circadian rhythms

Question 1

what are circadian rhythms?

Answer 1

• lasts for around 24 hours

- e.g the sleep/wake cycle

Question 2

what is meant by exogenous zeitgebers?

Answer 2

the fact that we feel drowsy when it’s night-time and alert during the day shows the effect of daylight as an external signal for when we need to be awake.

Question 3

what is meant by endogenous pacemakers?

Answer 3

• the biological clock, without an external stimuli is called free-running.
• there is a basic rhythm governed by the suprachiasmatic nucleus (SCN).

Question 4

what is the suprachiasmatic nucleus (SCN)?

Answer 4

• a bundle of nerves within the hypothalamus.

- receives information about light directly from the optic chiasm.

Question 5

what does the exogenous zeitgeber do to the SCN?

Answer 5

• the exogenous zeitgeber can reset the SCN.
• the SCN passes information to the pineal glands which increases the production of melatonin (sleep inducing hormone) during the night.

Question 6

describe Aschoff and Wever’s study into circadian rhythms.

Answer 6

• group of participants spent 4 weeks in a WW2 bunker
• they were deprived of light
• all but one (whose sleep/wake cycle extended to 29 hours) displayed circadian rhythm between 24 - 25 hours.

Question 7

one strength of circadian rhythms.

Answer 7

• it has practical applications to shift work.
• Boivin et al (1996) found that shift workers experience a lapse of concentration around 6 am so mistakes and accidents are more likely to happen.
• research also suggest a link between shift work and poor health, with shift workers three times more likely to develop heart disease.
• research into sleep/wake cycle may have economic implications in terms of the best way to manage worker productivity and safety.

Question 8

one limitation of circadian rhythms.

Answer 8

• one limitation is the common use of small samples in the research.
• Aschoff and Wever used a small group in their research.
• the participants may not be representative of the wider population and this limits generalisation.

Question 9

how was animal studies used to investigate the SCN?

Answer 9

• Ralph et al bred ‘mutant’ hamsters with a 20-hour sleep/wake cycle.
• when SCN cells from foetal tissue of mutant hamsters were transplanted into brains of normal hamsters, the cycle of the second group defaulted to 20 hours.
• this study emphasises the role of SCN in establishing and maintaining the circadian sleep/wake cycle.

Question 10

explain light as a key zeitgeber in humans.

Answer 10

• can reset the body’s main endogenous pacemaker (SCN).
• plays a role in the maintenance of the sleep/wake cycle.
• it has an indirect influence on functions such as hormone secretion and blood circulation.

Question 11

explain social cues as a key zeitgeber in humans infants.

Answer 11

• at about 6 weeks, circadian rhythms begin and by about 16 weeks, most babies are entrained.
• schedules imposed by parents are a key influence, including adult-determined bedtimes and mealtimes.