Why want to sleep?

1. Working biological clock. Sleep performs three main functions: 1) the brain is cleared of debris (from the intercellular space and deletes unwanted large molecules); 2) the whole body, including the brain, restores (repairs damage, replenishes stocks); 3) short-term memory is sorted: part of the information is forgotten, the part is translated into long-term memory. Such maintenance of the brain and the entire body should be held regularly, in certain intervals of time. In order to measure these intervals (diurnal cycles), in our brain there are “biological clock” that after every 14-16 hours awake automatically start the process of falling asleep. The daily cycle offline: even if you do “disable” day and night, placing subjects in complete darkness, and then the alternation of sleeping and waking will continue.
2. Darkened
If day and night do not disable, our internal circadian rhythm will adjust in accordance with the ambient light (the subjects that in the previous paragraph sitting in the dark, the cycle without “adjustment” gradually stretched up to 36 hours). For this “tuning” reply photosensitive ganglion cells (SGC), located in the retina of our eyes. These cells do not provide the images, they just define the illumination – day or night. If “night” then the brain go to sleep (still we don’t see in the dark; with our vision night need to sit quietly, and violent activity to deploy in the morning). Significant, for several hours “tuning” the diurnal cycle (for example, you flew from Moscow to Khabarovsk), is accompanied by unpleasant senses: fatigue, headache, loss of appetite. This condition is fashionably called “jetlag”.
3. The brain is clogged
During active work, the intercellular space of the brain become clogged with various debris (adenosine, GABA, glycine, prostaglandin-D2, interleukin-1β, tumor necrosis factor α)*. The accumulation of these substances inhibits the activity of the brain, it requires cleaning. During sleep, the glial cells (this is the serving cell of the nervous system) are compressed twice between them and formed quite a “sewer” of space in order to remove any, even very large waste.
If not a long sleep, all that waste accumulated. Perhaps the problem nedosypayuschih people (decreased attention, memory, performance) are partly linked to clogging of the brain.
4. The brain receives less power
I want to sleep after eating. The blood rushes to the stomach and intestines and pours from the brain. All decent animals after eating the rest; just look at the lions. (There is a more clever mechanism: “English scientists” reported that when the level of glucose in the blood decreases the activity of the centers of wakefulness”. One way or another to resist, I think, not worth it.)
I want to sleep in a stuffy room. With a lack of oxygen to the brain inevitably reduces its activity. (There is a version that is the same sedative mechanism of crying.) I want to sleep in the rain. When atmospheric pressure decrease the amount of oxygen in the air decreases, the brain gets less energy.
5. The program works sleep
1) Hereditary program. I felt our ancestral monkey, when I fell asleep? She had enough for the day, I’m tired; it’s dark, the monkey made herself a warm nest, took a specific pose (curled up), not moving around all relatives saaaaay, curled in a roll and go to sleep.
2) Program acquired in childhood. Psychologists write that the sickness does not require the child to sleep, the adults teach the children themselves to it (and then complain). Practice experienced kindergarten teachers confirms this view: in kindergarten children fall asleep by themselves, without sickness and quiet lullabies (although it works a lot of factors from the previous paragraph). If the conditions match, then these programs may include day and adults:
I want to sleep in the bus (the bird’s nest, you are rolled up and not moving around all the same, besides get carsick); I want to sleep in the winter (dark [getting light later and gets dark earlier than in summer], heat [in the premises], all around the same, besides stuffy [vents closed]).