0.14 Biological Rhythms

what are biological rhythms

bodily cycles that occur over different amounts of time

what kind of biological rhythms are there

ultradian

more than a day (menstrual cycle)

circadian

around a day (sleep)

infradian

less than a day (REM)

in the sleep wake cycle what happens around 10pm

melatonin begins to be released

pituitary gland

pineal gland

releases melatonin

in the sleep wake cycle what happens around 4am-7am

stop production of melatonin

start releasing adrenaline to wake up

what are endogenous pacemakers

internal body clocks

help regulate biological rhythms

suprachiasmatic nuclei

what is the suprachaismatic nuclei

an endogenous pacemaker

centre of the brain

• light info is taken in by the eyes

• sends messages to SCN

• SCN tells endocrine system - pituitary gland + then pineal gland to release melatonin if it is dark or adrenaline if it’s light

what exogenous zeitgebers

external cues

affect the regulation of endogenous pacemakers (light)

what can influence the SCN

exogenous zeitgebers

• social cues (meal-times)

• external temperatures

how does light affect the SCN

• Melanopsin - light sensitive protein in the retina

• continuously carries information to the SCN to regulate the sleep wake cycle

what is desynchronisation

where endogenous pacemakers and exogenous zeitgebers become out of sync

what can cause desynchronisation

• shift work

• jet lag

what is entrainment

where the endogenous pacemaker adjusts to the environment with the help of zeitgebers

what was the main study for circadian rhythms

Siffre

cave study

what were the aims of Siffre’s study

find out what his natural sleep-wake cycle would be without exogenous zeitgebers

what was the method of Siffre’s study

• stayed in the cave with lots of food and water supply

• when he woke up he phone the research team to turn on lights in the cave

• did daily experiments - memory, blood pressure …

• when he felt tired he phoned them to turn off the lights

• the research team recorded when he was asleep/awake

what were the findings of Siffre’s research

his sleep-wake cycle increased to 26 hours on average

could be from 18-52 hours

strengths of Siffre’s research

• supported by other research

• supports impact of exogenous zeitgebers BUT also shows endogenous pacemakers override

limitations of Siffre’s research

• case study - population validity

• self-testing - subjective

• not testing the impact of light as an exogenous zeitgeber as he asks to have lights turned on/off - so lacks internal validity