EEG Sleep Flashcards
Define sleep
State of unconsciousness from which an individual can be aroused by normal stimuli, light, touch, sound etc.
Is predictable and cyclical
Define coma
State of unconsciousness from which the individual cannot be aroused or not respond to stimuli
Is very complex
What does sleep deprivation cause?
Impaired cognitive function
Impairment of physical performance
Sluggishness
Irritability
What does sleep support?
Neuronal plasticity, learning + memory, cognition, clearance of waste from CNS, conservation of whole body energy and immune function
All can become compromised if poor sleep
Describe neuronal plasticity
Brains ability to change and adapt in response to learning and experience
How does sleep occur?
Due to inhibitory processes that originate in the pons
Activity originates in the reticular formation of brainstem - controls state of consciousness
Describe the function of reticular formation in sleep
Sends projection to thalamus and higher cortical areas
Arousal and sleep centres exist here and the level of consciousness depends on balance of these 2
What molecules are believed to contribute to sleep?
Delta sleep inducing peptides (DSIP)
Adenosine
Melatonin
Serotonin
How is the hypothalamus involved in sleep?
Hypothalamus and suprachiasmatic nuclei (SCN) are involved in induction of sleep
SCN activity demonstrates circadian rhythm - controls release of melatonin
Describe the inhibitory neurons in the SCN
Stimulated by light and act to inhibit the pineal glands which releases melatonin
Darkness removes the inhibition - feeling of sleepiness as melatonin released
What is circadian rhythm of melatonin release linked to?
Inhibition of Orexin
Describe orexin
Excitatory neurotransmitter released from hypothalamus - required for wakefulness
Orexin neurons are active during day and stop firing at sleep
What does defective orexin signalling lead to?
Narcolepsy - individual suddenly falls asleep
How does blocking serotonin formation inhibit sleep?
Many neurons within reticular formation are serotonergic - serotonin is precursor for melatonin
Describe serotonin reuptake inhibitors
Common treatment for depression when sleep disruption is often present
They increase serotonin levels in synapse
How is brain activity measured?
Recording patterns by Electroencephalogram EEG - electrodes placed on scalp to record activity in underlying neurons
What can the wave patterns on EEG be analysed by?
Amplitude and frequency
Describe frequency and amplitude with increasing neural excitement
Frequency - increases
Amplitude - decreases
Longer the wave length deeper into sleep and shorter is awake/alert
What are the 4 main types of wave pattern seen?
Alpha
Beta
Theta
Delta
Describe the alpha wave pattern
Associated with relaxed awake state
Is high frequency and medium amplitude waves
Describe the beta wave pattern
Associated with alert awake state
High frequency and low amplitude waves
Describe the theta wave pattern
Associated with early sleep
Low frequency waves which can vary enormously in amplitude
Describe the delta wave pattern
Associated with deep sleep
Very low frequency but high amplitude waves
How does Beta waves have low amplitude waves in awake state?
Increase in activity is asynchronous as brain doing so many things at once - opposing polarities of signals cancel each other out and not recorded on EEG
How is it high amplitude in relaxed state?
Synchronised activity - so as signals are doing same thing, the amplitude of voltage change is large but slow frequency
What is stage 1 of the sleep cycle?
Slow wave, non-REM, S-sleep
Slow eye movements , light sleep very early in sleep cycle
High amplitude and low frequency theta waves
What is stage 2 of sleep cycle?
Eye movements stop
Frequency slows further but EEG shows bursts of rapid waves called sleep spindles
What is stage 3 of sleep cycle?
Hight amplitude and low frequency delta waves interspersed with short episodes of faster waves and spindle activity declines
What is stage 4 of sleep cycle?
Exclusively delta waves
Very slow and high amplitude
Deep sleep
From 4 then move back to 3 and 2 before REM sleep
What is REM sleep?
Rapid eye movements - dreams occur
Low amplitude and and high frequency - similar to awake state
What are the physiological characteristics of deep slow wave sleep?
Deep sleep happens in first hours of sleep
Most restful type of sleep
Associated with decreased vascular tone, resp. and basal metabolic rate
Hippocampus very active
What follows initial slow wave sleep - stage 3 and 4?
Gradual awakening to stage 1 but not stage 1 - REM stage
Waves are desynchronised, high frequency and low amplitude
Why does dreams mostly occur in REM?
Neural connection being made randomly and illogically
Describe muscles during REM sleep
Eye muscles show rapid bursts of activity
Skeletal muscles are inhibited by inhibitory projections from pons to spinal cord - prevents acting out dreams
What pathways is REM sleep dependant on?
Cholinergic pathways within reticular formation and projection to thalamus, hypothalamus and cortex
Anticholinesterases increase time in REM
How long does REM last?
5-30 mins every 90 mins during normal nights sleep
Increasing in frequency and duration as night progresses
How does sleep change over lifetime?
Total sleep time decreases
Percentage of REM also declines and can be absent from 80 year old +
Describe insomnia
Defined as chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour
What is chronic primary insomnia?
Usually no identifiable psychological or physical cause
What is temporary secondary insomnia?
In response to pain, bereavement or other crisis
Usually short lived
Describe nightmares
Have a strong visual component and during REM sleep, typically occurring far on through the night
Have clear recollection of the dream
Describe night terrors
Occur in deep, delta sleeps and common in age 3-8 years, typically early in the night
Child does not remember the episode -screaming and sit up
Describe somnambulism
Sleep walking - occurs exclusively in non-REM sleep, mainly stage 4and more common in children and young adults
Appear awake
