Our sleep cycle and the stages of sleep are important. Humans spend about one third of their life asleep. That’s a pretty big portion of your life that you spend unconscious in a bed, but, sleep is not as simple as just being unconscious. Our brains and bodies move through the 5 stages of sleep several times a night through something called the sleep cycle. These stages include the 4 stages of NREM sleep, followed by a single stage of REM sleep. Although your body automatically moves through these stages, it can be beneficial to learn more about them to make sense of some of the sleep habits you have.
Stages of Sleep and the Sleep Cycle
There are five stages of sleep that the body moves through as it slumbers through the night. These stages repeat in a cycle up to six times, depending on the duration of your rest. Between these stages, and throughout your sleep, you occasionally experience short bouts of wakefulness,
Stage 1: This is the first step of NREM (Non Rapid Eye Movement) sleep and constitutes the lightest sleep. It’s easy to wake up from stage one, and in fact, you will be waking up often if there are any disturbances around. It is not uncommon to suddenly jerk your leg or feel like you’re falling. These reactions are normal, but not quite understood. Some believe it’s simply a misfire of the nerves as the body transitions into relaxation. Others assert that is is a reflex from when people still slept in trees or ledges to escape nocturnal predators, and the jerk is a reaction to keep us from falling. Either way, it is a normal reaction that almost 70% of people experience as their brains slow down and their muscles relax, preparing for stage two of NREM.
Stage 2: Stage 2 is the longest stage of the sleep cycle and composes up to 50% of your nightly cycle. It isn’t too different from stage one, in that it is a light sleep from which you can be easily roused from, though not as easily as in stage 1. The slow eye movements stop and the brain waves continue to slow. Occasionally, there will be short spikes in brain activity called sleep spindles, which are signs that the brain is consolidating memories. These spindles are also accompanied by K complexes, which are also a pattern of brain waves in stage two NREM sleep. It has a similar function. As this stage progresses, the body relaxes more to allow the brain to sleep into stage 3 of NREM: Deep sleep.
Stage 3: This is the deep sleep stage. It is hard to wake someone up from stage three sleep and if someone is woken up from stage 3 NREM, they will usually be groggy and disoriented for a little while. In this stage, you enter the deepest sleep of the night. Your brain waves are as low as they get, your muscles are relaxed, and your eyes do not move. Your breathing becomes slow, deep, and rhythmic as well. Stage 3 is arguably the most important stage, as this is when a majority of the restorative properties of sleep occurs. Your body releases hormones that aid in repairing and growing tissue and also a hormone to control your appetite to keep yourself from waking up feeling too hungry. Although your muscles are relaxed in this stage, they are still functional. Stage three is usually when people experience sleepwalking, sleep talking, and bed wetting.
Stage 4: Stage 4 is very similar to stage three. In fact, stage 3 and 4 are usually grouped together in “Slow Wave Sleep.” In stage 4, delta waves, which are the slowest brain waves, outnumber faster brain waves, indicating the deepest stage of sleep.
Stage 5: stage 5 is called REM (Rapid Eye Movement) Sleep, due to the characteristic movement of the eyes under the eyelids. In this stage of sleep, you are immobile, but your brainwaves are heightened to a point of nearly being awake. This is the dreaming stage of sleep and only accounts for about 20% of your nightly sleep cycle, or a total of 90-120 minutes a night. Although REM sleep is the fifth stage of the sleep cycle, it does not follow stage 4 in sequence. Instead, you progress through the stages of NREM sleep from light sleep to deep sleep. After stage 4, you go backwards through stage 3,2,and 1 before your body enters REM sleep for a short time. Although your brain activity in REM sleep is similar to being awake, waking up during this stage will leave your groggy and disoriented. Waking up during REM Sleep may also lead to sleep paralysis, where the muscles are immobile but your brain is awake and sometimes still dreaming.
Sleep Through the Ages
The sleep cycle is not the same for everyone, as people are all unique and can spend varying amounts of time in different stages. There are several variables that can affect the way someone sleeps, but one of the more consistent ones is age. People of different ages experience the stages of sleep in different ways.
Newborn (0-4 months): Newborns are pretty new to the whole sleeping thing, so they practice a lot. Newborns spend about 17 hours a day sleeping, though they wake up frequently. This is because they have three stages of sleep: Active, Quiet, and Intermediate. Active sleep is equivalent to REM sleep, in that the baby’s brain waves are active, however, in this stage they are prone to waking up, which is important for frequent feedings. Quiet sleep is most like NREM sleep, and this is when babies are deep asleep and not likely to fuss.
Infant (4-12 months): The sleep cycle becomes more apparent in infants, and they tend to start developing routines, which is to say they will sleep in big chunks rather than intermittently. Infants will sleep about 12 hours at night and a couple of naps a day.
Toddlers (1-3 years): between one and three years is when the sleep cycle becomes fully developed and the child will go through NREM and REM normally. Toddlers spend about a quarter of their sleep in stage 3 and four, while another quarter is spent in REM, leaving the remaining half for stage one and two. Toddlers tend to nap less than infants and sleep for about 10 hours a night.
Children (3-12 years): As a child develops more and goes through school, they become more accustomed to sleeping on a schedule. Naps become much less frequent after age five, but children still spend a lot of time in stage three sleep, which is important for growth.
Adolescence (12-18 years): During adolescence, there is a shift in the circadian rhythm. Teenagers tend to stay up late and sleep in. Despite this, it’s best for them to still receive a full 10 hours of sleep to promote growth.
Adulthood (18- 50 years): Throughout adulthood, the circadian rhythm shifts slowly again, causing people to sleep earlier and wake up earlier. This is usually a source of conflict between teenagers and their parents, or educational institutions. The average adult should try to get about 8 hours of sleep a night.
Seniors (50 years >): Now, fifty years isn’t old, but it’s around this time that the shift in circadian rhythm that one experiences in adulthood reaches a point of being noticeably altered. People in this age bracket tend to sleep for shorter amount of time - around six hours - and usually sleep lighter. They can be prone to waking up a few times a night, though often times this can be attributed to disturbances from medical conditions like arthritis. Consider investing in a high quality mattress to reduce these interruptions.
From the outside, sleeping looks like an inactive state of unconsciousness, but in actuality, sleep is an active process that follows a cycle of five stages. Four stages of NREM sleep, and a single stage of REM sleep, which repeats up to 6 times a night. Understanding the sleep cycle can help you manage your schedule and understand the source of some of your problems. As you get older, sleep patterns can change, and you will have to adapt your schedule to these normal stages of life. If you are interested in learning more about sleep, the best sleep position, and much more check out our blog. For the best sleep when camping, our RV mattress is worth checking out.