Frederic's experience with cross-circulation. Frederic Brochet's experience - do tasters "lie" or "don't lie"
Have you heard about such an experiment on wine experts? I was once in France, where we tried 10-15 varieties of cognac costing from 100 to 10,000 dollars per bottle - I couldn’t distinguish anything there at all. Firstly, I’m not a specialist at all and don’t have any rich drinking experience, and secondly, cognac is still a strong thing.
But what they write about experiments with wine seems to me to be very exaggerated, simplistic, or their experts are so worthless. See for yourself.
Once upon a time, a wine tasting was held in Boston, in which famous connoisseurs of this drink took part. The rules for wine tasting were very simple. Twenty-five of the best wines, the price of which should not exceed $12, were purchased in a regular store in Boston. Later, a group of experts was formed to evaluate red and white wines, who were supposed to blindly identify the best wine from the presented...
As a result, the winner was the cheapest wine. This once again confirms that tasters and wine critics are a myth. Based on the results of the analysis of the experts' responses, it was revealed that all tasters chose the wine that they simply liked the most in taste. So much for the "experts".
By the way, in 2001, Frederic Brochet from the University of Bordeaux conducted two separate and very revealing experiments on tasters. In the first test, Brochet invited 57 experts and asked them to describe their impressions of just two wines.
In front of the experts were two glasses, with white and red wine. The trick was that there was no red wine, in fact it was the same white wine, tinted with food coloring. But that didn't stop experts from describing "red" wine in the language they usually use to describe red wines.
One expert praised its "jamminess" and another even "felt" the "crushed red fruit." No one noticed that it was actually white wine!!!
Brochet's second experiment turned out to be even more damning for critics. He took regular Bordeaux and bottled it in two different bottles with different labels. One bottle was grand cru, the other was regular table wine.
Even though they actually drank the same wine, the experts rated them differently. The Grand Cru was "pleasant, woody, complex, balanced and enveloping" and the table was, according to experts, "weak, tasteless, unsaturated, simple."
At the same time, most of them did not even recommend “table” wine for consumption.
Experts are fashion indicators and their taste is no different from the sense of taste of an ordinary person. People just want to listen to someone’s opinion, that’s what an “expert” is for.
The question arises: Do “experts” exist? In other words, we are different people, and our tastes vary just like brands of cheap wine, some like them, some don't.
Or, if not the brand and year of harvest, then white and red wine can be accurately distinguished even by a weak expert? How do you feel about wine experts?
Claude Bernard's experience(1851). After cutting the sympathetic nerve on the rabbit's neck, 1-2 minutes. There was a significant dilation of the vessels of the auricle, which manifested itself in redness of the skin of the ear and an increase in its temperature. When the peripheral end of this cut nerve was irritated, the skin, reddened after cutting the sympathetic fibers, became pale and cold. This occurs as a result of narrowing of the lumen of the ear vessels.
| Rice. 11. Rabbit ear vessels; on the right side, where the vessels are sharply dilated, the sympathetic trunk in the neck is cut | ||||
| Bronjest's experience. Experience helps to understand the mechanism of muscle tone. The lumbar plexus is found on the spinal frog, an incision of about 1 cm is made on the side of the pelvis, and a ligature is placed under the plexus. Having secured the frog by the lower jaw on a tripod, note the symmetrical semi-bent position of the lower limbs: the equality of the angles formed by the thigh and lower leg, the lower leg and foot on both limbs and the same level of the fingers horizontally. Then the lumbar plexus is tightly bandaged and after a few minutes the angle and length of both legs are compared. It is noted that the operated paw is slightly elongated as a result of the elimination of muscle tone. | Fig. 12. Bronjest's Experience | |||
Gaskell's experiment. Gaskell used the fact of the influence of temperature on the rate of physiological processes to experimentally prove the leading role of the sinus node in the automation of the heart. If you heat or cool different parts of the frog’s heart, it is revealed that the frequency of its contraction changes only when the sinus is heated or cooled, while changes in the temperature of other parts of the heart (atria, ventricle) affect only the strength of muscle contractions. Experience proves that impulses to contract the heart arise in the sinus node.
Levi's experience. There are many examples that the creative work of the human brain also occurs during sleep. Thus, it is known that it was in a dream that the Periodic Table of Chemical Elements “appeared” to D.I. Mendeleev. The decisive experiment, with the help of which it was possible to prove the chemical mechanism of transmission of nerve signals, was dreamed of by the Austrian scientist Otto Levi. He later recalled: “The night before Easter Sunday, I woke up, turned on the light and quickly scribbled a few words on a tiny piece of paper. Then he fell asleep again. At six o'clock in the morning I remembered that I had written down something very important, but I could not make out my sloppy handwriting. The next night, at three o'clock, sleep visited me again. It was an idea for an experiment that would test the truth of the chemical transmission hypothesis that had haunted me for seventeen years. I immediately got up, rushed to the laboratory and performed a simple experiment on the heart of a frog, according to my nightly dream.”
Fig. 15. Experience of O. Levi. A – cardiac arrest due to irritation of the vagus nerve; B – arrest of another heart without irritation of the vagus nerve; 1 – vagus nerve, 2 – stimulating electrodes, 3 – cannula
The effects on the myocardium of nerve impulses arriving along the autonomic nerves are determined by the nature of the mediator. The mediator of the parasympathetic nerves is acetylcholine, and the sympathetic nerves are norepinephrine. This was first established by the Austrian pharmacologist O. Levi (1921). He connected two isolated frog hearts to the two ends of the same cannula. Strong irritation of the vagus nerve of one of the hearts caused the arrest of not only the heart innervated by this nerve, but also the other, intact one, associated with the first only with a common cannula solution. Consequently, when the first heart was irritated, a substance was released into the solution that affected the second heart. This substance was called "wagusstoff" and was later found to be acetylcholine. With similar stimulation of the sympathetic nerve of the heart, another substance was obtained - “sympathikusshtoff”, which is adrenalin or no-radrenaline, similar in their chemical structure.
