Sleep
Map
Arrows point from what you learn first to what it opens. Point at a concept to light up its chain and where it comes back deeper. Right-click a concept (or press and hold it) for its lessons and stories.
- Proven to depth123
- Open
- Locked
- Comes back deeper
Learning path
In the order the concepts build on each other.
- Body clockReadyA master clock in the brain runs a cycle of about 24 hours, making us sleepy at night (through the hormone melatonin) and alert in the day. Daylight resets it every morning; it shifts later at puberty, and jet lag is when it no longer matches the real clock.
- SleepReadyEach night we cycle through light sleep, deep sleep and REM (dreaming) sleep. Sleep helps memory, fighting infections and growth, and missing it slows us down like alcohol does - though its full purpose is still a mystery.
- Sleep habitsReadyHabits that help sleep: the same wake-up time every day, a quiet, dark and cool room, no caffeine after lunch, no big meal or alcohol late, screens away before bed, and getting up if sleep won't come. Caffeine blocks the brain's sleepiness signal for hours.
- Sleep needReadyHow much sleep a person needs depends on age: teenagers about 8 to 10 hours, adults at least 7 (most 7 to 9), young children more. Experts give ranges, not one number, and lost sleep can't simply be paid back at the weekend.