Sleep is one of the most essential things in life, and we spend about a third of our existence doing it. While all of us sleep – including most animals – scientists aren’t quite sure why we do. We know that sleeping clears the brain of toxins and helps us consolidate memories. It also repairs tissues. And all this work happens during the different stages of sleep.
There are four sleep stages of which three comprise non-rapid eye movement or NREM sleep and the last of which is rapid eye movement or REM sleep. They’re associated with various brain activities. We cycle through these stages every 90 minutes or so. Our ability to sleep at night and wake up in the morning is tied to what we call the circadian rhythm or more commonly, our internal clock. When it doesn’t function well, we can find it tough to sleep and don’t wake up when we should.
Stage 1: NREM sleep consists of three stages. The first stage is the transition from being awake to falling asleep. It lasts for several minutes, and during this time, sleep is light, and it doesn’t take much to wake you. You may also experience muscle contractions resulting from a sensation of falling.
Stage 2: In this stage sleep is also light but brain waves become slow as you prepare to move into stage 3 NREM sleep. Muscles further relax, and body temperature starts to drop. There are short bursts of brain activity. This is the time you’d want to wake up from a power nap since if you go into stage 3 and wake up from it, you’ll feel dizzy instead of alert.
Stage 3: As you enter stage 3 NREM sleep, it’s harder for you to wake up. Your body doesn’t respond much to external stimuli, and your muscles no longer move. This is the time your body does what it’s supposed to do during sleep. It builds tissues, stimulates growth and also helps consolidate memory. Stage 3 is also the time when parasomnia occurs. It includes night terrors and sleepwalking, which are caused by an over-arousal of the nervous system.
REM: REM sleep is where dreams are the most vivid. If you awake in this stage, it’s likely that you’ll remember what you were dreaming about. Brain waves are similar to when you’re awake, and your eyes move from side to side. However, your body doesn’t move, perhaps to prevent you from acting out your dreams. Memory consolidation also occurs at this stage.
It was once believed that dreams occurred only during the REM stage. However, research has found that they do happen during the deeper stages of sleep too. The difference is that dreams in REM sleep are more vivid and you can recall them better.
Circadian rhythm is a 24-hour body clock that’s controlled by the hypothalamus in the brain. It cycles from sleep to wakefulness at certain periods of the day, which is why we know when to sleep and wake up. We’re governed by it. And it’s not just us; most animals have it too. Aside from regulating our sleep-wake cycles, it also regulates the release of hormones, body temperature, and other bodily functions. It also determines our sleep patterns. When there’s less light – for instance, when night falls – that information is relayed to the brain which in turn triggers the production of melatonin, a hormone that makes you feel drowsy so that you’re ready to sleep.
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Sometimes, your circadian rhythm is thrown out of balance due to factors like food and drink, external temperature, and increased stress or activity too close to bedtime. Sleep disorders like apnea and insomnia and other conditions like restless leg syndrome (RLS) can also affect it. When this happens, your sleep cycle becomes interrupted, and you don’t get the sleep you’re supposed to.
Resetting your circadian rhythm can help you sleep better. If you’ve been having trouble sleeping well, you can try exposing yourself to bright artificial light during the day and gradually dimming it as the sun sets. Hiking during the day and camping at night can also help as you’ll be exposed to natural light schedules.
You should also try sleeping and waking at the same time each day so that your internal clock falls into the habit. Try to avoid sleeping in on the weekends or holidays as you don’t want to deviate from your schedule. Long naps can make sleeping at night difficult too so limit them to just 20 minutes.
Sleep is an intrinsic activity, and we can’t function without it. There’s a whole network at play from triggering our brains to release sleep hormones to entering the first stage of sleep and on to the last. Completing sleep cycles and letting sleep work its magic on our bodies is one of the best gifts we can give ourselves.