biological rhythms : circadian rhythms Flashcards
biologival rhythms are
periodic biological fluctuations in an organism that corresponds to environmental change
ie core body temp / sleep wake cycle
biological rhythms can be
endogenous or exogenous
exogenous Zeitgebers
external changes in the environment which effect or entrain our biologival rhythms
endogenous
controlled by internal body clocks ie supeachiasmatic gyrus
the three types of biological rhythms are
circadian
infradian
ultradian
circadian rhythms are
a type of biological rhythm which completes one full cycle every 24 hours eg the sleep wake cycle
affected by both exogenous zeitgebers and endogenous pacemakers
the main example of exogenous zeitgebers would be light changes in exposure can
trigger desynchronisation of a pre set sleep wake cycle
siffre 1962
descended into a cave on July 16th 1962 completely devoid of natural light and finished his experiment on September 14th thinking it was august 20th
this demonstrates that
prolonged exposure to a stong exogenous Zeitgeber such as light the sleep wake cycle becomes disrupted and thus a disconnection between psychological time and clock.
siffre 1962
his sleep wake cycle did not conform to a cyclical 24 your clock but was around
24 hours and 30 mins
demonstrating that there was abnormal internal clock , and it was a free running circadian rhythm , not affected by exogenous zeitgebers
Aschoff and wever 1967
55 participants were deprived of natural light whilst spending 4 weeks in an underground bunker the researchers found that
all subjects found free running circadian rhythms with the average periods of wakefulness and sleep ranging from 23.9 to 50.0 hours
36 subjects remained internally synchronised during the whole experiment
therefore siffre and Aschoff and wever demonstrate that although the free running circadian rhythm is more than 24 hours long and as a society
we have specific exogenous zeitgeebrs which entrain the rhythm to conform to a 24 hour cycle
- indvidual différences in circadian rhythms
circadian rhythms may not and do not always have to conform to cyclical 24 hour periods for example dr.espie a professor of sleep medicine at Oxford university delayed
the starting time at monkseaton school to 10am from 8am , and found gcse results went up from 34% to 53%
- the confounding effect of artificial light
as demonstrated by czeisler et al , artificial lightening can create shifts in circadian rhythms up to 6 hours , siffres research was conducted at the same time as
when researchers believed that artificial lightening had no effect on biological rhythms .
the use of artificial light means that over two months siffre could entrained his own circadian rhythm through signalling sleep and wake times by using the light , meaning the conclusions may not be entirely accurate
- detrimental impacts on health in shift workers
karlsson,knutsson and lineal found that shift work was assosictaed with obesity , high triglycerides and low concentrations of HDL cholesterol which the researchers suggest may
demonstrate a link between the desynchronisation of circadian sleep wake cycles in shift workers and the consequent disruptions in the biologival control of metabolism
suggesting there may be practical uses in an improved understanding of there effects of desynchronisation , in turn having economic impact as employers would have to revise polices
- use of case studies and small samples in isolation investigations
although siffre conducted multiple isolation studies his results may not be able to be generalised to the wider population hence
his results lacking ecological validity
siffre noted himself that as he aged his endogenous pacemaker ticked at a slower rate acting as a CV in his investigations .
limits the extent to which the findings represent the experiences of the general population
