How caffeine works?

I have searched some information for the mechanism of caffeine action. What's turned out is that there are many explanations. I'm quite confused if which explanation is more accurate.

1) Caffeine resembles adenosine, the chemical slowing down the nerve activity to produce drowsiness and caffeine binds to adenosine receptors to prevent the action of adenosine, keeping us awake.

2)the size and shape of caffeine is similar to that of phosphodiesterase(PDE).When caffeine is introduced to the body, it can block the receptors for phosphodiesterase. When phosphodiesterase binds with a cell, it can then break down cyclic adenosine monophosphate (cAMP), which leads to a release of adenosine. When caffeine blocks the phosphodiesterase receptor, it blocks the release of adenosine, preventing you from becoming sleepy.

Can someone teach me that which explanation is more accurate or exert a larger effect in the anti-drowsiness.

thanks a lot~~