Sleep: Study with Video Lessons, Practice Problems & Examples

Circadian Rhythms

Alright. So many of our bodily processes happen on a rhythmic schedule. Things like our body temperature regulation, hormonal cycles, particularly in women, as well as sleep. And for sleep, this is called our circadian rhythm. So our circadian rhythm is the sleep-wake cycle that we see in humans, and it is approximately a 24-hour cycle.

Now, the brain region that is most important for our circadian rhythm is a structure called the suprachiasmatic nucleus, which we're going to abbreviate to SCN because that is quite a mouthful. So our SCN is a structure in the hypothalamus. Remember that region, kind of right below our thalamus that's very important for, like, survival functions, right? And the SCN is really what is going to be controlling our circadian rhythm. So our suprachiasmatic nucleus responds mainly to external cues, specifically light or more specifically a lack of light.

So, to give you kind of a sense of what this might look like, our main stimulus would be a lack of light. So, for example, the sun setting, things getting dimmer, everything getting darker. Obviously, that information is being taken in through our eyes and then from there a neural impulse is going to travel to the SCN. Okay, so we have a neural impulse going from the eyes to the SCN which again is located in the hypothalamus which we have here in blue. Now from there our SCN is going to send an impulse and trigger the pineal gland.

And the pineal gland is this little gland that we depicted in green here, kind of right behind the thalamus. And the pineal gland is going to release melatonin, which is a hormone I'm sure you've probably heard of before that basically makes us a bit drowsy and kind of helps us wind down for sleep. And then multiple brain regions will respond to that, particularly some regions in the hindbrain. And eventually, we will have our body response which is to fall asleep. Now, lucky for us, the SCN can also respond to internal cues as well as external cues.

And that's important because I know for many of us, like where I live in the wintertime, it gets dark at like 4 PM and we don't want to be falling asleep at 4 PM every single day. Right? So our SCN will also respond to internal cues, things like hormone levels, which fluctuate throughout the day, temperature, which tends to get lower throughout the day, as well as eating patterns, and any particular, you know, bedtime habits that you may have, you know, kind of taught your brain over time means that we're going to be winding down for bed. So the SCN responds mainly to external cues, particularly that kind of light signaling, but it will be responding to internal cues as well. Now one last note about circadian rhythms and something I'm sure many of you are familiar with as college students, but circadian rhythms can become dysregulated.

So things like jet lag, working night shifts, staying up late studying can kind of mess up that 24-hour cycle and kind of, you know, shift it off balance a little bit. But usually, after a couple of good night's sleep, you'll get back onto that 24-hour pattern fairly easily. Alright. So those are circadian rhythms, and I will see you guys in our next video. Bye bye.

Sleep Example 1

Alright. So we're going to be answering a few questions about Circadian Rhythms. Question A reads, "2 structures are important for regulating the circadian rhythm: the suprachiasmatic nucleus or the SCN, and the pineal gland. Which of these structures receives a neural impulse from the eyes?" So between these two structures, the one that is going to respond to external cues, like for example, darkness or lack of light, is going to be our suprachiasmatic nucleus, or the SCN.

This is a structure within our hypothalamus that responds to both external and internal cues that signal that it's going to be time for us to go to sleep soon. Alright, question B reads, "Which structure is responsible for releasing hormones?" Now, a kind of easy way to remember this is that hormones often get released from glands, right, and only one of these two structures is a gland. So, we're going to have our pineal gland releasing our sleep hormones. Alright, and then question C reads "What hormone is released by this structure?" and the pineal gland is going to be releasing melatonin.

I'm sure many of you have heard of melatonin, in relation to sleep. We can even take melatonin supplements to help us feel sleepy and wind down. Right? Alright. So there you have it, and I will see you guys in the next one.

Bye bye.

True or False: if false, choose the answer that best corrects the statement.

Circadian rhythms describes the variation in body temperature.

• A. True.
• B. False; circadian rhythms describes the monthly hormonal cycle experienced by men.
• C. False; circadian rhythms describes the 24-hour sleep-wake cycle.
• D. False; circadian rhythms describes the daily changes in the ability to focus.

Basics of Sleep

Alright, so sleep is not just one continuous state. It's actually very dynamic and happens in cycles, and those cycles are called sleep cycles. So, a sleep cycle is basically going to be the movement through the different phases of sleep. Now, each sleep cycle will last approximately 90 to about 120 minutes and people will typically experience about 4 to 6 sleep cycles per night depending on how much sleep you are getting. Now, when we think about sleep, it's generally divided into two main phases.

