Why pain seems worse at night

As the song from the musical "Les Miserables," based on the novel by Victor Hugo, says, "But the tigers come at night, with their voices soft as thunder." We've all been miserable at night, when we find ourselves tossing ...


How does the body clock keep track of time?

Picture the scene: you wake up in the dim light of the morning, and wonder if it's already time to get up. Just as you reach for your bedside clock, your morning alarm goes off. It's a handy—if mysterious—skill. But how ...

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Circadian rhythm

A circadian rhythm is a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living entities, including plants, animals, fungi and cyanobacteria (see bacterial circadian rhythms). The term "circadian", coined by Franz Halberg, comes from the Latin circa, "around," and diem or dies, "day", meaning literally "approximately one day." The formal study of biological temporal rhythms such as daily, tidal, weekly, seasonal, and annual rhythms, is called chronobiology.

Circadian rhythms are endogenously generated, and can be entrained by external cues, called Zeitgebers, the primary one of which is daylight. These rhythms allow organisms to anticipate and prepare for precise and regular environmental changes.

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