The mechanism of sleep

In the previous article (click here if you missed it!) I anticipated one of the topics that I will discuss in my next book, which is part of the five pillars of my scientific method: “Sleep” and the disorders linked to its deficiency.

Today I will address with you another aspect of this vast topic: the Sleep Mechanism.

The alternation between sleep and wakefulness is regulated by two biological systems that work in parallel: the circadian rhythm and sleep/wake homeostasis.

The circadian rhythm is our internal biological clock. Under normal conditions it sends us signals when we are ready for sleep. The biological clock of the body is activated by triggers such as daylight (we feel alert) and darkness (we feel sleepy), thanks to the hormone called melatonin. Its production can also be activated by bright artificial light or stimulants such as caffeine, which make us feel awake even if it is nighttime.

Sleep/wake homeostasis works like an hourglass. In fact, from the moment of waking, certain molecules called “hypnogenic,” that is, sleep-inducing molecules, accumulate, like the grains of sand in an hourglass. The more time spent awake, the more hypnogenic molecules are released, the more sleep will be needed. When we finally sleep, the hourglass turns: the hypnogenic molecules are disposed of, and when we wake up we will start producing them again. For this reason, those who have slept too much during the day will have little sleep during the night.

Homeostasis works like an hourglass

But what are the molecules that regulate sleep cycles?

These are chemicals that are stimulated by light or darkness. Among these are:

Adenosine: this is a neurotransmitter that gradually accumulates in the brain during the day and at high concentrations makes us sleepy at night. Caffeine in coffee and other beverages can keep us awake because it blocks adenosine receptors in the brain.

Melatonin: is a hormone released by the brain when it is dark: it travels to the cells to “tell” the body to sleep. Sunlight or exposure to artificial light inhibits melatonin production and increases the release of cortisol, which instead wakes us up. In fact, if we are exposed to too much artificial light (such as the blue light emitted by smartphones or televisions) late at night, less melatonin may be released, making it more difficult to fall asleep.

Serotonin: the body’s “feel-good” chemical, is a neurotransmitter associated with both sleep and wakefulness. The brain releases it during the day, but also uses it to form melatonin at night. Nutrition can also promote its presence in our body.

Norepinephrine, adrenaline, histamine and cortisol on the other hand, are the hormones that inhibit sleep. They are secreted in response to stress and keep the body awake and alert. If you experience prolonged or chronic stress, your body releases adrenocorticotropic hormone (ACTH), which in turn releases cortisol.

I look forward to seeing you in the upcoming articles for more about sleep and all its facets!