9/16 Consciousness - Rasin Flashcards
components of consciousness
1. content of consciousness: substrate, content
- contribution from all systems (sensory, motor, limbic, etc)
2. level of consciousness
- three distinct but related processes (3xA)
- alertness
- attention
- awareness
levels of consciousness
- conscious
- confused
- delirious
- somnolent
- obtunded
- stuporous
- coma
- conscious: normal attn/wakefulness
- confused: disoriented, slow thinking/response
- delirious: disoriented, restless, marked attn def
- somnolent: sleepy, excessive drowsiness
- obtunded: decr alertness, slowed psychomotor responses
- stuporous: deep sleep, no spont activity, respond by grimace/withdrawal
- coma: unarousable, no resp to stim
disorders of consciousness
main diff b/w brain death and coma?
main diff between coma and veg state?
destruction of localized brain regions manifest as diff disorders of consciousness
- brain death : spinal cord functioning, but brain is not
- coma : severely depressed fx of cerebrum
- locked in syndrome : ventral pons depressed fx
brain death vs. coma
- no brainstem reflexes in brain death
- yes brianstem reflexes in coma
coma vs vegetative state
- diencephalon/upper_brainstem → behavioral/arousal/sleep-wake cycles
- no in coma
- yes in veg state
- (brainstem reflexes intact in both)
abnormal posturing
present in severe lesions
-
decorticate: upper midbrain damage
* brainstem motor centers working BUT no modulation from CST -
decerebrate: upper pontine damage
* no CST, no rubrospinal tract - flaccid: no CST, no rubrospinal tract, no vestibulospinal tract, no reticulospinal tract
progression from decorticate → decerebrate posture can indicate progressive damage!
- can affect medulla and resp arrest rapidly
metabolic encephalopathy
- pt tries to brush examiner away
- asymmetric motor response
- Babinski reflex
coma
definition
potentially dysfx systems
first systems to examin
unarousable unresponsiveness in which patient lies with eyes closed
- min duration: 1 hr
- NOT permanent! within 2-4wk, patients either deteriorate or recover
caused by dysfx of…
- ascending reticular activating system (ARAS)
- bilat regions of cerebral cortex
- bilat lesions of thalamus (medial)
first systems to examine: cardiovasc, respiratory
respiratory system response to injuries to…
- forebrain
- upper brainstem
- medulla
diffuse forebrain impairment without brainstem injury
- waxing/waning depth of resp with interposed apneas: Cheyne-Stokes respiration
- “fast breating, slow breathing, no breathing”
- lesion in upper brainstem*
- fast breathing
- lesion in medulla*
- respiratory arrest/apnea
pupillary effects of coma
next thing to check after resp/CV: pupils!
pontine lesion
- pinpoint pupils, but responsive to light bilat
- PSNS fx and oculomotor nuclei in midbrain are preserved
midbrain lesion/transtentorial herniation
- unilateral or bilateral “blown” pupil
metabolic coma
what is it?
effect on pupils?
coma caused by sedative drugs (NOT opioids)
- small reactive pupils
metabolic encephalopathy
vs
midbrain lesion (bilat)
- head turning results
- cold water test results
metabolic encephalopathy (brain stem intact)
- turn head → eyes move contralat
- cool water in ear → eyes move toward water
midbrain lesion
- turn head → eyes move contralat
- cool water in ear → ipsi eye moves toward water
- abducens nucleus intact!
- oculomotor (medial rectus m.) is not intact
*
neuro exam of unconscious patient
- locomotion assessment
- resp pattern
- examine eyes
- brainstem reflexes
- motor/sensory responses
brain death
extreme, irreversible form of coma
- NO evidence of forebrain/brainstem fx
- NO brainstem reflexes
- might have spinal cord reflexes
- ex. Lazarus reflex
- EEG shows electrocerebral activity
- cerebral perfusion and metabolism minimal
- angiogram shows no blood flow
- “empty bucket” metabolism
tests:
- caloric test + apnea test (brainstem fx)
- at least 2 sep brain death exams within an hour to confirm
- posturing reflexes? criteria not met!
vegetative state
follows coma or certain end-stage dementias, neurodegen, congenital disorders
- regains sleep/wake cycle
- regains primitive responses/reflexes
- remains unconscious
however…
- open eyes & are arousable by stimuli
- might turn eyes/head toward auditory/tactile stimuli
- might produce unintelligible sound and move limbs → not meaningful
implication/evidence: v low basic metabolic fx maintained
persistent vegetative state: > 1 month
minimally conscious state
appearance of visual tracking (one of earliest signs of recovery from veg state)
- minimal/variable degree of responsiveness
- follow simple commands
- say single words
- reach for/hold objects
- no reliable interactive verbal/nonverbal comm
- no reliable fx use of objects
locked-in syndrome
what is it?
classic vs. partial vs. total
why cant they move?
where is the lesion?
can be mistaken for coma, but consciousness is preserved!
