Sleep is vital to all functions of the body. It helps both physical health and mental health and maintains circadian rhythm. Sleep helps our bodies fight disease and is essential for retaining memory. The process of sleeping can be broken into four stages. The first three stages of sleep are the non-rapid eye movement sleep stages (NREM). NREM sleep is broken into three stages, N1, N2, and N3. Then comes the rapid-eye-movement sleep stage (REM). The body goes through these stages four to six times each night. [1]
N1
This is the shortest stage and only lasts one to five minutes. It is also referred to as “light sleep.” The body hasn’t fully relaxed yet, and it is easier to wake someone up during this stage. At this point, brain activity starts to slow down, transitioning to deeper sleep. [1]
N2
During this stage, your heart rate slows down, and you go into a “deeper sleep.” If you grind your teeth in your sleep, this is the stage where that occurs. During this time, “memory consolidation” happens. Memory consolidation is when short-term memory is processed in the brain and turned into long-term memory. This stage lasts about 25 minutes. However, this stage lasts longer every time you go through the sleep cycle. Overall, we spend the most time in this stage. [1]
N3
This is the stage where the deepest sleep happens. It is also called “slow-wave sleep.” It is difficult to wake someone up when they are in this stage. Studies show that even noises louder than 100 decibels won’t wake someone up when they are in this stage. This is the stage where the body builds and heals itself. Bones, muscles, and tissue grow during this time. The immune system also strengthens. If you are a sleepwalker or sleep-talker, this is the stage where that occurs. [1]
REM
The REM stage is when dreams occur. This stage is the most similar to being awake. Brain activity lights up, but the muscles in the rest of the body have no activity. The only movement occurs in the diaphragm, as the body continues to breathe, and in the eyes. This is where the name comes from; as the brain dreams, the eyes dart back and forth. The REM stage is essential for regulating emotions when awake and for memory processing. [2]
Conclusion
Going through each stage of sleep is vital for overall health and well-being. A typical sleep cycle will go in the order of N1, N2, N3, N2 again, and then REM. [1]
Resources
[1] Patel AK, et al. Physiology, Sleep Stages. In: StatPearls. Treasure Island (FL): StatPearls Publishing; April 28, 2022. [Times cited=74]
[2]Blumberg MS, et al. What Is REM Sleep?. Curr Biol. 2020;30(1):R38-R49. doi:10.1016/j.cub.2019.11.045 [Times cited=19] [Journal impact factor=10.83]
