Sleep Stages, Sleep Cycle, and the Biology of Sleep

we spend approximately a third of our lives asleep which means if you're lucky enough to live to 100 roughly 30 of those years you're in a deep deep slumber and if we do something this much it's important we understand what's happening in the mind and body in other words how does sleep work [Music] alright guys welcome to psych explained in this video we're going to dive into sleep specifically what happens in the brain to produce the onset of sleep and what happens during a long night's sleep so let's start with this question how do you know when to go to sleep and when to wake up and you might be thinking well i have a clock that lets me know what if i told you you didn't need a clock that instead you have an internal clock already that lets you know when you're tired and when it's time to wake up and we do and that clock and we'll write that in together is called your circadian circadian rhythm okay and the reason we call it your circadian rhythm is because it's latin for circa which means approximately and diem which means day so approximately during a 24 hour period your body is scheduling when to wake up when to go to sleep when you're hot when you're cold when you're hungry it is the schedule that you already have now what controls are circadian rhythm well what controls our circadian rhythm and i have a moon here is information from the outside world specifically light and dark signals so let's walk through together how this may work let's imagine it is 11 o'clock or midnight right and you're getting into bed how are we going to feel tired well the first thing that's going to happen is light is going to hit the eye and the eye is really what tells your brain whether it's time to go to sleep or not and this information is going to hit the back of the eye what we call the back of the eye this is the retina and why is this important this is where light converts into electrical impulses or action potentials and this electricity is going to travel up the optic nerve okay this is made up of ganglion cells and it's going to reach a really important part of your brain that regulates your entire circadian rhythm what part is this called this is your hypothalamus let's write that in here your hypothalamus and why do we call it your hypothalamus let's do a little error right here because the word hypo means below it is below our thalamus and your hypothalamus i like to think about it like your internal thermostat right it makes sure that your body maintains homeostasis if you're hungry you eat if you're thirsty you drink if you are cold you got to get warm and if you're sleepy you gotta sleep this is why it's so hard to stay up when we feel tired and if you're driving you know that feeling so this is our internal thermostat now within our thermostat within this hypothalamus is a group of cells that really regulates this entire circadian rhythm and gets the things in motion to produce sleep onset and what is that it is a tiny group of cells within the hypothalamus called this is a big one your suprachiasmatic nucleus let's write that in together your suprachiasmatic chismatic nucleus okay nucleus or and this is much better to abbreviate your scn and your scn is going to communicate to the rest of your brain different parts of the brain stem at different parts of your glands that it's time to go to sleep and produce different hormones and different chemicals so where is it going to go well the scn is going to communicate to really two parts and let's think about this together the first one is a major gland in your brain called and we'll fill in here your pineal gland what is it called your pineal gland penile rice part of the brain there pineal gland and that is located right here okay shape of the pine cone and that's why we call it the pineal gland now what does your pineal gland do and you probably know this word because you can buy it at a pharmacy it's going to reduce or secrete a major hormone that's going to start slowing your heart your breathing your temperature and produce sleep what do we call this we call this melatonin okay so we're gonna start produce melatonin okay so that's the first part your scn controls your entire circadian rhythm right through light and dark signals from your eye and it's also going to control and tell your pineal gland to start releasing melatonin your scn is also going to communicate with right down here your brain stem okay now your brain stem kind of does a few things right your brain stems kind of that middle pathway right between the body and the rest of the brain everything is going to flow through the brain uh the brain stem to go to the cortex or to the lower part of your body but your brainstem also controls a lot of other things because if you damage your brain stem you might go into a vegetative state or a coma that lets us know it definitely plays a role in arousal and sleep now are there any specific structures within the brain stem that help with sleep and alertness and there are let's talk about a few of these the first one is this band of fibers that rent up the brain stem that runs out the brain stem just like this and it's got all these fibers attached to it like this okay and it's gonna talk to the thalamus and the rest of the brain this is called the reticular activating system or the reticular reticular formation okay the reticular formation and that is this