Karius Brain Arousal Flashcards
Definition of arousal
Being awake
Definition of awareness
Conscious processing of inputs
Coma description
Neither awake nor aware. Don’t see reproducible sleep and wake cycles
Persistent vegetative state characteristics
Has sleep/wake cycles but no evidence of awareness
have reflexes ex. If they hear a sound they will move head of if you put something in their hand they will grasp it but that’s just survival mechanism not awareness
Minimally conscious state definition
Clear periods of sleep/wake cycles, reproducible awareness (ability to respond to command), but are limited or absent in communication
Timeline of Consciousness
Coma –>Arousal/Wakefulness–> Awareness–> Alertness
Misconception about comatose state
That it results from cerebral cortices damage (which is true) but the damage must be massive
How does disruption of consciousness occur
Small lesions in the brain from brainstem, midbrain, hypothalamus (central area)
What happens if there is damage of the very lower brainstem
Disrupt breathing and cardiac systems
*not viable living condition
Role of brainstem and cortex in consciousness
Brainstem regions are critical for arousing the cortex
Can the cortex initiate arousal on it’s own?
No, it needs input from the brainstem for activation
What are the 5 arousal systems needed for full consciousness
EAA, Cholinergic, Noradrenergic, Serotonergic, Dopaminergic
Components of the EAA arousal system?
Reticular activating syste and parabrachial nuclei
Where is the EAA arousal system located
“Mid-ventral portion”- Pons and upper medulla
What is the RAS system
Loose collection of neurons and fibers in the EAA
Inputs to RAS
All ascending sensory tracts, trigeminal, auditory, visual
Where do all sensory inputs converge in RAS
On post-synaptic cell of RAS
What happens if there is sufficient synaptic convergence on the RAS
Modal specificity is lost
Modal Specificity Loss
Refers to different senses but not being able to identify those sense
Ex. Knowing that something landed on you but don’t know what
Two pathways of the RAS system
Dorsal pathway and ventral pathway
How is the dorsal pathway sent out (location)
Via non-specific nuclei of thalamus including intra laminar nucleus of the thalamus
Where does the dorsal pathway diffuse to?
All higher pathway levels (all over the cortex)
How is the ventral pathway sent out?
Via basal forebrain and hypothalamus
Where does the ventral pathway diffuse to?
All higher levels BUT bypasses the thalamus
Purpose of the dorsal and ventral pathways of RAS
To excite the cortical areas
Function of parabrachial nuclei
Reinforce what the RAS is doing and are crucial for arousal and activation
Where is the parabrachial nuclei located
Pons
Outputs from parabrachial nuclei
Exclusively via the ventral pathway difference between parabrachial and RAS
If I damage the thalamus then how does the EAA system response?
Since the parabrachial system bypasses the thalamus then the cortex will still get stimuli from the ventral pathway via the parabrachial system
What is the major neurotransmitter utilized by RAS and parabrachial nuclei
EAA/Glutamate
2 unique characteristics of RAS
RAS pathway has lots of interneurons, and has a part that releases Ach
Baseline excitation to cortical activity
EAA system and cholinergic system
Gets cortical neurons close to threshold
What cycle is possible with at least EAA
Sleep/wake cycle
Cholinergic Nuclei
Pedunculopontine tegmental and lateral dorsal nuclei
Major neurotransmitter for PPT/LDT
Ach but is superimposed with excitatory amino acid pathway
Outputs of the PPT/LDT pathway
Dorsal and ventral pathway
Where are the cholinergic inputs from?
Pons
What is the role of the cholinergic system
Arousal and awareness
What happens if there is damage specifically to the PPN/LDT system?
Produce severe cognitive deficits from slowing of cortical processes
*not necessarily coma
Noradrenergic Arousal System
Locus Ceruleus
Main purpose of Noradrenergic arousal system
To cause periodic awareness
Outputs from the LC
Both ascending and descending
Ascending pathway output from the LC uses…
Dorsal and ventral pathway with RAS
What does the LC release
NE
What do the ascending fibers from this group of cell become?
Dorsal Noradrenergic bundle
Main function of the LC NA system
STARTLE and alerting response on EEG and behavioral vigilance
**very specific to LC
Behavioral Vigilance
Trying to figure out what the f is going on
What is the Serotonergic arousal system
Raphe nuclei
Inputs for the Serotonergic raphe nuclei
Multiple – difficult to determine
Outputs for Serotonergic raphe nuclei
Dorsal and ventral pathways
Functions of the Serotonergic arousal system
Quiet awareness
Dopaminergic arousal system location
Ventral tegmental area (VTA)
What functions does VTA provide input to?
Cognitive function, motor activity, emotion
Dorsal Pathway
Arousal system send axons to thalamus –> synapse –> go to cortex
Ventral Pathway
Arousal system axons sent straight to cortex –> synapse directly onto cortical neurons
Thalamic Arousal System
From thalamus, signal is sent to entire cortex through EAA as neurotransmitter
What to thalamus arousal system neurons interact with
Series of intra cortical neuron that release GABA
Function of GABA in thalamic arousal system
Mediate the mass of excitatory cortical neurons by inhibitory effect
Thalamic Arousal System during sleep
Thalami cortical neurons are hyperpolarized and show burst
*the hyper polarization cuts the cortex off from the excitatory influence during deepest sleep levels
2 parts of consciousness
Arousal and awareness
