Biological rhythms: Circadian rhythms

Question 1

What is a biological rhythm?

Answer 1

Distinct patterns of changes in body activity that conform to cyclical time periods. Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes to the environment (exogenous zeitgebers).

Question 2

What is a Circadian rhythm?

Answer 2

Biological rhythms, subject to a 24 hour cycle, which regulate a number of body processes such as the sleep/wake cycle and changes in core body temperature.

Question 3

Who is subject to a biological rhythm?

Answer 3

All living organisms (plants, animals and people).

Question 4

What are the 2 things that biological rhythms are governed by?

Answer 4

-Endogenous pacemakers.
-Exogenous zeitgebers.

Question 5

What is an endogenous pacemaker?

Answer 5

The body’s internal biological clocks.

Question 6

What are exogenous zeitgebers?

Answer 6

External changes in the environment .

Question 7

What are the two examples of circadian rhythms?

Answer 7

-Sleep/wake cycle.
-Core body temperature.

Question 8

What do the effects of daylight on our sleep/wake cycle look like?

Answer 8

Feeling drowsy when it’s night-time and alert during the day.

Question 9

What endogenous pacemaker is the sleep/wake cycle governed by?

Answer 9

A biological clock called the suprachiasmatic nucleus (SCN).

Question 10

Where is the suprachiasmatic nucleus (SCN) located?

Answer 10

The SCN lies just above the optic chiasm.

Question 11

What does the SCN do?

Answer 11

Provides information from the eye about light.

Question 12

What does the exogenous zeitgeber light have the ability to do to the SCN.

Answer 12

It has the ability to reset the SCN.

Question 13

What does ‘free-running’ mean?

Answer 13

When a biological clock is ‘let to its own devices’ without the influence of external stimuli such as light.

Question 14

Write a paragraph describing Siffre’s cave study.

Answer 14

-Siffre is a self-styles caveman who has spent several extended periods underground to study the effects on his own biological rhythms.
-Deprived of exposure to natural light and sound, but with access to food and drink, Siffre resurfaced in mid-September 1962 after 2 months in the Southern Alps caves.
-A decade later he performed a similar feat but this time for 6 months in a Texan cave.
-In both cases his ‘free running’ biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule.

Question 15

Write a paragraph describing Aschoff and Wever’s (1976) study.

Answer 15

-Convinced a group of participants to spend 4 weeks in a World War 2 bunker deprived of natural light.
-All but one participant (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.

Question 16

What do both Siffre’s cave study and Aschoff and Wever’s WW2 bunker study show?

Answer 16

They both suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but that it is entrained by exogenous zeitgebers associated with our 24 hour day.

Question 17

Write a paragraph describing Folkard et al’s dark cave study.

Answer 17

-Folkard et al. (1985) studied a group of 12 people who agreed to live in a dark cave for three weeks, retiring to bed when the cock said 11:45pm and rising when it said 7:45am.
-Over the course of the stud the researchers gradually sped up the clock (without the participants knowing) so an apparent 24 hour day was actually only 22 hours.
-Only one participant was able to comfortably adjust to the new regime.
-This would suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by exogenous zeitgebers.

Question 18

Write a PEEL paragraph about the strength of circadian rhythms:
Shift work.

Answer 18

P: One strength of research into circadian rhythms is that it provides an understanding of the adverse consequences that occur when they are disrupted.
E: Night workers engaged in shift work experience a period of reduced concentration around 6 in the morning meaning mistakes and accidents are more likely (Boivin et al. 1996).
E: Research has also pointed out a relationship between shift work and poor health: shift workers are 3 times more likely to develop heart disease than people who work more typical work patterns (Knutsson 2003).
L: This shows that research into the sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity.

Question 19

Write a PEEL paragraph about the counterpoint to the strength of circadian rhythms:
Shift work.

Answer 19

P: However, studies investigating the effects of shift work tend to use correlational methods.
E: This means it is difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects.
E: There may be other factors. E.g. Solomon (1993) concluded that high divorce rates in shift workers might be due to the strain of deprived sleep and other influences such as missing out on important family events.
L: This suggests that it may not be biological factors that create the adverse consequences associated with shift work.

Question 20

Write a PEEL paragraph about the strength of circadian rhythms:
Medical treatment.

Answer 20

P: A strength of research into circadian rhythms is that it has been used to improve medical treatments.
E: Circadian rhythms co-ordinate a number of the body’s basic processes such as heart rate and digestion, these rise and fall during the course of a day which has led to the field of chronotherapeutic (how medical treatment can be administered in a way that corresponds to a person’s biological rhythm).
E: For example, aspirin as a treatment for heart attacks is most effective taken last thing at night as heart attacks are most likely to occur early in the morning, so the timing of taking aspirin matters.
L: This shows that circadian rhythms research can help increase the effectiveness of drug treatments.

Question 21

Write a PEEL paragraph about the limitation of circadian rhythms:
Individual differences.

Answer 21

P: One limitation of research into circadian rhythms is that generlisations are difficult to make.
E: The cave/ bunker studies on circadian rhythms are based on very small samples of participants, sleep/wake cycles very widely from person to person. Czeisler et al (1999) found individual differences in sleep/wake cycles varying from 13 to 65 hours.
E: In addition, Duffy et al (2001) revealed that some people have a natural preference for going to bed and rising early (known as ‘larks) where as the opposite (‘owls’).
L: This means that it is difficult to use the research data to discuss anything more than averages, which may be meaningless.