Biological rhythms: Circadian rhythms Flashcards
what are biological rhythms
Biological rhythms are distinct patterns of changes in the body activity that conform to cyclical time periods. They are influenced by endogenous pacemakers and exogenous zeitgebers.
how long is a circadian rhythm
Circadian rhythms last for around 24 hours. E.g. sleep/wake cycle and core body temperature.
the sleep/wake cycle
Daylight is an important exogenous zeitgeber on our sleep/wake cycle. The sleep/wake cycle is ales governed by an endogenous pacemaker called the suprachiasmatic nucleus (SCN). The SCN lies above the optic chiasm which provides info from the eye about light. Exogenous zeitgebers (light) can reset the SCN.
Siffre’s cave study
Siffre was in a cave deprived of exposure to natural light and sound, but with access to food and drink. Siffre resurfaced in mid-September 1962 after two months in the cave believing it to be mid-August. His ‘free-running’ biological rhythm settled down to around 25 hours. He continued to fall asleep and wake up on a regular schedule.
Other research relating to circadian rhythms
Similar results to Siffre were recorded by Aschoff and Wever (1976) who had participants spend 4 weeks in a ww2 bunker deprived of natural light. All but one of the participants displayed a circadian rhythm between 24 and 25 hours. This suggests 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 (e.g. typical mealtimes, daylight hours).
evaluation of circadian rhythms (brief)
strength - understanding effects of shift work HOWEVER correlational
strength - chronotherapeutics
weakness - hard to make generalisations
strengths of circadian rhythms
one strength of research into circadian rhythms is that it provides an understanding of the adverse consequences of desynchronisation. For example, night shift workers engaged in shift work experience a period of reduced concentration at around 6am (a circadian trough) meaning mistakes are more likely. 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 hours. This shows research into the sleep/wake cycle can have real world implications on how best to manage worker productivity. HOWEVER, studies into shift work effects tend to use correlational methods meaning it’s difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects. There may be other factors. High divorce rates for example may be due to 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.
research into circadian rhythms has been used to improve medical treatments. Circadian rhythms coordinate a number of the body’s 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, which can reduce risk of a heart attack, is most effective taken at night as heart attacks are more common in the morning, so the timing of taking aspirin is important. This shows that circadian rhythm research can help increase the effectiveness of drug treatments.
weakness of circadian rhythms
Generalisations are difficult to make. The studies of Siffre and, Aschoff and Wever are based on a small number of participants. Sleep/wake cycles may vary widely from person to person. Research by Czeisler et al (1999) found individual differences in sleep/wake cycles varying from 13 to 65 hours. Even Siffre observed that his own sleep/wake cycle had slowed down since he was a young man. This means it is difficult to use the research data to discuss anything more than averages.
