biological rhythms: circadian rhythms

• what are biological rhythms ?

  distinct patterns of changes in body activity that conform to cyclical time periods. biological rhythms are influenced by internal body clocks as well as external changes to the environment
• what are circadian rhythms ?

  biological rhythms which regulate a number of body processes like the sleep wake cycle and changes in body temp
• what was siffre's cave study?

  siffre spent many periods underground studying effects of his own biological rhythms. deprived of exposure to light and sound but with access to food and drinks. resurfaced in mid sept after 2 months believing it to be mid august. he continued to wake up and fall asleep on a regular schedule and his free running biological rhythm settled to one that was beyond usual 24 hours
• strength of research into circadian rhythms?

  p- provides understanding of adverse consequences that occur when they're disrupted.

  e- night workers engaged in shift work experience a period of reduced concentration around 6am meaning mistakes and accidents more likely.

  l- research into sleep wake cycle has real world economic implications.
• CA for strength of research into circadian rhythms?

  p- studies investigating effects of shift work use correlational methods.

  e- so difficult to establish whether desynchronisation of sleep wake cycle is actually a cause of negative effects.

  e- Solomon concluded that high divorce rates in shift workers may be due to the strain of deprived sleep and other influences.

  l- may not be biological factors that create adverse consequences associates with shift work.
• Another strength of research into circadian rhythms

  
  

  P- used to improve medical treatments.

  E- Circadian rhythms co-ordinate a number of the body's basic processes. rise and fall during the course of a day which led to field of chronotherapeutics. E- For 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.

  L- circadian rhythm research help increase effectiveness of drug treatments.
• Limitation of research into circadian rhythms

  P- generalisations are difficult to make.

  E- The studies Aschoff and Wever, and Siffre based on very small samples of participants. sleep/wake cycles vary from person to person.

  E- Research by Czeisler et al found individual differences in sleep/wake cycles from 13 to 65 hours. study by Duffy et al revealed some people have a natural preference for going to bed early and rising early whereas others prefer the opposite

  L- difficult to use research data to discuss anything more than averages, so meaningless.
• What was aschoff and Wever ‘s study?

  they convinced a group of participants to spend four weeks in a WW2 bunker with no light. All but one of the participants (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours. Both Siffres experience and the bunker study suggest that the 'natural' sleep/wake cycle may be slightly longer than 24 hours but it is entrained by exogenous zeitgebers associated with our 24-hour day
• What is infradian rhythm?

  type of biological rhythm with a frequency of less than one cycle in 24 hours, such as menstruation and seasonal affective disorder.
• what is ultradian rhythm?

  type of biological rhythm with a frequency of more than one cycle in 24 hours, such as the stages of sleep
• what is a strength of menstrual synchrony research?

  P- may be explained by natural selection.

  E- Synchronisation of the menstrual cycle thought by some to have evolutionary value. For our distant ancestors it may have been advantageous for women to menstruate together and become pregnant at the same time. In a social group, this would allow babies who had lost their mothers during or after childbirth to have access to breast milk, thereby improving their chances of survival.

  L- This suggests that synchronisation is an adaptive strategy.
• Limitation of synchronisation studies

  P- methodological shortcomings.

  E- many factors may effect change to the menstrual cycle, like stress, changes in diet, exercise. may act as confounding variables, so any supposed pattern of synchronisation is no more than would have been expected to occur by chance. explainsnwhy other studies have failed to replicate the findings.

  L- menstrual synchrony studies are flawed.
• strength of research into ultradian rhythms?

  P- has improved understanding of age-related changes in sleep.

  E- Sleep scientists observed that SWS reduces with age. Growth hormone is mostly produced during SWS therefore this is reduced in older people. According to van Cauter et al. resulting sleep deficit may explain various issues in old age, like reduced alertness. In order to increase SWS, relaxation and medication may be used.

  L- knowledge of ultradian rhythms has practical value.
• Limitation of ultradian rhythms research ?

  P- significant variation between people. E- Tucker et al. found large differences between participants in terms of the duration of each sleep stage, particularly stages 3 and 4. Tucker et al. suggest that these differences are likely to be biologically determined.

  L- difficult to describe 'normal sleep' in any meaningful way.