Biological Rhythms: Circadian Rhythms Flashcards
What are circadian rhythms?
- Biological rhythms that last for around 24 hours
- Two examples of circadian rhythms are the sleep/wake cycle & core body temperatures
What are all biological rhythms governed by?
- By 2 things:
- The bodys internal biological ‘clocks’- called endogenous pacemakers
- And external changes in the environment known as exogenous zeitgebers
What are endogenous pacemakers?
- Internal body clocks which help regulate the sleep-wake cycle e.g. the suprachiasmatic nucleaus which is located in the central part of your brain & is most influential pacemaker on the body
Another e.g. of an EP is the pineal gland that works with the SCN - Contains light sensitive cells - When light is sensored melatonin production is inhibited, when light levels fall melatonin production increases
How is the sleep/wake cycle governed?
- By an internal (endogenous) pacemaker- A ‘biological’ clock called the suprachiasmatic nucleaus (SCN)
- The SCN lies just above the optic chiasm which provides information from the eye about light
- Exogenous zeitgebers (light) can reset the SCN
What is meant by ‘entrainment’
- The adjustment of the body clock to fit the environment
- This helps people to adjust when changing time zones, by using external cues to inform when they sleep & when they wake up
What research was carried out on the Suprachiasmatic nucleaus (SCN)?
Ralph et al (1990)
- Found that when the SCN of hamsters who displayed unusual sleep/wake cycles, was removed & placed into rats, the rats then showed an abnormal cycle of 20 hours
What other research was conducted on the SCN?
de Coursey et al (2000)
- Conducted a field experiment, leisoned SCNS of half of the chipmunks & released all the chipmunks into the nature reserve
- After some weeks, most of the leisoned chipmunks had been killed by weasels.
- This was because they wern’t asleep in their burrows at night before the weasels heard & caught them
- This indicates that the SCN is a physical part of the brain which plays a pivotal role in the internal clock, suggesting that the theory holds reliability
What is the issue with the research conducted on the SCN?
- Much of the research has been carried out by animals
- Research suggests that animal brain structures are physiologically different from humans & therefore the SCN might not be located in the same area/span the same amount of the brain
- Means we cannot generalise findings on influence of SCN on internal body of animals to humans
Give one strength for the role of endogenous pacemakers.
- The role of EPs in circadian rhythms is very strong.
- For example, people living in the artic cirlce, where there is no light for many months of the year & then no darkness during the summer, have similar sleep-wake cycles throughout the year
- This usggests that our sleep wake cycle is largely dictated by internal processes
What are Exogenous Zeitgebers?
- External cues, including light, that help to regulate the internal biological clocks.
- e.gs include: the biological clock is reset each day by cues in the environment like the light cues of sunrise & sunset
What positive research has been conducted on exogenous zeitgebers?
Bendetti et al (2007)
- EZ’s provide us with an intervention for those suffering from depression.
- Found that light therapy reduced 2/3rds of patients depression inventory scores by 50%
- Light therapy works by reducing feelings of fatigue by supressing melatonin secretion.
- Suggests the light is an EZ which has an effect on quality of sleep in those who are mentally ill
- This knowlege has provided real-world application to invent treatment for those suffering from the inability to function adequately
What research is there to show that exogenous zeitgebers have an important influence over endogenous pacemakers?
Micheal Siffre:
- EZ’s have an important influence of EP’s, this was shown in Micheal Siffres study as in the cave with hi he had a lantern.
- Which unbeknown to him at the time would have affected this circadium rhythm due to the light supressing his melatonin secretion & influencing his internal body clock
Give another study that can be used to discuss exogenous zeitgebers.
Campbell & Murphy (1998)
- Demonstrated that light may be detected by skin receptor sites on the body even when the same information is not recieved by the eyes
- 15 ppts were woken at various times & a light pas was shone on the back of their knees
- Researchers managed to produce a deviation in the ppts usualy sleep/wake cycle of up to 3 hours in some cases!
Suggests that light is a powerful exogenous zeitgeber that need not necessarily rely on the eyes to exert its influence on the brain
What was Siffres Cave Study?
- Micheal Siffre- self-styled caveman who has spent several extended periods underground to study his own biological rhythms
- Deprived of exposure to natural light & sound, but w access to adequate food & drink, Siffre resurfaced in mid september 1962 after 2 months in caves of the Southern Alps.
- A decade later he performed a similar feat but this time for 6 months in a Texan cave
- In each case his ‘free running’ biological rhythm settled down to one that was just beyond the usual 24 hours
- though he did continue to fall asleep & wake up on a regular schedule.
Give one strength of research into circadian rhythms.
- It provides an understanding of the adverse consequences that occur when they are disrupted (desynchronisation)
- For example night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (a circadian trough) meaning mistakes & accidents are more likely
Knutsson (2003)
- Pointed out a relationship between shift work & poor health- shift workers are 3 times more likely to develop heart disease thaan people who work more typical work patterns
This shows that research into sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity.
