The threshold potential for triggering an action potential is closest to which value?

The threshold potential for triggering an action potential is closest to which value?

• A. -40 mV
• B. -55 mV
• C. -70 mV
• D. -90 mV

Answer: (B)

Threshold potential is the membrane voltage at which voltage-gated Na+ channels open and trigger the rapid upstroke of an action potential. In many neurons, the resting membrane potential is about -70 mV, and depolarizing to a less negative level reaches a threshold around -55 mV. Once this threshold is reached, Na+ channels open in a positive feedback loop, producing the all-or-none spike. Values more depolarized than threshold, like -40 mV, would already unleash an action potential, while more negative values like -70 mV or -90 mV reflect resting or hyperpolarized states. So the value closest to the triggering point is about -55 mV.

Threshold potential is the membrane voltage at which voltage-gated Na+ channels open and trigger the rapid upstroke of an action potential. In many neurons, the resting membrane potential is about -70 mV, and depolarizing to a less negative level reaches a threshold around -55 mV. Once this threshold is reached, Na+ channels open in a positive feedback loop, producing the all-or-none spike. Values more depolarized than threshold, like -40 mV, would already unleash an action potential, while more negative values like -70 mV or -90 mV reflect resting or hyperpolarized states. So the value closest to the triggering point is about -55 mV.