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Biological rhythms
A cyclical variation over some period of time in physiological and psychological
· A cycle that occurs over a 24 hour period. E.g. the · A cycle that occurs in under 24 hrs. E.g. stages during REM and
sleep/wake cycle. SWS/NREM sleep.
· The sleep wake cycle is governed by knowing the time · There are 5 stages of sleep, the first 4 are NREM stages and the
of day. 5 is REM sleep.
· External cues help to guide the cycle. · Stages 1 and 2 sleep are categorised by alpha and theta waves,
· However there is also an internal clock which can run these waves are slower and becoming more regular. Sleep is
without outside cues on a 24-25 hr. basis, but is light and easy to wake, HR and temp drop. In stage 2 there are
normally aided and adjusted by external cues such as bursts of activity called sleep spindle, where the wave
light. frequency increases, and K complexes where the amplitude
· Core body temp also indicates the circadian rhythm. At increases.
its lowest early morning and highest late afternoon and · Stages 3 and 4 are called SWS sleep. Categorised by Delta
with a dip just after lunch. waves, which are very slow and regular. This is the deepest
· Hormones production is also on a circadian rhythm such sleep. This is the recovery stage where HGH is produced and
as cortisol which peaks at 6am and troughs at 12pm. It repair. Very hard to wave during SWS.
is associated with making alert on waking. · Stage 5= REM/ Paridoxical sleep. These are beta waves as with
· Melatonin and HGH both peak around 12pm. awake brain waves. This is associated with dreaming. The brain
and eyes are active, but the body is paralysed.
· A cycle that lasts longer than 24 hrs. E.g. Menstruation cycle.
· Menstruation is driven by fluctuating hormone levels, to
regulate ovulation. The pituitary gland released hormones
FSH and LH to stimulate a follicle in 1 ovary and trigger
Oestrogen release. Once the egg is ripened, the ruptured
follicle secretes progesterone which causes the womb lining
to prepare for pregnancy by increasing its blood supply.
About 2 weeks later if there in no pregnancy, progesterone is
reduced and the womb lining is shed.…read more

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Research into rhythms
Siffre 1975-Cave study Dement and Kleitman 1957- Russel et al 1980- sweat study
-Spent 6 months in a cave to REM/NREM study. · Applied the pheromones of 1
test length of circadian rhythm. - studied 9 pps, 7 male, 2 female, woman to a group of sexually
-No exogenous zeitgebers, intensely studied 5 pps, with the inactive women.
sound or natural light, but had other used for back up info. · The donor's sweat was collected
artificial light, a telephone and -Pps studied in a lab just before from pads under her arms.
food and water. bedtime, were told to eat and drink · Once every 24 hours the pads
- His eating, sleeping, waking normally, but not to consume caffeine were replaced, old pads were
and drinking were all or alcohol, and were then sent to bed dissolved in alcohol to remove
monitored. in a dark, quiet room. bacteria and then rubbed on the
-Found- his natural circadian -EEG amplified and recorded signals upper lip of the women.
rhythm was just over 24 hours of electrodes which were placed on · Repeated daily for 5 months.
but was sometimes 48. the pps face and scalp. 2 or more · Some women were in the control
-Concluded that the internal near the eyes recorded eye group, and received the same
clock must have a 25 hr. cycle movement, the scalp ones monitored treatment without the
depth of sleep. pheromones.
and zeitgebers reset it to 24.
-Pps woken when in REM sleep to · Found- 4 of 5 women had
see if they were dreaming. menstrual cycles that
Folkard et al 1985- Clock study -Found 70-80% reported to be synchronised to within a day of
· 12 pps in temporal isolation for 3 dreaming while in REM- the donors.
weeks- no natural light or natural Empson 1977- male rhythms
demonstrated nature of sleep stages. · Measured the body temp and
time cues, but had artificial light.
· Bed= 11.45pm and wake= 7.45 mood of 21 males over period
am. ranging 49-102 days,
· Clocks increased in speed until Freidman and Fisher 1967 · Found- evidence for a periodic
24 hr day was only 22 hrs. · Observed eating and drinking behaviour in variation of both body and
· Found- only 1 pps couldn't keep psychiatric patients over a 6hr period. subjective ratings of morning
pace with the clock · Found ­ that there was a 90 minute cycle alertness.
· Conclusion= suggests a strong in eating and drinking behaviour. · Cycle length of 20 days.
free running 24 hr rhythm.…read more

