Summary
Summary All A Level Biopsychology notes
- Module
- Biopsychology
- Institution
- AQA
Clear, accurate and useful notes.
[Show more]
Seller
Follow
Content preview
BIOLOGICAL RHYTHMS 1Biological rhythms are cyclical changes in the way that biological systems have
evolved because the environment in which organisms live has cyclic changes,
day/night, summer/winter, etc.
Circadian rhythms:
- Cycles that occur every 24 hours.
- Often referred to as “the biological clock”.
- These rhythms optimize an organism’s physiology and behavior to best meet
the varying demands of the day/night cycle.
- The most important of these rhythms are the circadian rhythms.
Example; the sleep/wake cycle
Biological rhythms are cyclical behaviors repeated periodically and controlled by
endogenous pacemakers (internal biological clocks) or exogenous zeitgebers
(external cues like light, seasonal changes, temperature, social cues).
Circadian rhythms are biological cycles lasting 24hours like the sleep/wake cycle,
which is facilitated by time-checks and regular events such as meal times (external
cues).
The main internal biological clock in mammals appears to be located in the
hypothalamus, which is responsible for “motivation” and is named the suprachiasmatic
nucleus (SCN). The SCN has an inbuilt circadian firing pattern as when damaged in
rats the circadian rhythm involving sleeping and feeding patterns has been disrupted
(Zucker et al). The SCN regulates the secretion of melatonin in the pineal gland
(another endogenous pacemaker which produces melatonin which affects sleep) and is
also connected to the retina of the eye through a separate pathway. This highlights the
indirect link between exogenous zeitgebers such as light and how melatonin production
,from the Pineal gland (endogenous pacemakers) works together with the SCN to
maintain a rhythm. Light can also reach the brain via other means as Campbell et al
demonstrated resetting the circadian rhythm through shining light on participants
knee’s. This shows other secondary oscillators exist throughout the body maintaining
circadian rhythms through the use of exogenous zeitgebers.
Core body temperature is another circadian rhythm which sees its lowest point at
4:30am (36 degrees c) and highest at around 6pm (38 degrees c). A slight trough
occurs after lunch and this dip occurs even when people do not eat.
Hormone production also follows a circadian rhythm with cortisol at its lowest around
midnight and peaking at 6am. Cortisol plays a role in making us alert and explains why
if awakened at 4am we struggle to think clearly. Melatonin and growth hormone also
have a circadian rhythm with both peaking at midnight.
Aschof and Weaver placed participants in a bunker without any external cues and found
participants to have circadian rhythms between 24-25 hours though some were as high
as 29hours. This demonstrated the existence of endogenous pacemakers (internal
clocks), which persisted even without exogenous zeitgebers to influence them. This
also highlighted the importance of external cues as these internal clocks were not
accurate without them. Due to the lab setting this may be low ecological as it is not
indicative of real world settings. Also low external validity as this may have then
affected the quality or quantity of sleep participants had. The sample was also small
meaning generalization is more difficult to the wider population. The participants were
also volunteers who were aware of being monitored on sleep patterns, which may have
caused demand characteristics.
Michel Sifre spent 6 months in a cave without external cues and found his circadian
rhythm varied from 25-30 hours again highlighting the existence of an internal
circadian clock. This also highlighted the importance of exogenous zeitgebers in
,regulating internal biological clocks. However this was a single case study involving
one individual and such generalizations may not apply to others due to individual
differences. Age may also have been a factor as results may also be limited to a
similar age group as other studies have shown sleep patterns vary among different age
groups. Other factors such as temperature, air pressure or even the use of
monitoring equipment could affect the quality of results. Artificial light was used and
may have been a confounding variable. Campbell et al and Cziesler et al showed even
this can affect rhythms manipulating circadian rhythms through artificial light.
Therefore such a study may have low external validity to others as well as low internal
validity and not actually measure what it was intending to measure (the absence of
light or external cues) due to this. Such experimental studies are important however
as they allow us to demonstrate causal relationships.
Dufy et al also found a case for individual differences in circadian rhythms. Morning
people preferred to rise early and go to bed early (6am and 10pm) while evening
people preferred going to sleep and waking up late (10am and 1am) showing peoples
circadian rhythms could vary from one another.
Zucker et al damaging the SCN in rats to disrupt circadian rhythms was an animal
study and may not apply to humans due to differences in anatomy. Therefore it may
lack external validity and generalisation in 6 humans. There are also ethical concerns
when it comes to intentionally harming such animals although others may argue the
benefits gained in understanding animal biology may lead to further understanding of
humans.
Such studies are typical of the biological approach to understanding human behaviour.
They propose behaviour can be explained due to biological structures in the brain or
hormonal activity. In truth our behaviour is much more complex and not so
deterministic as such biological explanations propose. “Nurture” is evidently a strong
, factor too with environmental influences and exogenous zeitgebers clearly having a
strong role in overriding internal biological clocks to some degree. On the other hand
Miles et al demonstrated how a blind man who had a circadian rhythm of 24.9 hours
struggled to reduce his internal pace no matter what exogenous zeitgebers were used
highlighting some biological clocks may be more ingrained and not in- fluenced.
The SCN is evidently not the only biological clock as other studies have shown that
there are other oscillators in the body that appear to regulate biological rhythms
through other means (temperature, light penetrating other parts of the body) and
explaining circadian rhythms as simply dictated by the SCN and pineal gland
connection is reductionist as oversimplifies human biology which is far more complex.
Understanding circadian rhythms has real world applications particularly in the field
of Chronotherapeutics. This is the study of how timing affects drug treatments and as
the circadian rhythm affects digestion, heart rate and hormones among other
functions, this can be taken into account when consuming drugs. For instance medicine
that affects certain hormones may have no effect if taken when the target hormone
level is low but more effective if taken when they are high. Aspirin for example is
most effective in treating heart attacks and most effective if taken in the late evening
as most attacks occur in the early hours of the morning.
The sleep- wake cycle; the circadian rhythm not only dictates when we should be
sleeping, but also when we should be awake. Light and darkness are the external signals
that determine when we feel the need to sleep and when we need to wake up. The
circadian rhythm also dips and rises at certain times of the day, so our strongest
sleep drive usually occurs in two dips (between 2-4am and between 1-3pm, the ‘post
lunch dip’). The sleepiness we feel during these circadian dips is less intense if we had
sufficient sleep, and more intense when we’re sleep deprived.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller luciarosnavarro. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £6.42. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
64438 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now