The Effect of Endogenous Pacemakers and Exogenous Zeitgebers on the Sleep/Wake Cycle

Question 1

What is the role of the suprachiasmatic nucleus (SCN)?

Answer 1

Relays information to the pineal gland about the light levels to elicit/inhibit the release of melatonin.

Question 2

What is the role of the optic chiasma?

Answer 2

Contains melanopsin that is sensitive to light and send information to the suprachiasmatic nucleus.

Question 3

Give some examples of exogenous zeitgebers.

Answer 3

Light, temperature, meal times, social activities.

Question 4

Where else on the body is sensitive to light, according to Murphy and Campbell?

Answer 4

Light shone on the back of the knees effected the circadian rhythm of the sleep-wake cycle.

Question 5

Give some advantages to the role of exogenous/endogenous zeitgebers on the sleep-wake cycle.

Answer 5

Advantages:
- Supporting evidence for the role of the SCN - Ralph found that when cells were transferred from abnormal hamsters to normal hamsters, there circadian rhythm also shortened - SCN had imposed its pattern on the hamsters.

• Decoursey et al - the SCN of 30 chipmunks was destroyed - many died when introduced to their habitat as they were awake at vulnerable times - SCN is the main influencer of the sleep wake cycle.
• Supporting evidence for the influence of exogenous zeitgebers - Miles et al - those who were completely blind had a highly abnormal circadian rhythm - demonstrates the importance of exogenous zeitgebers.

Question 6

Give some disadvantages of exogenous and endogenous zeitgebers on the sleep wake cycle.

Answer 6

Disadvantages:
- Ralph’s and Decoursey’s studies were animal studies - difficulty extrapolating findings to human populations - both studies are ethically questionable.

• Miles et al’s study was a case study - low population validity - though great detail about one individual.