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All cardiac muscle cells are electrically linked to one another, by intercalated discs which allow the action potential to pass from one cell to the next. [1] [2] This means that all atrial cells can contract together, and then all ventricular cells. Different shapes of the cardiac action potential in various parts of the heart
The shape of the action potential is stereotyped; this means that the rise and fall usually have approximately the same amplitude and time course for all action potentials in a given cell. (Exceptions are discussed later in the article). In most neurons, the entire process takes place in about a thousandth of a second.
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The cells that make up the SA node are specialized cardiomyocytes known as pacemaker cells that can spontaneously generate cardiac action potentials. These signals are propagated through the heart's electrical conduction system. [1] [2] Only one percent of the heart muscle cells are conductive, the rest of the cardiomyocytes are contractile.
The threshold potential is the potential an excitable cell membrane, such as a myocyte, must reach in order to induce an action potential. [7] This depolarization is caused by very small net inward currents of calcium ions across the cell membrane, which gives rise to the action potential. [8] [9]
The SR is a Ca 2+ stored within the cell and is located very close to the T-tubule. Activation of RyR2 causes it to open, releasing even more Ca 2+ into the cell. This release of calcium is called a calcium spark. The initial flow of Ca 2+ into the cell causes a larger release of Ca 2+ within the cell, so therefore the process is called calcium ...
The action potential of a ventricular myocyte. In electrocardiography, the ventricular cardiomyocyte membrane potential is about −90 mV at rest, [1] which is close to the potassium reversal potential. When an action potential is generated, the membrane potential rises above this level in five distinct phases. [1]
A pacemaker action potential is the kind of action potential that provides a reference rhythm for the network. The pacemaker potential is the slow depolarization because of sodium influx, and once threshold has been reached the continued depolarization due to calcium influx. [ 1 ]