Sleep - physiological state of relative peace in humans and animals, characterized by changes in the functions of organs and systems, coming after a certain period of time. The human need for sleep varies depending on the age: child under 1 year should 16-17 hours of sleep, people of elderly and senile age - from 4 to 10 hours.
The sleeping and waking is one of the important biological rhythms. This rhythm is inborn, but at birth, it is not quite strictly corresponds to a daily rhythm and only gradually develops. With the diurnal rhythm sleep - Wake" is connected rhythm fluctuations of body temperature: about 5 o'clock in the morning the body temperature is always lower than when falling asleep.
Although symptoms of sleep monotonous and consist in the lack of contact with the outside world, and reduced physical activity, currently using electroencephalography during night sleep found that sleep is not homogeneous, and includes at least two different States. With the gradual deepening of the sleep EEG there are characteristic successive changes, which are expressed in reducing the frequency and the amplitude of electric oscillations. In parallel with the slowing of EEG waves from sleeping slows breathing, slowed heartbeat, low blood pressure, decreases the activity of endocrine glands (glands, thyroid gland), lowers muscular tone, reduces the content of oxygen, increases the amount of carbon dioxide in the alveoli of the lungs, reduces the blood brain. This stage of sleep, characterized by a slow-amplitude oscillations in EEG, called "slow" bedtime. In 1,5 hours after falling asleep, when all these changes are expressed quite clearly, EEG changes: the slow-amplitude rhythms are changing fast low-amplitude, and EEG this period, sleep becomes similar to the EEG during wakefulness, but sleep won't Wake up and Wake him often difficult. At this time, pulse and breathing become irregular, with a tendency to increase, blood pressure fluctuates, blood levels of hormones increases muscle tone is reduced even more, brain blood supply and oxygen demand increase, men often comes erection. One of the most characteristic manifestations of this period are quick jerky movement of the eyes closed eyelids.
Stage of sleep characterized by a rapid pace of EEG and rapid eye movement, called "fast" dream. If you can Wake up the sleeping during this period of sleep, he in 80% of cases tells about the dreams which he had just seen. If a revival does not occur, then after 5-10 minutes the specified condition is interrupted, EEG re-appear slow wave and pulse and breathing ariaudo.
Normal night's sleep consists of 4-5 cycles. Cycle in the night sleep is the period, consisting of slow sleep, followed by a quick sleep. Each cycle lasts for 90-120 minutes. In the cycles of the first half of the night prevails "slow" sleep and in the cycles of the second half of the night - "fast". Since the "fast" sleep, usually associated with dreams, every healthy person during the night sees at least 4-5 of dreams, but remembers only, after which he woke up in a few minutes. "Slow" and "fast" sleep are equally necessary for the body. Long-term deprivation of "fast" sleep often leads to changes in the psyche (agitation, fear, increased libido).
To produce artificial deprivation of the "slow" sleep, sleep at night usually starts with "slow" sleep and to resolve it, it is necessary to deprive of the subject just a night's sleep. Full continuous sleep deprivation leads to General weakness, severe fatigue, mental disorders, down to hallucinations and other Denominated mental disorder usually develop after 5 nights of sleep deprivation, in some cases after 8-9 days. In experiments on animals prolonged sleep deprivation sometimes ends in death. With interrupted sleep, appears a feeling of dissatisfaction sleep, lethargy, fatigue, bad mood.
Each of these stages of sleep connected with the activity of certain brain structures. "Slow" sleep is caused by activity of some units of the thalamus, hypothalamus and the lower part of the brain stem, and the triggers to "fast" sleep are separate kernel reticular formation of the bridge (saralieva).
The question about the essence of the dream is still open. I. P. Pavlov believed that the dream is spilled cortical inhibition. Most modern scholars believes that sleep is an active process that serves as a special kind of processing of the information received during wakefulness.
NAPs are not fundamentally different from the night, but in the first half of the day during daytime sleep before you receive a "fast" sleep and he lasted longer than in the second half of the day, when more pronounced slow sleep. People who work the day shift, "slow" sleep predominates in the first half of the night, while working on the night shift "slow" dream prevails in the end of the dream.
Sleep is active and during sleep number of excited cells in the brain on average not less than during wakefulness. When taking sleeping pills and alcohol sleep is characterized by a significant reduction in the duration of the "fast" sleep. If you cancel pills duration "fast" sleep in the night sleep increases sharply, resulting in dissatisfaction of the subject of the dream (the feeling of lack of sleep). This is one of the reasons constant desire to sleeping pills.