#Suprachiasmatic Nucleus

[the-banks-of-lethe]

Circadian Rhythm: The Basics

As voted on on Wednesday, I'll be covering the basics of the circadian rhythm! When I say basics, I mean the basics, this isn't a deep dive by any means and really just scratches the surface of it. Feel free to add anything on or go and research more yourself if you find it interesting. I might do a deep dive once I get more knowledgable on the subject, but for now, this is it!

[My writing will be in blue for ease of recognising what is my writing and what is quoted. Quoted things will have their links attached.]

Dictionary definition: Circadian rhythm (sir-KAY-dee-un RIH-thum). The natural cycle of physical, mental, and behavior changes that the body goes through in a 24-hour cycle.

"Circadian rhythms are the physical, mental, and behavioral changes an organism experiences over a 24-hour cycle. Light and dark have the biggest influence on circadian rhythms, but food intake, stress, physical activity, social environment, and temperature also affect them. Most living things have circadian rhythms, including animals, plants, and microorganisms. In humans, nearly every tissue and organ has its own circadian rhythm, and collectively they are tuned to the daily cycle of day and night.

Circadian rhythms influence important functions in the human body, such as:

Sleep patterns

Hormone release

Appetite and digestion

Temperature" National Institue of General Medical Sciences

Basically, your circadian rhythm is your biological time clock*. Telling your body when to do stuff based on your environmental factors and habits; also called a Zeitgeber (German, literally translating to 'time giver', also translated to 'synchronizer'). A Zeitgeber is anything that resets the bio-time-clock. Most commonly its the sun, but it can really be anything that is consistently reoccuring enough in your scheduele for your body to recognize it as a signal of 24hrs passing. This could be food, excercise, social interactions, etc. Humans are creatures of habit, and our brain reflects that.

*Technically, it's not. I know, sorry. But it is at the same time. The suprachiasmatic nucleus (SCN) is your bio-time-clock; but the SCN is what triggers your circadian rhythm, not just for sleep but for all the other things affected by it; like body temperature, which rises during the day to keep you awake, and drops at night.

My personal favourite experiment / study on the circadian rhythm is the Richardson & Kleitman Mammoth Cave Experiment, 1938.

^^ short video from 1938, subtitles are available.

"Normal sleep--wakefulness cycles operate on a seven day, 24 hour cycle; Kleitman wanted to adjust himself and graduate student Richardson to a six day, 28 hour week."

"Kleitman and Richardson spent 32 days in the cave with a strict schedule of sleeping for 9 hours, working for 10, and 9 hours of leisure time. The absence of light and noise and a constant temperature made for a great experimental environment."

"The goal of their experiment was to determine if humans had an ingrained 24 hour cycle or if we can adjust our circadian rhythm. Measuring changes in body temperature shows a range of 1–2°F change with the highest value in the afternoon and the lowest in the early morning. This curve is not seen in infants, but develops as children adapt to rest-wakefulness cycle of 24 hours."

"It is known that the body temperature curve can be shifted any number of hours, as when a person moves from the United States to China, or it can be completely inverted as when a person regularly stays up at night and sleeps in the day-time [sic]. In either case, however, the duration of the cycle remains unchanged, namely, 24 hours. It is our purpose to find how easy or how difficult it is for a grown up individual to change his body temperature curve from a 24-hour to a 21-hour or 28-hour cycle."

^^ above four (4) paragraphs and video from here

After the experiment concluded, Kleitman wrote and published a study based on their findings called 'Sleep and Wakefulness'.

^^ you can borrow the book for free online, you kind find lots of books / videos / texts / media on here, you just need to sign up <33 (The Internet Archive)

"Nathaniel Kleitman, who died on August 13, 1999 at the age of 104, can be properly described as “the father of modern sleep research”. His claim on this title stems from both his scholarly integration of the work in the field and his own research. His 1939 compendium of prior work on sleep and wakefulness, revised in 1963 (18), includes thoughts on sleep ranging from Aristotle and other ancient thinkers to 20th century pioneers such as Pieron, Hess, Nauta and Kleitman’s contemporaries. The explosive recent growth of the field guarantees that this will be the last such comprehensive, research oriented integration of the literature in sleep research. In the introduction to the 1939 edition, Kleitman apologizes that his reading abilities are “limited to French, German, Italian and Russian” (and English). However, despite this “handicap” he critically integrates 4337 references covering sleep, circadian rhythms, sleep disorders, hibernation and theories of sleep function." - A Tribute to Nathaniel Kleitman

Okay, so not as short as I originally expected, but I could've written more, so yall are lucky I decided to cut it off there. If you have any questions or noticed that I got something wrong, or would ilike to add anything - please feel free!!

