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Electrical conduction in heart cells

Created by Bianca Yoo.

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• I don't understand how it is decided in which way the depolarizations occur. I thought it is always the same (from the atria to the ventricels, i.e. from the top to the bottom). How come the dipoles can occur in different directions?
Also: Why must there be a dipole? Why are there cells which are depolarized and others aren't yet?
Our script for our practical course says:
"The electrical field is composed of small ('elementary') dipoles which correspond to each longitudinal arrangement of cardiac muscle cells connected in series. Because the orientation of these stretches of cariac muscle is not parallel but in all directions within the heart, the addition of these elementary dipoles is not numerical Therefore, to understand how the total electrical field is generated, the dipoles are expressed as vectors and summed up by vector addition."

I'm very unsure what this actually means. What is meant by numerical in this context? I'd be happy if somebody could give an explanation for this. I'm a little confused. Thank you!
• I thought that the dipole arrow should be pointing so that the arrowhead is pointing towards the negative side, not the positive side?
• Are they any good videos/animations which depict the different heart rhythms in real time on a heart?
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• The electric potential should be referenced to the inside of the cell for measuring the voltage, right from the start of the video. More electropositive on the the outside, more electropositive negative so at rest, cells are resting with a negative potential.
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• what are sodium channel blockers?
• They block the influx of the Na+ ions inside the cells. The positive ions that she refers to in the beginning of the video are Na ions. They initiate the action potential of the heart through depolarization. So the Na channel blockers block/reduce that influx of Na ions inside the myocyte. They are used in treatment of certain arrhythmias
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• is there a certain reason that determines the direction of depolarization or is it just random?
• at , how would we know what state the heart is in if we can't differentiate between depolarizing or repolarizing since they both have the same effect on EKG?
• When discussing repolarization in the right lower quadrant, at she states that on EKG it is shown as a negative deflection. However, on EKG T-waves represent repolarization and the T-wave is a positive deflection. Can someone please clarify this?
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• yes,the T waves is able to try the positive repolarization
• what happens when the positive cells mix with the negitive cells
• It creates a concentration gradient, and that gradient becomes smaller as the positive want to go in because there is less of a positive charge in there. Then the gradient becomes negligible and it has to be reset.