circadian rhythms

Question 1

circadian rhythms

Answer 1

• biological rhythms that last 24 hours
• sleep-wake cycle

Question 2

free running system (homeostasis)

Answer 2

• morning energy levels are high
• energy expended in everyday activities
• evening energy levels are depleted
• night energy levels are replenished while we sleep
• cycle repeats

Question 3

endogenous pacemaker

Answer 3

• innate internal biological mechanism that regulated biological rhythms
• suprachiasmatic nucleus regulates sleep wake cycle and keeps it at 24 hours

Question 4

exogenous zeitgeber

Answer 4

• external environmental cue that helps maintain sleep wake cycle to 24 hours
• light, high levels we wake low levels we sleep
• social cues, everyday activities such as meal times, working hours also follow 24 hour cycle

Question 5

role of endogenous pacemaker and exogenous zeitgeber

Answer 5

• night, external light levels low
• photosensitive cells in retina send messages to SCN through optic nerve
• SCN sends messages to pineal gland instructing to secrete more melatonin making you feel sleepy
• during day, external light levels are high

Question 6

evidence supporting - siffre’s cave study

Answer 6

• michel siffre subjected himself to long periods of time living underground
• had no external cues (daylight clocks radio)
• woke,slept,ate when he felt it was appropriate
• turned on a lamp when he woke and turned it off when he wanted to sleep
• 61 days, emerged thinking it was aug 20 was actually sept 17
• free-running circadian rhythm settled down to just over 24 hours
• absence of external cues, sleep-wake cycle regulated by free-running cycle which is longer than 24 hours hence longer days
• suggests external zeitgebers are needed to regulate sleep-wake cycle and maintain it
• suggests there is an internal mechanism that regulates biological rhythms

Question 7

evidence supporting - aschoff and weber bunker study

Answer 7

• studies pps living in underground WW2 bunker which had no windows, no natural light
• pps were free to turn artificial lights on and off as they pleased
• after 4 weeks in bunker, found that pps settled into a longer sleep wake cycle of 24-29 hours
• czeilser et all altered circadian rhythms to 22-28 hours using artificial light as a resetting cue
• suggests that artificial light is an extraneous variable that may have effected their sleep-wake cycle, effects validity of their findings and conclusions

Question 8

evidence supporting role of SCN - animal studies

Answer 8

• morgan bred hamsters to have a 20 hour SCN
• SCN of the hamsters transplanted into the brains of hamsters with a normal 24 hour SCN
  -sleep-wake cycle of second group changed to 20 hours
• shows that SCN controls/regulates sleep-wake cycle

Question 9

evidence supporting role of SCN - studies of blind people

Answer 9

• previously believed that 24 hour clock was maintained by social cues
• found that blind people have light perception
• blind people with light perception compared to those without light perception
• first group had 24 hour sleep-wake cycle
• second group’s sleep wake cycle was longer at 25 hours
• shows that light is an important external cue that sends info about time of day to an internal mechanism to regulate sleep-wake cycle
• suggests that other social cues (mealtimes), arent as important