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Sleep stages and circadian rhythms

Sleep stages and circadian rhythms play a key role in our daily lives. The brain cycles through four stages of sleep: N1, N2, N3, and REM. Each stage has unique brain patterns and functions. Circadian rhythms, our internal biological clock, regulate our sleep cycle and body temperature. Understanding these processes can improve sleep quality and overall health. Created by Carole Yue.

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  • leaf blue style avatar for user Kevin D. Fettel
    Anyone have a good mnemonic on remembering the sleep stages and corresponding brain waves?
    (15 votes)
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  • piceratops ultimate style avatar for user Ray
    Aren't there 4 stages of NREM sleep?
    (14 votes)
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  • purple pi purple style avatar for user Jousboxx
    Usually when I go to sleep, my thoughts seem to merge into my dreams. Sometimes if I'm thinking about, say, riding a scooter, and then I think about falling off, my hands will jerk forward to 'catch myself', and then I'll wake up and find that I'm in bed. It's not quite a dream, but it's not quite thought either. Since my hands jerk forward, paralysis hasn't taken effect, and this would occur in late N1 stage. Whats happening?
    (8 votes)
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    • aqualine ultimate style avatar for user JLD
      In response to Nahn's comment,

      the evolutionary perspective suggests that hypnic jerks are a vestigial trait from our ancestors. Since our early ancestors did not sleep in well protected brick homes, they would sleep in trees to protect themselves from land predators. While sleeping, if they were to start rolling over in your sleep, their bodies would "jerk forward" and they would catch themselves before tumbling to the ground.

      From the biological perspective, some believe hypnic jerks may occur because of random involuntary muscle twitches which are referred to as myoclonus (myo- muscle and klonos -agitation, muscle agitations).
      (8 votes)
  • female robot ada style avatar for user Andrea
    Why is Stage Four NREM sleep not mentioned in this video? My textbook states there are four stages of NREM sleep as well as REM sleep.
    (5 votes)
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  • piceratops ultimate style avatar for user Isaac Deatherage
    At , the author says that the cycle goes from N1 to N2 to N3 to N2 to REM. I understand that in 2008, stage 4 was eliminated and so there are only three N stages. However, looking everywhere on the net and all over neuroscience papers, etc., there is nowhere that says that it goes from N2 to N3 back to N2 before REM except wikipedia, which does not have a citation for that sentence. I've noticed a lot of Khan Academy is from wikipedia, who any crazy person can write and edit. This is why my college professors would give you an F if you quoted wikipedia, because it's considered unscholarly versus quoting peer-reviewed scientific journals. So, does anyone have a citation of two with the quotes that specifically says we go from N2>N3>N2>REM? I don't mean a business cite that makes money off of sleep products with poor and inaccurate graphics; I mean an actual research article.
    (9 votes)
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  • male robot hal style avatar for user Enn
    At it is said that lightly touching a person sleeping, results in a k-complex wave that assess that the touch on the skin is non-threatening and hence suppresses the processing of that stimuli.
    How does the brain asses that the touch is threatening or non-threatening ?
    (5 votes)
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    • aqualine ultimate style avatar for user invictahog
      I'm not sure this can be answered exactly but I suspect that it has to do with how hard the touch is, where on the body the touch is, whether it causes pain, and whether it is repeated. This is then integrated with whether the person is under a lot of stress and whether they may be expecting a threatening touch.
      (7 votes)
  • sneak peak green style avatar for user hs4j
    What is it called when you are dreaming, but you can control the dream? I've had this a few times and in my dream I was aware I was dreaming and could control the events in the dream. It's almost as though it was a combination of a daydream and a dream. Does anyone know what this is and how it happens? Is it rare too?
    (5 votes)
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    • duskpin sapling style avatar for user Rachele Topper
      I believe what you are describing is called lucid dreaming.
      It sounds like they happen during REM sleep, and I've read some things where people claim to lucid dream every night, but I'm not sure how viable their claims actually are.

      In reality, lucid dreaming seems to be rare when it occurs naturally. There are devices that supposedly can induce lucid dreams, but I wouldn't recommend it. I prefer to simply take those dreams when I can get them.

      Hope this helps. :)
      (5 votes)
  • piceratops ultimate style avatar for user Darth Vader
    My textbook mentions that ONE sleep cycle is when an individual passes through stages 1, 2, 3, 4 - then back up - 4, 3, 2, 1 and then moves into REP sleep. Is this correct? Seems to differ slightly from the information presented in this video.
    (4 votes)
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  • leaf green style avatar for user jameseckles4
    is there an actual way to learn while you sleep? Also where are ways too find circadian rhythm?
    (2 votes)
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    • female robot grace style avatar for user Omar Olivares Urrutia
      Some evidence suggests that you can learn while sleeping but it's not very effective, but if you already know the material and you review while sleeping, it boost their effect on consolidate memories. In addition, when you sleep your brain IS learning but what you've learnt while awake, because of that is better to study before going to bed and let the brain does his work soundly at night.

      And a cool way to catch up your circadian rhythm is connect your body with the sunlight and do not use artificial light at night (almost impossible). But a good way too is going to bed when you feel sleepy and wake up without an alarm.

