Circadian Rhythms Flashcards
What does SCN stand for?
Suprachiasmatic nucleus
What is the main circadian rhythm, what is it and when does it repeat itself?
When are the strongest drives and what is the cycle linked to?
The sleep/wake cycle
The concept describes how humans sleep and wake up once a day, the cycle repeats itself every 24 hours and is controlled by exposure to light/ dark.
Strongest drives are between 2-4pm and 1-3pm (post-lunch dip)
The cycle is linked to an internal biological body clock (endogenous pace-maker ran by the SCN
What does the SCN do? How much information does it use from the retinas?
It monitors the amount of light entering the eyes by using 10% of the information of the retinas to coordinate the activity of circadian systems in the body.
When the system is sensing light, it remains a wakeful state and when it gets dark it prompts sleep.
What does the homeostatic system do? Even without light, what does the body do?
It monitors the expenditure of energy and triggers feelings of sleepiness when energy reserves need replenishing.
Even without light, the body tends to maintain the circadian rhythms at about 24-25 hours.
What is Jet Lag and how does it occur? Provide an example
This occurs when the circadian rhythm becomes out of sync when we travel long distances, so is the result of the rhythm no longer being synchronised with our environment.
E.g when our body thinks it’s morning / nighttime
What is melatonin released from and when are the levels high / low?
How is melatonin used in medicating insomnia?
It is released from the pineal gland in the brain
Levels peak when it’s dark that trigger feelings of sleepiness. These levels decrease when it’s lighter.
Some medications for insomnia target increasing melatonin levels at the right time to help somebody fall asleep
What did Michelle Siffer (1962) do in his original study and what did he find from this? ( 2 findings )
He spent 2 months living in total isolation in a subterranean cave without access to a clock, calendar or the sun.
He found that his body followed a reliable rhythm, supporting the idea of an internal body clock.
He also suggested that the SCN could be the body clock he found, with him settling into a pattern that was about 24.5 hrs long.
What did Michel Siffre’s later study and what did he find?
He stayed in the cave again for 6 months and found his biological rhythm occasionally reached a rhythm of about 48 hours, replicating this with other ppts.
What does the finding from Michel Siffre’s second study suggest about the internal body clock?
Suggests that it can keep reliable time, but doesn’t stay at 24hour rhythm, without an external indicator of tracking time.
What did Michel Siffre believe regarding the absence of light and its effects on the human brain?
He believed the absence of light meant his brain didn’t keep track of time in the same way as it does when there is light
What did Michel Siffre do when he was 60 and what were the 2 findings he found from this?
He stayed again in the cave for the last time
-found his circadian rhythm was much slower as an old man than it was as a young man
-found the duration of his sleep became unreliable with some sleep lasting 2 or 18 hours
What did Hughes (1977) study regarding cortisol levels?
He studied cortisol levels in men staying at the Antarctic research station.
When are cortisol levels highest/lowest?
During the 3 months of permanent darkness, what happened to the men’s that Hughes (1977) was studying?
The levels are highest during daylight hours and lowest at night
During the 3 months, the men’s cortisol levels started to peak at midday instead of the normal 6am
What does the finding from Hughes (1977) study suggest?
Suggests the lack
of light had influenced the circadian rhythms for cortisol. However, later studies were unable to replicate these findings, questioning the validity of this study.
What did Czeisler et al. (1999) find out regarding circadian differences and what does this suggest?
They found there are individual differences in circadian rhythm with differences from 13 to 65 hours.
Suggests we should be careful when generalising the results, due to some peoples rhythms being different from the norm.
What did Duffy Et al. (2001) study and what were the two different groups they concluded, regarding circadian rhythms?
They studied the time that the circadian rhythm resets each day in different people.
Found the two groups
- Morning people (larks) — people who rise/ sleep earlier
-Evening people (owls) — people who rise/sleep later
How is core body temperature important within circadian rhythms? ( 2 things )
The body temperature changes all day
—reliable pattern where the temp is lowest at 4am (36 °C) and highest at 6pm (38 °C)
—a drop between 2/4pm may explain the post-lunch dip
What did Buhr et al. (2010) find regarding body temperature ? (2 things)
— found it is more influential for the circadian rhythm than light, as it runs for 24-hour cycle and even small temp changes can cause big changes in our body clocks.
— found temperature triggers the timings of cells can be set, causing the cell tissue to either become active or inactive.
