According to the information discussed in the box "In Focus: What You Really Want to Know About Sleep," which of the following statements is TRUE? A. Sleep researchers have demonstrated that it is possible to have extended, meaningful conversations with people who are chronic sleeptalkers. B. A naturally occurring compound called "adenosine" seems to be involved in producing sleepiness. C. Yawning is caused by having too little oxygen or too much carbon dioxide in the blood. D. Sleep paralysis is a rare, progressive condition that can eventually lead to a permanent coma if left untreated.

An important chemical known as a nucleoside that exists naturally in all cells of the body is called Adenosine. It is used to transfer energy within the cells by forming molecules like adenosine triphosphate (ATP) and adenosine diphosphate (ADP), and it is also one of the chemical messengers, or neurotransmitters, within the brain.

The relationship between adenosine and sleepiness in humans is explained as follows:

Whilst we are alert, adenosine levels gradually increase in areas of the brain that are important for increasing arousal, especially the reticular activating system in the brainstem.

As the concentration of adenosine gets higher, it inhibits arousal and causes sleepiness. As soon as we are asleep, the levels of adenosine in our system decreases. This has let scientists to conclude that high levels of adenosine in effect cause sleep.

Studies have shown that caffeine found in coffee, tea, and other caffeinated beverages, is a xanthine chemical like adenosine and works to inhibit sleep by preventing the effect of adenosine within the brain, which increases wakefulness. Which means, the more caffeinated drink one takes, the less the brain is able to process adenosine.

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