Circadian Rhythms

Question 1

What is a biological rhythm

Answer 1

A change in the body processes or behaviour in response to cyclical changes within the environment

Question 2

What are circadian rhythms

Answer 2

Biological rhythms that have a periodicity of 24 hrs

Question 3

What is a sleep waking cycle

Answer 3

One period of sleep and one period of waking every 24 hrs

Question 4

What are core body temperatures

Answer 4

One peak and trough every 24 hrs

Question 5

What is hormone production

Answer 5

Melatonin levels peak in the dark and are at its lowest during daylight

Question 6

What do photosensitive retinal ganglion cells do

Answer 6

Detect the brightness of our surroundings and send information to the optic nerve to the Suprachaismatic Nuclei (brain’s master clock)

Question 7

What is the SCN (that nuclei shi im not writing out again)

Answer 7

The brain’s master clock that governs everything in our body to sleep and wake (cycles)

Question 8

What are our circadian rhythms driven by

Answer 8

Our body clocks found in all cells of the body and synchronised by the master circadian pacemaker (SCN) found in the hypothalamus
Must constantly be reset so that our bodies are in synchrony w the outside world
Light provides primary input to this system setting the body clock to the correct time in a process termed photoentrainment

Question 9

What do photosensitive cells do

Answer 9

Contribute to the regulation of pupil size and other behavioural responses to ambient lighting conditions

Question 10

Does the body make and keep its own circadian rhythms

Answer 10

Yes, natural factors in your body produce circadian rhythms. For humans, some of the most important genes in this process are the Period and Cryptochrome genes. These genes code for proteins that build up in the cell’s nucleus at night and lessen during the day

Question 11

What is the body’s internal body clock that regulates biological rhythms

Answer 11

Endogeneous pacemakers

Question 12

What are the external factors in the environment which reset our biological clocks

Answer 12

Exogenous zeitgebers

Question 13

How do circadian rhythms affect body function and health

Answer 13

Hormone release
Eating habits
Digestion
Body temperature
Too much light can be detrimental (diabetes, depression)

Question 14

What are ultradian cycles

Answer 14

More than once in 24 hrs - sleep cycle, for example

Question 15

What are infradian cycles

Answer 15

Less than once a day - menstrual cycles. for example

Question 16

How much does our body temperature vary during the day

Answer 16

2 degrees celsius
Lowest at 4am
Peak approximately 6pm
Warmer we are, the better we perform

Question 17

Describe Siffre’s 1962 cave study

Answer 17

Siffre spent 2 months living in total isolation in a subterran cave without access to clock, calendar or sun
Sleeping and eating only when his body told him so, goal was to discover how the natural rhythms of human life would b affected by living “beyond time”
His body clock remained the same despite being a lil caveman

Question 18

Describe Siffre’s 1972 cave study
kid cudnt stay away from the bats

Answer 18

Spent 6 months in Texan cave
Wud turn on lighting when he awoke and turned off in evening when wanted to sleep (no external light source)
Circadian sleep-wake cycle became longer than 24 hrs
Was also inconsistent (between 25-32 hrs), days r therefore longer
179 actual days passed, but 4 him was only 151 days
Body temp. was fairly consistent
Had depression n suicide thoughts (due to isolation not sleep deprivation as slept whenever he liked)

Question 19

What does Siffre’s study show

Answer 19

Circadian rhythm maintained without exogenous zeitgebers
Npot perfectly regulated tho
Must b at least 2 body clocks (sleep-wake cycle and body temp.)

Question 20

What was Aschoff and Rutger’s 1976 study that confirmed Siffre

Answer 20

Placed participants in a bunker for 4 weeks w no natural light
Settled into a sleep/wake cycle of between 24 n 25 hrs (apart from one which extended to 29 hrs)

Question 21

What do both Siffre and Aschoff suggest

Answer 21

Natural light sources in the environment are vital for keeping the individual to a 24 hr sleep cycle

Question 22

Describe Folkard et al 1985 study

Answer 22

Isolated 12 participants from natural light for 3 weeks (dark cave), manipulating the clocks that only 22 hrs passed a day
None of the participants cud adjust comfortable to the pace of the clock except one
This shows the strength of the circadian rhythm as a free-running cycle and questions the extent to which it can b overridden by exogenous zeitbegers

Question 23

Evaluate Folkdar’s study

Answer 23

Difficult to generalise findings from studies of the sleep/wake cycle because individual cycles can vary, in some cases 13-65 hrs
the fuck
i am in the bottom of this spectrum
and every other spectrum…
There are also differences in the sleep/wake cuycle

Question 24

Where is melatonin secreted

Answer 24

In breast milk
But varies throughout the day to help a baby know when to sleep or wake

Question 25

What can happy to babies who are fed formula instead of breast milk

Answer 25

Find it harder to regulate their sleep

Question 26

What is SCN
Suprachiasmatic nucleus

Answer 26

Tiny bundle of nerve cells located in the hypothalamus in each hemisphere in the brain
One of primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms
Nerve fibers connected to the eye cross in an area called optic chiasm on their way to the visual area of the cerebral cortex
Receives info about light directly from this - even when our eyes are closed

Question 27

What is entrainment

Answer 27

Process of resetting the biological clock in line w external time cues
Synchronises circadian rhythms

Question 28

Talk abt melatonin and cortisol roles in sleep/wake cycle

Answer 28

Melatonin triggers sleepiness in a dark environment of a typical physiological setting, and cortisol secretions sustain daytime consciousness throughout the morning

Question 29

Describe DeCoursey’s animal study on SCN

Answer 29

Decoursey et al 2000 - destroyed in the SCN connections in the brains of 30 chipmunks, who were then returned to their natural habitat an observed over 80 days
The sleep/wake cycle of the chipmunks disappeared and by the end of the study, a significant proportion of them had been killed by predators (due to being awake and vulnerable, when should have been asleep)

Question 30

Describe Ralph’s animal study on SCN

Answer 30

Ralph et al 1990 - bred ‘mutant’ hamsters with a 20-hr sleep/wake cycle. When SCN cells from the foetal tissue of mutant hamsters were transplanted into brains of normal hamsters, cycle of the second group defaulted to 20 hrs

Question 31

How did Burgess et al study jet lag using light exposure to avoid it (practical application of exogenous zeitgebers)

Answer 31

Found that exposure to bright light prior to an east-west flight, decreased the time needed to readjust to local time on arrival
Participans were exposed to continuous bright light shifted their circadian rhythm by 2.1 hrs whereas those exposed to intermittent bright light shifted their rhythm by 1.5 hrs and those exposed to dim light shifted theirs by just 0.6 hrs
As a result, participants in the 1st conditions felt sleepier 2 hrs earlier in the evening and woke 2 hrs earlier in the morning i.e. closer to local time conditions

Question 32

What are social cues for circadian rhyth,s

Answer 32

About 6 weeks of age, rhythm begins and by 16 weeks, most babies are entrained
Schedule imposed by parents said to have large influence here including adult-determined mealtimes and bedtimes
Jet leg - research has suggested that adapting to local eating and sleeping times is an effective way of entraining circadian rhythms