indicated mechanism of sympathetic influence is also supported by the long latent period before the effect manifests itself, its significant duration and the preservation of the maximum after the cessation of sympathetic stimulation. Naturally, in organs endowed with direct sympathetic innervation, such as the heart, blood vessels, internal organs, etc., such a long latent time is not required for the manifestation of trophic influence.
The main evidence of the mechanisms mediating neurotrophic regulation by the sympathetic nervous system was obtained on skeletal muscle tissue when studying functional overload, denervation, regeneration, and cross-connection of nerves suitable for various types of muscle fibers. Based on the research results, it was concluded that the trophic effect is due to a complex of metabolic processes that maintain the normal structure of muscles, ensure its needs when performing specific loads and restore the necessary resources after stopping work. A number of biologically active (regulatory) substances are involved in these processes. It has been proven that for the manifestation of a trophic effect, the transport of substances from the body of the nerve cell to the executive organ is necessary. This is evidenced, in particular, by data obtained in experiments on muscle denervation. It is known that muscle derenvation leads to its atrophy (neurogenic atrophy). Based on this, at one time it was concluded that the nervous system influences muscle metabolism through the transmission of motor impulses (hence the term “atrophy from inactivity”). However, it turned out that the resumption of contractions of the denervated muscle by electrical stimulation cannot stop the atrophy process. Consequently, normal muscle trophism cannot be associated only with motor activity. In these works there are very interesting observations concerning the significance of axoplasm. It turned out that the longer the peripheral end of the cut nerve, the later degenerative changes develop in the denervated muscle. Apparently, in this case, the amount of axoplasm remaining in contact with the muscle, containing substrates of trophic action transferred from the neuron body, was of decisive importance.
It can be considered generally accepted that the role of neurotransmitters is not limited to participation in the transmission of nerve impulses; they also influence the vital processes of innervated organs, being included in the mechanisms of energy supply to tissues and in the processes of plastic compensation of structural costs (membrane elements, enzymes, etc.).
Thus, catecholamines are directly involved in the adaptation-trophic function of the sympathetic nervous system due to their ability to quickly and intensely influence metabolic processes by increasing the level of energy substrates in the blood and enhancing the secretion of hormones; they also cause redistribution of blood and stimulation of the nervous system.
There is evidence of the participation of acetylcholine in changes in carbohydrate, protein, water, and electrolyte metabolism of innervated tissues, as well as observations of the positive effect of acetylcholine injections in certain diseases of the skin, blood vessels, and nervous system.
It is known that sensory nerve fibers also exhibit an adaptive-trophic effect. Recently, it has been established that the endings of sensory fibers contain various neuroactive substances, including neuropeptides. The most commonly detected are neuropeptides P and calcitonin gene-related peptide. It is assumed that these peptides, released from nerve endings, can have a trophic effect on surrounding tissues.
In addition, a number of studies in recent years have shown that in cell culture and in the body of experimental animals, the dendrites of nerve cells constantly undergo changes. They are actively shortened (process retraction) and as a result, their terminal parts are torn off (terminal amputation). Subsequently, new endings grow in place of the lost ones, and the amputated terminals are destroyed. This releases various biologically active compounds, including the peptides mentioned above. it is assumed that these substances may exhibit neurotrophic effects.
QUESTIONS AND TASKS FOR SELF-CONTROL
1. What centers of the brain stem are involved in regulating the visceral functions of the autonomic nervous system?
2. In regulating what functions does the hypothalamus play a role?
3. What interoreceptors send signals to the hypothalamus? To changes in what parameters of the internal environment do the receptor neurons of the medial hypothalamus react?
4. Name the segmental centers of the sympathetic nervous system.
5. What structures does the peripheral part of the sympathetic nervous system consist of?
6. Axons of which nerves form white and gray connecting branches?
7. Indicate the switching locations of the white connecting branches.
8. What are pre- and postganglionic fibers? How are the postganglionic fibers located from the nodes of the sympathetic trunk?
9. As part of which nerve conductors do the gray connecting branches go to their targets and what exactly do they innervate?
10. Name the main organs innervated by postganglionic fibers of the cervical nodes of the sympathetic trunk. What nodes of the sympathetic trunk are involved in the innervation of the heart?
11. Name the prevertebral nerve plexuses and indicate what formations they consist of.
12. Name the structural and functional features that distinguish the parasympathetic nervous system from the sympathetic one.
13. From which nuclei of the brain and spinal cord do preganglionic parasympathetic fibers emerge?
14. Where does the ciliary ganglion receive its preganglionic fibers, and what do its efferent neurons innervate?
15. From which nucleus do the preganglionic fibers of the pterygoid ganglion emerge; indicate which formations are innervated by the neurons of this node?
16. Name the sources of innervation of the parotid, submandibular and sublingual salivary glands
17. Describe the pelvic nerve plexus. How is it formed and what does it innervate?
18. List the main structural and functional features of the metasympathetic nervous system.
19. Describe the structure of the sympathetic nerve ganglion.
20. List the characteristic features of the structure of intramural nerve ganglia.
21. Describe the structural features of the vagus nerve that distinguish it from other nerve trunks.
22. A child has been diagnosed with Hirschsprung's disease. Explain its reasons. How does it manifest itself?
23. The anterior root of the spinal cord has been cut in an experimental animal. Will this affect the structure of effector fibers of the sosmatic and autonomic nervous systems?
24. A patient complains of severe sweating of the hands and armpits. What is the likely cause of this illness?
25. Name the structural and functional features of the autonomic nerves.
26. What afferent neurons make up the sensitive part of the reflex arc of the ANS.
27. How does the efferent link of the reflex arcs of the somatic and autonomic nervous systems differ?
28. The hypothalamus has special receptor neurons that are sensitive to changes in blood constants. Explain what features of the circulatory system of the hypothalamus contribute to the manifestation of this ability of these neurons.
29. What is the difference between cholinergic impulse transmission from preganglionic and postganglionic fibers of the parasympathetic system (H and M receptors).
30. What nerve branches form postganglionic fibers emerging from the nodes of the sympathetic trunk?
31. What features are characteristic of the structure of the nuclei and neurons of the reticular formation of the brain stem?