Signal intensity alters the frequency or number of action potentials. However, it does not change the size or amplitude of the action potential – these remain constant as the action potential propagates along the nerve fiber.  

Action potentials are frequency-modulated, not amplitude-modulated. Signal intensity is encoded by the frequency of action potentials. Stronger stimuli cause neurons to fire action potentials more frequently, while weaker stimuli result in a lower frequency of action potentials. This frequency coding mechanism allows the nervous system to convey information about the intensity of a stimulus.