Protective airway reflexes: sneezing and coughing (briefly). Reflex regulation of breathing Protective respiratory reflexes include

Details

The nervous system usually sets such alveolar ventilation rate, which almost exactly corresponds to the needs of the body, so the tension of oxygen (Po2) and carbon dioxide (Pco2) in arterial blood changes little even during heavy physical exertion and during most other cases of respiratory stress. This article sets out neurogenic system function breathing regulation.

Anatomy of the respiratory center.

respiratory center consists of several groups of neurons located in the brainstem on both sides of the medulla oblongata and the bridge. They are divided into three large groups of neurons:

dorsal group of respiratory neurons, located in the dorsal part of the medulla oblongata, which mainly causes inspiration;
ventral group of respiratory neurons, which is located in the ventrolateral part of the medulla oblongata and mainly causes exhalation;
pneumotaxic center, which is located dorsally at the top of the pons and controls mainly the rate and depth of breathing. The most important role in the control of breathing is performed by the dorsal group of neurons, so we will consider its functions first.

Dorsal group respiratory neurons extends for most of the length of the medulla oblongata. Most of these neurons are located in the nucleus of the solitary tract, although additional neurons located in the nearby reticular formation of the medulla oblongata are also important for the regulation of respiration.

The solitary tract nucleus is the sensory nucleus for wandering and glossopharyngeal nerves, which transmit sensory signals to the respiratory center from:

peripheral chemoreceptors;
baroreceptors;
various types of lung receptors.

Generation of respiratory impulses. Breathing rhythm.

Rhythmic inspiratory discharges from the dorsal group of neurons.

Basic breathing rhythm generated mainly by the dorsal group of respiratory neurons. Even after transection of all peripheral nerves entering the medulla oblongata and the brainstem below and above the medulla oblongata, this group of neurons continues to generate repetitive bursts of inspiratory neuron action potentials. The underlying cause of these volleys is unknown.

After some time, the activation pattern is repeated, and this continues throughout the life of the animal, so most physiologists involved in the physiology of respiration believe that humans also have a similar network of neurons located within the medulla oblongata; it is possible that it includes not only the dorsal group of neurons, but also the adjacent parts of the medulla oblongata, and that this network of neurons is responsible for the main rhythm of breathing.

Increasing inspiration signal.

Signal from neurons that is transmitted to the inspiratory muscles, in the main diaphragm, is not an instantaneous burst of action potentials. During normal breathing gradually increases for about 2 sec. After that he drops sharply for about 3 seconds, which stops the excitation of the diaphragm and allows the elastic traction of the lungs and chest wall to exhale. Then the inspiratory signal starts again, and the cycle repeats again, and in the interval between them there is an exhalation. Thus, the inspiratory signal is an increasing signal. Apparently, such an increase in the signal provides a gradual increase in lung volume during inspiration instead of a sharp inspiration.

Two moments of the rising signal are controlled.

The rate of increase of the rising signal, so during difficult breathing, the signal rises quickly and causes rapid filling of the lungs.
The limiting point at which the signal suddenly disappears. This is a common way to control the rate of breathing; the sooner the rising signal stops, the shorter the inspiratory time. At the same time, the duration of exhalation is also reduced, as a result, breathing quickens.

Reflex regulation of breathing.

Reflex regulation of breathing is carried out due to the fact that the neurons of the respiratory center have connections with numerous mechanoreceptors of the respiratory tract and alveoli of the lungs and receptors of vascular reflexogenic zones. The following types of mechanoreceptors are found in the human lungs:

irritant, or rapidly adapting, respiratory mucosal receptors;
Stretch receptors of smooth muscles of the respiratory tract;
J-receptors.

Reflexes from the mucous membrane of the nasal cavity.

