EPs + EZs

Question 1

Endogenous Pacemakers

Answer 1

Clocks, SCN

Question 2

Endogenous Pacemakers

Answer 2

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 3

The SCN

Answer 3

hypothalamus, primary EP
optic chiasm, light

Question 4

The SCN

Answer 4

SUPRACHIASMATIC NUCLEUS
- tiny bundle of nerve cells in the hypothalamus in each hemisphere.
- a primary EP in mammals and maintains circadian rhythms.
- acts as the ‘master clock’
- links to other parts of the brain associated with sleep and arousal, and has control over other biological clocks in the body.

Question 5

Where is the SCN located?

Answer 5

• Nerve fibres connected to the eye cross in an area known as the optic chiasm on their way to the visual area of the cerebral cortex.
• The SCN lies just above this area- receives info about light directly from this (continues when eyes are closed, enabling biological clock to adjust.

Question 6

How does the SCN function?

Answer 6

Neurons within the SCN spontaneously synchronise with each other, so their target neurons in other sites receive correctly time-coordinated signals.
These peripheral clocks can maintain a circadian rhythm, but not for very long and so must be controlled by the SCN.
It also regulates the manufacture and secretion of melatonin in the pineal gland via an interconnecting neural pathway.

Question 7

How is the SCN functioning possible?

Answer 7

The SCN’s built in circadian rhythm makes this possible, as this only needs resetting when external light levels change.
- Receives this information about light levels via the optic nerve, the clock adjusts according to light levels.

Question 8

The pineal gland

Answer 8

• The SCN sends signals to the pineal gland.
• It is directed to increase the production and secretion of melatonin at night and to decrease as light levels increase.
  (Melatonin induces sleep)

Question 9

Animal studies- Decoursey

Answer 9

Decoursey et al. (2000)
- destroyed SCN connections in 30 chipmunk brains.
- returned to natural habitat for 80 days.
- sleep/wake cycle disappeared, significant number were dead due to predators.

Question 10

Animal studies- Ralph

Answer 10

Ralph et al. (1990)
- ‘mutant’ hamsters with 20 hour sleep/wake cycle
- SCN cells from foetal tissue transplanted into brains of normal hamsters.
- sleep wake cycle of normal hamsters defaulted to 20 hours.
- emphasises role of SCN in establishing and maintaining circadian rhythms.

Question 11

Exogenous Zeitgebers

Answer 11

Cues, entrain

Question 12

Exogenous Zeitgebers

Answer 12

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

Question 13

How does light influence the sleep wake cycle?

Answer 13

• Receptors in SCN are sensitive to changes in light levels during the day and use this to synchronise the activity of organs and glands.
• Light resets the internal biological clock each day, keeping it on a 24 hour cycle.
• Scott Campbell and Patricia Murphy (1998):
  15 ppts woken at different times of day.
  Light shone at back of the knee once woken up.
  Deviation in sleep/wake cycle of up to three hours.
  Light is powerful- detected by skin receptors and not necessarily eyes.

Question 14

How do social cues affect the sleep wake cycle?

Answer 14

• Examples: mealtimes, social activities
• Social cues study:
  6 weeks- baby displays sleep/wake cycle.
  16 weeks- baby is entrained.
  Schedules are influenced and imposed by parents (including meal times and bed times).
  These should be followed out at local times rather than responding to our own feelings, entraining of circadian rhythms can overcome jet lag/ long distance travel easier.

Question 15

AO3 Points

Answer 15

1. Ethical issues
2. Methodological issues
3. Influence of EZ is over exaggerated
4. ‘Beyond the masterclock’
5. Artificial light as a zeitgeber

Question 16

AO3 1: Ethical issues

Answer 16

P: There are ethical issues in animal studies.
Ev: Decoursey (2000)- many of the chipmunks in the study were killed by predators due to their vulnerability. Huge loss of life as 30 were involved at the start.
Ex: Researchers put chipmunks in huge danger, meaning there was no consideration for protection from harm. Problem- subject to harm for results not necessarily generalisable to humans, reducing cost-benefit.

Question 17

AO3 2: Methodological issues

Answer 17

P- Methodological issues.
Ev- Murphy and Campbell’s study- sample size limited to 15 ppts.
Ex- Means results may not be generalisable to a larger group, or to all groups within society. Problematic as it is not representative of all social groups, reducing validity of the theory.

Question 18

AO3 3: Exaggeration

Answer 18

P: The influence of EZ’s is over exaggerated.
Ev: Campbell and Murphy’s study- deviation was within three hours.
Ex: Deviation could be due to other extraneous variables, or from natural variation in the sleep cycle- making the effects less significant.

It has been found through studies of those who live in Arctic regions (where sun does not set in summer months) show normal sleep patterns despite prolonged exposure to light.
Suggests occasions where EZs have little bearing on internal rhythms.

Question 19

AO3 4: ‘Beyond the masterclock’

Question 20

AO3 5: Role of artificial light