The first phase is called REM sleep which stands for Rapid Eye Movement and it's exactly what it sounds like. So REM sleep is characterized by darting movements of the eyes. So, your eyes are closed, of course, but you basically have very rapid darting movements of the eyeball underneath your closed eyelid. And during REM, this is when we have very vivid dreaming. Now we can have some dreaming during the other phases of sleep, but most, like, our longest dreaming and our most vivid dreaming is associated with our REM sleep.

Some additional characteristics of REM sleep are that we are going to see an increased heart rate as well as increased respiration. So you're kind of in a state of, like, physiological arousal almost. However, we also see the paralysis of skeletal muscle. So, obviously, all of your vital organs are still perfectly functional. Your eye muscles are still working. Right? But your skeletal muscles, so your arms and your legs, for example, are actually unable to move when you are in REM sleep. And we think the purpose of that is to basically stop you from acting out your dreams, which could potentially be quite dangerous for you and people around you. Right? So during REM sleep, basically, our body is in a slight state of physiological arousal, but the majority of our body is unable to actually move.

Now our other phase of sleep is called nREM sleep, which literally just stands for non-Rapid Eye Movement sleep. And NREM sleep is divided into 4 stages. So these stages kind of vary between light sleep and deep sleep, and these stages are distinguished by their unique brainwave patterns, and we're going to talk about that coming up pretty soon. Some additional characteristics of nREM sleep are that we are going to see decreased heart rate as well as decreased respiration. So basically, everything kind of slows down in the body, and that is especially true as we get into those kind of like nice deep sleep states.

Now the way that all of this ties together is that each sleep cycle that we go through is going to include the nREM stages as well as a REM phase. So if we're looking at our little kind of circular graph here, you would basically enter right about here. You would enter stage 1 sleep, you would go into stage 2 sleep, and then into stages 3 and 4 sleep, and those would, of course, be our nREM stages. And then following that, you would enter REM, you would have a period of very vivid dreaming, and then you would cycle back into nREM stages. So again, each of these cycles would last between 90 and 120 minutes and you would have between 4 and 6 of them per night. Now as I mentioned, we distinguish between these nREM stages by looking at their brain wave patterns, and you may recall from chapter 2 that brain waves are visualized using something called an EEG, which is an electroencephalogram, and that is going to be measuring the electrical activity in the brain.

So coming up next for you, we're going to have a little EEG primer to help you actually understand how to read an EEG, and then we'll go over what those nREM stages actually look like. So I will see you there. Bye bye.

Sleep Example 2

Alright. So, for this example, we're going to be matching these characteristics with the general sleep phase that they happen in, either REM or NREM. Alright. So a is increased heart rate. If we're thinking about increased heart rate or respiration and that kind of physiological arousal, that is going to be happening during REM.

So, we're going to put a right there. b is decreased breathing rate. So, if we're thinking about basically the opposite of this, kind of getting slower respiration, slower heart rate that happens during our NREM stages, particularly those like deep sleep stages. So, that is going to be NREM. c reads rapid eye movement, which is literally what REM stands for, right?

Then we'll put c there. d is 4 distinct stages and that is going to be NREM. Right? So, REM is kind of its own thing but NREM is divided into 4 distinct stages. So, we'll put d right there.

e is dreams and dreams are most associated with REM sleep. We'll put e there. f is decreased respiration. Again, if we're thinking of decreased heart rate, decreased respiration, that is happening during our NREM cycle, and then g is muscle paralysis, and muscle paralysis is going to be happening during REM. You can kind of think about how that muscle paralysis is most likely adaptive to help us from, you know, not acting out our dreams.

So, kind of dreaming and muscle paralysis go together really nicely. Alright. So there we have it, and I will see you guys in our next one. Bye-bye.

Which of the following statements are true about the sleep cycle.

I. The sleep cycle refers to the 24-hour cycle of sleeping and waking.

II. On average, people go through 4-6 cycles per night.

III. The sleep cycle has two general phases.

• A. I & II.
• B. II & III.
• C. I & III.
• D. I, II, & III

EEG Primer

Alright, so when we're looking at an EEG, we consider 2 things: We are thinking about the frequency of the waves and the amplitude. So, thinking about frequency, this is basically just the number of wave cycles per second, okay, or per some unit of time. And when I say wave cycle, what I mean by that is basically going from the bottom to the top and then back down to the bottom again. So you can see here, assuming that this is taking place in one second, that's only one unit of time, we have a lot of wave cycles happening here.