In 1936, O. Levy and G. Dale received the Nobel Prize for their discovery of the chemical nature of the transmission of nervous reactions.
Marriott's experience (blind spot detection). The subject holds Marriott's drawing at outstretched arms. Closing his left eye, he looks at the cross with his right eye and slowly brings the drawing closer to the eye. At a distance of approximately 15-25cm, the image of the white circle disappears. This happens because when the eye fixates on a cross, the rays from it fall on the yellow spot. The rays from the circle, at a certain distance of the pattern from the eye, will fall on the blind spot, and the white circle ceases to be visible.
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Fig. 16. Drawing by Mariotte
Matteucci's experience (secondary contraction experience). Two neuromuscular drugs are prepared. The nerve of one preparation is left with a piece of the spine, while in the other a piece of the spine is removed. The nerve of one neuromuscular preparation (with a piece of the spine) is placed using a glass hook on electrodes that are connected to the stimulator. The nerve of the second neuromuscular preparation is thrown onto the muscles of this preparation in the longitudinal direction. The nerve of the first neuromuscular preparation is subjected to rhythmic stimulation, the action potentials arising in the muscle during its contraction cause the excitation of the nerve of the other neuromuscular preparation superimposed on it and the contraction of its muscle.
Rice. 17. Matteucci Experience
The Stannius Experience consists in the sequential application of three ligatures (dressings), separating the sections of the frog's heart from each other. The experiment is carried out to study the ability of automation of various parts of the cardiac conduction system.
Fig. 18. Scheme of Stannius’ experiment: 1 – first ligature; 2 – first and second ligatures; 3 – first, second and third ligatures. Parts of the heart that contract after the application of ligatures are indicated in dark color.
Sechenov's experiment (Sechenov braking). Inhibition in the central nervous system was discovered by I.M. Sechenov in 1862. He observed the occurrence of inhibition of spinal reflexes when the diencephalon (visual thalamus) of a frog was irritated with a crystal of table salt. Outwardly, this was expressed in a significant decrease in the reflex reaction (increase in reflex time) or its cessation. Removal of the table salt crystal led to the restoration of the initial reflex time.
| B |
Fig. 19. Scheme of I.M. Sechenov’s experiment with irritation of the visual tuberosities of a frog. A – successive stages of exposing the frog’s brain (1 – a flap of skin cut above the skull is bent back; 2 – the roof of the skull is removed and the brain is exposed). B – frog brain with a cut line for Sechenov’s experiment (1 – olfactory nerves; 2 – olfactory lobes; 3 – cerebral hemispheres; 4 – cut line passing through the diencephalon; 5 – midbrain; 6 – cerebellum; 7 – medulla oblongata ). B – place of application of table salt crystals
Frederic-Heymans experiment (cross-circulation experiment). In the experiment, some dog carotid arteries (I and II) are ligated, while others are connected crosswise to each other using rubber tubes. As a result, the head of dog I is supplied with blood flowing from dog II, and the head of dog II is supplied with the blood of dog I. If you squeeze the trachea of dog I, then the amount of oxygen in the blood flowing through the vessels of its body will gradually decrease and the amount of carbon dioxide will increase. However, the cessation of oxygen access to the lungs of dog I is not accompanied by an increase in its respiratory movements; on the contrary, they soon weaken, but dog II begins to have very severe shortness of breath.
Since there is no nervous connection between the two dogs, it is clear that the irritating effect of lack of oxygen and excess carbon dioxide is transmitted from the body of dog I to the head of dog II through the blood flow, i.e. . humoral way. The blood of dog I, overloaded with carbon dioxide and poor in oxygen, entering the head of dog II, causes excitation of its respiratory center. As a result, dog II experiences shortness of breath, i.e. increased ventilation of the lungs. At the same time, hyperventilation leads to a decrease (below normal) in the carbon dioxide content in the blood of dog II. This carbon dioxide-depleted blood enters the head of dog I and causes a weakening of the work of its respiratory center, despite the fact that all tissues of this dog, with the exception of those of the head, suffer from severe hypercapnia (excess CO 2) and hypoxia (lack of O 2), caused by the cessation of access of air into her lungs.
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Fig.20. Cross-circulation experience
Bell-Magendie Law - Afferent nerve fibers enter the spinal cord as part of the posterior (dorsal) roots, and efferent nerve fibers exit the spinal cord as part of the anterior (ventral) roots.
Gaskell's Gradient Law of Automation – The degree of automaticity is higher, the closer the section of the conduction system is to the sinoatrial node (sinoatrial node 60-80 impulses/min., atrioventricular node - 40-50 impulses/min., His bundle - 30-40 impulses/min., Purkinje fibers - 20 impulses/min. ).
Rubner's body surface law - The energy expenditure of a warm-blooded organism is proportional to the surface area of the body.
Frank-Starling's Law of the Heart(the law of dependence of the energy of myocardial contraction on the degree of stretching of its constituent muscle fibers) - the more the heart muscle is stretched during diastole, the stronger it contracts during systole. Consequently, the force of heart contraction depends on the initial length of the muscle fibers before the start of their contraction.
Lomonosov-Young-Helmholtz theory of three-component color vision – In the vertebrate retina there are three types of cones, each of which contains a special color-reactive substance. Due to the content of various color-reactive substances, some cones have increased excitability to red, others to green, and others to blue-violet.
Heymans' theory of circular activation currents (theory of excitation propagation along nerves) – When a nerve impulse is carried out, each point of the membrane generates an action potential anew, and thus the excitation wave “runs” along the entire nerve fiber.
Bainbridge reflex– with increasing pressure at the mouths of the vena cava, the frequency and strength of heart contractions increases.
Hering's reflex - reflex decrease in heart rate when holding your breath at the height of a deep breath.
Goltz reflex– a decrease in heart rate or even complete cardiac arrest when the mechanoreceptors of the abdominal organs or peritoneum are irritated.
