8 - BIOLOGICAL RHYTHMS + TRADITIONAL VIEW OF SLEEP Flashcards
what is a biological rhythm?
regular changes in behaviour and internal states of a living organism
ultradian rhythm
= faster than a day
- sleep stages
- eating behaviour (meal times = prime us to feel hungry - usually rhythmic)
circadian rhythm
= take about a day
- sleep-wake cycle
- hormone production (some types - eg if only produced at day or night)
infradian rhythms
= slower than a day
- hibernation cycle (takes a year)
- menstrual cycle (takes a month / a few days in rats)
traditional view of sleep and wakefulness
= sleep is PASSIVE DEFAULT state
hypothesis: brain needs stimulation from the environment to wake up (without stimulation it remains asleep)
- leave brain to it’s own devices = it would be asleep
experimental evidence of the traditional view of sleep and wakefulness
Brèmer (1930s)
- transected cats brains
- cut between medulla and brainstem (encéphale isolé = isolated brain) - completely paralysed and needs ventilator to breathe
= normal sleep-wake cycle - cut at midbrain level (cerveau isolé = isolated forebrain) - disconnected pons
= constant sleep
traditional view: the reticulo-thalamus system wakes up the brain
- has an activating effect on the whole brain
- activates and excites the whole forebrain
- activity in this system = activity all over the brain
ARAS
what is the reticulo-thalamic system?
- from the medulla, through the pond and up into the thalamus
= bundle of fibres called the reticulate system
what is ARAS?
ascending reticular activating system
- wakes the brain
where does visual information enter the brain?
via the thalamus (LGN)
how does constant sleep work? - Bremer
- path from pontine nuclei to thalamus has been cut
- eyes closed = no visual information / sensory input
where does auditory information enter the brain?
- via brain stem nuclei in the pons
- and then to the thalamus (MGN)
information:
- once the visual / auditory information has enter their associated areas
- then passed onto their primary cortices
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where does other sensory information enter the brain?
- through medulla and pons and into the thalamus
information:
- Bremer didn’t use humans
- but could happen if neck broke in an accident
- patient would be complete paralysed and need a ventilator
- vision and audition would be in fact = normal sleep-wake cycle
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