Irritation of irritant receptors of the nasal mucosa, for example, tobacco smoke, inert dust particles, gaseous substances, water causes narrowing of the bronchi, glottis, bradycardia, decreased cardiac output, narrowing of the lumen of the vessels of the skin and muscles. The protective reflex is manifested in newborns during short-term immersion in water. They experience respiratory arrest, preventing the penetration of water into the upper respiratory tract.

Reflexes from the throat.

Mechanical irritation of the mucosal receptors of the back of the nasal cavity causes a strong contraction of the diaphragm, external intercostal muscles, and, consequently, inhalation, which opens the airway through the nasal passages (aspiration reflex). This reflex is expressed in newborns.

Reflexes from the larynx and trachea.

Numerous nerve endings are located between the epithelial cells of the mucous membrane of the larynx and main bronchi. These receptors are irritated by inhaled particles, irritating gases, bronchial secretions, and foreign bodies. All this calls cough reflex, manifested in a sharp exhalation against the background of narrowing of the larynx and contraction of the smooth muscles of the bronchi, which persists for a long time after the reflex.
The cough reflex is the main pulmonary reflex of the vagus nerve.

Reflexes from bronchiole receptors.

Numerous myelinated receptors are found in the epithelium of the intrapulmonary bronchi and bronchioles. Irritation of these receptors causes hyperpnea, bronchoconstriction, contraction of the larynx, hypersecretion of mucus, but is never accompanied by cough. Receptors most sensitive to three types of stimuli:

tobacco smoke, numerous inert and irritating chemicals;
damage and mechanical stretching of the airways during deep breathing, as well as pneumothorax, atelectasis, the action of bronchoconstrictors;
pulmonary embolism, pulmonary capillary hypertension and pulmonary anaphylactic phenomena.

Reflexes from J-receptors.

in the alveolar septa in contact with capillaries specific J receptors. These receptors are especially susceptible to interstitial edema, pulmonary venous hypertension, microembolism, irritating gases and inhalation narcotic substances, phenyl diguanide (with intravenous administration of this substance).

Stimulation of J-receptors causes first apnea, then superficial tachypnea, hypotension and bradycardia.

Hering-Breuer reflex.

Inflation of the lungs in an anesthetized animal reflexively inhibits inhalation and causes exhalation.. Transection of the vagus nerves eliminates the reflex. Nerve endings located in the bronchial muscles act as receptors for lung stretch. They are referred to as slowly adapting lung stretch receptors, which are innervated by myelinated fibers of the vagus nerve.

Hering-Breuer reflex controls the depth and frequency of breathing. In humans, it has physiological significance at respiratory volumes over 1 liter (for example, during physical activity). In an awake adult, short-term bilateral vagus nerve block with local anesthesia does not affect either the depth or the rate of breathing.
In newborns, the Hering-Breuer reflex is clearly manifested only in the first 3-4 days after birth.

Proprioceptive breath control.

The receptors of the chest joints send impulses to the cerebral cortex and are the only source of information about chest movements and tidal volumes.

The intercostal muscles, to a lesser extent the diaphragm, contain a large number of muscle spindles.. The activity of these receptors is manifested during passive muscle stretching, isometric contraction and isolated contraction of intrafusal muscle fibers. Receptors send signals to the corresponding segments of the spinal cord. Insufficient shortening of the inspiratory or expiratory muscles enhances the impulse from the muscle spindles, which dose the muscle effort through motor neurons.

Chemoreflexes of breathing.

Partial pressure of oxygen and carbon dioxide(Po2 and Pco2) in the arterial blood of humans and animals is maintained at a fairly stable level, despite significant changes in O2 consumption and CO2 release. Hypoxia and decrease in blood pH ( acidosis) cause increased ventilation(hyperventilation), and hyperoxia and increased blood pH ( alkalosis) - decrease in ventilation(hypoventilation) or apnea. Control over the normal content in the internal environment of the body of O2, CO2 and pH is carried out by peripheral and central chemoreceptors.

adequate stimulus for peripheral chemoreceptors is decrease in arterial blood Po2, to a lesser extent, an increase in Pco2 and pH, and for central chemoreceptors - an increase in the concentration of H + in the extracellular fluid of the brain.