Danini-Aschner reflex(ocular reflex) – decrease in heart rate when pressing on the eyeballs.
Parin reflex– with an increase in pressure in the vessels of the pulmonary circulation, cardiac activity is inhibited.
Dale's principle - one neuron synthesizes and uses the same transmitter or the same transmitters in all branches of its axon (in addition to the main transmitter, as it turned out later, other accompanying transmitters can be released at the axon endings, playing a modulating role - ATP, peptides, etc.).
M.M. Zavadsky’s principle (“plus-minus” interaction)– an increase in the hormone content in the blood leads to inhibition of its secretion by the gland, and a deficiency leads to stimulation of hormone secretion.
Bowditch staircase(1871) - if a muscle is stimulated with impulses of increasing frequency without changing their strength, the magnitude of the contractile response of the myocardium will increase to each subsequent stimulus (but up to a certain limit). Outwardly, it resembles a staircase, so the phenomenon is called the Bowditch staircase ( with increasing frequency of stimulation, the force of heart contractions increases).
The Orbeli-Ginetzinsky phenomenon. If, by stimulating the motor nerve, the frog muscle is brought to the point of fatigue, and then at the same time irritating the sympathetic trunk, the performance of the tired muscle increases. Stimulation of sympathetic fibers in itself does not cause muscle contraction, but changes the state of muscle tissue and increases its susceptibility to impulses transmitted through somatic fibers.
Anrep effect(1972) is that with an increase in pressure in the aorta or pulmonary trunk, the force of heart contractions automatically increases, thereby ensuring the possibility of ejecting the same volume of blood as with the initial value of blood pressure in the aorta or pulmonary artery, i.e. the greater the counterload, the greater the force of contraction, and as a result, the constancy of the systolic volume is ensured.
LITERATURE
1. Zayanchkovsky I.F. Animals are scientists' assistants. Popular science essays. –Ufa: Bash.book publishing house, 1985.
2. History of biology. From ancient times to the beginning of the 20th century / ed. S.R. Mikulinsky. –M.: Nauka, 1972.
3. Kovalevsky K.L. Laboratory animals. –M.: Publishing House of the Academy of Medical Sciences of the USSR, 1951.
4. Lalayants I.E., Milovanova L.S. Nobel Prizes in Medicine and Physiology / New in life, science, technology. Ser. "Biology", No. 4. –M.: Knowledge, 1991.
5. Levanov Yu.M. Facets of genius //Biology at school. 1995. No. 5. – P.16.
6. Levanov Yu.M., Andrey Vezaliy //Biology at school. 1995. No. 6. – P.18.
7. Martyanova A.A., Tarasova O.A. Three episodes from the history of physiology. //Biology for schoolchildren. 2004. No. 4. – P.17-23.
8. Samoilov A.F. Selected works. –M.: Nauka, 1967.
9. Timoshenko A.P. About the Hippocratic Oath, the emblem of medicine and much more // Biology at school. 1993. No. 4. – P.68-70.
10. Wallace R. The World of Leonardo /trans. from English M. Karaseva. –M.: TERRA, 1997.
11. Physiology of humans and animals /ed. A.D. Nozdracheva. Book 1. –M.: Higher School, 1991.
12. Human physiology: in 2 volumes. /ed. B.I. Tkachenko. T.2. – St. Petersburg: Publishing house International Foundation for the Development of Science, 1994.
13. Eckert R. Physiology of Animals. Mechanisms and adaptation: in 2t. –M.: Mir, 1991.
14. Encyclopedia for children. T.2. –M.: Publishing house “Avanta +”, 199
| PREFACE…………………………………………………... | |
| BRIEF HISTORY OF THE DEVELOPMENT OF PHYSIOLOGY…………… | |
| THE IMPORTANCE OF LABORATORY ANIMALS IN THE DEVELOPMENT OF PHYSIOLOGY ………………………………………………………. | |
| PERSONALIES ……………………………………………………. | |
| Avicenna …………………………………………………. | |
| Anokhin P.K. ………………………………………………………………… | |
| Bunting F. ………………………………………………………………... | |
| Bernard K. ……………………………………………………………. | |
| Vesalius A. ………………………………………………………………... | |
| Leonardo da Vinci……………………………………. | |
| Volta A. …………………………………………………. | |
| Galen K. ……………………………………………………………... | |
| Galvani L. ……………………………………………………………….. | |
| Harvey W. ……………………………………………………………. | |
| Helmholtz G. ……………………………………………. | |
| Hippocrates…………………………………………………………………… | |
| Descartes R.…………………………………………………. | |
| Dubois-Raymond E. ………………………………………… | |
| Kovalevsky N.O. ……………………………………... | |
| Lomonosov M.V. …………………………………………. | |
| Mislavsky N.A. ………………………………………… | |
| Ovsyannikov F.V. …………………………………………. | |
| Pavlov I.P. ……………………………………………. | |
| Samoilov A.F. ……………………………………………………………… | |
| Selye G. …………………………………………………… | |
| Sechenov I.M……………………………………………………………… | |
| Ukhtomsky A.A. …………………………………………. | |
| Sherrington C.S. ………………………………………… | |
| NOBEL LAUREATES IN THE FIELD OF MEDICINE AND PHYSIOLOGY ……………………………………………………. | |
| AUTHOR'S EXPERIENCES, LAWS, REFLEXES……………….. | |
| LITERATURE……………………………………………………... |
It just so happened that Most people don't like to read. There is more if it is difficult to read, for example in a foreign language, which every second person did not know from school, and then completely forgot. Modern businessmen take full advantage of this fact, releasing wonderful brochures like “Anna Karenina on 5 pages” to the market.
There are many very interesting and truly rich topics for reflection in winemaking and wine consumption, for example about how objective the perception of wine by this or that person can be. About how much in reality a person feels and experiences some emotions when tasting wine, and to what extent he imagines them for himself. These are excellent questions that deserve serious thought and debate. But the problem is that for a serious level of discussion of any issue, including this one, it is necessary to first spend a significant number of hours understanding it in various aspects and studying all existing works done previously on this topic.