So this would be a very high-frequency wave. You could also think of this as basically how many peaks do we see within that one unit of time. Obviously, here we have a lot of peaks happening, so this is a high-frequency wave. Whereas down here, you can see we really only have 2 wave cycles happening, or 2 peaks happening, within that unit of time, so this would be a very low-frequency wave. And frequency basically indicates different states of brain activity.

So, for example, we can use it to give us information about the level of consciousness that a person is in, or the different stages of NREM sleep, and you'll see the different stages will have very different frequencies that kind of easily tell them apart. Now, we're also going to be thinking about amplitude, and this is very similar to what we learned about in chapter 4 on sensation and perception when we talked about light waves. So basically, amplitude is just going to be the height of the waves. And so this wave here would have a high amplitude because it's very tall, and then this wave down here would have a lower amplitude because it's short. That one is pretty easy. So amplitude is essentially indicating the strength of the brain activity that we're seeing.

Alright, so when we're looking at our EEGs, we're going to be considering frequency, the number of wave cycles that we are seeing within a unit of time, and we're also going to be considering amplitude or the literal height of the waves. Alright. So I'll see you guys in our next one to actually get into those sleep stages. Bye bye.

Sleep Example 3

Alright, so for this one, first we're going to be answering which of these two waves has a higher frequency, and remember, frequency is just the number of wave cycles that we see per second or the number of peaks that we can see per second. So looking at answer choice A, we can only see 2 peaks, so that's probably pretty low frequency, and then over here, answer choice B, I'm not even going to bother counting them because what we can tell is it's definitely more than 2, right? So, it looks like answer choice B has a higher frequency there.

Alright, and then down here, we're going to be looking at these two waves to figure out which one has a lower amplitude. Amplitude literally just being the height of the waves. And just looking at them really easily, just visually, I can see that B has higher waves than answer choice A, and so A is going to be our lower amplitude wave there.

Alright, I will see you guys in our next one. Bye bye.

James is a graduate student working in a sleep lab. He is analyzing EEGs, focusing on the height of the waves. Based on this information, what specific aspect of the EEGs is James studying?

• A. Frequency
• B. Amplitude
• C. Wavelength

Stages of Sleep

Alright. So in this video, we're going to be going over those stages of sleep and talking about what EEGs look like for people who are awake in the different phases of non-REM as well as in that REM phase. Alright. So we're going to begin with people who are fully awake, so people who are fully conscious, not even beginning to sleep yet. And in people who are awake, we see a really characteristic EEG pattern called beta wake.

And I always remember that beta means awake by thinking about busy beta waves, that kind of busy, active, fully conscious brain, right? We have our busy beta waves, and these tend to be pretty high frequency. So we're going through a lot of wave cycles per second but relatively low in amplitude. So you can see we're not having any like really high amplitude spikes or anything like that happening with our beta waves. They're staying pretty low amplitude, they're pretty small, but pretty high frequency.

We're seeing a lot of waves per second. So those are our busy beta waves. Now from there, we would drop into stage 1 sleep, and stage 1 is considered a very light stage of sleep. Like if a person tapped you on the shoulder you'd probably jerk up immediately and say I wasn't even sleeping, you know, like that kind of that twilight phase before we really get to sleep. So in stage 1 we see a characteristic EEG pattern called theta wave.

So I always think, in contrast to our busy beta waves, we have our tired theta waves or kind of our twilight theta waves. You could also think of like any of those t words kind of going together. And theta waves are basically just going to be lower frequency than beta waves. So you can see the amplitude hasn't really changed, it's still pretty low amplitude, but things are kind of slowing down so we're seeing fewer waves per second basically. So they're just lower frequency than beta waves.

So our tired theta waves are going a little bit slower than our busy beta waves were. Alright, from there we go into stage 2, and stage 2 is considered moderately deep sleep. You are well and truly asleep at this stage and stage 2 actually evidences 2 very characteristic bursts of activity. So the first is called sleep spindles, and sleep spindles are little bursts of extremely high frequency activity. So if you are looking at our EEG here you can see our sleep spindle right there is really high frequency compared to the EEG on the left or right of it.

