Everybody suspected that our organism initially was made so as to know when to perform definite activities that it has so called biological clock. Marvelous fact of its presence was known long ago as ancient Greeks called it circadian (around a day) rhythm. But more wonderful thing is that exact location of it in mammals was pin-pointed.
In fact it is a cluster of neurons located in suprachiasmatic nucleus (SCN) - a group of 20 000 neural cells in hypothalamus above where the optical nerve cross. The SCN receives information about illumination through the eyes with the help of special photo responsive retinal ganglion cells. These cells contain photo pigment melanopsin and follow a pathway called the retinohypotalamic tract, leading to the SCN.
Besides light internal clock responds to other factors like temperature or even alarm clock or meal times. Receiving external cues it determines many of our body functions: sleep, body temperature, blood pressure, production of hormones and digestive secretions.
Regulation of sleep by circadian cycle is a topic of especial interest as even light violation can lead to serious sleep disturbances. Seasonal affective disorder (SAD), delayed sleep phase syndrome (DSPS) and jet lag are examples of changes in sleep cycle caused by environmental factors as lengths day or traverse of several time zones in a short period.
Hormone melatonin for the most part is responsible for sleep cycle as its produced by the pineal gland which has day/night function. The amount of sleep hormone is highest during darkness and become less during the day.
In 1999 humanity experienced melatonin boom. The substance was believed to provoke numerous additional (besides regulation of sleep cycle) health benefits. Being available over-the-counter melatonin became a popular supplement able to cure jet lag, to provoke bone growth and even to spark sexual desire. As its made from serotonin (neurotransmitter of happiness) melatonin may also cause depression in case of prolonged use.
To make changes in mental and physical characteristics during the day as regular as they should be, it is necessary to reset biological clock. Additional means to use of sleep hormones are: light therapy to treat jet lag or lithiums effect on clock genes to cure bipolar disorder.
Recently researches noticed one more peculiarity of human circadian clock. In the course of numerous observations they proved that lung function dropped by about 7-10 percent around noon and was the best around 4 and 5 p.m. The results of these and similar investigations of the internal clock function may help to provide more effective and appropriate treatment for patients with asthma or other disorders of periodical nature.
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