structure right here all right and what does it do let's write a few things out it is involved in arousal okay it's involved in consciousness okay consciousness and we know that because if you damage your shake formation you will fall into a vegetative state or coma okay and of course sleep so what does this have to do with sleep well as melatonin is being released and your brain stem is getting ready what's going to happen is your tick information is going to be kind of like a shut off valve right information likes to rise to the cortex that's the wrinkle layer to think and make decisions but we don't want that when you sleep we want some sort of off switch and that's what your reticular information is going to do it's going to kind of produce that off switch okay so information is not going to reach the cortex so we're not thinking it shuts off that arousal it shuts off that consciousness right so there's the first part that is our reticular formation now we also have we'll talk about this a little later on are pons which is this structure right here it's a little bulge right above the uh right above the brainstem and our pons what does it do it plays a role in muscle relaxation okay muscle relaxation so when you are in relaxation when you are in rem sleep we'll talk about rapid eye movement later your body is paralyzed right your pons plays a role in that as well so this is a nice anatomy a nice way to think about what is happening in the brain now are there neurotransmitters involved of course right serotonin is going to decrease we don't want to be alert dopamine is going to decrease we don't need pleasure reward when we're sleeping acetylcholine which controls muscle movement that's going to decrease we don't want that but is there something that's going to increase and there is so what's going to increase your brain stem area is going to produce a chemical called gaba or gamma amino butyric acid okay this is a major inhibitory neurotransmitter what does that mean your cells like to fire right neurons are communicating to each other we don't want neurons to communicate to each other we want you to go to sleep so what's going to happen is gaba is going to flood your brain it's going to flood everywhere and inhibit or stop things from talking to each other so if i put a little you know if i have my little stop sign right here where is this going to take place well we definitely don't want you thinking right we don't want your prefrontal cortex working we don't want your reticular formation to work right we want that to stop with arousal and wakefulness we don't want your hypothalamus to talk to things right so you have all this gaba all over the brain telling everything to stop working we want neurons to stop firing and this is going to occur everywhere we'll pull one there as well right so gaba is our main inhibitory neurotransmitter now here's the question now that we know what's happening neurologically what happens during a seven or eight hour night's sleep and how do we know what's happening well let's take a look here the reason we know it's happening is because scientists quite amazingly can peek into your brain as you sleep and yes i know it sounds like science fiction but we can actually do that and the way we do that is through this little machine right here now what is this called once again a big word just like the suprachiasmatic nucleus this right here this little machine is called the electro we'll break this up electro and cephalograph that's a big one or and this is much easier just like the scn we're going to call the e e g electro encephalograph or you might see the phrase electroencephalography right now what does this machine do it's measuring the electrical activity in your brain right when you're sleeping your brain isn't shut off right it's not an on off switch it's still highly active and your brain communicates with electrical impulses right action potentials so what this machine does is it captures and monitors all that activity that's happening in your brain and we find is that every stage of sleep over let's say eight hours you're going to produce different types of electrical activity so we're going to put all these electrodes on your brain i've actually had this done i'd sleep apnea when i was younger and they put all these little kind of metal discs on your head and these are going to be attached to a computer okay so all these will be attached to a computer they're going to glue them on and yes it kind of feels weird when they come off okay all these are attached we'll get each one of these electrodes to a computer okay and what it's going to measure is all this electroactivity and it's going to chart it out on a graph so what we're going to do in the next segment is understand what's happening during the sleep cycle what kind of waves is it showing and what are the stages of sleep that we see on electroencephalograph now the first to understand this there's actually two stages of sleep we'll dive into this and how this works with the eeg we have rem sleep and non-rem sleep what's the difference rem stands for rapid eye movement which means during the 1950s there was a really good discovery at the university of chicago that when you're sleeping your eyes are moving rapidly under your eyelids that's one stage the other is any stage in which your eyes are not moving we call that non-rem sleep so there are three non-rum stages in one