Circadian Rhythms

In humans, circadian rhythms are set to about 24.5 hours. The circadian rhythm is the internal clock that regulates the body's metabolism. If some people are left in a completely dark basement for a week, they will wake up each morning about half an hour later. (For some people this is what happens during the week end).

How does the circadian rhythm work?

In a very simplified schema, this is what happens:

The biological clock is reset every morning at dawn by having sunlight excite a system of cells responsive to light: the photosensitive ganglion cells. These cells are different from the rodes or cones used in vision, as with them you wouldn't be able to see anything. (image)

Once the photosensitive ganglion cells are activated they send electrical impulses via the use of melanopsin, to a part of the brain, the suprachiasmatic nucleus (in the hyppothalamus), who's role is to regulate hormone secretions in the body.

Now, at a genetic level, in the morning a set of genes are expressed, forming diamers (two molecules working together) in the cytoplasm. At night, those same diamers go back in the nucleus and turn off the transcription process. (For a more scientific article on a sleep disorder related to gene transcription look here).

I believe that more research on circadian rhtythms in humans might lead to a big improvements of health (by restoring healthy metabolism) and mood disorders.

There is another very interesting blog on the subject: look here.