<P> In the pacemaking cells of the heart ( e.g. , the sinoatrial node ) , the pacemaker potential ( also called the pacemaker current ) is the slow , positive increase in voltage across the cell 's membrane ( the membrane potential ) that occurs between the end of one action potential and the beginning of the next action potential . This increase in membrane potential is what causes the cell membrane , which typically maintains a resting membrane potential of - 70 mV , to reach the threshold potential and consequently fire the next action potential ; thus , the pacemaker potential is what drives the self - generated rhythmic firing ( automaticity ) of pacemaker cells , and the rate of change ( i.e. , the slope ) of the pacemaker potential is what determines the timing of the next action potential and thus the intrinsic firing rate of the cell . In a healthy sinoatrial node ( SAN , a complex tissue within the right atrium containing pacemaker cells that normally determine the intrinsic firing rate for the entire heart ) , the pacemaker potential is the main determinant of the heart rate . Because the pacemaker potential represents the non-contracting time between heart beats ( diastole ) , 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 contribution of several currents that flow with different voltage and time dependence . Evidence in support of the active presence of K , Ca , Na channels and Na / K exchanger during the pacemaker phase have been variously reported in the literature , but several indications point to the `` funny '' ( I ) current as one of the most important. ( see funny current ) . There is now substantial evidence that also sarcoplasmic reticulum ( SR ) Ca - transients participate to the generation of the diastolic depolarization via a process involving the Na -- Ca exchanger . </P>
where are the group of cells that control the natural resting heart rate found
sinoatrial node