What is the electrical charge of a neuron when it is not firing?

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When a neuron isn’t firing, its membrane potential sits at a resting level, usually about -70 millivolts, meaning the inside of the cell is negatively charged compared with the outside. This negative interior comes from ion gradients: there’s more potassium inside and more sodium outside, plus negatively charged proteins inside. The membrane is more permeable to potassium at rest, so potassium ions tend to leak out, pushing the inside further negative. The sodium–potassium pump also helps by actively moving three sodium ions out and two potassium ions in, maintaining these gradients over time. Because of this arrangement, the neuron is in a ready, polarized state and must be depolarized toward a threshold to trigger an action potential. The other terms describe what happens during or after firing: an action potential is the rapid voltage spike during signaling, the threshold is the level that must be reached to start firing, and the refractory period is the brief recovery time after firing when it’s harder to fire again.