I have gotten a lot of what I know of sleep from an amazing amazing book called 'Why We Sleep' - by Matthew Walker. I'm only part way through it but I love it so much, and can definitely see myself buying a copy in the future. Here's a link to his website: https://www.sleepdiplomat.com/ [I only just found his website and omg I didn't know he had a podcast, I know what I'm going to be listening toooo]

Anyway, I hope this has been informative and is a good starter to get you into the science of sleep! I love Hypnos and his realm.. and I hope I can spread further information on him and his domains to others!

Χαίρε Hypnos, and sweet dreams!

[mehmetyildizmelbourne-blog]

SCN, Circadian Rhythm, & Key Biochemicals for Sleep Regulation 

The body’s internal clock related to light & hormones/neurotransmitters for restful sleep I have deep empathy and compassion for those who experience sleep disturbances, as I, too, have faced the consequences. Sleep deprivation has negatively affected my health, wellness, and overall life satisfaction. Sleep is a fundamental need for all living beings. For years, I struggled with sleep…

[raffaellopalandri]

The Morning Chronotype

A chronotype refers to an individual’s predisposition towards a specific sleep-wake pattern. Often categorized into morning, evening, and intermediate types, chronotypes are fundamentally rooted in biological rhythms. Photo by Pixabay on Pexels.com Scientific research has illuminated the mechanisms underlying these sleep-wake patterns. At the core of chronotype differences lies the circadian…

[mrrichie88]

As the sun dips below the horizon, its rays align perfectly, creating a moment of harmony and balance, connecting with the rhythms of nature and the universe.

[dichromaniac]

Hey I'm currently in the process of getting certified as a sleep tech. The apnea being the only thing that really gets discussed is absolutely true. Now apnea sucks and it can fuck up your body big time. I've watched people stop breathing for a full minute. I've seen people desaturate into the 70s and back up for six hours on a loop.

The problem is that there's no good individual solution to disordered circadian rhythm/sleep drive. The problem is a social one. We need to have job options that allow for delayed or free range cycles. We need to recognize it as a disability and offer socioeconomic supports.

The reason sleep is so focused on apnea is because it's the only problem with an individual solution. Everything else requires a shift in our entire way of thinking about the human day/night cycle and how we structure our society.

Or you get trazodone and stimulants.

one of the most enlightening realizations ive had was finding out that non-24 hour circadian rhythm people were a pretty large group and most of us have oddly similar cycles of usually around 28hr internal "days" and this masquerades as "insomnia" but if allowed to sleep and wake naturally we will just advance forward through time an extra 2-4 hours a day at a relatively stable pace. we can't go to school or jobs or even run errands on normal schedules without massive pharmacological and behavioral intervention. most of the people who have been diagnosed or figured it out themselves will report horrific, life-ruining disruption in their professional lives and terrible health from accrued lack of sleep. this disorder is most common in vision-impaired people which seems to suggest it's related to light cues. anyway just thinking about this as extremely loud yard work woke me up at 8am for the second day in a row

[daily-pryce-and-carter]

Survival Tip No.872

Life on board a spacecraft will feature patterns of light and darkness that the normal human body is not properly equipped to deal with. Insomnia or extreme drowsiness during the initial weeks of your mission rotation are perfectly normal, if highly undesirable, side effects. But don’t worry, sooner or later your suprachiasmatic nucleus will remember who’s in charge and your circadian rhythms will change.

