endogenous pacemakers and exogenous zeitgebers

Question 1

explain the suprachiasmatic nucleus (SCN) for endogenous pacemakers

Answer 1

• tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
• it is a primary endogenous pacemaker and influential in maintaining circadian rhythms eg. sleep/wake cycle
• SCN is above the optic chiasm, receives info about light even when eyes are closed= enabling biological clock to adjust to changing patterns of daylight when asleep

Question 2

explain animal studies and the SCN for endogenous pacemakers?

Answer 2

• DeCoursey destroyed SCN connection in brains of 30 chipmunks and returned them to their natural habitat observed for 80 days
• sleep/wake cycle had disappeared
• large proportion had been killed, presumably because they were asleep when they should’ve been awake and able to protect themselves

Question 3

explain the pineal gland and melatonin for endogenous pacemakers?

Answer 3

• SCN passes info on day length and light to pineal gland
• during night Pgland secrets melatonin (induces sleep)
• suggested factor in SAD

Question 4

explain light as an exogenous zeitgeber?

Answer 4

• cambell and murphey showed that light may be detected by skin receptor sites on the body even when same info isn’t received by the eyes
• 15 pp’s were woken up at various times and a light pad was shone on the back of their knees
• produced a 3 hours sleep wake cycle
• shows light to be a powerful exogenous zeitgeber that doesn’t rely on the eyes

Question 5

explain social cues as an exogenous zeitgeber?

Answer 5

• in infants sleep wake cycle in random
• at around 6 weeks= circadian rhythm
• schedules imposed by parents is likely to be a key influence here including adaption to local times for eating/bedtimes
• both are effective ways of entraining circadian rhythms

Question 6

evaluate circadian rhythms?

Answer 6

• there are numerous circadian rhythms in in many organs in the body eg.lungs and can act independently
• study demonstrated how changing feeding patterns in mice could alter their circadian rhythms by up to 12 hours
• suggests there may be other complex influences on sleep/wake cycle aside from the SCN

Question 7

evaluate ethics in animal studies?

Answer 7

• DeCoursey put the animals at risk when returning them to their natural habitat as a large majority of the chipmunks were killed
• furthermore had to generalise animal findings to humans as their brains are not as complex as a humans

Question 8

evaluate how influence of exogenous zeitgebers may be overstated ?

Answer 8

• case study of a blind man showed a circadian rhythm of 25 hours
• but despite exposure to social cues, his sleep wake cycle couldnt be adjusted and had to take sedatives at night and stimulants in the morning to keep pace with the 24 hour world
• individuals who live in arctic regions show normal sleep patterns despite prolonged exposure to the light or the dark
• both examples show sometimes exogenous zeitgebers have little impact on internal rhythm