How sleep phases affect human health and what is the secret to good sleep

A person's proper sleep helps restore all functions of the body. During rest, physical strength and energy balance are restored, information received during the day is sorted and processed, the immune system is strengthened, and other important processes occur. The phenomenon of sleep has not been fully studied by scientists, but there is research data that helps us better understand it and understand why it is beneficial for health. During the night we are in different phases of sleep, during which certain changes occur in the body.

Dream scenario

Sleep has two main phases: slow (orthodox, deep) and fast (paradoxical, superficial).
The slow-wave sleep phase is the beginning of night's rest; it takes up three-quarters of the total time we spend in the arms of Morpheus. Next comes the REM sleep phase, during which brain activity increases. Our body does not sleep, consciousness and subconsciousness exchange data, information is filtered, which improves our cognitive abilities. NREM sleep and the following REM sleep together constitute one cycle. It lasts for the average person about 1.5-2 hours. In total, we go through 4 to 6 cycles per night, at the end of which we should get a good night’s sleep.

It is noteworthy that slow-wave sleep becomes shorter and shorter with each new cycle, and fast sleep becomes longer. In order for the restoration of body functions to take place fully, all cycles must be completed before 4 am. After this, rest continues, but the orthodox phase no longer occurs.

You need to wake up precisely at the moment of REM sleep, since at this time all our systems are activated.

Physiology of the sleep process

Healthy sleep can last from 4 to 8 hours. However, these indicators are quite subjective, since the duration of sleep depends on the person’s physical fatigue. A significant amount of work done during the day may require a longer night's rest. Normal sleep is cyclical and is required by the human body at least once a day. Sleep cycles are called circadian rhythms. Every 24 hours, circadian rhythms are redefined. Light is considered the most important factor in sleep. The concentration of photodependent proteins in the body depends on its natural cycle. Typically, the circadian cycle is related to the length of daylight hours. Just before sleep occurs, a person feels drowsy, his brain activity decreases, and there is also a change in consciousness. In addition, a person who is in a sleepy state experiences a decrease in sensory sensitivity, a decrease in heart rate, yawning, and also a decrease in the secretory function of the lacrimal and salivary glands. Another physiological feature of sleep is a process called “vegetative storm”, i.e. when various forms of arrhythmias are observed, an increase or decrease in blood pressure, increased blood supply to the brain and secretion of the adrenal glands, erection of the clitoris and penis.

Alternating stages of slow-wave sleep

Our falling asleep begins with slow sleep. It is divided into 4 stages, during which different processes occur in the body. With the help of electroencephalographic studies, scientists were able to obtain an electrical picture of sleep and find out how long each stage lasts, how the brain behaves, what electrical impulses pass through it at a certain time, and what they influence. At the same time, a person’s rest is not disturbed; special devices read information from the moment of falling asleep until waking up. With the help of such studies, the stages of orthodox sleep have been established, which we will consider in more detail.

What is slow wave sleep?

NREM sleep (also called orthodox sleep) lasts 80 to 90 minutes and occurs immediately after a person falls asleep. The formation and development of slow sleep is ensured by the anterior parts of the hypothalamus, raphe nuclei, nonspecific nuclei of the thalamus and the middle part of the pons (the so-called Moruzzi inhibitory center). At the first stage of slow-wave sleep, the alpha rhythm decreases, transforming into slow low-amplitude theta rhythms, equal in amplitude to the alpha rhythm or exceeding it. The person is in a state of drowsiness (half-asleep), and dream-like hallucinations are observed. Muscle activity decreases, heart rate and breathing decrease, metabolic processes slow down, and the eyeballs move slowly. At this stage of sleep, solutions to problems that seem unsolvable during wakefulness are intuitively formed. At the very least, the illusion of their existence may arise. The first stage of slow-wave sleep may also include hypnogogic jerks.

