Central Circadian Clock

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The circadian clock regulate the biology and behavior of a living organism throughout a day (about 24 hours). It can be affected by external factors such as daylight or darkness of the environment. The circadian system can modify the behavior and physiological functions to adapt the environment.

For mammals, the suprachiasmatic nucleus (SCN) are the central circadian clock of our body, which is located in the hypothalamus. Meanwhile, there are peripheral circadian clocks which located in most of our tissues. It is assumed that the peripheral clocks are subordinated to the central circadian clock. The mechanism is that the time cues from the external environment (e.g. light) set the phase in SCN (figure 1). Then, the central pacemaker (SCN) project the circadian rhythm onto the peripheral clocks in the tissues so that
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Light therapy is an effective therapy for reset the central clock. It is an existing treatment for sleep disorder and depression. This treatment involves exposing the patient to bright light which is about 10,000 lux for sleep disorder in order to have an effect on the circadian rhythm. The principle of the light therapy is that the bright blue light can activate the ocular photoreceptors and thus stimulate the firing of SCN. The SCN projects to other parts of the hypothalamus to regulate and. As a result, the central clock can be synchronized to the inverted sleeping time.

However, the peripheral clock needs a longer time to reset, which might bring negative effects to the patients. Hence, scientists are finding solutions for synchronizing both central and peripheral clock. Although the mechanism of the adjustment of peripheral clock to a shifted schedule in human has not been explored at this moment, scientists believe the cortisol and melatonin rhythms which control by central clock might have a relation with the resetting of peripheral

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