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Sleep - a unique combination of duty and pleasure

Michał Marciniak

You can read this text in 8 min.

Sleep - a unique combination of duty and pleasure

Panthermedia

Daytime naps

Is it possible to imagine life without sleep? Perhaps you can, but this is closer to science fiction. During the course of a day, we sleep, depending on the individual, 20-30% of the time. If something takes up so much time, it may be due either to a pleasure to which we are able to devote an unlimited amount of time, or to a duty we perform because we have an inner conviction of its necessity. Sleep is just such a unique combination of the two poles: duty and pleasure. What happens to the brain during sleep? When we fall asleep, does the 'brain switch off'?

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Table of contents:

  1. Falling asleep
  2. How we fall asleep..
  3. Stages of sleep
  4. Answers to questions, interesting facts
  5. Why do we actually need sleep?

Falling asleep

It would be great if every tired person, when going to bed, fell asleep relatively quickly. Unfortunately, how quickly we fall asleep is not just determined by the need for sleep, understood as fatigue, but by a number of external factors that need to exist for 'sleep to come'. Under normal circumstances, we will not begin to dream standing up - we need to take up a position as close to horizontal as possible. Falling asleep will also be hindered by our current emotional state - agitation, stress, anxiety, strong anger are also unfavourable circumstances. When we get up in the morning rested, regenerated and after an hour try to fall asleep again, it turns out that the brain currently has no need for sleep and, by activating certain hormonal pathways (associated with the release of, among other things, cortisol), will not allow us to fall asleep again. Other factors that make it difficult to fall asleep include: intense external stimuli (loud noises, sunlight, touch, etc.), eating a heavy, high-calorie meal before bedtime, taking substances that increase blood pressure (such as caffeine, nicotine).

During a sleep study (known as polysomnography, PSG), sleep latency is determined, i.e. the time we spend in bed before falling asleep. Falling asleep - the quieting of the electrical activity of the brain, the reduced awareness of incoming stimuli from the environment is the first phase of sleep - stage 1 of so-called NREM sleep. During this phase, a subjective sense of sleep is not always present, so its onset is measured from stage 2 of NREM sleep.

Once we have fallen asleep..

...this does not at all mean that our brain is switched off. The state of sleep differs from coma, anaesthesia or hibernation in that it is a completely reversible process under the influence of appropriately intensified stimuli. And since it is reversible it means that throughout its duration the electrical activity of the brain is preserved. Only different from the waking state.

During sleep, we can perform a polysomnographic study, which measures the body's activity during sleep - the bioelectrical activity of the brain (electroencephalography, EEG), eye movement activity (electrooculography, EOG), muscle tension (electromyography, EMG), heart activity, temperature and others. Based on the recorded measurements, sleep is divided into two main parts - NREM (non rapid eye movement) and REM (rapid eye movement), occurring alternately. NREM and the following REM form a so-called sleep cycle, which on average lasts 80 - 120 minutes. The length of a single sleep cycle is regulated by genetic factors. During the night, we "sleep" between 3 and 5 such cycles.

Sen rem, Sleep, Sleep nrem, Sleep-cycle, Stages-of-sleepHow to get a better night's sleep, photo: shutterstock

Stages of sleep

A healthy person's sleep starts with NREM sleep, which is definitely not a uniform time, which is why it has been divided into different stages:

  1. Stage 1 - this is actually the time when we just fall asleep. We assume the most comfortable sleeping position, the heart rate gradually slows down, blood pressure decreases, we breathe less frequently and more deeply, the brain becomes less and less aware of incoming information. Unless there is an intense stimulus, such as a sound, this stage usually lasts 5 - 10 minutes.
  2. Stage 2 - is determined by an EEG study, in which the characteristic "sleep spindles" appear. From this stage onwards, consciousness is switched off and from this time onwards, during the PSG examination, the length of sleep is measured (the first physiological harbinger of sleep). The first two stages are classified as shallow sleep.
  3. Stage 3 - waves with a frequency of no more than 2 Hz and an amplitude of no less than 75 µV are present on EEG examination. Such waves (so-called slow waves) are observed for 20 - 50% of the analysed time segment.
  4. Stage 4 - slow waves (described above) account for more than 50% of the time. Stages 3 and 4 are classified as deep sleep, otherwise known as slow-wave sleep.

The name 'NREM', or non-rapid eye movement sleep, was given based on the observation of the recording from the EOG test (electromyography). Eye movements are the feature, in addition to the electrical activity of the brain, that distinguishes NREM sleep from REM sleep. During NREM sleep, the muscles do not yet lose tension, they are just preparing for the actual rest that will come in the REM phase.