In the second stage of Non-REM sleep (this is usually light and shallow sleep), a further reduction in muscle activity occurs, the heart rate slows down, body temperature drops, and the eyes become motionless. The second stage is approximately up to 55% of the total sleep time. The first episode of the second stage lasts approximately 20 minutes. The electroencephalogram shows at this moment the predominant theta rhythms and the emerging sigma rhythms (the so-called “sleep spindles”), which are essentially rapid alpha rhythms. At the moment of the appearance of sigma rhythms, consciousness turns off. However, during pauses between sigma rhythms, which occur at a frequency of 2 to 5 times per minute, a person can be easily awakened.

At the third stage of slow-wave sleep, the total number of delta rhythms is no more than 50%. At the fourth stage this figure exceeds 50%. The fourth stage is slow and deep sleep. Quite often stages III and IV are combined and called delta sleep. It is extremely difficult to wake a person during delta sleep. Dreams usually appear at this stage (up to 80%). A person may begin to talk, sleepwalking is possible, nightmares may occur and enuresis may develop. At the same time, a person usually does not remember any of the above. The third stage lasts from 5 to 8% of the total sleep time, and the fourth stage takes from 10 to 15% of the entire sleep period. The first four stages of slow-wave sleep in a normal person last from 75 to 80% of the total duration of this physiological process. According to the researchers, Non-REM sleep provides complete restoration of the energy expended during the day. In addition, the slow-wave sleep phase allows you to record conscious memories of a declarative nature in your memory.

The importance of deep sleep for the body

Many scientists have conducted research into the functions of slow-wave sleep. During the experiments, volunteers were woken up when they were sleeping the deepest. The results showed that the subjects felt muscle pain during awakening, were poorly oriented in space and time, and could not think clearly. Their cognitive and physical performance also deteriorated during the day, even if the rest of the night's rest lasted the required amount of time.

Experts have come to the conclusion that the body perceives the lack of a slow phase as a completely sleepless night. During deep sleep, organs and tissues are restored, as the pituitary gland begins to actively produce somatotropin (growth hormone).

The areas of the brain responsible for storing information also renew their resources. The longer the orthodox phase lasts, the higher the physical and mental indicators become.

However, there are also not very pleasant phenomena in this phase. If a person suffers from enuresis, talks in his sleep, or is a somnambulist, then disorders manifest themselves precisely during delta sleep. This happens for the reason that consciousness is completely switched off, replaced by the subconscious, which we cannot control.

Dreams

Along with the corresponding physiological process, the word “sleep” also means a sequence of images that arise in the REM sleep phase and, in some cases, are remembered by a person. A dream is formed in the consciousness of a sleeping person, consisting of a variety of subjectively perceived tactile, visual, auditory and other images. Usually the person who is dreaming is not aware that he is in a dream state. As a result, the dream is perceived by him as an objective reality. An interesting type of dreams are lucid dreams, in which a person understands that he is dreaming and therefore can control the development of the plot in the dream. It is believed that dreams are inherent in the REM sleep phase, which occurs once every 90-120 minutes. This phase is characterized by rapid movement of the eyeballs, increased heart rate and breathing, stimulation of the pons, as well as short-term relaxation of skeletal muscles. According to the results of recent research, dreams may also be characteristic of the slow-wave sleep phase. At the same time, they are less emotional and do not last as long as REM dreams.

Duration of the slow phase

Every person knows approximately how much time he needs to sleep. But calculating how long the slow phase should have is quite difficult. In general, it takes up from 30 to 70% of the total night's rest and will vary from person to person.

In studies conducted at the University of Surrey, it was found that subjects aged 20 to 30 years spent more time in the Orthodox phase than representatives of older age groups. Older people almost always have problems with sleep; their delta phase is much shorter than that of young people.

