How sleep works: what pulls you to bed, and what your brain does all night
Sleep pressure: why every hour awake makes you sleepier
At noon, staying awake for 24 hours sounds easy. By midnight, your eyes are heavy. Something has been building up in your brain since the moment you woke.
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Saturday, noon. You and your friends Miva and Rono start a board game marathon for charity: 24 hours, no sleep. Everyone feels great.
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2
Midnight. You yawn every few minutes and read the same card twice. Rono pours his third coffee and says he is fine.
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3
Inside your head, the trouble has been growing since morning. When brain cells burn energy, they leave a small leftover behind: adenosine. Hour after hour, it piles up.
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Some of your brain cells keep you awake. Adenosine settles into small docks on them, called receptors, and slows them down. The fuller the docks, the heavier your eyes.
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Picture the pile as a jar that fills up: this is your sleep pressure. Every hour awake adds to the jar, and sleep is what empties it.
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6
Tonight, nobody sleeps, and the jar only fills. Miva counts the hours left: "So the last hour will be the worst."
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Quick check
Last night you slept only 4 hours. Why do you feel sleepy earlier than usual today?
Show the answer
Four hours of sleep did not empty the jar. You start the day with adenosine left over, so the sleep pressure gets high sooner.
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Go further
Two things to know about the jar.