endogenous pacemakers exogenous zeitgebers Flashcards
What does SCN stand for?
Suprachiasmatic nucleus
What is the SCN?
Bundle of nerves in hypothalamus in each hemisphere
Primary EP, maintains circadian rhythms
Nerve fibres connected to eye cross in optic chiasm on their way to visual area of cortex
SCN lies above optic chiasm where it receives info about light
Describe Decoursey’s research
Destroyed SCN connections in chipmunks, returned to habitat
Sleep/wake cycle disappeared
Most were killed by predators - awake when they should’ve been asleep
Describe Ralph’s research
Bred mutant hamsters with 20 hour sleep/wake cycle
Their SCN cells transplanted into normal hamsters - cycles defaulted to 20 hours
Shows role of SCN in sleep/wake cycle
What is the role of the pineal gland?
SCN passes info on light to pineal gland
Pineal gland increases production of melatonin - induces sleep
What are exogenous zeitgebers?
Reset biological clocks through entrainment
What is light?
Resets body’s main pacemaker - SCN
Maintains sleep/wake cycle
Indirect influence on processes which control hormone secretion
Describe Campbell and Murphy’s study
Light may be detected by skin receptor sites on body without eyes
Pps woken with light pad on back of knees
Produced deviation in sleep/wake cycle up to 3 hours
Light is powerful, doesn’t rely on eyes
What are the rhythms of infants?
Infant sleep/wake cycle is random
Circadian rhythms begin at 6 weeks
16 weeks - most babies entrained
How are the sleep/wake cycles of babies entrained?
Social cues - schedule imposed by parents
Adults determine bedtime, mealtime
What does research suggest about jet lag?
Adapting to local times for eating and sleeping effectively entrains circadian rhythms
Beats jet lag through social cues
Evaluation - beyond the master clock
Numerous circadian rhythms in organs and cells - peripheral oscillators
Influenced by SCN but can act independently
Damiola - changing feeding patterns in mice = alters circadian rhythms in liver, SCN unaffected
Other complex influences on cycles
Evaluation - ethics in animal studies
Animals exposed to harm and risk
Do our findings justify the means?
Evaluation - influence of exogenous zeitgebers may be overstated
Miles - man blind from birth with circadian rhythm of 24.9 hours
Exposure to social cues - sleep/wake cycle still not adjusted
Occasions when EZ don’t affect us
Evaluation - methodological issues
Campbell and Murphy’s findings have not been replicated
Some light exposure to their eyes
Isolating one zeitgeber does not give us insight into others