On average, young people spend 118 minutes per night in slow-wave sleep. However, it was found that in emergency conditions the body can independently extend this time. The Orthodox phase becomes longer if a person suddenly loses weight, so ladies on a diet often experience fatigue and cannot get enough sleep in the same amount of time that they had before body correction. Also, this mechanism is triggered when the functioning of the thyroid gland is disrupted; it is activated by an imbalance of hormones.

People who engage in heavy physical labor should have more deep sleep, so athletes rest for 11-12 hours.

Main stages of slow-wave sleep

When falling asleep, a person finds himself immersed in a slow phase. It received this name because of the leisurely movement of the pupils at this stage. In this phase, all natural processes in the body calm down. Blood pressure decreases, the brain begins to rest, relaxes, and the heartbeat becomes less frequent.

The nightly rest cycle consists of four stages of slow-wave sleep and two stages of fast sleep. With the onset of night, slow-wave sleep has an advantage; towards the end of the rest, the share of fast sleep increases.

In slow-wave sleep there are stages of drowsiness, then there are “sleep spindles”, then delta sleep follows. Real deep sleep will occur during the deep delta stage of sleep. These stages differ from each other in physiological parameters and actions occurring in the body.

When falling asleep, physiological categories change. The heartbeat decreases, blood pressure decreases, and blood moves more slowly through the vessels. When the last stage is reached, the heartbeat becomes faster and blood pressure begins to rise. At the same time, the body prepares to move on to the next fast phase. During the slow-wave sleep stage, the events of the past day are replayed in the memory, so a special rhythm of breathing and twitching of the limbs is possible.

During deep sleep, damaged cells are restored, which is why this stage is so important for maintaining youth and healing.

In difficult situations, the body independently prolongs this stage. So a person who adheres to a strict diet will feel weak and begin to sleep a lot. This body requires more time to recover. This happens in diseases of the thyroid gland, in professional athletes, and in people engaged in heavy physical labor.

The norm of deep sleep in adults should not be disturbed. If you don't get enough sleep, it will be difficult to compensate for the deficit in the slow stage of sleep. The shortage will constantly accumulate and negatively affect well-being and performance. With a prolonged disruption in the sleep schedule, for example, during a night work schedule, disturbances in the endocrine system begin. Growth hormone stops being produced, which means that a person’s abdominal fat increases. Tissues cease to renew themselves steadily, new pathologies develop, and chronic diseases worsen.

Nap

The first stage is the slow phase, lasts up to 10 minutes. In this case, slow movements of the pupils under closed eyelids are noted. The body is in a soft, sleepy state, in which the physiological indicators of pulse, respiration, and pressure decrease. But it’s still easy to wake a person up. The brain is not resting yet, but is actively working. In this state, you can find answers to unsolvable problems. One has only to remember about them. In the morning it will not be possible to restore the chain of decisions, but the conclusion will remain in memory. If you constantly wake a person up during the slow phase, he will gradually become irritable and nervous.

For every person, the importance of a good night's sleep cannot be overestimated. This is the key to good performance the next day and the health of the body.

During the night, 4-5 cycles alternate, each of which includes a slow phase and a fast one. It is difficult to say which of them is more important for the body, but most scientists are inclined to believe that deep sleep is responsible for restoring many functions of the human body.

Deep phase compensation

Often people who do not have a stable schedule think like this: “Today I’ll work late, and tomorrow I’ll get a good night’s sleep.” If you wake up earlier in the morning, you will create a deficit of REM sleep, which can actually be compensated for with a 20-30 minute rest at lunch or the next night. However, such tricks will not work with the slow phase, because our rest begins with it.

Lack of deep sleep gradually accumulates in the body, which negatively affects a person’s ability to work. However, there are other, more serious problems that you may face with chronic sleep deprivation.

First of all, the endocrine system malfunctions, growth hormone ceases to be produced, which causes a person’s belly to suddenly increase in size. Tissues and organs also stop renewing normally. Lack of sleep is a catalyst for aging. Immunity drops sharply, chronic diseases worsen, and the risk of viral, fungal and bacterial infections appears.

