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
histaminergic consciousness system
nt
main role
origin/projections
histamine
main role: neuromodulation (excitatory, inhibitory)
origin: posterior hypothalamus, exclusively produced in
* tuberomammillary nucleus → forebrain (cortex, thalamus)
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
attention
general awareness of world
process of choosing what limited information deserves further processing by the brain = attention
types:
1. sustained attn (vigilance, concentration, non-distractability) : ability to maintain alertness continuously over time
- imp for tasks that have to be performed nonstop
2. selective attn : focusing attn on a particular domain above others
- selection of information relevant to a task (ex. ignoring background noise)
anatomy of attn
systems involved
same ones involved in alertness → involved in attn
- widespread projection systems (RAS)
- frontal and parietal association cortex
- anterior cigulate cortex, limbic pathways → motivational aspect of attn
- tectum, pretectal area, thalamus (pulvinar)
- cerebellum and basal ganglia
thalamic projections to brain
thalamus → neocortex uses glutamate excitatory projections
medial dorsal, intralaminar, reticular nuclei : modulate level of arousal
thalamic pulvinar nucleus : associated with selective attn (makes sense given that sensory info is relayed through thalamus)
hemispheric asymmetry
R hemisphere more important for attn mechanisms in most individs
- lesions to R hemisphere → prominent, long-lasting deficits in attn to L side
- lesions to L hemisphere → minimal R neglect
- bilat lesions → severe R neglect
causes: infarct, hemorrhage, seizures, head trauma, tumors affecting parietal/frontal cortex
awareness
poorly understood
consciousness awareness is the ability to combine various forms of sensory, motor, emotional, mnemonic information into an efficient summary of mental activity that can be potentially remembered at a later time
anatomy of awareness
dont know, but assume the following are involved
- prefrontal cortex (working memory)
- medial temporal and diencephalic regions (declarative memory)
- medial parietal region, posterior cingulate, retrosplenial cortex
- self-reflection, introspection, self-awareness
- limbic networks
