BP- Pacemakers Flashcards
What are endogenous pacemakers?
Internal biological rhythms
What is the most important endogenous pacemaker?
Suprachiasmatic nuclei (SCN)
What is the SCN and what is it responsible for?
- The SCN is a tiny cluster of nerve cells in the hypothalamus.
- It has built a circadian rhythm that resets when external levels of light change every 24 hours.
- It acts as the master clock, linking other brain regions that control sleep and arousal, and controlling all other biological clocks throughout the body.
How does the SCN regulate sleep?
1) The SCN receives information from the optic nerve and regulates sleep by influencing activity of the pineal gland.
2) The SCN sends signals to the pineal gland, instructing the increase of melatonin at night (inducing sleep) and decrease of melatonin in the morning as light increases.
3) The pineal gland and the SCN collectively control the sleep-wake cycle which must be synchronised with the light-dark cycle outside.
Give advantages of research into endogenous pacemakers
1) Folkard (1996) studied a university student, Kate Aldcroft, who spent 25 days in a laboratory.
- She had no access to daylight or other exogenous zeitgebers that might have reset the SCN.
- At the end of 25 days her core temperature rhythm was still at 24 hours.
2) Research support for the role of endogenous pacemakers.
- Siffre spent 7 months in a cave, where despite being fed and physically active, he lacked any cues about when it was day or night such as clocks and night.
- Despite this, it was found that his sleeping pattern settled to just over 24 hours.
Give disadvantages of research into endogenous pacemakers
1) Regarding to Kate Aldcroft’s case, her sleep-wake cycle extended to 30 hours, with periods of sleep as long as 16 hours. We do need external influences to maintain our circadian rhythms.
What are exogenous zeitgebers?
Exogenous zeitgebers are environmental events responsible for maintaining the biological clock of an organism.
What is the most important zeitgebers for animals?
Light
What is melanopsin and what does it do?
- A protein in the retina of the eye which is sensitive to natural light
- It allows signals to be carried to the SCN via the optic nerve
What happens when people move to a night shift or travel to a country?
- Their endogenous pacemakers are out of synchrony with the exogenous zeitgeber of light.
- Disrupted biological rhythms lead to disrupted sleep patterns, increased anxiety and decreased alertness and vigilance.
Advantages of exogenous zeitgebers.
1) research support for the role of melanopsin
- skene found that despite blind people lacking visual perception, a vast majority of them are still able to have some light perception due to the functioning of cells containing melanopsin.
- this allows them to reset their circadian rhythms
- even though they lack visual perception, blind people’s circadian rhythms are still influenced by the presence of external light and shows that exogenous pacemakers have a strong influence over our sleep wake cycle.
2) Vetter et al (2011) investigated the importance of light in the regulation of the sleep-wake and activity-rest patterns of two groups of volunteer ppts over a 5 week study period.
- One group remained in normal ‘warm’ artificial light while the other group experienced artificial ‘blue enriched’ light that had a spectral composition close to daylight.
- All ppts kept a daily sleep log and wore devices that measured their movement over each 24 hour period.
- Ppts working under the warmer light synchronised their circadian rhythms each day with the natural light of dawn.
- Over the course of the study, sunrise advanced by 42 minutes. - The ppts who were exposed to blue enriched light did not show the same 42 minute adjustment and instead synchronized their rhythms to office hours.
- The results confirm that light is the dominant zeitgeber for the SCN and that its effectiveness depends on its spectral composition.
3) Burgess et al (2003) found that exposure to bright light prior to an east-west flight decreased the time needed to readjust to local time on arrival.
- When pps were exposed to continuous bright light before their long flight to a far destination, their circadian rhythms shifted by 2.1 hours over the course of their study.
- As a result, pps felt sleepier 2 hours earlier in the evening and were well adjusted to the local time at their destination upon arrival.
- This supports our understanding of exogenous zeitgebers as it shows the influence that external cues such as bright light can have over our sleep wake patterns.
Who studied Kate Aldcroft in a laboratory?
Folklard
How long was Kate Folklard studied for?
25 days
Who spent their time in a cave?
Siffre
How many months did he spend in a cave ?
7 months
