On p. 84 of the text, in the Thinking Clearly section, the conduction action potentials and activation of neurotransmitters is related to a row of mousetraps on a wobbly shelf. Think of another analogy you can use to describe the conduction of action potentials and activation of neurotransmitters.
What you need is an analogy that has something building up until a critical level is reached, and then an action will result.
Your searching for your own analogy will help you understanding of the concepts.