Pathways to Sleep I: An Introduction
We now know that melatonin is not sufficient to create high quality sleep. The band can-t play the sleepy-time tune with only the chemical instrumentation of melatonin. We turn again to the insights offered by Matthew Walker:
. . . melatonin helps regulate the timing of when sleep occurs by systematically signaling darkness throughout the organism. But melatonin has little influence on the generation of sleep itself. . . . Melatonin corrals [the]sleep-generating regions of the brain to the starting line of bedtime. (Walker, 2017, p. 23) . . .
The circadian clock itself is an important companion with Melatonin in getting us to the starting line (I apologize for the missing of metaphors between Walter and myself—I actually like the bedtime tune metaphor – it reminds me of the lullabies that helped me fall asleep for many years). Still there is the need for additional assistance. This is where the much more mysterious chemical called adenosine comes into the picture. Walker (2017, p. 27) offers us a useful description of the role played by this chemical:
. . . a chemical called adenosine is building up in your brain [as you become sleepy]. It will continue to increase in concentration with every waking minute that elapses. The longer you are awake, the more adenosine will accumulate. Think of adenosine as a chemical barometer that continuously registers the amount of elapsed time since you woke up this morning. (Walker, 2017, p. 27)
If I can reintroduce my own metaphor, adenosine is a clock that signals how long the band has been on break (often signaled by the growing restlessness of the crowd) or more accurately how many hours since the band last played (usually the night before). The crowd grows restless or at the start of the evening, the crowd begins to line up at the door. Biologically, this is known as an increase in sleep pressure. We all know what this sleep pressure feels like—it is that increasing demand of our body and brain to fall asleep. Many of the pathways to sleep I will be identifying help to either stimulate this pressure or respond to the pressure once it builds up.
There we have it: the circadian clock and melatonin provide us with the band and the tune, while the chemical adenosine is building up and demanding that the sleepy time tune is played. Officially, the circadian clock and the melatonin produce what is known as Process-C, while adenosine produces something called Process-S. When the two processes meet, we get sleep; but as the night goes on the circadian clock will produce variations in level of sleep (the sleep stages I identified earlier) while adenosine is gradually expended. By the end of the night and the first burst of sunshine, there is very little sleep pressure and we are ready to gain consciousness once again (or at least that is what is supposed to happen if we get high quality, non-fragmented and interrupted sleep).