biological rhythms - circadin rhythms Flashcards
biological rhythms
all living organisms are subject to biological rhythms
these exert an important influence on the way in which body systems behave
governed by two things - the body’s internal biological clocks - endogenous pacemakers
external changes in the environment - exogenous zeitgeist’s
some of those rhythms occur many times during the day - ultradian rhythms
others take longer to complete - infradian rhythms
some take much longer - circannual rhythms
circadian rhythms are those that last for around 24 hours
example - sleep/wake cycle and cor body temperature
the sleep/wake cycle
the fact that we feel drowsy when its night and alert during thr fay demonstrates the effects of daylight - important exogenous zeitgeber on our sleep/wake cycle
also is governed by internal (endogenous) pacemaker - a biological clock called the suprachiasmatic nucleus (SCN)
SCN lies just above the optic chasm which provides information from the eye about light
exogenous zeitgebers (light) can reset the SCN
Siffres cave study
siffre is a self styled caveman who has spent several extended periods underground to study the effect on his own biological rhythms
deprived of exposure to natural light and sound but with access to food and water
siffre resurfaced in mid september 1962 after two months in caves of the southern alps and believed it to be mid-august
a decade later he performed a similar things but this time for six months in the texan cave
in each study his free-running biological rhythms settled down to one that was just beyond the usual 24 hours
though he did continue to fall asleep and wake up on a regular schedule
other research
similar results were recorded by Aschoff and Wever 1976 who convinced a group of participants to spend four weeks in a world war 2 bunker deprived of natural light
all but one of the participants whose sleep/wake cycle extended to 29 hours displayed circadian rhythm between 24 and 25 hours
both siffes expertness and the bunker study suggest that the natural sleep wake cycle may be slightly longer than 24 hours but that is entertained by exogenous zeitgebers associated with our 24 hour day such as number of daylight hours
despite this we should not overestimate the influence of exogenous zeitbergers on outer internal biological clock
Folkard et al 1985 studied a group of 12 people who agreed to live in a dark cave for three weeks
retiring to bed when the clock said 11;45pm and rising when it said 7;45 am
over the course of of this study the researchers gradually speed up the clock not known to the participants
so an apparent 24 hour dy eventually only lasted 22 hours
only one partisans was able to comfortably adjust to the new regime
could suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers
strength
shift work
strength of research into circadian rhythms is that is provides an understanding of the adverse consequences that occur when they are disrupted (desynchronisation)
example - night workers engaged in shift work experienced a period of reduced concentration around 6 in the morning (a circadian trough)
meaning mistakes and accidents are more likely (Bolivian et al 1996)
research also pointed to a relationship between shift work and poor health
shift workers are three times more likely to develop heart disease than people who work more typical patterns (knutson 2003)
shows that research into the sleep/wake cycle may have real world economic implications in terms of how best to manage worker productivity
strength
medical treatment
another strength of research into circadian rhytms is that it has been used to improve medical treatments
circadian rhythms co-ordinate a number of thr body’s basic processes such as heart rate, digestion and hormone levels
these rise and fall during the course of. day which had led to the field of chronotheraputics - how medical treatment can be administered in a way that corresponds to a persons biologivsl rhythms
example - aspirin as a treatment for heart attacks is most effective if taken last thing at night
aspirin reduces blood platelet activity and this can reduce the risk of heart attack
heart attack are most likely to occur early in the morning so the timing og taking aspirin matters
shows circadian rhythm research can help increase the effectiveness of drug treatments
limitation
individual differences
generalisations are difficult to make
studies such as aschoff wever and siffre are based on very small samples of participants
seeems that the sleep/wake cycle may vary widely from person to person
research Czeisler et al 1999 foundindivual differences in sleep/wake cycles varying from 13 - 65 hours
Duffy 2001 revealed that some people have natural preference for going to bed early and rising early whereas others prefer the opposite
siffre in a later study observed that his own sleep/wake cycle had slowed down since he was a young man
means that it is difficult to use the research stat to discuss anything more than averages which may be meaningless