[transgenderer]

Natural Sleep and Its Seasonal Variations in Three Pre-industrial Societies

How did humans sleep before the modern era? Because the tools to measure sleep under natural conditions were developed long after the invention of the electric devices suspected of delaying and reducing sleep, we investigated sleep in three preindustrial societies [1–3]. We find that all three show similar sleep organization, suggesting that they express core human sleep patterns, most likely characteristic of pre-modern era Homo sapiens. Sleep periods, the times from onset to offset, averaged 6.9–8.5 hr, with sleep durations of 5.7–7.1 hr, amounts near the low end of those industrial societies [4–7]. There was a difference of nearly 1 hr between summer and winter sleep. Daily variation in sleep duration was strongly linked to time of onset, rather than offset. None of these groups began sleep near sunset, onset occurring, on average, 3.3 hr after sunset. Awakening was usually before sunrise. The sleep period consistently occurred during the nighttime period of falling environmental temperature, was not interrupted by extended periods of waking, and terminated, with vasoconstriction, near the nadir of daily ambient temperature. The daily cycle of temperature change, largely eliminated from modern sleep environments, may be a potent natural regulator of sleep. Light exposure was maximal in the morning and greatly decreased at noon, indicating that all three groups seek shade at midday and that light activation of the suprachiasmatic nucleus is maximal in the morning. Napping occurred on <7% of days in winter and <22% of days in summer. Mimicking aspects of the natural environment might be effective in treating certain modern sleep disorders.

particularly interesting, on insomnia:

Since insomnia is a complaint and does not closely correspond to sleep time [19, 20], we investigated the prevalence of this complaint in the Tsimane and San groups. At the time of application of Actiwatches on the Tsimane, G.Y. and a Tsimane translator visited the participants in their homes early in the morning to conduct an interview on fatigue and sleep quality. A similar interview was done by J.M.S. on the San group. Neither group has a word for insomnia in their language, so we explained the concept in terms of sleep onset insomnia and sleep maintenance insomnia not due to illness. Five percent of the participants said they sometimes had sleep onset problems and 9% sometimes had sleep maintenance problems. Less than one-third of these participants said that they had these problems regularly, i.e., more than once a year (1.5% and 2.5% of the total number of participants). These numbers are far lower than the 10%–30% chronic insomnia rate reported in industrial societies [19, 20]

this is kind of a crazy plot, but communicates the similarity in sleep patterns between the three far-flung societies

[gojostan-doodles]

Note to self: the suprachiasmatic nucleus is located in the HYPOTHALAMUS!! NOT THE BRAINSTEM! IF YOU PUT BRAINSTEM ONE MORE TIME I'M GONNA BEAT YOUR ASS!!👹 DO YOU HEAR ME??!!1 👹👹🛴💥🩼

[aloysiavirgata]

Dancing that ISNT the PMP scene. Fucking love you gorgeous. ❤️❤️❤️

3 AM finds him waking up stiff and disoriented in the vinyl chair of her hospital room, his feet propped on an upside-down plastic wastebasket. His tie is hanging from the IV pole.

Mulder tests his joints, grimaces at the left shoulder. He’d overstretched it at the pool, shredding 2000 meters in under 30 minutes. He’s been lifting more, been running until he vomits. He doesn’t know if he’s punishing his body for being fit or trying to radiate so much health she’ll absorb it.

Perhaps if it’s the second he’ll need to feed it something other than coffee, Diet Coke, and sunflower seeds. Must be the first.

He examines her narrow form in the bruised light. Scully’s breath snuffles a bit at the cannula and he scans for blood at it but sees none. Her cheekbones curve resolutely past her patrician nose, down to her full, dry lips. There is a small tin of Smith’s Rosebud Salve on the fake wood nightstand. He resists the urge to rub a layer over them. He resists the urge to kiss her beautiful, cracked mouth.

Mulder sighs a bit, runs a finger around the back of his collar. She looks warm to him, looks safe and cared for and utterly beyond his ability to be of use. But he stays anyway, like one of those dogs that sleeps at the grave of its master.

He roams past the nurse’s station, where Jane and Esther give him sympathetic looks. They aren’t supposed to let him sleep in Scully’s room, but Esther is from Yorkshire and calls him lamb and duck and love, and he’s pretty sure he could get the lithe Jane in bed if he wanted to.

He’s drowned his sorrows in lanky brunettes before though, and it never quite took. Turns out he’s a man for dainty gingers.

