Sleep and Biological Rhythms Flashcards
How is sleep defined? (simple)
A normal absence of consciousness
What does Siegel’s definition of sleep include? (3)
Rapidly reversible
Reduced sensory responsiveness
Homeostatically regulated - lost sleep increases drive for ‘sleep rebound’
Reasons for sleep? (4)
Energy conservation
Growth and repair
Metabolic clearance
Learning and memory
How does sleep vary across organisms/time?
Need decreases with age
Larger organisms tend to sleep for longer
Smaller sleep in bouts
Patterns change e.g. newborns also may sleep in bouts
Ecological influences of sleep? (4)
Predation risk suppresses
Thermoregulation suppresses
Foraging for food suppresses
Swimming suppresses e.g. dolphins 1/2 a brain at a time to breath at the surface
Intrinsic influences on sleep? (3)
Memory consolidation increases
Energy conservation
Metabolic clearance (byproducts accumulate in wakefulness)
Sleep stages?
Awake
Stage 1, 2, 3, 4
REM
Brain waves of each sleep stage?
Awake - alpha, beta (=alertness) 1 - theta 2 - sleep spindles form, slow waves 3, 4 - slow waves, delta activity REM - theta and beta (resembles awake)
Sleep cycles?
Around 5 per night, with deep sleep (stage 4) only in first 2.
Around 90 minutes in humans
Homeostasis in sleep?
Cycle with homeostatic sleep pressure and internal circadian clock -internal clock pushes past need to sleep until homeostasis kicks in in the evening
Neural systems of sleep? (2)
Forebrain systems - support SWS
Brainstem - activates forebrain for waking, triggers REM
What is the ascending arousal system?
Neural system in rats to govern sleep
Role of orexin?
In sleep - peptide secreted by neurons in lateral hypothalamus and stimulates feeding, related to wakefulness.
Orexin knockouts destroy bout-sleeping in rats and cause narcolepsy like symptoms
Symptoms of orexin knockouts? (4)
Narcolepsy-like; Sleep attacks in the day Cataplexy (weakness after strong emotion) Sleep paralysis Hypnagogic hallucinations
What is unihemispheric sleep (USWS) and where is it found?
Sleeping with on side of the brain - seen in aquatic mammals and fish
Unihemispheric sleep in ducks?
Sleep with one eye open, brain hemisphere on opposite side awake.
Used where there is high predation risk, and often seen depending on location in group i.e. outer edges
USWS in frigate birds?
Large, making long flight trips up to 3000km over water
When flying, they spiral up thermals and glide straight down - USWS associated with the spiralling up, where the same brain side as direction of turn sleeps so they can still see other birds to avoid them.
Sleep in reptiles?
More rapid REM/NREM cycle than mammals/birds - 80s in Australian dragon, but same pattern as us
Zimmerman’s properties of sleep? (4)
Why do we need them?
In simpler nervous systems, we cannot use EEGs.
- Quiescence with species specific posture
- Increased arousal threshold
- Quick reversibility
- Homeostasis i.e. interruption leads to greater need
Measuring sleep in flies?
Test tube - food and cotton at opposite ends with infrared sensor detecting crossing frequency.
Overall conclusions about sleep across taxonomic ranks?
Very similar features - e.g. neurochemicals (exception of orexin, not in flies), patterns and overall properties
Certain features species-specific e.g. cycle length and side of brain
Two mechanisms of biological rhythm control?
Passive/retroactive - relies on homeostasis adapting to changes
Proactively - biological timekeepers
Examples of circadian rhythms? (7)
Body temp Hormone secretion Locomotion Sleep Alertness/cognition Muscle strength Immune function
What is voluntary activity?
Our main source of study for bio rhythms - behaviours that the animals would do anyway, e.g. hamsters running on a wheel
What is an actogram?
Plot for rhythms - each successive day is a new row, and we can see the rhythm shifting:
- - - -
/ - - - -
// - - - -
Entrainment?
Training the biological clock to sync with environmental cues - this gives an aligned actogram
Circadian rhythms in insects?
Flies - crepuscular i.e. active at twilight and dawn
Crickets - start calling at dusk
Key characteristics of circadian rhythms? (3)
Free-run in constant environments, around 24hrs
Synchronised by recurring changes in the environment
Anticipate these change i.e. occurs slightly before
SCN?
Suprachiasmatic nucleus, in the hypothalamus, the master pacemaker in mammals
More active during the day
Neurons of the SCN?
Also demonstrate individual clock activity - isolated ones give rhythmic output, synchronised in intact SCNs
Genes involved in light/day cycle?
CLOCK and BMAL1 - stimulatory
PERIOD/CHRYPTOCHROME - inhibitory
(These are mammalian)
Where does the SCN obtain info about time of day?
Retinohypothalamic tract (RHT) via the optic nerve
Effector mechanism of the SCN?
SCN signals to pineal gland in absence of light, from which melatonin is secreted to induce sleep
Examples of ultradian rhythms?
Human sleep cycles, growth hormone release
Examples of infradian rhythms?
Bird migration, hibernation, reproductive cycles
Circannual timer in sheep?
Short coat and small testes in summer, opposite in winter
Role of prolactin in circannual timers? (sheep example)
Prolactin secretion in summer shrinks testes
Associated with melatonin, which detects day length changing to indicate season
Neural control of prolactin?
Pituitary pars tuberalis - acts on secreting cells in association with melatonin to control levels seasonally
Control of rhythms in marine environments? (2)
Gravitational force of the moon
Rotational force of the earth
What is the tidal cycle?
2 high tides a day when moon is overhead = 12.4 hour cycle
One tide is the highest = 24.8 hour high tide cycle
What is the bi-lunar cycle?
Moon and sun align giving spring tides, neap tides when they do not - 14 day cycle
Circa-tidal rhythm in eurydice?
Lives in sand and emerges at high tide to swim and feed
Considers both the tidal cycles (24.8 hours) and which tide is the highest (increased swimming every 12.8 hours)
Pigmentation cycle in eurydice?
More pigmentation deposited during light (to protect from UV) and less at night
Sleep stage and eye movement?
REM
Sleep stage and neck movement?
Waking/REM transitions
Sleep stage and respiration/heart rate?
Highest when awake and REM
Frequency of each sleep stage
Awake - 15-30Hz 1-4-8Hz 2-10-15Hz 3-2-4Hz 4-0.5-2Hz REM - 15-30 Hz
