Biological Rhythms Flashcards
What are circadian rhythms ?
Biological rhythms lasting 24 hours
For example the sleep/ wake cycle including hormones like melatonin.
What provides primary input into the circadian rhythm?
Light - it acts as the external cue for sleeping or waking.
How does the detection work ?
Light is detected by the eye , a message (concerning the brightness) is sent to the SCN.
The SCN uses the info to coordinate activity of the C system
Research into Circadian Rhythms ?
Siffre
- Used himself as a case study. A French man spent 6 months in a cave without natural light or cues.
- When he woke up , he had artificial light to help him.
- His internal body was allowed to free fun and his cycle was 25-30 hrs.
What did Siffre find , what’s this suggest ?
- Found that when he returned , he believed the date to be a month earlier than it was.
- Suggests the 24 hr cycle was increased by lack of external cues : believed one day = longer than it was and he thought fewer days had passed
What else are sleep and wakefulness determined by ?
Homeostasis
- when someone has been awake a while, homeostasis tells the body there is need to sleep due to energy consumption.
- The homeostatic drive for sleep ^ during the day , reaching max in late evening.
Another example of a circadian rhythm ?
Body temperature
When is human body temp lowest and highest ?
- Human BT is at lowest in early hours and highest early evening
When does sleep occur ?
- Sleep occurs when core temp drops , BT rises toward end of sleep cycle - promotes alertness 1st thing in morning
A weakness of circadian rhythms ?
( differences )
P : Individual differences
E : Duffy found morning people rise early , go bed early whereas evening people wake and go to bed later.
L : Shows that there may be innate differences in circ. rhythms which suggests researchers should focus on differences during investigations
Weakness of circadian rhythms (Temp)
P : There is suggestion that temp is more important than light in determining circ. rhythms.
E : Buhr found fluctuations in temp set the timing of cells in the body and caused tissues and organs to be active or inactive.
E : Body temp fluctuates on a 24hr rhythm - small changes can send a signal to body clocks.
L: Shows c rhythms are controlled and affected by diff factors - more holistic approach is necessary.
Weakness of Siffre ‘s research
(Case study)
P: Case study , Siffre conducted multiple isolation studies but his results can not be generalised to the wider population - lack of ecological validity
- E.g even Siffre found that as he grew older, his pacemaker slowed which may have been an uncontrolled confounding variable in investigations
- limits the extent to which findings represent general population.
External factors affect sleep wake cycles, what are they called?
Exogenous zeitgebers - for example daylight.
What is an infradian rhythm ?
These are biological rhythms lasting longer than 24 hours and can be weekly, monthly or annually.
Example of infradian rhythms ?
The menstrual cycle, regulated by hormones to promote ovulation.
Length can vary from 23-36 days.
A second example of infradian rhythms?
SAD - seasonal affective disorder
- psychologists believe melatonin may be partially responsible.
- Lack of light in winter - longer period of melatonin secretion = linked to depressive symptoms
Evaluation of infradian rhythms - reinberg
Examined woman who spent 3 months in a cave w only a small lamp to give light.
Her cycle decreased from 28 - 25.7 days. The exogeneous zeitgeber of light - affected the infradian rhythm
Further evidence showing the effect of exogenous zeitgebers - Russell
- Sweat from one group of women to other group’s upper lip.
- Their cycles synchronised - suggesting synchronisation can be affected by pheromones.
What does Russell’s research show ?
Shows that external factors must be taken into consideration when investigating infradian rhythms - more holistic approach rather than reductionist view that only endogenous factors cause influence.
What is a strength of Russell’s experiment ?
- there is an evolutionary strength as if women synchronise periods, they can synch pregnancies meaning childcare can be shared among multiple mothers w kids at the same time.
What is an ultradian rhythm ?
A biological rhythm lasting less than 24 hours and an example is the pattern of human sleep
Describe the cycle of human sleep
Starts at light sleep - deep sleep - REM sleep, brain waves speed up, dreaming occurs and this repeats every 90 minutes
Stages 1 and 2
Light sleep - brainwave patterns are slower, more rhythmic , starting with alpha and progressing to theta waves
Stages 3 and 4
Deep sleep - slow wave sleep stages where it is hard to wake someone - associated with delta waves
Stage 5
REM or dream sleep - body is paralysed and brain activity resembles someone who is awake
Another ultradian rhythm example ?
Appetite/ meal patterns in humans - most eat 3 meals a day and appetite falls and rises due to food consumption
A weakness of studying ultradian rhythms - ID
P: One weakness is individual differences
E: Tucker found differences in duration of each stage in Ps - particularly in stages 3 and 4
E: suggests innate differences in Ultradian rhythms
L: It is worth focusing on these differences when investigating sleep cycles
Another weakness - research into ultradian rhythms
P : Tucker carried out experiment in a controlled lab setting
E: means differences could not be attributed to situational factors but only biological differences
E: The study provides support for the role of biological factors on ultradian rhythms, no situational factors were examined which play a factor
Weakness of research into ultradian rhythms - Eco Val
P: Way in which research is conducted - tells us little about Ult. rhythms
E: When investigating sleep Ps must be subjected to a level of control.
E: may be invasive for the participant leading them to sleep in a way that doesnt represent their actual sleep cycle
L : This makes investigating rhythms hard due to lack of MR therefore false conclusions may be drawn.