From here only one conclusion follows: it is unrealistic to sleep through the slow phase on subsequent nights or to “sleep” it in advance; the normal functioning of the body can only be maintained by observing a strict schedule of rest and wakefulness.

Phases and stages

There are 4 main stages of sleep:

1. Falling asleep.
2. Slow sleep.
3. Fast.
4. Awakening.

Each phase is characterized by a certain duration and accompanying physiological processes.

Falling asleep

1st phase - falling asleep. While a person falls asleep, the sensitivity of his sensory systems and heart rate decrease, and his consciousness gradually “turns off.” Even the glands begin to work less actively. This can be noticed by burning eyes and dry mouth. The approaching phase of falling asleep can be easily determined by obsessive yawning.

Night owls who stay up late reading or watching TV often notice such sensations. If all the described signs are present, it’s time to give the body a rest. The falling asleep phase is the shortest. It usually lasts about 10 minutes. Then slow-wave sleep begins, which in turn is divided into several stages.

What is slow wave sleep

Slow rest is a rest in which brain activity remains in the low amplitude range. Scientists record this using an EEG (electroencephalogram).

All phases of human sleep take different durations. If it takes 10 minutes to fall asleep, then the slow-wave sleep phase requires from 80 minutes to 1.5 hours. The duration depends on the individual characteristics of a person’s physiology, as well as on his rest regime. Unlike REM sleep, the NREM sleep phase is divided into several stages.

Stages

Slow wave (aka slow wave) sleep has the most complex structure. It is divided into the following 3 phases (or cycles):

Increasing Orthodox phase

If you feel that the slow phase does not have as much time as is needed for normal rest, you can increase it. Most often, such problems appear in people who cannot fall asleep for a long time, because the first sleep cycle contains the longest orthodox phase, and then it becomes less and less long. To get rid of this problem, you should follow these simple recommendations:

• Establish a rational sleep-wake schedule.
• Go to sleep and wake up at the same time, even on weekends.
• Play sports during the day, but physical activity should not be given to the body 3 hours before resting at night.
• Organize a favorable climate in the relaxation room and a comfortable sleeping place.
• Do not drink alcohol, caffeinated drinks, energy drinks, or smoke before going to bed.
• Watch your diet - you cannot overeat at night, eat chocolate or any other sweets, as these foods have a stimulating effect on the nervous system.

Sleep: functions, structure, prevention of disorders. Reference

The average duration of sleep is usually 6-8 hours a day, but fluctuations are possible: with sleep disorders, its duration can range from several minutes to several days.

The duration of sleep in newborns, adults and the elderly is 12-16, 6-8 and 4-6 hours per day, respectively. Sleep duration of less than 5 hours - hyposomnia - or disruption of its physiological structure are considered risk factors for insomnia.

Considering that a person spends a third of his life sleeping, the nature of sleep has always aroused increased interest among scientists.

One of the first and most important results of laboratory research was the discovery that a sleeping person periodically experiences so-called headaches during the night. rapid eye movements (REM). The phase of sleep during which REM is recorded has been called "rapid eye movement" (or paradoxical) sleep or REM sleep. During this phase, a person most often dreams. The remaining stages of sleep, during which rapid eye movements are not observed, have been collectively called "non-REM" sleep or non-REM sleep.

The transition from wakefulness to sleep is accompanied by repeated floating sensations, often interrupted by a sudden start that awakens the person again. This sudden jerk is called a myoclonic jerk. The significance of this twitching is unknown, but it is believed that it may be an activation reaction to a significant, albeit weak, external stimulus.

During sleep, two main phases alternate. REM sleep occurs on average every 70 to 90 minutes of sleep. In this case, the first 75–100 minutes are spent in non-REM sleep. REM sleep occurs four to six times each night, depending on the total sleep duration rather than the individual. The first period of REM sleep lasts approximately 10 minutes, and the last period lasts 20–35 minutes. In general, REM sleep takes up about 20% of total sleep time.

