Blood flows throughout life. The power of blood flow comes from the contraction of the heart. When the heart contracts, the blood in the heart can be squeezed out and become the driving force for blood flow. Because the heart can contract at a certain rhythm and never stop, the blood can always flow. So, what kind of mechanism makes the heart beat non-stop?
A heart conduction system that stimulates the beating of the heart
The outer wall of the heart is made up of muscle tissue called myocardium, which is made up of cardiomyocytes. Cardiomyocytes have a characteristic, that is, even if there is only one cell, they can contract and beat with a certain regularity. But if each cardiomyocyte beats arbitrarily according to its own rules, the whole heart cannot become an efficient pump. That is to say, a command system that can command all cardiomyocytes is needed to drive the heart to beat in order to effectively punch out the blood.
The heart's command system is the cardiac conduction system. The cardiac conduction system sends out electrical stimulation signals that travel throughout the heart, causing myocardial contractions. It sounds like something a nerve does, but this system is not triggered by nerves, but by special myocardial fibers, which lie deep within the myocardium.
The sinoatrial node produces regular electrical stimulation signals
The sinus node, located in the upper part of the right atrium, produces a regular electrical stimulation signal that allows the heart to beat regularly. The sinoatrial node produces a regular electrical stimulation signal that spreads along the outer wall of the left and right atrium to the entire atrium, and the stimulated atrial muscle cells contract together, squeezing blood from the atrium to the ventricles.
When the electrical stimulation signal conducted along the outer wall of the atrium comes to the atrioventricular node located at the junction of the atrial ventricles, the electrical stimulation signal will immediately enter the median septum of the left and right ventricles along the atrioventricular bundle connected to it, and is divided into left and right bundle branches, and then transmitted to the Purkinye fibers with many branches, at which time the electrical stimulation signal will be rapidly transmitted to the entire ventricle, so that the left and right ventricles contract strongly, and the blood of the ventricles will be punched out to the aorta and pulmonary arteries.
Although the sinoatrial node emits regular electrical stimulation signals, the sympathetic excitement of the autonomic nerve also speeds up the rhythm of the signals. So when we exercise or get excited, the heartbeat accelerates; when we relax, the parasympathetic nervous system is excited, and the heartbeat slows down.