7. Brain Arousal Systems Flashcards
Consciousness is recognized as having two parts, what are they and what do they mean?
arousal (being awake)
awareness (conscious processing of inputs)
Coma means one is neither awake nor aware (conscious) which a persistent vegetative state means?
physiologically identifiable sleep/wake cycles appear
no evidence of awareness
What is classified as having sleep/wake cycles, ability to respond to simple commands, and limited/absent communication?
minimally conscious state
What is the tree from least to most conscious? 4
coma to arousal/wakefulness to awareness to alertness
What kind of damage must occur in order for someone to be in a comatose state due to a cortical issue?
massive and bilateral cerebral cortex damage
More often, disruptions of consciousness result from smaller lesions in which locations? as compared to the cortex
Brainstem
midbrain
hypothalamus
Arousal and awareness require activation of the cortex but the cortex has no intrinsic mechanism for activation. so what provides the activation?
sub-cortical structures
Which of the following can be seen with a Coma? Eye/head movement Sleep/wake cycle awareness verbal response
Eye/head movement: Sometimes
Sleep/wake cycle: no
awareness: no
verbal response: no
What can be seen with Persistent vegetative state? Eye/head movement: Sleep/wake cycle: awareness: verbal response:
Eye/head movement: yes
Sleep/wake cycle: yes
awareness: no
verbal response: no
What can be seen with minimally conscious state? Eye/head movement: Sleep/wake cycle: awareness: verbal response:
Eye/head movement: yes
Sleep/wake cycle: yes
awareness: maybe
verbal response: maybe
What can be seen with aware/alert state? Eye/head movement: Sleep/wake cycle: awareness: verbal response:
Eye/head movement: yes
Sleep/wake cycle: yes
awareness: yes
verbal response: yes
EAA arousal system has a reticular activating system (RAS), which are loose connections ofneurons and fiber tracts which occupy what region of the brain?
midventral portion of medulla and midbrain
The RAS takes input from all ascending sensory tracts as well as what three?
trigeminal
auditory
visual
There are so many synaptic convergence of input to the RAS that what is lost?
modal specificity is lost
Modal specificity can be best described as?
the brain ONLY knows something happened, not exactly WHAT happened
The output of information from the EAA RAS has two pathways, one is the dorsal pathway via the non-specific nuclei of the thalamus, including?
intralaminar nucleus of the thalamus, which diffuses to all high levels
The second pathway for output of info from the RAS in the midventral portion of medulla and midbrain is the ventral pathway via?
basal forebrain and hypothalamus
The parabrachial nuclei (medial lateral and intermediate) is located in the pons and are crucial for arousal /activation. What is the one BIG difference between parabrachial nuclei and RAS?
outputs are exclusively via ventral pathway through basal forebrain and hypothalamus
What is the major NT utilized by both the parabrachial and RAS neurons?
EAA/Glutamate (dorsal and ventral pathways)
EAA provides baseline excitation crucial to cortical activity (via dorsal and ventral pathways). The next arousal system is the cholinergic system which consists of which nuclei?
pedunculopontine tegmental and laterodorsal nuceli (PPT/LDT)
Like RAS, PPT/LDT receives alot of info so modality is lost and outputs are via dorsal/ventral pathways but what is different?
NT is acetylcholine
Damage to the PPN/LDT doesnt cause a coma but does produce what?
severe cognitive deficits which slow cortical processes (in pons)
What will get you from coma to arousal/wakefulness?
EAA (RAS/parabrachial) and Cholinergic Systems
To move from arousal/wakefulness to awareness you need more input via the noradrenergic system located?
locus ceruleus
The noradrenergic system receives inputs from paragigantocellularis N (sensory info), periaqueductal grey (PAG) and what else?
higher centers / cortex
Outputs from the locus ceruleus (noradrenergic) are both ascending and descending. Ascending paths go via?
become dorsal noradrenergic bundle and run with RAS in dorsal and ventral pathways
What are the very important functions of the locus ceruleus noradrenergic system? (3)
startle and alerting (on EEG)
Sleep-wake
behavioral vigilance
(AWARENESS)
The next arousal system is known as the serotonergic system located at the raphe nuclei. Receiving inputs from? (3)
sensory from SC, trigeminal, PAG
What paths does the serotonergic system use for output for arousal?
VENTRAL and some dorsal pathways
What are the main functions of the serotnergic system?
Quiet awareness
What two things together gets you from arousal/wakefulness to awareness?
Noradrenergic and serotonergic systems
The dopaminergic system is located at the ventral tegmental area and provides dopaminergic input that is important in? (3)
cognitive functions, motor activity, and emotion
What system will get you from awareness to alertness?
Dopaminergic system
Reminder: what is the dorsal pathway?
send axons to thalamus, synapse and axons sent to cortex
Reminder: what is the ventral pathway?
axons to cortex, bypassing thalamus and synapse in cortical neurons
From the thalamus, there is diffuse projection into the entire cortex using EAA at the NT. The neurons with EAA then do what?
interact with a series of intracortical neurons that release GABA to creat oscillations that are seen on the EEG
The RAS and parabrachial EAA system are crucial for increasing general what?
excittability of cortical neurons (cholinergic adds to this)
in a persistent vegetative state the rostral regions of pons/midbrain/thalamus shows neuronal loss that exceeds that of the cortex. Cortical neurons are 10-30 mV what?
hyperpolarized to their threshold
Which system is hit hardest with a disease like alzheimers, which leads to slowe mental processing and impaired memory formation?
Cholinergic system
The noradrenergic/serotonergic systems move us from awake to being aware of information. Alerting response in EEG is early indicator of?
cortex ‘looking’ / expecting sensory input
The dopaminergic systems adds to the awareness. In a limited number of people in persisten vege state, treatment with what has produced a dramatic increase in cognitive function?
levaDOPA
During sleep, the thalamocortical neurons are hyperpolarized and show occasional bursts. What does this hyperpolarization do?
cuts the cortex off from excitatory influence during deepest levels of sleep
