Why are cells more negative inside if K+ and Na+ are both positive??
In: Biology
Firstly there are also lots of negative ions – chloride, bicarbonate, ammonium, phosphates and proteins which have negative charge to balance the positive ions – sodium, potassium, calcium, magnesium.
Secondly the levels of K+ and Na+ are strictly controlled by the cell membrane which won’t let them through except through special channels and the sodium/potassium pump system. This means there is a difference between the inside and outside, with more sodium outside than inside and more potassium inside than outside. This causes a gradient of charge (see Nernst and Goldman equations for non-5 year olds). The gradient means the inside is more negative than the outside by a really small amount (-60-90 millivolts depending on the cell).
This is only really important in cells like nerves and muscles which transmit electrical signals – a channel opens allowing lots of sodium to come in down its concentration and electrical gradients (ie from lots and positive to little and negative) which means a change in the gradient, that gets transmitted along the cell membrane. The cell then corrects the charge gradient by moving potassium then sodium with a special pump as pumps can work against the gradient.
Latest Answers