Lesson 10 - Circadian Rhythms

Question 1

Biological Rhythms

Answer 1

Cyclical changes in the physiological systems
Evolved because the environments in which organisms have cyclical changes
Three types:
Circadian, ultradian and infradian

Question 2

Circadian Rhythms

Answer 2

Cycle that lasts 24 hours
Nearly all organisms possess a biological representation of the 24 hour day
These optimise an organism’s physiology and behaviour to best meet the varying demands of the day/night cycle

Question 3

Circadian Rhythms
Suprachiasmatic Nuclei (SCN)

Answer 3

Circadian rhythms driven by the SCN in the hypothalamus
This pacemaker must constantly be reset so our bodies are in synchrony with the outside world
Natural light provides the input to this system, setting the SCN to the correct time in a process called photoentrainment
The SCN then uses this information to coordinate activity of circadian rhythms throughout the body

Question 4

Circadian Rhythms
Examples

Answer 4

Sleep/Wake Cycle
Core Body Temperature
Hormone Production

Question 5

Circadian Rhythms
Examples
Sleep/Wake Cycle

Answer 5

Light and darkness are external signals that determine when we need to sleep/wake
Rhythm dips and rises at different times of the day
Release of melatonin from pineal gland is at peak during dark hours
Melatonin induces sleep - suppressed by light
Internal circadian rhythm mains cycle of 24-25 hours, even without natural light

Question 6

Circadian Rhythms Evaluation Points

Answer 6

Practical Applications
Cziesler et al. (1999) - Natural Light
Cziesler et al. (1999) - Individual Differences
Individual Difference
Artic Studies

Question 7

Circadian Rhythms Evaluation
Practical Applications
Positive

Answer 7

Chronotherapeutics
Time patients take medication is important
Essential that right concentration is released in target area at time drug is needed
E.g. risk of heart attacks is greatest during early morning
Medications have been developed that are taken before person sleeps but not released until vulnerable time of 6:00am

Question 8

Circadian Rhythms Evaluation
Cziesler et al. (1999) - Natural Light
Negative

Answer 8

Research has not isolated people from artificial light, because it was believed only natural light affected circadian rhythms
More recent studies suggest this is not true
Cziesler et al. (1999) altered participant’s circadian rhythms down to 22 hours and up to 28 hours using artificial light alone

Question 9

Circadian Rhythms Evaluation
Cziesler et al. (1999) - Individual Differences
Negative

Answer 9

Individual differences in length of circadian rhythm
One research study found that cycles can vary from 13 to 165 hours

Question 10

Circadian Rhythms Evaluation
Individual Differences
Negative

Answer 10

When rhythm reaches peak
Morning people prefer to rise early and go to bed early whereas evening people prefer to rise late
Shows circadian rhythm differs for all

Question 11

Circadian Rhythms Evaluation
Artic Studies
Negative

Answer 11

Show normal sleeping patterns despite prolonged exposure to light during summer months
Suggests that there are occasions where the exogenous zeitgebers of light may have very little bearing on our internal biological rhythms