I know the sodium-potassium pump pumps out 3 Na+ ions and pumps in 2 K+ ions per reaction so the negative charge in the axon increases. However, once the voltage (difference of charge inside and outside of the neuron) gets down to -70 mV, this stops going further below. Why?
I know that this is because of other transport proteins and the presence of anions and cations in the axon, but what are those proteins and ions precisely? There are always negatively charged proteins inside a cell, including a neuron, so I assume there must be a strong force which keeps the voltage from going down.
By the way, is the opening and closing of an ion channel triggered by the voltage of the neuron or the concentration of the ion?