Circadian Rhythm - The "Biological Clock"

The Circadian Rhythm is what we call informally - the "biological clock". This rhythm is a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living entities. Circadian rhythms are generated from within living organisms and can be synchronized by external events, called Zeitgebers. The primary Zeitgebers is daylight. These rhythms allow organisms to anticipate and prepare for precise and regular environmental changes.



The main biological clock in mammals is located in part of the brain (the suprachiasmatic nucleus - SCN). Destruction of the SCN results in the complete absence of a regular sleep/wake rhythm. The SCN receives information about illumination through the eyes. The retina of the eyes contains not only photoreceptors but also photoresponsive cells. These cells, which contain a photo pigment are linked to the SCN. If cells from the SCN are removed and cultured, they maintain their own rhythm in the absence of external triggers (interesting!). It appears that the SCN takes the information on day length from the retina, interprets it, and passes it on to the pineal gland. In response the pineal secretes the hormone melatonin. Secretion of melatonin peaks at night and recedes during the day.

There are many health problems associated with disturbances of the human circadian rhythm. Disruption to the rhythm usually has a negative effect. Many travelers have experienced the condition known as jet lag, with its associated symptoms of fatigue, disorientation and insomnia. A number of other disorders are associated with irregular functioning of circadian rhythms. Disruption to rhythms in the longer term is believed to have significant adverse health consequences on peripheral organs outside the brain, particularly in the development or exacerbation of cardiovascular disease. The suppression of melatonin production associated with the disruption of the circadian rhythm may increase the risk of developing cancer.

NB: A number of studies have concluded that a short period of sleep during the day, a power-nap, does not have any effect on normal circadian rhythm, but can decrease stress and improve productivity.


[Source: http://en.wikipedia.org/wiki/Circadian_rhythm#Origin]