Modern people are increasingly saving on sleep, devoting this most important time for recuperation to watching movies, working or night gatherings. But healthy sleep helps the brain reboot, strengthens the immune system and normalizes the psycho-emotional state. The condition of the skin, mood during the day, and the body’s resistance to stress and illness depend on it.
Sleep, as a physiological process, consists of two phases that are repeated 5-7 times per night. If the body does not pass them during a healthy night's sleep, fatigue, apathy and health problems may appear.
Human sleep according to the rules: sleep phases by the clock and their features
Sleep consists of slow and fast phases, alternately replacing each other. The duration of an individual stage ranges from one to two hours. In turn, the slow phase is divided into 3 stages. In general, our dream looks like this:
- Falling asleep
– preparing the body for rest. If you start yawning, then it's the perfect time to go to bed. While falling asleep, biological processes slow down and the body's sensitivity decreases. This stage should normally take no more than 10 minutes.
- Slow phase
– the longest stage of sleep (occupies 75% of the total). Its main task is to restore the body. This phase consists of a drowsiness (about 10 minutes), a light stage (about 20 minutes, when consciousness turns off, but hearing activity remains) and a deep stage (lasts about 90 minutes). By the way, dreams can appear at a deep stage, but, as a rule, a person does not remember them.
- Fast phase
– short stage (about 25% of the total). As we enter REM sleep, we begin to have vivid dreams. At the same time, the information received during the day is processed, and the body’s activity increases.
Dreams themselves are formed under the influence of emotional experiences, memories, physical sensations, etc. According to Hippocrates, dream plots, being the result of the work of the subconscious, can tell a lot about a person’s physical state.
Neurodegenerative diseases and sleep
The most common neurodegenerative diseases are Alzheimer's disease [21], [22] and Parkinson's disease. Unfortunately, their fame is sad. In Alzheimer's disease, beta-amyloid plaques accumulate in neurons, and in Parkinson's disease, Lewy bodies (alpha-synuclein) are formed in neurons. The amount of amyloid in this case correlates with sleep quality in healthy people aged 60–65 years [23]. However, it is not a fact that sleep disturbances occur due to the increased content of this protein in neurons. The opposite has also not been proven: there is no reason to claim that lack of sleep provokes Alzheimer's disease. However, sleep disturbances can potentially help diagnose Alzheimer's disease at an early stage. This is also supported by the fact that as the symptoms of this dementia intensify, the severity of sleep disorders increases (the same applies to dementia with Lewy bodies - a disease that resembles Parkinson's disease in some symptoms, and Alzheimer's disease in some others.) In addition, despite frequent naps; in patients with Alzheimer's dementia, sleep duration is significantly reduced [24].
In Parkinson's disease, sleep becomes interrupted, the REM sleep phase is disrupted, the frequency of sleep spindles and the duration of slow-wave sleep decreases, and diurnal fluctuations in cortisol levels are smoothed out. It turns out that in Parkinson's patients, sleep and wakefulness are not clearly divided into periods, the boundaries between them are to some extent blurred.
In Huntington's chorea, sleep and wakefulness are fragmented [25]. A person is active at night and falls asleep late. He has a reduced proportion of REM sleep, an increased frequency of sleep spindles, and during stage 1 non-REM sleep, chorea can be observed - chaotic uncontrolled movements of the limbs, the main manifestation of this disease during wakefulness.
With ALS (amyotrophic lateral sclerosis), breathing disorders occur during sleep. REM sleep becomes intermittent, and the proportion of slow-wave sleep decreases. In addition, the course of daily fluctuations in cortisol is disrupted.
Interestingly, the manifestation of almost all of the above sleep disorders can be weakened with the help of phototherapy (periodic exposure to bright light) and organized (not uncontrolled!) melatonin intake.