And this is a lot of work, which requires, first of all, the skill of serious analytical reading. Which, as I mentioned above, people in general are not capable of. Therefore, today I will also have to practice translating the “theory of partial differential equations for preschool reading.”
We will talk about the experiment (more precisely, the first part of the experiment) Frederica Brochet, which, at the suggestion of tabloid journalists eager for “yellow” and “fried”, became widely known as “deception of tasters.” The essence of the experiment was that the author took white wine, poured it into two containers and tinted one of the containers with tasteless red food coloring. Then he asked his subjects, whom he recruited “through an advertisement” on the university campus, to describe the taste and aroma of each wine.
As a result, those students who tried “white” wine talked about its aroma using associations with white fruits and flowers, mentioning lilies of the valley, peaches, melon, etc., and those students who tried “red” wine talked about roses, strawberries and apples. Nothing in common! Hooray! The tasters are all lying and in fact do not understand anything, we brought them to clean water! General celebration and rejoicing!
It would seem. In fact, the situation is simple and banal: none of us were ever taught to describe taste and aroma in words. No one in any country in the world. Just like the color. Or sound. Try to tell what does blue look like and you will be faced with a big problem, which is that the phrase “radiation with a wavelength of about 440-485 nm” does not say anything at all to anyone. This is actually a simple experiment that anyone can do. Get up from your chair and approach 10-20 people with the question “what does the color blue look like?” And a person who has recently been to the sea will first say, “ at sea", aviation enthusiast - " to heaven", nerd - " to cornflowers", geologist - " for lapis lazuli and sapphire" and so on. Nothing in common! Does this mean that Are people really color blind?
Trying to tell another person about those sensations (in the case of flowers - visual) for which there are no established uniform measures, we call for help associations, trying to choose something that is closest, most similar and most familiar to everyone. Associations, mental images, ideas. Nothing more.
Does the color of the item affect on what associations will they come to our minds? Undoubtedly! In the illustration for this text there is a picture with two images of speed, which the artists embodied in the coloring of cars. What do a snowstorm and a fast-moving forest fire have in common? One is white, cold, prickly, piercing, freezing. The other is mercilessly scorching, assertive, leaving behind fumes, smoke and ash. But does this mean that in reality “there is no speed!”? Of course not! She is great to eat. Did the original color of the car influence the choice of metaphor, association, or idea for the painting? Undoubtedly! Is there any sensation in this? Not a penny.
But who cares?
The main humoral stimulator of the respiratory center is excess carbon dioxide in the blood, as demonstrated in the experiments of Frederick and Holden.
Frederick's experience on two dogs with cross circulation. In both dogs (first and second), the carotid arteries are cut and cross-connected. The same is done with the jugular veins. The vertebral arteries are ligated. As a result of these operations, the head of the first dog receives blood from the second dog, and the head of the second dog from the first. The first dog's trachea is blocked, which causes hyperventilation (fast and deep breathing) in the second dog, whose head receives blood from the first dog, depleted in oxygen and enriched in carbon dioxide. The first dog has apnea; blood enters its head with a lower CO2 voltage and approximately the usual, normal content of 02 - hyperventilation washes out CO2 and has virtually no effect on the content of 02 in the blood, since hemoglobin is saturated
0 2 almost completely and without hyperventilation.
The results of Frederick's experiment indicate that the respiratory center is excited either by an excess of carbon dioxide or by a lack of oxygen.
In Holden's experiment in a closed space from which CO 2 is removed, breathing is weakly stimulated. If CO2 is not removed, shortness of breath is observed - increased and deepening of breathing. Later it was proven that an increase in CO 2 content in the alveoli by 0.2% leads to an increase in lung ventilation by 100%. An increase in the content of CO 2 in the blood stimulates respiration both due to a decrease in pH and the direct effect of CO 2 itself.
The effect of CO 2 and H + ions on respiration is mediated mainly by their effect on special structures of the brain stem that are chemosensitive (central chemoreceptors). Chemoreceptors that respond to changes in the gas composition of the blood are found externally in the walls of blood vessels in only two areas - in the aortic arch and the sinocarotid region.
The role of aortic and sinocarotid chemoreceptors in the regulation of respiration has been shown experimentally with voltage reduction 0 2 in arterial blood (hypoxemia) below 50-60 mm Hg. Art. - at the same time, ventilation of the lungs increases within 3-5 s. Such hypoxemia can occur when climbing to a height, with cardiopulmonary pathology. Vascular chemoreceptors are also excited under normal blood gas tension; their activity increases greatly during hypoxia and disappears when breathing pure oxygen. Stimulation of respiration when voltage decreases 0 2 is mediated exclusively by peripheral chemoreceptors. Carotid chemoreceptors are secondary - these are bodies synaptically connected to the afferent fibers of the carotid nerve. They are excited by hypoxia, a decrease in pH and an increase in Pco 2, while calcium enters the cell. Their mediator is dopamine.
The aortic and carotid bodies are also excited when the CO2 voltage increases or when the pH decreases. However, the effect of CO 2 from these chemoreceptors is less pronounced than the effect of 0 2 .
Hypoxemia (decreased partial pressure of oxygen in the blood) stimulates breathing much more if it is accompanied hypercapnia, which is observed during very intense physical work: hypoxemia increases the response to CO 2. However, with significant hypoxemia, due to a decrease in oxidative metabolism, the sensitivity of central chemoreceptors decreases. Under these conditions, a decisive role in stimulating respiration is played by vascular chemoreceptors, whose activity increases, since for them an adequate stimulus is a decrease in 0 2 tension in the arterial blood (emergency mechanism for stimulating respiration).