To me, these almost look like the EEG kind of gets, like, squished together a little bit. So it's like this is this little tiny pocket of really, really high frequency activity where we're seeing a lot of waves per second. So those are our sleep spindles, very high frequency. Now we also have K complexes, and K complexes are basically very high amplitude spikes, and these really stick out because as you can see for the majority of our EEG here our amplitude is pretty like low to moderate, it's not spiking really high, so these K complexes really stand out because they're these super, super high peaks that you'll see in stage 2 sleep. Alright, so in stage 2 we have two characteristic bursts of activity, our high frequency sleep spindles and our high amplitude K complexes.

Alright, from there we would go into stages 3-4 sleep, and stages 3-4 are considered very deep sleep. So it's very difficult to wake up a person who is in stage 3-4 sleep, and both stage 3-4 sleep show delta waves on an EEG. So I always think of kind of deep sleep delta waves, those d's kind of going together, and these really stand out compared to all the other ones because they are very high in amplitude. They're going to be our lowest frequency, that we're going to see, so they're kind of pretty slow, but they're really high in amplitude very consistently. So you'll see a lot of, like, these really, really tall peaks with delta waves, very consistent on the EEG and much higher than what you would see in any other type of wave except for those K complexes in stage 2.

So we have our deep sleep delta waves, nice tall peaks there. And then finally, we go into REM. Of course, in REM we would have our dreaming, that kind of partial paralysis, as well as that slight, like, physiological arousal, so our increased heart rate, increased respiration. And very interestingly, REM EEGs really resemble beta waves. So they basically resemble being awake, and we're actually going to talk about some kind of more like conceptual or theoretical reasons as to why we think that may be when we talk about dreaming a bit later in the chapter.

But as you can see, these REM EEGs are relatively high frequency, not quite as high frequency as we saw and our beta waves are not identical by any means, but they are pretty similar and you can see they're also pretty low amplitude. We're not seeing any really high spikes with our REM EEGs. So REM and our awake beta waves look the most similar out of all the EEGs we would see with our different sleep stages. Alright. So just to kind of sum everything up, as you can see here we have our busy beta waves that we have when we are awake, very high frequency, lots of brain activity happening when we are awake, of course.

From there we go into our tired theta waves, things are kind of slowing down. We're lower frequency than before. In stage 2, we have our 2 characteristic types of activity, those high frequency sleep spindles, and those high amplitude K complexes. In stage 3 and 4, we have our deep sleep delta waves, right? Everything is kind of slowing down, lower frequency, and really really high amplitude spikes pretty consistently in that EEG.

And then finally, we have our REM EEG which looks fairly similar to what we see in our beta waves, so pretty low amplitude, relatively high frequency. Alright. So those are our different sleep stages and their characteristic EEGs, and I will see you guys in our next video. Bye-bye.

Sleep Example 4

Alright, so for this one, we're going to be looking at these 2 EEGs and we're going to be figuring out what stage of sleep we are looking at and we're going to take note of any particular key features that helped us to make that determination. Alright, so starting with our first EEG here. So one thing I'm noticing about this right away is that this is pretty high amplitude, right? We have a lot of really high amplitude waves happening here and it's happening pretty consistently so this seems to be a really consistent feature within this EEG. I'm also noticing that compared to many of the other EEGs that we saw in our lesson, this is relatively low frequency.

We're not seeing a huge amount of wave cycles within any particular unit of time here, right? So those two things in combination tell me that we are probably looking at stages 3-4. We're looking at some delta waves here, and I can tell that because of the very high amplitude and the relatively lower frequency. Alright, so that is our first wave. Now looking at our second wave, so I think obviously our eyes are going to be drawn right away to this really high amplitude spike there, and as we can see, the rest of this wave is not high amplitude so this is not characteristic of the wave as a whole, which tells me that this really high amplitude spike is probably a K complex.

Right? I'll write that down. We're noticing a K complex, and then looking at this wave I also notice right here we have this kind of burst of really high frequency activity. So compared to the EEG that kind of bookends it on either side, you can see we're cycling through a lot more full wave cycles within this unit right here, so it's a very high frequency burst. So that is probably a sleep spindle, right?

So I'm just going to abbreviate that as SS and if we're seeing K complexes and sleep spindles we are looking at stage 2 of sleep, right? So there you go. That's my favorite to ID because they're so easy. I love those nice obvious K complexes, they make it so nice. Alright, and then finally we have C, what stage would be the most difficult to distinguish from being awake on an EEG?

So if we are awake, we are going to have those beta waves, pretty high in frequency, pretty low in amplitude, and that is also what our REM EEG looks like. Right? So very, very interesting and we will talk about some theories of this a bit later, but our REM EEG is going to look very similar to our beta waves that we would see when we are awake. Alright, so there you guys have it, and I will see you in the next one. Bye bye.

