Question

Threshold potential is a state of depolarisation at which

• A. An action potential is sure to fire
• B. Voltage gated Na+ channels open
• C. Membrane potential is near -55mV
• D. Ca+ ion leakage channels open.

Answer 1

Answer: (A), (B), (C)

The correct options are
A An action potential is sure to fire
B Voltage gated Na+ channels open
C Membrane potential is near -55mV

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. Up until this time, only the K⁺ & Na⁺ leakage channels were open but K⁺ ion leakage channels are more than Na⁺ leakage channels. Once the voltage gated Na⁺ channels open, there is no preventing of 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.