Falling asleep and waking up are complex processes, which couldn’t happen without a certain hormone.
Melatonin is a natural hormone found in plants and animals. It is vital to regulating a variety of bodily functions that we rarely think about unless they go wrong. These include sleep-wake cycles, dreaming, maintaining the immune system and regulating ageing.
In humans, melatonin is made in the pineal gland, located near the centre of the brain. Its chemical form is N-acetyl-5-methoxytryptamine, and once produced it is released directly into the bloodstream. The pineal gland produces melatonin during the night, typically in response to darkness detected by the eyes. Melatonin reduces alertness, induces drowsiness and drops the body temperature; all this helps us to drop off. During the day, melatonin production dramatically declines so that we stay alert. This 24-hour cycle is referred to as the circadian rhythm.
1. Photoreceptors – Changes in light levels are detected by the retina, which produces a photopigment called melanopsin that sends signals to the brain.
3. Pineal gland – The SCN’s activity causes the pineal gland to synthesize and produce melatonin, which is released into the circulation.
4. Melatonin – Most of this hormone is produced at night, and it has a wide range of important effects throughout the body, including regulation of the sleep-wake cycle.