🟢 Biopsychology - Circadian Rhythms Flashcards
What are biological rhythms
Repeating patterns of changes that occur over a set period of time
What is a circadian rhythm
A rhythm that occurs once per 24 hours for example sleep wake cycle
What 2 things are biological rhythms regulated by
- Endogenous pacemaker
- Exogenous zeitgebers
What is an exogenous zeitgeber
External factors in the environment which reset out biological clocks
E.g clocks
What is an endogenous pacemaker
The body’s internal body clock that regulate biological rhythms
What is the SCN
Suprachiasmatic nucleus - the SCN is a tiny region in the brain’s hypothalamus that controls circadian rhythms—basically, your internal body clock. It receives light information from the eyes and helps regulate sleep, hormone production, and other daily cycles.
Primary endogenous pacemakers which are influential in circadian rhythms
Where does the word circadian come from
Circa (about)
Dies (a day)
What is the purpose of circadian rhythms
Optimises an organisms physiology and behaviour to best meet the varying demands of the day/night cycle
How does light cause wake up
When light first comes up in the morning, even with eyes closed, it is detected. SCN receives information about the light via the optic nerve. Signals then sent from SCN to the pineal gland. This will reduce melatonin allowing us to awaken
Animal study on SCN
Patricia DeCoursey et al (2000)
Martin Ralph et al (1990)
Patricia DeCoursey et al (2000)
- destroyed the SCN connections in the brain of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
- RESULTS: The sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed for predators (due to them being awake and vulnerable to be attacked when asleep)
Martin Ralph et al (1990)
- Bred ‘mutant’ hamsters with a 20 hour sleep/wake cycle
- when SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours
- study emphases role of the DCN in establishing and maintaining the circadian sleep wake cycle
Study on endogenous pacemakers
Michael Siffre (1962)
Michael siffre (1962)
- tested internal body clock
- spent 61 days and nights underground in a cave with no Exogenous zeitgebers (light, clocks, radio)
- only influence was endogenous pacemakers
- emerged 17th September and thought it was the 20th August
- natural rhythms extended to over 24 hours
- supports endogenous pacemakers
Conclusion of Siffre study
- without zeit sleep wake circadian rhythm extends to 25-32 hours. Circadian rhythm more stable at about 25 hours
- supports assumption that endogenous pacemakers exert an influence on circadian rhythms
- showing the strengths of the circadian rhythm as a free running cycle
Siffre (1975)
Found that the absence of external cues significantly altered his circadian rhythm
What is made at the pineal gland and what does it allow
Melatonin. The pathway allows the SCNA to control the manufacture and secretion of melatonin
Melatonin = controls sleep
Study on jet lag
Kelvin and Wegmann (1974)
Klein and Wegmann (1974)
The circadian rhythms of travellers adjusted more quickly if they went outside more at their destination and were exposed to social cues of their new time zones. Meal times and social activities have a role as Zeit
Practical application of shift work
● Given researchers a better understanding of the adverse consequences that can occur due
to disruption.
● Shift workers experience a period of reduced concentration (circadian trough) at around 6 in
the morning making mistakes more likely.
● Researchers suggested a correlation between shift work and poor health- shift workers are 3
times more likely to develop heart disease.
● Economic implications in terms of how to manage worker productivity.
Practical application to do with drugs
Chrontherapeutics - time drugs are taken / delivered