The radio at the nurse’s station plays “Carolina In My Mind” and he hums along softly, making a styrofoam cup of tea. His father was happy in Raleigh. He was too, as much as he was happy anywhere. He thinks he might move down when Scully goes into the ground, a truth he can only admit at 3 AM. At all other times he will save her.

“Nah then, duck,” Esther says. “Tea from the machine, yer daft ‘apeth, when I’ve a proper kettle ‘ere? ‘Ow’s thy lass?”

He shrugs, smiles vaguely. Jane smiles back. Vaguely.

Mulder presses his head to the faded green wall as his tea steeps. It’ll be terrible, but strong. That’s good enough for him.

He hears a soft shuffling and looks up.

Scully in her spotless white robe and soft slippers, Scully like a Willow Ptarmigan approaching winter. The skin around her eyes is the delicate color of sublimated iodine.

“Scully,” he says, at a loss. She is beautiful in the way of alabaster vases, of all things that can shatter.

She yawns, lips shiny with the salve. Her hands are very thin when she covers her mouth. “Wonderful Tonight” begins on the radio now.

Esther smiles, looks away. Jane checks her watch and walks down the opposite corridor.

“Tea?” Scully says. “That’s more my brand. Why are you still here?”

He gulps the bitter brew. Winces. “I fell asleep,” he says, which is an answer but no answer at all.

“Mmm,” Scully says. She prepares herself some tea as well. Her white hands on the cup, her lower lip snagged between her teeth.

“I’m sorry I woke you,” Mulder says.

“You didn’t. I just woke up. I do that a lot. My circadian rhythm…”

They don’t talk about her suprachiasmatic nucleus of the hypothalamus deep within her brain. Of what it might mean if it’s off kilter.

“I was noisy,” Mulder lies, looking at her nose again. He moves like a cat in her room. Like a thief in the night. “Banged into the bed.”

Scully smiles serenely. “It’s all right.”

Jane stalking the perimeter, Jane frowning at her clipboard.

The moon out the window like a scythe in the dark.

He loves her, does she know? Does he know what he would do to save her and how he’d do it and that he’d swim through blood and blood and blood for her, 2000 meters and back again in a heartbeat?

Scully puts her tea down, Scully looks at him with her late summer eyes in this month of her birth. Scully is dying.

On the radio, The Beatles begin “Let It Be,” and what the fuck, he draws her in, her tousled hair and fluffy robe and her rattan ribs.

“Mulder,” she says, peering up. She clutches his left hand with the pale garden spider of her right.

He twirls her beneath the fluorescent lights. He kisses her her forehead because if he kisses her mouth like he wants to she will die.

Jane does another lap and Esther pretends to read a chart and Scully murmurs along with Paul McCartney.

Mulder watches the flat light bounce off her hair, watches her sway, watches her smile for a moment. She tucks her head against his chest as the song ends, doesn’t withdraw.

“Angel Is A Centerfold” begins, which is hardly the mood he wanted, but they both laugh and the scythe of a moon fades away as they sing Na-na, na-na-na-na, Na-na-na, na-na-na-na in something like harmony.

He doesn’t know what song is next, but he holds her through it and the next one and a few more and Esther and Jane are replaced and the sun begins to burn the blackness away and Scully is warm and awake and alive in his arms for at least another day.

[mnrpardiman]

Chronobiology is the scientific study of biological rhythms and their mechanisms. It explores how living organisms, including humans, plants, animals, and even microorganisms, adapt their biological processes to the timing of environmental cycles such as day and night, tides, seasons, and lunar phases.

Key Concepts in Chronobiology:

1. Biological Rhythms: These are cyclic patterns in biological processes or behaviors. They are categorized based on their frequency:

Circadian Rhythms: Approximately 24-hour cycles, like the sleep-wake cycle.

Ultradian Rhythms: Shorter than 24 hours, such as heartbeats or hormonal release.

Infradian Rhythms: Longer than 24 hours, such as menstrual cycles or seasonal behaviors.

2. Circadian Clock:

This is an internal mechanism that helps organisms maintain a roughly 24-hour cycle, even without external cues.

It is regulated by a "master clock" in the brain, specifically in the suprachiasmatic nucleus (SCN) of the hypothalamus, which is synchronized by environmental light and dark cycles.

