The Circadian Rhythm
Circadian is Latin for “around the day” and circadian rhythms are regular changes in mental and physical characteristics that occur during the course of a day. The body’s biological clock which is the suprachiasmatic nucleus (SCN) is a pair of pinhead sized structures of the brain that contain around 20,000 neurons. The SCN is situated in a part of the brain called the hypothalamus which is just above the point where the optic nerves cross. There are photoreceptors at the back of the eye (retina) that respond to light which then creates a signal that travels along the optic nerve to the SCN.
Signals from the SCN travel to several brain regions including the pineal gland. The pineal gland secretes the hormone melatonin and is influenced by the amount of light entering the eye over a 24 hour period, being highest at night and lowest at midday, thus making you sleepy at nightfall. Also the SCN governs functions that are synchronized with the sleep wake cycle such as hormone production, body temperature, hormone secretion, urine production and changes in blood pressure.
Scientists have worked on depriving people of light and other external time influences and have found that most people have a 25 hour biological time clock but because we are affected by sunlight, bright lights, the alarm going off, car doors banging or the neighbours coming home late singing – these rhythms are affected.
Jet lag, this is another one that disrupts the circadian rhythm you feel tired and sleepy when those who habitate in other climes are wide awake or vice/versa.
Shift and night workers, they are up when it is dark and trying to go to bed when it is light, thus the melatonin production has slowed down and sleep is difficult for some, others for whatever reason seem to cope very well.
What can be done to ensure one gets enough light ?
People suffering from Seasonal Affective Disorder often use light therapy, this is when one is exposed to daylight or to specific wavelengths of light using lasers, LEDs, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, for a certain amount of time and at specific times of the day depending on the problem or sleep patterns, also light therapy works with SAD (seasonal affective disorder) for the same reason, not enough daylight for some people although this disorder has other associations, see article on SAD
See the Chinese Clock too – this makes interesting reading…
