In this note
summaries of chapters, themes in my own language.
Melatonin | pp. 22-24
The suprachiasmatic nucleus communicates its repeating cycle of day and night using a circulated messenger called melatonin. Melatonin signals that it is nighttime and helps prepare the body to sleep.
It's known with other names like "vampire hormone" due to its occurrence only at night. Melatonin begins rising shortly after night falls until dawn when light reaches our eyes. To understand what it is, let's say the sleep is an olympic 100-meter race and melatonin is the timing official that governs the race, though it doesn't necessarily participate in the race.
In short, melatonin doesn't make us fall asleep. Instead, it signals to the body that nighttime has arrived and prepares it for sleep.
Jet lag | pp. 24-27
The advent of jet engines enabled rapid travel across time zones, leading to a biological time mismatch known as jet lag. Jet engines allow us to travel much faster than our biological clock, governed by the suprachiasmatic nucleus could adapt. Once the circadian rhythm is disrupted, the sync process is quite slow, the shift is around one hour a day. Traveling east is harder than west because staying awake is generally easier than falling asleep earlier.
edited