Thus, vascular chemoreceptors respond predominantly to a decrease in oxygen levels in the blood, central chemoreceptors - to changes in the blood and cerebrospinal fluid pH and PCO g
The importance of pressoreceptors of the carotid sinus and aortic arch. An increase in blood pressure increases afferent impulses in the sinocarotid and aortic nerves, which leads to some depression of the respiratory center and a weakening of pulmonary ventilation. On the contrary, breathing increases somewhat with a decrease in blood pressure and a decrease in afferent impulses into the brain stem from vascular pressoreceptors.
The main function of the respiratory system is to ensure gas exchange of oxygen and carbon dioxide between the environment and the body in accordance with its metabolic needs. In general, this function is regulated by a network of numerous CNS neurons that are connected to the respiratory center of the medulla oblongata.
Under respiratory center understand a set of neurons located in different parts of the central nervous system, ensuring coordinated muscle activity and adaptation of breathing to the conditions of the external and internal environment. In 1825, P. Flourens identified a “vital node” in the central nervous system, N.A. Mislavsky (1885) discovered the inspiratory and expiratory parts, and later F.V. Ovsyannikov described the respiratory center.
The respiratory center is a paired formation consisting of an inhalation center (inspiratory) and an exhalation center (expiratory). Each center regulates the breathing of the same side: when the respiratory center on one side is destroyed, respiratory movements on that side cease.
Expiratory department - part of the respiratory center that regulates the process of exhalation (its neurons are located in the ventral nucleus of the medulla oblongata).
Inspiratory department- part of the respiratory center that regulates the process of inhalation (localized mainly in the dorsal part of the medulla oblongata).
The neurons of the upper part of the pons, regulating the act of breathing, were called pneumotaxic center. In Fig. Figure 1 shows the location of the neurons of the respiratory center in various parts of the central nervous system. The inhalation center is automatic and in good shape. The exhalation center is regulated from the inhalation center through the pneumotaxic center.
Pneumotaxic complex- part of the respiratory center, located in the area of the pons and regulating inhalation and exhalation (during inhalation it causes excitation of the exhalation center).
Rice. 1. Localization of respiratory centers in the lower part of the brain stem (posterior view):
PN - pneumotaxic center; INSP - inspiratory; ZKSP - expiratory. The centers are double-sided, but to simplify the diagram, only one is shown on each side. Transection along line 1 does not affect breathing, along line 2 the pneumotaxic center is separated, below line 3 respiratory arrest occurs
In the structures of the bridge, two respiratory centers are also distinguished. One of them - pneumotaxic - promotes a change from inhalation to exhalation (by switching excitation from the center of inspiration to the center of exhalation); the second center exerts a tonic effect on the respiratory center of the medulla oblongata.
The expiratory and inspiratory centers are in a reciprocal relationship. Under the influence of the spontaneous activity of the neurons of the inspiratory center, the act of inhalation occurs, during which mechanoreceptors are excited when the lungs are stretched. Impulses from mechanoreceptors enter the inspiratory center along the afferent neurons of the excitatory nerve and cause excitation of the expiratory center and inhibition of the inspiratory center. This ensures a change from inhalation to exhalation.
In the change from inhalation to exhalation, the pneumotaxic center is of significant importance, which exerts its influence through the neurons of the expiratory center (Fig. 2).
Rice. 2. Scheme of nerve connections of the respiratory center:
1 - inspiratory center; 2 — pneumotaxic center; 3 - expiratory center; 4 - mechanoreceptors of the lung
At the moment of excitation of the inspiratory center of the medulla oblongata, excitation simultaneously occurs in the inspiratory section of the pneumotaxic center. From the latter, along the processes of its neurons, impulses come to the expiratory center of the medulla oblongata, causing its excitation and, by induction, inhibition of the inspiratory center, which leads to a change in inhalation to exhalation.
Thus, the regulation of breathing (Fig. 3) is carried out thanks to the coordinated activity of all parts of the central nervous system, united by the concept of the respiratory center. The degree of activity and interaction of the parts of the respiratory center is influenced by various humoral and reflex factors.
Vehicle respiratory center
The ability of the respiratory center to be automatic was first discovered by I.M. Sechenov (1882) in experiments on frogs under conditions of complete deafferentation of animals. In these experiments, despite the fact that afferent impulses did not enter the central nervous system, potential fluctuations were recorded in the respiratory center of the medulla oblongata.
The automaticity of the respiratory center is evidenced by Heymans' experiment with an isolated dog's head. Her brain was cut at the level of the pons and deprived of various afferent influences (the glossopharyngeal, lingual and trigeminal nerves were cut). Under these conditions, the respiratory center did not receive impulses not only from the lungs and respiratory muscles (due to the preliminary separation of the head), but also from the upper respiratory tract (due to the transection of these nerves). Nevertheless, the animal retained rhythmic movements of the larynx. This fact can only be explained by the presence of rhythmic activity of the neurons of the respiratory center.
The automation of the respiratory center is maintained and changed under the influence of impulses from the respiratory muscles, vascular reflexogenic zones, various intero- and exteroceptors, as well as under the influence of many humoral factors (blood pH, carbon dioxide and oxygen content in the blood, etc.).
The influence of carbon dioxide on the state of the respiratory center
The effect of carbon dioxide on the activity of the respiratory center is especially clearly demonstrated in Frederick's experiment with cross-circulation. In two dogs, the carotid arteries and jugular veins are cut and connected crosswise: the peripheral end of the carotid artery is connected to the central end of the same vessel of the second dog. The jugular veins are also cross-connected: the central end of the jugular vein of the first dog is connected to the peripheral end of the jugular vein of the second dog. As a result, blood from the first dog's body goes to the second dog's head, and blood from the second dog's body goes to the first dog's head. All other vessels are ligated.
