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I am taking a course on the nervous system and I am do not have any physics background. Therefore, I would like to know, what are we precisely talking about when we talk about current in the nervous system?

At the same time what are we talking about when we talk about potential (i.e membrane potential or action potential.

I once heard an analogy about waterfall and water comparing current and potential (voltage), can someone elaborate on that for me.

Also, I know that electrical activity is the flow of electrons. Therefore does that mean that passive current in an axon/nerve is a flow of electrons? And is it also a flow of electrons when we have action potential.

Thank you in advance for all the help.

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Current flow is the movement of charged particles (ions in this case). The membrane potential is the charge difference across the cell membrane. Usually there is more negative charge inside the cell than out, so the membrane potential is said to be negative. When ion channels open, typically positive ions (Na+, K+) will flow into the cell as they are flowing from a medium that is approximately uncharged (extracellular space) into an environment that is highly negatively charged. By analogy, the positive ions can be viewed as water flowing down a gradient (waterfall). Electrical activity is not a flow of electrons per definition, especially not so in nervous tissue where it is ions that move (it is indeed electrons in electric circuits and the likes). During an action potential, therefore, it is not electrons that are moving across the cell membrane, but ions, most notably Na+ and K+, but also Ca+, Cl- among other charged particles.

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