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

Question 1

What are endogenous pacemakers?

Answer 1

Internal body clocks that regulate many of our biological rhythms such as the influence of the suprachiasmatic nucleus (SCN) on the sleep-wake cycle

Question 2

What are exogenous zeitgebers?

Answer 2

External cues that may affect or entrain our biological rhythms, such as the influence of light on the sleep-wake cycle

Question 3

What is the superchiasmatic nucleus (SCN)?

Answer 3

Tiny bundle of nerve cells located in the hypothalamus in each hemisphere

Question 4

What is the role of the superchiasmatic nucleus (SCN) in the sleep wake cycle?

Answer 4

• Even when eyes are shut , the SCN gets information on light from the optic nerve
• It sends messages (light) to another endogenous pacemaker (pineal gland) to increase or reduce the melatonin production

Question 5

What does entrained mean?

Answer 5

Restarting our body clock to the environment

Question 6

What was DeCoursey at al’s study (2000) on endogenous pacemakers?

Answer 6

• Destroyed SCN connections in brains of 30 chipmunks in their natural environment who were observed for 80 days
• He found that the sleep wake cycle disappeared and by the end of the study a significant proportion of them killed predators

Question 7

What was Ralph et al’s study (1990) on endogenous pacemakers?

Answer 7

• He bred ‘mutant’ hamsters with a 20 hour sleep wake cycle
• SCN cells from the foetal tissue of the mutant were transplanted into the brains of normal hamsters
• When transplanted, the cycles of the normal hamsters defaulted to 20 hours

Question 8

What conclusions can be made about DeCoursey and Ralph’s studies?

Answer 8

The SCN is important as it plays a role in regulating the sleep wake cycle

Question 9

What did Campbell and Murphy find and what was their study?

Answer 9

Findings:
- Light can be detected by skin receptors even when the same information is not received by the eye
Procedure:
- 15 participants were woken at various times and a light pad shone on the back of their knees
- Researchers produced a deviation in the participants’ usual sleep-wake cycles, up to 3 hours for some
Conclusions:
- Light is a powerful exogenous zeitgeber that influence our brain and body