When I was studying the ECG chapter in the book "Guyton and Hall Textbook of Medical Physiology", I noticed something odd in one of the pictures:

enter image description here

As you can see the current is shown to be flowing from the area with a more negative potential towards the area with a more positive potential. Also here's the part of the text that alludes to the image:

This process provides electronegativity on the insides of the ventricles and electropositivity on the outer walls of the ventricles, with electrical current flowing through the fluids surrounding the ventricles along elliptical paths, as demonstrated by the curving arrows in the figure.

How is this possible? Isn't the current supposed to flow from an area with a higher potential towards an area with a lower potential?


By convention, positive current is assumed to be the direction of flow of positive charges. The trouble is that in many common situations (like this one), the current is actually carried by electrons which are negatively charged.

It can be confusing. Blame it on Benjamin Franklin. The convention for current flow was based on his work, before anyone knew about electrons, protons, and ions.

  • $\begingroup$ So basically what is shown in the image is the direction of the flow of the electrons and not the flow of the current, correct? $\endgroup$ – IdaM Nov 3 '20 at 20:49
  • 3
    $\begingroup$ Not literally electrons, the flow is mostly Chloride ions that direction, and Sodium, Potassium and Calcium ions the other way. $\endgroup$ – Polypipe Wrangler Nov 4 '20 at 4:13

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