endogenous pacemakers + exogenous zeitgebers

Question 1

endogenous pacemakers

Answer 1

• internal biological rhythms
• most important = superachiasmatic nuclei (SCN)
• located in hypothalamus
• important role in generating circadian rhythms
• aka master clock, controls other biological clocks in the body
• neurons within the SCN synchronise w/ each other
  = target neurons elsewhere in the body receive time-coordinated signals
  = maintain a circadian rhythm
• SCN regulates production + secretion of melatonin
• melatonin –> pineal gland
  = induces sleep by inhibiting brain mechanisms that promote wakefulness
• SCN send signal to pineal gland
  = increase melatonin P+S at night (low levels of light)
  = decrease in morning

Question 2

exogenous zeitgebers

Answer 2

• environmental events that are responsible for maintaining the biological clock of an organism
• external cues/ factors e.g. light (most important)
  = reset our internal biological clock each day
  = 24 hour cycle
• receptors in the SCN = sensitive to changes in light levels
• uses this info to synchronise body’s organs + glands
• move to a night shift/ travel to a different country
  = endogenous pacemakers try to impose their inbuilt rhythm of sleep (circadian rhythm)
  = now out of synchrony w/ exogenous zeitgeber of light
• out of sync biological rhythms lead to:
• disrupted sleep
• increased anxiety
• decreased alertness + vigilance

Question 3

ad of endogenous pacemakers

Answer 3

• psych studied a uni student, Kate Aldcroft
• she spent 25 days in a laboratory
• she had no access to the exogenous zeitgeber of light to reset the SCN
• HOWEVER at the end of the 25 days
• her core temp rhythm was still at 24 hours
  = indicates that we DON’T need the exogenous zeitgeber of light to maintain our internal biological rhythms

Question 4

disad of endogenous pacemakers

Answer 4

• Kate Aldcroft’s sleep- wake cycle extended to 30 hours
• w/ periods of sleep as long as 16 hours
• suggests that we DO need the exogenous zeitgeber of light
• to maintain our internal biological rhythms

Question 5

blind people - ad of exogenous zeitgebers

Answer 5

• vast majority of blind people who still have light perception
  = have normal circadian rhythms
• blind people w/ out light perception show abnormal circadian rhythms
  = shows vital role that the exogenous zeitgeber of light levels play in maintaining our internal biological rhythms

Question 6

flights - ad of exogenous zeitgbers

Answer 6

• psych found that exposure to bright light prior to an east-west flight
• decreased the time needed to adjust circadian rhythms to local time

Question 7

disad of exogenous zeitgbers

Answer 7

• studies of individuals who live in Arctic regions
• where sun doesn’t set in the summer
• show normal sleeping patterns
• despite prolonged exposure to light
  = suggests that there are occasions where the exogenous zeitgeber of light may have very little bearing on our internal biological rhythms