 Dear students, in this topic we shall discuss the role of ion channels in self-excitation. The basis of self-excitation of pacemakers is the inherent leakiness of sinoatrial nodal fibers to sodium and calcium ions. This leakiness is due to the presence of three types of ion channels in their membranes. These are the fast sodium channels, slow sodium calcium channels and potassium channels. These channels activate and deactivate at a pace that keeps the resting membrane potential much less negative that is only minus 55 millivolt as compared to minus 85 to minus 90 millivolt in other cells. It also keeps an unstable and rising resting membrane potential due to continuous influx of sodium and calcium ions. Dear students, the fast sodium channels open immediately as the membrane potential goes less negative than minus 55 millivolt after an action potential when hyperpolarization occurs. They remain open for only few milliseconds because as they open they let the sodium ions to immediately move inside the cell. This sodium ion influx prevents developing a stable and more negative resting membrane potential. These channels become inactivated and blocked above minus 55 millivolt. Dear students, minus 55 millivolt and above the level per slow sodium calcium channels open. These channels are comparatively slowly open and that is why sodium ions start leaking through them slowly. As a result, membrane potential gradually rises. This rise prevents to establish a stable resting membrane potential. This way, even at minus 55 millivolt, the resting membrane potential does not become stable but gradually rises. Rising membrane potential at minus 40 millivolt, this is the threshold level at which the sodium calcium channels become activated maximally. So the influx of sodium and calcium ions starts rapidly that triggers an action potential. Dear students, the rise in membrane potential is slower in the range of minus 55 to minus 40 millivolt. So the sinoatrial nodal action potential is slower to develop. As compared to the action potentials of ventricular muscle fibers, dear students, now we shall discuss the role of potassium channels. Considered the action potential, the potassium channels open slowly. Their opening causes the return of membrane potential back to its negative state. However, owing to their slow activation, duration of sinoatrial nodal action potential is longer.