What is the relationship between stimulus strength and action potential as described in the all-or-none principle?

The all-or-none principle states that once a neuron's threshold is reached due to a sufficient stimulus, an action potential is triggered and it occurs at a consistent amplitude and duration, regardless of the strength of the initial stimulus. This means that action potentials are not graded; they do not vary in size or intensity based on the strength of the incoming stimulus.

If a stimulus is strong enough to surpass the threshold, an action potential will occur. However, if the stimulus is too weak to reach that threshold, no action potential will be generated. Thus, while the strength of the stimulus might determine whether or not an action potential occurs, it does not influence its size or speed once that threshold is met, which is key to the all-or-none principle. The other options misinterpret the relationship between stimulus strength and the characteristics of the action potential.