With development of electric devices, continuous exposure of electromagnetic (EM) fields to human bodies has become great concerns. Despite our interest, their effects on human bodies have not been well-determined. We have an interest in the non-thermal effects of the EM fields on neurons and attempt to establish a scientific explanation. Elucidation of the EM effects on neurons could allow us to make use of the induced current for spike initiation. As the first step toward understanding the connection between the applied current and the triggering action potentials, we simulated how the generated action potential would change depending on the applied current using a fundamental mathematical model on a simple geometry. Five periodic waves having different shapes were used as the applied current. Analysis showed that not only how the current increased the value but also how it decreased the value was important. We also concluded that the sine wave would be the best as the applied current among the five to generate action potentials.