REM sleep, on the other hand, is a relatively uniform sleep phase, also not divided into stages. It is a time of eminently 'deep' sleep, in which the brain is least likely to respond to external stimuli. It is a phase of deep muscle relaxation - apart from the muscles that move the eyeballs, breathing and...inner ear, all muscles are characterised by atonia, i.e. lack of tension. Colourful dreams are also characteristic of this stage of sleep, which is explained by the rapid eye movements that also occur during this stage. It is as if the brain "follows" shifting images with its eyes. The length of this sleep phase is most responsible for rest and recuperation.

Answers to questions, interesting facts

Why is it sometimes easier for me to wake up and get up at 6am than 8am?

Very important in this aspect is the phase of sleep we are in when we wake up. Sleep is cyclical (consecutive NREM and REM sleep phases), and it can happen that at 6 a.m. the alarm clock hits stage 2 of NREM sleep (shallow sleep) and at 8 a.m. it hits stage 4 (deep sleep) and, paradoxically, it is easier to wake up at 6 a.m. than at 8 a.m.

Why is it that I sleep 8h (and I could sleep 12h) and am sleep-deprived, while my grandfather barely sleeps 6h (and that too intermittently) and is sleepy?

As we get older, the NREM sleep phase shortens and the length of REM sleep remains similar. Also the total sleep time is shortened (reduced NREM phase), but its 'efficiency' is sufficient. Therefore, neither 8-10h of sleep in a teenager nor 5-6h in a 70-year-old is surprising.

Why do I even wake up several times during the night?

Most likely, this is a normal phenomenon, related to the transition from REM sleep (deep sleep) to stage 1 NREM sleep (shallow sleep). These differences can cause awakenings, and which occur in most of us, only in the morning after waking up we do not remember them.

A number of mechanisms are responsible for stabilising the sleep (and wakefulness) period, one of which is an adequate concentration of the protein hypocretin. Hypocretin acts as a 'fixer' of the state we are currently in. Its reduced concentration is observed, for example, in narcolepsy - a disease characterised, among other things, by uncontrolled 'falling asleep' during the day.

I go to bed, feel hungry, but nevertheless fall asleep, and in the morning I do not wake up as hungry as I would have done if 8 hours had passed. Why?

Sleep is a time of increased activity for the liver, which thus removes the toxic substances accumulated in the body during the day. But in addition to detoxification, it also breaks down glycogen (stored in the liver, amongst other things) into easily digestible sugar - glucose. Sugar is food, so in the morning we do not usually feel as hungry as before going to sleep

Often, when I fall asleep, I have a sudden feeling of falling, of stumbling. So abrupt that I can wake up, is this normal?

Completely normal, it should not cause alarm. This phenomenon is called a myoclonic spurt. When falling asleep, the brain is put into a specific state - some centres are already "off" and others are still conscious. Some muscles tremble, some are already completely relaxed. To check the state of tension of a particular muscle, an electrical impulse is sent to it, which causes a strong contraction of the muscle, which can give a sensation as in the question posed.

Sen rem, Sleep, Sleep nrem, Sleep-cycle, Stages-of-sleepPleasant sleep, photo: panthermedia

What do we actually need sleep for?

It is certainly possible to answer what causes sleep deprivation. The best known effects are those related to the mental state. General mental performance is reduced, expressed in reduced concentration, slowed down reactions. Deprived of sleep, we have difficulty remembering, focusing attention, reasoning logically.

During sleep, we do not supply the body with substances with food, so this is the time that the liver, kidneys can allocate for the elimination of toxins. When we sleep, we do not succumb to addictions, so we do not provide for "processing" new doses of nicotine or ethyl alcohol, with which we so often poison ourselves. Sleep also has a salutary effect on the regeneration of the skin, epidermis, epithelium of the digestive tract and others.

Long-term (approx. one week) sleep deprivation or REM-phase disturbances can lead to states similar to psychotic disorders, hallucinations and paranoid states. REM phase disturbances also occur in alcoholism.

Sleep is therefore absolutely essential for us to function properly on a daily basis. Our activity is determined by the functioning of the central nervous system, which, without sufficient sleep, is unable to work properly. It is the best remedy for fatigue and no coffee, not even the best Italian espresso, can replace it.

Perhaps one of the spring resolutions (as it is already a bit difficult to make a New Year's resolution) should be "I will get enough sleep". It's definitely worth it!