circadian rhythms

• endogenous pacemakers - mechanisms within the body that govern the internal, biological bodily rhythms
• exogenous zeitgebers - environmental cur, such as light or social cues that help regulate biological clock
• master circadian rhythm pacemaker is suprachiasmatic nuclei (SCN) found in the hypothalamus

  receives light information
• light induced activation of SCN prevents the production of melatonin by pineal gland
• light - optic nerve - SCN - pineal gland - sleep wake cycle
• circadian rhythm - pattern of behaviour that occurs approx every 20 hours, set and rest by environmental light levels
• how sleep cycle is maintained

  dictates sleep/wake periods

  24-25 hours

  light/darkness are EZs that determine when we sleep/wake

  homeostatic system is trying to enable homeostasis - notes changes, energy dips (EPs)

  means internal/external factors combine to enable rhythm and adjust to changes
• cave study - siffre

  evidence for 'free running' circadian rhythm, subjected himself to extended periods underground

  61 days underground in alps (lost track of days/months)

  texas- 6 months underground, circadian rhythm settled to just over 24 hours

  1999 older body stretched circadian rhythm to 48 hours

  absence of all EZs, light, clocks, radio, just woke ate and slept when he felt needed
• +research support

  mutant hamsters study: breeding (genetic) of hamsters with a 20 hour rhythm

  SCN removed and transplanted in 'normal' hamsters, who then displayed 20 hour rhythm too and vice versa

  = SCN plays vital role in shaping of cycle
• +seperate rhythms

  aldcroft - spent 25 days in lab with no EZs (light), found sleep/wake cycle slipped to 30 hours

  = effects of EZs
• +blind people and circadian rhythms

  estimated that vast majority of blind people still have some light perception - pathway from retinal cells containing melanopsin to the SCN is still intact
• +real world application

  light exposure to avoid jet lag

  exposure to bright light prior to an east-west flight decreased the time needed to readjust to local time on arrival - this can shift rhythm up 2 hours with continuous bright light