Circadian rhythms

Question 1

what are biological rhythms

Answer 1

• biological rhythms are governed by :
  -endogenous pacemakers
  -exogenous Zeitgebers

Question 2

What are circadian rhythms?

Answer 2

Rhythms that last for around 24 hours

Question 3

examples of circadian rhythms -

Answer 3

-Sleep wake cycle
-core body temperature

Question 4

Sleep wake cycle -

Answer 4

-Dictates when humans and animals should be asleep and awake
-Light provides the primary input to this system, acting as the external cue for sleeping or waking (exogenous zeitgeber)

Question 5

Light detection -

Answer 5

Light is first detected by the eye, which sends messages concerning the level of brightness got the suprachiasmatic nuclei - which coordinates the activity of the circadian rhythm
- homeostasis tells the body that there is a need for sleep because of energy consumption. This homeostatic drive for sleep increases throughout the day, reaching its maximum in the late evening, when most people fall asleep.

Question 6

Research support - Siffre (1975)

Answer 6

evidence from ‘free running’ circadian rhythm comes from a series of studies conducted by Siffre.
-He subjected himself to long periods of time underground to explore and study the effect on his own circadian rhythms - no daylight, clock or radio to help him and ate and slept at times he felt it was appropriate.
-the only influence was his internal body clock

Question 7

Siffre results

Answer 7

-His natural circadian rhythm settled to just over 24 hours

Question 8

hormone production

Answer 8

Hormone release follows a circadian rhythm. For example, the production and release of melatonin from the pineal gland in the brain follows one, with peak levels occurring during the hours of darkness. By activating chemical receptors in the brain, melatonin encourages feelings of sleep. When it is dark, more melatonin is produced, and when it is light again, the production of melatonin drops and the person wakes.

Question 9

supporting study (Aschoff and Wever)

Answer 9

convinced a group of ppts to spend 4 weeks in a WW2 bunker deprived of natural light.
All but one of the ppts displayed a circadian rhythm between 24 and 25 hours.
Both this study and Siffres suggest that the ‘natural’ sleep wake cycleway be longer than 24 hours but is entrained by exogenous zeitgebers associated with 24 hour day (daylight, mealtimes)

Question 10

Strength - shift work

Answer 10

research provides an understanding of the adverse consequences that occur when they are disrupted
-eg night workers engaged in shift work experience a period of reduced concentration leading to mistakes and accidents (Boivin et al)
This shows that research into sleep/wake cycle may have real-world Economic implications in terms of worker productivity

Question 11

strength - medical treatment

Answer 11

Research has been used to improve medical treatments
-circadian rhythms co ordinate a number of the bodies basic processes such as heart rate, digestion and hormone levels
-the rise and fall of these has led to the field of chronotherapeutics - how medical treatment can be administered in a way that corresponds to a persons biological rhythm
-increased effectiveness

Question 12

limitation - individual differences

Answer 12

-generalisations are difficult to make
-based on small samples of participants (case study for siffre) and it seems that sleep/wake cycles may vary from person to person