Endogenous pacemakers and exogenous zeitgebers Flashcards
What does endogenous mean
Anything whose origins are within the organism
What is the most important pacemaker in humans
The Suprachiasmatic nucleus
Where is the Suprachiasmatic nucleus
In the hypothalamus
What does the Suprachiasmatic nucleus do
Acts as the ‘master clock’ with links to other brain regions that control sleep and arousal, and has control over other biological clocks throughout the body
How does the Suprachiasmatic Nucleus work
Neurons within the Suprachiasmatic nucleus spontaneously synchronise with one another, so that target neurons in other locations in the body receive correctly time-controlled signals
How is the Suprachiasmatic Nucleus reset
Using light levels detected via the optic nerve
How does the Suprachiasmatic Nucleus control sleepyness
By regulating the production and secretion of melatonin in the pineal gland via an interconnecting neural pathway
What does exogenous mean
This refers to anything whose origins are outside the organism
What are two examples of exogenous zeitgebers
Light and Social Cues
How does light effects biological rhythms
Receptors in the SCN are sensitive to changes in light levels and use this information to synchronise the activity of the body’s organs and glands
How do retinal cells help reset the biological clock
A small number of retinal cells contain melanopsin, a protein sentsitive to natural light, which carry signals to the SCN to reset the daily body cycle
How do social cues effect biological rhythms
Social cues such as mealtimes and social activities may also have a role. Aschoff et al showed that individuals are able to compensate for the absence of zeitgebers by responding to social zeitgebers instead.
What did one study on jet lag find
That the circadian rhythms of air travelers adjusted more quickly if they went outside more at their destination, and this was theorised to be because they were exposed to the social cues of the new time zone, however this can be better explained by light
How do the circadian rhythms of blind people remain the same as non-blind people
They are reset by social cues, however this could be that their sleep-wake cycle is still influenced by light, as connections still exist between the eye and the SCN that do not involve those parts of the visual system on which the perception of light depends
What study emphasised the importance of the SCN
Morgan’s study on hamsters, where he bred a strain of hamsters so they had abnormal circadian rhythms of 20 hours rather than 24 hours. SCN neurons from these hamsters were then transplanted into the brains of normal hamsters, and these normal hamsters displayed the same abnormal circadian rhythm of 20 hours. The opposite also applied when the SCN of normal hamsters was implanted in the brains of abnormal hamsters.
Who did mad science shit on the brains of hamsters to prove points about the SCN
Morgan, who implanted the SCN of hamsters into other hamsters
Discuss research into the effects of artificial light in adolescents
Touitou et al argued that exposure to artificial light at night results in disruptions of circadian rhythms, with his research showing that teenagers exposed to electronic media at night (particularly blue light LED) had suppression of melotonin secretion and circadian disruption. As a result, adolescent sleep becomes irregular. In the long run this is detremental to health.
What is support for the role of light in the sleep wake cycle from blind people
A study of blind people showed the importance of light in setting circadian rhythms. Some blind people are able to reliably entrain their circadian rhythm in response to light despite a total lack in image forming visual perception. Skene and Arendt estimate that the vast majority of blind subjects who still have some light perception have normally entrained circadian rhythms. This suggests that the pathway from the retinal cells containing melanopsin to the SCN is still intact. As further evidence of this pathway’s importance in setting the biological clock, people without light perception show abnormal circadian entrainment
What is the role of articifical light as a exogenous zeitgeber (Blue light vs Warm Light)
Vetter et al demonstrated the importance of light in the regulation of the sleep-wake and activity-rest pattern of two groups of volunteer participants over a five week study period. One group remained in normal ‘warm’ artificial light over the five weeks while the other group experineced artificial ‘blue-enriched’ light that had a spectral composition close to daylight. They found that participants working under ‘warm’ light synced their circadian rhythms each day with the natural light of dawn. Over the course of the study, sunrise advanced by 42 mins, but participants exposed to blue-enriched light did not show the same 42 minuite adjustement and instead synchronised their rhythms in office hours. The results confirm that light is the dominant zeitgeber for the SCN and that it’s effectivness depends on spectral compostion
Who demonstrated the importance of light in sleep wake cycle using blue light
Vetter et al
Who estimated the amount of blind people with normal circadian rhythms
Skene and Arendt estimate that the vast majority of blind subjects who still have some light perception have normally entrained circadian rhythms.
Who is worried about teenagers being on their phones at night
Touitou
