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Caffeine, also known as trimethylxanthine, coffeine, theine, mateine, guaranine, methyltheobromine and 1,3,7-trimethylxanthine, is a xanthine alkaloid found naturally in such foods as coffee beans, tea, kola nuts, Yerba mate, guarana berries, and (in small amounts) cacao beans. For the plant, caffeine acts as a natural pesticide since it paralyzes and kills some of the insects that attempt to feed on the plant.
Caffeine's main properties are: a stimulant action on the central nervous system with psychotropic effects and stimulation of respiration, a stimulation of the heart rate, and a mild diuretic effect.
Caffeine is thought to act on the brain (and, in fact, most cells of the body, since all cells have adenosine receptors) by blocking adenosine receptors (thereby blocking a pathway that leads to the breakdown of cyclic adenosine monophosphate, cAMP). Adenosine, when bound to receptors of nerve cells, slows down nerve cell activity; this happens, among other times, during sleep. The caffeine molecule, being similar to adenosine, binds to the same receptors but doesn't cause the cells to slow down; instead, the caffeine blocks the receptors and thereby the adenosine action. The resulting increased nerve activity causes the release of the hormone epinephrine (adrenaline), which in turn leads to several effects.
Caffeine is quickly and completely removed from the brain, and its effects are short-lived. In many people, caffeine does not negatively affect concentration or higher mental functions, and hence caffeinated drinks are often consumed in the course of work.
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