Circadian Rhythms

Question 1

biological rhythms

Answer 1

• distinct patterns of change within the body activity
• they conform to cyclical time periods
• influenced by endogenous pacemakers (internal body clocks) and exogenous zeitgebers (external changes)

Question 2

circadian rhythms

Answer 2

• 24 hours long

- regulate several body processes, e.g. core body temperature and sleep/wake cycle

Question 3

hormones affected by circadian clock

Answer 3

• melatonin and cortisol

Question 4

sleep/wake cycle affected by daylight

Answer 4

• daylight is a very important exogenous zeitgeber
• the affect that it has on out sleep/wake cycle is demonstrated by people feeling sleepy at night and alert in the daytime

Question 5

Sleep/wake cycle breakdown

Answer 5

• core temperature reaches minimum at around 4:30am when we are asleep
• melatonin starts to be produced around 8/9pm, and stops around 7/8am
• deepest sleep is at 2/3am
• there is also a shorter and shallower period of sleepiness at 2/3pm

Question 6

Siffre’s cave study - aim

Answer 6

• wanted to investigate the effects of a lack of exogenous zeitgebers on our sleep/wake cycle
• he was studying ‘free-running’ circadian rhythms

Question 7

Siffre’s cave study - method

Answer 7

• Siffre spent multiple extended periods underground, in a cave
• he was deprived of expose to natural light and sound
• he did still have food and water
• he re-surfaced after two months, in mid-september of 1962
• however, he believed it to be mid-August
• a decade later he did a similar experiment, this time for 6 months in Texas

Question 8

Siffre’s cave study - findings

Answer 8

• he found that his sleep/wake cycle settled at around 25 hours, as opposed to being 24

Question 9

Wever and Aschoff (1976) - aim

Answer 9

• investigate sleep/wake cycle without any exogenous zeitgebers

Question 10

Wever and Aschoff (1976) - method

Answer 10

• group of participants stayed in a WW2 bunker for 4 weeks, without any natural light

Question 11

Wever and Aschoff (1976) - findings

Answer 11

• the sleep/wake cycle of all of the participants seem to increase to between 24 and 25 hours, bar one, whose cycle increased to 29hrs
• suggests that natural sleep/wake cycle is actually longer than 24hrs, but is reduced by exogenous zeitgebers, e.g. mealtimes, daylight hours, conditioning, clocks, etc.

Question 12

Folkard et al. (1985)

Answer 12

• study with group fo 12 people
• they lived in a cave for 3 weeks
• they were instructed to go to bed when the clock showed 23:45 and wake when it showed 7:45
• the clock was gradually sped up by the researchers as the study went on, unbeknownst to the participants
• the once 24hr day was reduced to 22hrs
• however, only one of the 12 participants was comfortable with the shorter cycle
• this suggests that the free-running rhythm can’t easily be altered by changing exogenous zeitgebers
• therefore we shouldn’t overestimate the influence of environment cues on our internal body clock

Question 13

(+) EVAL - practical application to shift work

Answer 13

• there is a greater understanding of the negative consequences which may occur as a result of disrupting circadian rhythms thanks to the studies done
• desynchronisation is the name given to this disruption
• night workers on shifts may experience reduced concentration around 6am due to chemicals being secreted in line with out sleep/wake cycle
• this could mean that accidents are much more likely to happen, according to Boivin et al. (1996)
• a correlation between shift work and poor health is suggested by research
• heart disease is 3x more likely to develop in shift workers according to Knutsson (2003)
• this may relate to the stress of adjusting to different sleep/wake patterns and lack of sleep

Question 14

(+) EVAL - practical application to drug treatment

Answer 14

• circadian rhythms co-ordinate heart rate, digestion, hormone levels and other systems
• understanding of circadian rhythms is therefore important to pharmacokinetics, the action of drugs on the body, how well they are absorbed and how well they are distributed
• through research, certain peak times have been identified where drugs are most effective

Question 15

(-) EVAL - use of case studies and small samples

Answer 15

• in all of the studies, a small sample is used, or just one participant
• the generalisability of the findings is affected by this, since the people involved may not be representative of the wider population
• as an example of this, Siffre found that his internal clock was much slower on his earlier study when he was younger compared to later on
• as for siffre’s study, the presence of artificial light may also affect results, acting as an alternative exogenous zeitgeber, as well as others