In the non-rapid eye movement sleep stage, the whole body muscles relax, there is no eye movement, and the visceral parasympathetic nerve activity is dominant. Heart rate and respiration slow down, blood pressure decreases, gastrointestinal peristalsis increases, basal metabolic rate is low, brain temperature is slightly lower than when waking up, and total cerebral blood flow is lower than when waking up. Non-eye rapid movement sleep can be divided into four stages according to its EEG characteristics: in the first stage, the brain waves are mainly θ waves, without spindle waves or K complex waves. In fact, it is a transitional stage from full wakefulness to sleep, where the response to external stimuli is weakened, mental activities enter a floating realm, and thinking is out of touch with reality; In the second stage, the brain wave is a composite wave of shuttle wave and K wave, and the δ wave is less than 20%. In fact, people have entered the real sleep, which belongs to shallow sleep. In the third stage, the delta wave of brain waves accounts for 20% ~ 50%, which is a moderate deep sleep; In the fourth stage, the delta wave of brain waves accounts for more than 50%, which belongs to deep sleep and is not easy to be awakened.
Rapid eye movement sleep stage
During REM sleep, desynchronized low-amplitude brain waves with mixed frequencies appear. Eye movements are rapid, there are a lot of paroxysmal convulsions in the muscles of face and limbs, sometimes lips suck, throat makes short sounds, hands and feet creep, visceral activity is highly unstable, breathing is irregular, heart rate changes frequently, gastric acid secretion increases, sometimes penis erects, and blood flow in various parts of the brain increases significantly compared with when waking up; The diencephalon and brain stem are the most obvious, while the hippocampus and anterior commissure of the brain increase more, and the oxygen consumption of the brain is also significantly higher than that of waking.
Dormancy mode
It should be noted that the sleep stage is artificially defined according to brain waves and physiological manifestations for the convenience of research. In fact, it is difficult to draw a clear line at each sleep stage, which is often gradual, overlapping and staggered, with different emphases. People's sleep has about 4 ~ 6 sleep cycles in one night, which are interrelated and repeated.
First of all, the time from going to bed to falling asleep is called sleep latency, which is generally 20 ~ 23 minutes for adults. Then enter the first stage of NREM sleep, and after about 0.5 ~ 7 minutes, enter the second stage of NREM sleep; After 30 ~ 38 minutes, enter the third and fourth stages of NREM sleep (collectively referred to as δ sleep), lasting for about a few minutes to 1 hour; Return to the second stage of NREM sleep; Go to REM sleep about 70 ~ 90 minutes after you start to fall asleep, usually only about 5 minutes; Then return to the second stage of NREM sleep, which is the beginning of the second sleep cycle.
From the second sleep cycle, δ sleep gradually shortens, while REM sleep gradually prolongs, with a cycle of about 90 minutes. In the second half of the night, the NREM sleep in the fourth and third stages becomes less and less, and gradually disappears in the fourth stage. REM can even sleep for 60 minutes, and its physiological performance (rapid eye movement period) and psychological performance (dreaming) are getting stronger and stronger.
Generally speaking, young people sleep for one night, the first phase of NREM sleep accounts for about 5% ~ 10%, the second phase accounts for 50%, the third and fourth phases account for 20%, and REM sleep accounts for 20% ~ 25%. From childhood to old age, with the growth and development to aging, REM sleep and NREM sleep in the third and fourth stages gradually decrease. After 60 years old, there is basically no NREM sleep in the fourth stage, and the number of waking up at night increases.
Sleep stage
The connection between people and the external environment weakens or even disappears during sleep. Therefore, people have long believed that sleep is a complete rest process needed by the body to eliminate fatigue. However, the measurement of human and animal EEG activity shows that the brain activity during sleep is not in a static state, but presents a series of periodic changes of active regulation. At this time, various physiological functions of the body, such as sensory function, motor function, autonomic nerve function, etc., are also carrying out regular activities to varying degrees with the change of sleep depth. The common method in the world is to divide sleep into two different stages according to the changes of EEG, eye movement and muscle tension during sleep, namely non-eye rapid movement sleep (NREM) and eye rapid movement sleep (REM).
Non-eye rapid movement sleep (NREM): characterized by falling asleep at night, and progressing with the deepening of sleep. At this stage, people's breathing becomes shallow, slow and even, their heart rate slows down, their blood pressure drops, their muscles relax (they can still maintain a certain posture), and there is no obvious eye movement. At this stage, it can be divided into four stages, the 1 stage is a sleep stage, the second stage is a light sleep stage, the third stage is a moderate sleep stage, and the fourth stage is a deep sleep stage. During this period, normal people have a big posture adjustment every 20 minutes on average, and some people even have a posture adjustment activity every 5 minutes.
Rapid eye movement sleep (REM): After about 90 minutes of sleep, the human body enters REM, which is characterized by rapid eye movement. At this stage, the sensory function of human body is further reduced, muscles are more relaxed and tendon reflex disappears. At this time, blood pressure rises slowly during eye movement sleep, breathing is slightly faster and irregular, and body temperature and heart rate also rise. At this stage, various metabolic functions in the body are significantly increased to ensure the synthesis of protein in brain tissue and the supplement of consumables, so that the nervous system can develop normally and store energy for the next day's activities. When the sleeper is awakened at this stage, 74%-95% people complain that they are dreaming and can remember the content of the dream. During slow eye movement sleep, only a few people complain that they are dreaming. It is considered that NREM sleep is mainly a rest of cerebral cortex, while REM sleep is mainly a rest of the whole body.