EEG & Sleep Flashcards
Define Sleep
A cyclical state of consciousness from which an individual can be roused by normal stimuli such as light, sound, touch.
What chemicals are involved in the sleep/wake process?
- Seratonin- released by seratogenic cells within the reticular formation of the brain stem
- Melatonin released by pineal gland which is triggered by SCN (Increased melatonin = sleepiness)
- Delta sleep inducing peptides in CSF
- Oxerin from hypothalamus= keep us awake
How do seratogenic sleep centres in the pons affect sleep?
- Recticular Formation in the Pons
- Contains seratonin releasing neurons
We know this is involved in sleep as destroying it or blocking seratonin prevents sleep
How is the hypothalamus involved in inducing sleep?
- Suprachiasmaticnuclei in Hypothalamus
- SCN activity leads to melatonin release from pineal gland –> Corresponds with sleepiness
We know that electrically stimulating the SCN induces sleep and damages it disrupts sleep-wake cycle
How is the hypothalamus involved in wakefullness?
Excitatory neurons in the hypothalamus release Orexin (hypocretin) during waking, this maintains wakefullness.
They stop during sleep
Describe how the sleep wake cycle occurs:
Balance between arousal centres & sleep centres
Excitatory neurons (in Ascending Reticular Activating System) overtake inhibitory cells
–> Stimulates excitatory pathways in CNS/PNS
–> +ve feedback maintains wakefulness for many hours
–> Excitatory cells fatigue & signals fade
–> Inhibitory signals from the reticular formation sleep centres overtake the excitatory signals
–> Sleep
–> Overnight the inhibitory cells fatigue, excitatory ones rest and take over again in the morning
What would we do to assess the level of consciousness in a patient?
- Electroencephalogram
- Behaviourly
Alertness = Speech content/patterns = Reading = Writing = Calculating skills = Spell/count backwards
What does an electroencephalogram measure?
Electrical activity of the brain
In Amplitude and Frequency (rises with neuronal excitation)
Sometimes brain activity is very high but the amplitude is low, why is this?
The brain waves are asynchronous.
This means the brain is doing lots of things at once and the opposing polarities of its signals cancel eachother out on the EEG
What are the types of EEG wave patterns?
Alpha
Beta
Theta
Delta
When do each type of EEG wave occur?
Alpha - Awake but relaxed
Beta - Awake and Alert
Theta - Emotional stress/frustration/sleep stage 1&2
Delta - Deep Sleep (stages 3 & 4)
Describe the characteristics of the different EEG wave types?
Alpha- relaxed awake state
- High F & medium A
Beta- alert awake state
- High F
- Low A (Asynchronous)
Theta- early sleep
- Low F
- Variable A
Delta- deep sleep
- Low F
- High A
What are the stages of the sleep cycle?
Stage 1 - Slow Wave non-rem sleep (S-sleep) - Theta Stage 2 - Theta (but even slower F) Stage 3 - Delta Waves Stage 4 - Delta Waves Stage 5 - REM Sleep (Beta Waves)
1-4 are known as slow wave sleep
REM sleep has rapid waves
During what stages of sleep do eye movements occur?
Stage 1 - Slow eye movements
REM - Rapid eye movements
Stage 2 of sleep is very low Frequency Theta waves, what else happens?
Bursts of rapid waves called sleep spindles
