Lecture 12 - Function of Sleep - Part 2 Flashcards
What is the Sleep as Restoration hypothesis of the function of sleep?
The idea that when we sleep we engage in restoring the body.
What are some examples used to support the sleep as restoration hypothesis?
We sleep more when we are fighting off infection, viruses, bacteria etc.
We sleep more when we have injured ourselves, such as broken a bone.
It has long been thought that adenosine causes sleepiness. Exercise increases amount of adenosine (due to increased energy expenditure).
Does exercise increase amount of sleep?
No. Acute exercise does not appear to have a direct relationship with increasing amount of sleep.
In fact, severe exercise can negatively impact sleep.
Does sleep deprivation negatively impact our fever response?
yes.
Do those who are chronically sleep deprived at higher risk of getting infection?
Yes.
A study that looked at sleep and the common cold found what about those who got cold symptoms and those who did not?
Found that those who slept over 7 hours a night the week before were less likely to develop cold and flu symptoms compared to those who got less. Those who got less than 5 hours sleep were the most likely to develop cold symptoms.
What is the glymphatic system?
The glymphatic system is responsible for clearing waste from the brain, such as metabolic waste and beta amyloid.
Astrocytes (a subtype of glial cells) wrap their ‘feet’ around the arteries and veins that run through the brain. There is a space between the astrocyte feet and the artery/vein, where CSF flows. It gets pumped along by the pressure and pulses in the arteries/veins. It can also move out of this space, between the feet of the astrocytes, and move around the neurons (known as interstitial fluid), where it collects metabolic waste etc, and then goes back into the space between astrocyte feet and vein and gets pumped out of the brain. This is how the brain clears waste.
How does sleep impact the glymphatic system?
When we are awake the astrocytes are full of water and are larger, reducing the interstital space, that allows CSF to flow out and collect metabolic waste in the brain.
When we are asleep, astrocytes water content goes down and the interstitial spaces become bigger, allowing the fluid to move around neurons and collect metabolic waste and beta-amyloid etc.
In short, sleep allows the brain to clean itself.
What percentage of beta-amyloid is removed from the brain during sleep?
65%
What is the potential role of sleep in Alzeihmer’s disease?
Alzeihmer’s disease is thought to be caused by a build up of beta-amyloid plaques in the brain.
The brain clears beta-amyloid from the brain during sleep.
Sleep problems have long been a complaint of those with Alzheimer’s. It is therefore thought that these peoples’ lack of sleep contributed/contributes to the build of beta-amyloid and the development of this disease.
Does poor sleep increase risk of developing Alzeihmer’s, especially in those who are genetically predisposed?
Yes.
Has it been found that the more sleep spindles an individual has over a night of sleep, the better they consolidate memory/learning?
Yes.
What is the Synaptic Homeostasis Hypothesis of sleep?
SHY contents that sleep involves us returning our brain’s synaptic weight to homeostasis.
When we learn we increase the number of neuronal/synaptic connections. If we never pruned these we would have a brain much bigger than ours that requires far more energy than we could provide.
This hypothesis proposes that when we sleep we prune or grow these connections based on usage.
This can be reflected in the early hours of sleep where we have more slow-wave sleep (which is indicative of lots of neurons firing a the same time. If we have been learning all day then there are more neurons firing). This slow-wave sleep decreases across a night of sleep, indicating that synaptic connects are being lost/removed to return the brain to synaptic homeostasis.
What does the Synaptic Homeostasis Hypothesis of sleep say about how sleep improves memory/learning?
This hypothesis states that the synaptic connections are made during the day when we learn/experience new things. When we sleep we then prune away the synapses that we no longer require/do not use. This reduces noise in the brain and makes the synaptic response from the learned information more clear. The signal to noise ratio is reduced.
What evidence has there been to support the Synaptic Homeostasis Hypothesis of sleep?
Structural evidence in drosophila shows that there are more neural connections during the day and after sleep the neural connections decrease. In sleep deprived flies the neural connections do not decrease.
Rats who have had the whiskers cut off on half their face show more slow wave sleep earlier on in their sleep on the hemisphere contralateral to their whiskers, compared to the hemisphere contralateral to the side of the face whose whiskers had been cut off.
