A cluster of neurons just above the optic nerve — the suprachiasmatic nucleus — keeps your body on a roughly 24-hour schedule. Drag the clock hand and watch melatonin, alertness, and body temperature rise and fall together.
24-hour body clock
Drag the hand around the clock — or press Play.
The 24-hour rhythm
MelatoninAlertnessBody temp
Set the timedrag the clock to begin
🌙 Melatonin–
⚡ Alertness–
🌡️ Body temperature–
Two forces set this pattern: a circadian wake signal from the SCN, entrained by daylight, working against steadily rising sleep pressure — the two-process model of sleep (Borbély, 1982).