After such an operation, the trachea was clamped (suffocated) in the first dog. This led to the fact that after some time an increase in the depth and frequency of breathing was observed in the second dog (hyperpnea), while the first dog experienced respiratory arrest (apnea). This is explained by the fact that in the first dog, as a result of compression of the trachea, there was no exchange of gases, and the content of carbon dioxide in the blood increased (hypercapnia occurred) and the oxygen content decreased. This blood flowed to the head of the second dog and influenced the cells of the respiratory center, resulting in hyperpnea. But in the process of enhanced ventilation of the lungs, the content of carbon dioxide in the blood of the second dog decreased (hypocapnia) and the oxygen content increased. Blood with a reduced carbon dioxide content entered the cells of the respiratory center of the first dog, and the irritation of the latter decreased, which led to apnea.
Thus, an increase in the content of carbon dioxide in the blood leads to an increase in the depth and frequency of breathing, and a decrease in the content of carbon dioxide and an increase in oxygen leads to a decrease in it until breathing stops. In those observations when the first dog was allowed to breathe various gas mixtures, the greatest change in breathing was observed with an increase in the content of carbon dioxide in the blood.
Dependence of the activity of the respiratory center on the gas composition of the blood
The activity of the respiratory center, which determines the frequency and depth of breathing, depends primarily on the tension of gases dissolved in the blood and the concentration of hydrogen ions in it. The leading importance in determining the amount of ventilation of the lungs is the tension of carbon dioxide in the arterial blood: it, as it were, creates a request for the required amount of ventilation of the alveoli.
To denote increased, normal and decreased carbon dioxide tension in the blood, the terms “hypercapnia”, “normocapnia” and “hypocapnia” are used, respectively. The normal oxygen content is called normoxia, lack of oxygen in the body and tissues - hypoxia, in the blood - hypoxemia. There is an increase in oxygen tension hyperxia. The condition in which hypercapnia and hypoxia exist simultaneously is called asphyxia.
Normal breathing at rest is called eipnea. Hypercapnia, as well as a decrease in blood pH (acidosis) are accompanied by an involuntary increase in pulmonary ventilation - hyperpnea, aimed at removing excess carbon dioxide from the body. Ventilation of the lungs increases mainly due to the depth of breathing (increasing tidal volume), but at the same time the breathing frequency also increases.
Hypocapnia and an increase in blood pH levels lead to a decrease in ventilation, and then to respiratory arrest - apnea.
The development of hypoxia initially causes moderate hyperpnea (mainly as a result of an increase in respiratory rate), which, with an increase in the degree of hypoxia, is replaced by a weakening of breathing and its cessation. Apnea due to hypoxia is deadly. Its cause is a weakening of oxidative processes in the brain, including in the neurons of the respiratory center. Hypoxic apnea is preceded by loss of consciousness.
Hypercainia can be caused by inhaling gas mixtures with carbon dioxide content increased to 6%. The activity of the human respiratory center is under voluntary control. Voluntary holding of breath for 30-60 s causes asphyxial changes in the gas composition of the blood; after the cessation of the delay, hyperpnea is observed. Hypocapnia is easily caused by voluntary increased breathing, as well as excessive artificial ventilation (hyperventilation). In a awake person, even after significant hyperventilation, respiratory arrest usually does not occur due to the control of breathing by the anterior parts of the brain. Hypocapnia is compensated gradually over several minutes.
Hypoxia is observed when rising to a height due to a decrease in atmospheric pressure, during extremely hard physical work, as well as when breathing, circulation and blood composition are impaired.
During severe asphyxia, breathing becomes as deep as possible, auxiliary respiratory muscles take part in it, and an unpleasant feeling of suffocation occurs. This kind of breathing is called dyspnea.
In general, maintaining a normal blood gas composition is based on the principle of negative feedback. Thus, hypercapnia causes an increase in the activity of the respiratory center and an increase in ventilation of the lungs, and hypocapnia causes a weakening of the activity of the respiratory center and a decrease in ventilation.
Reflex effects on breathing from vascular reflexogenic zones
Breathing responds especially quickly to various irritations. It quickly changes under the influence of impulses coming from extero- and interoreceptors to the cells of the respiratory center.
The receptors can be irritated by chemical, mechanical, temperature and other influences. The most pronounced mechanism of self-regulation is a change in breathing under the influence of chemical and mechanical stimulation of vascular reflexogenic zones, mechanical stimulation of the receptors of the lungs and respiratory muscles.
The sinocarotid vascular reflexogenic zone contains receptors that are sensitive to the content of carbon dioxide, oxygen and hydrogen ions in the blood. This is clearly shown in Heymans' experiments with an isolated carotid sinus, which was separated from the carotid artery and supplied with blood from another animal. The carotid sinus was connected to the central nervous system only by a neural pathway - Hering's nerve was preserved. With an increase in the content of carbon dioxide in the blood washing the carotid body, excitation of the chemoreceptors in this zone occurs, as a result of which the number of impulses going to the respiratory center (to the center of inspiration) increases, and a reflex increase in the depth of breathing occurs.
Rice. 3. Regulation of breathing
K - bark; GT - hypothalamus; Pvts — pneumotaxic center; APC - respiratory center (expiratory and inspiratory); Xin - carotid sinus; BN - vagus nerve; CM - spinal cord; C 3 -C 5 - cervical segments of the spinal cord; Dfn - phrenic nerve; EM - expiratory muscles; MI - inspiratory muscles; Mnr - intercostal nerves; L - lungs; Df - diaphragm; Th 1 - Th 6 - thoracic segments of the spinal cord
An increase in the depth of breathing also occurs when carbon dioxide affects the chemoreceptors of the aortic reflexogenic zone.
The same changes in breathing occur when the chemoreceptors of the named reflexogenic zones of the blood with an increased concentration of hydrogen ions are stimulated.
In those cases when the oxygen content in the blood increases, the irritation of the chemoreceptors of the reflexogenic zones decreases, as a result of which the flow of impulses to the respiratory center weakens and a reflex decrease in the respiratory rate occurs.
