biological rhythms

AO1

  • patterns of changes in body activities that conform to cyclical time periods

  • governed by endogenous pacemakers and exogenous zeitgeibers

circadian rhythms

  • last around 24 hours (circa = about, diem = day)

  • sleep wake cycle

    • determined by exogenous zeitgeibers (sunlight, darkness)

    • determined by endogenous pacemakers (superchiasmatic nucleus) - when light is detected by the eyes, an impulse is sent to the SCN, which then acts to control the body’s circadian system

ultradian rhythms

  • shorter than 24 hours

  • stages of sleep

    • one sleep cycle occurs every 90 minutes and has 5 distinct stages

    • during stage 1 and 2, a person is in light sleep and is easily woken up - displays mostly alpha waves when monitored via EEGs

    • stage 3 and 4 is deep sleep - brain waves are delta waves and a person is difficult to wake in this stage

    • stage 5 is REM sleep - the body is paralysed in this stage, the eyes also occasionally move, dreams are often experienced during REM

infradian rhythms

  • occur less frequently than 24 hours

  • menstruation

    • approx 28 days, in which women’s uterus shed their lining

    • it is controlled by hormones (endogenous pacemakers) oestrogen and progesterone and leutinising hormone

    • however, menstruation is also affected by exogenous zeitgeibers such as alcohol, stress and pheromones etc

AO3

  • one strength of circadian rhythms is there is supporting research of endogenous pacemakers

  • siffre spent extended periods underground, away from external cues such ad natural light and sound, which could inform biological rhythms. despite this he maintained a regular sleep-wake cycle, which settled at around 25 hours

  • this supports the idea of endogenous pacemakers and circadian rhythms as, despite the lack of exogenous zeitgeibers, siffre’s free running biological rhythm still maintained a circadian pattern, suggesting that circadian rhythms can be maintained, albeit not as accurately, by enogenous pacemakers, and are this innate traits of humans.

  • this supports the idea that humans have circadian rhythms which are in part controlled by endogenous pacemakers

    • CA - however one could argue that this research is not as strong because it has low generalisability. siffre’s study only had one ppt: himself. this means that results could be anomalous and unique to himself alone, so one should take caution when generalising results of his study to all humans on a nomothetic level

  • one strength of exogenous zeitgeibers controlling infradian rhythms is that there is supporting research

  • mcclintock and stern studied 29 women with irregular periods. samples of pheromones were gathered from 9 of them via their sweat at different points of their cycle. after alcohol treating, the pheromones were rubbed on the upper lips of other ppt each day. 68% of the women’s periods changed to closer to the women who’s pheromones they were exposed to

  • this suggests that external factors, such as pheromones, have a direct effect on a person’s infradian rhythm, supporting the existence of exogenous zeitgeibers and that they help control one’s biological rhythms

  • one weakness of research into sleep cycles is that it is dependent on ppts sleeping in a lab setting, which may result in unrepresentative sleep patterns

  • EEGs are the predominant method of observing brain activity during sleep, however it relies on the ppt wearing an uncomfortable cap with electrodes. with the additional complicated machinery of a lab, ppt may not sleep in a way which matches their ordinery sleep patterns

  • this means that data collected via these studies may lack external validity

  • therefore, it can be argued that current research into sleep cycles may not produce results which are accurately representative of normal sleep in the home.