Every neuron has a separation of electrical charge across its cell membrane, and the membrane potential results from a separation of positive and negative. The relative excess of positive charges outside and negative charges inside the membrane of a nerve cell at rest is maintained because the lipid bilayer acts as a barrier to the diffusion of ions. It gives rise to an electrical potential difference, which ranges from about 60 to 70 mV. The potential across the membrane when the cell is at rest (i.e., when there is no signalling activity) is known as the resting potential. Because, by convention, the potential outside the cell is arbitrarily defined as zero, and given the relative excess of negative charges inside the membrane; the potential difference across the membrane is expressed as a negative value: Vr = -60 to -70 mV, where Vr, is the resting potential voltage.

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