Biological Rhythms: Carcadian Rhythms

Question 1

What are all biological rhythms governed by?

Answer 1

The body’s internal biological ‘clocks’ - endogenous peacemakers
The external changes in the environment - exogenous zeitgebers

Question 2

Which rhythms occur in the day?

Answer 2

Ultradian rhythms

Question 3

Which rhythms take longer than a day to complete?

Answer 3

Infradian rhythms

Question 4

What are circadian rhythms?

Answer 4

Rhythms that last for around 24 hours

Question 5

What are two examples of circadian rhythms?

Answer 5

Sleep/ wake cycle and core body temperature

Question 6

When we feel drowsy at nighttime and alert during the day what does this demonstrate the effect of?

Answer 6

Daylight

Question 7

What is daylight?

Answer 7

An important exogenous zeitgeber

Question 8

What is the sleep/ wake cycle also governed by other than daylight?

Answer 8

An internal pacemaker (endogenous)

Question 9

What is the ‘biological clock’ called?

Answer 9

Suprachiasmatic nucleus

Question 10

What does the SCN lay above and what does this provide?

Answer 10

Lies just above the optic chasm which provides information from the eye about light

Question 11

What can reset the SCN?

Answer 11

Exogenous zeitgebers

Question 12

What did Siffre do?

Answer 12

Spend several extended periods underground to study the effects on his own biological rhythms

Question 13

What was Siffre deprived of underground and what did he have access to?

Answer 13

Deprived of: exposure to natural light and sound
Access to: adequate food and drink

Question 14

How long did Siffre spend in the cave the first time and what month did he beehive it to be?

Answer 14

Spent 2 months in the caves of the southern alps and came out believing it to be mid-august when it was actually September

Question 15

When Siffre did the same experiment 10 years later how long did he spend in the cave?

Answer 15

6 months in a Texan cave

Question 16

In each case what did his ‘free running’ biological rhythm settle down to?

Answer 16

Just beyond 24 hours though he did fall asleep and wake up on a regular schedule

Question 17

What did Aschoff and Rutger research?

Answer 17

A group of participants who spent 4 weeks in a WW2 bunker deprived of natural light

Question 18

What were the findings of Aschoff and Rutgers’ experiment?

Answer 18

All but one displayed a circadian rhythm between 24 and 25 hours

Question 19

What do both study’s suggest about the natural sleep/wake cycle?

Answer 19

It may be slightly longer than 24 hours but that is entrained by exogenous zeitgebers associated with our 24 hour day

Question 20

What did Folkard et al study?

Answer 20

A group of 12 people who agreed to live in a dark cave for 3 weeks

Question 21

What time did participants in Folkard et als’ study sleep and wake up?

Answer 21

Slept when the clock said 11:45 pm and woke when the clock said 7:45 am

Question 22

What did researchers do over the course of Folkard et als’ study?

Answer 22

Gradually sped up the clock so an apparent 24 hour day eventually lasted only 22 hours

Question 23

What were the findings of Folkard et als’ study?

Answer 23

Only one of the participants could adjust to the new regime which suggests the existence of a strong free-running circadian rhythm cannot be easily overridden by exogenous zeitgebers

Question 24

Provides an understanding of the consequences that occur when they are disrupted

Answer 24

• e.g. night workers engaged in shift work experience a period of reduced concentration around 6 am meaning mistakes and accidents are more likely.
• research has also pointed to a relationship between shift work and poor health
• shift workers are 3x more likely to develop heart disease than people who work more typical work patterns
• this shows that research into the sleep/wake cycle has real-world economic implications in terms of how best to manage worker productivity

Question 25

Used to improve medical treatments

Answer 25

• circadian rhythms co-ordinate a number of the body’s basic processes e.g. heart rate
• these rise and fall during the day which has led to the field of chronotherapeutics which is how medical treatment can be administered in a way that corresponds to a persons biological rhythms
• e.g. aspirin to treat heart attacks is most effective when taken last thing at night
• this shows that circadian rhythms research can help increase the effectiveness of drug treatment

Question 26

Generalisation is difficult

Answer 26

• studies are based on a very small sample of participants
• therefore the sleep/wake cycle may vary widely from person to person
• Research by Czeisler et al found individual differences in sleep/wake cycles varying from 13 to 65 hours
• also a study by Duffy et al revealed that some people have a natural preference of going to bed early and getting up early whereas others prefer the opposite
• this means that it is difficult to use research data to discuss anything more than averages which may be meaningless

Question 27

Poor control in studies

Answer 27

• participants were deprived of natural light but had access to artificial light
• it was assumed this would have no effect on the free-running biological rhythm
• however in tests Czeisler et al was able to adjust participants circadian rhythms from 22 hours to 28
• therefore use of light may be analogous to participants taking a drug that resets their biological clock