Question

At the membrane potential when voltage gated Na⁺ channels open, an action potential is sure to fire. This membrane potential is called _____.

• A. Depolarising potential
• B. Threshold potential
• C. Resting potential
• D. Action potential

Answer 1

The correct option is B

Threshold potential

Threshold potential can be defined as the state of depolarisation at which an action potential is sure to fire. When a neuronal membrane depolarizes to about -55mV, the voltage gated (Na⁺) channels open. Once these channels open there is no preventing an action potential because these channels, regulated by voltage open causing a positive cascade i.e. opening of these channels depolarises the membrane further by allowing (Na⁺) ions inside the cell and more depolarisation opens more voltage gated sodium channels.