Lecture 5- Sleep Flashcards
What is sleep?
-readily reversible state of reduced responsiveness -recumbent posture (lie down) -raised threshold to sensory stimuli -low level of motor output -intermittent high levels of brain activity (bursts) -dreaming -all animals seem to do it
What are the possible reasons for sleeping? (6)
1.memory stabilisation, memories strengthen when asleep 2.cleaning and maintenance 3.for unlearning, getting rid of unwanted memories 4.restoring something (energy, neurotransmitters?) 5.adaptive inactivity: protection as it keeps you from the outside world where you wouldn’t do well 6.rewiring preprogrammed brain in light of experience
How much time in a lifetime do you spend sleeping?
-on average about a third
Do all higher vertebrates sleep?
-yes -but even drosophila does
What are the physiological changes in your body when you sleep?
-temperature drops -respiration slows (saves energy) -alertness decreases -brain activity changes
What do you look at when examining sleep wave patterns?
-EEG
How do you utilise EEG to examine sleep patterns?
-scalp electrodes record the electrical potential of cortex -measures activity in populations of cortical neurons -voltages generated by dendrites of pyramidal neurons acting synchronously -in form of rhythmic bursts of activity (brain waves) -multiple leads on scalp and ears -each traces reflect activity in different cortical regions
What is the EEG signature when awake?
-small, high frequency waves -a lot of activity in the cortex when awake
What is the EEG pattern of a sleeping brain?
-two characteristic brain wave patterns 1. Non-REM sleep: larger more rhythmic brain waves, low frequency, small 2. REM sleep has small hight frequency waves indistinguishable from waking state
What does the EEG of an awake person look like (picture)?
- awake or REM sleep
- low voltage, random, fast
- when drowsy= alpha waves
What does the EEG of a person sleeping look like (picture)?
- 3 stages (or 4 in the old system) of nonREM sleep
- stage 1: theta waves
- stage 2: sleep spindles and K complexes
- stage 3: delta waves
When do you enter non-REM sleep?
-enter into this stage first, just after you fall asleep
How many stages are there of non-REM sleep?
-3 or 4 (old system)
What stage of non-REM sleep is the deepest?
-3rd
Do you dream in non-REM sleep?
-very rare only about 10% of dreaming occurs here -if dreaming then mundane and not very vivid, usually the worst nightmares in stage 3-4 sleep -often dream of chocking, anxiety and paralysis -not narrative, but locked in one unpleasant situation (e.g., locked in a tomb)
What is non-REM sleep called?
-slow wave sleep SWS -N3 sleep
What is your body like when you are in non-REM sleep?
-muscles relaxed but body capable of movement -temperature drops, metabolism down -difficult awaken
When does sleepwalking occur?
-in non-REM N3 sleep -also nocturnal enuresis occurs her (bed wetting)
What are the stages in sleeping like? (graph)
-sleep spindle in stage II
What is the EEG signature of a person in REM sleep?
-EEG looks “awake” -called “hallucinating brain in a paralysed body”
What is the brain O2 consumption when in REM sleep?
-higher than when you are awake
What is the mobility of the body in REM?
-immobilised -only eyeballs can move (rapid eye movement)
How hard is it to wake up a person in REM sleep?
-easy
What is the physiological state of a body in REM sleep?
-temperature control lost, high but irregular heart and respiratory rates -clitoral and penile erection in this stage
How does the amount of REM sleep and sleep in general change with age?
- at 20- sleep about a third of the day, chunk of REM
- older= less REM sleep, and sleep less -young children= at 1 year= 50/50
- when born= sleep 2/3 of the day, and half of that is REM sleep
- REM is more important when younger
- this is when brain is maturing,the plasticity still on -in utero=sleep the entire time and all of it REM
Where do the Raphe nucleus and the Ascending reticular system project to in the brain?
- Raphe: forward into the thalamus and lot of fibres forward and sweeping through the whole cortex
- Ascending reticular system: to the thalamus and back through the brainstem to the spinal cord
Where do the Locus coeruleus and Tuberomammillary nucleus project to?
- Locus Coeruleus: into thalamus and the whole cortex
- Tuberomammillary nucleus: to thalamus and whole cortex and spinal cord
What are the thalamocortical interactions?
- thalamus innervates the cortex -has two states, one directly reflects sensory inputs and one where thalamic neurons fire in a coordinated, slow rhythm -the latter prevents sensory inputs being passed to the cortex
- brainstem activity switches rhythmic state OFF in thalamic neurons
- explanation of non-REM sleep
- so can regulate whether you are awake or in non-REM sleep
- thalamus sends most of its projections to the cortex, wide distribution
- two situations to consider: thalamus getting lot of sensory input and relay to cortex
- when these arousal centres are active and their projections to the thalamus are firing they gate the thalamic cells to pay attention to the inputs -so can get relayed to cortex and as a result get the high frequency activity -if the brain stem inputs shut down, the thalamic neurons start ignoring the sensory input and start signing their own song= this is slow and rhythmic -so the big waves seen in nonREM sleep is a thalamic signal
How are the arousal centres controlled?
- when arousal nuclei active: the thalamus listens to inputs
- TMN- tubemammilary: have two types of cells, ones using histamine and the other using orexin -orexin ones are part of the swicth, if the orexin ones are active they are switching the whole system on and you are awake
- VLPO- this is the offswitch = this inhibits the whole system
- two systems feed into the brainstem arousal centres -orexin releasing neurons in the tubulomammillary nucleus (TMN) stimulate the arousal centres, promoting wakefulness -the ventrolateral preoptic nucleus (VLPO) in hypothalamus inhibits the arousal centres, promoting sleep
What is the arousal system control when awake?
-during arousal (wakefulness) brainstem and hypothalamic inputs excite cortex and allow thalamus to pass sensory information
What is the arousal system control when in non-REM sleep?
- during non-REM sleep brainstem and hypothalamic inputs inhibited, cortex entrained by thalamus, no sensory input
- thalamic rhythm dominates
What is the arousal system control when in REM sleep?
- during REM sleep, most brainstem and hypothalamic inputs inhibited but ascending reticular system still partly active so cortex still active with sensory input
- REM sleep is an intermediate position
- it is possible to gate the inhibitory influences of VLPO
- and if that inhibits a little bit hard then some of the ascending reticular system can escape the inhibition and can send some infor onto the thalamus, so thalamus isn’t the only one in charge
In an EEG which waves mean what?
-theta waves (stage 1)= hippocampal activity -sleep spindles(stage 2) =thalamic -K complexes (stage 2)=cortical -delta waves (stage 3 and 4)
Reason for sleep 2: Cleaning/maintenance: glymphatic system.
- CSF from subarachnoid space flows into brain
- enters channels around blood vessels (made by astrocyte endfeet)
- flows into parenchyma (though glial aquaporin channels)
- enters space around veins and flows to subarachnoid space -brain doesn’t have lymphatic system (drains away ECF)
- has surrogate lymphatic system
- the blood vessels in brain accompanied by channels and in that channel the ECF flows,
- when deep in the brain (parenchyma) the water leaks across through aquaporin
- then collects all the crap and back into channel
- the glymphatic system
What is the synaptic homeostasis hypothesis?
- during sleep, strength if synapses wound back (synaptic depression)
- something preserves most important ones
- improves signal to noise, net gain in strength of important connections
- sleep is the price we pay for plasticity
