= 生理時鐘 = 晝夜節律

Circadian rhythm is the conductor of your body’s orchestra/symphony.

What is Circadian Rhythm?

The circadian rhythm is an internal biological clock that governs/modulates the sleep-wake cycle. It operates on a roughly 24-hour cycle, responding primarily to light and darkness in the environment.

Key Features

• Generated from within, but synchronized (entrained) by external cues, especially light (zeitgebers).
• Found in almost all living organisms, from plants to animals to humans.
• Can be shifted by travel (jet lag), shift work, or changes in routine, but prefers regularity.

Examples

• Morning sunlight triggers a rise in cortisol, helping you feel alert and awake.
• Body temperature drops to its lowest point (temperature minimum) a few hours before waking, then rises through the day.
• Melatonin (the sleep hormone) increases in the evening as it gets dark, signaling the body to prepare for sleep.
• Adenosine builds up during wakefulness, creating sleep pressure, and is cleared during sleep.