What does circadian mean?
This term comes from the Latin “circa”, meaning “about” and “dies”, meaning “day”.
There are many biological rhythms that vary regularly but following this basic 24 hour pattern.
These include; heart rate, urine secretion, metabolic rate, respiration (breathing) and temperature.
All the above cycles reach their peak at around 4p.m, and are at their lowest around 4 a.m.
Other cycles include hormone production and milk production in females.
The sleep-wake cycle
This is the most obvious circadian rhythm, as we normally follow a regular 24-hour cycle of sleeping and waking.
This regular pattern is maintained by exogenous (external) factors, cues such as light and dark.
These factors are known as zeitgebers (which is German for “time-givers”).
The role of zeitgebers was established in a classic study by the French explorer Michel Siffre...
Aim: To establish the role of light as a Zeitgeber in the sleep-wake cycle.
Procedure: Siffre spent 7 months underground. He had adequate food and opportunities to take exercise and was always able to contact others by phone, but had no cues as to whether to it was…