Which term is defined as the minimal stimulus intensity required to trigger an action potential?

Which term is defined as the minimal stimulus intensity required to trigger an action potential?

• A. Stimulus
• B. Threshold
• C. Sub-threshold
• D. Response

Answer: (B)

Threshold is the minimum depolarization needed to trigger an action potential. When the membrane at the trigger zone reaches this critical level, voltage-gated Na+ channels open in a rapid, coordinated way, producing the all-or-none spike that defines an action potential. Subthreshold stimuli only produce graded potentials that fail to reach this level, so no spike occurs. Stimuli above threshold still yield the same spike height, but they can increase how often the neuron fires. The generic term stimulus doesn’t specify the necessary level, sub-threshold describes insufficient input, and response refers to the result rather than the triggering threshold.

Threshold is the minimum depolarization needed to trigger an action potential. When the membrane at the trigger zone reaches this critical level, voltage-gated Na+ channels open in a rapid, coordinated way, producing the all-or-none spike that defines an action potential. Subthreshold stimuli only produce graded potentials that fail to reach this level, so no spike occurs. Stimuli above threshold still yield the same spike height, but they can increase how often the neuron fires. The generic term stimulus doesn’t specify the necessary level, sub-threshold describes insufficient input, and response refers to the result rather than the triggering threshold.