rem stage okay so we'll dive into that as well all right so let's start with the first one okay what is happening well let's say and we'll stick to our scenario it is 11 o'clock and you are uh you're about to go to bed but you're still alert okay well right now you're awake so there you are okay and if i put an eeg on your head what you would see and i'll use a different color here are things called i'll write this in right here beta waves okay beta waves and beta waves look like this okay and what does this mean high frequency uh high amplitude sorry high frequency low amplitude okay and uh frequency refers to peak to peak right everything every wave is very close together there's our frequency and our amplitude is the peak right how high the wave gets so when you're awake you're listening right now your brain is producing what beta waves okay so that's the first part but then you start getting tired okay and you start getting drowsy drowsy drowsy more drowsy and your brain is actually going to start producing alpha waves instead of beta waves right all this is from the greek alphabet alpha beta gamma delta so forth and then what's going to happen is you're going to enter what we call non-rem one right your eyes aren't moving this is considered stage one what's happening in this stage well first let's draw some of these brain waves okay and they're going to look something like this okay very similar to being awake okay you have high frequency low amplitude and we'll do it down here these are called i'll use a different marker for this this is gonna be called uh light uh theta waves okay theta waves okay now this is a stage of sleep where like people are sleeping but you're not sure if you're sleeping do you ever have that you wake up you're like was i sleeping you were probably in non-rem one so because of that we like to consider this light sleep okay where you're kind of sleeping you're kind of dozing in and out of consciousness it is considered light sleep now there's other really cool things that happen one in non-run one you might experience something called hypnic jerks okay and as a teacher i experience this all the time do you ever have that moment you're like this oh right and you just wake up your head jerks up oh and i love my students they're like oh they do this and they look around i'm like hypnic jerk it's a muscle twitch a muscle contraction that happens when you are non-rem one another thing that happens during nano m1 is something called and this is a big one hypnagogic or hypnogogic hallucinations okay and a hallucination is kind of you know hallucinations is a essentially kind of a false sensory experience right you might hear a voice that's not there you might see something that's not there you know i asked my students i'm like how many of you seen a ghost edward's hand goes up how many of you ever seen a ghost during the day nobody's hand goes up right people only see ghosts at night and that might be because during non-rem one you hear things aren't there you see objects aren't there your mind is kind of hallucinating because you're in this weird transition period between consciousness and sleep or wakefulness and sleep right all right so there's non-rem one what happens next you're going to keep transitioning down away from wakefulness away from light sleep to we call non-ram ii okay what happens in non-rum 2 let's start here first you still experience theta waves okay data waves but then something also happens right your body temperature's dropping your heart beats dropping your breathing is dropping or everything is slowing down your muscles etc is you can actually tell your non-rem to because of two things on your eeg one is called and we'll draw this together sleep spindles okay sleep spindles and the other one is called k complexes okay a complex and a sleeve spindle so what would this look like we have our brain waves still high frequency low amplitude and then what happens is you have these brief bursts of brain activity okay so it's like go go and then right a lot of activity in the brain okay and then by the way that's a sleep spindle you have a k complex which is this high you know amplitude kind of this high delta wave followed by a big drop and then returning to high frequency low amplitude so here's our sleep spindle i'll do ss and here is our k complex and there's some theories about why we have spindles and complexes and one of the theories is that if we go back to the brain structure information is trying to enter your brain and wants to wake you up but your reticular formation your thalamus is like no no we still need sleep right so this kind of information entering your brain and your thalamus is like no no we still need to filter it out we still need to sleep all right so there we go we're non-rem one non-run two what's gonna happen we are continuing our night sleep and we enter non-rem three this is a good stage non-rem three if we look at a brain wave you tell me what difference you see okay what difference do you see in the first two okay we have low frequency the waves are really far apart instead of low amplitude we have high amplitude much more uh stronger right so the waves look very different this would tell a scientist or a doctor looking at you they'll say oh you've entered deep sleep so let's write that in together we have theta theta we are now into what we call delta waves okay delta waves and once again delta