Circadian rhythms
Summary
TLDRThis lesson in biopsychology delves into the intricacies of biological rhythms, distinguishing between Circadian, infradian, and ultradian rhythms. It explores the interplay of endogenous and exogenous factors in regulating the sleep-wake cycle, with a focus on the role of the suprachiasmatic nucleus and melatonin. The lecture examines the implications of these rhythms on health and behavior, including the effects of desynchronization in shift workers and the use of light therapy for seasonal affective disorder. It also highlights the individual variability in circadian rhythms and the methodological challenges in studying them.
Takeaways
- 🕒 Biological rhythms are periodic cycles that occur at regular frequencies, with Cadian rhythms happening once every 24 hours, infradian less than once, and ultradian more than once.
- 🌓 Endogenous refers to internal body clocks, while exogenous refers to external factors that influence our rhythms, such as light, social cues, and meal times.
- 🔄 Entrainment is the synchronization of external and internal factors, highlighting the interaction between nature and nurture in regulating biological rhythms.
- 🌡️ Core body temperature is an example of a Cadian rhythm, with the lowest at 4 a.m. and the highest at 6 p.m., affecting alertness and cognitive ability.
- 💉 Hormones like cortisol follow a Cadian rhythm, peaking in the morning to help with stress response and alertness, and lowest in the middle of the night.
- 🌙 Melatonin and growth hormone peak at midnight, aiding in body restoration and growth, demonstrating the importance of sleep for overall health.
- 🛌 The sleep-wake cycle is a focus of the lesson, questioning whether our natural cycle is 24 hours or influenced by societal norms and external cues.
- 🧠 The superchiasmatic nucleus (SCN) in the hypothalamus is crucial for the sleep-wake cycle, receiving light information and signaling the pineal gland to produce melatonin.
- 🐹 Studies on animals, such as transplanting the SCN in hamsters and removing it in chipmunks, show the evolutionary importance and internal regulation of Cadian rhythms.
- 🕳️ The 'caveman' study, where an individual lived in isolation without external cues, revealed a natural tendency towards a slightly longer than 24-hour cycle.
- 💡 Light is a significant exogenous factor, affecting the sleep-wake cycle even when not perceived through the eyes, with implications for phototherapy and treating conditions like Seasonal Affective Disorder.
Q & A
What are the three main types of biological rhythms mentioned in the script?
-The three main types of biological rhythms are Circadian, infradian, and ultradian rhythms. Circadian rhythms occur once every 24 hours, infradian rhythms occur less than once every 24 hours, and ultradian rhythms occur more than once every 24 hours.
What does the term 'endogenous' refer to in the context of biological rhythms?
-Endogenous refers to the internal body clock, which is the internal mechanism within an organism that influences its biological rhythms.
What is the role of the exogenous factors in the sleep-wake cycle?
-Exogenous factors are external to the body and can influence the sleep-wake cycle. These factors include the time of day, the presence or absence of light, social cues, and meal times.
What is the concept of entrainment in relation to biological rhythms?
-Entrainment refers to the synchronization of external and internal factors. It is the process by which an organism's internal clock becomes aligned with external cues, such as light and dark cycles.
Can you provide an example of a Circadian rhythm other than the sleep-wake cycle?
-An example of a Circadian rhythm is the core body temperature, which has its lowest point around 4:00 a.m. and its highest around 6:00 p.m.
What is the significance of the hormone cortisol in relation to the sleep-wake cycle?
-Cortisol is a hormone that helps in the stress response and alertness. It is lowest in the middle of the night and starts peaking in the morning, preparing the body to deal with the day's demands.
What is the role of the superchiasmatic nucleus (SCN) in the regulation of the sleep-wake cycle?
-The superchiasmatic nucleus (SCN) in the hypothalamus is responsible for receiving light information from the eyes and sending signals to the pineal gland to produce melatonin, which induces sleepiness in the absence of light.
What did the study involving the transplantation of the SCN in hamsters reveal about the role of the SCN in Circadian rhythms?
-The study showed that the SCN is the main initiator of the Circadian rhythm, as the transplanted SCN from hamsters with a 20-hour sleep cycle into normal hamsters resulted in the 20-hour cycle being adopted by the recipients, demonstrating the SCN's influence over the rhythm regardless of external factors.
What was the outcome of the study involving the removal of the SCN in chipmunks?
