What is the resting potential for a neuron?

Question

+70 milli Volts, --70 milli Volts, -55 milli Volts, +20 milli Volts or +90 milli Volts? And Why?

Answer 1

It is approximately -70mV.  The resting potential is the usual electrical difference across the membrane when a cell is at rest (eg, when there is no action potentials or other things affecting it).  It is negative because of ions inside and outside of the neural cell membrane (potassium, calcium) and maintained through the sodium-potassium pump (active transport of ions across the cell membrane).  There are also large, negative proteins inside of the neurons, causing the interior to have a net negative charge.

Answer 2

The resting potential of a cell is the membrane potential that would be maintained if there were no action potentials (no voltage-gated channels), synaptic potentials, or other active changes in the membrane potential. In most neurons the resting potential has a negative value of ~-70mV, which by convention means that there is excess negative charge inside compared to outside. The resting potential is mostly determined by the concentrations of the ions in the fluids on both sides of the cell membrane and the ion transport proteins that are in the cell membrane.

Answer 3

To follow up on Kity's answer, the membrane potential is determined by the ion which can most easily cross the cell membrane.  At rest, the cell membrane has a very low permeability, but it is most permeable to potassium.  Potassium is positively charged, and the concentration is higher inside the cell.  To keep a positively charged ion inside the neuron, the potential on the inside must be negative (I am sure that somewhere you have heard that opposites attract).  This charge on the membrane is called the equilibrium potential for the ion.  For potassium it is negative, for sodium it is positive.