circadian rhythms Flashcards
what are biological rhythms
biological rhythms are periodic activity governed by internal biological clocks and external changes to the environment
what are circadian rhythms
circadian rhythms are a type of biological rhythm which occur approximately every 24 hours. eg. the sleep-wake cycle or body temperature
‘Circa’ meaning ‘about’ and ‘Dia’ meaning ‘day’
what are endogenous pacemakers
endogenous pacemakers are internal biological clocks in the brain that control biological rhythms, most notably the suprachiasmatic nucleus (the SCN) in the hypothalamus.
what are exogenous zeitgebers
external stimuli/changes in the environment which regulate biological rhythms to the outside world through a process called entrainment eg. the sun
biological process of when darkness falls
- darkness falls
- optic chiasm in eye (retina)
- stimulates the SCN
- stimulates the pineal gland
- produces melatonin
- brain activity falls
- sleep
Michael Siffre’s temporal isolation study
Michael Siffre spent 7 months in dark caves to examine the effects of free running biological rhythms. He had no exogenous zeitgebers present: no sun light or watch. His sleep-wake cycle lengthened to 25 hours, and the time went quickly. He had a regular sleep-wake cycle.
This proves that circadian rhythms persist despite isolation from natural light, which proves the existence of an ‘endogenous clock’
Proves the dominant role of endogenous pacemakers.
how does this research also support the role of exogenous pacemakers
This research shows the importance of external cues as Siffre’s biological clock was not entirely accurate, it varied from day to day. This shows how external cues ENTRAIN our exogenous pacemakers
Aschoff and Wever study
A group of participants spent four weeks in a WWII bunker deprived of natural light. All but one, who’s sleep wake cycle extended to 29 hours, displayed a circadian rhythm between 24 and 25 hours.
Siffre’s study and Aschoff and Wever’s study both suggest the natural sleep-wake cycle is slightly longer than 24 hours, but is entrained by exogenous zeitgebers associated with our 24 hour day. eg. daylight, mealtimes, etc.
Folkard et al. study
Folkard et al. studied a group of 12 participants who lived in a dark cave for 3 weeks. They went to bed at 11:45 pm and woke up at 7:45 am. The researchers gradually sped up the clock (unbeknownst to the participants) so that the 24 hour day was actually 22 hours. None of the participants but one adjusted comfortably to the new regime. This suggests the existence of a strong free-running circadian rhythm not controlled by exogenous zeitgebers.
Morgan study
bred mutant hamsters to have circadian rhythms of 20 hours instead of 24 hours. Their SCN’s were transplanted into normal hamsters, which resulted in them displaying the mutant rhythms.
This suggests the SCN is the basis of the endogenous pacemaker and circadian rhythms.
limitation of Morgan’s study
the physiology between humans and animals are different, so the extent to which we can generalise these findings to humans is limited.
one strength of circadian rhythm research (application to shift work)
Shift work creates a desynchronisation of biological rhythms. Boivin et al. found that shift workers have a lapse in concentration at around 6am so accidents are more likely. Shift work is also linked to poor health, with shift workers more likely to develop heart disease.
Thus, research into the sleep-wake cycle may have economic implications in terms of how to best manage shift work.
counterpoint for research on shift work
The research on shift work is correlational, therefore desynchronisation may not be the cause of observed difficulties. For example, Solomon found that high divorce rates in shift workers was due to missing out on important family events. This suggests that it might not be biological factors that create the consequences of shift work.
strength of circadian rhythm research (real world application to medical treatment)
Circadian rhythms coordinate the body’s basic processes (eg. heart rate, hormone levels) with implications for chronotherapeutics (timing medication to maximise effects on the body). Aspirin reduces heart attacks which are more likely in the morning. Researchers found that taking aspirin is most effective last thing at night.
This shows circadian rhythm research can help increase effectiveness of drug treatments.
one limitation of circadian rhythm research (generalisability)
studies of the sleep-wake cycle often use small groups of participants (Aschoff and Wever) or even single individuals (Siffre).
Participants may not be representative of the wider population and this limits making meaningful generalisations.
Siffre observed that his internal clock slowed down as he grew older.
This suggests that even when the same person is involved there are factors that may prevent general conclusions from being drawn.
