The Nobel Prize site has a nice animated "game" that goes through the basics of nerve signaling. It features explanatory text alongside some nifty, simplified diagrams that are animated.
The level of coverage may be sufficient for some courses . . . but if not, then it's a good preview or review, which will help students see how it all fits together.
Try it out at Nerve Signaling.
Here's a brief video introducing this FREE online activity for your students.