Anooshka's Blog

     An electrocardiogram (ECG or EKG) is a test of heart function. It measures the heart's electrical activity, indicating how well each heart chamber is contracting and ejecting blood. Recall from my previous post that the heart's autorhythmic cells can generate their own action potentials which result from ion movement across cells. Ion movement results in a difference in charge across the heart, producing a potential difference. An ECG, a graph of voltage versus time, represents the combined action potentials that autorhythmic and contractile cells generate at a particular time.       The action potential initiated by the heart's sinoatrial node spreads not only through the heart but also throughout the body. In an ECG, electrodes measure heart electrical activity from the chest, arms, and legs, enabling us to observe cardiac electrical activity from multiple locations. An essential point about ECG electrodes is that they do not produce or send electricity into the b

     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