3. Zeitgebers: External cues, like light, temperature, and food availability, that help synchronize biological rhythms with the environment.

4. Chronotypes: Individual variations in circadian rhythms that determine whether a person is a "morning person" or a "night owl."

5. Disruptions in Chronobiology:

Jet Lag: A temporary misalignment of the circadian clock due to rapid travel across time zones.

Shift Work Disorder: Chronic disruption caused by working non-traditional hours.

Seasonal Affective Disorder (SAD): Depression linked to seasonal changes in light exposure.

Applications of Chronobiology:

Medicine: Timing treatments (chronotherapy) to align with biological rhythms for better efficacy and reduced side effects.

Agriculture: Optimizing planting and harvesting schedules based on plant rhythms.

Sleep Science: Understanding and treating sleep disorders.

Workplace Productivity: Designing schedules that align with workers' natural rhythms.

Chronobiology is a multidisciplinary field, drawing from biology, neuroscience, psychology, and even physics to understand how time influences life.

[swede1952]

Good morning. 😴😫☕

12 December 2024

Charlie is in here just sitting next to my chair. They both do that, though Ben isn't here right now. I did a sleep study last night; I left here a little after eight yesterday evening and was home before six this morning. It was mildly interesting, sleeping with a bunch of wires connected to my head and body, who came up with that? I saw myself in a mirror this morning before the nurse removed the wires and wow. If not for the wires, I might have passed for a zombie, but with the wires perhaps a rough looking Frankenstein. Maybe I was receiving a download, I better put my tin foil hat today. Hmmm … I think I left the book I was reading on the bed.

“Your suprachiasmatic nucleus communicates its repeating signal of night and day to your brain and body using a circulating messenger called melatonin.” - Matthew Walker

[tchaikovskym]

When I was doing some research due to MASSIVE problems with my sleeping pattern I've read somewhere that even though chronotypes differ ultimately it would be healthiest to get up and go to bed early due to melatonin- and metabolism-cycles (what you wrote about cortisol was mentioned also) - which made me wonder why so many people seem to suffer then from going against their chronotypes (including claims of destroying their health and cognition). Do you happen to know more/have any advice? :(

Hi

I get why it would be advised to go to bed early and wake up early, because melatonin reacts to light, and melatonin is the one of the main hormones involved in keeping your "biological" clock.

For a long time it was believed that a region in your brain (suprachiaszmatic nucleus in hypothalamus) is responsible for regulating your internal clock, by mostly reacting to light signals from your eyes.

First, modern human life is very illuminated due to artifical light and it might be the first problem with the sleep/wake cycle. Thus, the first recommendation I would make, is to get rid of light when you're asleep, be it black out curtains or sleeping eye mask. + blue light filter on devices before bed

But it's probably going to have only a small impact. And besides, blind people have internal clocks too, so light being the only internal clock regulator is a pretty shabby claim alone.

There are also peripheral clocks, that tune the same region in the brain (suprachiasmatic nucleus), according to what's going on with your body. And those signals are everywhere, your heart, your liver, your muscles, your intestines etc. They account for your physical activity, meals, stressors etc.

So, melatonin is not the only player, and also not the strongest one. Yeah it can help, but your lifestyle is a huge factor too.

Besides, going against your chronotype is actually harmful. "Evening" people are more likely to have metabolic, cardiovascular, mental and other problems, because we live in a "morning" people world. Honestly, it sounds fake but it really is like that. And it's not because of melatonin, it's because of your body and how you're used to living.

The same cortisol I mentioned is not working according to the time of day or the light outside. It's working according to your actions and schedule you live in. The same goes for other things in your body.

But of course, it would be cool if everything would be aligned in your body, so it would be ideal to have your melatonin rhythm align with your peripheral clocks. Thus the well-intentioned advice to go to sleep early and wake up early.

I wouldn't apply that advice to everyone. If your sleep schedule is messed up, I doubt forcing yourself to morning bird schedule would help you. My best bet is that you'd lie awake staring at the ceiling until wee hours in the morning, force yourself to wake up, be tired for the whole day, and repeat the thing again. (Because by forcing yourself to sleep by melatonin schedule will ruin your cortisol secretion schedule, as I talked in the cortisol post).

