The Heart's Electrical Conduction Pathway
The heart is a remarkable organ. It can pump blood in an intrinsic fashion, which means that it does not depend on nerve signals to contract rhythmically. If all nerves supplying the heart are severed, the heart can still beat, as observed in patients who receive heart transplants. The heart has a conduction system that enables it to contract periodically. The heart has two cell types: contractile and autorhythmic. Contractile cells have a stable resting membrane potential because they contract only after receiving nerve signals. They are not intrinsic and only depolarize when cells around them have depolarized. On the other hand, autorhythmic cells can contract independently of the nervous system and can depolarize by themselves. This principle is called automaticity. Unlike contractile cells, autorhythmic cells have an unstable resting potential that constantly fluctuates and reaches the depolarization threshold. These membrane potential fluctuations are called pacemak