1 · Adenosine builds up
While you are awake, adenosine from neuronal metabolism builds up in the brain and binds A1 and A2A receptors to cause drowsiness; sleep clears it.Every second you are awake, adenosine slowly accumulates in the brain — a byproduct of neurons metabolizing . Adenosine is not a "poison"; it is the body's endogenous sleep-pressure molecule:· Awake 8 h: adenosine pool moderate → alert
· Awake 12 h: adenosine pool half full → starting to feel sleepy
· Awake 16 h: adenosine pool near saturation → strong drowsiness
· Sleep (especially deep NREM): adenosine is cleared → reset for the next day
Receptors of action: A1 + A2A
· A1 receptors — most widely distributed, inhibit neuronal firing + inhibit neurotransmitter release → "slow everything down"
· A2A receptors — mainly in the striatum + nucleus accumbens, modulate dopamine signaling → "tell you you're tired, don't want to move"
· Adenosine binding these receptors → drowsiness + poor attention + low motivation
This is the chemical root of "a person collapses after two or three sleepless days" — the adenosine pool overflows, and willpower can no longer suppress it.