Endogenous pacemakers

• What is one of the primary endogenous pacemakers in mammals?

  SCN
• What does SCN stand for?

  Suprachiasmatic nucleus
• What is the SCN?

  Tiny bundle of nerve cells
• Where is the SCN located?

  Hypothalamus in each hemisphere
• What does the SCN maintain? 


  Sleep/wake cycle
• What is the optic chiasm?

  The area nerve fibres connect to the eye
• How does the SCN receive information about light?

  From the optic chiasm
• How does the biological clock adjust to changing daylight even while asleep?

  SCN receives information from optic chiasm even when asleep
• How has the influence of the SCN been demonstrated?

  Animal studies
• Who demonstrated the influence of the SCN through chipmunk studies?

  DeCoursey
• What was the procedure in DeCoursey's study?

  Destroyed SCN connections in chipmunks and observed them for 80 days
• How many chipmunks were in DeCoursey's study?

  30
• How long did DeCoursey observe the chipmunks for?


  80 dats
• What were the findings in DeCoursey's study?

  Sleep/wake cycle of chipmunks disappeared and significant proportion of them were killed by predators
• Who demonstrated the influence of the SCN through 'mutant' hamster studies?

  Ralph
• What was the procedure in Ralph's study?

  Bred 'mutant' hamsters with 20-hour sleep/wake cycle - then SCN cells transplanted into brains of normal hamsters
• What was the findings in Ralph's study?

  Sleep/wake cycle in normal hamsters defaulted to 20 hours
• Where does the SCN pass information about day length and light it receives to?


  Pineal gland
• When does the pineal gland increase production of melatonin?

  Night
• What is melatonin?

  A chemical that induces sleep
• What has melatonin been suggested to be a causal factor in?

  Seasonal affective disorder