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Rubidium and potassium are very similar, yet the body utilizes sodium and potassium for nerve impulses. Why is this the case? Why not any other element? Likewise, why not Lithium? I've read a research (https://www.ahajournals.org/doi/pdf/10.1161/01.RES.24.2.157) that says that rubidium has similar results as potassium in nerve impulse transmissions, the only difference being slight differences in intensity of muscle contraction (K leading to slightly stronger contractions). Additionally, it seems Rubidium, Lithium, Potassium, and Sodium have very similar Standard Electrode Potentials in Aqueous Solution at 25°C. Furthermore, why wouldn't calcium be used for nerve impulses? Does that extra electron make a difference?

Background: I am currently preparing a presentation for a chemistry class at my university. The presentation deals with periodicity. Basically, I am required to select three elements and explain how their chemical and physical properties differ according to their place in the periodic table. Thus, since there are differences between Group 1 elements, I believe there should be a reason as to why we use potassium and sodium for nerve impulses instead of other elements. In other words, I want to be able to explain why the body uses potassium and sodium instead of other elements by basing myself off the periodic table (i.e. atomic radii, electron configuration, etc).

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Look to the stars to see your fate. No, seriously! Rubidium costs about 1/3 as much as gold because it is a heavy, rare element. Lithium is cheaper, but it is still a comparatively rare element. What the two have in common? The CNO cycle doesn't make them. (I'll leave you to guess three elements of life it does make) You could go into nucleosynthesis much more deeply than I understand it, but rubidium is apparently r process or s process, while lithium is apparently produced in small amounts by proton bombardment.

The problem for living things is that they can't make elements. A biochemistry that depends on an ion will be restricted according to its occurrence. Related taxa that lack this limitation should thrive and evolve over a wider area, eventually supplanting their competitors.

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  • $\begingroup$ It does make sense if we look at abundance. However, why not use Calcium. That element is quite abundant. I think what I am trying to ask is if there is some sort of chemical or physical property that both K and Na have that makes them ideal for nerve impulses. $\endgroup$ Commented Apr 25, 2021 at 3:06
  • $\begingroup$ @BrianBlumberg Calcium is quite important for neurons as well. $\endgroup$
    – Bryan Krause
    Commented Apr 25, 2021 at 4:45

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