Your cycle of wakefulness and sleep is set by the body’s internal clock — something like a metronome in the brain. The biological processes of your body obey the internal rhythm: changes in temperature, blood pressure and the production of hormones. All these things, in turn, affect the cycle of wakefulness and sleep, it depends on them whether you feel tired or revitalized.
Hormones and sleep
Your sleep and wake cycle is controlled by specific hormones. When you wake up, stress hormones, or “activity hormones,” corticosteroids, enter the blood. Because of them, you begin to feel cheerfulness, willingness to act. At the same time, they suppress the growth hormone production: the body begins to spend more energy on daily activities and less on the restoration of cells and tissues.
During the day, sleep hormones, such as melatonin, are produced in small quantities, but when it gets dark, more melatonin begins to flow into the blood, and you tend to sleep. Stress hormones become less, and growth hormones stimulate the body’s recovery processes.
Hormonal changes inside the body during the day regulate sleep and wakefulness.
Five stages of sleep:
Sleep consists of two large phases – slow and fast sleep. Under normal circumstances, during the average eight-hour sleep, these phases alternate four to five times.
This stage lasts about ten minutes. Your eyes are closed, and you gradually relax as your brain activity decreases: it is a state of half-awake, half asleep. You can easily wake up and not even realize that you were asleep.
This is also a period of relatively light sleep. Brain activity becomes irregular but still strong enough. At this time it will not be so easy to wake up: your body is preparing to move to the first stage of deep sleep.
Stage 3 and 4
These stages of deep sleep are also called the phase of “slow waves”. At stage 3 it is quite difficult to wake up, the body temperature drops, muscles relax, and breathing and heart rate become slow. In order to feel rested in the morning, the body must now move to the deepest sleep phase.
Here, the sleep begins about half an hour after you fall asleep. Brain activity remains almost at the level of wakefulness; blood pressure, pulse, body temperature, and breathing rate increase. Pupils move quickly under the eyelids and the person clearly has dreams.
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