Lecture eight - Sleep Regulation Flashcards
What is the ‘hypnotoxin’ theory of sleep?
During a course of wakefulness we get a build up of a ‘sleep toxin’ that makes us tired. When we sleep, we break down this toxin.
What was the proposed molecule responsible for sleepiness in the 1990s?
Adenosine.
How does caffeine increase wakefulness?
It is antagonist for the adenosine (A2A) receptor in the brain and heart, i.e. it prevents us from feeling the effects of adenosine build up.
What evidence was found that conflicted the idea that adenosine was the ‘hypotoxin’ that induces sleepiness?
Studies looking at adenosine levels across prolonged wakefullness found that it actually went down and then increased when sleep was finally had.
Other studies have found that different brain regions have different levels of adenosine across wakefullness and sleep.
Neither of these points feel that compelling to be fair, but adenosine as the sole molecule causing sleepiness is also not convincing.
Are cytokines thought to also play a role in sleepiness and wakefulness?
Yes.
People with certain autoimmune conditions with elevated levels of particular cytokines experience increased levels of sleepiness (also not that convincing to be fair).
What are circadian rhythms?
What are the four characteristics required for a circadian rhythm?
Circadian rhythms are self-sustaining oscillations in the body that are associated with our 24-hour sleep/wakefulness cycle. examples are melatonin levels and body temperature.
- Persist without time cues.
- The phase of the rhythm can be shifted by light or drug cues.
- Period (length) of the rhythm can change based on cues and patterns.
- Temperature does not influence the period or phases of the rhythm.
What is the “master clock” of the body?
The SUPRACHIASMATIC NUCLEI.
This set of two nuclei is found in the hypothalamus above the optic chiasm. These nuclei are considered to contain a biological clock that regulate circadian rhythms.
When there is damage or removal of these nuclei circadian rhythms become dysregulated/cease to occur.
Do the SCN requrie neural connections to surrounding neurons in the brain to regulate circadian rhythms?
No. It seems that they do not, as circadian rhythms are restored with transplant of the SCN before neural connections are able to be formed.
It is thought that the SCN regulates circadian rhythms via chemical messengers.
What is one of the main signals the SCN uses to regulate circadian rhythms?
Light.
Light-sensitive protein in the retina, melanopsin, send signals to the SCN.
What is the light-sensitive protein in the retina called that sends signals to the SCN?
MELANOPSIN. This protein is stored in ganglion cells in the retina.
Why do people who are blind tend to have regimented routines?
Without input of light signals to the SCN, circadian rhythms become difficult to regulate and maintain. Having other signals, such as when one eats and sleeps, can aid in regulating the circadian rhythms via other pathways.
Are circadian rhytms slightly longer than 24 hours?
If so, how do we manage this?
Yes.
We need to slightly adjust our circadian rhythms daily and this is done by exposure to light.
Light exposure at night (when body temperature drops) shifts the phase forward.
Light exposure in the morning (as body temperature increases) shifts the phase back, for example.
Are melanopsin containing ganglion cells more sensitive to short length light?
Yes.
Hence why we have blue light reducing mechanisms on digital devices.
What properties of light influence the response the SCN has?
Intensity of light source.
Wavelength of lgiht - we are more sensitive to shorter wavelength light.
Prior light experiences can sensitise or habituate SCN response.
Duration of light exposure.
Is it recommended to get daylight exposure in the middle of the day?
Yes. This helps to regulate the circadian rhythms.