- all voluntary muscles except controlling eye movements are PARALYZED
- may be able to communicate through vertical eye movements, eye blinks
no tx or cure
classic (quadriplegia w consciousness/eye movement) vs. partial (classic plus weak hand/arm/facial movements) vs. total (total immobility, inability to comm)
why can’t they move?
- lesion in brainstem motor pathways controlling face, trunk, limbs
- peripheral neuromuscular blockade
where is the lesion?
- lesion of ventral brainstem (motor pathways) at or below trigeminal nerve level
- most freq due to ischemic pontine lesion → stroke of basilar artery
- also poss: traumatic brain injury, demyelinating disease, brain hemorrhage
consciousness system
cortical structures
- medial and lateral frontoparietal association cortex
- cingulate gyrus
subcortical structures (THUB)
- thalamus
- hypothalmus
- upper brainstem
- basal forebrain
consciousness system fx
depends on normal fx of cortex
arousal circuits arrive from brainstem, diencephalon
upper brainstem sends signals/excites:
- thalamus
- basal forebrain/hypothalamus
both of which project to and excite the cortex
role of reticular formation
reticular formation fo brainstem activates cerebral cortex and maintains consciousness via direct or thalamocortical projections
- present as loosely clustered neurons within white matter
- extends through axis of CNS (central core of medulla, pons, midbrain)
functions:
- control of skeletal muscle (via reticulospinal, reticulobulbar tracts)
- control of somatic and visceral sensations (pain perception)
- control of autonomic nervous system
- control of endocrine nervous system
- influence on biological clocks
- reticular activating system influences level of consciousness
- affects all three levels: alertnes, attn, awareness
- damage to RF → coma, death
reticular formation affecting consciousness
pathway
inputs to arousal system
ascending reticular activating system (ARAS) aka pontomesencephalic reticular formation (aka rostral RF) sends continuous stream of impulses → thalamic intralaminal nucleus → cerebral cortex
pontomesencephalic RF receives inputs from…
- sensory pathways (via anterolateral system spinoreticular pathway)
- pain can increase alertness
- fronto-parietal association cortex (mental activation)
- limbic and cingulate cortex (emotional activation, cognitive processes)
- hits both pontomesencephalic RF and intralaminal thalamus
- posterior lateral hypothalamus
projection systems
neurotransmitters involved
reticular system has widespread diffuse projections that innervate many structures/whole nervous system
upper brainstem → forebrain
lower brainstem → brainstem, cerebellum, spinal cord
neurotransmitters: HANDS (monoamines)
- Ach
- dopamine
- norepinephrine
- serotonine
- histamine
lesions that block nt systems → confusion/drowsiness (not coma!)
- effect of many psych disorders (dysfx diffuse proj nts)
- target of many psychoactive drugs (diffuse proj)
cholinergic consciousness system
nt
main role
acetylcholine
main role: neuromodulation
arousal
origin: basal forebrain
- nucleus basalis (of Meynert) near anterior commisure → projects directly to entire cerebral cortex
- medial septal nuclei & nucleus of diagonal band (of Broca) → projects to hippocampus
projections to: why
- hippocampus: learning, memory
- cortex/limbic system: emotional states, cortical responsiveness
Ach-receptor targeting drugs used in tx of Parkinson’s, Alzheimers
dopaminergic consciousness system
nt
origin/projections
dopamine
origin: mesencephalon
- substantia nigra pars compacta → striatum
-
ventral tegmental area →
- limbic structures (amygdala, cingulate, n. accumbens, temporal)
- prefrontal cortex
3 key projections:
- mesostriatal (nigrostriatal) proj → forebrain [striatum (putamen, caudate)]
- mesolimbic proj → limbic system
- mesocortical proj: prefrontal cortex
noradrenergic consciousness system
nt
origin/projections
noradrenaline/norepi
functions associated with:
- alertness (incr firing in wake than sleep)
- new, attended-to, sensory stimulus (esp noxious, fear-provoking)
origin: pons/medulla
- locus ceruleus (rostral pons) → cortex (inhib/excit effects)
-
lateral tegmental area (pons/medulla) →
- limbic structures (amygdala, cingulate, n. accumbens, temporal)
- prefrontal cortex
3 key projections:
- mesostriatal (nigrostriatal) proj → forebrain [striatum (putamen, caudate)]
- mesolimbic proj → limbic system
- mesocortical proj: prefrontal cortex
serotonergic consciousness system
nt
main role
origin/projections
serotonin
main role: neuromodulation (excitatory, inhibitory)
functions associated with:
- alertness (incr firing in wake than sleep)
- new, attended-to, sensory stimulus (esp noxious, fear-provoking)
origin: all levels of brainstem, most imp in upper brainstem
- dorsal raphe nucleus
- medial raphe nucleus
roles:
- rostral: psych disorders (depression, anxiety, OCD, aggression, eating)
-
caudal: pain modulation, breathing, temp, motor control
- possiblity assoc with SIDS
cocaine, amphetamines, MDMA (ecstasy) have potentiating effect on serotonergic terminals
