Why We Sleep At the Same Time Every Night
Although we might not put our feet on one reason, that because the sun has set and the need to recharge our energy levels are compelling truths. However, that’s not the whole truth or, empirically, not the truth at all. Would we still sleep at the same time if the sun refuses to set or doesn’t rise at all, and with a passive day?
To test the preceding question, a researcher and his student journeyed to a cave, locked themselves in it, and made sure the sun rays did not penetrate.
The result was revolutionary: both slept at almost the exact time when under the bright sun’s influence. How? Why?
Like we hang clocks on our walls and lace smaller ones on our wrists to plan the day, the body has a natural biological clock, the suprachiasmatic nucleus, situated above the chiasma of the optic nerve(the nerve that carries impulses from the eyes), hence the name supra(above) chiasmatic.
This nucleus regulates the body’s wakefulness and sleepiness — the circadian rhythm. It does so by stimulating the release of melatonin (not melanin, as it’s for skin pigmentation), the sleep hormone, from the pineal gland into the blood.
while the sun doesn’t determine when we should or not sleep, it reconfigures, readjusts and re-aligns our biological clock.
Onwards, melatonin travels to a different part of the body, signals either wakefulness, when concentration is mild, or sleep when at peak. More of like a town crier shouting: ‘it’s dark!’ ‘Go to sleep!’ Melatonin is also called the vampire hormone. Sure you know why now. Observe the graph below of melatonin secretion against time:
Do you know that the internal biological clock has 24 hours in its cycle, like our modern-day clock? Yes, it does; though with fifteen minutes extra. Back to the almost in the research, the researcher and his student slept close to their routine sleeping time — a fifteen-minute difference.
Does this mean the sun plays no role?
Yes and no. Yes, because it doesn’t determine when we should or not sleep as we’ve determined. And no, because it does something else: it reconfigures, readjusts, and re-aligns our biological clock of 24hrs:15mins to the daily 24hrs on the watches we carry around. This function is probably the wisdom behind the location of the biological clock (suprachiasmatic nucleus) above the light carrying optic nerve.
Anything else apart from the effect of melatonin?
Yes, sleep pressure.
Another workaholic hormone called adenosine increases in concentration with every waking second that elapses, ultimately building up sleep pressure.
Therefore the longer we’re awake, the higher the adenosine concentration, the stronger the pressure/urge to sleep. As a side note, the adenosine receptors(acting sites of adenosine) get blocked when we take caffeine ( this found in coffee and tea), thus preventing sleep.
The image below is the effect of caffeine on web building ability of a spider compared to other drugs. Imagine the result on humans’ productivity.
Adenosine concentration is eliminated when we sleep by hepatic (liver) enzymes; for that reason, failure to sleep translates to no elimination of adenosine, which is responsible for the irresistible urge to sleep for extended duration after the caffeine wears off — a caffeine rush.
Noteworthy, both sleep-regulating systems, suprachiasmatic nucleus and adenosine, are uncoupled and work independently, unaware of each other. How intricate the human model!
Back to the starting question: Why do we sleep at the same time every night? We do because:
1. The suprachiasmatic nucleus (internal biological clock) tells us to and
2. Adenosine pressures us to.
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