What is the term for the minimum membrane potential change required to trigger an action potential?

• A. Resting potential
• B. Equilibrium potential
• C. Gate potential
• D. Threshold potential

Answer: (D)

Threshold potential is the minimum depolarization needed to trigger an action potential. When a neuron is at its resting potential (about -70 mV in many cells), a stimulus must depolarize the membrane to a certain level, typically around -55 to -50 mV, to initiate the spike. Reaching this threshold opens a large number of voltage-gated Na+ channels, creating a positive feedback loop that drives rapid depolarization and the upstroke of the action potential. If the depolarization stays below threshold, the neuron doesn’t fire and simply returns to rest.

Resting potential is just the baseline voltage when the neuron isn’t signaling. Equilibrium potential refers to the voltage at which a specific ion would have no net flow across the membrane. The term you’re looking for—threshold potential—specifically captures the trigger point that converts a subthreshold stimulus into an all-or-nothing action potential.