endogenous pacemakers and exogenous zeitgbers on sleep/wake cycle

Question 1

where is the suprachiasmatic nucleus (SCN)?

Answer 1

• bundle of nerves in hypothalamus of each hemisphere

- nerve fibres connect to eye across optic chiasm on way to visual art of cerebral cortex

Question 2

what is the suprachiasmatic nucleus (SCN)?

Answer 2

• primary endogenous pacemaker and influence in maintain circadian sleep cycle
• receives info about light even when eyes are closed so bio clock can adjust even when asleep

Question 3

what was Decoursey’s animal study on effect of endogenous pacemakers on the sleep cycle?

Answer 3

• Decoursey (00) destroyed SCN in 30 chipmunks and retuned them to natural habitat for 80 days
• sleep wake cycle disappeared by end and most died from predator attack

Question 4

What was Ralph’s animal study on effect of endogenous pacemakers on the sleep cycle?

Answer 4

• Ralph (90) bred mutant hamsters with 20hr sleep cycle
• SCN cells from mutant hamsters put into normal hamsters
• cycles of normal hamsters fell to 20 hrs

Question 5

how does the pineal gland and melatonin effect the sleep wake cycle?

Answer 5

• SCN passes info on day length and light to the pineal gland
• pineal gland increased production of melatonin at night to make us sleepy

Question 6

what is an exogenous zeitgeber?

Answer 6

• external factor in environment that resets our biological clock through entrainment

Question 7

what is Campbell and Murphy’s study on light as a exogenous zeitgeber?

Answer 7

• Campbell and Murphy (98) showed light can be detected in skin receptors, not just eyes
• 15 participants woken up at various times and light shone on back on knee
• sleep cycles had deviation of unto 3 hours doing this (light is powerful influence!)

Question 8

how is light an exogenous zeitgeber?

Answer 8

• can rest the body’s endogenous pacemaker and SCN meaning it influence sleep wake cycle
  (effects hormones and blood circulation)

Question 9

how are social cues a zeitgeber on the sleep/wake cycle?

Answer 9

• sleep cycle random in infants until entrained at 16 weeks
• likely due to mealtimes and bedtimes imposed by parents
• research shows adapting to local and eating and sleeping times can help with jet lag

Question 10

+ Beyond the master clock

Answer 10

• Damilola (00) found organs had circadian rhythms
• showed how changing feeding patterns in mice can alter circadian rhythm of liver by upto 12 hours (SCN rhythm unaffected

Question 11

• ethics in animal studies

Answer 11

• hard to generalise findings from animal studies
• Decoursey protested the animals were exposed to harm and subsequent risk when returned to habitat
  (chipmunks killed by predators)

Question 12

• influence of EZ’s may be overstated

Answer 12

• Miles (77) found man blind from birth with circadian rhythm of 24.9 hours
• despite social cues, he had to take sedatives at night and stimulants in the morning to maintain 24hour cycle (Zeitgeber’s had little influence)