-The removal of the SCN in chipmunks resulted in a complete disruption of their Circadian rhythm, leading to irregular sleep patterns and an increased vulnerability to predators, highlighting the evolutionary importance of maintaining natural biological rhythms.
What are some practical applications of understanding the effects of endogenous and exogenous factors on the sleep-wake cycle?
-Practical applications include using light therapy for treating Seasonal Affective Disorder, synchronizing medication schedules with the body's rhythm for better pharmacokinetics, and using melatonin supplements to help blind patients establish a 24-hour sleep-wake cycle.
What are some methodological issues or considerations when evaluating studies on biological rhythms?
-Methodological issues include the individual differences in Circadian rhythms, the lack of population validity due to unique cases like the cave study, and the fact that conclusions drawn may not be reliable over time or across individuals due to factors like age and personal preferences.
Outlines
🌓 Understanding Biological Rhythms and Sleep-Wake Cycle
This paragraph introduces the concept of biological rhythms, focusing on the differences between Cadian, infradian, and ultradian rhythms. It explains that Cadian rhythms occur about every 24 hours, infradian rhythms less frequently, and ultradian rhythms more frequently within a 24-hour period. The paragraph also discusses the impact of endogenous pacemakers, such as the body's internal clock, and exogenous factors like light and social cues on the sleep-wake cycle. The concept of entrainment, which is the synchronization of external and internal factors, is introduced as a key to understanding the regulation of these rhythms. Examples of Cadian rhythms include the body's core temperature and hormone levels like cortisol, which fluctuate over a 24-hour period, affecting cognitive ability and stress response.
🧬 Internal and External Factors in Sleep-Wake Cycle Regulation
This paragraph delves into the internal and external factors that regulate the sleep-wake cycle, emphasizing the role of the hypothalamus and the superchiasmatic nucleus (SCN) in receiving light information and influencing the production of melatonin, a hormone that induces sleepiness. It highlights studies involving animals with genetic mutations affecting their sleep cycles and the transplantation of the SCN, demonstrating the SCN's role in maintaining Cadian rhythms. The paragraph also discusses the consequences of removing the SCN in chipmunks, leading to disrupted rhythms and highlighting the evolutionary importance of maintaining natural biological rhythms. The 'caveman' experiment is mentioned, showing that even without external cues, the body tends to adapt to a rhythm, suggesting an innate cycle that may be slightly longer than 24 hours.
💡 The Impact of Light and Other External Factors on Biological Rhythms
This paragraph explores the impact of light as a primary exogenous factor on the sleep-wake cycle, noting that light exposure can affect the cycle even without passing through the eyes, as demonstrated by studies applying light at the back of the knees. It also discusses experiments involving the manipulation of clocks to alter the cycle, suggesting that internal factors tend to override external ones. The paragraph emphasizes the significance of light in phototherapy and its potential application for blind individuals to adapt to a rhythmic cycle. It also touches on the limited evidence for other external factors significantly changing biological rhythms, indicating that the body has a natural tendency to maintain a rhythm.
🛌 Applications and Methodological Issues in Biological Rhythm Research
The final paragraph discusses the practical applications and implications of the research on biological rhythms, including the treatment of insomnia with melatonin supplements for blind patients and light therapy for seasonal affective disorder. It also addresses the methodological issues in the studies, such as the individual differences in Cadian rhythms and the lack of universality in the findings due to factors like age and unique cases like the 'caveman' study. The paragraph concludes by cautioning against drawing universal and reliable conclusions over time and across individuals, given the variability in cycle lengths and the influence of individual differences.
Mindmap
Keywords
💡Biological Rhythms
💡Circadian Rhythms
💡Infradian Rhythms
💡Ultradian Rhythms
💡Endogenous Pacemaker
💡Exogenous Factors
💡Entrainment
💡Cortisol
💡Melatonin
💡Superchiasmatic Nucleus (SCN)
💡Desynchronization
Highlights
Biological rhythms are periodic cycles with different types: Circadian, infradian, and ultradian.
Circadian rhythms occur once every 24 hours, while infradian and ultradian rhythms have different frequencies.
Endogenous pacemakers are internal body clocks, and exogenous factors are external influences on these rhythms.
Entrainment is the synchronization of external and internal factors affecting biological rhythms.
Circadian rhythms, such as core body temperature and hormone levels, have a significant impact on cognitive ability and stress response.
The sleep-wake cycle is a focus of Circadian rhythm studies, questioning whether it is naturally 24 hours or influenced by societal norms.
