Brain Arousal Flashcards
What are the 2 parts of consciousness?
Arousal
Awareness
What is arousal?
Being awake
What is awareness?
Conscious process of inputs
What needs to be activated in order to have arousa land awareness?
Cortex using brainstem
What is a coma?
Not awake or aware
What is a persistent vegetative state?
Have sleep/wake cycles
No awareness
Cortical neurons = 30 mV below threshold
What comprises a
Minimally conscious state?
Sleep/wake cycles
Evidence of awareness (can respond to simple commands)
Limited to absent communication
What does a comatose state result from?
Massive and bilateral damage to cerebral cortices
What can disrupt consciousness?
Smaller lesions in brain stem, midbrian, or hypothalamus
What are the levels of perception?
Least to greatest
Coma —> arousal wakefulness—>awareness—>alertness
What will a COMA have in terms of
- Eye/head motions
- Sleep/wake cycles
- Awareness
- Verbal responses ?
- May be present
- No
- No
- No
What will a PERSISTENT VEGETATIVE STATE have in terms of
- Eye/head motions
- Sleep/wake cycles
- Awareness
- Verbal responses ?
- Yes
- Yes
- No
- No
What will a MINIMALLY CONSCIOUS have in terms of
- Eye/head motions
- Sleep/wake cycles
- Awareness
- Verbal responses ?
- Yes
- Yes
- May be present
- May be present
What will AWARE/ALERT have in terms of
- Eye/head motions
- Sleep/wake cycles
- Awareness
- Verbal responses ?
- Yes
- Yes
- Yes
- Yes
What are the arousal system?
EAA Cholinergic Noradrenergic Serotonergic Dopamineragic
What comprises the EAA arousal system?
Reticular activating system
Parabrachial nuclei
What is the role of the EAA arousal system?
Provides baseline excitation that is crucial to cortical activity
What are the nuclei found in the
Cholinergic arousal system?
Pedunculopontine tegmentum
Laterodorsal nuclei (PPT/LDT)
Where is the
Noradrenergic arousal system?
Locus ceruleus
Where is the
Serotonergic arousal system?
Raphe nuclei
Where is the
Dopaminergic arousal system?
Ventral tegmentum area
Where is the
Reticular activation system (an EAA arousal system)
Mid ventral potion of medulla and midbrain
What is the Reticular Activating system
Loose collection of neurons and fiber tracts that receive info from all ascending sensory tracts
As well as info from trigeminal, auditory, and visual tracts
Is modal specificity kept in the RAS?
Why or why not?
It is lost
Bc of Synaptic convergence that allows neurons of RAS to respond equally well to multiple sensory modalities
What are the 2 pathways used by RAS?
Dorsal and ventral pathway
What is the dorsal pathway?
Diffuse pathway to high levels via non-specific nuclei of THALAMUS (including intralaminar nucleus of the thalamus)
What is the ventral pathway?
Bypasses thalamus!!!!
Diffuses to high levels via basal forebrain and hypothalamus
Which path bypasses the thalamus?
Ventral
What do the interneurons of the ventral pathway and its neuronal population do?
Interneurons release GABA - Major excitatory
Neuronal population release ACh
Where are the Parabrachial Nuclei of the EAA arousal system found?
In the pons
What are the parabrachial nuclei for?
Crucial for arousal and activation
What is the input to the parabrachial nuclei of the EAA arousal system?
All/most Sensory inputs to body
How does the RAS and Parabrachial Nuclei of the EAA arousal system differ?
What does this mean?
Outputs of Parabrachial exclusively use the
VENTRAL PATHWAY
=Bypasses the thalamus
What do both the RAS and Parabrachial Nuclei use?
EAA/Glutamate
Where is the cholinergic arousal system?
In PPT/LDT nuclei
Does the cholinergic arousal system keep modality specificity?
No - receives too much input
What output pathways does the Cholinergic arousal system use?
With what NTR?
Dorsal and Ventral pathways
Use ACh
What is the role of the cholinergic arousal system?
