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Because the pacemaker potential represents the non-contracting time between heart beats , it is also called the diastolic depolarization. The amount of net inward current required to move the cell membrane potential during the pacemaker phase is extremely small, in the order of few pAs, but this net flux arises from time to time changing ...
The voltage region encompassed by this transition is commonly known as pacemaker phase, or slow diastolic depolarization or phase 4. The duration of this slow diastolic depolarization (pacemaker phase) thus governs the cardiac chronotropism.
However, in pacemaker cells, this potassium permeability (efflux) decreases as time goes on, causing a slow depolarization. In addition, there is a slow, continuous inward flow of sodium , called the "funny" or pacemaker current .
The L-type calcium channels are activated more slowly than the sodium channels, therefore, the depolarization slope in the pacemaker action potential waveform is less steep than that in the non-pacemaker action potential waveform. [11] [20]
On the microscopic level, the wave of depolarization propagates to adjacent cells via gap junctions located on the intercalated disc. The heart is a functional syncytium as opposed to a skeletal muscle syncytium. In a functional syncytium, electrical impulses propagate freely between cells in every direction, so that the myocardium functions as ...
Since the 1940s, the concept of diastolic depolarization, or "pacemaker potential", has become established; this mechanism is a characteristic distinctive of cardiac tissue. [16] When the threshold is reached and the resulting action potential fires, a heartbeat results from the interactions; however, when this heartbeat occurs at an irregular ...
HCN4 is the main isoform expressed in the sinoatrial node, but low levels of HCN1 and HCN2 have also been reported.The current through HCN channels, called the pacemaker current (I f), plays a key role in the generation and modulation of cardiac rhythmicity, [13] as they are responsible for the spontaneous depolarization in pacemaker action potentials in the heart.
A pacemaker, also known as an artificial cardiac pacemaker, is an implanted medical device that generates electrical pulses delivered by electrodes to one or more of the chambers of the heart. Each pulse causes the targeted chamber(s) to contract and pump blood, [ 3 ] thus regulating the function of the electrical conduction system of the heart .