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
-
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
-
information:
- if no eyes/completely blind = not a normal sleep-wake cycle
-
cutting below the pons
- won’t affect ARAS
- will still have sensory input
- eyes and ears
- NORMAL SLEEP CYCLE
cutting above the pons (thalamus)
- signal can’t be passed to thalamus
- can’t wake the brain
- severs connections between pons and rest of the brain
- CONSTANT SLEEP
fact:
cortisol is a stress hormone
-
cutting through the pons
- NEAR CONSTANT WAKEFULNESS
- ARAS damaged
- but would predict a mixture between constant sleep and normal cycle (according to Bremers assumptions)
- ruins idea that sleep is default state
information:
sleep is a multilevel process - doesnt just involve alertness
-
what happens when we sleep
alertness/body temp/growth hormones/cortisol
alertness
- differing levels of alertness during the day
- not alert when we sleep
body temp
- decreases at night
growth hormones
- only released during first half of sleep
cortisol
- low when we go to sleep
- peaks at transition from sleep to wake
biological clock
- a cells internal cycle
- doesn’t need internal cues
- can be affected by zeitgebers, but doesn’t need them in order to have a rhythm
- they can shift the natural rhythm
- ENTRAINED it
