Sleep presents a cyclical and regular alternation of phases : at the stages of the Non-Rem phase, the Rem phase alternates, the phase in which one rests deeply and dreams. Let's find out how many and what are all the stages of sleep .
Phases of Sleep
It is easy to say "I sleep", or "I slept a whole sleep", as if sleep were a simple pause from waking, without particular implications.
The reality, the most natural act in the world, is a complex of mechanisms, modalities, chemical exchanges and modifications at different levels, which removes it from its position as a simple act of rest and gives it precise functions, phases of paths, gradual depth levels and connotes it as a real activity, from which it seems impossible to avoid.
Through specific instruments, sleep was analyzed and the main changes and their cyclicality were recorded.
How to calculate the hours of sleep we need?
Phase NonRem
Even during sleep the brain is active : always evolving investigations through electroencephalograms for monitoring brain waves, electrooculograms for recording eye movement and electromyograms to investigate muscle activity testify how sleep is a complex system articulated in more phases, where multiple interactions of various kinds occur.
The two macro-phases in which to divide the activity of sleep are NON REM sleep and REM sleep (REM is the acronym of "Rapid Eye Movement" - Rapid Eye Movement).
In reality the NON REM phase is structured in four stages characterized by more or less deep sleep levels and rhythmic waves of different frequencies . In general, in NREM sleep there is a slowing of the heartbeat, a total relaxation of the musculature and a lowering of the body temperature.
Stage 1 (3'-12 ')
In this phase that goes from sleep to the earliest days of sleep, there is a slowing of eye movement, the muscles are not yet completely relaxed, the body temperature is slightly lowered, the breath becomes slower and deeper. Beta brain waves, typical of the waking state, leave room for the Alpha .
Their frequency varies from 7 to 13 Hz. And in this condition the mind is calm, the consciousness is still alert but relaxed. These waves are typical in states of relaxation, in the first approaches to meditation, in which the mind is receptive and concentrated.
When sleep enters sleep, the Tetha waves appear, whose frequency varies from 3 to 7 Hz. They are also present in states of deep meditation, or when the mind is involved in imaginative activities.
Stage 2 (10'-20 ')
In the second phase one is completely asleep, in fact one has entered real sleep, without any alternation with states of consciousness. Ocular movement does not appear, muscle activity remains present but very low, body temperature is further decreased and breathing is deep.
In addition to Theta waves, there are also two components in the brain, the K complexes and the sleep zones . The K complexes are biphasic waves that have a sudden tracing upwards and downwards at the speed of a variation per minute. They are defined as "the biggest event in the electroencephalogram of a healthy man" and perform two functions: they suppress cortical excitation and favor memory consolidation .
Sleep spindles are defined as trains of waves of 12-16 Hz with a duration of between 0.5 and 1.5 seconds and last throughout sleep. They have the function of inhibiting the processing of unnecessary information and guaranteeing undisturbed sleep from possible light solicitations.
Stage 3 (10 ')
The K complexes help deepen sleep from the second stage to the third. In this phase the Delta waves are associated with Theta waves, spindles and K complexes. They are slower and more regular brain waves, their frequency varies from 0.1 to 3 Hz. In this stage the sleep is deep, the body it's almost completely relaxed.
Stage 4 (30'-50 ')
The Delta waves completely replace those Theta. These lower frequency waves are associated with deeper relaxation, dreamless sleep, and the unconscious mind .
The body temperature drops further, the heart rate is slowed and relaxed, the deep breath and the eyes move slowly from right to left and from top to bottom. Muscles are almost completely relaxed and sleep is heavy .
Once they reach the fourth stage, the sleep is relieved, the brain waves change and the Theta, the K complexes and the spindles of the second stage reappear. We are about to enter a new phase, REM!
Rem phase
The REM phase is also referred to as a paradoxical sleep phase, because although we are sleeping brain activity becomes frenetic, the eyes take a rapid movement and it is not possible to control the musculature that is almost paralyzed: the body temperature continues to fall, the cardiac rhythm becomes irregular alternating slower beats with faster beats, the breath speeds up.
Theta waves alternate, of reduced amplitude compared to those present in the second NREM stage, accompanied by short snapshots of Alpha and Beta. This is the phase in which dreams are made, in which an active subconscious that moves freely in thin spaces "awakens" in the face of a completely helpless musculature.
The Sleep Cycle
From this window on dreams we return to the deep sleep of the NREM stage 3 and 4 and then resurface at the second stage and go back to the REM phase. It is possible to define these steps as the five sleep phases, which are repeated cyclically 4 or 5 times when sleeping and each cycle lasts an average of 90 minutes . In the NRem phase there are also many micro-awakenings, which generally leave no trace in the memory.
