What is heart automatism? The answer to this question can be found in the article below. In addition, it contains information about human he alth disorders associated with the named concept.
What is heart automatism?
Muscle fibers in the human body have the ability to respond to an irritating impulse by contraction and then consistently transmit this contraction throughout the muscle structure. It has been proven that an isolated cardiac muscle is able to independently generate excitation and perform rhythmic contractions. This ability is called automatism of the heart.
Causes of cardiac automatism
You can understand what the automatism of the heart is from the following. The heart has a specific ability to generate an electrical impulse and then conduct it to muscle structures.
Sinoatrial node - an accumulation of pacemaker cells of the first type (contains about 40% of mitochondria, loosely located myofibrils, no T-system, contains a large amount of free calcium, has an underdevelopedsarcoplasmic reticulum), located in the right wall of the superior vena cava, at the confluence of the right atrium.
The atrioventricular node is formed by transitional cells of the second type, which conduct an impulse from the sinoatrial node, but under special conditions they can independently generate an electrical charge. Transitional cells contain fewer mitochondria (20-30%) and somewhat more myofibrils than first-order cells. The atrioventricular node is located in the interatrial septum, through it the excitation is transmitted to the bundle and legs of the bundle of His (they contain 20-15% of mitochondria).
Purkinje fibers are the next step in the transmission of excitation. They depart approximately at the level of the middle of the septum from each of the two legs of the bundle of His. Their cells contain about 10% mitochondria and are somewhat more similar in structure to cardiac muscle fibers.
The spontaneous occurrence of an electrical impulse occurs in the pacemaker cells of the sinoatrial node, which potentiates a wave of excitation that stimulates 60-80 contractions per minute. He is a first order driver. Then the resulting wave is transmitted to the conductive structures of the second and third levels. They are capable of both conducting excitation waves and independently inducing contractions of a lower frequency. The driver of the second level after the sinus node is the atrioventricular node, which is able to independently create 40-50 discharges per minute in the absence of overwhelming activity of the sinus node. Further excitementis transmitted to the structures of the His bundle, which reproduces 30-40 contractions per minute, then the electric charge flows to the legs of the His bundle (25-30 pulses per minute) and the Purkinje fiber system (20 pulses per minute) and enters the working muscle cells of the myocardium.
Usually, impulses from the sinoatrial node suppress the independent ability to electrical activity of the underlying structures. If the functioning of the driver of the first order is disturbed, then the lower links of the conducting system take over its work.
Chemical processes that ensure the automatism of the heart
What is the automatism of the heart in terms of chemistry? At the molecular level, the basis for the independent occurrence of an electric charge (action potential) on the membranes of pacemaker cells is the presence of a so-called impulsator. His work (heart automatism function) contains three stages.
Stages of the pulser:
- 1st phase preparatory (as a result of the interaction of superoxide oxygen with positively charged phospholipids on the surface of the pacemaker cell membrane, it acquires a negative charge, this violates the resting potential);
- 2nd phase of active transport of potassium and sodium, during which the external charge of the cell becomes +30 mW;
- 3rd phase of the electrochemical jump - uses the energy that occurs during the utilization of reactive oxygen species (ionized oxygen and hydrogen peroxide) using the enzymes superoxide dismutase andcatalase. The resulting energy quanta increase the biopotential of the pacemaker so much that it causes an action potential.
The processes of generating an impulse by pacemaker cells necessarily occur in conditions of sufficient presence of molecular oxygen, which is delivered to them by erythrocytes of the flowing blood.
Decrease in the level of work or partial cessation of the functioning of one or more stages of the impulse system disrupts the coordinated work of the pacemaker cells, which causes arrhythmias. Blocking one of the processes of this system causes sudden cardiac arrest. Having understood what the automatism of the heart is, one can realize this process as well.
Influence of the autonomic nervous system on the functioning of the heart muscle
In addition to its own ability to generate electrical impulses, the work of the heart is controlled by signals from the sympathetic and parasympathetic nerve endings innervating the muscle, the failure of which may disrupt the automatism of the heart.
The impact of the sympathetic department accelerates the work of the heart, has a stimulating effect. Sympathetic innervation has a positive chronotropic, inotropic, dromotropic effect.
Under the predominant action of the parasympathetic nervous system, the processes of depolarization of pacemaker cells slow down (inhibitory effect), which means that the heart rate slows down (negative chronotropic effect), the conduction inside the heart decreases (negative dromotropic effect), the energy of systoliccontraction (negative inotropic effect), but the excitability of the heart increases (positive bathmotropic effect). The latter is also taken as a violation of the automatism of the heart.
Causes of impaired automatism of the heart
- Myocardial ischemia.
- Inflammation.
- Intoxication.
- Sodium, potassium, magnesium, calcium imbalance.
- Hormonal dysfunction.
- Violation of the impact of autonomous sympathetic and parasympathetic endings.
Types of arrhythmias due to impaired automatism of the heart
- Sinus tachy- and bradycardia.
- Respiratory (juvenile) arrhythmia.
- Extrasystolic arrhythmia (sinus, atrial, atrioventricular, ventricular).
- Paroxysmal tachycardias.
Distinguish between arrhythmias due to impaired automatism and conduction with the formation of a circulation wave of excitation (re-entry wave) in one specific or several parts of the heart, resulting in atrial fibrillation or flutter.
Ventricular fibrillation is one of the most life-threatening arrhythmias, resulting in sudden cardiac arrest and death. The most effective treatment is electrical defibrillation.
Conclusion
So, having considered what the automatism of the heart is, we can understand what violations are possible in case of a disease. This, in itsturn, makes it possible to fight the disease with more optimal and effective methods.
