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→The ECG represents the sum of the action potentials of millions of cardiomyocytes
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==The ECG represents the sum of the action potentials of millions of cardiomyocytes== | ==The ECG represents the sum of the action potentials of millions of cardiomyocytes== | ||
{{multiple image | |||
| align = right | |||
| direction = horizontal | |||
| width = 250 | |||
| image1 = Ion_currents_en.png | |||
| caption1 = Ion currents of the cardiomyocytes | |||
| image2 = Hart_cells_en.png | |||
| caption2 = The heart consists of approximately 300 billion cells | |||
{| class="wikitable" | | image3 = cells_in_rest_en.png | ||
| caption3 = In rest the heart cells are negatively charged. Through the depolarization by surrounding cells they become positively charged and they contract. | |||
}} | |||
{| class="wikitable" border="1" style="float: left" | |||
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| < | | align="center" width="800" | <flashow>http://nl.ecgpedia.org/images/5/50/Single_cardiomyocyte.swf|height=350px|width=400px</flashow> | ||
| rowspan="2" align="center" width="800" | <youtube>j9w1qylp4TY</youtube> | |||
|- | |- | ||
| width="800" | <small>This movie shows the contraction of a single (rabbit) heart cell. The glass electrode measures the electrical current in the heart cell (with the[[w:Patch_clamp|patch-clamp method]]). The electrical signal is written in blue and shows the action potential. ''Courtesy of Arie Verkerk and Antoni van Ginneken, AMC, Amsterdam, The Netherlands''.</small> | |||
|} | |} | ||
The individual [[action potential|action potentials]] of the individual cardiomyocytes are averaged. The final result, which is shown on the ECG, is actually the average of billions of microscopic electrical signals. | |||
During the depolarization, sodium ions stream into the cell. Subsequently, the calcium ions stream into the cell. These calcium ions cause the actual muscular contraction. Finally the potassium ions stream out of the cell. During repolarization the ion concentration returns to its precontraction state. On the ECG, an action potential wave coming toward the electrode is shown as a positive (upwards) signal. Here the ECG electrode is represented as an eye. | |||
{{clr}} | {{clr}} | ||