Answer
Stronger stimuli open more ion channels than do weaker stimuli.
Work Step by Step
A stronger mechanical stimulus opens more mechanically-gated ion channels than does a weak mechanical stimulus. Similarly, a strong neurotransmitter stimulus opens more ligand-gated ion channels than does a weaker neurotransmitter stimulus. In either case, the stronger stimulus allows more ions into the cytosol which naturally potentiates the size of the graded potential generated.