The superchiasmatic nucleus (SCN) in the hypothalamus plays a crucial role in the sleep-wake cycle and is influenced by light.
Transplantation studies with hamsters show that the SCN is a primary initiator of Circadian rhythms, overriding external factors.
Desynchronization of internal and external factors can lead to disrupted biological rhythms and has real-world consequences.
Light exposure, even without passing through the eyes, can impact the sleep-wake cycle, which has implications for phototherapy.
Experiments with clock manipulation show that internal factors tend to override external factors in maintaining rhythm.
Desynchronization can lead to health issues such as reduced concentration and increased risk of heart disease among shift workers.
Melatonin supplements can help blind patients establish a 24-hour cycle, compensating for the lack of light perception.
Light therapy is beneficial for Seasonal Affective Disorder patients, showing the importance of light exposure across the body.
Pharmacokinetics can be optimized by synchronizing drug administration with the body's natural rhythms.
Individual differences in Circadian rhythms, such as age and personal tendencies, affect the generalizability of rhythm studies.
The study of biological rhythms and their regulation has practical applications in treating insomnia, optimizing medication effectiveness, and managing Seasonal Affective Disorder.
Methodological issues in rhythm studies include the validity of case studies, individual differences, and the impact of age on rhythm length.
Transcripts
so this is a lesson on biopsychology
biological rhythms for biological
rhythms you need to know the difference
between Cadian infradian and ultradian
rhythms you also know have to know about
the effect of endogenous pacemakers and
exogenous cabers on the sleep wake cyle
so we're going to look at those key
words to begin
with so biological rhythms are periodic
Cycles it means that they happen at a
regular frequency Cadian rhythms happen
once every 24 hours Circa means about
every 24 hours Al tradan means more than
once in 24 hours and infradian means
less than once every 24 hours we'll look
at examples of ultradian and infradian
rhythms in the next lesson endogenous
means inside it's the internal body
clock whereas exogenous means outside so
factors outside are body clock that
might influence our rhythms it could be
uh the time of the day the presence or
absence of light um social cues meal
times all these are factors that might
influence and lastly entrainment is not
a named key word but it's concept that
means basically the
synchronization of external and internal
factors as usual when we look at these
nature nurture questions nature internal
factors Nur external factors it always
ends up being an inter interaction
between the two and that's what
entrainment basically
means so although the focus is on the
sleep wake cycle Cadian rhythms are
mentioned so they might ask you to give
more than one example of Cadian rhythms
so we're briefly going to look at two
more examples of Cadian rhythms one
example is core body temperature the
lowest body temperature happens at 400
a.m. the highest at 6:00 p.m. and then
we have a dip after lunch if you notice
that you're a bit less efficient less
alert after lunch that might be because
of a drop in body temperature it's
linked to co cognitive ability so it
makes sense that in the middle of the
night we have our lowest cognitive
ability because we don't need to use
it a second example of Cadian rhythm is
hormones cortisol helps in stress
response and alertness and it's it's its
lowest again in the middle of the night
and then it starts peaking in the
morning when we start having to deal
with the stress of just starting a new
day or the kind of Demands of the new
day melatonin and the growth hormone
peak at midnight because actually
they're helping our body restore grow de
and kind of fix any issues that have
happened during the day so these work in
a cyclical pattern over 24 hours as
[Music]
well so the sleep wake cycle is the
Circadian rhythm that we're going to be
focusing on that is named on the
syllabus and the kind of questions that
you might be asked to think about is
whether our natural sleep wake cycle is
actually 24 hours or is that to do with
society that has kind of arbitrarily
decided that a day lasts 24 hours how
would our body work if it was on kind of
free flow without any social cues what
conditions could make you wake up
earlier or later what might make you
sleep longer or
shorter and therefore the focus of this
lesson will be what regulates the sleep
wake cycle and to what extent is it
endogenous pacemakers internal factors
that regulate the sleep wake cycle is it
more to do with exogenous zabas the
external factors as usual the conclusion
is never one way or another but it's
combination of the two but the studies
that we'll look at focus on trying to
understand and answer this question by
looking at what would happen if we
remove or external factors what would
happen if we remove internal factors and
to what extent that influences the sleep
wake cycle and that would be how you
would develop your answer just as a
quick guideline from experience from
when this has come up as an essay
question you need to think about what
would you use as ao1 and AO3 now
typically ao1 will be discussing as you
can see here the extent to which we know
about influences of endogenous factors
and to what extent we know about the
influence of exogenous factors so there
are studies that we're going to look at
