Threshold potential is to –55 mv as potential is to mv.

Resting potential is to -70 mV. Therefore, when there is an influx of ions in a neuron sufficient to reach -55 mV, an action potential will occur and that neuron will fire. That action potential will result in a refractory period for that neuron where it will then fall below a -70 mV and will not be prone to firing. Then it will reach resting potential again until another action potential is reached.