A Moment of Science

Human Sleep Cycle Slightly Longer Than A Day

Starved of environmental cues telling us when it's time to go to sleep, our sleep cycles are actually a little longer than twenty-four hours.

Fingers appear to pinch the sun

Photo: roxweb (flickr)

The suprachiasmatic nucleus is the part of the brain in charge of keep us synched up with the rising and setting of the sun.

Most of us humans sleep at night and are active during the day. Some of us, though, are up all night and slumber in the afternoons. Is it more natural or healthy for us to sleep at night rather than the day?

The answer is that as long as there is a night and a day, it is more natural for us to sleep at night, but when environmental influences are removed, our sleep drifts away from a twenty-four hour schedule.

Every animal has a basic cycle of activity and rest. For humans, this cycle lasts about twenty-four hours. However, research shows that our cycle is really a little more than that. That means that if all environmental influences like light, temperature, and sound are removed, we begin to fall asleep eleven minutes later each night.

Thankfully, however, besides our internal clock, we also have a mechanism in our brain which functions to synchronize our internal clock with the environment.

When the light dims, for example, this mechanism signals a release of a chemical which makes us sleepy. Our bodies naturally like to sleep at night, so this mechanism works in conjunction with the environment in order to program us so that we do just that.

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