One of the cardinal discoveries in the field of sleep research was the fact that in 80% of cases, dreams were reported by people awakened in the REM phase. The same people who were awakened in the non-REM phase rarely reported dreams. Other studies have shown that people who are awakened during REM sleep in the second half of the night report better dreams.

In general, the threshold for awakening is lowest during REM sleep, which is the easiest sleep to interrupt. According to research, it is more difficult to wake a person at any stage of sleep at the beginning of the night than at the same stage in the second half of the night.

The most comfortable sleep, according to experts, is facilitated by physical activity during the day, proper diet and a clear daily routine (do not have dinner after 6-7 pm and go to bed at the same time). A warm bath with pine extract or sea salt or a hot foot bath before bed is also an effective prevention of insomnia.

If you feel hungry late at night, doctors advise eating only sleep-stimulating foods that are high in the amino acid tryptophan, which helps the brain produce the calming substance serotonin. Tryptophan-rich foods include bananas, wholemeal biscuits, tuna, lettuce, yogurt, peanuts, butter and dates. It is worth excluding chocolate, sugar, salty foods, cheese (they can cause thirst), as well as eggplant, spinach and tomatoes (they have a stimulating effect on the body).

To prevent insomnia, doctors advise not to drink alcohol or coffee immediately before bed, to use a small pillow with natural filling, and to drink a glass of warm milk or warm water with honey before bed.

The material was prepared based on information from open sources

In conclusion

Slow-wave sleep is very important for humans, as it is responsible for restoring physical performance, the immune system and cognitive abilities. It is also necessary to maintain youth, since it is in the orthodox phase that skin cells are renewed.

You need to fall asleep at 21.00-22.00 in order to get your “portion” of deep sleep and get quality rest during the night. If you follow the schedule, you will notice within 2 weeks how your well-being and appearance will improve.

Author: Dasha Pashchenko

Fast phase

Scientists have not fully figured out what REM sleep is, how such strange processes can occur in the body, and what significance it has for humans. If everything is more or less clear with slow sleep - this is a period of active recovery of the body and complete relaxation, then the reactions of the brain and the vital functions of the body during REM sleep are completely different.

During REM sleep, a person's eyeballs under closed eyelids begin to move quickly along a chaotic trajectory. From the outside it seems that a person is closely watching something. In fact, this is so, since it is in this phase that dreams appear. But eye movement is not the only and far from the main difference between REM sleep.

What was seen on the encephalogram, and later on the tomogram of the brain during the fast phase, so amazed scientists that it received another name: “paradoxical sleep.” All readings during this period may be practically no different from those taken in a state of active wakefulness, but at the same time the person continues to sleep:

• blood pressure rises sharply;
• certain muscle groups become toned;
• various parts of the brain become active;
• body temperature changes;
• heart rate increases;
• breathing becomes fast and intermittent.

In fact, the entire body is “turned on” in the dream as if it were a real event, and only the person’s consciousness is turned off. But if you wake him up at this moment, he will be able to tell the plot of the dream in great detail and at the same time will experience emotional experiences.

Interestingly, it is during REM sleep that hormonal changes occur. Some scientists believe that it is necessary for emotional “reset” and balancing of the endocrine system.

REM sleep also helps in regulating the level of sex hormones. Nocturnal erections, wet dreams and spontaneous orgasms occur during this phase. Moreover, they are not always accompanied by dreams of an erotic nature.

At the same time, most heart attacks or strokes occur, due to the fact that the relaxed heart and blood vessels are subjected to sudden stress.

At the beginning of the night, the fast phase does not last long - from 5 to 10 minutes, and a person spends most of the time after falling asleep in slow-wave sleep. But in the morning the phase relationship changes. The periods of REM sleep become longer and longer, and the periods of deep sleep become shorter and shorter, and at one point the person wakes up.