Provides baseline excitation that is crucial to cortical activity
Arousal and awareness
What happens if the PPT or LDT is damaged?
Affects cholinergic system.
Will NOT cause a coma
BUT
Does produce severe cognitive deficits
Assoc. w/ generalized slowing of cortical processes
Where is the NOradrenergic arousal system found?
Locus ceruleus
What feeds into the Noradrenergic arousal system?
Paraginganto cellularis n. (Sensory Info)
Periaqueductal gray
Higher centers, incl. cortex
How do the inputs to the Noradrenergic arousal system differ from those of the Cholinergic or EAA arousal systems?
Inputs have been processed more for NE!
Does the Noradrenergic arousal system maintain modality specificity ?
Yes!
It’s inputs have been more processed
What are the outputs of the NE arousal system related to?
What pathways do they use to ascend?
Related to consciousness
Ascend using dorsal and ventral pathways
What are the functions of the NE arousal system?
Startle and alerting responses ‘
Sleep-wake
Behavioral vigilance
Where do you find the Serotonergic arousal system?
In raphe nuclei
What are the inputs to the serotonergic arousal system?
Sensory from Spinal cord for fine proprioception and trigeminal n.
What is the output of the serotonergic arousal system?
What pathways does it use?
Quiet awareness
Arousal
Mood and affect
Modulation of pain
Uses both dorsal and ventral
Where is the dopaminergic arousal system found?
Ventral tegmental area
What provides input to the Dopaminergic arousal system?
Ventral tegmental area
What is the role of the dopaminergic arousal system?
Cognitive functions
Motor activity
Emotion
how do you move from
coma —> arousal/wakefulness?
EAA/ACh
How do you move from
arousal/wakefulness —> awareness?
NE/Serotonin
How do you move from
Awareness —> Alertness?
Dopaminergic system
Describe the dorsal pathway.
Arousal system send axons to thalamus
Synapse and thalamicocortical neurons go to cortex
Synapse in non specific nuclei of thalamus (incl. intralaminar)
Diffuse and project to entire cortex where TCNs release EAA as NTR
TCNs also synpase on intracortical neurons to release GABA
What do the 2 places of TCN synapsing release?
What does this cause?
- TCNs release EAA
- TCNs synapse on intracortical neurons to release GABA
Results in alternating waves of excitation and inhibition (waves recorded on EEG)
Describe the Ventral System.
Arousal system that bypasses the thalamus
Synapses directly onto cortical neurons
(parabrachial nuclei uses this pathway exclusively)
What does the RAS/Parabrachial EAA system do?
Increase general excitability of cortical neurons
What do we see in a persistent vegetative state?
Neuronal loss in rostral regions of pons, midbrain, and thalamus that is greater than that of cortex
What does the cholinergic system do?
Adds to general excitation made by RAS/Parabrachial system
What system is associated with Alzheimers?
What does absence of this system cause?
Cholinergic system
Absent excitation makes
Mental processes slow
Impair memory formation profoundly
What moves us from being awake to being more aware?
NE and Serotonergic systems
What does the EEG alerting response mean?
Indicator that cortex is looking for sensory input
What does the dopaminergic system do?
Adds focused awareness w/ novel stimuli
What can patients in a persistent vegetative state do to increase cognitive funciton?
Tx w/ L-Dopa
What does the Thalamus arousal system do during sleep?
TCNs hyperpolarized during sleep
W/ occasional bursts of AP
What does hyperpolarizations of TCNs do during sleeP?
Cuts cortex off from excitatory influence during deepest level of sleep
What NTR is associated with hyperpolarization and memory?
Between what levels is this seen?
EAA/ACh
Between coma and arousal/wakefulness
What NTR is assoc. w/ startle/awareness?
Between what levels is this seen?
NE/5HT
Between arousal/wakefulness and Awareness
What NTR is associated with focus and attention?
Between what levels is this seen?
Dopamine
B/w Awareness and Alertness