uh Cave studies that are people that
isolate themselves from external factors
so obviously this is looking at to what
extent the internal factors Run free if
you remove all external factors and then
there's studies on surgeries that have
been used to uh remove parts of the
brain that seems to be responsible for
Cadian rhythms and Transplant them in
other animals to see whether those
Cadian rhythms change therefore for
again proving that internal factors
override external factors on the other
hand in uh the effects of external
factors there are experiments using
light on um participants to see to what
extent exposure to light can impact on
the sleep wake cycle and also uh
experiments where the clocks have been
changed sped up to see whether that has
an impact on the sleep wake cycle so
your ao1 is looking at the effect of
endogenous and exogenous Pacemakers in
which case your evaluation will be more
on the line of real world applications
real world examples practical
applications uh in uh for example
treating insomnia pharmacokinetics that
will come back to uh and also evaluation
so methodological evaluation of studies
especially the fact that there are
individual differences in the Cadian
rhythms of of people and therefore any
study can't necessarily be generalized
to the entire
population so for A1 we're going to look
at these key studies on endogenous and
exogenous pacemakers endogenous
pacemakers first of all you would look
at the biology underlying the sleep wake
cycle there's a part in the hypothalamus
called the super chiasmatic nucleus that
meets at the crossover of the two optic
nerves and it receives from the eyes
information about whether it's light or
not now once that happens the supermatic
nucleus that you can called SC you don't
have to write the entire word it sends
information to the pineal gland that
then if there is no light then it will
start producing melatonin and melatonin
induces sleepiness so the conclusion is
that the natural currence of the sleep
wake cycle is determined by hormonal
factors however already we have to
acknowledge that that hor hormone or
release is triggered by the presence or
absence of light that would be an
exogenous sight
Gaber as I mentioned we've got studies
on animals where the scn was
transplanted from one hamster to the
other so this Morgan study was found
that there was some hamsters that had a
genetic mutation whereby they had a 20
hour sleep cycle rather than 24 hours so
what they did is they took the scn the
supermatic nucleus of the mutant
hamsters and transplanted it in normal
wild type hamsters and what they found
is that in fact the mutant uh period the
20-hour cycle uh was transplanted also
into the wild type h hamsters showing
that the scn does seem to be the
main initiator of the Cadian Rhythm
regardless of external factors because
the transplant of that part of the brain
did result in a change in Cadian Rhythm
we've also got uh the deos chipm study
and this was the removal of supermatic
nuclei in Chipmunks so that meant that
uh they lost their internal Pacemaker
and what that resulted in you can uh
guess was that their Cadian Rhythm
became completely disrupted they were up
up in the night sleeping in the day and
this shows how evolutionary important it
is to have natural biological rhythms
not only dictated from the outside
because actually sadly a lot of these um
Chipmunks died because of predators
catching them because they were out and
about at inappropriate times so there is
an evolutionary basis of the need for
Cadian Rhythm and that can kind of
justify why internal natural factors are
more important than external
factors s
is a famous um caveman he named himself
the caveman because he spent a long
amount of time all by himself 6 months
as you can see in a cave with no natural
light no clocks no television no radio
basically he had no clue as to what day
it was whether it was day or night and
whether it was time to sleep or not so
he decided himself what to do and when
on the basis of what his body was
telling him again an example of how
isolated external factors can it help us
explain whether internal factors
override everything there are
contrasting interpretations here of the
findings because what we found is that
he did adapt to a slightly longer Cadian
rhythm of 25 hours uh because when he
came out he thought it was a month
earlier than it was because his days
were kind of prolonged in his head
however it does show that he still got
into a kind of a rhythm and a cycle so
it can be interpreted in two ways one
way is our natural cycle is not 24 hours
so the fact that it's 24 hours is
because of external cues Demand on the
other hand that we do have a tendency to
work at a certain
Rhythm um now we're moving on to
external factors so that light is the
main ex exogenous zit Gaber and the
effects of light in this case was
studied by looking at to what extent
light has an effect on us even if it
doesn't pass through the eyes this is
significant because if it doesn't come
through Through The Eyes it's not
necessarily communicated to the scn and
what was found here is that light
applied at the back of the knees of
individuals still impacted on their
sleep wake cycle by about 1 to three
hours shifting it so waking them up
basically meaning that exposure to light
happens regardless of whether it happens
Through The Eyes this is very
significant in terms of phototherapy in
terms of how blind people can adapt uh
to a kind of cycle rythm even if they
can't perceive light through their
