After drinking coffee we feel so relaxed and our brains feel so free. Why this happens?
Caffeine blocks the adenosine methabolism in the neurons which normally manages the tiredness and sleep.
Adenosine molecules are released by neurons during the day and after they reach some concentration, they activate the adenosine receptors of the neurons of our brains. This is a mechanism to stop us being extremely tired and makes us sleep regularly for daily maintenance of our body.
Caffeine is a very similar molecule to adenosine in the molecular scale. So, it tricks the receptors as if it is adenosine. But, it doesn't activate the sleeping procedure. So, as a result, we block our sleeping cycle by masquerading adenosine with caffeine for a while. After a while, caffeine is removed from our brain by blood flow and everything returns to normal.