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📘 How sleep cycles through the night

Follow circadian timing, sleep pressure, NREM and REM stages, brain activity, and hormone rhythms.

lessons

~20 min

to learn

🔬 Science

subject

Adults

level

Start the course →

What you’ll learn

Clock
Sleep pressure
NREM 1
NREM 2
NREM 3
REM
First cycle
Later cycles
Recording
Hormones
Temperature
Memory
Arousal
Age
Circadian mismatch
Full night

Questions this course answers

What are the two major sleep phases?

Sleep cycles through rapid-eye-movement and non-REM phases.

When is deep slow-wave sleep usually more common?

NREM stage 3 is usually concentrated in early cycles.

What characterizes REM sleep?

REM combines waking-like brain activity with rapid eye movements and limp skeletal muscles.

What does the circadian clock do?

The central clock helps schedule sleep, wakefulness, temperature, and hormone timing.

Why can shift work disrupt sleep?

External schedules can become misaligned with the internal circadian rhythm.

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