Stages of the Sleep Cycle

by CRfan

Most people are aware of the REM cycle of sleep where a person's eyes move rapidly. But there are a subset of NREM (non-REM) stages of sleep you may not be aware of.

Most people go to sleep without knowing exactly the things that go on while they were sleeping. People experience a few dreams and eventually wake up without even remembering some of them. In fact, there are a lot of things that people are unaware of during their sleep.

The sleep cycle is made up of two distinct phases namely the REM sleep and the Non-REM sleep. REM is defined as rapid eye movement since this is a common characteristic that occurs during this stage of sleep. The Non-REM phase encompasses all the other stages of sleep. The REM stage is also the period or phase where people encounter dreams. It is also the time when the major muscles of the body become frozen or paralyzed. According to studies, freezing of the body is a natural reaction to prevent harming others by acting the scenes in the dreams.

Aside from this, there are also some specific brainwave patterns observed during the different periods of sleep. These things make it easier for people to identify the REM stage. On the other hand the NREM is divided into three sub-phases. Before, the division is composed of four different stages. However, the N3 and N4 stages were later on combined into a single group. The letter “N” simply stands for Non-REM.

Stages of the NREM Sleep

•             N1 – N1 is considered the first stage of cycle. This is also classified as light sleep. This is where the transition from being awake to falling asleep occurs. People who are in this stage are easily awoken. In fact, people who are awoken in this stage will not even consider that they were asleep. This is also the stage where jerky movements of the leg or feet occur while falling asleep. These characteristics are all considered normal.

•             N2 – Just like N1, N2 is also considered as light sleep. It is also easy for people to be awakened in this stage. However, there are significant changes that draw people closer to sleep. The heart rate begins to slow down and the body temperature also begins to decrease. The brainwave patterns will also show activities that are related to sleep such as the sleep spindles and the K-complexes. During the N1 and N2 stages, it is very unlikely to have dreams.

•             N3 – The N3 part of NREM is considered to be the deepest phase of sleep. This is why it is called as the deep sleep stage. Just like the two previous stages, N3 can also be recognized by the brainwave patterns produced. These patterns are quite slower compared to brainwaves produced while awake. Unlike N1 and N2, people in this stage are very hard to wake. It usually takes a loud alarm clock to do the job. Once awake from N3, it is common for people to experience grogginess. This is a sign that the person was awoken during deep sleep. Since the body is not paralyzed in any of these three stages, it is common for some people to experience sleep abnormalities such as parasomnia or night walking, teeth grinding and night terrors.

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The Full Sleep Cycle

A normal sleep cycle will last for approximately 90 minutes for an adult. This cycle will repeat for about 4 to 6 times in a night. It is important to know that cycles vary from one person to another. The time for a cycle to complete will be static; however, the range will be from 90 to 100 minutes.  There are several techniques to figure out a person’s sleep cycle. This is because the phases of sleep will be different or unique for everyone including the stages in between the cycles. A regular person will experience all the cycles but in his or her own way and schedule.

Updated: 09/23/2012, CRfan
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