Effects of norepinephrine and acetylcholine on spontaneous diastolic depolarization (automaticity) in a pacemaker cell for the sinoatrial node. The pacemaker cell discharges spontaneously when the threshold potential (TP) is attained. The rate of spontaneous discharge is determined by the initial slope of the membrane potential and the time required to reach the threshold potential. A. Control recording showing the spontaneous diastolic depolarization. B. The effect of norepi-nephrine is to increase the slope of diastolic depolarization. The frequency of spontaneous discharge is increased. This effect is mediated through the activation of p-adrenoceptors in sino-atrial nodal cells. C. Acetylcholine stimulates muscarinic receptors in sinoatrial nodal cells. There is a decrease in the slope of diastolic depolarization as well as hyperpolarization of the cell. The time to reach the threshold potential is prolonged, with the net effect being a decrease in the rate of spontaneous depolarization.
tential, or hyperpolarization, of the sinoatrial cells. Thus, during vagal stimulation, the threshold potential of the sinoatrial node pacemaker cells is achieved more slowly and the heart rate is slowed.
Was this article helpful?
Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.