How is the resting membrane potential produced in typical mammalian neurons?

The membrane potential describes the movement of charged ions across a membrane. A positive membrane potential indicates net movement of positive charge into the cell, or net movement of negative charge out. A negative membrane potential indicates the reverse: net movement of negative charge into the cell, or net movement of positive charge out.

The resting potential in typical mammalian neurons is around -70mV. We can therefore deduce that there is either net movement of positive charge out of the cell, or net movement of negative charge into the cell, or both. In fact, positively charged sodium and potassium ions dominate the mechanism. The sodium-potassium pump actively transports two potassium ions into the cell and three sodium ions out, using one molecule of ATP. This means there is a net loss of 1 positively charged ion for each round of transport. There is also a high potassium permeability in the membrane, meaning that potassium passively diffuses down its concentration gradient and out of the neuron, increasing the loss of positively charged ions. Both of these mechanisms combine to give the neuron an overall negative resting membrane potential.