Biopsychology: Endogenous pacemakers

Question 1

What two key factors regulate biological rhythms?

Answer 1

1. Endogenous pacemakers
2. Exogenous zeitgebers

Question 2

What are endogenous pacemakers?

Answer 2

Internal body clocks that regulate many of our biological rhythms

Question 3

What is one example of an endogenous pacemaker?

Answer 3

The suprachiasmatic nucleus (SCN)

Question 4

What is the SCN?
- where is it located?

Answer 4

Tiny bundle of nerve cells

• Located in the hypothalamus in each hemisphere of the brain

Question 5

What kind of endogenous pacemaker is it in mammalian species?

Answer 5

Primary endogenous pacemaker

Question 6

What does the SCN maintain? + give an example

Answer 6

Circadian rhythms

e.g. sleep/wake cycle

Question 7

How does the SCN link to the sleep/wake cycle? (4 steps)

Answer 7

1. Eye detects low light levels
2. This info is then sent to the SCN
3. SCN alerts the pineal gland to secrete melatonin
4. Melatonin levels increase, which induces sleep

Question 8

How else has the SCN been demonstrated? What studies? Name of researcher?

Answer 8

Animal studies

DeCoursey et al

Question 9

DeCoursey et al’s animal study:
Procedure?
Results?

Answer 9

Procedure:
- destroyed the SCN connections in the brains of 30 chipmunks
- the chipmunks were returned to their natural habitat and observed for 80 days

Results:
- chipmunks sleep/wake cycle disappeared
- By end of study, a significant proportion of them had been killed by predators

Question 10

Who else did research into the SCN in animals?
Procedure?
Results?

Answer 10

Ralph et al

Procedure:
- bred ‘mutant’ hamsters with a 20-hour sleep/wake cycle

Results:
- SCN cells from tissues of mutant hamsters transplanted into brains of normal hamsters
- Their cycles defaulted to 20-hours

Question 11

EVALUATION: 1/2 Limitations of SCN research

Answer 11

POINT: The SCN may obscure other body clocks

EVIDENCE:
- Damiola et al, showed how changing feeding patterns in mice could alter the circadian rhythm of cells in the liver up to 12 hrs
- whilst leaving the rhythm of the SCN unaffected

EXPLAIN:
- Research shows there are numerous circadian rhythms in many organs and cells in the body
- Which are influenced by actions of the SCN, but also act independently

LINK: Suggests there are other complex influences on the sleep/wake cycle

Question 12

EVALUATION: 2/2 Limitations of SCN research

Answer 12

POINT: Endogenous pacemakers cannot be studied in isolation

EVIDENCE:
- Isolation studies (e.g. Siffre’s cave study) are extremely rare
- Siffre also used artificial light= could have reset his biological clock every time he turned his lamp on

EXPLAIN:
- Everyday life= pacemakers & zeitgebers interact so makes little sense to separate the two for the purpose of research

LINK:
The more researchers attempt to isolate the influence of internal pacemakers= lower the validity of the research