Calcium and Potassium are the specific ions used to create the polarity changes in neurons that open up the gates that let those ions through making the signals that "travel" down the axon. Muscles do make use of the ions but I've gone and fuzzed up my memory of quite how the chemistry of that works. I've just got all the useless unlabelled diagrams in memory now -_-
Well this is massively off-topic, but anyway, it's actually sodium and potassium which are thought to be most important for travelling action potentials Calcium plays an important role in synapses though, and is especially important in muscles, where it regulates muscle contraction. Also in the heart calcium instead of sodium is used in signalling. How this relates to elephant intestines etc., I cannot say :p
Alright my memory is refreshed n_n
Calcium interacts with the molecule that blocks ATP binding sites on muscles so that that reaction can go forward.
I never quite had a proper understanding of how the ions worked out to up the membrane voltage so I'll probably forget which ions are involved again quickly :b
If dwarves have non-ion metals making up parts of their bodies they might not need to bother with this set up though as their nerves could actually conduct electricity for a decent distance. Or maybe they'd do the same thing but they'd have faster impulses as if the neurons were myelinated or maybe just like the giant ones in squid.
No idea how it would affect the capacitor effect of the membrane though.
If you want to be a stickler, corn itself isn't a human food either. We can not properly digest it, causing pellagra where it has been used as a dietary staple without being processed with lye in a way similar to what the native americans did.
I was going to bring up sweet corn, but apparently even that causes nutritional deficiencies (although any overly homogenous diet is going to be deficient). Though supposedly if you eat corn *and* beans regularly, they balance out. Dorf burritos, anyone? (I swear, between this and the bio-electricity discussion, DF has been highly educational today.)
Wheat did a decent enough job for Europeans but adding potatoes to their diet was useful for stabilizing their diet further. They've got wheat in northern China as well but I'm not familiar with the usual deficiencies in a rice based diet (or are there none?) They've got soy beans there though so maybe they've always been supplementing their diets with those.