Circadian rhythms

Circadian rhythms ao1 points

1. Circadian rhythms are biological cycles lasting about 24 hours, such as the sleep–wake cycle or body temperature regulation.

2. Circadian rhythms are controlled by endogenous pacemakers and exogenous zeitgebers. 

3. Endogenous pacemakers are our body’s internal biological clock. The suprachiasmatic nucleus (SCN) in the hypothalamus acts as the main internal biological clock, controlling the pineal gland and release of melatonin. 

4. Another example of an endogenous pacemaker is the pineal gland which is a small structure in the brain that secretes the hormone melatonin whic in turn regulates many of our biological rhythms.
   

5. Exogenous zeitgebers are external cues, like light and social activity, that help synchronise the body’s internal clock with the environment.
   
   

6.  Light is detected by retinal cells in the eye and information is sent to the SCN, which adjusts melatonin release to regulate sleep and wakefulness.
   
   

7.  The SCN signals the pineal gland to release melatonin during darkness, causing drowsiness, and suppresses it in daylight to promote wakefulness.
   
   

8. The sleep–wake cycle typically runs on a 24-hour rhythm, with sleepiness peaking at night and alertness highest during the day.
   
   

9.  When Michel Siffre lived underground with no light cues, his sleep–wake cycle extended to about 25 hours, showing the rhythm is endogenous but influenced by light.
   
   

10.  Circadian rhythms vary between people — some are “morning types” (larks) who prefer early activity, while others are “evening types” (owls) who function better later in the day

supporting reserach for circadina rhythms

Point: One strength of research into circadian rhythms is the supporting evidence from Siffre’s cave study.
Evidence: Siffre lived in a cave for several months without natural light or external cues and his sleep–wake cycle extended to between 25 and 32 hours.

 Explanation: This shows that circadian rhythms are endogenous but can be influenced by external factors like light.
Link: Therefore, Siffre’s findings support the idea that our biological clock operates independently but is entrained by environmental cues.

controlled condtions

Point: Another strength is that studies on circadian rhythms are often conducted under highly controlled conditions.
Evidence: For example, researchers can carefully control light exposure, temperature, and sleep duration in laboratory experiments.
Explanation: This allows for the isolation of specific variables affecting circadian rhythms, making the research more reliable and replicable.
Link: As a result, the use of lab studies increases the internal validity of research into circadian rhythms.

limited generalisability

Point: However, a weakness is that much research into circadian rhythms relies on case studies or small samples.
Evidence: Siffre’s study, for instance, only involved one participant, and he later found that his rhythms changed with age.
Explanation: This suggests that individual differences such as age, lifestyle, or gender may influence circadian patterns, making it difficult to generalise findings.
Link: Therefore, conclusions drawn from such studies may lack population validity.

practical applications

Point: A major strength of circadian rhythm research is its real-world applications, especially for shift work.
Evidence: Research has shown that disruption of the sleep–wake cycle in shift workers can lead to reduced concentration, accidents, and health issues.
Explanation: Understanding circadian rhythms has helped employers design better shift patterns and use light exposure to improve alertness.
Link: This means circadian rhythm research has useful practical value in improving workplace safety and wellbeing.