Circadian Rhythms Flashcards
What are biological rhythms?
Distinct patterns of changes in body activity that conform to cyclical time periods.
What is a circadian rhythm?
A type of biological rhythm that recurs approximately every 24 hours, which regulates a number of body processes. Light and heat reset the rhythm
What are the 3 main body processes circadian rhythms regulate?
- Sleep-wake cycle 2. Core body temperature 3. Hormone production
What do we mean by a ‘free-running’ sleep-wake cycle?
It will maintain a cycle of about 24-25 hours even in the absence of external cues
Name the 2 research studies that showed support for a ‘free-running’ circadian rhythm?
Michel Siffre’s cave study (1962)
Aschoff and Weaver
Describe Michel Siffre’s cave study
x He spent several extended periods underground with no external cues to guide his rhythms such as clocks or daylight
x Found that his ‘free-running’ circadian rhythm was 25 hours.
x Shows that we have an internal rhythm which guides our sleep-wake cycle in the absence of external cues.
Describe Aschoff and Weaver’s study
A group of participants spent 4 weeks in a WW2 bunker deprived of natural light. All but one of the participants displayed a circadian rhythm of between 24-25 hours.
How does our circadian rhythm control release of hormones?
x Controls release of melatonin
x During darkness- high levels of melatonin released to make us feel sleepy
x When its light melatonin drops to wake us up
How does our circadian rhythm control our core body temperature?
x Drop in body temp. makes you feel sleepy (between 2 and 4pm and at 4.30am).
X Body temp. rises towards last hours of sleep to promote alertness first thing in the morning
2 strengths for circadian rhythms
Practical application to shift work:
Knowledge of circadian rhythms has given researchers a better understanding of the adverse consequences that can occur as a result of their disruption= desynchronisation.
E.g Boivin found night workers engaging in shift work, experience a period of reduced concentration around 6am resulting in more mistakes and accidents.
Thus, research into the sleep/wake cycle may have economic implications in terms of how to best manage worker productivity.
Practical application to drug treatments
One real-world application of circadian rhythms is chronotherapeutic- the study of how timing affects drug treatments.
There are certain peak times during the day or night when drugs are likely to be at their most effective. This has led to the development of guidelines to do with the timing of drug dosing for a whole range of medications such as anticancer, cardiovascular, anti-epileptic etc.
1 limitation for circadian rhythms
Individual differences:
Cycle length: Research has found that circadian cycles can vary from 13 to 65 hours.
Cycle onset: Individuals appear to be innately different in terms of when their circadian rhythms reach their peak.
This explains why some people prefer to rise early and go to bed early, whereas others prefer to wake late and go to bed later.
