Biological Rhythms and Sleep

Ao1 and Ao2 notes on Biological Rhythms and Sleep, can be used to plan essays etc. 

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Ao1 ­ Sleep Wake Cycle
Circadian = 24 hour cycle
External cues (sunlight, knowing time) guide circadian rhythm.
Internal endo clock is free running (works w/o external cues), sets cycle of 24-25hrs, ext cues just
help adjust it
Research ­ circ rhythm persists without ext cues (light), sowing existence of internal endo clock
Ao2 ­
Dim artificial light can affect circ rhythm. ­ CZEISLER ET AL altered PPs circ rhythms to 22 hrs and up to
28 hrs using only artificial dim light.
SIFFRE ­ Lived underground w/o ext cues ­ based solely on his endo clock (SUPPORTS ITS PRESENCE)
ASCHOFF + WEAVER ­ PPs put in bunker w/o external cues, found most followed 24/25 hr cycles.
Some reached 28. Shows cycle does work without ext cues.
FOLKARD ­ Changed clock to make it appear day less than 24 hrs. Initially cycle quickened, then
returned to 24 hrs. Conclusion ­ ext cues cannot entirely overrule endo clock.
Ao1 ­ Core body temperature
Body temp lowest at 4.30am and highest at 6.00pm
Post lunch dip also occurs in individuals who don't eat lunch as a bi-daily rhythm (ultradian)
Ao2 ­
FOLKARD ­ Link between core body temp + cog ability. 12/13 y/os had stories read to them at 9am
or 3pm. PM group better recall, comprehension + retained 8% more useful material.
GUPTA ­ better performance on IQ tests at 7pm compared to 9am/12pm
Ao1 ­ Hormones
Cortisol highest at 6am, lowest at midnight. Produced when individual stressed, but also makes us
alert when we wake. Explains why we can't think properly if woken in middle of night
Melatonin (induces sleepiness) + growth hormone have circadian rhythms, peaking at around
Ao2 ­
IDA: Biological + Determinist ­ Misleading. We can sleep later + wake at same time. (Blind man, light
did not reset rhythm). Ignores other reasoning.
IDA: Real World Application ­ Chronotherapeutics (study of effect of time meds taken), meds that act
on certain hormones may have less effect if target hormone levels are low.

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Ao1 ­ Infradian Rhythms (more than 24 hours, less than year)
EXAMPLE ­ FEMALE MENSTRUAL CYCLE (regulates ovulation)
Pituitary gland releases FSH + LH ­ stimulate a follicle in ovary to ripen an egg, triggers release of
oestrogen. --> Once egg ripened, ruptured follicle releases progesterone, causes womb lining to
prep for pregnancy.…read more

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BRAC important - ensures bio process work in unison.…read more

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Ao1 ­ Shift Work and Shift Lag
Nightworkers experience trough of decreased alertness during shifts between midnight and 4am
(cortisol levels and body temp lowest) BOIVIN ET AL
Sleep deprivation experience as finish work during day. Daytime sleep difficult due to other factors
(noise). Daytime sleep 1-2 hours shorter than nocturnal sleep. Deprivation makes it harder to work at
night, especially during trough.
Link between shift work + organ disease.…read more

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Social customs (eating and sleeping at correct times) help too
Individual differences exist in coping with disruption ­ some not as badly affected as others
Ao1 ­ Babies and Children
Babies sleep for approx 16 hrs a day, non-continuously, wake up every hour or so as their cycles
much shorter than adults
Infants have immature versions of SWS + REM ­ quiet and active sleep. At birth most is active.…read more

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Childhood parasomnias rare but other disorders (insomnia + apnoea) more common
Old age ­ sleep time remains same but more difficulty so wake more during night, naps during day to
satisfy needs
Time in REM decreases to about 20% and SWS reduces to 5%, with other non-REM sleep increasing
Experience phase advance ­ sleepier earlier in evening, wake up very early
Ao2 ­
KRIPKE ET AL ­ increased mortality rate associated w/too much sleep.…read more

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Ao1 ­ SWS
SWS in stages 3+4 of non-REM sleep
Growth Hormone (GH) secreted during SWS.…read more

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Ao1 ­ Energy Conservation (WEBB)
Sleep provides a period of inactivity to conserve energy, which is essential for animals with high
metabolic rates (smaller animals, warm blooded)
Ao1 ­ Foraging
Herbivores spend less time sleeping, carnivores spend longer as their food full of protein + nutrients.
Grass is not rich in nutrients so herbivores sleep less to ensure they can eat pretty much continuously
to keep nutrient levels up.…read more

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Ao1 ­ Short Term Insomnia
May be due to immediate worries (e.g. exams/death in the family, noises at night or jet lag)
Ao1 ­ Long term Insomnia
Primary insomnia ­ not associated with any medical condition (So due to bad sleep habits)
The individual has come to expect difficulty sleeping, leads to anxiety, continues to cause insomnia
Secondary insomnia ­ a symptom or condition of a medical disorder such as depression/heart
disease.…read more

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Ao1 ­ Narcolepsy
Early approach suggested that sudden attacks of sleepiness disguise sexual fantasies
REM HYPOTHESIS - 1960s explanation was that it was due to malfunctions in the regulation of REM, as
they have abnormal REM sleep, similar to loss of muscle tone which narcoleptics suffer
HLA HYPOTHESIS - 1980s explanation was narcolepsy was due to a mutation of the immune system.…read more


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