Regulations

• Endogenous pacemakers

  • Aspect of biological rhythm are set by genetically determined biological structures and mechanisms within the body
  • Suprachiasmatic nucleus part of hypothalamus seems to act as an internal clock to keep 24 cycle
  • Sensitive to light regulating pineal gland secreting melatonin a hormone inducing sleep
  • Less light = more melatonin
• Endogenous pacemakers

  Menaker et al lesioned structure in hamsters, disturbing sleep wake cycle
• Exogenous zeitgebers

  • Influences outside body trigger biological rhythm
  • Light is most important zeitgeber
  • Siffre spent 6 months in a cave, sleep wake cycle became 25-30 hours, natural light keeps 24 hour clock
• Endogenous and exogenous interact

  • Regulate biological rhythms
  • Endogenous factors completely determine cycle
  • Culture factors - eskimo live in permanent day or night , cycle not just determined by light on pineal glamd
  • Individual differences - group of people isolated from daylight, some maintained regular sleep-wake cycle, others displayed extreme idiosyncrasies