Week 4 - Chronobiology Flashcards
what does a normal sleep cycle consist of? how long is it?
Light sleep: Stage 1 = 6%, 2 = 49%
Deep sleep: Stage 3/4 = 23%
Dream sleep: REM = 22%
cycles are 90 minutes, that go from wake –> 1 –> 2 –> 3 –> 4 –> 3 –> 2 –> REM –> 2…
-there may be brief arousals from stage 1 that are not remembered
what happens to the REM and stage 4 amount throughout the night?
REM increases as stage 4 lessens
what is an EEG?
electroencephalogram; measures cyclic predictable pattern
what is seen during wakefulness on an EEG, for both alert and “drowsy”
alert: low-voltage, fast, random activity with high frequency beta waves
drowsy/relaxed: low voltage, fast, random activity with alpha waves
what does the EEG show for the 4 stages of non-REM (NREM) sleep/
1: lightest sleep, high frequency, low voltage with theta waves
2: light sleep with sleep spindles and K complexes
3: deep/slow wave sleep, synchronous delta waves
4: deepest sleep, delta waves >50%
what happens during stage 4 NREM?
deepest sleep, parasympathetic control, lowered vital signs, restorative sleep
what happens during in REM sleep? what does the EEG look like?
desynchronized, paradoxical, activated
- low voltage, high frequency, random, fast sawtooth waves
- EEG appears awake
- paralysis and dreams occur
- eyes move and erections occur
- sympathetic tone dominates
how many hours of sleep has the soonest mortality?
short sleepers: 8 hours
how does sleep length change as we age?
III/IV (deep sleep) decreases while I/II (light sleep) increases
what does melatonin do for sleep chemistry? what receptors does it stimulate?
made in the pineal gland at night due to a loss of light-induced neuronal firing in retinohypothalamic tract
- stimulates MT1: lower brain activation/arousal (turns off midbrain and suppresses sympathetic)
- stimulates MT2: facilitates 24 hr circadian clock
what does cortisol do for sleep chemistry?
peaks in the morning (4-5 AM) linking the HPA (hypothalamic-pituitary axis) to the circadian system
what is the reticular formation (ascending reticular activating system)?
runs through core of brainstem from medulla to midbrain to posterior hypothalamus
- “monolithic” system that incorporates systematic input from many entities that cause arousal
- -ACh, glutamate, monoamines (NE, DOPA, SE, His)
- -these act directly on certain brain areas and modulate other transmitters’ effects, and allow amplification of arousal signals
what are the 6 nt that make up the RAS?
ACh, glutamate, and the monoamines (norepinephrine, dopamine, serotonin, histamine)
how is ACh involved in waking? what makes it? when is it active? what does it do?
made in basal forebrain, and active during wakefulness and REM
- in pons, the laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT)
- from these, project to sub-cortical regions like thalamus, lateral hypothalamus, then back to basal forebrain
how is it that the basal forebrain can promote wakefulness and lower sleepiness?
ACh is active during wakefulness (most robustly via projection to thalamus) and REM
GABA inhibits inhibitory neurons in sleep promoting centers, meaning that sleep drive is diminished
how is NE involved in waking?
made by locus coeruleus under 4th ventricle
- neurons fire during wakefulness, less during NREM and none during REM
- optimizes attention and task performance while awake
how is NE involved in insomnia/anxiety? what is it inhibited by?
excessive firing causes insomnia and anxiety at night (anxious and worried at bed time)
inhibited by alpha-1/2 receptors in a feedback loop
-use BP medications to lessen nightmares and anxiety
how is histamine involved in waking? what receptors does it bind to?
made in tuberomammilary nucleus in posterior hypothalamus
- increased firing when awake > NREM > REM
- H1 receptors –> wakefulness
- H3 autoreceptors –> inhibit histamine activity
- -blocking/antagonizing H3 receptors promote wakefulness
how is serotonin involved in waking? which receptors increase wakefulness? which blocking drugs promote NREM or promote/correct circadian rhythms?
there are 15 different receptors, so sometimes will wake or sleep
- serotonin supply is the dorsal raphe
- generally promotes wakefulness and inhibits REM (stimulate 5HT1a,1b,2,3)
- drugs that block 5HT2 promote NREM
- drugs that block 5HT1D and 5HT7 promote/correct circadian rhythms
how is dopamine involved in waking?
made in substantia nigra (promotes movement) and ventral tegmental area (reward)
- ventral periaqueductal gray in pons fires durign wakefulness
- provides motivational arousal as opposed to task oriented alertness
how is orexin/hypocretin involved in waking? what happens if you don’t have it?
NOT part of RAS, but rather innervates and controls all other wakefulness areas
- excitatory neuropeptides orexin A/B made in lateral hypothalamus as wakefulness regulators
- fire only when awake, not in NREM or REM
- sustain wakefulness when other systems falter
- if missing this, will go to sleep randomly
how is the thalamus involved in waking?
all of RAS is coordinated/gated via thalamic relay tracts/systems
-brain stem arousal center info must go thru thalamus to arouse cortex to wakefulness