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The role of endogenous pacemakers (SCN)
· Endogenous pacemakers= internally managed rhythms or our `body clocks'
· They are vital for survival (evolutionarily important)
· Allows us, as animals, to attune to cycles in nature. E.g. day/night, summer/winter. The clock also has
similar patterns to environmental changes.
· They serve as a `conductor' for complex chemical processes in the body.
· It must be remembered that the running of our biological clock is by a `blended system' of both EPs and
· The two EPs are:
The ticking of the biological clock-
· In the morning, two proteins called CLOCK and CYCLE bind
Suprachiasmatic Nucleus- SCN/Central Oscillator
together to form CLK-CYC.
· Main EP in mammals.
· This joined protein creates two others called PERIOD and
· Tiny cluster of a few thousand neurons based in
TIME, which bind to create PER-TIM.
the hypothalamus, deep in the brain.
· PER-TIM renders the CLK-CYC protein inactive, and so CLK-
· Located jus above the place where the optic
CYC begins to decrease, therefore decreasing the amount of
nerves cross over (optic chiasm).
PER-TIM. This is known as negative feedback.
· SCN primarily receives info about the
· This loop takes 24hrs and forms the biological clock, controlled
environment through the amount of light received
by the central oscillator.
through optic nerves at the back of the eyes.
This happens even when they are closed.
· If the EP clock is running slowly, light adjusts it. De Coursey et al 2000- Brain damaged Chipmunks.
· The SCN is divided into the ventral and dorsal · Lesions (cuts) in the connections between the SCN and other
SCN. Ventral is quickly reset by light. Dorsal is areas of the brain were made in 30 chipmunks.
less effected. (Albus et al 2005) · The chipmunks were then returned to their natural habitat and
observed with two other groups, 1 group of 24 chipmunks who had
Research support- undergone the operation, but had no lesions and 1 group of 20
· Morgan 1995- Mutant hamsters chipmunks who were intact.
-bred mutant hamsters so that they had circadian · Found- after 80 days significantly more SCN-lesioned chipmunks
rhythms of 20 hours instead of 24. had been killed by Weasels as they remained awake at night due
-He removed their SCN's and found that their to their lack of circadian rhythm.
rhythms ceased. · Concl- SCN and circadian rhythms play a vital role in survival..
-he then transplanted their SCNs into normal
hamsters who then developed the mutant rhythms.
· Concl- demonstrates the importance of SCN in
establishing a circadian rhythm.…read more

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The role of endogenous
pacemakers (Pineal gland and
· melatonin)
The Pineal gland contains light-sensitive cells.
· The SCN sends signals to the pineal gland triggering it to release more melatonin at night.
· Melatonin inhibits brain mechanisms that cause wakefulness, therefore causing sleep.
· Light causes the production of melatonin in the pineal gland to be stopped, ergo causing
· Light, the pineal gland and melatonin regulate the sleep-wake cycle (a key circadian rhythm)
· The pineal gland is very important in birds and reptiles and is close to the surface, so easily reset by
Research Support-
· Potocki et al 2000
-Levels of melatonin are inverted (low when there's low light) for those who suffer from Smith-
Magenis syndrome (a developmental learning difficulty) which often leads to difficulty falling
-also found that taking supplements of melatonin at night could help with symptoms.
-Supports the role of melatonin in the sleep-wake cycle as melatonin supplements relieve
sleeplessness in Smith-Magenis syndrome suffers.
- seems to give clear evidence of melatonin's importance as an EP
-Only correlational (no cause and effect)
-Uses abnormal sample (lacks generalisability)
- Biological reductionism.…read more

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The role of exogenous
Exogenous zeitgebers are used to reset the biological clock. This process in known as
entrainment. The opposite of entrainment is `free-running' where the bio clock operates even in
the absence of EZ's.
· There are 3 main EZs: · Until recently it was thought that · In cold-blooded animals the
LIGHT- these were the main EZs in variations in temp affects the
· Light is the dominant EZ in entraining our daily circadian rhythms.
humans and It resets the SCN. rhythms e.g. eating, sleeping. · Cold signally time for reduced
· It resets other oscillators in the · All parts of the body produce their activity and warm signally activity.
body because the CRY protein, own oscillating rhythms, some of · In warm blooded animals
which is part of the protein clock which are not primarily reset by research suggests that daily body
is light sensitive. light. temp changes are governed by
RESEARCH SUPPORT LIGHT- RESEARCH SUPPORT their circadian clock and that
· Campbell and Murphy 1998 these changes entrain other
-Shone a bright concentrated circadian rhythms.
· Davidson 2006 RESEARCH SUPPORT
light on the back of patients
-supports the idea that oscillators TEMPERATURE-
can be reset by social cues. · Buhr et al 2010
-This shifted their circadian
-suggested that the zeitgeber for -put forward the theory that the
rhythms, therefore supporting the
cells in the liver and heart is likely daily changes in temperature of
theory that light can reset the
to be mealtimes (social cue) warm blooded animals are
oscillators within the body.
EVALS AND IDA LIGHT- because the cells are reset by the governed by their own circadian
process of eating. clock and that is how some other
· C & Ms study ignored the affects
of artificial light- Boivin et al 1996 EVALS AND IDA SOCIAL circadian rhythms are entrained.
found that circadian rhythms can CUES- EVALS AND IDA TEMPERATURE-
be entrained by ordinary, dim, · Luce and Segal 1966- found that · Generalizability issues- a lot of
artificial lighting, although bright people who live in the artic circle evidence for plant and animals
light was more effective. sleep for 7 hrs despite a sun that circadian's being reset by temp,
· Evolutionary approach support, if never sets in the summer. but for humans, temp is not the
the bio clock falls out of sync then · The theory is reductionist as in main EZ.
animals are at risk of predators certain circumstances other · E.g. some animals hibernate in the
and so light resets the clock. external cues take over e.g. cold, humans do not, suggests a
social customs dictate time to get large difference in the role of temp
up and sleep. as an EZ.…read more

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