A reflex stimulus of the respiratory center and a factor influencing breathing is a change in blood pressure in the vascular reflexogenic zones. With an increase in blood pressure, the mechanoreceptors of the vascular reflexogenic zones are irritated, resulting in reflex respiratory depression. A decrease in blood pressure leads to an increase in the depth and frequency of breathing.
Reflex influences on breathing from the mechanoreceptors of the lungs and respiratory muscles. A significant factor causing the change in inhalation and exhalation are influences from the mechanoreceptors of the lungs, which was first discovered by Hering and Breuer (1868). They showed that every inhalation stimulates exhalation. During inhalation, stretching of the lungs irritates the mechanoreceptors located in the alveoli and respiratory muscles. The impulses that arise in them along the afferent fibers of the vagus and intercostal nerves come to the respiratory center and cause excitation of expiratory and inhibition of inspiratory neurons, causing a change in inhalation to exhalation. This is one of the mechanisms of self-regulation of breathing.
Similar to the Hering-Breuer reflex, reflex influences on the respiratory center are carried out from the receptors of the diaphragm. During inhalation in the diaphragm, when its muscle fibers contract, the endings of the nerve fibers are irritated, the impulses arising in them enter the respiratory center and cause the cessation of inhalation and the occurrence of exhalation. This mechanism is especially important during increased breathing.
Reflex influences on breathing from various receptors in the body. The considered reflex influences on breathing are permanent. But there are various short-term effects from almost all the receptors in our body that affect breathing.
Thus, when mechanical and temperature stimuli act on the exteroreceptors of the skin, breath holding occurs. When cold or hot water hits a large surface of the skin, breathing stops on inhalation. Painful irritation of the skin causes a sharp inhalation (scream) with simultaneous closure of the vocal cord.
Some changes in the act of breathing that occur when the mucous membranes of the respiratory tract are irritated are called protective respiratory reflexes: coughing, sneezing, holding your breath when exposed to strong odors, etc.
Respiratory center and its connections
Respiratory center called a set of neural structures located in various parts of the central nervous system, regulating rhythmic coordinated contractions of the respiratory muscles and adapting breathing to changing environmental conditions and the needs of the body. Among these structures, vital parts of the respiratory center are distinguished, without the functioning of which breathing stops. These include sections located in the medulla oblongata and spinal cord. In the spinal cord, the structures of the respiratory center include motor neurons that form their axons, the phrenic nerves (in the 3-5 cervical segments), and motor neurons that form the intercostal nerves (in the 2-10 thoracic segments, while the aspiratory neurons are concentrated in the 2-10 thoracic segments). 6th, and expiratory ones - in the 8th-10th segments).
A special role in the regulation of breathing is played by the respiratory center, represented by sections localized in the brain stem. Some of the neuronal groups of the respiratory center are located in the right and left halves of the medulla oblongata in the region of the bottom of the fourth ventricle. There is a dorsal group of neurons that activate the inspiratory muscles, the inspiratory section, and a ventral group of neurons that primarily control exhalation, the expiratory section.
Each of these sections contains neurons with different properties. Among the neurons of the inspiratory region, the following are distinguished: 1) early inspiratory - their activity increases 0.1-0.2 s before the onset of contraction of the inspiratory muscles and lasts throughout inspiration; 2) full inspiratory - active during inspiration; 3) late inspiratory - activity increases in the middle of inspiration and ends at the beginning of exhalation; 4) neurons of the intermediate type. Some neurons in the inspiratory region have the ability to spontaneously excite rhythmically. Neurons with similar properties are described in the expiratory section of the respiratory center. The interaction between these neural pools ensures the formation of the frequency and depth of breathing.
An important role in determining the nature of the rhythmic activity of the neurons of the respiratory center and breathing belongs to the signals coming to the center along afferent fibers from receptors, as well as from the cerebral cortex, limbic system and hypothalamus. A simplified diagram of the nerve connections of the respiratory center is shown in Fig. 4.
Neurons of the inspiratory region receive information about gas tension in arterial blood, blood pH from vascular chemoreceptors, and cerebrospinal fluid pH from central chemoreceptors located on the ventral surface of the medulla oblongata.
The respiratory center also receives nerve impulses from receptors that control the stretching of the lungs and the condition of the respiratory and other muscles, from thermoreceptors, pain and sensory receptors.
Signals received by the neurons of the dorsal part of the respiratory center modulate their own rhythmic activity and influence their formation of streams of efferent nerve impulses transmitted to the spinal cord and further to the diaphragm and external intercostal muscles.
Rice. 4. Respiratory center and its connections: IC - inspiratory center; PC—inspection center; EC - expiratory center; 1,2- impulses from stretch receptors of the respiratory tract, lungs and chest
Thus, the respiratory cycle is triggered by inspiratory neurons, which are activated due to automaticity, and its duration, frequency and depth of breathing depend on the influence on the neural structures of the respiratory center of receptor signals sensitive to the level of p0 2, pCO 2 and pH, as well as on others intero- and exteroceptors.
Efferent nerve impulses from inspiratory neurons are transmitted along descending fibers in the ventral and anterior part of the lateral cord of the white matter of the spinal cord to a-motoneurons that form the phrenic and intercostal nerves. All fibers leading to the motor neurons innervating the expiratory muscles are crossed, and of the fibers following the motor neurons innervating the inspiratory muscles, 90% are crossed.
Motor neurons, activated by the flow of nerve impulses from the inspiratory neurons of the respiratory center, send efferent impulses to the neuromuscular synapses of the inspiratory muscles, which provide an increase in the volume of the chest. Following the chest, the volume of the lungs increases and inhalation occurs.
During inhalation, stretch receptors in the airways and lungs are activated. The flow of nerve impulses from these receptors along the afferent fibers of the vagus nerve enters the medulla oblongata and activates expiratory neurons that trigger exhalation. This closes one circuit of the breathing regulation mechanism.
