Sleep, Wakefulness and EEG Flashcards
What are the three states of consciousness?
Wakefulness
Core consciousness
Extended consciousness
What does an EEG pick up from the brain?
Synchronised dendritic activity
What do peaks on EEG correlate to?
The more neurons that are synchronised
How is EEG carried out?
19 pairs of electrode are put at internationally agreed points on surface of head
Comparison between electrodes give an implication of the activity in various areas of the brain
When do you see beta waves?
When eyes are open and awake
When do you see alpha waves?
Awake with eyes closed
What are K complexes?
Sudden increase in amplitude of waves
What are sleep spindles?
Sudden increase in frequency of signal
Which stage of sleep are sleep spindles and K complexes present?
Stage 2
What are the names of the waves that are slower?
Theta
Delta
What are the characteristics of REM on EEG?
Fast beta waves
How do sleep stages change as number of sleep cycles increases?
Stage 4 only reached in initial sequences
Increasing time spent in REM
What are the characteristics of REM?
Easier to rouse than stage 4 Dreaming Rapid eye movements Low muscle tone - effectively paralysed Increased HR, RR, O2 consumption and neural activity Penile erection Drop in body temp
Which neurotransmitters from the RF are involved in arousal?
NA
5-HT
ACh
What happens when you excite the thalamus?
Increase in sensory output
What happens if the thalamus is lesioned?
No synchronous waves on EEG
What is the effect of excitation of the reticular formation on the thalamus?
Causes depolarisation of thalamus which exerts non-rhythmic output which increases arousal
What causes non-REM sleep?
Hyperpolarised thalamus due to decreased activity in arousal centres of reticulum
What causes K complexes and sleep spindles?
Inherent rhymicity of thalamic neurones as they hyperpolarise due to reduced ascending reticular formation input
What happens when the thalamus develops slow wave rhythmicity?
Blocks ascending sensory input
Which part of the brainstem blocks descending motor output in REM sleep?
Locus coeruleus
Which motor systems are spared during REM?
Eyes
Middle ear
Respiratory centres
What is the role of cholinergic neurones in REM?
Project from midbrain RF and excite thalamus to provide descending inhibitory stimuli to the motor pathways
Describe the indirect arousal pathway
Midbrain RF projects cholinergic excitation onto thalamus
When is the indirect arousal pathway inactive?
NREM sleep
Describe the direct arousal pathway
Direct cortical excitation by various NTs e.g. orexin, NA, 5-HT, histamine, DA
When is the direct pathway active?
When awake and in NREM
What would a lesion affecting the direct pathway cause?
Sleepiness and coma
What is the centre of non-REM sleep promotion?
Ventrolateral pre-optic nucleus of the hypothalamus (VLPO)
How does VLPO promote sleep?
Inhibitory projects to all the major direct arousal centres
What does the extended VLPO promote?
REM sleeo
What does the VLPO cluster promote?
Non-REM sleep
Which hormone flips the switch between awake and sleep?
Orexin
When are orexinergic neurones usually active?
When awake
Where do orexinergic neurones project?
Arousal nuclei
VLPO
Cerebra
How do orexinergic neurones enhance arousal?
Stimulate arousal centres
Inhibit VPLO
How does the VLPO affect orexin?
Inhibits release as well as arousal centres
Where controls circardian rhythms?
Suprachiasmatic nucleus
What is a major input into the SCN that rests the clock?
Receptors in the retina containing melanopsin (react to light)
What are two causes of permanent narcolepsy?
Inherited neurodegenerative process
Stroke from basilar artery
What causes locked in syndrome?
Occlusion of blood supply to brainstem e.g. basilar artery resulting in infarction of RF
What causes narcolepsy?
Inherited autoimmune condition causing loss of orexin containing neurons
What are the symptoms of narcolepsy?
Falling asleep during ay
Limb weakness during emotional episodes
Night time or morning wakening with muscular paralysis
Vivid dream recollection
Why do narcoleptics have vivid dream recollection?
Pass straight from awake into REM
What are the features of REM sleep behaviour disorder?
Act out dreams leading to injury of themselves or others
Occurs during REM
Pontine RF fails to immobilise body
Memory of dreams
What are the features of somnambulance?
Non-REM sleep
No memory of dreams enacted
Failure of midbrain RF to paralyse body
