Control of the heart action

This whole process works automatically – but without a connection to the nervous system of the body, the heart has hardly any possibilities to adapt to the changing requirements (= changing oxygen demand) of the whole organism. This adaptation is mediated via the heart nerves from the central nervous system (CNS). The heart is supplied by nerves of the sympathetic nervous system (via the boundary strand) and the parasympathetic nervous system (via the nervus vagus).

They give the signals whether the performance of the heart should be increased or decreased. The sympathetic nerve and the vagus nerve are nerves of the autonomous nervous system, whose activity cannot be controlled voluntarily and whose function is to intervene in a variety of organ functions as needed to regulate them (breathing, heart action, digestion, excretion, etc.). If the cardiac output is to be increased – the ejection rate can be increased from 5 l/min to up to 25 l/min – there are various ways in which this can be achieved: Overall, after activation by the sympathetic nervous system, more blood is released per unit of time and thus more oxygen is pumped through the body.

However, the heart also needs more oxygen for its increased work, which is why strict rest is prescribed for a weakened or damaged heart (cardiac insufficiency) or if the blood supply to the heart’s own vessels is known to be inadequate (coronary heart disease). The information from the nerves is transferred to the muscle cells via special proteins of the cell wall (so-called beta-receptors). This is the point of attack of the beta-blockers, which are frequently used therapeutically: they limit the increase in the work of the heart; in this way they reduce the oxygen consumption of the heart (application in the case of angina pectoris heart attack) and thus indirectly reduce blood pressure (application in the case of high blood pressure).

When the body wants to reduce the work of the heart, it has fewer mechanisms at its disposal because the slowing nerve fibers from the parasympathetic vagus nerve only reach the atrium up to the atrial-ventricular junction. The possibilities are therefore limited to the atrium: In extreme cases, the effect of the vagus nerve can be seen in the so-called athlete’s heart. The performance of a cyclist, for example, is so great that he needs only a fraction of it at rest.

Thus one finds resting pulse frequencies of 40 and less; this is controlled by the parasympathetic nervous system.

The heart rate / function heart (in the sinus node) is increased (positive chronotropic). More heart beats mean more ejection rate in the same time. The pulse rate increases.
The punching power (and thus the amount of blood ejected) is increased.
The excitability of the muscle cells is increased. If the muscle cells react faster to the electrical stimuli, the cardiac cycle can run more easily and effectively (positive bathmotropic).
The delay of the excitation line in the AV node is reduced (positive dromotropic).
Decrease of the heart rate / heart sign (negative chronotropic) and
Increase of AV transition time (negative dromotropic).