Endogenous Pacemakers

Question 1

What are endogenous pacemakers?

Answer 1

Internal clocks in the brain and body which help to govern biological rhythms in the body

Question 2

Why are endogenous pacemakers so important in terms of cyclic changes?

Answer 2

The world has cyclic changes that need to be attuned with so we have endogenous pacemakers that are similar to the likely cyclic changes

Question 3

Why are endogenous pacemakers so important in terms of our bodies?

Answer 3

We are complex systems with lots of different chemical processes so we need something to coordinate it - the endogenous pacemaker

Question 4

How are endogenous pacemakers governed?

Answer 4

It is thought that they’re generated by protein synthesis; a protein is produced until it inhibits further production so the level falls until production re-starts

Question 5

How are endogenous pacemakers regulated?

Answer 5

Through exogenous zeitgebers to keep in line with the environmental rhythms

Question 6

What is the main endogenous pacemaker?

Answer 6

The Suprachiasmatic Nucleus (SCN)

Question 7

What is the SCN?

Answer 7

A tiny cluster of nerve cells in the hypothalamus just above the optic nerve

Question 8

What does the SCN do?

Answer 8

It receives information about the amount of light on the retina and when light is low, it triggers the pineal gland to release melatonin and when there is enough of it, we fall asleep. When there is light, it produces an inhibiting factor for melatonin, reducing its levels

Question 9

What happens in the absence of light?

Answer 9

Melatonin is released in a cyclical manner but if the SCN is destroyed, the cycle disappears

Question 10

Name 6 studies showing evidence for the endogenous pacemaker

Answer 10

1) Rusak & Zucker (1975)
2) Ralph (1990)
3) DeCoursey (2000)
4) Schochat’s ‘sleep gate’ study (1997)
5) Siffre (1975)
6) Kleitman (1963)

Question 11

Outline Rusak & Zucker (1975)

Answer 11

Found that SCN-lesioned hamsters secrete testosterone all year rather than just breeding season

Question 12

What does Rusak & Zucker (1975) show?

Answer 12

When the SCN is removed or severely damaged, rhythms are practically destroyed also, and are all over the place

Question 13

Outline Ralph (1990)

Answer 13

Bred mutant hamsters with a 20 hour rhythm, then transplanted these SCN cells into normal hamster foetuses. These were born displaying the mutant 20 hour cycle. They then transplanted normal SCN cells into these mutant hamsters who started to show a 24 hour cycle within a week

Question 14

What does Ralph (1990) show?

Answer 14

The SCN has a major role in regulating rhythms

Question 15

Outline DeCoursey (2000)

Answer 15

Removed the SCN in 30 chipmunks and returned them to their natural habitat and observed them with 24 surgical controls and 20 intact controls. After 80 days, significantly more SCN-lesioned chipmunks killed by weasels presumably because they remained awake making noise and so could be located by the weasels.

Question 16

What does DeCoursey show?

Answer 16

The SCN has a major role in regulating rhythms, and thus helping us to survive

Question 17

What are 2 negative points about studies involving animals?

Answer 17

1) Ethical issues

2) Issues with generalisability to humans - results have to be replicated in human studies

Question 18

Outline Schochat’s sleep gate study (1997)

Answer 18

6 ppts spent 29 hours in a sleep lab where 7 minutes in every 20 they had to try and sleep. This meant that they were able to measure tendencies to sleep at different times of the day. The highest sleep propensity was recorded late evening and the highest levels of melatonin preceded this by about 100-120 minutes

Question 19

What does Schochat’s sleep gate study (1997) show?

Answer 19

It shows that melatonin plays a major role in the sleep wake cycle and thus supports the role of endogenous pacemaker

Question 20

Name a positive point of Schochat’s sleep gate study

Answer 20

Scientific data was collected so it was objective

Question 21

Name 2 negative points of Schochat’s sleep gate study

Answer 21

1) Correlational study

2) Very small sample of which were all men so generalisability

Question 22

Outline Kleitman (1963)

Answer 22

Placed ppts in an underground bunker with no light cues so they could choose their own sleep and wake times. They found that their rhythms were between 25-27 hours

Question 23

What does Kleitman (1963) show?

Answer 23

That the natural rhythm is slightly longer than the natural day, and that endogenous pacemakers exist and that exogenous zeitgebers play a role

Question 24

Name a negative of Kleitman (1963)

Answer 24

Group of students so generalisability

Question 25

Explain an IDA point for endogenous pacemakers

Answer 25

The biological approach - human behaviour is more complex than just structures in the brain and hormonal activity

Question 26

Outline Siffre (1975)

Answer 26

Spent 6 months in a cave without light or time cues, he quickly settled into a regular 24.9 hour rhythm so shows a consistent rhythm (but need exogenous zeitgebers to get rhythms to fit with the natural 24 hour day)

Question 27

Name a positive about Siffre (1975)

Answer 27

Supported by Aschoff & Wever (1976) who put ppts in an underground WW2 bunker, most circadian rhythms between 24-25 hours but some 29 hours. This shows they still operate in the absence of exogenous zeitgebers

Question 28

Name 2 negatives about Siffre (1975)

Answer 28

1) Case study so generalisability

2) Cave is not a real-life setting and temperature cannot be controlled which could have affected them