#91 Circadian rhythm II (English)

The circadian clock/rhythm is a 24 hour cycle that fells our bodies when to sleep and regulates many other psychological processes. The environment, like sunlight or temperature, affect the clock. This internal clock is controlled by the Suprachiasmatic Nucleus (SCN). The SCN is located in the hypothalamus in the brain and responds to light and dark signals. When there is light, the SCN sends signals by delaying the release of hormones and raising body temperature. The SCN can be separated into two parts, the dorsal and the ventral. The dorsal part of the brain works 24 hours regardless of the amount of light received. The ventral distinguishes between night and day. One natural human circadian rhythm is close to 24 hours and 11 minutes. Some indicators for measuring the timing of a mammal's circadian rhythm include:

• Melatonin secretion- During the daytime, Melatonin levels are low or there is no melatonin in the system. Production begins when the light levels begin to lessen. Melatonin is a hormone that helps regulate waking and sleeping cycles. People who have insomnia use melatonin supplements.

• Core body temperature- the average human adult's temperature is at a minimum at around 5am. Normally the minimum temperature is two hours before wale time. People who are 'morning people' tend to have a minimum temperature at 4am while evening types of people had a minimum temperature at around 6am. Morning people have their lowest body temperature closest to the middle of their sleep period while evening people have it closer to waking time

Jet lag is an example of needing to reset our internal clocks. For example, If you travel from Switzerland to India, you lose 4 hours and 30 minutes. You will probably have trouble going to sleep at 10pm there because it will feel like it is 5:30pm to your body.

However, circadian clocks are not the only biological clocks that humans have. Different organs have different clocks, including the: liver, heart, lungs, intestine, and even the skin. These organs are normally only impacted by factors like meal times, and temperatures of the environment rather than light.

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