However, as per usual, gradual changes with tiny steps could lead you to where you want to be with your sleep schedule. See what works best for you, maybe you can go to bed a minute earlier, maybe you can eat breakfast (it helps), maybe you can eat a bit earlier in the evening, maybe take a nap, just try stuff out and see how it goes.

Idk what you can find out there, but meal timing is also important. If you want to go to sleep earlier and wake earlier, big meals should be in the first half of the day.

Physical activity and sports help, no matter what kind, no matter what time (but like, stick to the hours you want to be awake when doing sports). (Although it's recommended that sports is better in the later half of the day but not for chronibiology reasons as far as I remember)

So yeah, just do what you can, and hope for the best. Sorry I don't have a clear simple answer and a clear simple advice.

Here is one review that I assume has a lot more information (just glanced over it but it seems good), and idk how familiar you are with the topic and terminology, but like, feel free to contact me if you want me to explain something from the review or other article or another topic honestly I'm a nerd I love rambling about this

[mehmetyildizmelbourne-blog]

Sleep Regulation Insights

I summarize the key points of an exceptional article about sleep regulation written by Dr Mehmet Yildiz on Medium.com.

Neurobiology of the Suprachiasmatic Nucleus A remarkable article by Dr Yildiz titled Sleep Regulation: Neurobiology of the Suprachiasmatic Nucleus explains how the brain regulates circadian rhythms and whether a literal “clock” exists within it in simple terms based on experience and research. Sleep is the cornerstone of human and organismal well-being, highlighted in my previous health and…

[iguanablues]

Not to mention that a few major factors in being a 'morning' or 'evening' person are genetics and age, two things we absolutely can't control.

Looking at the neurobiology of sleep, the suprachiasmatic nucleus (SCN) is the primary circadian oscillator in the brain (meaning it acts as a pacemaker of sorts through various positive and negative feedback loops).

Studies initially done on the fruit fly identified three mutant alleles of a single gene that had the properties of either increasing or decreasing the circadian period or of disrupting the rhythm altogether.

Studies which were later replicated in mammals. This shows us that our genes can have an impact on if we feel more awake in the morning or evening hours.

Now let's look at age. The way that the circadian rhythm changes based on how old you are is really interesting. Babies synch with their mother's circadian rhythm before they're born, and then get thrown totally out of whack after they've been separated. They also need comically large amounts of sleep, and end up only having 7ish hours of wake time during the day. Similar to cats. Eventually this shifts to a more stable morning chronotype (the timing of behaviors that manifest from one’s circadian rhythm, most notably the tendency to sleep and eat at certain hours of the day) as babies age into adolescence, and then shifts much later as kids age into teens/young adults. Then it shifts AGAIN in adulthood back to an earlier chronotype. Into older adulthood, it continues to drift earlier.

We also know that the variance of the general population's chronotype follows a normal distribution. Meaning we have some very early risers, some super night owls, and a bunch of people that fall somewhere in between.

The paper below is interesting, as it provides a great overview of the topics we've covered thus far and introduces the two-process model. The model describes how sleep regulation relies on both the circadian system, and sleep homeostasis. The basic tennent of sleep homeostasis being that the longer you are awake, the greater your body feels the need to sleep.

The paper suggests that there are modern stressors like artificial lighting and reduced reliance on the sun that puts stress on the two-process system. Social and occupational obligations can desynchronize your internal circadian rhythm and the timing of your sleep.

It concludes by saying that "it is imperative that we did not impose rigid recommendations for what constitutes a “healthy” amount of sleep or “healthy” timing of sleep for an individual based on population averages. It is clear that an individual who does not sleep at his or her ideal circadian timing or for his or her ideal duration will suffer consequences."

So yeah.

Ok wait let her speak

[ilearnedthistodaysblog]

#1292 How do circadian rhythms work?