waves are low frequency high amplitude another way to think about the uh deep sleep non-rem 3 is instead of deeps instead of oh yeah we call deep sleep by the way deep sleep it's you can call slow wave sleep so we have deep sleep also known as slow wave sleep okay right this is the type of sleep where it's impossible to wake up right you feel like you're a zom you you can't you can't wake up right you're just dead to the world this is deep sleep it is very hard to wake somebody up in deep deep slow wave sleep now other things happen during deep sleep one is we know growth hormones are released right body is going to repair itself so we know at different stages of sleep different things happen your cells are going to repair themselves your body's going to get better that happens during deep sleep also during non-rep 3 is parasomnias or sleep disorders ok a lot of sleep disorders are going to happen in this stage of sleep things like sleepwalking and sleep talking sleepwalking we talk about as somnambulism is the technical name um bedwetting right um all those things happen technically or during non-rem three okay all right what happens next something magical happens instead of just waking up right we start to go back to the original stages one two three we go back up you go to an iron two and all the way up okay what happens next right before you wake up something happens okay what happens rem sleep rapid eye movements your eyes are going to start moving rapidly under your eyelids okay what does this look like on a little eeg the waves are going to look like wakefulness okay they're almost going to look like theta waves like up here okay in other words your brain might not know the difference between being awake and being in rem it almost looks identical now what does this mean why is rapid eye movement so important well one we find and scientists will find this out in the 1950s that this is typically when we dream now yes you can dream in non-rem sleep but majority of dreaming occurs in rem sleep so when you see somebody's eyes moving back and forth wake them up they're likely to remember a very vivid dream during rem sleep all right what else do we know about rem sleep we know that also you have muscle paralysis your muscles don't work okay you're paralyzed muscle paralysis okay and a lot of people will say you know paralysis you know i've woken up during rem sleep and you're aware of the world but you can't move your muscles of course because your muscles are paralyzed right you don't have acetylcholine you can't move and things like that all right what else do we have another way to think about this and this is a big phrase as well is paradoxical sleep okay it's like a paradox this is another name we use for rem sleep why is rem sleep paradoxical because it doesn't make sense your brain is highly active you got a lot of activity up there but your body's paralyzed it's a paradox right so you have this irregular heartbeat your your breathing's irregular your your your temperature is starts to uh change right everything's changing but you're paralyzed so that's we call paradoxical sleep all right anything else important about rem sleep it is also important in memory and learning in other words if i deprive you of rem sleep and you learn something the night before you might have trouble remembering it the next day so rapid eye movement is important for dreaming and memory learning and we know our bodies paralyzed but our mind is active hence paradoxical sleep okay all right let's continuous what happens during night everything's going to keep going right we're going to go back down to stage 2 stage 3 right and then we go back up again right and by the way each one of these cycles lasts about 90 minutes about an hour and a half for each cycle and we go back and right before you wake up back into rem sleep okay and notice also is my line is getting a little bit longer in other words as the night goes on you start you spend more and more time in rem sleep so a bigger night little rem at the end of night a lot of rep and we go back and we're gonna go up again and notice also you spend less and less time in deep sleep a lot of deep sleep in the first half of the night less deep sleep later in the night a lot of ram okay and let's just for imagination we have one more and then we'll say you have a big rem moment you spend an hour in ram and then you wake up there is a perfect night's sleep and i like this kind of graph here you can kind of see that deep sleep decreases as you get through the night and of course longer ram moment now this is a perfect night's sleep right now already have a perhaps not everybody has a perfect night's sleep but that would be one all right guys thanks for watching i really hope you took something away don't forget to like the video subscribe and i'll see you next time oh and most importantly get some good sleep

Channel: Psych Explained

Views: 200,346

Keywords: sleep, sleep stages, sleep cycle, GABA, REM, rapid eye movement, pineal gland, melatonin, SCN, hypothalamus, circadian rhythm, EEG, beta waves, delta waves, hypnic jerk, theta waves, sleep walking, sleep spindles, k-complexes, retina, cones, rods, reticular formation, reticular activating system, pons, NREM 3, light sleep, nrem sleep, electroencephalogram, thalamus, optic nerve, suprachiasmatic nucleus

Id: Byrh3s3BFjM

Length: 22min 17sec (1337 seconds)

Published: Fri Nov 26 2021