Consciouness Flashcards
What is consciousness?
oA very slippery concept
oRelated to awareness of external environment and internal states
oArousal is a related concept which is associated with goal-seeking behaviour and avoidance of noxious stimuli
What are the components which are needed to function normally for consciousness
oCerebral cortex – the site where conscious thoughts arise
- Receives many inputs, including from the reticular formation
oReticular formation (particularly the reticular activating system in the brainstem) – the circuitry that keeps the cortex ‘awake’ - Receives many inputs, including from the cortex and sensory systems
How are the cortex and reticular formation connected?
Cortex and reticular formation are connected by reciprocal excitatory projections, forming a positive feedback loop
Positive feedback loops are seen when there is a binary outcome (e.g. sleep/awake, ovulating/not ovulating etc)
Occurs via three major relay nuclei
What are the relays between the cortex and reticular formation and how do they communicate?
Reticular formation sends cholinergic (excitatory) projections to these relays
- Basal forebrain nuclei send excitatory cholinergic fibres to cortex(think sedative side effects of anticholinergics)
- The hypothalamus sends excitatory histaminergic fibres to the cortex (think sedative side-effects of sedating antihistamines)
- The thalamus sends excitatory glutamatergic fibres to the cortex
oThe reticular formation also sends projections down the cord, responsible for maintaining muscle tone
What is used in assessment of consciousness
GCS is commonly usedFour components, looking for best response in each
Describe how eye opening is assessed in the GCS
Eye opening oSpontaneous eye opening (4) suggests normal cortical and brainstem function oResponse to speech (3) suggests slightly diminishedcortical function but still functioning brainstem oResponse to pain (2) suggests impaired cortical function but brainstem preserved so that reflex opening can occur oNo response (1) suggests severe damage to brainstem +/- cortex
How is motor response assessed in the GCS?
oObeys commands (6) suggests normal function with working connections from auditory system to brainstem/cord
oLocalises to stimuli (5) suggests diminished higher cortical function but still connections working from sensory to motor cortex
oWithdraws to pain (4) suggests that there is still a ‘physiological’ reflex response to stimuli
oFlexor response to pain (3) suggests a lesion above the level of the red nuclei. This response is still ‘semi-physiological’
oExtensor response to pain (2) suggests a lesion below the red nuclei. This response is not physiological at all
oNo response to pain (1) suggests severe damage to brainstem +/- cortex
Describe verbal response assessment in the gCS
oOriented in time/place (5) suggests normal cortical function oConfused conversation (4) suggests diminished higher cortical function but language centres are still functioning adequately oInappropriate words (3) suggests language centres have been damagedoIncomprehensible sounds (2) suggests cortical damage with brainstem mediated groans oNo response (1) suggests severe damage to brainstem +/- cortex
What is the electroencephalogram
oMeasures the combined activity of thousands of neurones in a particular region of cortex
oHigh temporal resolution, low spatial resolution
oGood for detecting neuronal synchrony (a phenomenon which occurs commonly in the brain during both physiological and pathological processessuch as sleep and epilepsy), and evidence of normal cerebral function
What are the fucntions of sleep?
oFunctions Generally unknown Energy conservation / repair? Memory consolidation? Clearance of extracellular debris? ‘Resetting’ of the CNS?
Give an overview of the stages of sleep
4 major stages + rapid eye movement (REM) sleep
Typically pass through around 6 cycles of sleep per night
Stages are characterised by typical EEG pattersn
•Awake with eyes open
oBeta waves – irregular, 50Hz
•Awake with eyes closed
oAlpha waves – regular, 10Hz
Describe stage 1 sleep
•Stage 1 sleep
oBackground of alpha + interspersed theta waves (theta at around 5Hz, regular)
Describe stage 2 sleep
Stages 2/3 sleep
oBackground of theta + interspersed sleep spindles and k-complexes:
- Sleep spindles are high frequency bursts arising from the thalamus
- K- complexes represent the emergence of the ‘intrinsic rate’ of the cortex
Describe stage 4 sleep
•Stage 4 sleep
oDelta waves – regular, 1Hz
- Related to k-complexes seen in stages 2/3
Describe REM sleep
REM sleep
oEEG similar to beta waves
oDreaming occurs in this stage, so similar to the EEG in a conscious patient
REM sleep
- Initiated by neurones in the pons (i.e. initiation appears to be an active process)
- Similar EEG to when awake with eyes open (beta waves), but difficult to rouse due to strong thalamic inhibition
- Decreased muscle tone due to glycinergic inhibition of lower motor neurones
- Eye movements and some other cranial nerve functions can be preserved (e.g. teeth grinding)
- Autonomic effects are seen (e.g. penile erection, loss of thermoregulation)
- Essential for life – long term deprivation leads to death
