The 'all or nothing' firing refers to

• A. Action Potential
• B. Resting Potential
• C. Depolarization
• D. Repolarization

Answer: (A)

Action potentials are all-or-nothing events: once the membrane potential reaches the threshold, a full spike is generated and travels along the axon with a fixed, consistent amplitude and duration. This happens because threshold triggers opening of voltage-gated sodium channels, causing a rapid, self-sustaining depolarization to a peak around +30 mV, followed by inactivation of sodium channels and opening of potassium channels to repolarize and reset the cell. If the stimulus is too weak to reach threshold, no spike occurs at all. Strengthening the stimulus doesn’t make a bigger spike; instead, it can increase the firing rate or recruit more neurons to convey stronger signals.