Sleep Flashcards
How does sleep volume reflect how safe an animal is when they sleep?
Very safe = lots of sleep
Moderately safe = moderate amount of sleep
Vulnerable = small amount of sleep
Give some examples of animals turning off their need for sleep.
- Dolphins&whales stay awake 24hrs a day for first couple of weeks after they give birth as baby is very vulnerable, so does baby
- Migratory birds forage for food during the day & fly at night during migration in Spring & Autumn
- Male sandpipers are active up to 23hrs a day for nearly 3 weeks during the Spring breeding season
Why do some animals hibernate?
What happens to them during hibernation?
- To conserve energy whilst food is scarce
- Slows down ageing process
- Temperature & heart rate decrease
- Dendrites lose almost 1/4 of their branches
- Come out of hibernation every few days to raise body temperature (but stay asleep)
What is Unihemispheric sleep?
What animals can sleep unihemispherically?
One hemisphere sleeps (and the contralateral eye) while the other stays awake
- Aquatic mammals
- Many birds
- Some reptiles
What is Inactivity theory of sleep?
- The ‘adaptive’ or ‘evolutionary’ theory
- Suggests inactivity at night helped animals to survive, as they didn’t injure themselves in the dark & weren’t killed by predators
- This trait was passed on through natural selection
A problem with this theory is that it is always safest to remain conscious, even if lying still in the dark
What is Energy conservation theory of sleep?
- Food is not always to come by, so an animal must conserve its energy
- Especially important at night when it may be harder to find food
Support: energy metabolism is reduced during sleep (by 10% in humans)
Problems: animals engaging in Unihemispheric sleep are still using up energy
How do Restorative theories explain the need for sleep?
- During sleep there is restoration of what has been lost from the body while awake
Support: Many major restorative functions occur mainly in sleep e.g. muscle growth, tissue repair, protein synthesis, etc.
What is Brain plasticity theory of sleep?
- Sleep is a time in which the brain develops and changes
Support:
- Sleep appears to be crucial for initial brain development
- Extensive research to suggest improvement in cognitive function following sleep e.g. Ellenbogen et al., 2006
What is a circadian rhythm?
The human biological clock, synchronises to the Earth’s 24hr rotation using signals from the environment, known as zeitgebers (“time-giver”)
What are the Earth’s signals from the environment that control circadian rhythms known as?
Zeitgebers (“time-givers”)
What is the strongest Zeitgeber?
Light
- (although social cues have an influence e.g. getting used to waking up at a certain time to go to work)
- some adaptations have led to stronger temperature zeitgebers
What is the evidence that supports light being the strongest Zeitgeber?
- After an entire night without sleep, you will start to feel more awake when it becomes light (Babkoff et al., 1991)
- When have no reason to wake at a certain time, people in eastern Germany wake 30mins earlier than those in Western Germany - consistent with 30min difference in sun timing (Roennebery, Kumar & Merrow, 2007)
Describe morning people (“Morning Larks”)
Wake early, alert, reach their peak of productivity early
Describe evening people (“Night owls”)
Take longer to warm up in mornings, reach peak of productivity later
What are the negative impacts of being an evening person?
Can lead to ‘social jet lag’
- Lower grades (despite average/above-average intelligence)
- Increased alcohol use & overeating
- Less happy overall
What are mammalian cells?
- Cells that contain “circadian clocks”
- Collections of genes which regulate the expression (‘switching on’) of other genes critical for cell physiology and metabolism
What genes have a direct implication with sleep disorders, diabetes, cancer and bipolar disorder?
Circadian Clock Genes
What does the Suprachiasmatic Nucleus (SCN) do?
Synchronise all circadian clocks in the body to the same 24hr cycle
- Is the master circadian pacemaker
- Main driver of rhythms for sleep
How does the Suprachiasmatic Nucleus (SCN) work?
- Has direct photic input from retina
- Has mechanisms which allow them to remain synchronised to each other even in darkness
- Generates circadian rhythm of firing frequency allowing them to synchronise other cells
- Light hits the SCN via a small branch on the optic nerve, known as the retinohypothalamic path
What happens if the Suprachiasmatic Nucleus (SCN) is damaged?
- Causes the peripheral clocks to lose their rhythm
What did Welsh, Takashi & Kay (2010) do in their study of the Suprachiasmatic Nucleus (SCN)?
- SCN cells cultured from a genetically modified mouse were fused with a bioluminescent from a firefly
- Each time the neuron fires the enzyme releases a photon
- Photon (therefore action potential) frequency recorded over 2 weeks showed distinct circadian rhythms
When does Melatonin secretion begin?
