Biopsychology: Pacemakers And Zeitgebers Flashcards
Define Endogenous Pacemakers
Internal body clocks that regulate many of our biological rhythms.
Such as the influence of the suprachaismatic nucleus on the sleep/wake cycle
Define Endogenous Zeitgebers
External cues that may affect or entrain our biological rhythms.
Such as the influence of light on the sleep/wake cycle.
Define Sleep/wake cycle
A dairy cycle of biological activity based on a 24hrs period (aka circadian rhythm) that is influenced by regular variations in the environment, such as the alternation of night and day
What is the suprachiasmic nucleus (SCN)
- Main endogenous pacemaker in both humans and animals
- Mentains sleep/wake cycle
- A bundle of nerves in the hypothalamus in each hemisphere of the brain
- SCN lies above the optic chiasm and receives light from this structure
- Continues even when eyes are closed
Role of the Pineal Gland and Melatonin
The SCN passes information about light that it receives to the pineal gland
The pineal gland is just behind hypothalamus.
The pineal gland increases melatonin production: a chemical that induces sleep and is less during moment of wake fullness
Melatonin causes seasonal affective disorder
Animal studies and the SCN
Ralph et al:
SCN was taken from hamsters that operated on a 20 hr sleep/wake cycle
They placed this SCN into normal hamsters
The cycles of the second group became defaulted to 20hrs.
This emphasises the importance of SCN in establishing and maintains the sleep/wake cycle
The exogenous zeitgeber Light:
Light is a key zeitgeber and it can reset the body’s main endogenous pacemakers
Role of exogenous zeitgebers
Role: reset our biological clocks through a process called entrainment
Stops our free running biological clock which is 25hrs
Eg. Social cues and Light
Social cues
Infants have irregular sleep/wake cycles
They begin at around 16 weeks because they are imposed by parents through meal times and bed times.
It is entrained
Exogenous zeitgeber of light:
Light can reset the important SCN and therefore regulate the sleep/wake cycle to be in sync with outside.
Campbell and Murphy:
15 pps woken with a light shone on the back of their kneee
Light was detected by receptors and influenced their sleep/wake cycle by 3 hrs
This shows that light is a powerful zeitgeber
Simplistic SCN
Damiola: found that there are many other complex influences on the sleep/wake cycle other than the SCN.
Changing feeding pattern in mice altered the circadian rhythm of cells in the liver by up to 12hrs.
While the SCN was unaffected.
Other circadian rhythms called peripheral
Oscillators in adrenal gland and liver
Ethics of animal studies
Decoursey and chipmunks
They all died when placed back in their natural habitat.
Exposed to harm and risk
Does the ends justify the means?
Miles et al
Blind from birth and has a circadian rhythm of 24.9 hrs. Despite cues his behaviour could not be adjusted and therefore had to take sedatives and stimulants
Countries with little darkness during the summer months still have normal sleep patterns
Shows the insignificance of exogenous zeitgebers
Internationalist approach
Total isolation such a siffre’s lacks validity as in real life zeitgebers interact and it makes little sense to separate them
