Circadian rhythms

Question 1

What is a biological rhythm?

Answer 1

influence the way bodys system behaves

Question 2

What is an endogenous pacemakers

Answer 2

the body’s intertnal biological clock

Question 3

What are exogenous zeitgebers

Answer 3

external changes in the environment

Question 4

What is a circadian rhythm

Answer 4

a biological rhythm that lasts 24 hours

Question 5

What does the circadian cycle regulate

Answer 5

• sleep/wake cycle
• core changes in body temperature

Question 6

What is the sleep wake cycle

Answer 6

dictates when we should be sleeping or awake

Question 7

What controls the sleep wake cycle

Answer 7

suprachiasmatic nucleus

Question 8

Outline the sleep/wake cycle

Answer 8

• light/ dark (exogenous zeitgbers)
  are external signals that determine when we feel the need to sleep and wake up
• rhythm dips/rises at certain times are strongest sleep drive is 2-4 am and 1-3pm
• sleepiness we feel during dips is less/more intense based on the amount of sleep we had
• the free running internal clock maintains a cycle of 24-25 hrs even in the absence of external cues

Question 9

Outline the core body temperature circadian rhythm

Answer 9

• indicator of circadian rhythm
• lowest at 4.30 am and highest at 6pm
• sleep occurs when core temp begins to drop, temp rises during the last hours of sleep promoting alertness in the morning
• small drop in body temp occurs between 2-4pm

Question 10

What was the aim of Siffre’s study

Answer 10

to investigate the duration of circadian rhythms particularly the sleep/wake cycle

Question 11

What was the method of Siffres study?

Answer 11

Isolated himself from all daylight by spending 6 months in a dark cave with only artificial light. He has no clock but he had verbal contact with the outside world

Question 12

What were the results of Siffres study?

Answer 12

His internal body clock was allowed to free run and at first it was erratic. It eventually settled into a sleep wake cycle of 25-30 hrs. He continued to fall asleep and wake up on a regular schedule. However he lost track of how long he has been in the cave. He thought was one month less that he actually did

Question 13

What was the conclusion of Siffres study?

Answer 13

suggests that the absence of exogenous zeitgebers and circadian rhythms are roughly maintained which supports the existence of the internal body clock and that is lasts 24 hrs.

Question 14

What are limitations of Siffres study?

Answer 14

• case study
• used artificial light

Question 15

Evaluate case study as a limitation of Siffres study

Answer 15

• he was the sole ppt so unrepresentative snd has low population validity
• so we cant be certain his findings that exogenous zeitgebers and endogenous pacemakers work together are valid as they may apply universally
• however theres no reason to believe that Siffre isn’t a normal member of the human race and its perfectly possible that his findings indeed apply to others

Question 16

Evaluate the use of artificial light as a limitation of Siffres study

Answer 16

• he has access to artificial light which he assumed wouldn’t affect his circadian rhythms
• However Czeizler et all managed to alter ppts circadian rhythm to 22 hours and up to 28 hrs using dim artificial light alone
• limitation of Siffres findings because it may have been the artificial light maintaining his sleep wake cycle therefore his conclusion that a free running circadian rhythm of 24 hours exists may not be valid

Question 17

What is a limitation of circadian rhythms

Answer 17

individual differences in cycle length

Question 18

What are strengths of circadian rhythms

Answer 18

• supported by research (Siffre)
• practical applications

Question 19

Evaluate supported by search as a strength of circadian rhythms

Answer 19

• supported by Siffres study
• his study supports the claim that humans have circadian rhythms that last 24 hours. When he isolated himself from all daylight and his internal body clock was allowed to free run it eventually settles into a sleep wake cycle of 25-30 hours
• strength of the endogenous pacemakers theory because results suggest that in the absence of exogenous zeitgebers such as natural light circadian rhythms are roughly maintained supporting the existence of an internal body clock

Question 20

Evaluate practical applications as a strength of circadian rhythms

Answer 20

• has practical applications for shift work
• research has shown that night workers experience a period of reduced concentration at around 6am meaning mistakes and accidents ate more likely.
  Research has also suggested a relationship between shift work and poor health, night workers are 3x more likely to develop heart disease which may be due to the stress of adjusting to different sleep wake patterns and lack of poor sleep quality during the day
• strength because research into sleep wake cycle may have economic implications in terms of how to best manage worker productivity snd safety

Question 21

Evaluate individual differences as a limitation of circadian rhythms

Answer 21

• claim that all humans have the same circadian rhythm has been criticised as some research has demonstrated individual differences in the sleep wake cycle
• For example Czeisler et al found that sleep wake cycles varied in some cases from 13 to 65 hours. Duffy et al found some people display natural preferences for going to bed early and rising early and others are the opposite
• limitation for some research into circadian rhythms as is suggests that not everyones sleep wake cycles are the same therefore its not possible to claim that all individuals have the same endogenous pacemakers