The Structure Of Sleep

What stages of sleep are there, and what are the characteristics of each of the stages of sleep?

What stages of sleep are there, and what are the characteristics of each of the stages of sleep?

Sleep is a certain state of human consciousness caused by the activity of various brain structures. Sleep includes several stages that repeat throughout the night.

It is known that during sleep, 2 key phases of sleep successively alternate: slow sleep and rapid sleep. At the very beginning of sleep, the duration of the slow phase is longer, and at the stage before awakening, the duration of REM sleep increases. Polysomnography (a system that includes recording of electroencephalogram, electromyography and electrooculogram) shows that in most people sleep consists of an average of 4-6 cycles lasting 80-100 minutes.

Each such cycle includes phases of slow (orthodox) sleep, the share of which is 75% of sleep, and fast (paradoxical) sleep, the share of which is 25%.

Let's dwell in more detail on both phases of sleep .

Slow-wave sleep (orthodox, slow-wave sleep)

Slow sleep consists of four stages :

The first stage : in the first stage of sleep, the alpha rhythm decreases, and low-amplitude slow delta and theta waves appear. At this moment, a person is in a state of slumber, he may be visited by half-asleep hallucinations or delusions. It is believed that intuitive ideas can appear at this stage, contributing to a potentially successful solution to the problem that occupies a person.

The second stage : in the second stage of slow sleep, a sigma rhythm and an accelerated alpha rhythm (12-14-20 Hz) appear. With the beginning of this stage, there is a disconnection of consciousness. In the pauses between the increased rhythm (2-5 times per minute), a person can be easily woken up. The threshold of perception increases. The most sensitive analyzer is auditory. Yes, a mother wakes up when a child cries, or any person wakes up at loud enough extraneous sounds.

The third stage : the third stage of slow-wave sleep has all the features of the second stage, but slow high-amplitude delta oscillations (2 Hz) are also added.

The fourth stage : The fourth stage is the stage of the deepest sleep. Delta oscillations predominate during this stage. Often the third and fourth stages are combined under the general name delta sleep. During the fourth stage of slow-wave sleep, it is difficult to wake a person. Dreams usually occur precisely at this stage, in addition, sleepwalking attacks and nightmares may occur at this stage.

All four slow-wave sleep stages usually occupy approximately 75-80% of the total sleep period. It is believed that a person needs slow sleep to restore energy.

REM sleep (paradoxical, rapid-wave sleep, rapid eye movement sleep, REM sleep)

This is the fifth stage of sleep : the fifth stage of sleep is characterized by rapid fluctuations in the electrical activity of the brain, close in value to beta waves. The fifth stage resembles a state of wakefulness, but due to a sharp decrease in muscle tone, a person is in a motionless state. The eyeballs periodically make rapid movements. The connection between dreams and rapid eye movement has been proven. If you wake up the sleeping person in this phase of sleep, then, most likely, he will tell you about a vivid dream.

From cycle to cycle , the phase of REM sleep lengthens, and the depth of sleep, in turn, decreases. Slow-wave sleep is easier to interrupt than REM sleep, despite the fact that REM sleep is significantly closer to the threshold of wakefulness.

Experiments have confirmed that regular interruption of rapid-wave sleep threatens with serious mental disorders, while in case of disruption of slow-wave sleep, the body is able to adapt. To avoid serious consequences, the part of interrupted REM sleep must be filled in the following cycles.

It is believed that rapid sleep ensures processing of information, exchange of information between consciousness and subconsciousness.

Sleep cycle in children

Sleep cycles, corresponding to fast and slow phases, are formed even before birth - at the 20th week. In premature babies, REM sleep makes up 60-80% of the total amount of sleep, in full-term babies, approximately 40-50% of the total amount of sleep. Newborns are characterized by a rapid transition from wakefulness to REM sleep, bypassing slow-wave sleep.

Sleep cycle in young people

In young people, sleep begins with the 1st phase, successively passes to the 2nd, third and 4th phases. Then the countdown to phase 2 begins. Thus, the phases replace each other from the 2nd to the 5th (quick sleep). In the morning, the fourth stage is absent.

Healthy sleep of the elderly

What should you do to fall asleep easily every night and wake up in the morning refreshed and rested? The periodicity of the REM sleep phase is 70-90 minutes. The first period of REM sleep lasts about 10 minutes, and the last one extends to 20-35 minutes. Closer to the morning hours, stages 3-4a take less time, and 2a and 5a take more time.

Sleep cycle in the elderly

Older people sleep less than young people, more than half of older people take a nap during the day. During the night, the elderly wake up more often. REM sleep is interrupted much more often in them, although in percentage it remains the same as in young people. The elderly have difficulties falling asleep (they do not manage to fall asleep for a long time), and it is easier for them to wake up in the morning. Over time, the structure of an elderly person's sleep begins to resemble the structure of a child's sleep.