Every second, small electric currents are created in our heart to initiate contractions and ensure that it continues to work
The heart moves by electrical impulses.
Our heart is like a pump that never rests. The distribution of blood is made for the lungs and clean blood, the whole body is organized by a system that produces an electric current. Every second, small electric currents are created in our heart to initiate contractions and ensure that it continues to function. Each impulse of current begins in a certain place and is distributed throughout the heart.
The heart is composed of four compartments: two atria or atria and two ventricles. The blood that reaches the heart first accumulates in the atria and, from there, it is sent to the ventricles. Then, it is redistributed to the rest of the body by means of the contractions that occur in the ventricles. The balance of this whole process depends on the electric currents in our heart.
How is the electric current formed?
There is a specific region of the heart called the sinus node. The sinus node is an area approximately 15 mm long, 3 mm wide and 1 mm thick, and is located in the right atrium of the heart. The cells in this area are responsible for producing the electric currents, and they are formed in a different way from the rest of the cells responsible for producing the contractions. This is where the electric currents of our heart rhythmically occur. Every cell of our body contains elements such as sodium, calcium, potassium and chlorine, with electric charge. The electrically charged elements are called ions.
Ions also exist in the extracellular environment. The cell nuclei on these sides, both internal and external, differ from each other. This situation causes a difference in the electrical potential between the inside and the outside of the cell.
This difference is called membrane potential. Periodically, cases of sinus cells show sudden changes, which implies that they increase and decrease suddenly. Since the cells are in close contact with each other, a change in a cell’s membrane potential triggers the change in the membrane potential of another cell. The electrical current that allows the contraction of the heart is produced by this continuous influence between the cells. As an average figure, approximately 70 electrical impulses per minute occur in the sinus node. These currents begin to occur when the person is in the womb of his mother and continues throughout his life. The heart of a creation begins to beat with only 22 days of age. However, the size of the embryo at this time has not yet reached 1 cm. Is not that force the one that creates the heartbeat of such a small nation and keeps the heart incredible for all of life?
How is the electric current distributed?
Another nodule called the atrioventricular nodule was created between the atria and the ventricles of our heart. While the current comes from the sinus node is transmitted to the entire atrium, through this nodule the current is sent to certain fibers in particular. The mission of this nodule is to stop the current coming from the sinus node for a while. Why does this current stop momentarily? As the blood can only enter the ventricles at rest and in them, the contraction of these ventricles is deactivated while the contraction of the atria occurs.
Through this process, the blood from the atrium can enter the ventricle. Therefore, the blood fills the ventricles and from there it can be distributed throughout the body. The blood circulation is activated impeccably, allowing the atrium to perform its function while the ventricles wait.
After passing through the atrioventricular nodule, electrical current passes through the Purkinje fibers. These fibers surround the ventricles like a tissue and are made up of cells that can conduct electrical current very quickly. Compared to the atrioventricular node, in Purkinje fibers, the electric current can be approximately 150 times faster. Therefore, the current reaches all points of the ventricles in a short period of time. Each muscle in the ventricles contracts in less than a tenth of a second.
The muscles of the ventricles contract rapidly, one by one, depending on when the current arrives. The contraction begins at the end of the ventricles and continues to the main veins that leave the heart. Thanks to this ordered and harmonious contraction, the blood is pumped from the end of the heart to the main veins that leave it to be distributed throughout the body. Because all the muscles of the ventricle are stimulated so quickly, the contraction also occurs very quickly, producing a strong pumping effect. The design of this system is incredibly intelligent, even in its smallest detail.
The potential movement of the heart muscle
Like all cells in our body, the cells of the heart also have a membrane potential. As we said earlier, this membrane potential is the result of the difference in the concentrations of inter and extracellular ions. The charges of these ions are different from each other. For example, sodium and potassium have a positive charge (+1), calcium has two positive charges (+2), and chlorine has a negative charge (-1). The potential of a cell at rest is negative. This means that there are more negative ions inside the cell if we compare it with their environment. Sodium, calcium and potassium ions have mobility through the membrane. While sodium and calcium are found in higher concentrations outside the cell, potassium is concentrated in a greater extent inside it, compared to the environment that surrounds it. In the cell membrane there are channels that have been created to allow the passage of ions through them. The sudden increase in membrane potential referred to above causes a sudden surge of sodium ions going into the cell. This movement is so fast that it ends in a tenth of a second. Just after the entry of sodium ions, calcium ions also penetrate. Because these ions have a positive charge, the membrane potential becomes positive.
Once inside the cell, calcium ions also release those that are stored inside the cell. By generating the protein necessary for these contractions to occur, calcium ions become a means to produce contraction of the heart muscles. Simultaneously, the potassium channels open, and these ions, which are inside the cell, pass to the extracellular medium. The loss of positive ions causes the membrane potential to be negative again. This again produces a sudden change in the membrane potential, which is the way in which the electric current is produced.
However, at this point there is an extra amount of calcium and sodium inside the cell and additional amounts of potassium out of it. These concentrations have to return to their initial values so that the next change in the membrane can occur. This task is assigned to a protein called sodium-potassium pump, which expels sodium from the cell and introduces potassium. If this pump had not been created, it would be impossible to re-establish the ionic balance in any of the cells within the body, and this would have caused the life of these cells to come to an end. However, precisely because of the remarkable complexity of our cells, life becomes possible for us.
Subsequently, a certain amount of calcium ions are pumped out of the cell by means of a similar mechanism, while the remainder is stored inside it. The decrease in calcium concentration relaxes the muscle. Now, the heart muscle has entered a state of relaxation and, therefore, is ready for the next contraction.
If the movement of the ions is unbalanced, the rhythm of our heart changes. The imbalance in the movements of ions or the obstruction of the veins of the heart can cause disorders of the cardiac rhythm. Even small inherited defects in the ion pumping affect the movement of these ions and can cause heart rhythm disorders. This fact shows that nothing is created by mere coincidence.
Movement in the sinus node
The change in the membrane potential of a cardiac cell depends on the previous change in the membrane potential of the contiguous cell. Through the intercellular spaces that connect the cells to each other, the positive ions that leave a cell reach the membrane of the cell that is next to it and cause the opening of its ion pumps and thus, the membrane potential of said cells. Cell begins to change. At this point, we can ask ourselves a question: How is the start of the electric current at one end of the sinus node produced if it has not previously been triggered by any cell?
This fact is explained by the mechanism of ion transfer in the sinus node of the cells, which differs from that of muscle cells. Before explaining this, it should be noted that, even when at rest, a mechanism has been created to allow the exchange of ions between the cell and its environment. In the nodules, when they are in the resting period, this mechanism has been created in such a way that the exchange of sodium and calcium is greater, while that of potassium is less compared to what occurs in the muscle cells during the conditions of repose. Therefore, the membrane potential of the nodule cells is less negative and increases gradually. As a result of this slow and steady increase, behind a certain time the threshold is reached. Once this is reached, the calcium channels in the membrane open suddenly and a wave of calcium ions enters the cell. Therefore, the change in membrane potential is created independently from another cell.
As we can see, even a single contraction of our heart depends on a very detailed, delicate and complex system. In addition, this system is repeated more than one hundred thousand times a day. After reflecting on all this, how could we say that this system works by chance or by chance?