Each of us has an internal clock that, among other things, dictates when we get sleepy and hungry. Scientists call our biological clock a "circadian clock."  The word circadian comes from two Latin words: circa, which means about; and dies, which means day.

Our internal clock is almost parallel to the twenty-four hour cycle of a day, but not quite.

Circadian Clock

Research has shown that most people's circadian clock, left on its own, works on an approximately twenty-five hour cycle.

Without any external stimulus, our internal clock would usually gain about an hour each day and would be synchronized with the earth's time only one day out of every twenty-four.

In effect, our biological clock must reset itself each day to become attuned to the twenty-four hour clock we all live by.

Rhythm

Scientists are not exactly sure how the resetting of our clock happens, but they are fairly confident that our brains uses sunlight to fine tune our internal clock.

Our biological clock influences practically all of our bodily functions.  Our temperature rises and falls according to this clock.  And because our body is set to a daily rhythm, we react to chemical and physical stimuli differently at various times of the day.

Alcohol Effects Our Clocks

For instance, studies have shown that our liver processes alcohol more efficiently in the evenings than in the mornings, and that we are more likely to have allergic reactions in the middle of the night than in the afternoon.

Tune in next time for more on circadian clocks when we will look at how subjects in an experiment reacted to a month of isolation from the influences of the sun, clocks, or any other devices that would mark time for them.