A01

• What is the suprachiasmatic nucleus (SCN)?

  A tiny bundle of nerve cells
• Where is the SCN located?

  In the hypothalamus of the brain
• What role does the SCN play in mammals?

  It maintains circadian rhythms
• What circadian rhythm is the SCN influential in?

  The sleep/wake cycle
• What happens to nerve fibers connected to the eye?

  They cross at the optic chiasm
• What does 'supra' mean in relation to the SCN?

  Above
• How does the SCN receive light information?

  Directly from the optic chiasm
• What is the significance of the SCN receiving light information even when eyes are closed?

  It adjusts the biological clock to daylight
• What was the method used by DeCoursey et al. (2000) in their study?

  They destroyed SCN connections in chipmunks
• What was the outcome of DeCoursey et al.'s study on chipmunks?

  Their sleep/wake cycle disappeared
• What happened to the chipmunks by the end of DeCoursey et al.'s study?

  Many were killed by predators
• What did Ralph et al. (1990) study in hamsters?

  Mutant hamsters with a 20-hour cycle
• What occurred when SCN cells from mutant hamsters were transplanted?

  Normal hamsters defaulted to a 20-hour cycle
• What does the SCN pass to the pineal gland?

  Information about day length and light
• Where is the pineal gland located?

  Behind the hypothalamus in the brain
• What does the pineal gland produce during the night?

  Melatonin
• What is the role of melatonin?

  It induces sleep and is inhibited during wakefulness
• What condition has melatonin been suggested to influence?

  Seasonal affective disorder