Biological Rhythms: Circadian

Question 1

what are biological rhythms

Answer 1

cyclical patterns within biological systems = evolved in response to environmental influences

Question 2

types of biological rhythms, with examples

Answer 2

1. circadian = last for around 24 hrs
   e.g. sleep/wake cycle, body temp
2. ultradian = last less than 24 hrs
   e.g. stages of sleep
3. infradian = lasts more than 24 hrs
   e.g. menstrual cycle, SAD

Question 3

how does the sleep/wake cycle work

Answer 3

body’s biological clock
- controlled by SCN (suprachiasmatic nuclei)
detects the level of light present
= pass info onto pineal gland = regulate melatonin production
= triggers sleep/tiredness or tells body to wake up

light = reset cycle

Question 4

outline Siffre’s research into the sleep/wake cycle (1975)

Answer 4

• spent 6 months in Texan cave, no exogenous zeitgebers, e.g. natural light/sound
• had no idea what time it was
• sleep/wake times, food = monitored
• sleep/waking cycle = erratic at first, then settled into fairly regular cycle of about 25 hours - slightly longer than the 24 hour day regular

Question 5

how does Siffre’s research provide evidence for circadian rhythms

Answer 5

• lack of exogenous zeitgebers in cave = found absence of external cues alters circadian rhythm

Question 6

cons of research into circadian rhythms

Answer 6

CONS
= low generalisability, individual differences
- use of small sample sizes in research
- sleep/wake cycles appear to vary widely from person to person (13-65hrs found Czeisler et al)

• ppl have natural pref for early bedtime/wake up and vice versa = morning vs night person

= suggest research data to discuss anything more than averages, is meaningless

Question 7

pro of research into circadian rhythms

Answer 7

= help increase effectiveness of drug treatments
- CR co ordinate several basic processes, e.g., heart rate, digestion, hormone levels

(chronotherapeutics = administering medical treatment to correspond with biological rhythms)

e.g., aspirin (for heart attacks) most effective to take last thing at night = reduce blood platelet activity = reduce heart attack risk
- heart attacks most likely to occur first thing in morning, so aspirin taking time matters

= improve medical treatments

Question 8

further pro of research into circadian rhythms

Answer 8

provide understanding of consequences caused by desynchronisation

boivin at al = nightworkers doing shift work experiences reduced conc. around 6am = increase likelihood of mistakes/accidents

other research = shift workers 3x more likely to develop heart disease than ppl with typical work patterns

= research into CR has practical value
- employers advised not to allocate night shift work to employees for long periods of time to minimise negative consequences

Question 9

2 influences on biological rhythms

Answer 9

Endogenous pacemakers
= internal body clocks, keep biological processes to time

Exogenous zeitgebers
= external cues, entrain internal body clock

Question 10

factors affecting sleep/wake cycle

Answer 10

endogenous
= SCN ‘master clock’

exogenous
= light (natural or artificial)
= social cues, e.g., meal times, others’ bedtimes
= clocks
= jet lag/shift work

Question 11

entrainment meaning

Answer 11

exogenous zeitgebers alter body clock to match environment

Question 12

EVAL of exogenous zeitgebers

Answer 12

PRO
Skene & Arendt (2007)
- pointed out most blind people who still have some light perception = normal circadian rhythms of 24 hours
- blind people with no light perception = display irregular circadian rhythms

= demonstrates the importance of light in terms of the internal sleep-wake cycle

Question 13

EVAL of endogenous pacemakers

Answer 13

PRO
Research Support
= Morgan
- bred hamsters so had circadian rhythms of 20 hours rather than 24
- transplanted SCN neurons from abnormal hamsters into the brains of normal hamsters
= subsequently displayed the same abnormal circadian rhythm of 20 hours

= demonstrate significance of the SCN and how endogenous pacemakers are important for biological circadian rhythms

COUNTER
- animal study
= behavioural discontinuity
= cannot extrapolate onto humans

Question 14

con of both endo/exo explanations

Answer 14

Biologically Reductionist

= behaviourist approach would suggest bodily rhythms influenced by other people/social norms
- i.e. sleep occurs when dark because that is the social norm = wouldn’t be socially acceptable for a person to conduct daily routines during night

= can criticise for being reductionist = only considers singular biological mechanism, fails to consider other widely divergent viewpoints