Biological Rhythms Flashcards
What is a biological rhythm?
A series of repetitive biological processes regulated by your internal clock.
What are biological rhythms regulated by?
-Endogenous pacemakers.
-Exogenous zeitgebers.
What is the main example of an endogenous pacemaker?
-SCN.
What are examples of an exogenous zeitgeber?
-Light.
-Social cues (e.g. meal times).
What are endogenous pacemakers?
The body’s internal body clocks that regulate biological rhythms.
What are exogenous zeitgebers?
External environmental cues that reset our biological clocks.
Can endogenous pacemakers be affected by the environment?
Yes.
What do external cues do to biological rhythms?
External cues entrain biological rhythms.
What is a free running cycle?
Where one’s daily sleep cycle does not depend on external cues.
Where is the SCN?
The hypothalamus.
What is the SCN linked with?
The pineal gland.
How does the sleep/wake cycle work?
- The SCN (E.P.) receives information about light levels (E.Z.) from the optic nerve.
- This sets the circadian rhythm so that it is in synchronisation with the outside world (e.g. day and night).
- The SCN sends signals to the pineal gland (E.P.)
- This leads to an increase in the production of melatonin (sleep hormone) at night, helping to induce sleep.
If there is a lack of natural light, what exogenous zeitgebar can substitute for it?
Social cues (e.g. meal time).
What are circadian rhythms?
Any cycle that lasts 24 hours.
What is an example of a circadian rhythm?
The sleep/wake cycle.
What does circadian mean in Latin?
About day.
Why are circadian rhythms important?
It optimises an organism’s physiology and behaviour to meet the varying demands of the day/night cycle.
What is the purpose of circadian rhythms?
Regulating behaviour and body states in response to environmental changes.
How did Folkard (1985) research circadian rhythms?
Folkard placed 12 participants in a cave for three weeks with no E.Z., subtly giving them 22 hour time cues (e.g. by speeding up the clock).
Only 1 out of 12 participants couldn’t adjust to the shortened day.
This suggests the flexibility of the circadian system and how it differs between individuals.
How did Siffre (1962) research circadian rhythms?
Siffre (1962)
Siffre tested his internal body clock (E.P.) by spending 61 days & nights in a cave with no E.Z. He settled into a 25-30 hour sleep/wake cycle.
This supports the assumption that endogenous pacemakers exert an influence on circadian rhythms, while showing the strength of circadian rhythms as a free running cycle.
What is a limitation of Siffre’s (1962) circadian rhythm study?
He used artificial light (headlight), which could act as an E.Z.
What are infradian rhythms?
A cycle that lasts longer than 24 hours (e.g. weekly, monthly, annually).
What are examples of infradian rhythms?
-Female menstrual cycle.
-Season affective disorder (SAD).
Features of the female menstrual cycle (infradian rhythms):
-24-35 days long.
-Ovulation (egg release) occurs.
-The thickening womb lining sheds if there is no pregnancy.
Features of seasonal affective disorder (SAD) (infradian rhythms):
Lack of light in winter months results in a longer period of melatonin secretion, which is linked to depressive symptoms.
How did McClintock (1998) study infradian rhythms?
McClintock conducted a longitudinal field study where the menstrual cycles of women became synchronised after being exposed to a ‘donor’ pheromone (E.Z.).
What are ultradian rhythms?
Any cycle that lasts less than 24 hours.
What is an example of ultradian rhythms?
The stages of the sleep/wake cycle.
How many stages of the sleep/wake cycle are there?
5.
How long does each stage of the sleep/wake cycle last?
90 minutes.
Stages 1 & 2 of the ultradian cycle:
‘Light sleep’ stages.
One can be easily woken up.
Slower alpha wave brain patterns start to form, becoming even slower in the form of theta waves as sleep becomes deeper.
Stages 3 & 4 of the ultradian cycle:
‘Deep sleep’ stages.
It will be more difficult to wake someone up.
Involves delta waves.
Stage 5 of the ultradian cycle:
‘REM (rapid eye movement) sleep’ stage.
The body is paralysed while brain activity speeds up.
Highly correlated with people dreaming.
How did Dement & Kleitman (1967) study ultradian rhythms?
Dement & Kleitman (1967) measured brain activity on 9 participants using EEG. When waking people up during the REM stage, people would recall what they had dreamt about clearly.