The second regulatory circuit also starts from the inspiratory neurons and conducts impulses to the neurons of the pneumotaxic section of the respiratory center, located in the pons of the brain stem. This department coordinates the interaction between inspiratory and expiratory neurons of the medulla oblongata. The pneumotaxic department processes information received from the inspiratory center and sends a stream of impulses that excite the neurons of the expiratory center. Streams of impulses coming from the neurons of the pneumotaxic department and from the stretch receptors of the lungs converge on the expiratory neurons, excite them, and the expiratory neurons inhibit (but according to the principle of reciprocal inhibition) the activity of the inspiratory neurons. The sending of nerve impulses to the inspiratory muscles stops and they relax. This is enough for a calm exhalation to occur. With increased exhalation, efferent impulses are sent from expiratory neurons, causing contraction of the internal intercostal muscles and abdominal muscles.
The described scheme of nerve connections reflects only the most general principle of regulation of the respiratory cycle. In reality, afferent signal flows from numerous receptors of the respiratory tract, blood vessels, muscles, skin, etc. arrive to all structures of the respiratory center. They have an excitatory effect on some groups of neurons, and an inhibitory effect on others. The processing and analysis of this information in the respiratory center of the brain stem is controlled and corrected by the higher parts of the brain. For example, the hypothalamus plays a leading role in changes in breathing associated with reactions to painful stimuli, physical activity, and also ensures the involvement of the respiratory system in thermoregulatory reactions. Limbic structures influence breathing during emotional reactions.
The cerebral cortex ensures the inclusion of the respiratory system in behavioral reactions, speech function, and the penis. The presence of influence of the cerebral cortex on the parts of the respiratory center in the medulla oblongata and spinal cord is evidenced by the possibility of arbitrary changes in the frequency, depth and holding of breathing by a person. The influence of the cerebral cortex on the bulbar respiratory center is achieved both through the cortico-bulbar pathways and through the subcortical structures (stropallidal, limbic, reticular formation).
Oxygen, carbon dioxide and pH receptors
Oxygen receptors are already active at normal levels of pO 2 and continuously send streams of signals (tonic impulses) that activate inspiratory neurons.
Oxygen receptors are concentrated in the carotid bodies (the bifurcation area of the common carotid artery). They are represented by type 1 glomus cells, which are surrounded by supporting cells and have synaptic connections with the endings of the afferent fibers of the glossopharyngeal nerve.
Type 1 glomus cells respond to a decrease in pO 2 in arterial blood by increasing the release of the mediator dopamine. Dopamine causes the generation of nerve impulses in the endings of the afferent fibers of the lingual pharyngeal nerve, which are conducted to the neurons of the inspiratory section of the respiratory center and to the neurons of the pressor section of the vasomotor center. Thus, a decrease in oxygen tension in arterial blood leads to an increase in the frequency of sending afferent nerve impulses and an increase in the activity of inspiratory neurons. The latter increase ventilation of the lungs, mainly due to increased breathing.
Receptors sensitive to carbon dioxide are present in the carotid bodies, aortic bodies of the aortic arch, as well as directly in the medulla oblongata - central chemoreceptors. The latter are located on the ventral surface of the medulla oblongata in the area between the exit of the hypoglossal and vagus nerves. Carbon dioxide receptors also perceive changes in the concentration of H + ions. Arterial vessel receptors respond to changes in pCO 2 and blood plasma pH, and the flow of afferent signals from them to inspiratory neurons increases with an increase in pCO 2 and (or) a decrease in arterial blood plasma pH. In response to the receipt of more signals from them to the respiratory center, ventilation of the lungs reflexively increases due to deepening of breathing.
Central chemoreceptors respond to changes in pH and pCO 2, cerebrospinal fluid and intercellular fluid of the medulla oblongata. It is believed that central chemoreceptors primarily respond to changes in the concentration of hydrogen protons (pH) in the interstitial fluid. In this case, a change in pH is achieved due to the easy penetration of carbon dioxide from the blood and cerebrospinal fluid through the structures of the blood-brain barrier into the brain, where, as a result of its interaction with H 2 0, carbon dioxide is formed, dissociating with the release of hydrogen gases.
Signals from central chemoreceptors are also carried to the inspiratory neurons of the respiratory center. The neurons of the respiratory center themselves exhibit some sensitivity to shifts in the pH of the interstitial fluid. A decrease in pH and accumulation of carbon dioxide in the cerebrospinal fluid is accompanied by activation of inspiratory neurons and an increase in pulmonary ventilation.
Thus, the regulation of pCO 0 and pH are closely related both at the level of effector systems that influence the content of hydrogen ions and carbonates in the body, and at the level of central nervous mechanisms.
With the rapid development of hypercapnia, the increase in ventilation of the lungs is only approximately 25% caused by stimulation of peripheral chemoresceggors of carbon dioxide and pH. The remaining 75% is associated with activation of the central chemoreceptors of the medulla oblongata by hydrogen protons and carbon dioxide. This is due to the high permeability of the blood-brain barrier to carbon dioxide. Since the cerebrospinal fluid and intercellular fluid of the brain have a much lower capacity of buffer systems than blood, an increase in pCO2 similar in magnitude to blood creates a more acidic environment in the cerebrospinal fluid than in the blood:
With prolonged hypercapnia, the pH of the cerebrospinal fluid returns to normal due to a gradual increase in the permeability of the blood-brain barrier to HC03 anions and their accumulation in the cerebrospinal fluid. This leads to a decrease in ventilation, which has developed in response to hypercapnia.
An excessive increase in the activity of pCO 0 and pH receptors contributes to the emergence of subjectively painful, painful sensations of suffocation and lack of air. This is easy to verify if you hold your breath for a long time. At the same time, with a lack of oxygen and a decrease in p0 2 in arterial blood, when pCO 2 and blood pH are maintained normal, a person does not experience discomfort. The consequence of this may be a number of dangers that arise in everyday life or when a person breathes gas mixtures from closed systems. Most often they occur with carbon monoxide poisoning (death in a garage, other household poisonings), when a person, due to the absence of obvious sensations of suffocation, does not take protective actions.
