Sinus node

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The sinus node is the heart's primary pacemaker. It sends out electrical signals that are passed on from cell to cell via the heart's conduction system until the entire myocardium is excited. One speaks of a sinus rhythm when the heart beats regularly and with a frequency of 60 to 70 contractions per minute. Read everything you need to know about the sinus node!

Sinus node: primary pacemaker

The sinus node is a dense network of specialized heart muscle cells and nerve cells in the wall of the right atrium at the point where the superior vena cava joins. The node, which is around two millimeters wide and two to three centimeters long, can independently generate and send out electrical impulses and thus control the contraction behavior of the myocardium. The sinus node thus acts as the heart's primary pacemaker.

The electrical impulses generated by the sinus node spread through the muscle cells of the atria as part of the atrial contraction to the AV node. It is the secondary pacemaker and is also located in the wall of the right atrium, but on the border with the right ventricle and near the septum of the heart. From here, the electrical impulses spread via the conduction system over the remaining work muscles of the heart, which leads to the contraction of the heart chambers (systole).As a result, the blood is pressed from the heart chambers into the large arterial vessels: from the right heart chamber into the pulmonary artery and thus into the small bloodstream (pulmonary circulation); from the left ventricle into the main artery (aorta) and thus into the great blood circulation (body circulation).

Heart rate

The normal rate of the heartbeat in a healthy adult is 60 to 70 beats per minute. The sinus node works autonomously and automatically adjusts the heart rate to the respective needs: for example, the heart beats faster during sport and physical exertion and slower during rest and sleep.

Nervous system affects the sinus node

The autonomic nervous system influences the sinus node via the sympathetic and parasympathetic nervous system and thus intervenes in the regulation of the heart rhythm:

The parasympathetic nervous system exerts its influence on the sinus node via the vagus nerve: stimulation of the nerve leads to the release of the messenger substance acetylcholine at its ends, which reduces the pacemaker rate in the sinus node - the heart beats more slowly.

Activation of the sympathetic nerve fibers that reach the heart, on the other hand, has the opposite effect: the transfer time of the impulses from the atrium to the ventricle is accelerated, the heart beats faster, the cardiac output increases.

Sinus node problems

If the sinus node fires more than 100 regular pulses per minute (the heart beats more than 100 times a minute), you have sinus tachycardia. This happens during sport, for example, but it can also be caused by a disease such as febrile illnesses, Graves' disease (thyroid disease), heart failure, myocarditis (inflammation of the heart muscle) or heart attack.

In sinus bradycardia, the sinus node produces fewer electrical impulses than normal, causing the heart to beat too slowly - less than 60 times per minute. Thanks to their regular training, athletes get by with such a slow heart rate at rest. Sinus bradycardia can also occur during sleep, with intracranial pressure, jaundice, digitalis poisoning, diseases of the sinus node or coronary heart disease (CHD).

In the case of a sinus arrhythmia, the sinus node sends out very irregular impulses. In rare cases, sinus arrhythmia can occur, for example in coronary sclerosis, cerebral sclerosis or hypertension.

Sick sinus syndrome is a group of complicated cardiac arrhythmias that originate from the sinus node. It mostly affects the elderly.

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