EEG, Sleep, and Circadian rhythms Flashcards
why does sleep occur?
due to active inhibitory processes that originate in the pons
where in the brain does evidence suggest that the activity required for sleep occurs?
reticular formation of the pons
why do drugs that block serotonin formation inhibit sleep?
serotonin is critical to sleep induction
what part of the diencephalon does evidence suggest is vital to sleep?
hypothalamus
what is the effect of electrical stimulation of the suprachiasmatic nuclei of the hypothalamus?
promotes sleep
what can damage to the suprachiasmatic nuclei cause?
disruption of the sleep-wake cycle
what neurotransmitter released by the hypothalamus is essential for wakefulness?
orexin
what condition is associated with defective orexin signalling?
narcolepsy
what is the ascending reticular activating system a part of?
the reticular formation
what happens to excitatory neurones in the ARAS during wakefulness?
the are released from inhibition from sleep centres in the reticular formation
what do the excitatory neurones in the ARAS stimulate?
excitatory pathways of the CNS and PNS
what happens when the active cells of the CNS and PNS become fatigued?
excitatory signals fade and inhibitory peptide signals from the sleep centres in the reticular formation take over
what is the effect of the sleep centres in the reticular formation when they release inhibitory peptides?
rapidly inhibit the weakening excitatory signals leading to the rapid progression into the sleep state
what are some methods of assessing the level of consciousness in an awake person?
look at: behaviour general alertness speech patterns speech content reading writing calculating skills perform an electroencephalogram
what are 2 ways in which EEG wave patterns can be analysed?
amplitude
frequency
what are the 4 main types of wave patterns on an EEG?
alpha
beta
theta
delta
when would you expect to see alpha waves on an EEG recording and what do alpha waves look like?
in a relaxed, awake state, you would expect to see the high frequency high amplitude alpha waves
when would you expect to see beta waves on an EEG recording and what do beta waves look like?
in the alert awake state, beta waves are very high frequency, low amplitude waves
why are beta waves low amplitude?
the increase in brain activity is asynchronous as the brain is doing so many things at once and the opposing polarities of the signals cancel each other out and do not get recorded on the EEG
what are theta waves characterised and when would you expect to see them?
low frequency waves which vary enormously in aplitude. common in children and during times of emotional stress and frustration in adults. also occur in sleep in both children and adults
what are delta waves characterised by and when do they occur?
low frequency and high amplitude, they occur in deep sleep
what is stage 1 of the sleep cycle characterised by?
slow eye movements
easily roused
high amplitude, low frequency theta waves
what is stage 2 of the sleep cycle characterised by?
no eye movement
frequency slows further but EEG shows bursts of rapid waves called “sleep spindles”
what is stage 3 of the sleep cycle characterised by?
high amplitude, very slow frequency delta waves
still some spindle activity, but declining compared to stage 3
what is stage 4 of the sleep cycle characterised by?
exclusively delta waves
when does sleep walking/talking occur?
stage 3 and 4
what is REM sleep characterised by?
Rapid Eye Movement during sleep, 25% of sleep is REM.
what occurs during REM sleep?
dreams
what is different about the EEG readings of REM sleep compared to stages 1-4?
stages 1-4 of sleep are characterised by slow waves, whereas REM sleep is characterised by fast waves which are very similar to the awake state
when does stage 3 and 4 sleep tend to occur?
in the first hours of sleep
what is “deep sleep” associated with systemically?
decreased vasular tone (BP)
decreased respiratory rate
decreased basal metabolic rate
what happens to skeletal muscles during normal REM sleep?
inhibition of all skeletal muscles except those of the eye
what happens to skeletal muscles in REM sleep disorder?
they are not inhibited, so sometimes people may act out what is happening in their dreams
what part of the reticular formation is REM sleep dependent on?
cholinergic pathways and their projections to the thalamus, hypothalamus and cortex
what drugs can increase time spent in REM sleep?
anticholinesterases
what happens to heart rate/respiratory rate during REM sleep?
they become irregular
what happens to brain metabolism during REM sleep?
increases
what features do sleep deprived subjects show?
impairment of cognitive function impairment of physical performance sluggishness irritability psychosis also observed in some subjects
what 6 things does sleep support?
neuronal plasticity learning and memory cognition clearance of waste products from CNS conservation of whole body energy immune function
what happens to total sleep time throughout the course of a lifetime?
total sleep time declines rapidly through childhood and adolesence
what happens to the percentage of REM sleep experienced throughout the course of a lifetime?
declines; 50% in an infant declining to a stable 25% in adulthood
what is insomnia defined as?
a chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour
what is insomnia often associated with?
depression and PTSD
what is the effect of barbiturates in regard to sleep?
depress REM sleep and delta sleep
increases no. of times awake during night
what is the effect of stopping barbiturate use?
“rebound effect” - marked and immediate increase in the quantity of REM sleep
what stage of sleep do night terrors occur in?
deep delta sleep
what kind of patients are night terrors common in?
children 3-8 years
what are some characteristics of night terrors?
children can thrash and scream and may sit or stand up with their eyes open
they are not properly awake
do not remember the episode upon waking up in the morning
what is the clinical term for somnambulism?
sleep walking
what stage of sleep does sleep walking occur in?
occurs exclusively in non REM sleep, mainly stage 4
what type of patients is sleep walking most common in?
childre and young adults
what is narcolepsy?
condition where patients enter directly into REM sleep with little warning - intrusion of REM sleep characteristics onto the waking state
where is the control centre of the circadian rhythm?
in the suprachiasmatic nucleus
what happens if the SCN is destroyed?
circadian rhythm of sleep is lost
where is the SCN of the hypothalamus located?
just above the optic chiasma
why does the light/dark cycle have an effect on the SCN neurons?
some nerve fibres in the optic nerve may pass to the SCN
what can happen to workers who have their shifts/time zones that they work in changed often?
disruption of behaviours, particularly sleep and attention deficits
can lead to long term health effects such as GI and CVS pathology