How do circadian rhythms work? Your circadian rhythm is governed by a small group of cells in the center of the brain called the suprachiasmatic nucleus. Most living organisms has a circadian rhythm. It governs the processes of the organism and sets a cycle over a 24-hour period. The word “circadian” is from the Latin “circa”, which means “around”, and “dies”, which means “day”. We use the word “circa” to mean around even today, as in “circa 1977”. The circadian system controls all of the systems in the body and it tells them when to work and when to stop. It controls your hormones, your digestion, your temperature, your breathing, and your cardiovascular system. It is regulated by light, and it tells your body’s systems when to go to peak activity and when to slow down. Light can have different effects though, depending on the type of animal. Diurnal animals and nocturnal animals have different effects. Light wakes diurnal animals up and sends their bodily systems messages to work. Light tells nocturnal animals to shut down for sleep and it is a lack of light that tells them to wake up and start moving. We have evolved a 24-hour circadian rhythm because there are 24 hours on our planet. If we had evolved on Jupiter, were that possible, a day there is only 9 hours and 56 minutes, so that is how long our circadian rhythm would work for. I’m not sure what would happen if we had evolved on Mercury where one day lasts 176 of our days. The goal of the circadian rhythm is twofold. The first goal is to make sure we know when to sleep. Sleep is necessary, although no one precisely knows why. Our circadian rhythm prepares us for sleep when it starts to get dark and starts to wake us up when it gets light. The second goal is to make sure we are as active as possible when our food source is around. We eat animals that are awake in the daytime, so we have evolved to be awake in the daytime. Everything with a circadian rhythm is the same. It is the circadian rhythm that tells plants to unfurl and photosynthesize in the sunlight. So, how does the circadian rhythm work? It is controlled by a tiny group of cells in the center of the brain called the suprachiasmatic nucleus (SCN). The SCN is inside the hypothalamus. When it is daytime, light comes in through the eyes and travels up the optic nerve to the brain. Our eyes have rods and cones, which receive light and analyze it for vision, but we also have ganglion cells, which just register light. The sunlight activates genes in the SCN, which sends out signals to different parts of the brain to start various processes. One signal the SCN sends is to the pineal gland, which produces melatonin. When there is a lot of light, as in early in the morning, the SCN signals the pineal gland to stop producing melatonin, and as the amount of light decreases, the SCN increases the production of melatonin, which builds up in the early evening. Melatonin is the hormone that makes you want to sleep.  The SCN also speeds up the heart rate in the morning and raises the body temperature. It speeds up breathing and increases digestion, producing proteins to aid digestion. It also increases the levels of cortisol in your body. Cortisol is a hormone that regulates the body’s stress response and can trigger the release of glucose from your liver, giving you fast energy. This is necessary in the day for animals that hunt, as we used to.  As the amount of light decreases, the opposite happens. Melatonin increases and cortisol decreases. Your digestion slows down, and your body temperature drops. During the night, your body temperature, heart rate, and breathing all drop. Cerebrospinal fluid is also washed through the brain to remove waste products and clean it up. Without sleep, these waste products build up. Our circadian rhythm is not actually 24 hours. It is a little bit over and needs to be reset by sunlight. If you put someone in a dark room, they will sleep and wake for longer periods, slowly going out of sync with the real day. Our circadian rhythm can also cause us problems when we fly around the world because it takes several days to adjust. It is fine if you take a slow boat across time zones, but not if you fly. There are some organisms that don’t have a circadian rhythm, or a shorter one. Some animals that live at the poles, such as Svalbard reindeer, don’t have circadian rhythms because they are faced with 6 months of light and 6 months of dark. Hibernating animals have different circadian rhythms as well. Sharks and some insects don’t have circadian rhythms either. That’s nice to know. While you are sleeping in your life raft, the sharks are awake. And this is what I learned today. Try these next: - #393 Why do we get jet lag? - #937 How do polar bears find enough food? - #149 Why do cats sleep for so long? - #260 How do some animals sleep standing up? - #405 Do ants need to sleep? Sources https://www.sleepfoundation.org/circadian-rhythm https://my.clevelandclinic.org/health/articles/circadian-rhythm https://my.clevelandclinic.org/health/articles/22187-cortisol https://www.uclahealth.org/medical-services/sleep-medicine/patient-resources/patient-education/circadian-rhythms https://en.wikipedia.org/wiki/Circadian_rhythm https://pmc.ncbi.nlm.nih.gov/articles/PMC3712434 https://the-gist.org/2020/10/rhythm-of-the-night-how-circadian-clocks-influence-nocturnal-creatures/ https://science.nasa.gov/mercury/facts https://science.nasa.gov/jupiter/jupiter-facts https://www.nhlbi.nih.gov/health/sleep/sleep-wake-cycle https://www.nih.gov/news-events/nih-research-matters/how-sleep-clears-brain Photo by Aleksandar Cvetanovic: https://www.pexels.com/photo/orange-cat-sleeping-on-white-bed-1560424/ Read the full article

