AO1

• What is a circadian rhythm?

  Biological rhythm that lasts around 24 hours
• Example of circadian rhythms?

  Sleep wake cycle, release of hormones, varying our body temperature and blood pressure
• There must be an internal body clock (endogenous pacemaker) that keeps this sleep wake cycle

  We are aware of conflicts between the endogenous pacemakers and the exogenous zeitgebers like light and social cues in situations like jet lag. The EP will be entrained by the EZ‘s to the new time zone, but it can take several days
• What is the endogenous pacemaker for the sleep wake cycle?

  The suprachiasmatic nucleus (SCN)
• What is the suprachiasmatic nucleus also known as?

  The master clock
• The SCN is a part of what?

  The hypothalamus within the lambic system
• Where is the suprachiasmatic nucleus located?

  At the optic chasm, the point on the optic nerves where they cross
• When light is detected by the SCN, it sends light to the pineal gland, stopping the production of melatonin, a hormone that results in a sleep response
• What is thought to be the primary exogenous zeitgeber in the sleep wake cycle?


  Light
• What can also act as EZs in sleep wake cycles?

  Social cues (when we time our meals, when others go to bed) or environmental cues (like clocks)
• The circadian sleep wake cycle endogenous pacemaker is thought to be free running, maintaining a predictable cycle without constant entrainment by exogenous zeitgeber
• Who tested free running circadian rhythm?

  Siffre (1975)
• What did Siffre do?

  Spent 2 months in a cave deprived of natural light and sound
• What did Siffre find?

  Free running biological rhythm settled down to around 25 hours though he did continue to fall asleep and wake up on a regular schedule