What are the phases of sleep and how do they affect our health?

That a good night’s sleep can be a privilege is probably known to anyone who has confidently entered adulthood. Getting a full 7-8 hours of uninterrupted sleep is not at all a matter of course, and in highly urbanized areas, with dense buildings and streets right under the windows, it can even be a challenge. To improve sleeping comfort and, as a result, health, one should take a closer look at the architecture of sleep.


Sleep consists of four basic phases: 3 NREM phases, customarily called N1, N2 and N3, and one REM phase. These phases are named after the eye movements during sleep. NREM is an acronym for non-rapid eye movement , and REM is analogous rapid-eye movement. Among adults, the full cycle of 3 NREM phases and 1 REM phase lasts about 90 minutes and repeats at night usually four times.


During these sleep phases, the eyes move very slowly or not at all, the muscles may move (although they usually do not), the heart rate and blood pressure are low, and the brain is least active.

The N1 phase is the first phase of sleep in adult humans. It is problems with this part of sleep that cause difficulty in falling asleep. It is also very short, lasting less than 10 minutes, and is a kind of bridge to further deep rest. Physiologically, in addition to the closing of the eyelids and relaxation of the muscles, the body temperature also decreases, and melatonin – the sleep hormone – is emitted from the pineal gland. During the N1 phase, there are also characteristic muscle contractures, which are often accompanied by an unpleasant sensation of falling. Researchers at the University of Colorado have hypothesized that this may be an echo of our distant evolutionary past, when human ancestors slept in trees. Such a reflex was thought to help grab onto a branch and prevent a dangerous fall.

The N2 phase begins immediately after N1 and is by far the longest of the sleep phases, taking up almost half the time of a full cycle. During N2, eye movements cease, heart rate and body temperature drop even further, muscles tighten and relax in slow intervals. It is also during the N2 phase that sleep talking is most common. There are also interactions between the thalamus and the cerebral cortex, which can be seen on the EEG. Sleep spindles, as these short impulses are called, are responsible for the formation of memories and the transfer of events from short-term to long-term memory.

The next and final phase of NREM, or N3, usually begins about 40 minutes after falling asleep. This is the deep phase of sleep on which the feeling of rest and a good night’s sleep depends most. During N3, the body produces many hormones, responsible, for example, for appetite or growth, regulates immune system functions, and even regenerates muscle and bone tissue. Proper sleep hygiene requires that we are not awakened precisely during this phase.


The NREM phases are followed by the next and probably the most interesting part of sleep – the REM phase. There are very big differences between the previous N3 and REM phases, REM is right after N1 the most shallow part of sleep; waking up in this phase is easy. Nevertheless, it is responsible for the most vivid dreams. Physiologically, during this part of the cycle, there are characteristic muscle paralysis, rapid eye movements, body temperature rises, and breathing and heart rate accelerate. The brain goes into an active state. Biologically, the REM phase is the closest to being awake, but it is the furthest removed from the state of full consciousness. Only infants and people suffering from narcolepsy are able to go directly into REM.

8 hours of silence

The Espirio system, designed to control the quality of the environment in enclosed spaces hides not only precise sensors for air, temperature, humidity and lighting, but also noise. The device’s software also has some very useful features, one of which is to record and save silence disturbances. If you happen to wake up sleep-deprived despite a full 8 hours of sleep, it could be a sign that something or someone is disturbing your rest. It could be a falling piece of home decor, a cat that has decided that the middle of the night is the perfect time to hunt imaginary game, or an outside factor like a car horn. If such a noise awakens us in the N2 or N3 phase, we may not remember it at all in the morning.

To check the record of silence disturbances, simply connect Espirio to your phone or computer, and the fully personalized home screen will show a graph with accurate measurements and archived data. Leave the control of ambient parameters to Espirio and enjoy undisturbed rest.