Arterial (peripheral) chemoreceptors.

Peripheral chemoreceptors found in carotid and aortic bodies. Signals from arterial chemoreceptors through the carotid and aortic nerves initially arrive at the neurons of the nucleus of the single bundle of the medulla oblongata, and then switch to the neurons of the respiratory center. The response of peripheral chemoreceptors to a decrease in Pao2 is very rapid, but non-linear. With Pao2 within 80-60 mm Hg. (10.6-8.0 kPa) there is a slight increase in ventilation, and when Pao2 is below 50 mm Hg. (6.7 kPa) there is a pronounced hyperventilation.

Paco2 and blood pH only potentiate the effect of hypoxia on arterial chemoreceptors and are not adequate stimuli for this type of respiratory chemoreceptors.
Response of arterial chemoreceptors and respiration to hypoxia. Lack of O2 in arterial blood is the main irritant of peripheral chemoreceptors. Impulse activity in the afferent fibers of the carotid sinus nerve stops when Pao2 is above 400 mm Hg. (53.2 kPa). With normoxia, the frequency of discharges of the carotid sinus nerve is 10% of their maximum response, which is observed at Pao2 of about 50 mm Hg. and below. The hypoxic respiration reaction is practically absent in the indigenous inhabitants of the highlands and disappears approximately 5 years later in the inhabitants of the plains after the beginning of their adaptation to the highlands (3500 m and above).

central chemoreceptors.

The location of the central chemoreceptors has not been definitively established. Researchers believe that such chemoreceptors are located in the rostral regions of the medulla oblongata near its ventral surface, as well as in various zones of the dorsal respiratory nucleus.
The presence of central chemoreceptors is proved quite simply: after transection of the sinocarotid and aortic nerves in experimental animals, the sensitivity of the respiratory center to hypoxia disappears, but the respiratory response to hypercapnia and acidosis is completely preserved. Transection of the brainstem directly above the medulla oblongata does not affect the nature of this reaction.

adequate stimulus for central chemoreceptors is change in the concentration of H * in the extracellular fluid of the brain. The function of a regulator of threshold pH shifts in the region of central chemoreceptors is performed by the structures of the blood-brain barrier, which separates blood from the extracellular fluid of the brain. O2, CO2, and H+ are transported through this barrier between the blood and the extracellular fluid of the brain. The transport of CO2 and H+ from the internal environment of the brain into the blood plasma through the structures of the blood-brain barrier is regulated by the enzyme carbonic anhydrase.
Breathing response to CO2. Hypercapnia and acidosis stimulate, while hypocapnia and alkalosis inhibit central chemoreceptors.

The airways are divided into upper and lower. The upper ones include the nasal passages, nasopharynx, the lower larynx, trachea, bronchi. The trachea, bronchi and bronchioles are the conduction zone of the lungs. The terminal bronchioles are called the transition zone. They have a small number of alveoli, which contribute little to gas exchange. The alveolar ducts and alveolar sacs belong to the exchange zone.

Physiological is nasal breathing. When cold air is inhaled, a reflex expansion of the vessels of the nasal mucosa and a narrowing of the nasal passages occur. This contributes to better heating of the air. Its hydration occurs due to moisture secreted by the glandular cells of the mucosa, as well as lacrimal moisture and water filtered through the capillary wall. Purification of the air in the nasal passages occurs due to the deposition of dust particles on the mucosa.

