Circadian Rhythms and Sleep

Circadian Rhythms and Sleep

The word circadian comes from the Latin circa diem meaning about a day, which starts out as a good definition for circadian rhythms. Circadian rhythms do not have to be daily and in fact can happen in multiple periods per day or periods that last longer than days such as circannual rhythms. The most thought of circadian rhythm is sleep but other examples include, body temperature, blood pressure, production of hormones and digestive secretions. These rhythms do not only take place in humans but are present in a wide variety of other organisms, the simplest being cyanobacteria. Circadian rhythms are usually controlled by a combination environmental factors and internal factors. The most common environmental factors are temperature and light.

Circadian rhythms are controlled by a circadian pacemaker, or a biological clock. This "clock" is the section of the brain known as the suprachiasmatic nucleus (SCN). The SCN is a pair of structures that contain about 20, 000 neurons and is located in the hypothalamus above where the optic nerves cross (1). This proximity to the optic nerve explains its reaction to light. Signals from light are received by the SCN taken in by the retina. Circadian rhythms include three different parts, a central oscillator, afferent pathways that carry environmental information to the oscillator, and efferent pathways that communicate the rhythm of the oscillator to the physiology and behavior of the organism (2).

A specific example of circadian rhythms, or in this case circannual, is in birds. When it comes time for birds to migrate south and then, back north they are signaled by circannual rhythms. Both the change in temperature and the change in length of day have some...

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5) Glowing Cyanobacteria Gives Researchers New Clues to Circadian Rhythms

http://www.nsf.gov/search97cgi/vtopic

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http://www.csa1.co.uk/hottopics/circad/oview.html

7) The Miracle of Melatonin: Fact, Fancy and Future

http://enviro.mond.org/9617/961712.html

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http://www.jneurosci.org/cgi/content/full/19/2/828?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=neurobiology+AND+circadian+rhythms&searchid=QID_NOT_SET&FIRSTINDEX=10

9) Working Group Report on Problem Sleepiness

http://www.nhlbi.nih.gov/health/prof//sleep/pslp_wg.pdf

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http://bmj.bmjjournals.com/cji/content/full/317/7174/1704

Other Sources

11)Gwinner, "Internal Rhythms in Bird Migration". Scientific American. April, 1986.