Table 1. Summary table of associations of the most common sleep disorders with neurodegenerative diseases.
| Age-related degeneration | Alzheimer's disease | Parkinson's disease | Huntington's chorea | Amyotrophic lateral sclerosis | |
| Which neurons and structures are damaged? | Basal forebrain, locus coeruleus, cerebral cortex, dopaminergic neurons, orexin neurons, acetylcholine receptors | Basal forebrain, cerebral cortex, cholinergic neurons | Substantia nigra, dopaminergic neurons, orexinergic neurons | Basal ganglia, dopaminergic neurons | Motor neurons of the motor cortex, spinal cord and brain stem. Accompanied by a decrease in the activity of neurons that secrete serotonin |
| Sleep disorders | Fragmented sleep and wakefulness, out of phase with normal circadian rhythms, increased daytime sleepiness | Reduced total sleep time | Fragmented sleep, behavioral disturbances during REM sleep (moving limbs, making sounds) | Sleep and wakefulness are fragmented, the proportion of REM sleep is reduced | Breathing disorders during sleep, insomnia. The degree of deterioration in sleep quality corresponds to the severity of other manifestations of the disease |
| Signs of probable violations | Disturbance of the melatonin system of the brain | The order and timing of REM sleep | REM sleep behavior disorder | Many sleepy spindles | Various sleep disturbances (a likely sign of sleep apnea) |
| Circadian rhythm disorders | Peak and trough episodes are out of phase relative to normal circadian rhythms | Disturbances of the melatonin system and diurnal changes in core body temperature | Shift in periods of greatest and least activity, smoothed daily changes in cortisol concentration (peaks become lower and less pronounced) | Falling asleep is shifted to a later time, at night the patient shows increased activity compared to peers | Daily fluctuations in cortisol levels do not correspond to the normal rhythm |
| Non-REM sleep | Short slow-wave sleep | Short slow-wave sleep, few sleep spindles | Short slow-wave sleep, few sleep spindles | At the first, extended stage of sleep, chorea is observed. Many sleepy spindles | Short slow-wave sleep |
| REM sleep | Shortened REM sleep | Shortened REM sleep, increased activity of inducible NO synthase | REM sleep behavior disorder, symptoms of REM sleep appear during non-REM sleep | Shortened REM sleep, difficulty transitioning into it from non-REM sleep | Breathing disorders, short and fragmented REM sleep |
| Wakefulness | Fragmented wakefulness, frequent episodes of dozing, increased daytime sleepiness | Fragmented wakefulness, frequent episodes of dozing | Increased daytime sleepiness | Some studies indicate disturbances in awakening, but deviations from healthy peers in patients are insignificant | Increased daytime sleepiness |
| Treatment options for disorders | Phototherapy | Phototherapy, exercise, orexin/hypocretin receptor antagonists (used in mice) | Phototherapy | Setting the circadian rhythm by eating according to a clear schedule, alprazolam (restores circadian rhythms and slows down the decline in intelligence) | Melatonin preparations, mechanical ventilation (CPAP) |
About the most valuable time for sleep and easy awakening
The most important recovery processes and restart of the central nervous system occur between 22:00 and 24:00. If you want to wake up rested and fresh, it is best to go to bed at this time. Going to bed after midnight is not recommended. Due to the lack of proper rest, the nervous system wears out faster, and irritability and nervousness appear.
It is best to wake up during the REM phase of sleep, when the body's sensitivity and activity increase. If you wake up at a slow stage, weakness and fatigue arise, which will accompany the person throughout the whole day. To calculate your ideal time to wake up, you can use a sleep sensor or fitness bracelet. These devices analyze your pulse, blood pressure and heart rate and tell you the time when you can get up.
To summarize, it is worth emphasizing that getting enough hours of sleep is important, but the quality of sleep should also be good. You can sleep for 8 hours straight and wake up completely exhausted. Therefore, a light dinner, less active leisure time in the evening, fresh air and lack of light in the bedroom are what will help you sleep not only for a long time, but also soundly.
Physiological mechanisms of sleep
I.P. Pavlov and his colleagues were always concerned with the question: is there a “sleep center” in the brain? In the second half of this century, a number of studies were conducted indicating that our brain has several systems of so-called tonic depolarization that ensure its activity in a state of wakefulness. There are at least five or six of them, and they are located along the entire length of the conventional cerebral axis. Also the site of wakefulness zones are the stem reticular formation, the dorsal raphe nuclei, the locus coeruleus and several other brain regions.
The logical conclusion follows that if there are “waking” centers in the brain, then “sleepy” ones must also be present. However, everything is far from so simple. Nature has endowed the centers responsible for wakefulness with a feedback mechanism with special types of nerve cells that inhibit active neurons. It is noteworthy that these cells are located in different parts of the brain, but most of them are concentrated in the reticular formation. The mediator secreted by these cells is called gamma-aminobutyric acid. It is the main “inhibiting” brain substance.
