Most people get a temporary increase in wakefulness or better ability to concentrate after caffeine intake.
There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system.
How does caffeine block the adenosine receptors? How does it stimulate the autonomic nervous system?