      I hope you find this helpful.
      Have a nice day :)
      (7 votes)
  • old spice man green style avatar for user Christi
    If you are sleeping, during Rapid Eye Movement(REM), your body is paralyzed and cannot move, so why do some children sleepwalk?
    (2 votes)
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Video transcript

Voiceover: Even though you're not conscious during sleep, your brain is deceptively active. It goes through multiple cycles with distinct brain patterns, and it's very important to your ability to perform normal functions when you're awake. You have four main stages of sleep which occur in approximately 90 minute cycles during a normal night of sleep. The first three stages are all considered non-rapid eye movement, or non-REM which I'm going to abbreviate as N1, N2, and N3. N1 is the stage between sleep and wakefulness. This is when your brain starts producing theta waves. You might experience strange sensations known as hypnagogic hallucinations, just kind of a fun name. These can include hearing or seeing things that aren't there such as seeing a flash of light, or a lot of people hear someone calling their name, or a phone ring, or a doorbell, or something like that. Or if you've been doing something really repetitive just before bed, then that can recur in your hypnagogic state. For example, if you've been on a boat all day, you may still feel like you're on water when you drift off to sleep even if you're on dry land. Or something that's actually called the Tretis effect, if you've been playing Tetris for a long time right before bed, then you might experience visual images of blocks or something all moving in the same direction kind of like the blocks in the game. Another common feeling during this stage is a feeling of falling. That leads to what's called hypnic jerks, or those muscle twitches you sometimes experience as you fall asleep. So that's N1, our first, lightest stage of sleep. Then we move into N2 which is a slightly deeper stage of sleep. Although it's still pretty easy to wake up someone in N1, people in N2 are harder to awaken. We see more theta waves as well as something called sleep spindles and K-complexes. Sleep spindles are these bursts of rapid rhythmic brain activity. There's a lot we don't know about the purpose of each sleep stage and the function of these brain waves, but some researchers think that sleep spindles help inhibit certain cognitive processes or perceptions so that we maintain a tranquil state during sleep. For example, sleep spindles in some parts of the brain are associated with people's ability to sleep through loud noises. K-complexes are kind of similar, but they're a different type of brain activity that's also thought to suppress cortical arousal and keep you asleep basically. They're also thought to help with sleep-based memory consolidation which is the theory that some memories are transferred into your long-term memory during sleep. What's cool is that even though K-complexes do occur naturally, you can also make them occur by gently touching someone who's in this stage of sleep like just brushing against their skin and that will induce some K-complex activity. What your brain does is sort of assess that the touch on the skin is non-threatening, and it suppresses the processing of that stimuli to help keep you asleep. Beyond N2 we have N3. This is our last non-REM stage. N3 is also called slow-wave sleep because as you might guess brain waves are very slow. These are called delta waves. They have a range of about point five to two hertz. You get basically a half to two oscillations of these brain waves per second. When you're in N3 sleep, you are very much dead to the world, and really difficult to wake up. If you walk or talk in your sleep, this is the stage where those things happen. The last stage we need to talk about is REM sleep. REM is R-E-M, stands for rapid-eye movement. That's because this stage is when your eyes move really rapidly beneath your lids. Also, most of your other muscles are paralyzed. This paralysis might actually be a good thing because most dreaming occurs during REM sleep. If you weren't paralyzed your muscles might act out whatever you were dreaming about which could be unsafe for you and anyone sleeping near you depending on what type of dreams you have. REM sleep is sometimes called paradoxical sleep because your brain actually seems very active and awake, but your body is prevented from doing anything. It's kind of crazy. Now in a normal night of uninterrupted sleep, you cycle through these stages about four or five times each. It takes about 90 minutes to go through a complete cycle, but the order, it doesn't just go one, two, three, REM. The order within a cycle tends to go from N1 to N2 to N3 and then back to N2 before entering REM sleep, and then back to N1, and then it starts all over again. How long each stage lasts depends partially on how old you are, and partially on how long you've been asleep. You tend to do a lot more slow-wave sleep, or N3 sleep in the first few hours, and then more REM sleep right before you wake up. That's why if you really want to try to remember your dreams, you can set your alarm to go off a little earlier than usual like 15 minutes so you'll get jerked out of REM sleep and are more likely to remember what you dreamed. You know that you get tired probably around the same time every afternoon or evening, and you might wonder how your body knows when to fall asleep, or why a lot of people get tired in the afternoon. The answer lies in something called our circadian rhythms. Just like our sleep has cyclical stages, so does our wakefulness, and our transition for wakefulness to sleeping. Circadian rhythms are our regular bodily rhythms across a 24-hour period which is also called our internal biological clock. These cycles control our body temperature which rises during the day, and then takes a brief dip in the early afternoon, and then goes up again in the evening, and then falls during the nighttime. So it can control our body temperature, and our sleep cycle, all sorts of things. Daylight is a big queue for circadian rhythms, and even artificial light can affect your circadian clock. That's why when you travel somewhere with a big time difference, airplanes will usually adjust the lights in accordance with the time zone of your destination. They're trying to help you reset your biological clock, but resetting that clock can take time which is when you experience jet lag. Your biological clock says it's time to go to sleep, but your new time zone says it's time to wake up. That transition can be a little taxing if you're traveling. These circadian rhythms also change as you age which is why a lot of younger people tend to be night owls, but as they age older people tend to wake up and go to bed early. Your circadian rhythms can also prevent you from sleeping in when you want to sometimes. So maybe you get up every day at six AM Monday through Friday, and then Saturday you can finally sleep in, but you'll still wake up around six AM. That's because your internal biological clock has adjusted to you waking up at that time so it regulates your metabolism, body temperature, sleep cycles so that you wake up at the same time.