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).