Circadian Rhythms, EP & EZ

Question 0

Sleep wake cycle

Answer 0

-Regular 24 hour sleep/wake cycle, reset by EZ (external time cues) -eg Light or an alarm clock.
-Evidence of endogenous pacemakers (internal clock)
-ie hormones; control the sleep/wake cycle internally.
-Influence of EZ & EP on sleep studied via isolation studies;
pps are cut of from all external cues that reset the circadian rhythm.

Question 1

3 biological rhythms

Answer 1

• Circadian: repeats approx once every 24 hours
  
  • i.e sleep/wake cycle or body temperature.
• Infradian: repeats less than once a day
  
  • described as seasonal i.e menstrual cycle or SAD.
• Ultradian: repeats more than once every 24 hours
  
  • i.e stages of sleep occur every 90 mins and attention span.

Question 2

Endogenous Pacemakers: SCN

Answer 2

• EP set free running internal rhythms.
• Hypothalamus is main EP involved in controlling biological clock
• Specifically Suprachiasmatic nucleus (SCN) which when damaged in rats it was found their sleep cycle was affected (Zucker et al).
• SCN connected to the eyes = light sensitive.
• Dark at night = SCN activated which activates pineal gland ^secretion of melatonin which induces sleep.
• Light in the morning v melatonin levels causing wakefulness.
• Hence pineal gland & melatonin regulate the sleep/wake cycle.

Question 3

Exogenous Zeitgebers

Answer 3

• light = dominant zeitgeber affecting S/W c
• Exposure to bright light slows down melatonin production.
• Daylight will re-set the biological clock.
• Although light = primary EZ it’s not alone in affecting CR.
• other EZ entrain our biological rhythms are mealtimes, clocks, temperature and social customs.

Question 4

Duffy et al: individual differences

Answer 4

• //Found a case for individual differences in circadian rhythms.
• Morning people prefer to rise early & go to bed early (6am & 10pm) -Evening people prefer going to sleep & wakeup late (10am & 1am) -Showing peoples circadian rhythms could vary from one another.

Question 5

Michael Siffre: EP (underground)

Answer 5

• Michael Siffre case study in which he spent 7 months underground
• Had food, exercise & contact with outside world via phone
• No exogenous cues about it being day or night.
• Sleeping pattern settled at just over 24 hours
• Concluded the sleep cycle is free running when there are no EZ.
• gives V clear evidence for CR controlled by EP thus biology.

Question 6

Campbell et al: Siffre methodological (artificial light)

Answer 6

• Argued that Siffre study flawed methodologically.
• Campbell et al found even artificial light affect circadian rhythms.
• Such a study may have low internal validity as well as low EV
• Not actually measure what intending to measure (absence of EZ)
• R should be used with caution in support of the importance of EP in CR as it could also undermine the explanation.
• //Such studies important; they allow us to demonstrate causal relationships.

Question 7

Morgan: RS (Hamsters SCN)

Answer 7

• Removed SCN from hamsters & found CR disappeared.
• Further mutant hamsters bred with 20 hr CR.
• Their SCN’s transplanted into normal hamsters = mutant rhythms.
• Study provides strong EE for importance of SCN in providing & maintaining the circadian rhythm.

Question 8

Animal research & Ethics

Answer 8

• // Morgan’s R & much of R into bio rhythms done on NH-animals
• Raises concerns regarding extrapolating findings to humans.
• Important; cross reference these findings with R done on humans -Different species have different neuroanatomies.
• Ethical issue is raised regarding harm.
• //If perceived benefit of R for humans outweighs harm to animals; be considered acceptable as long as key principles are adhered to.

Question 9

RWA: Chronotherapeutics

Answer 9

• Field of Chronotherapeutics, study how timing affect DT’s potency
• CR affects digestion, heart rate & hormones; taken into account when prescribing drugs.
• Medicine that affect certain hormones may have RPA if taken when target hormone level is low. e.g. Aspirin ^effective treating HA if taken in late evening; most HA occur in early hours of morning.

Question 10

EP reductionist

Answer 10

• By identifying the SCN as the main pacemaker we are OS S/Wc.
• As with most bio mech the SCN is part of a larger system
• Only way to achieve holistic understanding is to study interactions between our EP & EZ such as light or social cues.
• Realistically S/Wc is complex mech; can’t be exp as endogenous

Question 11

Miles: blind people

Answer 11

• Studied man blind from birth showing he had CR of 24.9 hours.
• Despite exposure to other EZ (clocks) couldn’t v internal pace.
• Severely affected functioning; dependant on stimulants & sedatives to alter his BR.
• Supports the role of light as the dominant zeitgeber, regardless of other EZ without exposure to light S/Wc severely affected.

Question 12

Luce & Segal: Inuits

Answer 12

• Regardless, need for sleep isnt always determined by L/Dc.
• Found that people living near arctic circle slept for about 7/24 hours during summer months when the sun doesn’t set.
• Fm, found Inuits had natural tendency to make most of longer summer days often hunting for 24+ hours.
• Display absence of CR.
• All in all light can’t be primary zeitgeber if certain cultures can override its effect.

Question 13

Born: Determinism (wake me up)

Answer 13

• Evidence suggests we can ‘will’ our BR to change.
• Without EP we’d be at mercy of our env,sleep most of day (winter). -are EP & effects of EZ biologically determined? Born argues not
• Found people told to wake up at earlier time of night than usual did wake up at the designated time.
• Suggests body clocks and EZ affecting CR can be overcome, particularly if an incentive is provided.