Endogeneous pacemakers and exogeneous zeitgebers

Question 1

What is the SCN?

Answer 1

• A bundle of nerves in the hypothalamus in each hemisphere of the brain
• lies above the optic chiasm and recieves information from this, even when our eyes are closed

Question 2

What links animal studies and the SCN?

Answer 2

• Decoursey destroyed the SCN in the brains of 30 chipmunks and returned them to their natural habitat and observed them for 80 days
• Their sleep wake cycle and a significant proportion of them were killed by predators

Question 3

Give an other study that investigates the link between animal studies and the SCN

Answer 3

• Ralph bred mutant hamsters with a 20hour sleep wake cycle. When SCN cells from the tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycle of the second group defaulted to 20hrs

Question 4

What is the role of the SCN in melatonin release

Answer 4

• passes info about change in light to the pineal gland which secretes melatonin, making us tired at night

Question 5

Evaluate the SCN (endogenous pacemakers)

Answer 5

L - ethics, animals died as a result of Decoursey’s research
L - endogenous pacemakers can not be studied in isolation. For exampe, in siffres study there was still a lamp providing exogenous zeitbegers, light. This shows normally endogeneous and exogeneous pacemakers are interacting and we can not isolate one
L - May be other body clocks such as peripheral oscillators in our organs which act independently and can be influenced by the SCN.

Question 6

Describe light as an exogenous zeitgeber

Answer 6

• light can reset our main endogenous pacemaker, the SCN and control hormonal levels and blood circulation
• Campbell and Murphy demonstrated that light may be detected by skin receptors on our skin.
• 15 participants were woken up at various times and a light pad was shone at the back of their knees
• This produced a deviation in their sleep/wake cycles of 3 hours in some cases
• This shows light is an important exogenous zeitgeber

Question 7

Describe social cues as an exogenous zeitgeber

Answer 7

• at 6 weeks of age, circadian rhytms begin and at about 16 months they are entrainted by the schedules imposed by parents including adult determined mealtimes and bed times
• Jet lag also suggests that adapting to local times of locals is important to beat jet lag

Question 8

Evaluate exogenous zeitgebers

Answer 8

L - exogenous zeitgebers do not have the same effect. For example, people who live in places such as the Artic circle, who have 6 months in darkness still have the same sleep/wake cycles, which shows that they are primarily controlled by endogenous pacemakers
L - Evidence challenges the role of exogenous zeitgebers. Miles recounts the study of a young man, blind from birth who had an abnormal circadian rhythm of 24.9hrs. Despite social cues this could not be adujsted, this shows social cues are limited