Body clock

A 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.

Watch · Depth 1 · 90 sThe clock light setsWhy you get sleepy at about the same time every evening. The master clock in the brain, melatonin, why daylight has to set it every morning, why teenagers' clocks run later, and why flying east is harder.