Differences
Their differences include:
- Different number of stages.
- Eye movement. When slow, they move smoothly, and when fast, their movement is more active and continuous.
- Impact on growth. During the slow period, growth hormone is produced.
- The emergence of dreams. They can be seen in REM sleep.
- Breath. As you fall asleep, your breathing becomes louder but less deep.
- Brain temperature. In slow mode it decreases, and in paradoxical mode - vice versa.
Also in these phases there is a different state of the autonomic nervous system.
How to distinguish slow-wave sleep from fast sleep?
It is possible to roughly determine the sleep phase. To do this, you need to observe your body signals. During the fast phase, a person moves his arms or legs. During the slow stage, the muscles are relaxed and breathing is slow.
You can more accurately determine your sleep phase using electroencephalography.
Reference. Electroencephalography is a highly informative method that is used to diagnose the state of the nervous system. It is based on recording the bioelectric potentials of the cerebral cortex during human life.
Features of awakening
It is best to wake up during the fast phase. It is very difficult to wake up a sleeper during a deep cycle.
Waking up during slow wave sleep is unpleasant. A person will feel depressed and sluggish throughout the day. If he wakes up on his own at another time, he will be full of energy and feeling good.
In order to continue to lead an active lifestyle, he needs to rest daily for at least 4 completed cycles. They usually end before 4am. The last hours are spent restoring the nervous system.
If a person likes to sleep during the day, then the duration should not exceed 40 minutes. A longer rest will become deeper. Then the climb will be difficult, and you will feel tired and lethargic.
Sleep Research: Interesting Facts
The paradox of time perception is often encountered in relation to sleep. There are times when it seems like you just closed your eyes, and several hours have already passed. The opposite also happens: it seems that you slept all night, but 30 minutes have passed.
It has been proven that the brain analyzes sounds, sorts them, and can weave them into a dream. Moreover, in some phases people can awaken if they are called by name in a whisper. The greater the biological age of a person, the shorter the duration of the paradoxical stage. In infants it exceeds the slow one.
A person spends a third of his life sleeping. If you sleep less than a quarter of a day for two weeks, the state of the body will correspond to being intoxicated. Memory will deteriorate, concentration and reaction will suffer, and problems with coordination will arise. But many geniuses practiced polyphasic rest over a long period of time, the total duration of which was no more than half the norm. At the same time, they felt cheerful, their performance improved, and discoveries were made.
Absolutely all people see dreams, but almost all of them are forgotten. Animals also dream. Not so long ago, most of humanity saw black and white dreams, but now 85% of men and women view vivid stories. The explanation for this is the creation of color television broadcasting.
Blind people are also not deprived of dreams. If the blindness is acquired, then the pictures represent what was previously seen. In congenital blindness, vision consists of sounds, smells, and sensations. They do not experience the phenomenon of rapidly moving eyes under their eyelids. These people are much more likely to have nightmares.
The longest period of wakefulness of a healthy person was the period of 11 days during which an American schoolboy did not sleep. After a head injury and brain damage, a Hungarian soldier did not take a nap for 40 years. At the same time, he felt cheerful, did not experience fatigue or discomfort.
It is important to know! Few girls who dream of a slim figure know the following fact. Systematic lack of sleep leads to excess weight gain. One of the important conditions for losing weight is sufficient sleep.
Women's deep rest is often 20 minutes longer than men's, but the latter sleep more restlessly and wake up more often. The weaker sex complains more about sleep disturbances and gets less sleep. Ladies are more susceptible to emotionally strong visions and nightmares.
Features of the slow phase
There are 4 stages inside it. They all have different bioelectrical characteristics. As a person goes deeper into it, it becomes more and more difficult to wake him up.
To fall asleep, the brain begins to secrete a special substance. It causes lethargy and slows down your metabolism.
Periods
They include: nap, light, moderately deep and deep. The last two are collectively called delta sleep. At this time, specific delta waves are observed.
Signs
The sleeper begins to breathe slowly, his pulse slows down, and his eyes gradually stop moving.
Influence
The body is restored and healed, the body is filled with energy. The body is physically recovering.
