I was reading a physio book at got confused about one part of potentials. I want to start off by saying that anything with a charge has never been my forte (be it chem or physics) so I appreciate anything anyone can offer that would englighten me! According to the text "increasing extracellular cation concentration causes a more positive potential; this is called depolarization, since the normal membrane potential is negrative. Decreasing extracellular concentration causes a more negative potential; this is called hyperpolarization." My first rxn to this was "if intracellular is normally more negative than extracellular, then wouldn't dumping more + outside make the cell even more negative relatively? and isn't this hyperpolarization?" The book goes on to say increasing K+ or Na+ concentration outside will depolarize the cell while decreasing K+ or Na+ concentration outside will hyperpolarize the cell. This seems to play off the above statement - which confuses me. However, the book says changing the conductances of these ions has opposite effects (that part I get - if K+ conductance increases, K+ will leave the cell, cell becomes more negative/hyperpolarized - where increasing Na+ conductance --> Na+ enters the cell, cell becomes less negative = depolarized). So I guess my confusion lies in this changing the extracellular milleu of ions and why that has the effect it does on the cell.... Thanks in advance for any help!!!