circadian rhythms

• circadian rhythms - biological rhythms that take around 24 hours to complete one full cycle
• sleep/wake cycle - circadian rhythms = synchronised by the SCN, in the hypothalamus. this keeps the body in line with the environment, through the use of exogenous zeitgebers such as light. different light intensities can tell the scn whether to produce melatonin or not. it takes in light through light sensitive cells in our eyes. this gives us a feeling of wakefulness/sleepiness.

  sleep/wake cycle is also controlled by homeostasis where we feel more tired if we use up large amounts of energy

  CIRCADIAN RHYTHMS = FREE RUNNING - follow a 24 hour cycle regardless of external factors
• SIFFRE

  spent 2 months in a cave with no access to natural light or what time of day it was. despite this, siffre followed a circadian rhythm of around 25 hours thus supporting the idea that we have a free running circadian rhythm
• A03 +practical application- research into circadian rhythms can explain effects of desynchronisation. shift work been found to cause problems such as infertility, high triglycerides and decreased alertness. this is because individuals work through a circadian trough which can cause an increased risk of accidents in the workplace. this knowledge has enabled changes to be made such as brighter lights to increase awakeness, aswell as planning when breaks should be taken etc to help people accustom to desynchronisation of their natural biological rhythms
• A03-methodological issues - a case study was used meaning individual differences were been present so results lack generalisability due to low population validity. beta bias is also involved in the study ; half of the population is women meaning biological differences may have an effect on our circadian rhythms. individual differences regarding age may also have impacted the results. as we get older our scn tends to slow down meaning that the results cannot be applied to whole populations as age would affect our free running circadian rhythms
• A03 - lack of control over confounding variables - at time of siffres study researchers didn't believe that artificial lighting has an affect on biological rhythms. however recent research has found that this can disrupt circadian rhythms by up to 6 hours. this means the light in sniffer's study may have caused changes to his natural rhythms, and he could've used the light to entrain when he slept and woke. this therefore suggests that causation conclusions are unreliable and the study lacks internal validity