Biological rhythms: Circadian rhythms

Question 1

When is melatonin released?

Answer 1

When light levels drop.

Question 2

What are endogenous pacemakers?

Answer 2

The body’s internal clock, most importantly the superchiasmatic nucleus (SCN).

Question 3

What is arguably the most important endogenous pacemaker?

Answer 3

Superchiasmatic nucleus (SCN).

Question 4

What two things have an influence on the way which biological rhythms act?

Answer 4

Endogenous Pacemakers and Exogenous Zeitgebers.

Question 5

Dissect the origins of the term ‘circadian rhythms’?

Answer 5

'circa' = about
'diem' = day

Question 6

What are circadian rhythms?

Answer 6

A biological cycle which regulates over a 24-hour cycle.

Question 7

Give two examples of circadian rhythms:

Answer 7

The sleep / wake cycle and the care body temperature.

Question 8

Crudely speaking, what is the sleep / wake cycle?

Answer 8

We go to bed when it is dark and we get up when it is light.

Question 9

What are exogenous zeitgebers?

Answer 9

External factors to do with the environment, most importantly light levels.

Question 10

What is the role of the SCN?

Answer 10

It detects light levels all the time, even when we are sleeping.

Question 11

What effect does melatonin have on the body?

Answer 11

Melatonin makes us tired and drowsy.

Question 12

Are social cues an example of exogenous zeitgebers or endogenous pacemakers?

Answer 12

Exogenous zeitgebers.

Question 13

Who conducted the famous ‘cave study’?

Answer 13

Michel Siffre (1960’s)

Question 14

If you left your body to run without any exogenous zeitgebers, what is the natural cycle time?

Answer 14

About 25 hours, but is different for each person.

Question 15

What research has shown the human circadian rhythm is closer to 25 hours than to 24?

Answer 15

Michel Siffre (1960's).
Aschoff and Wever (1976).

Question 16

What is arguably the most important exogenous zeitgeber?

Answer 16

Light levels.

Question 17

Describe the research of Michel Siffre:

Answer 17

Siffre spent several extended periods underground to study the effects on his own biological rhythms. Siffre found his free-running clock become 25-hours long when he was deprived of natural light (an exogenous zeitgeber).

Question 18

Describe the study of Folkard et al (1985):

Answer 18

He had 12 participants live in a cave for 3 weeks, they were told to go to bed when the clock said 11:45pm and wake up at 7:45am. During the study, the researchers sped up the clock so there was only 22 hours in the day. Only one participant was able to adapt to this 22-hour day, which suggests exogenous zeitgebers do not override free running rhythms.

Question 19

Describe the circadian rhythm which naturally occurs in the core body temperature of a human?

Answer 19

The lowest is at 4am (36°) and highest at 6pm (38°), at 5/6am the temp creeps up as you wake up to increase alertness.

Question 20

Describe the research of Aschoff and Wever:

Answer 20

A group of participants spent four weeks in a WWII bunker with no natural light, all but one of the participants had a shifted circadian rhythm.

Question 21

AO3 - Practical application (shift work).

Answer 21

Knowledge of circadian rhythms has given researchers a better understanding of desynchronisation. Night workers engaged in shift work experience a period of reduced concentration around 6 in the morning meaning mistakes and accidents are more likely. Thus, research into the sleep / wake cycle may have economic implications in terms of how best to manage worker productivity.

Question 22

AO3 - Practical application (drug treatments).

Answer 22

Circadian rhythms have an affect on biological processes and pharmokinetics. Research has revealed that there are certain peaks when drugs are likely to be most effective. This has led to the development of guidelines related to timing and dosages of medications.

Question 23

AO3 - Sample sizes.

Answer 23

Studies of the sleep / wake cycle typically involve small groups of participants (Aschoff and Wever) or case studies (Siffre). This means that the sample is not representative of the wider population and therefore meaningful generalisations cannot be made.

Question 24

AO3 - Poor control in studies.

Answer 24

Participants in experiments such as Siffre’s cave or Aschoff and Wever had no access to natural light, but they still had access to artificial light. It was assumed that artificial light would have no effect on biological rhythm. However, in tests Czeisler (1999) was able to adjust participants’ circadian rhythm s from 22 to 28 hours using dim lighting.

Question 25

AO3 - Individual differences.

Answer 25

In studies of the sleep / wake cycle, the cycles have been seen to vary from 13 to 65 hours. A further study also revealed some people display a natural preference for going to bed early and others the opposite, this decreases generalisability.

Question 26

What is pharmokinetics?

Answer 26

The action of drugs on the body and how well they are absorbed and distributed.