Also, melatonin and adenine both help one fall asleep. However, I’m not a neurochemist so I can’t claim to be sure about the exact pathways.
However, that is how caffeine works, it’s an adenine mimic and blocks the adenine receptors in your brain, thus stopping the sleep signals from getting through.
Also, in general it’s a safe bet that pretty much anything that occurs in your brain can be tracked down to a chemical (or, usually, a large number of chemicals). We, naturally, only know a very small range of what they all do or how, but it’s mostly all chemical and electrical signals in the end.