In nerve axon (the wire-like part), signals are transmitted by a mechanism involving ion of one element being forced out and ion of another element forced in across cell membrane and vice versa. Thus electric waves are created due to differing electro-polarity of the elements. Natural Selection of Evolution appears to have been based on maximum sensitivity for least calory, i.e. maximum polarity with lightest weight of atoms, & easy availability of the elements as nutrition. Again these 2 ions raise the base potential around which nervous signals operate too high to be affected by interference from other normal electrochemical reactions in the cell. What are the 2 elements?