Brain Arousal Systems Flashcards
What is the difference between arousal and awareness?
Arousal = being awake Awareness = conscious processing
What is a persistent vegetative state?
Physiologically identifiable sleep/wake cycles with no evidence of awareness
What is a minimally conscious state?
Sleep/wake cycles, some evidence of awareness, ability to respond to simple commands, may have limited communication (yes/no)
What are the most common causes of disruptions to consciousness?
Lesions in the brainstem, midbrain, or hypothalamus (rather than bilateral injury to cerebrum)
Where do the EAAs arise?
Reticular activating system (RAS) and parabrachial nuclei
Where is the RAS located?
Mid-ventral portion of medulla and midbrain
What is the RAS?
A loose collection of neurons and fiber tracts
Where does the RAS receive sensory input information from?
All ascending sensory tracts as well as trigeminal, auditory, and visual (but no specificity)
What happens after RAS receives input?
Dorsal pathway: neurons ascend to the thalamus and release EAAs activating neurons that go all over the brain
Ventral pathway: bypasses thalamus, instead synapses occur in hypothalamus and basal forebrain
What is the parabrachial nuclei?
Located in pons, crucial for arousal/activation via EAAs. Receives all sensory inputs to the body
What happens after parabrachial nuclei receives input?
Only uses ventral pathway
What are the pedunculopontine tegmental and laterodorsal nuclei?
Also receive sensory input that is non-specific like RAS. Major NT is Ach rather than EAA
What systems must be in place to move from coma to arousal/wakefulness?
EAA/Ach (parabrachial nuclei and PNT/LDT)
What systems must be in place to move from arousal/wakefulness to awareness?
Locus ceruleus (norepi) and raphe nuclei (serotonin/5HT)
What is the locus ceruleus?
Area in same level of pons as parabrachial nuclei, processes sensory information in more specific way though. Uses both dorsal and ventral pathway to send information to the cortex. Important in startle/alerting responses (norepinephrine)
What is the raphe nuclei?
Receives sensory input from spinal cord, uses both dorsal and ventral pathway to pass information along to cortex. Important in “quiet awareness” via serotinin. (Recognition of things going on but not focused on them)
What systems must be in place to move from awareness to alertness?
Dopaminergic (ventral tegmental area)
What is the ventral tegmental area (VTA)?
Provides dopaminergic input important in cognitive functions, motor activity, emotion
What are the neurons in the dorsal pathway called?
Thalamocortical neurons (go from thalamus to cortex) and intercortical neurons (stay in cortex)
What pathway is disrupted in Alzheimer’s patients?
Ventral pathway
What do thalamocortical neurons and intercortical neurons release?
Thalamocortical neurons release EAA, intercortical neurons release GABA
