1. There is much greater concentration of K+ ions inside the cell than outside, why then is the resting membrane potential always negative?
2. If you poison a neuron with a metabolic inhibitor that stops operation of the Na-K pump, can the neuron still generate APs?
3. What happens to the size of an AP if you increase the external Na+ concentration?
Chapter 5 of the book Medical Physiology Guyton and Hall can help you find the answer for your first question. Membrane potential have been explained well in this chapter.
The potassium concentration is great inside but very low outside the membrane. Because of the large potassium concentration gradient from inside toward outside, there is a great tendency for potassium ions to diffuse outward through the membrane. So carry positive electrical charges to the outside, thus creating electropositivity outside the membrane and electronegativity inside because of negative anions that remain behind and do not move outward with the potassium. Hence, electrical potential difference begins to develop. If there are only K+ channels in a cell, membran potential (Vm) in this cell will becomes the K+ equilibrium potential which can be obtained from the Nernst potential. This is because only K+ can cross the membrane and influence the electrical potential difference. For K+, assuming that the concentration of potassium intracelluler 140 mM, and extracellüler concentration 4 mM, according to the Nernst equation this value as approximately around -94 mV. I hope that it is useful.
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