Answer:
Sub-threshold
Explanation:
If the stimulus is too small to generate the action potential, it is considered as subthreshold stimulus. Subthreshold stimulus causes the opening of small number of sodium channel i.e. not enough to generate action potential because action potential is generated by complete reversal of membrane polarity. Slight depolarization is caused by subthreshold stimulus by the opening of inadequate number of sodium channel but its magnitude is not enough to reach the threshold voltage. Consequently the action potential is not generated.
The response produced by subthreshold stimulus is called as local response or local depolarization because it could not travel further. The minimum stimulus required to generate the action potential is call as threshold stimulus and stimulus greater than threshold stimulus is called as suprathreshold stimulus. It changes the frequency of generated action potential.