Select the answer choice that correctly defines the EEG feature.

• A. Beta waves: lowest frequency & highest amplitude.
• B. Sleep spindles: very high amplitude.
• C. K complex: very high frequency.
• D. Delta waves: lowest frequency & highest amplitude.

Sleep Patterns in a Typical Night

Okay, so to finish up this section we're going to talk about what sleep patterns look like in a typical night because as the night progresses the amount of time that we spend in each stage of sleep actually changes a little bit. We're going to go over what those patterns look like. So, let’s say it's about 11 pm, we're heading to bed, so obviously we start off awake and then we're going to enter our first sleep cycle. And this will pretty much look like what we've been talking about. So we'll go into stage 1, from there we'll go into stage 2, we'll go into stages 3 and 4 for our nice first kind of deep sleep stage.

But then what we do is we actually cycle back up, so we go backwards into stage 2. We then skip stage 1 entirely and would enter our first REM stage. Okay, so we go 1, 2, 3, 4, backwards to 2, skip 1, and then enter our first REM phase, so our first dream basically. Now from there, remember we're doing this, you know, 4 to 6 times per night, right? So for our next one we would skip stage 1 completely again, so no stage 1, we'd go right into stage 2, stages 3 and 4, back up to stage 2, and then into REM, just like that.

Now, what is going to happen usually once or twice a night is that you are going to wake up. Quite often this happens so quickly you aren't even aware that it does happen but it usually happens at least once a night. So if you wake up during the night then you would have to go back into stage 1 sleep before continuing through that cycle just like we've been talking about. So you only re-enter stage 1 if you wake up during the night. If you never wake up during the night then you would never re-enter stage 1 sleep.

So we're going to keep going through this pattern of 2 down to 3 and 4 back to 2 and then into REM over and over throughout the night. Now there are a couple major takeaways and kind of common patterns that we see. The first is that, as you can see here, stages 3 and 4 sleep actually get shorter as the night goes on. So that will be decreasing over time to the point where quite often your final sleep cycle won't even include stage 3 and 4 sleep. So you basically don't have any deep sleep happening in that final sleep cycle.

Now in contrast to that, the pattern that we see with REM is that it actually gets longer during the night. So our REM phases get longer and longer. Usually, the first one will be really quick. It’s like, you know, 15 minutes or so. Usually by our final sleep cycle it can be, like, a full hour long.

So stage 3 and 4 sleep is decreasing. REM is increasing throughout the night. And then our other big takeaway, like we talked about, is that you are only going to re-enter stage 1 sleep if you wake up. Okay? If you never wake up you just never go back into stage 1 and we'll just continue through stage 2, 3, and 4, back to 2, into REM over and over throughout the night.

Alright. So those are what sleep patterns look like in a typical night, and I will see you guys in our next video. Bye bye.

Sleep Example 5

Alright. So for each scenario listed here, we're going to be saying what stage of sleep would most likely come next? I drew a shoddy little graph to help us think through it. So scenario A is leaving stage 3 and 4 sleep. Pretty much always, if we are leaving stage 3 and 4, we're going to start going backwards.

Right? So basically, every time we leave stage 3 and 4, we will go back up into stage 2. Right? So our answer there is going to be stage 2, most likely will come after stages 3 and 4. Alright.

So B reads after waking up in the middle of the night. Remember, you don't re-enter stage 1 sleep during the night unless you wake up. Right? And if you do wake up during the middle of the night, whether you are consciously aware of it or not, you will have to drop back into stage 1 sleep. So if we wake up in the middle of the night, our next stage is going to be stage 1.

Alright, and then finally, after REM sleep. Typically, after REM sleep, we are going to re-enter stage 2, right? We are going to skip over stage 1 completely and go right down into stage 2. Now, the only time that wouldn't happen is if you woke up, but most likely, and we're kind of answering with just most likely what is going to come next, and on average, after REM sleep, you're going to drop back down into stage 2 sleep. Alright.

So there are our answers, and I will see you guys in the next one. Bye bye.

Which of the following statements are true about sleep patterns?

I. Stages 3 & 4 gets longer as the night goes on.

II. Each sleep cycle typically last between 90-120 minutes.

III. REM cycles get longer as the night goes on.

• A. I & II.
• B. I & III
• C. II & III
• D. I, II, & III.