Adenosine is a neuromodulator or chemical in nervous system that makes humans feel tired while caffeine act as adenosine antagonist of adenosine blocker that makes human feel fresh.
Adenosine and caffeine both binds to the same receptor and compete for the same binding site. When adenosine binds to its receptors, the neural activity slows down but when caffeine binds to the same receptor, it do not allow adenosine to bind the same receptor and do not slows down the neural activity.
Hence, the correct answer is "Competition on the same receptor binding site".
