Explaining the Sleep Cycle

Almost every person knows something about the sleep cycle. They may have read an article about it online, heard it mentioned on a TV program, or perhaps downloaded an app that helps them regulate their own sleep cycle. For many years, scientists and most people believed that sleep was just a way for your body to recharge, peaceful time with not a lot going on, but further research showed that while a person is asleep, their brain is actually quite active. The activity is a predictable cycle with four stages that fall into two categories. The brain is one of the most complex parts of a human being, and scientists are continually studying how it works when we are asleep, and how to better regulate the sleep cycle for a good night’s sleep.

Asleep and Awake

There are two processes that control when a person is asleep and awake, called sleep/wake homeostasis and the circadian biological clock. Because of sleep/wake homeostasis, your body becomes more tired the longer you are awake, and if this process was the only one involved in maintaining the waking and sleeping of a person, then sleepiness and wakefulness would work the way it seems it should work; a person has the most energy in the morning when they wake up from sleeping and is tired at the end of the day. However, the circadian biological clock, controlled by the SCN section of the brain, causes lows and highs for sleepiness and wakefulness. The SCN is triggered by light, and releases chemicals that help a person either wake up or fall asleep. These chemicals and other neurotransmitters help your body recharge while you sleep, so losing time while sleeping, even just an hour, can have a significant impact on a person. The more regular a person’s sleep schedule is, the more regularly chemicals are dispersed throughout the brain, and the better and more refreshed the person will feel. Of course, the way a person feels after waking up also depends on what stage of the sleep cycle they are in when they wake up.

Non-REM Sleep

Non-REM sleep is the overarching category encompassing the first three stages of the sleep cycle. Stage One is the first stage of Non-REM, and it occurs almost immediately after a person falls asleep. It is relatively short-for most people, it lasts only seven minutes-and while a person is going through Stage One, they can be easily disturbed by sounds or other kinds of interruptions. REM stands for rapid eye movement, but as Stage One takes place during Non-REM, the only kind of eye movement is slow, as are the brain waves. Stage One is the transition from being awake to being asleep, and is followed by Stage Two, which is still relatively light sleep, but not as light as Stage One.

During Stage Two, brain activity continues to slow, but something unique begins to happen-sudden bursts of quick brain waves called sleep spindles. The mix between sleep spindles and another form of wave movement called K-complexes both serve to protect the brain from waking up during this stage of the sleep cycle. Stage Two is
followed by Stage Three, the last part of the Non-REM phase, and the beginning of deep sleep.

Stage three is the part of the sleep cycle in which it is hardest to wake someone up. Delta waves are produced by the brain, and Stage Three is where the body is restored; the body gains energy, repairs itself, and grows and develops. Additionally, sleepwalking and night terrors, as well as other kinds of sleep oddities, occur during Stage Three of Non-REM.

REM Sleep

Approximately an hour and a half after a person fall asleep, they will enter REM Sleep, which, as mentioned, stands for rapid eye movement, and is known by most people as the dreaming stage. REM is the most active stage of the sleep cycle; dreams are the most vivid, brain activity, blood pressure and heart rate is increased, and breathing is irregular. The eyes jerk in many different directions, which is where the stage gets its name. Another process that happens during REM is one of the brain’s most important; it processes information and events from the previous day so it can be stored in a person’s long-term memory. REM is deep sleep, and if a person awakes feeling groggy or sleepy, it is very likely they woke in the middle of a REM cycle. REM is a short part of the overall sleep cycle-almost as short as Stage One.

The average adult has five or six complete sleep cycles a night, as the first one takes about 90 minutes and the ones that follow are approximately 100 to 120 minutes each. With sleep taking a more important role in society today, many different solutions to a better night’s sleep are being developed, but the ultimate solution will be to better understand individual sleep cycles, as well as understand when to wake up and when to go to sleep so everyone is feeling as refreshed as possible.