L13 - Sleep Flashcards
Behaviourally, what is sleep?
A normal absence of consciousness
Electrophysiologically, what is sleep?
A pattern of specific brain wave activity
What shows that sleep is a basic homeostatic need?
- Requirement for sleep increases with time awake
- Sleep/sleep-like behaviour occurs in all multicell organisms
In humans, what does sleep duration change with?
Age
What is the relationship between organism size and length of sleeping period?
Smaller organisms alternate short periods of sleeping/waking whereas bigger organisms have less longer periods of sleep
What ecological factors suppress sleep?
Protection against predators, enhanced mating success, incompatibility with swimming, thermoregulation, need to forage for food, adaptive inactivity
What intrinsic factors promote sleep?
Enhancement of memory consolidation, rewiring of CNS, energy conservation, metabolic clearance, sensorimotor tuning, synaptic homeostasis
As someone becomes “more unconscious” what happens to the amplitude and frequency of their EEG waveforms?
Amplitude increases and frequency decreases as person becomes “more unconscious”
What is alpha activity associated with?
Awake but with eyes closed
What is beta activity associated with?
Being alert, attentive & actively thinking.
What is theta activity associated with?
Stage 1 sleep
What are sleep stages 2-4 called?
slow wave sleep (SWS) or
non-rapid eye movement (NREM) sleep
What is REM sleep also known as?
paradoxical sleep
What is delta activity associated with?
Stage 3 and 4 sleep
How many sleep cycles are in average night?
5
What happens to length of REM and SWS throughout each sleep cycle?
Length of REM increases, length of SWS decreases
Which cycles is deep sleep present in?
Only first 2 cycles
What determines sleep patterns?
Interaction between homeostatic
sleep pressure and an internal (circadian) clock
What could explain smaller animals sleep patterns?
The homeostatic sleep pressure being stronger and the circadian clock being weaker
What are the three neural systems actively involved in controlling sleep?
Forebrain system (SWS sleep)
Brainstem system (activates forebrain system into waking)
Brainstem system (triggers REM sleep)
What have nerve transection studies by Frédéric Bremer shown?
When nerves were cut below the brainstem all stages of sleep were maintained
When the brainstem was cut off the rat was in a constant state of SWS
What brain structures are in the ascending arousal system?
Dorsal Raphe, Lateral Dorsal Tegmentum, Pedunculopontine Tegmentum, Locus Coeruleus, Basal Forebrain, Lateral Hypothalamus, Tuberomammillary nucleus
What does the dorsal raphe release?
Serotonin
What does the Locus Coeruleus release?
Noradrenaline
What does the Lateral Hypothalamus release?
Orexin
What does the Tuberomammillary nucleus release?
Histamine
What is orexin also known as?
Hypocretin
Where does orexin project to?
- projects all over the brain
- Signal through the Ox1R and Ox2R receptors in target regions
What do orexin KO (knockout) mice show?
Reduced wakefulness and increased SWS/ REM
What does orexin promote?
Wakefulness
What are the 4 main symptoms of narcolepsy?
- Excessive daytime sleepiness with irresistible sleep attacks during the day
- Cataplexy (brief episodes of muscle weakness/paralysis precipitated by strong emotions such as laughter or surprise).
- Sleep paralysis
- Hypnagogic hallucinations or dream-like images that occur at sleep onset
What did post-mortem brains from humans with narcolepsy show?
Reduced number of orexin neurons
What is unihemispheric sleep?
When only one hemisphere of the brain/ one eye sleeps at one time
What is relationship between unihemispheric sleep and risk of predation?
More likely to perform unihemispheric sleep if risk of predation is high
How do great frigate birds sleep when flying for 10 days at a time?
They unihemispherically sleep on the ascension of their flight
They sleep a much lower percentage of the time compared to when they aren’t flying
How do great frigate birds fly long distances?
- Primarily rely on a soaring–gliding strategy
- Circular rising on thermals (air currents)- soaring followed by straight gliding down
Which hemisphere is asleep for great frigate birds when ascending while circling right?
Their left hemisphere, always opposite to direction of circling
In reptiles, what did video analysis of closed eyes paired with EEG recordings reveal about sleep patterns?
- Regularly occurring episodes of REM
- sleep cycles take ~80s in this species (P. vitticeps)
What 4 factors are used to define sleep when EEG cannot be used?
- A period of quiescence associated with a species specific posture
- An increased arousal threshold (reduced responsiveness to external stimuli)
- Quick reversibility to wakefulness
- Homeostasis
Evidence for flies sleeping:
- Flies in this ‘Resting’ Posture Show Elevated Arousal Thresholds
- Deprivation results in rebound ‘Rest’
What occurs in honey bees when sleep deprived?
- learning and memory impaired
- Waggle-dance precision reduced
- navigational memory is impaired
