Excitation formation and conduction system

The work of the heart/function of the heart is triggered and controlled by electrical impulses.This means that the impulses are created somewhere and are passed on. These two functions are performed by the excitation and conduction system. The sinus node (Nodus sinuatrialis) is the origin of the electrical impulses.

It is capable of spontaneously and regularly generating electrical excitation and thus functions as the heart muscle’s clock generator. If the function of the sinus node is disturbed, heart rhythm disturbances occur. The signals from the sinus node are conducted in the form of electrical excitation via the cell-cell connections of the muscle cells (not nerves!).

Some muscle cells have special equipment, which is why they can conduct particularly fast or slow. The excitation of the heart signs spreads mainly through these pathways; they are therefore called the conduction system. The excitation goes from the sinus via the atrium to the AV node, then through further defined sections into the ventricles, where the bundles finally branch out into the Purkinje fibers.

From these the excitation spreads across the ventricle muscles. The sinus node as the origin of the excitation of the heart is located in the muscle wall of the right atrium and consists of specialized muscle cells that can produce electrical excitation without any external influence. These excitations propagate through the atria and then reach the AV node, a group of cells near the atrial-ventricular junction.

It consists of the cells of the atrium with the slowest conduction velocity. The cells of the AV node are also special heart muscle cells in that, like the sinus node, they can autonomously produce excitation (electrical impulses measured as heart signals) – but only at half the frequency. The function of the AV node is explained by the fact that the AV limb is the only electrically conductive connection between the atrium and the ventricle – the AV node is thus a kind of filter station to protect the vital and more sensitive chamber muscles.

Its slow excitation transmission serves to ensure that the excitation is only transmitted into the chamber after the atrial contraction, so that the atrial contraction still falls within the diastole of the chamber muscles. The ability to generate excitation on its own is needed when, for some reason, the electrical impulses from the sinus node are missing. Then the AV node takes over the task of the sinus node at least partially.