Biological Rhythms: Circadian Rhythms

Question 1

Biological Rhythms

Answer 1

Biological rhythms are periodic activity, governed by:
-Internal body clock (endogenous pacemaker)
-External changes in the environment (Exogenous Zeitgebers)
Some rhythms occur many times a day (ultradian). Others take more than a day to complete (infradian)

Question 2

Circadian Rhythm

Answer 2

-Lasts about 24 hours.
-There are several important types of circadian rhythms such as the sleep/wake cycle

Question 3

Sleep/Wake Cycle

Answer 3

-Governed by internal and external mechanisms
-The basic rhythm is governed by the suprachiasmatic nucleus (SCN). The SCN lies just above the optic chiasm which provides information from the eyes about the light.
-Exogenous zeitgebers (light) can reset the SCN

Question 4

Endogenous Pacemakers

Answer 4

A biological clock ‘left to its own devices’ without the influence of external stimuli (e.g. light) is called ‘free running’

Question 5

Exogenous Zeitgeber

Answer 5

The fact we feel drowsy when it is night-time and alert during the day shows the effect of daylight.

Question 6

Siffre

Answer 6

-French caver Siffre spent long periods in dark caves to examine the effects of free-running biological rhythms- two months (in 1962) and six months (in the 1970s).
-In each case study, Siffre’s free-running circadian rhythm settled down to about 25 hours.
-Importantly, he did not have a regular sleep/wake cycle.

Question 7

Aschoff + Wever

Answer 7

-A group of participants spent four weeks in a World War 2 bunker deprived of natural light.
-All but one (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.
- Siffre’s experience and the bunker study suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with our 24-hours day (e.g. daylight hours, mealtimes, etc.).

Question 8

Folkard Et Al.

Answer 8

-Studied a group of 12 people who lived in a dark cave for three weeks, going to bed when the clock said 11:45 pm and waking when it said 7:45 am.
-The researchers gradually speeded up the clock (unbeknown to the participants) to a 22-hour day.
-Only one participants comfortable adjusted to the new regime. This suggests the existence of a strong free-running circadian rhythm not controlled by exogenous zeitgebers.

Question 9

A03 (Application To Shift Work)

Answer 9

E- Shift work creates desynchronisation of biological rhythms. Boivin et al. found shift workers experience a lapse of concentration around 6 am (a circadian trough) so accidents are more likely. Research also suggests a link between shift work, and poor heath, with shift workers three times more likely to develop heart disease.
E- Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage shift work.

Question 10

Counterpoint

Answer 10

-The research is correlational, therefore desynchronisation may not be the cause of observed difficulties. For example, Solomon concluded that high divorce rates in shift workers might be due to missing out on important family events.
-This suggests that it may not be biological factors that create the adverse consequences associated with shift work.

Question 11

A03 (Real-World Application To Medical Treatment.)

Answer 11

E- Circadian rhythms co-ordinate the body’s basic processes (e.g. heart rate, hormone levels) with implications for chronotherapeutics (timing medication to maximise effects on the body). Aspirin reduces heart attacks, which are more likely in the morning. Bonten et al. found taking aspirin is most effective last thing at night.
E- This shows that circadian rhythm research can help increase the effectiveness of drug treatments.

Question 12

A03 (Generalisations Are Difficult To Make)

Answer 12

E- Studies of the seep/wake cycle often use small groups of participants or even single individuals. Participants may not be representative of the wider population and this limits making meaningful generalisations. Siffre observed that his internal clock ticked much more slowly at 60 than when he was younger.
E- This suggests that, even when the same person is involved, there are factors that may prevent general conclusions being drawn.

Question 13

A03 (Shifting The School Day)

Answer 13

E- Research shows benefits for teenagers’ academic and behavioural performance when lessons start later in the day. However, a later start is disruptive for parents and teachers, and teenagers may simply stay up later and still be exhausted.
E- This suggests changing the school day may not be practical even though it may be desirable.