B7.048 Sleep, Wakefulness, and the EEG Flashcards
components of reticular activating system
cerebral cortex thalamic nuclei -intralaminar nuclei -thalamic reticular nucleus pontomesencephalic reticular formation
function of reticular activating system
diffuse projecting system
turns on brain
heavily involved in wakefulness and sleep
segments of the reticular formation
stuff in between CN nuclei and long tracts rostral reticular formation caudal reticular formation -raphe -medial (magnocellular) -lateral (parvocellular)
what is an EEG
electroencephalogram
measures electrical activity in brain with sensitive electrodes
produces a graph of voltage (uV) by time
EEG frequency bands
beta: >12 Hz
alpha: 8-12 Hz
theta: 4-8 Hz
delta: <5 Hz
2 EEG activities seen during wakefulness
B activity, > 20 Hz
a activity, 8-12 Hz
beta activity
low amplitude
high frequency
occurs during alert wakefulness
front of brain
alpha activity
higher amplitude
lower frequency
relaxed wakefulness with eyes closed
back of brain
distribution of alpha and beta waves over the brain
alpha rhythm largest over parietal, occipital, and posterior temporal lobes
alpha replaced by beta when eyes are opened
beta rhythm most prominent in front of brain
current source of EEG
cortical neurons changes in RESTING membrane potentials -synaptic potentials -summed EPSP and IPSP NOT action potentials (too brief)
synchronization of cortical neurons
if resting membrane potential oscillations of cortical neurons were independent and random, electrical activity would cancel out
a pacemaker is required to synchronize the oscillations
pacemaker of cortical neurons
thalamic reticular nucleus
thalamocortical circuits
how does the thalamic reticular nucleus operate
receives excitatory input from the thalamocortical and corticothalamic axon collaterals
neurons are GABAergic
reticular activating system (RAS) input to thalamus (TRN)
regulates wakefulness
thalamus synchronizes the oscillations of cortical neurons at different frequencies during wake and sleep
EEG appearance changes
sleep stages
awake: a and B stage 1 (drowsy): a drops out, theta waves stage 2: sleep spindles and k-complexes stages 3-4: slow wave sleep, D waves REM sleep: looks like awake, B waves
REM sleep
metabolically active brain
EEG appearance similar to awake EEG
brain during non REM sleep
less physiologically active
prominent slow waves
synchronized waves
high amplitude
low frequency waves
sleep spindles, a, and D rhythms
desynchronized waves
low amplitude
high frequency
b rhythm
neuronal physiology during wakefulness and REM
neuron depolarizations with short refractory periods
tonic mode
neuronal physiology during slow wave sleep
stimulus from RAS results in hyperpolarization
post stimulation latency period so that neuron cannot be stimulated again
phasic mode
the sleep cycle
descends from stage 1, 2, 3, 4 back up to REM and then back down
90 minute cycles throughout the night
REM cycles become longer closer to morning
when is a person most likely to spontaneously awake from sleep
after a REM cycle
changes to the sleep cycle with age
older people have less time in slow wave sleep
more fragmented
more waking up
physiologic characteristics of slow wave sleep
neuronal activity low, metabolic rate and brain temp at their lowest
sym output decreases, HR and BP decline
muscle tone low, but present
reflexes present
physiologic characteristics associated with REM sleep
rapid eye movements dreaming high cortical activity irregular changes in BP, HR , and breathing penile erection, clitoral engagement atonia
explain atonia in REM sleep
active inhibition of alpha motoneurons prevents movements
occasional jerky movements escape
reticulospinal tract responsible for this inhibition (so you don’t act out your dreams)
REM sleep disorders
reticulospinal dysfunction
muscles don’t shut down
common in people with dopaminergic issues, may later get Parkinson’s
diffuse projection systems involved in regulation of wakefulness and sleep
cholinergic
noradrenergic
serotonergic
dopaminergic
cholinergic projection system
important component of reticular activating system (RAS)
located in basal nucleus of the forebrain, rostral pons, and midbrain tegmentum
ACh causes depolarization of forebrain neurons, thus causing cells to discharge in the tonic move which results in desynchronized EEG
keeps you awake
noradrenergic system
locus ceruleus
wakefulness and REM sleep
serotonergic system
median raphe of reticular formation
slow wave sleep maintenance
effect of serotonin inhibition drugs
can cause insomnia
dopaminergic system
substantia nigra
deficiency: REM sleep disorder
circadian rhythm
sleep and wakefulness occur in an approximate 24 hours cycle (25-26ish for most)
rhythm is entrained by exogenous stimuli (visual input)
circadian rhythm pacemaker
suprachiasmatic nucleus in anterior hypothalamus
monitors light/dark cycle
receives input from retino-hypothalamic tract
retino-hypothalamic tract
light sensitive retinal ganglion cells contain melanopsin
these cells go straight to hypothalamus SCN > pineal gland > melatonin
