EEG, Sleep and Circadian Rhythms Flashcards
How does EEG work?
Uses electrodes placed on the scalp to record activity of the underlying neurons
EEG readings show
wave patterns that reflect the electrical activity of the brain which can be analysed by amplitude and frequency
In general, the frequency of wave patterns on EEG increase with
neuronal excitation
What four main types of wave pattern are seen on EEG?
Alpha
Beta
Theta
Delta
The characteristic of the wave pattern varies with
different states of consciousness
In the relaxed awake state, EEG is characterised by
high frequency, high amplitude alpha waves
In the alert awake state, EEG is characterised by
higher frequency (than relaxed), low amplitude, asynchronous beta waves
Theta waves are characterised by
low frequency waves which vary enormously in amplitude
Theta waves occur in
children
times of emotional stress/frustration in adults
during sleep in both adults and children
Delta waves are characterised by
low frequency
high amplitude
Delta waves occur in
deep sleep
How many sleep stages are there?
5
Describe stage 1 of the sleep cycle and types of wave present
Slow wave, non-REM sleep
Slow eye movements
Light sleep (easily roused)
High amplitude low frequency theta waves
Describe stage 2 of sleep and type of waves present
Eye movements stop
Frequency slows
EEG shows busts of rapid waves (sleep spindles)
Describe stage 3 of sleep and type of waves present
High amplitude very slow delta waves interspersed with episodes of faster waves
Spindle activity declines
Wave type present in stage 4 sleep
Exclusively delta waves
It is most difficult to rouse someone from what stages of sleep?
Stages 3 and 4
What is stage 5 known as?
REM sleep (paradoxical sleep)
REM sleep is characterised by
fast waves, similar to those of the awake state
Deep sleep is the most restful type of sleep and is associated with
decreased vascular tone and BP
decreased respiratory rate
decreased basal metabolic rate
Pattern of REM sleep
Lasts 5-30 mins every 90 mins during a normal nights sleep, becoming more frequent as the night progresses
What prevents the “acting out” of dreams?
Inhibition of other skeletal muscles due to inhibitory projections from pons to spinal cord
REM sleep is dependent on
cholinergic pathways within the reticular formation and their projections to the thalamus, hypothalamus and cortex
What is insomnia?
Chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour
What are the two types of insomnia?
Chronic primary - no identifiable psychological or physical cause
Temporary secondary - response to pain, bereavement or physical cause
At what point in sleep do night terrors occur?
In deep delta sleep, typically early in the night
What is somnambulism?
Sleep walking
At what point in sleep does somnambulism occur?
Exclusively in non-REM sleep, mainly stage 4
What happens in narcolepsy?
Patients enter directly into REM sleep with little warning
Consequences of chronic use of hypnotic drugs e.g. barbiturates
Increased time taken to fall asleep
Decreased time spent in REM and stage 3 and 4 sleep
Increase number of times awake a night
What are circadian rhythms?
Physical, mental and behavioural changes that follow a roughly 24-hour cycle
Respond primarily to light ad dark in the environment
Function of suprachiasmatic nucleus
Contains neurons which have an inherent 24-hour cycle entrained by external cues
If the suprachiasmatic nucleus is destroyed, the circadian rhythm of sleep is
lost
What is orexin?
Neuropeptide that regulates wakefulness, appetite and arousal