Protective respiratory reflexes occur in the airways. When inhaling air containing irritating substances, there is a reflex slowdown and a decrease in the depth of breathing. At the same time, the glottis narrows and the smooth muscles of the bronchi contract. When the irritant receptors of the epithelium of the mucous membrane of the larynx, trachea, bronchi are stimulated, impulses from them arrive along the afferent fibers of the upper laryngeal, trigeminal and vagus nerves to the inspiratory neurons of the respiratory center. There is a deep breath. Then the muscles of the larynx contract and the glottis closes. Expiratory neurons are activated and exhalation begins. And since the glottis is closed, the pressure in the lungs increases. At a certain moment, the glottis opens and air leaves the lungs at high speed. There is a cough. All these processes are coordinated by the cough center of the medulla oblongata. When dust particles and irritating substances are exposed to the sensitive endings of the trigeminal nerve, which are located in the nasal mucosa, sneezing occurs. Sneezing also initially activates the inspiratory center. Then there is a forced exhalation through the nose.

There are anatomical, functional and alveolar dead space. Anatomical is the volume of the airways - the nasopharynx, larynx, trachea, bronchi, bronchioles. It does not undergo gas exchange. Alveolar dead space refers to the volume of alveoli that are not ventilated or there is no blood flow in their capillaries. Therefore, they also do not participate in gas exchange. Functional dead space is the sum of anatomical and alveolar. In a healthy person, the volume of alveolar dead space is very small. Therefore, the size of the anatomical and functional spaces is almost the same and is about 30% of the respiratory volume. On average 140 ml. In violation of ventilation and blood supply to the lungs, the volume of functional dead space is much larger than the anatomical one. At the same time, the anatomical dead space plays an important role in the processes of respiration. The air in it is warmed, humidified, cleaned of dust and microorganisms. Here respiratory protective reflexes are formed - coughing, sneezing. It senses smells and produces sounds.

sneezing- this is an unconditioned reflex, with the help of which dust, foreign particles, mucus, vapors of caustic chemicals, etc. are removed from the nasal cavity. Due to this, the body prevents them from entering other respiratory tracts. The receptors for this reflex are located in the nasal cavity, and its center is in the medulla oblongata. Sneezing can also be a symptom of an infectious disease accompanied by a runny nose. With a stream of air from the nose, when chi-hani, a lot of viruses and bacteria are thrown out. This frees the body from infectious agents, but contributes to the spread of infection. That's why, When you sneeze, be sure to cover your nose with a tissue.

Cough- it is also a protective unconditioned reflex, aimed at removing dust, foreign particles through the oral cavity, if they got into the larynx, pharynx, trachea or bronchi, sputum, which is formed during inflammation of the respiratory tract. Sensitive cough receptors are found in the mucous membrane of the respiratory tract. Its center is in the medulla oblongata. material from the site

In smokers, the protective cough reflex is first enhanced through irritation of its receptors with tobacco smoke. That's why they cough all the time. However, after some time, these receptors die along with the ciliary and secretory cells. The cough disappears, and the sputum continuously formed in smokers lingers in the unprotected airways. This leads to severe inflammatory lesions of the entire respiratory system. Smoker's chronic bronchitis occurs. A person who smokes snores loudly during sleep due to the accumulation of mucus in the bronchi.

On this page, material on the topics:

Tidal volume respiratory center protective respiratory reflexes briefly
What reflexes are sneezing and coughing
Sneezed and phlegm got into the respiratory tract
Protective respiratory reflexes sneezing and coughing

Questions about this item:

It has now been established that stimulation of any visceral or somatic nerve can affect respiration and that many afferent pathways are involved in respiratory reflexes. There are at least nine respiratory reflexes originating from the organs of the chest, and five of them are well enough appreciated and deserve special mention.

Inflate reflex(Hering Breuer). Hering and Breuer in 1868 showed that keeping the lungs inflated reduced the rate of inspiration in anesthetized animals, keeping the lungs collapsed had the opposite effect. Vagotomy prevents the development of these reactions, which proves their reflex origin; Adrian in 1933 showed that this reflex is carried out through stretch receptors in the lung, which are not encapsulated and are believed to be smooth muscle endings, usually located in the walls of the bronchi and bronchioles. The inflation reflex is present in newborns, but weakens with age. Its importance faded into the background when the role of the chemical regulation of respiration was established. At present, it is considered only as one of the many chemical and neural mechanisms that regulate respiration. Apparently, it affects the tone of the bronchial muscles.

