Circadian Rhythms

Question 1

What is a circadian rhythm

Answer 1

A cycle which lasts about 24 hours

Question 2

Name three circadian rhythms

Answer 2

The sleep-wake cycle, core body temperature and hormone production

Question 3

What synchronises all of the body’s body clocks

Answer 3

The suprachiasmatic nuclei (SCN), found in the hypothalamus

Question 4

How does the Suprachiasmatic nuclei reset and how often must it be reset

Answer 4

The suprachiasmatic nuclei must be reset every day to keep us in synchorony with the outside world. Light is the primary input to this system, with light sensitive cells in the eye acting as brightness sensors

Question 5

What are the external signals that determine when we feel the need to sleep and to wake up

Answer 5

Light and Darkness

Question 6

Is the circadian rhythm constant throughout the day

Answer 6

No we experience dips and rises, such as our sleep drive, which is strongest between 2-4 am and 1-3 pm. A small drop in body temperature also occurs between 2 and 4 pm.

Question 7

What other factor controls sleep and wakefulness

Answer 7

Homeostatic control also affects these factors, as when we have been awake for a long time homeostasis tells us that the need for sleep is increasing because of energy being used up. This drive for sleep increases throughout the day, reaching it’s maximum in the late evening.

Question 8

What hormone is released to make us feel sleepy when it’s dark

Answer 8

Melatonin from the pineal gland

Question 9

What happens when there is a major alteration in sleep and wake shedules, such as jet lag

Answer 9

The biological clock and internal physiological systems that are dependent on this become out of balance

Question 10

How is core body temperature a circadian rhythm

Answer 10

It is lowest at 4:30 and highest at about 6pm. As sleep occurs it begins to drop, then rises during the last hours of sleep, prompting a feeling of alerness in the morning. A small drop also occurs between 2pm and 4pm

Question 11

How is hormone production a circadian rhythm

Answer 11

Release of melotonin to make us sleepy when it’s dark, and production of melotonin (in the pineal gland) drops when a person wakes

Question 12

Who is THE case study for circadian rhythms

Answer 12

Michel Siffre. On several occasions he lived undergroud to study his own circadian rhythms. Whilst doing this he had no external cues, such as daylight or clocks. The only thing influencing his behaviour was his internal clock. His first undergroud stay was 61 days, and his second was six months. His natural rhythm settled down to just over 24 hours, but with some variations. His body clock ticked more slowly, sometimes stretching his circadian rhythms to 48 hours.

Question 13

How long did Siffre spend underground

Answer 13

61 days on first go
6 months on second

Question 14

What did Siffre find

Answer 14

His natural circadian rhythm settled to just over 24 hours

Question 15

Who did studies on circadian rhythms in the Arctic

Answer 15

Hughes

Question 16

What did Arctic studies reveal surronding cicadian rhythms

Answer 16

Research support surrounding importance of light, with Hughes testing on 4 participants stationed at the British Antarctic Station. In Feburary, at the end of the Antarctic summer, cortisol levels were normal. However, after three months of continous darkness, the pattern changed, with peak cortisol being at noon rather than when the particpants awoke. This suggests that the extremes of daylight in the polar region could be responsible for variations in circadian hormone release. However other research on scientific communities in the arctic have found no such disruption (unreplicable)

Question 17

What is a possible flaw in the methodology of research into the ‘free running’ cycle of the human circadian rhythm

Answer 17

In most studies particiapants were isolated from variables which may affect their circadian rhythms, such as clocks and daylight, however they weren’t isolated from artificial light because it was believed that dim artificial light would not affect their circadian rhythms. Research suggests this may not be true, with Czeisler et al altering particpants ciracdian rhythm down to 22 hours and up to 28 hours using dim artificial lighting alone. This suggests that other studies may have confounding variables.

Question 18

How has research into circadian rhythms been used in real life

Answer 18

It has been used in chronotherapeutics, the study of how timing affects drug treatments. The time that patients take their medication can have a large impact on treatment success, so it is essential that the right concentration is released at the time the drug is most needed. As a result, chronotherapeutic medication has been developed with a deivery system where the drug is not released until hours after being administered, for example so that it can be released during sleep.

Question 19

What are some individual differences in circadian rhythms

Answer 19

Research has found that one cycle length can vary from 13 to 65 hours and that individuals are innately different in terms of when their circadian rhythm reaches it’s peak. According to Duffy et al, this would explain why some people prefer to rise early and go to bed early, whereas others prefer to wake and go to bed late. These differences may confound research into sleep wake cycles

Question 20

Who suggested innate differences determine when we wake/ go to sleep

Answer 20

Duffy et al said individual differences explain the night owl/early riser duo

Question 21

Who managed to alter participants circadian rhythms using artificial light

Answer 21

Czeisler