Biological Rhythms: circadian rhythms Flashcards
circadian rhythms definition
biological rhythms, subject to a 24 hour cycle, which regulates a number of body processes such as sleep/wake cycle and changes in core body temperature
biological rhythms definition
distinct patterns of changes in body activity that conforms to cyclical time periods. biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers)
who is subject to biological rhythms
all living organisms such as pants, animals and people
what do biological rhythms exert
an important influence on the way in which body systems behave
what are all biological rhythms determined by
-endogenous pacemakers
-exogenous zeitgebers
what are endogenous pacemakers
the body’s internal biological clocks
what are exogenous zeitgebers
external changes in the environment
are endogenous pacemakers internal or external
internal
are exogenous zeitgebers internal or external
external
what rhythms occur during the day
ultradian rhythms
what rhythms take longer than a day to complete
infradian rhythms
what rhythms take much longer than a day to complete
circannual rhythms
how long do circadian rhythms last
about 24 hours
2 examples of circannual rhythms
-sleep/wake cycle
-core body temperature
what does feeling drowsy at night and alert in the day demonstrate
the effect of daylight which is an exogenous zeitgeber on our sleep/wake cycle
what is the sleep wake cycle also governed by in addition to exogenous zeitgebers
an internal endogenous pacemaker (biological clock) called the suprachiasmatic nucleus (SCN)
what is the suprachiasmatic nucleus (SCN)
an internal endogenous pacemaker (biological clock) in the sleep/wake cycle
where is the suprachiasmatic nucleus (SCN)
lies just above the optic chiasm which provides information form the eye about light. exogenous zeitgebers (light) can reset the SCN
Siffre research
spent several extended periods underground in a cave to study the effects of his own biological rhythms, as had no exposure to natural light
Siffre 1962 research
spent 2 months in caves in the southern alps, with no natural light. he left the caves in mid September and believed it to be mid august. his free running biological rhythm settled down to about 25 hours and continued to fall asleep and wake on a regular cycle
Siffre 1972 study
stayed in a cave again but this time for 6 months and in a Texan cave, with no natural light. again, his free running biological rhythm settled down to about 25 hours and continued to fall asleep and wake on a regular cycle
when did Aschoff and Wever do research
1976
Aschoff and Wever procedure
group of participants stayed in world war 2 bunker for 4 weeks, with no natural light
Aschoff and Wever findings
all but one participant displayed a circadian rhythm of between 24 and 25 hours. the one participants was 29 hours. both this and Siffre study suggest that the natural sleep/wake cycle may be longer than 24 hours but it is entrained by exogenous zeitgebers associated with our 24 hour day
who did research saying we should not overestimate importance of exogenous zeitgebers on our internal biological clock
Folkard et al (1985)
Folklard et al sample
12
Folkard et al procedure
studied a group of 12 who agreed to live in a cave with no natural light for 3 weeks. they went to bed when the clock said 11:45 and woke when the clock said 7:45. however, over the study the clock was sped so what seemed like a 24 hour day was only 22 hours
Folkard et al findings
-only one participant was able to comfortably adjust to the 22 hour day
-this suggests that the existence of a string free-running circadian rhythm cannot be easily overridden by exogenous zeitgebers
limitation of Circadian rhythms- shift work
-research into circadian rhythms provides and understanding of the adverse consequences that occur when they are disrupted (desynchronisation)
-night workers engaged in shift work experience a period of reduced concentration at around 6 am called a circadian trough, this means mistakes and accidents are more likely to happen (Bovin et al 1996). Research also pointed to a relationship between shift work and poor health as shift workers are more than 3x likely to develop heart disease than those with a more typical work pattern (Knutsson 2003) –> shows that research into sleep/wake cycle can have a real-world economic implication in terms of how best to manage worker productivity
limitation of circadian rhythms- counterpoint to shift work
-studies investigating effects of shift work tend to use correlational methods. can be difficult to establish if desynchronisation of the sleep/wake cycle can actually cause negative effects as there may be other factors. Soloman 1993 concluded that high divorce rates in shift workers may be due to strain of sleep deprives or other influences such as missing family events –> suggests may not be biological factors creating the adverse consequences associated with shift work
strength of circadian rhythms- medical treatment
-used to improve medical treatments
-circadian rhythms co-ordinate a number of the bodys basic processes such as heart rate, digestion and hormone levels. these rise and fall during the day which has led to the field of chronotherapeutic (how medical treatment can be administered in a way that corresponds to a person’s biological rhythms) for example, how aspirin as a treatment for heart attacks is most effective when taken last thing at night. aspirin reduces blood platelet activity and can reduce risk of a heart attack. as heart attacks are most likely to occur in the morning, the time of taking aspirin matters. Bonten et al 2015 research has supported this –> shows that circadian rhythm research can help increase effectiveness of drug treatments
limitation of circadian rhythms - individual differences
-generalisations can be difficult to make
-studies such as ASchoff and Wever, Siffre are based on very small samples of participants. it seems sleep and wake cycles vary widely form person to person. Czeisler et al 1999 found individual difference in sleep/wake cycles varying from 13 to 65 hours. in addition Duffy et al 2001 revealed that some people have natural preferences for going to bed early and rising early (larks) whilst others going to bed late and rising late (owls). Even Siffre, later in 1999 study observed his own sleep/wake cycle had slowed down since he was young –> means it is difficult to use research data to discuss anything more than averages, which may be meaningless
evaluation of circadian rhythms - shifting the school day
-number of researchers such as Wolfson and Carskadon 1998 recommend that the school day start a couple of hours later to fit in with the typical teenage chronotype (sleep pattern). hormonal shifts in the teenage body mean that getting to sleep becomes more difficult and therefore adolescent students tend to be rather sleepy at the start of the school day. research has shown benefits for academic and behavioural performance when lessons start in the day, including reduced dependence on caffeine
-however, shifting the start of the day is disruptive for parents and teachers, and limits the number of extracurricular activates after school, also critics of the proposal suggest that a later school day would not actually reduce sleep deprivation, it would simply mean that teenagers stay up later and would still be exhausted
