the minimal point at which a stimulus causes an action potential to occur

the minimal point at which a stimulus causes an action potential to occur

• A. Threshold
• B. Plays
• C. Latency
• D. Saturation

Answer: (A)

The main idea is the threshold. It’s the minimum depolarization the neuron must reach to trigger an action potential. When a stimulus pushes the membrane from its resting potential (about −70 mV) up to near the threshold (often around −55 mV), voltage-gated Na+ channels open and a rapid, self-reinforcing depolarization begins, producing the spike. Subthreshold stimuli don’t reach this level, so they only cause small, passive changes that fade away and no action potential occurs. Once threshold is crossed, an action potential is generated with a consistent amplitude—the all-or-none response. Stronger stimuli don’t make the spike bigger, but they can increase firing rate or help reach threshold sooner through temporal or spatial summation.

The main idea is the threshold. It’s the minimum depolarization the neuron must reach to trigger an action potential. When a stimulus pushes the membrane from its resting potential (about −70 mV) up to near the threshold (often around −55 mV), voltage-gated Na+ channels open and a rapid, self-reinforcing depolarization begins, producing the spike. Subthreshold stimuli don’t reach this level, so they only cause small, passive changes that fade away and no action potential occurs. Once threshold is crossed, an action potential is generated with a consistent amplitude—the all-or-none response. Stronger stimuli don’t make the spike bigger, but they can increase firing rate or help reach threshold sooner through temporal or spatial summation.