circadian rythms Flashcards
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 (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers).
what are circadian rhythms?
Biological rhythms, subject to a 24-hour cycle, which regulate a number of body processes such as the sleep/wake cycle and changes in core body temperature.
what are biological rhythms governed by?
the body’s internal biological clocks, which are called endogenous pacemakers and external changes in the environment known as exogenous zeitgebers
what is the effect of daylight on out sleep/wake cycle?
The fact that we feel drowsy when it’s night-time and alert during the day demonstrates the effect of daylight - an important exogenous zeitgeber - on our sleep/wake cycle.
what endogenous pacemaker governs the sleep/wake cycle?
a biological ‘clock’ called the suprachiasmatic nucleus (SCN). The SN lies just above the optic chiasm which provides information from the eye about light.
what was Siffre’s 1962 cave study?
he spent several extended periods underground to study the effects on his own biological thythms. Deprived of exposure to natural light and sound, but with access to adequate food and drink, he spent 2 months in the caves, it was sep but he thought it was august
what happened in his studies?
In each case, his ‘free-running’ biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule.
what was Aschoff & Weber 1976’s study?
they 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 a circadian rhythm between 24 and 25 hours.
what do these studies suggest?
the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with our 24-hour day (such as the number of daylight hours, typical mealtimes, etc.).
what was Folklard et al 1985’s study?
they studied a group of 12 people who agreed to live in a dark cave for three weeks, retiring to bed when the clock said 11.45 pm and rising when it said 7.45 am. Over the the study, the researchers gradually speeded up the clock (not known to the participants) so an apparent 24-hour day eventually lasted only 22 hours
what did they find from this?
only one of the participants was able to comfortably adjust to the new regime. This would suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers.
what is the shift work strength?
-it provides an understanding of the adverse consequences that occur when they are disrupted (desynchronisation).
-For example, night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (a circadian trough) meaning mistakes and accidents are more likely (Boivin et al. 1996).
-Research has 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 work patterns (Knutson 2003).
-This shows that research into the sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity.
what is the shift work counterpoint?
-studies investigating the effects of shift work tend to use correlational methods. -meaning it is difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects.
There may be other factors.
-For example, Charlene Solomon (1993) concluded that high divorce rates in shift workers might be due to the strain of deprived sleep and other influences such as missing out on important family events.
-This suggests that it may not be biological factors that create the adverse consequences associated with shift work.
what is the medical treatment strength?
-research has been used to improve medical treatments.
-Circadian rhythms co-ordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels. These rise and fall during the course of a day which has led to the field of chronotherapeutics - how medical treatment can be administered in a way that corresponds to a person’s biological rhythms.
-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. Heart attacks are most likely to occur early in the morning, so the timing of taking aspirin matters. Research has supported this (e.g. Bonten et al. 2015).
-This shows that circadian rhythm research can help increase the effectiveness of drug treatments.
what is the individual differences limitation?
-generalisations are difficult to make.
-Aschoff and Wever, and one of Siffre studies are based on very small samples of participants. It seems that sleep/wake cycles may vary widely from person to person.
-Research by Charles Czeisler et al. (1999) found individual differences in sleep/wake cycles varying from 13 to 65 hours.
-Even Siffre, in a later 1999 study, observed that his own sleep/wake cycle had slowed down since he was a young man.
-This means that it is difficult to use the research data to discuss anything more than averages, which may be meaningless.