eyes so it shows the importance of
light this was the study I mentioned
before they another one on exogenous
light gers this time it's not light but
it's the clocks they had 12 people live
in isolation again so no cues at all no
idea what time it was except for the
clocks that were in the in the rooms and
they tried to change the the the timing
of the clocks so they would go fast and
they would run on a 22h hour cycle
rather than 24hour and actually although
participants initially uh seemed to
match the clocks eventually as it got
quicker they didn't manage to keep up
suggesting again that internal factors
did seem to override external factors so
besides light there's not strong
evidence that external factors can
actually significantly change our
biological Rhythm and that our body body
does have a tendency to want to
maintain uh a
rhythm so now we're going to move on to
the A3 we're going to look at
applications implications so the
consequences of the reearch and actual
issues with research that you can um
comment on in your AO3 if you present
your research in ao1 okay so first
implications are um desynchronization so
there is real world evidence that when
the external factors and the internal
factors are desynchronized like in the
Chipmunks where they they remove the the
supermatic nucleus and most of them a
lot of them died we have real world
evidence in the human world as well
meaning you can't say animal studies
don't generalize because here we have
the same findings shift workers
experiened reduced concentration at 6:00
a.m. and this is real world because cob
and the free mile island that were both
nuclear disasters happened in the middle
of the night EXP explaining that
probably because people are not supposed
to be awake at night their cognitive
ability is much decreased and it was
because of human era that these
disasters happened we've also got
evidence that shift workers are three
times more likely to develop heart
disease probably because they have to
put extra strain on their body to remain
awake when they're supposed to be
sleeping so this shows us definitely
that the interaction between external
and internal factors is that entrainment
where they matched is the optimal
condition for
survival we've also got uh practical
applications as I mention for insomnia
in blind patients it was found that uh
giving melatonin supplements to these
patients actually helped them to get
into a 24-hour cycle so because the the
light wasn't perceived by the supermatic
nucleus by the SC and therefore
melatonin might not have been produced
taking me melatonin supplement
actually compensated for for that
absence so that shows that still even
though light has an effect uh reducing
uh insomnia is linked to taking
supplements that reproduce that scn
pineal gland and melin
cycle we've also got implications for
light therapy and that's especially for
Seasonal effective disorder patients
that experience depression in in Darker
nights this just shows that we can shine
light on on individuals not only through
their eyes but across their whole whole
body and that should decrease the
symptoms of Seasonal effective
disorder um pharmacokinetics is another
example of practical application and
that's when uh we synchronize the body
Rhythm whe with the time that the drugs
are taken we optimize their
effectiveness because if the drug is
taken regularly then then it becomes
part of the biological Rhythm meaning
that it might will respond and kind of
syn up with the body much more
effectively so our knowledge of Cadian
rhythms and the effect of endogenous and
exogenous pacemakers doesn't only exist
in theory but actually has an impact on
the well-being of people with insomnia
people taking medication and people with
Seasonal effective
disorder lastly as I mentioned we're
going to talk about methodological
issues the first one is that for example
cph was a case study so we could argue
that it's a unique case and it lacks
population validity we do however have a
replication uh in the same conditions
there's these a series of studies by
ashro and Weaver in uh these World War
Two Bonkers in Germany where they had
lots of volunteers uh going into these
Bonkers again with no external cues and
they found quite similar results
everybody adapted to slightly longer
side than the 24 hour cycle so agreeing
with those conclusions that it is an
interaction between internal and
external factors that result in that
24-hour cycle however there were some
that had Cycles as long as 28 hours
again highlighting the matter of
individual differences and the lack of
population validity regardless of the
size of the sample because we don't have
consistent
outcomes in terms of individual
differences you can mention the L Al
test dafal developed the questionnaire
you can take it you can find it online
that basically shows that some people
morning people some people are evening
people so not everybody's rhythm is
exactly synced with the time of the day
and also the length of the cycle can
vary from person to person another
factor that CH changes our cycle is age
for example the the amount of sleep that
we get H redu significantly as we grow
older and also CRA himself repeated his
study um about 25 years later when he
was much older and he found that his
clock was also much slower than he was
younger so we can't draw conclusions
that are Universal and even if they were
Universal they're not uh reliable over
time and across individuals so we need
to draw conclusions with some caution
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