The initial depolarization must reach or surpass a certain threshold in order to activate voltage-gated Na+ channels.
This cycle leads to a very rapid rise in Na+ conductance (gNa), which moves the membrane potential close to VNa.
This positive feedback loop means that the closer these voltage-gated Na+ channels are to each other, the lower the threshold of activation.
In a healthy cell at rest, the intracellular area is usually negatively charged relative to the extracellular region.
The concentration of sodium ions is intimately related to the electrical potential across a membrane.