Usually two to three hours before bedtime
When is Melatonin production at its highest?
At night
What is the Brainstem responsible for?
Mediating levels of arousal - including the cycles of Non-REM and REM sleep
What is the reticular formation? What is it responsible for?
A collection of nuclei (bundles of cells bodies), fibres and tracts (bundles of axons), running through the Medulla, Pons and Midbrain
What is the Brainstems role in sleep?
- GABA-ergic neurons in the brainstem increase their firing rate
- This widespread release of GABA to the thalamus and cortex inhibits the brain - producing sleep
What happens in the 1st stage of sleep?
This is the transition period between sleep and wake
The EEG is dominated by irregular, jagged, low-amplitude waves of different frequencies
How are the different stages of sleep recorded?
Through the use of polysomnograph, which uses electrodes to record a combination eye-movement activity and EEG
What happens in the 2nd stage of sleep?
Characterised by sleep spindles and K- complexes
- Sleep spindles: 12Hz waves during a burst lasting at least 0.5 seconds
- K- complexes: a sharp wave associated with temporary inhibition or neuronal firing
What happens in Stages 3 and 4 of sleep?
Heart rate, breathing rate and brain activity decrease
Slow-frequency, large-amplitude waves become more common
- Stages 3 & 4 often grouped together into a single stage (slow-wave sleep)
What happens in the 4th stage of sleep (that doesn’t happen in the 3rd stage)?
Has a greater prevalence of slow-waves than stage 3
- but there isn’t a clear boundary
What happens in stage 5 of sleep?
- REM sleep (also known as ‘paradoxical’ sleep)
- EEG shows irregular, low-amplitude, high-frequency oscillations, indicating increased neuronal activity that suggests a ‘lighter’ sleep
- REM sleep also features deep sleep
- Postural muscles are more relaxed than in other stages
- Heart and breathing rates are highly variable, face twitches,, vagina moistens & men get erections
- GABAergic neurons from the medulla are responsible for initiating REM sleep
How are sleep stages grouped?
Non-REM
- stages 1-4
REM
- stage 5
What sequence do the sleep stages follow?
1 -> 2 -> 3 -> 4 -> 3 -> 2 -> REM
- and them begins again from stage 2
How long does each cycle of the sleep stages last?
Roughly 90 minutes
How many cycles of the sleep stages do most people experience in one night of sleep?
Four or Five cycles
In which stage of sleep does most dreaming occur?
REM
- but it does occur in all stages
What is narcolepsy?
A condition characterised by frequent periods of sleepiness during the day
How many people are affected by narcolepsy?
1/1000
- relatively rare
How many suffers of narcolepsy carry the HLA-DR2/DQ1 gene?
90%
What are the four main symptoms of narcolepsy?
The symptoms are an intrusion of a REM-like state into wakefulness
- Attacks of sleepiness during the day
- Occasional cataplexy (losing muscle tone)
- Sleep paralysis (awake but unable to move)
- Hypnogogic hallucinations
What is the link between narcolepsy and Orexin?
People with narcolepsy lack hypothalamic cells that produce and release orexin-potentially due to an auto-immune condition
How is narcolepsy treated?
Mainly with stimulants such as Ritalin
- cannot be treated with Orexin as it cannot cross the blood-brain barrier
What is REM Behaviour Disorder?
For most people the postural muscles are inactive during REM sleep, people with REM Behaviour Disorder move around vigorously (often violently) during REM
Movement displayed by sufferers during REM is thought to be ‘acting out’ dreams
What is Sleepwalking?
The complex movements carried out during sleep such as:
- eating, rearranging furniture, driving cars, walking long distances
In what stage of sleep does sleepwalking occur?
NREM (Non-REM)
What are the causes of Sleepwalking?
Not well understood BUT
- runs in families & occurs mainly in children
- risk factors include sleep deprivation, stress & alcohol
How is sleep deprivation (SD) studied?
Experimentally depriving humans of sleep
Experimentally depriving animals of sleep
- rotating platform over water so animals has to continue to move so they don’t fall in water
Examining case studies
- e.g. people who work nights
Examining people with sleep disorders
How does sleep deprivation (SD) affect the brain and cognition?
SD is associated with:
- reduced functional connectivity of the amygdala & executive control regions
- difficulties in emotional regulation
- explicit learning & memory problems
- reduction in functional connectivity between amygdala & regions associated with executive control & inhibition (Shao et al., 2014)
- deficit in sustained attention
- in sea slugs: memory impairment
