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Depolarization is essential to the function of many cells, communication between cells, and the overall physiology of an organism. Action potential in a neuron, showing depolarization, in which the cell's internal charge becomes less negative (more positive), and repolarization, where the internal charge returns to a more negative value.
Repolarization usually takes several milliseconds. [1] Repolarization is a stage of an action potential in which the cell experiences a decrease of voltage due to the efflux of potassium (K +) ions along its electrochemical gradient. This phase occurs after the cell reaches its highest voltage from depolarization.
(A brief chemical gradient driven efflux of Na+ through the connexon at peak depolarization causes the conduction of cell to cell depolarization, not potassium.) [27] These connections allow for the rapid conduction of the action potential throughout the heart and are responsible for allowing all of the cells in the atria to contract together ...
Delayed afterdepolarizations (DADs) begin during phase 4, after repolarization is completed but before another action potential would normally occur via the normal conduction systems of the heart. They are due to elevated cytosolic calcium concentrations, classically seen with digoxin toxicity.
A typical action potential begins at the axon hillock [41] with a sufficiently strong depolarization, e.g., a stimulus that increases V m. This depolarization is often caused by the injection of extra sodium cations into the cell; these cations can come from a wide variety of sources, such as chemical synapses, sensory neurons or pacemaker ...
This causes the repolarization to occur more slowly, making the refractory period as long as the action potential, preventing sustained contractions. The T wave is representative of the repolarization of the membrane. In an EKG reading, the T wave is notable because it must be present before the next depolarization.
This allows for increased flow of sodium and potassium ions, causing depolarization of the sarcolemma (muscle cell membrane). The small depolarization associated with the release of acetylcholine from an individual synaptic vesicle is called a miniature end-plate potential (MEPP), and has a magnitude of about +0.4mV.
The pattern of prepotential or spontaneous depolarization, followed by rapid depolarization and repolarization just described, are seen in the SA node and a few other conductive cells in the heart. Since the SA node is the pacemaker, it reaches threshold faster than any other component of the conduction system.