Brain Arousal Systems Flashcards
Persistent vegetative state
Physiologically identifiable sleep/wake cycles appear
No evidence of awareness
Minimally conscious state
Sleep/wake cycles
Reproducible evidence of awareness- ability to respond to simple commands
Limited or absent communication
Most common reason for disruption of consciousness
Lesions in the brainstem, midbrain or hypothalamus
Cortex of people in vegetative state
Cortical neurons are usually alive but highly hyperpolarized
Suggests that different levels of consciousness are correlated to levels of cortical excitation
Cortex has no intrinsic mechanism for excitation
Excitatory amino acids arise from
Reticular activating system
Parabrachial nuclei
Acetylcholine is produced/released by
Pedunculopontine tegmental and laterodorsal nuclei (PPT/LDT)
Noradrenergic arousal system
Locus ceruleus
Serotonergic arousal system
Raphe nucleus
Dopaminergic arousal system
Ventral tegmental area
Reticular activating system
Located in ventral portion of medulla/midbrain
All ascending sensory tracts send info to the RAS and so do trigeminal, auditory and visual systems
No modality specificity in RAS post synaptic neurons because there are too many different systems sending info to it (brain knows something has happened, but not what)
RAS dorsal pathway
Via non specific nuclei of the thalamus, including the intraluminar nucleus of the thalamus.
From there, diffuse pathway to all higher levels
RAS ventral pathway
Bypasses thalamus
Via basal forebrain and hypothalamus
From there, diffuse to higher levels of brain
Uses EAA/glutamate all though some interneurons in system can use GABA/Ach
Parabrachial nuclei
Located in the pons
Receives sensory info from pretty much all of body
Only uses ventral pathway (bypassing thalamus and instead synapsing in hypothalamus)
Uses EAA/glutamate although some interneurons in the system can use GABA/Ach
Same function as RAS
Pedunculopontine tegmental and laterodorsal nuclei
Receives info from all over body like the others
Outputs via dorsal and ventral pathways like RAS
MAJOR difference is that NT used is Ach
This ventral pathway can be affected in Alzheimer’s
PPN/DLT damage
Doesn’t necessarily cause coma, but does produce severe cognitive deficits that are associated with a generalized slowing of cortical processes
What do you need to move from coma to arousal/wakeness
Need systems that release EAA and those that release Ach
Moving from arousal/wakeness to aware
Need noradrenergic/serotonergic system plus EAA and Ach
Noradrenergic-Locus ceruleus
Inputs: paragigantocellularis (in medulla) - sensory info
Periaquaductal gray- pain
Higher centers including the cortex
This information has actually undergone more neural processing than the sensory inputs received by EAA/Ach systems
Outputs: both dorsal and ventral pathways
Function: startle & alerting responses on EEG, sleep/wake cycle, behavioral vigilance
Serotonin-Raphe nuclei
Inputs: sensory from spinal cord (fine proprioception from trigeminal nuclei)
Outputs: both dorsal and ventral pathway
Function: produces quiet awareness, plays role in mood and affect
Going from aware to alert
Need dopaminergic system as well as all the others
Dorsal and ventral pathways
Dorsal arousal systems send axons to the cortex from thalamus using thalamocortical neurons
They synapse on neurons in the cortex including intercortical neurons that release GABA this causes a wave of excitation followed by inhibition
The RAS/parabrachial EAA system is crucial for
Increasing general excitability of cortical neurons
This general excitation is also contributed to by Ach systems
Persistent vegetative state neuron activity
Rostral regions of pons, midbrain and thalamus show neuronal loss that exceeds that of the cortex
Thalamocortical neurons during sleep
Hyperpolarized and show occasional short bursts of action potentials
