Circadian

• superchiasmatic nucleus (SCN)

  a bundle of nerves in the hypothalamus where it receives optic signals from the environment , the SNC passes information to the pineal gland which produces melatonin to induce drowsiness
• What is the biological clock?

  Biological pacemaker that controls the circadian rhythm. An endogenous pacemaker
• Where is the biological clock located?

  Superchiasmatic nucleus in the hypothalamus
• What factors affect circadian rhythms?

  • Internal factors: endogenous pacemakers
  • External factors: exogenous zeitgebers
• How long does a circadian rhythm last?

  24 hours/one day
• What does the pineal gland produce?

  Melatonin
• What is the function of melatonin?

  Increases sleepiness
• How does the SCN respond to exogenous zeitgebers?

  Low levels of light are detected by the retina and send an impulse to the brain. This is detected when the impulse passes over the optic chiasm, which sends an impulse to the SCN, which activates the pineal gland and produces melatonin. This produces serotonin which causes sleepiness and entrains the biological clock to the environment.
• Siffre study

  • lived in a cave for 3 months
  • found that without exogenous zeitgebers, his day lengthened to 25 hours
  • shows that exogenous zeitgebers work