6. Brain Arousal Systems (Karius) Flashcards
What is the general function of the serotonergic pathway in awareness?
“Quiet awareness”
What system of awareness is particularly affected in Alzheimers?
The cholenergic system.
Where is the start of the cholinergic pathway?
Pedunculopontine tegmental nuclei
laterodorsal nuclei
What is the location for the start of the noradrenergic pathway?
Locus ceruleus.
What specific part of the thalamus were we asked to remember as a part of the dorsal pathway?
The intralaminar nucleus of the thalamus.
What is the general function of the noradrenergic pathway in awareness?
The “startle and alert” functions we can see on an EEG.
From where does the raphe nuclei receive stimulus as a part of its awareness pathway?
Spinal cord
Trigeminal nerve
Periaqueductal grey
(Serotonergic pathway)
What are the general functions of each of the awareness pathways in order from least aware to most?
EAA / Cholinergic = Awake
Noradrenergic = Startle and alert
Serotonergic = Quiet awareness
Dopaminergic = Alert and focused awareness (not as well defined)
Which pathway for activation of the cerebral cortex bypasses the thalamus?
The ventral pathway.
What three places provide input to the locus ceruleus and the noradrenergic pathway of awareness?
Paragigantocellularis nuclei
Periaqueductal grey
Cortex itself
What pathway of awareness uses only the ventral pathway to activate the cortex?
The excitatory amino acid pathway traveling through the parabrachial nuclei.
In a persistent vegitative state, what is the membrane potential of the neurons?
cortical neurons are up to 30mV below threshold than under normal conditions
AKA hyperpolarized, cannot be stimulated at all.
Excitatory Amino Acids: Reticular Activating Systems
- mid-ventral portion of medulla and midbrain
- made of neurons and tracts
- ALL ascending TRACTS send information here as does trigeminal/auditory/visual
- Modal specificity is lost
- Dorsal and Ventral pathways
Dorsal Pathway
Ventral Pathway
arousal systems send axons to thalamus–>synapse
–>axons from thalamus to cortex are known as thalamocortical neurons
arousal systems send axons straight to cortex –>synapse directly onto cortical neurons
Excitatory Amino Acids: Parabrachial Nuclei
- located in pons in parabrachial nuclei
- crucial for arousal/activation
- All Sensory
- Output via ventral pathway
- GLUTAMATE
- crucial for cortical activation
Cholinergic: Pedunculopontine Tegmental and Laterodorsal Nuclei
- No modal specificity
- outputs via dorsal and ventral pathways used by RAS
- Main: Ach
- Crucial for cortical activity
- associated with arousal/awakeness
Noradrenergic: Locus Ceruleus
- Inputs sensory info via paragigantocellularis and Periaquaductal grey
- undergoes more neural processing than EAA/Ach systems
- Outputs via dorsal and ventral pathways and some unrelated to spinal cord
- Startle/Alert, sleep/wake, behavorial vigilance
Serotonin: Raphe Nuclei
- inputs: sensory from spinal cord, fine proprioception, trigem. n.
- outputs: dorsal and ventral paths
- Quiet awareness, mood/affect, modulation of pain
Dopaminergic: Ventral Tegmental Area
- cognitive/motor/emotion
Thalamic Arousal Systems
- these neurons with EAA input synapse on intracrotical neurons that release GABA on other cortical neurons
- alternating waves of excitement and inhibition (gaba) lead to the waves seen on EEG
- during sleep, thalamocortical neurons are hyperpolarized and shot short bursts of AP.
- Hyperpolarization allows cortex to be cut off from excitation during sleep
Four steps of creating consciousness
- RAS/parabrachial EAA system is crucial for increasing general excitability of cortical neurons
* in vegetative state-pons, MB, and thalamus show nueronal loss greater than cortex - Cholinergic system adds general excitation
* In Alz. this system is hit, mental processes slow, memory impaired w/o excitation - Noradrenergic and seritonergics move from awake to aware
* “alerting” response on EEG is early indicator that cortex is looking for sensory input “booting up” - dopaminergic adds to awareness with novel stimuli
* Levodopa tx in vegetative pt may help
