1. At rest, the interior of a neuron is negatively charged relative to the exterior. This negative charge is due mainly to...?

Answer 1

Membrane potential (i.e. voltage) represents the net charge generated by positive and negative ion concentrations in the inside of the cell relative to the outside of the cell (see Goldman's Equation for more details). More specifically, in terms of a neuron's negative resting membrane potential (approx. -70 mV), the inside of the neuron has fewer positive ions (namely sodium ions, or Na+) relative to to the outside of the neuron.

This difference in charge and ion concentrations of intracellular relative to extracellular environments creates an electrochemical gradient that generates an electrical potential, allowing neurons to depolarize ("fire") and ultimately communicate with other neurons or cells.