Endogenous and Exogenous

Question 1

What are EnDOGENOUS PACEMAKERS?

Answer 1

biological clocks that set our free running internal rhythm. Most organisms have an internal clock that matches the time passage of the 24 hour day

Question 2

What are endogenous pacemakers and exogenous zeitgebers relationship with each other thought to be?

Answer 2

Thought to interact in the control and fine-tuning of our bio rhythms

Question 3

What is the main pacemaker?

Answer 3

Cluster of nerve cells known as the suprachiasmatic nucleus (SCN)

Question 4

How does the SCN work?

Answer 4

• Information obtained via optic nerves about light
• Sends signals to pineal gland
• Regulates production of melatonin, which in turn induces sleep and inhibits mechanisms that promote wakefulness

Question 5

What happens to melatonin production in the presence of light?

Answer 5

Inhibits the production, with the SCN indirectly involved in this process and causing an individual to feel more alert

Question 6

Evidence for the importance of the SCN has been found in a study by Morgan…

Answer 6

Mutant hamsters bred with circadian rhythms of 20 hours rather than 24. SCN of mutant hamsters transplanted into normal hamsters, where normal hamsters developed rhythm

Question 7

What does Morgans mutant hamster study demonstrate?

Answer 7

The key role the SCN plays as the main endogenous pacemaker

Question 8

How does the SCN support an evolutionary approach?

Answer 8

• May have adaptive advantage

- Allows animal to anticipate daily environmental events

Question 9

What did Decoursey find regarding adaptive advantages of the SCN?

Answer 9

• SCN destroyed in some chipmunks

- Far more active at night that non-modified, so more likely to be harmed by nocturnal predators

Question 10

Why has Decourseys/SCN research been criticised?

Answer 10

• Involvement of non-human studies
• Different anatomy, so findings may be lacking in external validity and cannot be generalised
• Ethical concerns

Question 11

What can’t endogenous pacemakers function accurately in the absence of?

Answer 11

Exogenous zeitgebers - in it’s absence, EP’s can become desynchronised

Question 12

What did Folkard et al find regarding Kate Aldcroft

Answer 12

• Short amount of time in a cave, so was free from EZ’s

- After 25 days, her temp rhythm was 24 hour cycle but her sleep rhythm was 30 hours

Question 13

What does Kate Aldrofts results show?

Answer 13

• Existence of separate EPs aside from the SCN

- Can become desynchronised without EZ’s

Question 14

What is the role of exogenous zeitgebers?

Answer 14

Keeps the free running biological rhythm regulated effectively

Question 15

What are some examples of EZ’s?

Answer 15

• Social cues like meal times and other social conventions entrain our bio rhythms
• Dominant zeitgeber is light
• Temperature e.g. deciduous trees

Question 16

What is the effect of bright light as a dominant EZ?

Answer 16

Inhibits melatonin, meaning that daylight ‘sets’ the biological clock at the beginning of each day. Hold the potential to shift the internal clock forwards or backwards

Question 17

What did Campbell and Murphy do in their study of bright light as a EZ?

Answer 17

• Light shone on back of PPS knees

- Shifted circadian rhythms

Question 18

Why might the SCN not be the main endogenous pacemaker?

Answer 18

Other oscillators must exist that compensate by keeping bio clock in tune with outside world

Question 19

There is conflicting evidence to suggest that artificial light is the dominant zeitgeber.

Answer 19

• Siffre and Aschoff assumed that it would not be efficient enough
• Boivin: rhythms can be entrained by dim lighting

Question 20

What do Boivins findings pose the question of?

Answer 20

Negative consequences for individuals if it does in fact reset the bio-clock

Question 21

What negative consequences might artificial light have?

Answer 21

Stevens - artificial light - disrupts melatonin production leading to higher incidences of breast cancer in well lit areas

Question 22

What is a positive application of Stevens’ research?

Answer 22

-Could be used to influence shift work patterns and thus aid workers in avoiding devastating health complications

Question 23

What is the overall point?

Answer 23

Necessary to emphasise - intertwined sysyem that are not separately existing