Endogenous Pacemakers and Exogenous Zeitgebers

Question 1

What are endogenous pacemakers?

Answer 1

Internal body clocks that regulate our biological rhythms.

Question 2

What is the suprachiasmatic nucleus?

Answer 2

A bundle of nerve cells near the hypothalamus that sends information about light from the optic nerve to the pineal gland, telling it about how much melatonin to release.

Question 3

What animal was used in Decoursey’s study?

Answer 3

Chipmunks

Question 4

Describe what Decoursey did in her study.

Answer 4

She destroyed the SCN connections in the brains of 30 chipmunks, returned them to their natural habitats and observed for 80 days

Question 5

What did Decoursey find from her study?

Answer 5

The sleep/wake cycle of the chipmunks had disappeared and by the end of the study, many of them were killed by predators, as they should have been asleep.

Question 6

What animal did Ralph use in his study?

Answer 6

Hamsters

Question 7

Describe the procedure of Ralph’s study.

Answer 7

He bred mutant hamsters with a 20 hour sleep/wake cycle. The SCN cells from foetal tissue was transferred from the mutant hamsters to the brains of normal hamsters.

Question 8

Describe the findings from Ralph’s study.

Answer 8

The normal hamsters sleep cycle defaulted to 20 hours.

Question 9

What is an exogenous zeitgeber?

Answer 9

External factors that influence biological rhythms.

Question 10

Our circadian rhythms would be ____ if it wasn’t for exogenous zeitgabers.

Answer 10

Free running.

Question 11

What do exogenous zeitgebers do to our natural sleep/wake cycle?

Answer 11

They entrain it.

Question 12

How does light act as an exogenous zeitgeber?

Answer 12

Light is an external factor that can be detected by the suprachiasmatic nucleus. Its intensity determines the amount of melanin produced.

Question 13

Describe Campbell and Murphy’s knee light pad study.

Answer 13

15 PPTs were woken at various times in the night and a light pad was shone on the back of their knees.

Question 14

Describe the findings from Campbell and Murphy’s study.

Answer 14

The researchers were able to produce a deviation in the PPTs usual sleep wake cycle of up to 3 hours.

Question 15

Give 2 examples of social cues that entrain our biological rhythms.

Answer 15

Regular set mealtimes, bedtimes

Question 16

What has research suggested we do when experiencing jet lag?

Answer 16

We should adapt to local eating/sleeping times rather than eating when hungry or sleeping when tired.

Question 17

Explain the strength of endogenous pacemakers being useful.
Use the example of what would happen in winter without them. Also consider how eskimos have a regular sleep pattern despite living in darkness for 6 months.
Also explain how exogenous zeitgebers allow us to respond to environmental changes.

Answer 17

There would be problems if our rhythms were controlled solely by the environment. For example, during the winter, we would spend most of the day sleeping because of a lack of light. However, this isn’t the case, as eskimos have a similar sleep pattern all year round, despite spending 6 months in darkness. Additionally, exogenous zeitgebers allow us to respond to changes in our environment – without them, we may be awake at certain times, which could make us vulnerable.

Question 18

EXplain the strength of research support from Miles (Blind man study) showing the effect of internal and external factors on the sleep/wake cycle.
What was the length of the blind man’s circadian rhythm?

Answer 18

Miles studied a man who was blind from birth and found that he had a circadian rhythm of 24.9 hours, not 24 hours. The man had to use sedatives and stimulants (exogenous zeitgebers) to maintain a 24-hour circadian rhythm, so he could fit in with the rest of society. Blind people don’t have light as a time giver. His research demonstrates the importance of light, as it reduces the near 25-hour cycle back to 24 hours.

Question 19

Explain the limitation of sleep/wake studies using animals.
Consider the argument that the animals used have the same biological structures as humans, but counter this with that some animals, such as birds, are different.

Answer 19

Animal studies may be justified in the sense that they have similar mechanisms and structures to the human brain. For examples, the hamsters used in Ralph’s study had a circadian rhythm and the chipmunks in Decoursey’s study had a SCN and pineal gland. However, many other animals differ, such as birds and reptiles, in relation to how they process light info. This means that findings about the influence of exogenous zeitgebers/endogenous pacemakers are not applicable to all organisms.

Question 20

Explain the limitation of contradictory research from Ciezler. What did the circadian rhythm extend/lessen to?
Explain the issues with artificial light being present in some of the cave studies.

Answer 20

In some of the sleep/wake cycle studies, there were high levels of artificial light. Ciezler suggested that this skewed results, as light acts as an exogenous zeitgeber. This means that light could increase the length of the circadian rhythm meaning that findings will not be reflective of an actual circadian rhythm without the influence of light. Ciezler found that artificial light could adjust the sleep/wake cycle from 22 to 28 hours using dim lighting. This means that our understanding of the influences of exogenous zeitgebers may not be fully accurate.