[nursingwriter]

Psychology States of Consciousness: Sleep Deprivation- Circadian rhythms are normal changes in mental and physical characteristics that take place in the course of a day. The majority of circadian rhythms are controlled by the body's biological clock. "This clock, known as the suprachiasmatic nucleus or SCN is in fact a pair of pinhead-sized brain structures that jointly contain about 20,000 neurons. The SCN rests in a part of the brain called the hypothalamus which is located just above the point where the optic nerves cross. Light that reaches photoreceptors in the retina creates signals that travel along the optic nerve to the SCN. Signals from the SCN travel to several brain regions, including the pineal gland, which responds to light-induced signals by switching off production of the hormone melatonin. The body's level of melatonin normally increases after darkness falls, making people feel drowsy and ready to go to sleep" (Brain Basics: Understanding Sleep, 2007). A person who suffers from Circadian rhythm sleep disorders are normally sleep deprived. All of these disorders entail a problem in the points of when a person sleeps and when they are awake. A person's internal clock controls the regulation of such body rhythms as temperature and hormone levels. The main circadian rhythm that this body clock manages is the sleep-wake cycle. The circadian clock works in a cycle that lasts a little longer than 24 hours. The circadian clock is set mainly by visual light cues darkness cures that are communicated down a path from the eyes to the SCN. This keeps the clock coordinated to the 24-hour day. Circadian rhythms and their sensitivity to time cues may alter as a person ages. Each circadian rhythm sleep disorder entails having a hard time falling asleep, struggling to stay asleep, and waking up frequently during the night, waking up too early with the inability to go back to sleep and experiencing poor quality sleep (Circadian Rhythm Sleep Disorders, 2008). The results of the sleep deprivation assessment (Carpenter & Huffman, 2009) were very accurate. I am definitely sleep deprived. Not only did I find it difficult to trace the star I answered yes to almost all of the questions contained in part 2. I find that I could fall asleep almost anywhere, but especially after eating or when trying to relax. I am usually asleep within minutes of going to bed, but struggle mightily to get up in the morning. On a daily basis I find myself stressed to get through the day without felling tired, irritable and drowsy. According to the Mayo Clinic's Sleep tips: 7 steps to better sleep (2012) there are 7 steps that one can use to achieve better sleep. These include: Sticking to a regular sleep timetable -- going to bed and getting up at the same time every day, even on weekends, holidays and days off strengthens ones sleep-wake sequence and helps encourage better sleep at night. Paying attention to what one eats and drinks -- one should never go to bed either hungry or stuffed as the discomfort might keep them up. Creating a bedtime ritual -- one should do the same things each night in order to tell their body it's time to wind down. Getting relaxed -- one should make a room that's perfect for sleeping. This frequently, means a cool, dim and silent place. Incorporating physical activity in ones daily routine - regular physical activity can endorse better sleep, aiding one to fall asleep sooner and to benefit from deeper sleep. Managing stress - when one has too much that they need to get done and too much to think about their sleep is likely to suffer. In order to help restore peace, one should consider healthy ways to manage stress. Before bed, one should jot down what's on their mind and then set it aside for the next day. If a person attempts to put these things into practice they are likely to achieve better sleep at night and therefore be more functional during the day. References Brain Basics: Understanding Sleep. (2007). Retrieved from http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm Carpenter, S. & Huffman, K. (2009). Visualizing Psychology (2nd ed.), John Wiley & Sons. Circadian Rhythm Sleep Disorders. (2008). Retrieved from http://www.aasment.org/resources/factsheets/crsd.pdf Sleep tips: 7 steps to better sleep. (2012). Retrieved from http://www.mayoclinic.com/health/sleep/HQ01387 Read the full article