FIGURE 3.3 Action potential Bodily sensations and actions—detecting a hug or kicking a soccer ball—happen when our neurons are stimulated enough that their membrane’s electrical charge reaches a threshold (−55 mV in this example—see graph above). This prompts each of those neurons to “fire” an impulse—an action potential—which travels down its axon (see numbered drawings above) and transmits a message to other neurons, muscles, or glands.