Biological rhythms: Circadian rhythms

• Biological rhythms: circadian rhythms

  Biological rhythms

  Exert important influence on the way in which body systems behave. Governed by endogenous pacemakers (body's internal biological 'clock') and exogenous zeitgebers (external changes in envi). Some occur many times during the day (ultradian rhythms) or take longer than a day to complete (infradian rhythms). Circadian rhythms last around 24 hours. E.g., sleep/wake cycle and core body temperature.
• Biological rhythms: circadian rhythms 2

  Sleep/wake cycle

  Daylight (exogenous zeitgeber) has effect on sleep/wake cycle - is why we feel drowsy at night and alert during the day. But what if biological clock was 'left to its own devices' without influence of external stimuli? Would we fall asleep at regular times?
• Biological rhythms: circadian rhythms 3

  Siffre's cave study (1962)

  Spent several extended periods underground to study effects of own biological rhythms. Deprived of natural light and sound, re-surfaced after 2 months believing it had only been 1. A decade later performed similar feat but for 6 months in Texan cave. In each case 'free-running' biological rhythm settled down to around 25 hours.
• Biological rhythms: circadian rhythms 4

  Aschoff and Wever (1976)

  Ppts spent 4 weeks in WWII bunker deprived of natural light. Everyone displayed a circadian rhythm between 24 and 25 hours except for 1 (29 hours). This and Siffre's research suggests natural cycle is longer than 24 hours but is entrained by exogeneous zeitgebers associated w/ our 24 hour day (daylight hours, typical meal times, etc.)
• Biological rhythms: circadian rhythms 3

  Folkard et al. (1985) studied 12 ppts who lived in a cave for 3 weeks, retiring to bed at 11.45pm and rising when it said 7.45am. But gradually sped up clock unbeknown to ppts so 24 hour day eventually lasted only 22. Only 1 was able to comfortable adjust to new regime. Suggests existence of strong free-running circadian rhythm cannot easily be overridden by changes to external environment.
• Biological rhythms: circadian rhythms- evaluation

  Practical application to shift work. Knowledge of circadian rhythms has given researchers a better understanding of the adverse consequences that can occur as a result of their disruption. Night workers engaged in shift work experience a period of reduced concentration around 6 in the morning, meaning mistakes and accidents are more likely (Boivin et al. 1996). Thus, research into sleep/wake cycle has economic implications in terms of how best to manage worker productivity.
• Biological rhythms: circadian rhythms- evaluation 2

  Practical application to drug treatments. Circadian rhythms co-ordinate a number of the body's basic processes such as heart rate, digestion and hormone levels. This in turn has an effect on pharmacokinetics (the action of the drugs on the body and how well they are absorbed and distributed). Research into circadian rhythms has revealed there a peak times during day and night when drugs are most effective, leading to development of guidelines to do with timing of drug dosage for a whole range of medications.
• Biological rhythms: circadian rhythms- evaluation 3

  Studies of the sleep/wake cycle tend to involve small sample sizes, and so the people may not be representative of the wider population and this limits the extent to which meaningful generalisations can be made.