Automaton of the human heart: definition, description, nodes and gradient

The automaton of the heart is a rhythmic contraction of the organ under the action of impulses that arise in it without the influence of stimuli from the outside. Automatism is inherent in the entire body and in separate parts, but not in the heart muscle. There is evidence of this phenomenon - the rhythmic contraction of the organ of animals and man, isolated from everything and taken out of the body.

First-Order Drivers

In determining what is meant by automatic heart, it was found that nerve impulses can be generated in cells of the atypical myocardium. If the person is healthy, then this process is observed next to the sinoatrial node due to the difference in the cells by properties and structure from other structural components. They are arranged in groups, have the form of a spindle, and they are surrounded by a basal membrane. The second name of these cells is the drivers of the rhythm of the first order (pacemakers). Exchange processes in them occur at a high rate, and for this reason, metabolites remain in the intercellular fluid, not having time to endure.

In addition, the characteristic properties are as follows:

• Quite high permeability for calcium and sodium ions.
• A small value of the membrane potential.

Due to the difference in the concentration of sodium and potassium, the sodium-potassium pump is not very active.

Heart Automatics Research

For quite a long time, the automatic heart was not completely investigated, even despite the increased interest of scientists in this process. The method of Stannius ligatures is a well-known cycle of experiments carried out on the basis of the removal of certain parts of the frog's heart by the application of dressings. As a result, it turned out that there are 2 centers of automation in the body at least.

One of them is located in the venous sinus, promotes the rhythm of contractions, the second - is in the part between the ventricle and atria (it is also called hidden). His work begins only after the exclusion of 1 center. The heart muscle, which is remote from both centers, works - shrinks - on its own. Thus, the automaton of the human heart is associated with the impulses emanating from these centers.

The Landerhard Method

In order to reduce the heart out of the body, the method of Landergorf is used. The meaning is as follows:

1. The heart is excised and a cannula is inserted into the aorta, which is connected to a vessel of glass.
2. Ringer's solution is poured into the vessel together with glucose, or it is possible to add defibrinated blood.
3. The solution is saturated with oxygen and heated to a certain temperature (about 48 degrees Celsius).
4. The fluid begins to flow under pressure into the aorta, the valves overlap, and the fluid is directed to the coronary arteries, the function of which is to feed the entire organ.

Under such conditions, the organ of an animal or a human being is able to work for a long time, this is the automaton of the heart. Using this method, you can return the pulse of the heart, which has already stopped a few hours ago. In the early 20th century, for the first time, the organ of a young child was revitalized, and later the heart was restored , which did not function for almost 48 hours. After passing the solution through the vessels, the heartbeat lasted about 15 hours.

Description of the process of automation

The automaton of the human heart begins with the diastole phase, its manifestation is the movement of sodium into the cell. The membrane potential in this case is significantly reduced, the value tends to the minimum level of depolarization. The charge of the membrane decreases, and a slow depolarization of the diastole begins. The channels for calcium and sodium are opened in the phase of rapidly flowing depolarization, the ions begin to actively go to the cell. As a result, the charge first decreases sharply and reaches zero, after which it changes to the opposite one. The sodium moves until the equilibrium of its ions (electrochemical) is reached.

The plateau phase comes. Here the movement of calcium continues. The tissue of the heart remains unexcitable at this moment. When equilibrium is reached over the corresponding ions, the phase ends and repolarization occurs, which means the return of the membrane charge to the initial mark.

Automated Heart Units

A special place in the complex process is occupied by the nodes of the heart's automaticity. A first-order node is called a sinoatrial. It is the driver of a rhythm of the first order, which provides a normal frequency of contractions of the heart. It is located near the place where the upper vena cava enters. Its structure is a small number of fibers of the heart muscles with neuronal endings. A node of the second order is called the atrioventricular node. This is a hidden driver of rhythm of the second order. The third-order node is represented by the cells of the conducting ventricular system.

All low-order rhythm drivers support the frequency of organ contractions if there is a complete heart block. In this case, the frequency of contractions of the ventricles approaches the minimum mark, and patients are implanted with an electric pacemaker, that is, an artificial pacemaker.

The emergence of potentials

The potential of the sinoatrial node differs from the usual smaller amplitude - by 50 mV. In the normal state, potentials appear at the site due to the presence of cells that are drivers of the first-order rhythm. The rest of the cardiac parts, under certain conditions, also generate nerve impulses when an additional stimulus is turned on, and also the first-order node is turned off. In this case, the generation of pulses at a second-order site (frequency about 60 times / min) is observed. When stimulated at the node, the cells of the bundle are excited, the frequency decreases to 30 (the drivers of the third-order rhythm).

The action potential of all pacemakers is directly proportional to the high membrane permeability for calcium and sodium ions, as well as to a decrease in the permeability of potassium ions.

Automatic gradient

Automaton of the heart in normal conditions of all parts of the system is suppressed by a sino-arterial node, which "imposes" its rhythm. For this reason, all components of the system with their own rhythm are rebuilt to work at a single pace. The gradient of the heart's automaticity is a phenomenon in which the ability to automate decreases with distance from the place of generalization of impulses, that is, a node of the first order.

It is still unknown what causes a sharp change in the cellular charge, which arises spontaneously. Automaton of the heart can be associated with the maintenance in the drivers of the rhythm of acetylcholine. Many scientists believe that the phenomenon is due to the peculiarities of metabolic processes in these driver cells, which are able to change the state of surface membranes.