Answer:
Adenosine.
Explanation:
Adenosine is a neurotransmitter that is created in the brain and when it binds to the adenosine receptors, it slows down nerve activity and it creates a sensation of drowsiness.
<u>Caffeine</u> looks like adenosine to the receptors, therefore, when we have caffeine, <u>it binds to these receptors and there is no room left for the adenosine to bind</u>. However, the caffeine doesn't slow down nerve activity but, in the contrary, it speeds it up.
Therefore we can tell that caffeine blocks the receptors for the adenosine thus promoting wakefulness.
