Sinus node

The sinus node, rarely also called Keith-Flack node, consists of specialized heart muscle cells and is responsible for the contraction of the heart by transmitting electrical potentials, and is thus the clock of the heartbeat. The sinus node is located in the right atrium just below the orifice of the right vena cava. Its size is usually less than one centimeter.

The specialized cells are not nerve cells, although they generate an electrical potential that leads to a contraction due to conduction in the atrium. Histologically, it is specialized heart muscle cells that have the ability to depolarize, resulting in a heart rate of 60-80 beats in healthy patients. The blood supply to the sinus node is through the right coronary artery.

In the heart, the sinus node takes over the function of a clock generator. If the healthy heart is removed from a person, it will continue to beat if it is still supplied with blood. This is because the normal heart rate is not controlled by the brain, but by the sinus node.

However, the brain influences the speed at which the heart beats through other nerves (sympathetic and parasympathetic) that lead to the heart. Thus, it can beat faster (sympathetic nervous system), like when you are excited, or it can beat slower (parasympathetic nervous system). The sinus node has different ion channels that cause the cells to depolarize.

This means that an electrical signal is given and transmitted. This signal now flows through the atrium and meets another node. The so-called atrioventricular node, AV node for short.

The name of the AV node is derived from its location, since it is located between the atrium (atrium) and the ventricle (ventricle). It serves as a filter for the incoming sinus signals. A short failure of the sinus node is not noticed at first, since the AV node also spontaneously forms action potentials and can thus also contribute to the transmission of stimuli.

However, these actions are not sufficient, since the AV node does not depolarize at the same frequency as the sinus node, but is only capable of a heart rate of approx. 40 beats per minute.If this node also fails, the heart stops. However, this is rarely the case. If the sinus node fails completely, this is called sinus arrest. Diseases that affect the sinus node are summarized under sick sinus syndrome.