Health

Why You Need Sleep, How Much You Need, and How to Get More

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You may not remember everything that happens each night when you’re asleep, but if you’re doing it right, there’s a lot going on in your brain and your body, Pelayo says. “There are differences between sleep and awake for every single body system but nothing as dramatic as the changes of consciousness during sleep,” he says.

During sleep the brain cycles, repeatedly, through different stages.

Stage 1: Non-REM (Rapid Eye Movement) Sleep The first stage is when you’re falling asleep — stage 1 non-REM. Your heartbeat, breathing, and eye movement start to slow down, and your muscles relax. Your brain waves also slow down, and it’s still very easy to wake up during this preliminary stage of sleep.

Stage 2: Non-REM Sleep In the second stage, your heart rate drops, and your body temperature falls even more. Eye movement stops completely, and your brain slows way down, except for brief bursts of activity.

Stage 3: Non-REM Sleep Next comes deep sleep. This stage is heavy and restorative. Your heartbeat and breathing slow down the most during this type of sleep, and now is the time when it’s hardest to awake.

REM Sleep Finally comes REM sleep, when your eyes begin to dart quickly back and forth from side to side (even though your eyelids are still closed). Brain activity speeds way up, closer to the amount of activity that happens when you’re awake. This is the stage of sleep when most of your dreaming happens. Your breathing speeds up and becomes irregular during REM sleep. Heart rate and blood pressure start to climb back to waking levels, but the muscles of your arms and legs become temporarily paralyzed. Sleep experts suspect this paralysis is a mechanism our bodies developed to protect us from injury or other harm that might otherwise ensue if we were to “act out” our dreams.

Each cycle of sleep (a set of all the stages) usually takes about 90 minutes. And most people tend to spend more time during each cycle in deeper sleep earlier in the night — and more time in REM sleep later on. Each stage of sleep is important, and both deep sleep and REM sleep play critical roles in the learning and memory consolidation processes that happen during sleep.

Learn More About the Sleep Cycles and the Stages of Sleep

What Drives Sleep

Two internal systems control when we sleep and when we’re awake. First, there’s the sleep-wake homeostatic drive. The longer we’re awake, the more our bodies crave sleep — and the longer we’re asleep, the more the body wants to wake up.

 The homeostatic sleep drive affects how deeply we sleep, too. For instance, if you stay awake for 24 or 36 hours instead of the typical amount of time you spend awake during a day, such as 16 or 17 hours, sleep-wake homeostasis is the mechanism that drives you to sleep longer and deeper once you do sleep.

Then there’s our circadian rhythm, our body’s biological clock, which syncs our body functions with environmental cues. These internal clocks are what drive us to feel sleepy at night and more awake in the morning (even, for instance, if you slept poorly the previous night, or pulled an all-nighter). They’re regulated by hormones, such as the stress hormone cortisol and the sleep hormone melatonin, which get secreted by the brain to send these wake and sleep signals to the body.

“They’re two complementary systems in the brain,” Pelayo says. And when there’s a discrepancy between the homeostatic drive to sleep and the signal to sleep that comes from the circadian system, problems like jet lag and other disordered sleep occur.

“This is why people who wake up at different times every day may feel tired a lot,” Pelayo says. “The brain doesn’t know how to predict when they should be awake. It’s like being constantly jet-lagged.”

The more sleep researchers learn about these two systems that control sleep, the more it is clear why not only sufficient hours of sleep but also good sleep habits (such as going to sleep and waking up at the same time each day) are important.

Learn More About Your Circadian Rhythm and How It Affects Sleep

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