A01 Biological Rhythms: Circadian Rhythms

• Biological rhythms


  All living organisms are subjects to biological rhythms and they exert an important influence on the way in which body systems behave.
• Governing biological rhythms


  All biological rhythms are governed by two things: the body's internal clocks ( the endogenous pacemakers) and the external changes in the environment (the exogenous zeitgebers)
• Rhythms and time


  Some of these rhythms occur many times during the day (ultradian rhythms) and others take longer than a day to complete (infradian rhythms) and sometimes much longer (circannual rhythms) lasting around 24 hours
• Sleep/wake cycle


  Daylight is an important exogenous zeitgeber shown by the fact we feeel drowsy when it's nightime and alert during the day.
• Siffre's cave study


  Self-styled caveman who spent several extended periods underground to study effects of his biological rhythms. He studied the effects of his endogenous pacemaker when he deprived himself of natural light and spent 2 months in the cave of the southern alps. Again, he spent 6 months in a Texan cave a decade later.
• Findings of Siffre's research

  His free running biological rhythm settled to one just beyond 24 hours (around 25) but did fall asleep and wake up on a regular schedule
• Other research


  Aschoff and Wever convinced ppts to spend four weeks in a WWII bunker deprived of natural light. One ppt had a sleep/wake cycle of 29 hours but the rest displayed a circadian rhythm of 24-25 hours. This and Siffre show the sleep/wake cycle is slightly longer than 24 hours but we are entrained by exogenous zeitgebers associated with the 24-day.
• Folkard et al study


  Studied 12 ppts who agreed to live in a dark cave for three weeks, retiring to bed at 11.45pm and rising at 7.45am. Over the course of the study, researchers gradually increased the speed of the clock so eventually, the '24-hour' day was 22 hours.
• Findings of Folkard et al study

  Only one ppts was able to comfortably adjust to the new regime. This suggests the existance of a strong free-running circadian rhythm that can't be easily overridden by changes in the external environment