circadian rhythms

• What is a circadian rhythm?

  A biological rhythm that follows a 24-hour cycle.
• How are Circadian rhythms set?

  Driven by body clocks found in all cells, synchronised by Supra Chiasmatic Nucleus found in Hypothalamus

  • photoentrainment sets body clocks found to correct time
  • light sensitive cells act as brightness detectors
• What is the Sleep-Wake cycle?

  External signals of light and dark, 2 dips:

  • 2-4am
  • 1-3pm
• What is the importance of the Sleep-Wake cycle?

  If we have had sufficient sleep, the sleepiness we feel during these dips are less intense

  • homeostatic drive for sleep gradually increases throughout the day
  • acts as a free running circadian clock
• What is the significance of hormone production?

  Melatonin activates chemical receptors in the brain

  • when it is dark, more melatonin is produced
• What is the importance of core body production?

  Lowest (36°C) at about 4:30am

  Highest (38°C) at about 6pm

  • sleep occurs when body is at lowest temperature
• A03: Research support for importance of sleep

  Hughes - tested circadian hormone release in 4ppts at British Antarctic Station

  • February (end of Antarctic summer), cortisol levels reach their highest point as ppts awoke, lowest when they went to bed
  • 3 months of continuous darkness, peak levels at noon
  • Responsible for variations
• A03: Individual differences

  1 cycle length can vary from 13-65 hours

  • individuals are innately different in terms of Circadian Rhythms peak time
  • explains why some sleep and wake up earlier
• A03: Research methodology

  Most studies are isolated from variables such as clocks, radios and daylight that may affect Circadian Rhythms, but not isolated from artificial light

  • Czeiler - altered rhythms down to 22h and up to 28h by using dim artificial lighting
• A03: Real world application

  Chronotherapeutics - specific times that patients take their medication matters

  • essential for right concentration