Outline and evaluate the effect of endogenous pacemakers and exogenous zeitgebers on the
sleep wake cycle (16 marks)
Periodic activity governed by:
- Internal biological clocks (endogenous pacemakers)
- How it effects the sleep wake cycle a biological clock left to its own devices without
the influence of external stimuli like light.
- External changes in the environment (exogenous zeitgebers)
- How it effects the sleep wake cycle for example the fact we feel drowsy when its
night-time and alert during the day shows effects of daylight.
Research to support
Folkard et al
- Showed endogenous pacemakers are stronger than exogenous zeitgebers.
- Convinced a group of 12 people to live in a cave, they went to sleep at 11:45pm and
woke up at 7:45am.
- Researchers then slowly sped up the clock to be just 22 hours.
- Only one participant was able to easily adjust.
- This suggests the existence of a strong free running circadian rhythm that isn’t controlled
by exogenous zeitgebers (these are external factors for example the fact we feel drowsy
when its night time and alert during the day)
Evaluation
application to shift work.
- Bolvin found shift workers have a dip in concentration around 6am (circadian trough)
causing accidents to be more likely.
- Found it’s more likely for shift workers to develop heart disease.
- The research into the sleep wake cycle may have economic implication in terms of how
to best manage shift work.
research support (siffres cave study)
- Demonstrated a free running circadian rhythm of about 25 hours.
- He spent long periods in dark caves to test the internal body clock.
- He lived underground for 2 months and later 6 months.
- His circadian rhythm settled down to 25 hours.
- Suggesting exogenous zeitgebers entrain the circadian rhythm to just short of natural.
generalisations are difficult to make.
- Studies on the sleep wake cycle often involve small groups of participants or even single
individuals.
- May not be representative of the wider population, limiting meaningful generalisations.
- Siffre found his body clock was much slower at 60 then when he was younger.
, - Suggests that even when the same person is involved, there are factors preventing
general conclusions being drawn.
Outline and evaluate two or more ways of studying the brain (16 marks)
fMRI – highlight active areas of the brain, is functional magnetic resonance imaging.
- Scan is absorbed by deoxygenated blood in the brain and areas with high activity will
require more oxygenated blood so in turn have more deoxygenated blood.
- This is called a haemodynamic response.
EEG – shows overall electrical activity.
- Measures electrical activity in the brain via electrodes using a skull cap.
- Used to diagnose unusual arrhythmic patterns of brain activity (for example epilepsy)
Evaluation
fMRI
- Has no radiation and is safe, produces images with high spatial resolution and can be
used whilst a patient is carrying out a task. Although its very expensive and has poor
temporal resolution meaning there will be gaps between images.
EEG
- Has contributed to the understanding of sleep, with high temporal resolution, helps
diagnose epilepsy. Although it’s difficult to establish the exact source of neural activity
and we can’t distinguish the activity of different but adjacent neurons.
sleep wake cycle (16 marks)
Periodic activity governed by:
- Internal biological clocks (endogenous pacemakers)
- How it effects the sleep wake cycle a biological clock left to its own devices without
the influence of external stimuli like light.
- External changes in the environment (exogenous zeitgebers)
- How it effects the sleep wake cycle for example the fact we feel drowsy when its
night-time and alert during the day shows effects of daylight.
Research to support
Folkard et al
- Showed endogenous pacemakers are stronger than exogenous zeitgebers.
- Convinced a group of 12 people to live in a cave, they went to sleep at 11:45pm and
woke up at 7:45am.
- Researchers then slowly sped up the clock to be just 22 hours.
- Only one participant was able to easily adjust.
- This suggests the existence of a strong free running circadian rhythm that isn’t controlled
by exogenous zeitgebers (these are external factors for example the fact we feel drowsy
when its night time and alert during the day)
Evaluation
application to shift work.
- Bolvin found shift workers have a dip in concentration around 6am (circadian trough)
causing accidents to be more likely.
- Found it’s more likely for shift workers to develop heart disease.
- The research into the sleep wake cycle may have economic implication in terms of how
to best manage shift work.
research support (siffres cave study)
- Demonstrated a free running circadian rhythm of about 25 hours.
- He spent long periods in dark caves to test the internal body clock.
- He lived underground for 2 months and later 6 months.
- His circadian rhythm settled down to 25 hours.
- Suggesting exogenous zeitgebers entrain the circadian rhythm to just short of natural.
generalisations are difficult to make.
- Studies on the sleep wake cycle often involve small groups of participants or even single
individuals.
- May not be representative of the wider population, limiting meaningful generalisations.
- Siffre found his body clock was much slower at 60 then when he was younger.
, - Suggests that even when the same person is involved, there are factors preventing
general conclusions being drawn.
Outline and evaluate two or more ways of studying the brain (16 marks)
fMRI – highlight active areas of the brain, is functional magnetic resonance imaging.
- Scan is absorbed by deoxygenated blood in the brain and areas with high activity will
require more oxygenated blood so in turn have more deoxygenated blood.
- This is called a haemodynamic response.
EEG – shows overall electrical activity.
- Measures electrical activity in the brain via electrodes using a skull cap.
- Used to diagnose unusual arrhythmic patterns of brain activity (for example epilepsy)
Evaluation
fMRI
- Has no radiation and is safe, produces images with high spatial resolution and can be
used whilst a patient is carrying out a task. Although its very expensive and has poor
temporal resolution meaning there will be gaps between images.
EEG
- Has contributed to the understanding of sleep, with high temporal resolution, helps
diagnose epilepsy. Although it’s difficult to establish the exact source of neural activity
and we can’t distinguish the activity of different but adjacent neurons.