Decay reflex. Lung collapse stimulates respiration by activating a group of receptors thought to be located in or distal to the respiratory bronchioles. The precise role of the collapse reflex is difficult to determine, as lung collapse alters breathing through many other mechanisms as well. Although the extent of the effect of the collapse reflex during normal breathing is not clear, it probably has a role in forced collapse of the lung and in atelectasis, with the frequency and force of inspiration being increased by its action in these circumstances. The vagotomy usually removes the relapse reflex in animals.

paradoxical reflex. Head in 1889 showed that inflation of the lungs in rabbits with partial blockade of the vagus nerve (during the recovery period after freezing) does not give an inflation reflex, but, on the contrary, leads to a prolonged and powerful contraction of the diaphragm. The reflex is removed by crossing the vagus and, since its action is opposite to that of the normal inflation reflex, it is called "paradoxical". Two observations support the possible physiological role of the paradoxical reflex. Occasional deep breaths interspersing normal quiet breathing and apparently preventing microatelectasis that might otherwise occur disappear after vagotomy and have been suggested to be related to the paradoxical reflex. Cross et al. convulsive sighs were observed during inflating the lungs of newborns in the first 5 days. They suggested that the mechanism in this case is similar to the paradoxical reflex and may provide aeration of the lung of the newborn.

Reflexes of irritation. The cough reflex is associated with subepithelial receptors in the trachea and bronchi. Accumulations of these receptors are usually found on the posterior wall of the trachea and bronchial bifurcations (up to the proximal end of the respiratory bronchioles) and are most numerous in carina. In order to perform well bronchoscopy under local anesthesia, it is essential that the bifurcation of the trachea is adequately anesthetized.

Inhalation of mechanical or chemical irritants leads to reflex closure of the glottis and bronchospasm. There is likely a peripheral internal reflex arc in the bronchial wall with a central component acting through the vagus nerve.

Pulmonary vascular reflex. An increase in pressure in the lungs of cats and dogs leads to the appearance of accelerated shallow breathing in combination with hypotension. This action can be prevented by vagotomy, and it manifests itself more when stretching not so much the arterial as the venous bed. The exact location of the receptors has not yet been determined, although recent information suggests that they are located in the pulmonary veins or capillaries.

With multiple pulmonary embolism in animals and humans, prolonged, rapid, shallow breathing occurs. In animals, this action is stopped by vagotomy. As well as this respiratory reflex, many other changes that affect breathing occur during embolism. These include a drop in blood pressure and increased heart rate, generalized pulmonary vasospasm and possible edema, decreased lung compliance, and increased airflow resistance. Since the administration of 5-hydroxytryptamine closely resembles the action of an embolism, it is believed that this substance is released during the formation of vascular thrombi, probably from platelets. That this is not a complete explanation is supported by the fact that anti-5-hydroxytryptamine drugs have only a partial effect in reversing the events associated with embolism.

Reflexes in the upper airways. They are primarily protective. Sneezing and coughing are marked efforts of a reflex nature. Sneezing is a reaction to irritation in the nose, but can also occur when a bright light is suddenly shining on the retina. Cough is a reaction to irritation of the departments located downward from the throat. The closure reflex (gag) prevents unwanted substances from entering the esophagus, but the glottis also closes. There are reports that as a result of irritation of the nose or pharynx, bronchoconstrictor inhibitory cardiac activity and vasomotor reflexes occur.

Other respiratory reflexes. Reflexes from the respiratory muscles, tendons and joints, from the heart and systemic circulation, from the digestive tract, from pain and temperature receptors, and some postural reflexes can all affect breathing. A well-known example is the gasping for air after sudden exposure to cold on the skin.

For a detailed description of respiratory reflexes, we refer the reader to the review of Widdicombe.