There are two phases of sleep: REM sleep and NREM sleep. The phenomena related to night rest are more interesting than you could potentially imagine - few people know, for example, that during sleep there are phases when we experience rapid eye movements or even such moments when - although we are not rather aware - we wake up for a few moments from sleep. But what exactly characterizes the different stages of sleep and what happens during them?

The phases of sleepare the stages of sleep, arranged in cycles. Sleeping to live is simply necessary - theoretically everyone knows it, but in practice, the growing number of people simply underestimate it and for various reasons (e.g. due to a large number of professional duties) sleep too shortly. This has a negative impact on the functioning of the entire body - not only do we feel exhausted then, but also become susceptible to the appearance of various infections (which may be due to disorders of the immune system).

It would seem that sleep is nothing more than a state in which we simply embrace Morpheus and our body rests - nothing could be more wrong. During sleep, there are changes in muscle tone, eye movement or a number of other phenomena - different of them occur in particular moments of sleep, which are referred to as sleep phases.

Phases of sleep: waking

Before finally falling asleep and during short awakenings, people are in the waking stage. In this phase of sleep, we blink our eyelids, and there is also the movement of the eyeballs, which is still dependent on us. The place is then - also dependent on our will - the movements of various muscles of our body.

The bioelectric activity of the brain also changes gradually in the waking phase: when our eyes are open, low-voltage mixed activity with a predominance of beta waves appears, while after we close the eyelids, the bioelectric activity of the brain is still low-voltage mixed, but alpha waves prevail in it then.

Awake is the phase of sleep that is most easily interrupted. However, then, when the surrounding conditions are favorable for the night rest, it may lead to full fall asleep and the emergence of subsequent sleep phases.

Sleep phases: NREM sleep

NREM sleep phase(short for non-rapid eyemovement sleep) in Polish is sometimes referred to as sleep without rapid eye movements. NREM is divided into three stages, which are:

  • N1 stage: the shallowest part of NREM sleep, with slow eye movements, gradually decreasing muscle tone, in the bioelectrical activity of the brain, which remains mixed and low voltage, theta waves begin to dominate; from the N1 stage it is possible to wake up quite easily, sudden muscle jerks are characteristic phenomena, in addition, in this phase of sleep there may also be a feeling resembling falling down
  • N2 stage: another part of NREM sleep, in which eye movement gradually ceases, muscle tone reaches minimal values, while the characteristic manifestations of the brain's bioelectrical activity (which can be visualized in some study, which will be discussed later) are sleep spindles and K-complexes (which are considered to be manifestations of the central nervous system's "defense" against waking up from sleep), other phenomena specific to this phase of sleep are a drop in body temperature and a slowdown in heart rate
  • N3 stage: the last stage of NREM sleep, in which the eyeballs do not move, the muscle tone remains low, and the characteristic high-voltage slow delta waves appear in the brain's bioelectrical activity record; it is most difficult to wake us up from this stage of sleep (it is considered the deepest stage of sleep), in addition, if someone, for example, sleepwalks, it takes place during the N3 stage of NREM sleep

Phases of sleep: REM sleep

The REM sleep phase(short for rapid eye movement sleep) in Polish is defined as sleep with rapid eye movements. In her case, unlike in the NREM dream, the stages are not specified.

REM sleep is characterized - as its name implies - rapid eye movements, the lowest muscle tension (however, phasic contractions of muscle groups appear here) and a different than before bioelectric activity of the brain (it is mixed, low-voltage, additionally dominating in theta and beta waves).

The REM sleep phase is special, however, mainly due to the fact that it is during it that our dreams appear.

Sleep phases: study

As some of the phenomena described above, related to individual sleep stages, can be noticed quite easily (for example, the rapid eye movements), and others - e.g. muscle tension or the bioelectrical activity of the brain - it is impossible to assess without using specialized research.

For the analysis of the first mentionedparameters related to sleep are used electromyography (EMG), electrical activity of the brain can be assessed by electroencephalography (EEG), and eye movements during sleep can be accurately assessed by electroencephalography (EEA).

Sleep phases: How long is your sleep cycle?

For the average person, what happens to him during sleep may not seem particularly important. The truth is, however, that it is completely different - for example, depending on which phase of sleep we will be in when the alarm clock rings us in the morning, it depends on whether we feel asleep or whether we feel completely the opposite.

We usually need 4 to 6 sleep cycles to get enough sleep. One sleep cycle consists of the successive stages of NREM sleep, followed by the stages of REM sleep. After each of these, there is usually a very short awakening, which we may not even be aware of.

How long does one sleep cycle last? Well, it is actually a variable value, even overnight. Typically, the first cycle takes about 90 minutes, and the next cycle takes from 100 to 120 minutes.

Variability also applies to which phases and stages are dominant during night rest - the first half of the night is usually spent in the stage of deep sleep (N3 stage of the NREM sleep phase), while in the second half of it, deep sleep lasts much shorter or even does not appear at all.

It has been mentioned above that waking up in an "inadequate" phase of sleep may be associated with an unpleasant feeling of lack of sleep - such a phenomenon is actually possible and its risk occurs when the moment of waking up from sleep falls in the REM phase.

Sleep phases: regulating factors

Above are general features of each sleep phase. The truth is, however, that not all people sleep in the same way - for example, the length of each sleep cycle depends on both genetic factors and age.

There are, for example, people in whom one cycle lasts not 120, but only 80 minutes - such people need much less time to sleep than those with longer sleep cycles.

The ratio of the duration of individual sleep phases is also variable - e.g. in newborns, unlike in adults, a large part of the total night rest (reaching even half) is REM sleep (where in adults this phase is sleep takes 90 to 120 minutes, and NREM sleep takes 4-7 hours.)

Given the above dependencies, some may consider counting exactly when exactly which phase of sleep falls and try to wake upwhen they are in a NREM dream. However, doing so may not necessarily help; on the contrary, it may cause sleep difficulties. It's best to just remember to get enough hours of sleep each night - as a reminder - the average adult should sleep 7 to 9 hours a night.

Read also

  • Sleep disorders
  • Parasomnia - bizarre sleep behavior
  • Lucid dream
  • Dream interpretation - the meaning of dreams
About the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.

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Category:

Neurology