Mechanisms of Arousal: Brain arousal systems Flashcards
When an individual is in a Coma: what are they considered
neither awake nor aware
has some eye motions
What are the characteristic of an individual in a persistant vegetative state
physiologically identifiable sleep/wake cycles appear
no evidence of awareness
What are the characteristics of an individual who is minimally conscious
Eye/head motions
sleep/wake cycle
inconsistant awareness
inconsistent verbal responses
What are the characteristics of an individual who is aware and alert
eye/head motions
sleep/wake cycle
awareness
verbal responses
What is the hierchy of consciousness
coma to
Arousal/wakefulness to
awarness to
alertness
where does injuries happen in the brain that disrupts consciousness?
much smaller lesions in the brainstem, midbrain or hypothalamus
what is significant about the threshold for cortical neurons under a vegetative state?
the cortical neurons are up to 30mV velow threshold than under a normal conditions: this makes it very hard to depolarize the cell
(the cell is very hyperpolarized)
What does the hierchy of consciousness suggest about the physiological basis of consciousness?
Different levels of consciousness/awareness are the result of different levels of cortical excitment
What does the cortex need to become activated
both arousal and awareness require multiple sub cortical structures function to activate the cortex
where does the production of EAA occur
Reticular Activating system
Parabrachial nuclei
Where does the production of Cholinergic neurotransmitters occur
Pedunculopontine tegmental and laterodorsal nuclei
Where does the production of noradrenergic occur
Locus ceruleus
Where does the production of Serotonergic occur
Raphe nuclei
Where does the production of the dopaminergic arousal system occur
ventral tegmental area
Function, location, component and pathway of Reticular activating system
Occupies the mid-ventral portion of medulla and midbrain
loose collection of neurons and fiber tracts
receives all ascending sensory tracts, vision, and auditory, however the modal specificity of input converging here is lost, there fore the information all synapses on the same neuron, so the brain knows something happened but not what happened
Dorsal pathway and ventral pathway
Uses EAA/Glutamate
but has some interneurons releasing GABA and Aceytylcholine
What is the dorsal pathway
info via non specific nuclei of the thalamus including the intralaminar nucleus of the thalamus
and then the info will move from there to higher levels of cortex
Arousal systems synapse on thalamus and then thalamocortical neurons travel to the cortical neurons
What is the ventral pathway
Bypasses the thalamus
via the basal forebrain and hypothalamus
from there the info will diffuse to all higher levels of cortex
Travel straight from the arousal systems and synapse directly on cortical neurons
Function, location, component and pathway of parabrachial nuclei
located in the pons (there is a medial, intermediate, and lateral nucleus)
crucial for arousal activation
similar sensory to RAS: receives all ascending sensory tracts, vision, and auditory
Output is just the ventral pathway with very extensive, very diffuse innervation of the entire cortex
uses EAA/Glutamate
Function, location, component and pathway of Pedunculopontine tegmental and laterodorsal nuclei
Receive much input from all over that loses its modality specific information
output via the dorsal and ventral pathways
Pons
Acetylcholine
damage here can cause generalized slowing of cortical processes
What arousal transmitters are important for achieving Arousal and wakefulness
EAA and Aceytlcholine (hyperpolarization and memory)
Function, location, component and pathway of locus Ceruleus
Found in the pons
inputs: Paragignatocellularis nerve - sensory
Periaqueductal grey
higher centers including the cortex
Outputs: info releated to consciousness ascend to the cortex via both the dorsal and ventral pathways
also unrelated output to the spinal cord
help with startle and alerting responses
sleep wake
behavioral vigilance
Norepinephrine
Function, location, component and pathway of Raphe nuclei
Inputs: Sensory from spinal cord (fine proprioception) trigeminal n
found in pons
Output: dorsal and ventral pathways
quiet awareness (arousal)
mood andaffect
modulation of pain
serotonin: 5HT
What do we need to move from Arousal/wakefulness to Awareness
Norepinephrine and serotonin (startle/awareness)
Function, location, component and pathway of Ventral tegmental area
Midbrain
Dopaminergic that is important for cognitive functions, motor activity and emotion
What gets us from awareness to alertness
Dopamine (focus, attention)
what do the non specific thalamocortical neurons release as neurotransmitters
EAA
also they will synapse on intracortical neurons that will release GABA on other cortical neurons
What leads to the waves on the EEG
the alternating waves of excitation from EAA and GABA
What is the RAS/Parabrachial EAA system crucial for
increasing general excitabillity of cortical neurons
What does the cholinergic system add and what happens in alzheimer paitients with the cholinergic system
adds to that general excitation
in alzheimers the cholinergic systems are hit
mental processes slow dramatically and memory formation is profoundly impaired in the absence of excitation
What does the noradrenergic and serotonergic systems do and how do these relate to an EEG
move us from being awake to being more generally aware of the incoming info
the alerting response in the EEG is an early indicator that the cortex is looking for sensory input
What does the dopaminergic system add and what is the significance of Levodopa
adds focused awareness associated with novel stimuli
individuals in the persistent vegetative state can get treated with levodopa and produce dramatic increases in cognitive function
During sleep what happens to thalamocortical neurons
they are hyperpolarized but will show slow occasional short bursts of action potentials
this hyperpolarization cuts the cortex off from the excitatory influence during the deepest levels of sleep
