Consciousness Flashcards
Define consciousness
awareness of external environment and internal state
what is arousal ?
associated with goal - seeking behaviour and avoidance of noxious stimuli
what 2 neural components are needed to be connected for consciousness?
Cerebral cortex
reticular formation
what does the cerebral cortex do in consciousness?
site where conscious thoughts arise
Receives many inputs, including from the reticular formation
what does the reticular formation do in consciousness?
– the circuitry that keeps the cortex ‘awake’
Receives many inputs, including from the cortex and sensory systems
describe the nature of the connection of the reticular formation and cerebral cortex ?
reciprocal excitatory
projections, forming a positive feedback loop
due to binary outcomes e.g. sleep/awake
what 3 outputs does the reticular formation send out to cortex ?
what about the 4th one?
Basal forebrain nuclei via excitatory cholinergic fibres
hypothalamus via excitatory histaminergic fibres
thalamus via excitatory glutamatergic fibres
projections down cord for muscle tone
what 3 components of the GCS are used to asses consciousness?
Eye opening (4) Motor response (6) • Verbal response (5)
when should you get a senior after GCS assessment ?
A sustained (that is, for at least 30 minutes) drop of one point in GCS level
what does an EEG do ?
Measures the combined activity of thousands of neurones in a particular
region of cortex to a very high temporal resolution but low spatial
what happens when the brain is deprived of sensory inout ?
can you give a physiological and pathological example ?
Neuronal synchrony
Sleep and epilepsy
what are the theories on why we need sleep ?
Energy conservation / repair
Memory consolidation
clearance of extracellular debris?
“Resetting’ of the CNS
how many cycle so sleep per night on avg do we go through ?
6 cycles of sleep per night
what are the stages of sleep ?
describe the EEG pattern
stage 1 sleep = Awake with eyes closed Alpha waves – regular, 10Hz stage 2/3 = Background of theta + interspersed sleep spindles and k-complexes stage 4 = Delta waves – regular, 1Hz REM = similar to beta waves
what do K complexes represent ?
what about Sleep spindles ?
Sleep spindles are high frequency bursts arising
from the thalamus
K-complexes represent the emergence of the
‘intrinsic rate’ of the cortex
What kind of EEG in seen in normal awake consciousness ?
Beta waves – irregular, 50Hz
why is beta waves seen in REM sleep ?
similar to awake consciousness as dreaming is occuring
describe the neural mechanism of Non-REM sleep
Deactivation of the reticular activating system (and hence cortex)
inhibition of the thalamus.
facilitated by removal of sensory inputs (fewer
positive influences on positive feedback loop)
describe the neural mechanism of REM sleep
Initiated by neurones in the pons- active process
difficult
to rouse due to strong thalamic inhibition
Essential for life – long term deprivation leads to death
what can be seen during REM sleep ?
Decreased muscle tone due to glycinergic inhibition of lower motor
neurones
Eye movements and some other cranial nerve functions can be
preserved
Autonomic effects are seen
What can cause insomnia ?
underlying psychiatric disorder as
opposed to ‘primary’ insomnia
what can cause narcolepsy ?
mutations in the orexin gene.
Orexin is a peptide transmitter involved in sleep
what can cause sleep apnoea ?
excess neck fat leading to
compression of airways during sleep and frequent waking
• Causes excessive daytime sleepiness
what are the features of a coma ?
widespread brainstem/ cortical damage
EEG disordered with no sleep wake cycle
unresponsive
what are the features of a PVS?
Widespread cortical damage with disordered EEG
some spontaneous eye opening and responsed to stimuli via brainstem reflexes
sleep/cycle detectable
what are the features of Locked in syndrome ?
caused by basilar / pontine artery occlusion
eye movements preserved but all other somatic motor function lost form pons down
