Often a per­son does not even imag­ine what is hap­pen­ing to his body, brain, how blood pres­sure and breath­ing change, while ordi­nary sleep lasts. Mean­while, when he sleeps, com­plex work does not stop in his body for a moment, which entails very curi­ous changes in the state of health, well-being and even con­scious­ness.

Despite the close atten­tion of sci­en­tists, sleep is still large­ly a mys­tery. Sci­ence rec­og­nizes it as an “absolute neces­si­ty” for man. More­over, it is known for cer­tain that lack of sleep (and, pos­si­bly, its excess) neg­a­tive­ly affects the state of peo­ple’s health, increas­ing the risk of many patholo­gies, includ­ing:

  • type 2 dia­betes;
  • stroke
  • obe­si­ty, etc.

While sleep con­tin­ues, the body and brain are work­ing, “repair­ing” them­selves after the past work­ing day and prepar­ing for the upcom­ing one.

A lot of amaz­ing meta­mor­phoses take place with the human body at this time.

sleep stages

sleep stages

A per­son­’s sleep through­out its dura­tion has sev­er­al stages that form a cycle. Not all stages are equal.

  • Falling into the pow­er of drowsi­ness, peo­ple fall into a very light sleep, which then deep­ens.
  • The cycle begins with the so-called non-REM sleep (Stage 1 Non-REM sleep). It is char­ac­ter­ized by smooth move­ments of the eye­balls and usu­al­ly lasts no more than 10 min­utes.
  • Then there is a tran­si­tion to a deep­er stage (stage 2 Non-REM sleep). It lasts an aver­age of 20 min­utes.
  • Then comes the turn of the 3rd Non-REM sleep and the deep­est 4th stage of Non-REM sleep or delta sleep, also relat­ed to slow sleep.
  • Fol­low­ing this, the cycle returns to the sec­ond stage and ends with a stage called REM sleep or REM sleep. It lasts only about five min­utes and is accom­pa­nied by rapid move­ments of the eye­balls and intense (with incred­i­ble speed!) The work of con­scious­ness, thanks to which dreams are born, some­times “prophet­ic” or giv­ing answers to the most dif­fi­cult ques­tions for a per­son.

The entire sleep cycle usu­al­ly takes 90 to 120 min­utes. There­fore, dur­ing the night, sleep­ing peo­ple go through four or five such cycles, wak­ing up for only one sec­ond. How­ev­er, they usu­al­ly do not even real­ize that they are awake! This occurs after the end of the REM sleep stage, before the start of a new cycle begin­ning with Non-REM stage 1. At the same time, the 3rd stage of deep slow sleep is reduced and the dura­tion of REM sleep is length­ened.

“Dur­ing the night, as the num­ber of sleep cycles increas­es, the body spends less time in deep stage 3 Non-REM sleep, so it is not uncom­mon for a per­son to wake up in an alarm state in the mid­dle of a bizarre dream,” says Sigrid C. Veasey, neu­ro­sci­en­tist, pro­fes­sor of med­i­cine at Cen­ter for Sleep and Cir­ca­di­an Neu­ro­science at the Uni­ver­si­ty of Penn­syl­va­nia.

“We don’t know why, but peri­ods of REM sleep do get longer as cycles change,” says Daniel A. Barone, MD, assis­tant pro­fes­sor of neu­rol­o­gy at Weill Cor­nell Med­ical Col­lege. One the­o­ry, he says, is that REM sleep pre­pares the human body for awak­en­ing.

Brain cleansing

The famous Amer­i­can prose writer John Stein­beck argued that the “sleep com­mit­tee” was able to solve the most dif­fi­cult day­time prob­lems overnight. One can­not but agree with him, since every per­son (more than once!) Ben­e­fit­ed from the painstak­ing work of this “com­mit­tee”.

The human brain stays in “work mode” all night, espe­cial­ly dur­ing REM sleep, when it’s almost as active as when it’s awake. He is busy pro­cess­ing new infor­ma­tion. The brain “sorts” every­thing that it received dur­ing the day and fil­ters out the unnec­es­sary.

Accord­ing to a new sci­en­tif­ic the­o­ry, it is pos­si­ble that con­nec­tions between brain cells are strength­ened or weak­ened dur­ing sleep, depend­ing on how active­ly they were used dur­ing wake­ful­ness.

While a per­son is sleep­ing, his brain can do anoth­er, very impor­tant thing — to get rid of the accu­mu­lat­ed “garbage”. And this is one of the fresh­est and most excit­ing sci­en­tif­ic ideas about sleep tasks.

A 2013 study in mice found that the waste dis­pos­al sys­tems in the brain are more active dur­ing sleep. Sci­en­tists have the­o­rized that humans sleep to give the body time to clear the brain of tox­ic by-prod­ucts that would oth­er­wise accu­mu­late and cause a vari­ety of prob­lems and dis­or­ders down the road, includ­ing Alzheimer’s dis­ease.

Changes in breathing and heart rate

Changes in breathing and heart rate

All kinds of nor­mal phys­i­o­log­i­cal process­es slow down when a per­son falls asleep. Breath­ing calms down, the rate of con­trac­tion of the heart mus­cle decreas­es, all organs “slow down” their work.

Some­times, nor­mal­ly, dur­ing sleep, a per­son­’s breath­ing is inter­rupt­ed for a few sec­onds. When such paus­es last more than 10 sec­onds and occur more than 9 times per hour, we are talk­ing about sleep apnea syn­drome.

Decreased blood pressure

When a per­son falls asleep, the gen­er­al relax­ation of the body is accom­pa­nied by the expan­sion of blood ves­sels. As a result, blood pres­sure decreas­es, reach­ing its low­est lev­el between 0 and 4 a.m., dur­ing stage 3 non-REM sleep. By 5–6 o’clock in the morn­ing, when the body is prepar­ing for the moment of awak­en­ing, it returns to nor­mal.

In absolute­ly healthy sleep­ing peo­ple, an aver­age decrease in blood pres­sure by 5–7 points is record­ed. And this is con­sid­ered the norm.

How­ev­er, if a per­son­’s blood pres­sure drops sharply by 20 or more mm Hg dur­ing sleep. Art., we can talk about a seri­ous pathol­o­gy:

  • inter­nal bleed­ing;
  • endocrine dis­or­der;
  • inflam­ma­to­ry dis­ease;
  • kid­ney dis­ease, etc.

If blood pres­sure indi­ca­tors do not decrease, but increase at night, there is a sig­nif­i­cant risk of devel­op­ing hyper­ten­sion.

Decrease in body temperature

Decrease in body temperature

One of the most com­mon tips found in pop­u­lar sci­ence arti­cles on the top­ic “How to improve sleep?” Is the rec­om­men­da­tion to sleep in a cool room. It has a sci­en­tif­ic basis.

The fact is that the cool atmos­phere of the room imi­tates what hap­pens to the body while a per­son is sleep­ing: his body tem­per­a­ture drops slight­ly. There­fore, air­ing or air con­di­tion­ing the bed­room before going to bed helps to ward off insom­nia.

Dur­ing stage 3 REM sleep, the human body can cool down by 0.5–1°C. This usu­al­ly hap­pens around 2–3 am. By the time of awak­en­ing, the tem­per­a­ture returns to nor­mal.

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