Circadian Rythms

• Biological rhythms are repeated patterns of changes in the body that are regulated by an internal clock
• Circadian rhythms take 24 hours to complete a cycle
• Sleep wake cycle is an example of a circadian rhythm
• Endogenous pacemakers - internal body clocks that regulate our biological rhythms
• Exogenous zeitgebers are external cues that influence ad reset our internal biological clocks
• SCN regulates pineal gland which secretes melatonin, thus sleep
• SCN receives information about light from the eyes and the optic nerve (even while eyes are shut)
• Less light = SCN stimulates the pineal gland to produce MORE melatonin to help us fall asleep
• More light = SCN stops the pineal gland producing melatonin to help us feel awake
• Siffre - spent two month underground in a cave with no lights or clocks
• Despite the a scene of natural daylight, Siffre maintained a regular sleep wake cycle of around 25 hours
• Siffre believed date was a month earlier when experiment had finished
• Conclusions from Siffre’s study -

  • Sleep wake cycle is nearer to 25 hours than 24 hours
  • Humans have a need for exogenous zeitgebers such as light to regulate sleep wake cycle
• Limitation of Siffre’s study - artificial light could be seen as an exogenous zeitgeber, which undermines the research
• Practical application - understanding of circadian rhythms has related to chronotherapeutics