Why does the amplitude of the Compound Action Potential increase when the stimulus intensity is increased?

Answer 1

Assuming you're referring to an electrode-induced stimulus, the reason that the cAP increases is due to the following reasons.

1. Large diameter axons require less intense stimulation to activate than smaller axons. (So at a low intensity, you are only triggering APs in large axons. As you increase intensity, you also begin triggering APs in smaller axons. Thus the compound action potential increases).

2. Axons that are close to the site of stimulation are activated at lower intensity than those that are farther away. (So at low intensity, you only recruit neurons near the electrode, and as you increase intensity, neurons further away also begin firing).

If you're talking about salient stimuli (like touching the skin and recording from the associated nerve), than in that particular case both the increased firing frequency due to stronger stimulation and the recruitment of more receptors to convey the signal would affect the shape of the cAP.

Simply...

More neurons firing faster = bigger cAP

Answer 2

Action Potential Amplitude

Answer 3

It's the nerve cells way of saying "things are worse than we thought - act quickly and more intensely than previous amplitude indicated."