Mechanisms of Arousal Flashcards
arousal =
being awake
Consciousness is recognized by having two parts
- arousal
2. awareness
awareness=
conscious processing of inputs
Coma
neither awake (arousal absent) nor aware
Persistent vegetative state
physiologically identifiable sleep/wake cycles appear (arousal)
no evidence of awareness
minimally conscious state
sleep wake cycles (arousal)
reproducible evidence of awareness - ability to respond to simple commands
limited or absent communication
Misconception with comatose state
primarily from damage to cerebral corticies
(this can be true, but damage must be massive)
Led to the hypothesis that BRAINSTEM regions are critical for arousing the cortex
Both arousal and awareness require the activation of the _____
what is the caveat to this
how do we resolve it
cortex
the cortex has no intrinsic mechanism for activation
there are multiple subcortical structures that function to provide the activation required for the cortex to function
What are the 5 types of arousal systems
EAA cholinergic noradrenergic seratonergic dopaminergic
What are the EAA activating regions
Reticular activating system (RAS)
parabrachial nuclei
What are the Cholinergic activating regions of the brain
pedunculopontine tegmental and laterodorsal nuclei
PPT and LDT
What is the Noradrenergic activating region of the brain
locus ceruleus
what is the seratonergic activating region
raphe nuclei
What is the dopaminergic activating region
ventral tegmental area
EAA: inputs to the RAAS
all ascending sensory tracts send information to the RAS, as well as
trigeminal
auditory
visual
EAA: inputs to the RAS
describe how the RAS responds to multiple sensory modalities
there is sufficient synaptic convergence of input to the neurons of the RAS that MODAL SPECIFICITY IS LOST.
the neurons of the RAS respond equally well to multiple sensory modalities.
EAA: Outputs from the RAS - waht are the two pathways
- dorsal pathway
2. ventral pathway
Dorsal pathway
via non specific nuclei of the thalamus, including the intralaminar nucleus of the thalamus
from there, diffuse pathway to all higher levels
Ventral pathway
via basal forebrain and hypothalamus,
from there diffuse pathway to all higher levels.
EAA: RAS where is it found
occupies midventral portion of medulla and midbrain
EAA parabrachial nuclei - where are they located
located in the pons, (medial, intermediate and lateral parabrachial nuclei)
EAA - parabrachial nuclei inputs
sensory inputs are similar to those seen in RAS, all/most of the sensory inputs in the body
EAA parabrachial nuclei - outputs
exclusively via the ventral pathway, with extensive very diffuse innervation of the entire cortex
EAA RAS and Para brachial nuclei - major NT used
EAA, glutamate - for both dorsal and ventral pathways
Things to be aware of with EAA arousal systems
within RAS, there is a substantial number of interneurons that release GABA
RAS also has a neuronal population that releases Ach
EAA - its role in arousal
regardless of path (dorsal or ventral) the EAA system appears to provide a baseline excitation that is crucial to cortical activity
AROUSAL
Cholinergic arousal system inputs
like the RAS, the PPT/LDT nuclei receive so much input that all modality specific information is lost
cholinergic arousal system output and major NT
output - dorsal and ventral pathways used by the RAS
major NT - Acetylcholine
Cholinergic - its role in arousal
regardless of path (dorsal of ventral) the cholinergic system appears to provide a baseline excitation that is crucial to cortical activity (arousal)
Cholinergic - Role in arousal/awareness
activity in the cholinergic inputs from the pons is also associated with arousal and awareness
damage specifically to the PPT and DLT doesn’t necessarily cause coma, but does produce severe cognitive deficits that are associated with a generalized slowing of cortical processes.
Noradrenergic - outputs from LC
both ascending and descending
ascending= dorsal AND ventral with the RAS
the ascending fibers from this group of cells become the dorsal noradrenergic bundle
Noradrenergic functions in arousal/awareness
startle and alerting responses to the EEG
sleep wake
behavioral vigilance (takes us to awareness)
Serotonergic inputs
multiple, difficult to decide which ones relate to arousal systems.
Serotonergic outputs
for arousal both dorsal and ventral paths are used
Serotonergic functions
quite awareness
other non RAS activities include mood and affect, modulation of pain
Dopaminergic - Ventral tegmental area provides a dopaminergic input that is important to many functions including
cognitive functions
motor activity
emotion
(dopamine is our icing on the cake)
Thalamic arousal systems
Dorsal pathways synapses in the non specific nuclei of the thalamus
from thalamus, there is a diffuse projection to the entire cortex utilising eaa as the NT
these neurons interact with a series of intracortical neurons that releas GABA, to create oscillations seen in the EEG
Thalamic arousal systems
from the thalamus, the diffuse projections release what NT?
EAA
The RAS/ parabrachial _____ system is crucial for increasing________. in a persistent vegitative state, the rostral regions of the pons/midbrain/thalamus show neuronal loss that ____ that of cortex.
Cortical neurons are _______ relative to their threshold
EAA
general excitability of cortical neurons.
exceeds
hyperpolarized
The cholinergic system does what
adds to general excitation
In alzheiers, metnal processes slow dramatically and memory formation is impaird profoundly. what system is damaged
cholinergic system
The noradrenergic and seroterneric systems do what
move us from being awake to being more generally aware of incoming information.
the alerting response in the EEG is an early indicator that the cortex is ‘looking for’ or ‘expecting’ sensory input
The dopaminergic system does what
adds to awareness, but its role is not as well defined.
Thalamic arousal systems
the activity of the thalmocortical neurons does or does not change with state
explain
does
during sleep these neurons are hyperpolarized and show occasional bursts (spindle- like discharges)
this hyperpolarization essentially cuts the cortez off from the excitatory influence during the deepest levels of sleep.
