The control over the circadian and homeostatic mechanisms is under the hypothalamus. The frontal part of hypothalamus can be stimulated to producing sleep if warmed or stimulated with electricity. The suprachiasmatic nucleus controls the day-night rythm. Lack of sleep causes tiredness mainly because adenosin is building up in the CNS. Caffeine is an antagonist of adenosin and can therefore used temporarily to counter its effects.
The main sleeping phases can be divided three categories. Awareness, NREM-sleep and the REM-sleep. When awake the EEG shows desynchronization of the brainwaves which can be reduces by closing the eyes. Once the eyes are closed the impulses that come from the eyes through the optic nerve to the optical cortex decline and you can start to see the synchronization of the nervecells.
NREM-sleep can be divided in to four subcategories S-1, S-2, S-3 and S-4. In S-1 sleep the slight synchronization of the awarness starts to break up and longer-wave sleep starts showing up in the EEG in small parts. When the sleep gets deeper the percentage of the long wave sleep increases until S-3 and S-4 sleeps are achived. S-4 sleep consists 25% of long-wave sleep. Long wave sleep enables growth hormone excretion in unconventionally large doses. Long-wave sleeping has the highest wake-up treshold and can be concidered as the most rejuvenating sleep. If you are having trouble sleeping your sleep will be mostly long-wave sleep when you finally do get some sleep.
Before REM-sleep is achieved the EEG desynchronizes to resemble the awareness. When REM-sleep is achieved muscle tonus completely disappears and short bursts of rapid eye movements are observed. This is why all kind of contacts lenses and color contacts should be removed before sleeping so no eye damage is experienced. Short bursts of muscle contractions are also seen. Paradoxal in REM-sleep is that your brain seems to be “awake” but your body is completely resting. Dreams are also seen during REM-sleep, and one can only remember their dreams if awaken from REM-sleep.
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