Brain Arousal Systems Flashcards
Being awake
Arousal
Conscious processing of inputs
Awareness
Neither awake or aware
Coma
- physiologically identifiable sleep/wake cycles appear
* no evidence of awareness
Persistent vegetative state
- sleep/wake cycles
- reproducible evidence of awareness – ability to respond to simple commands.
- limited or absent communication
Minimally conscious state
Order of consciousness
Coma –> Arousal/Wakefulness –> Awareness–> Alertness
It is a common misperception that the comatose state results from damage to the cerebral cortices. But really?
More often, disruptions of consciousness result from much smaller lesions in the brainstem, midbrain, or hypothalamus
What does this “hierarchy“ of consciousness suggest about the physiologic basis of consciousness?
(first stage)
- Different levels of consciousness/awareness are the result of different levels of cortical excitation.
Arousal Systems
EAA:
- ?
- ?
- Reticular Activating System (RAS)
* Parabrachial nuclei
Arousal Systems • Cholinergic : ? • Noradrenergic: ? • Serotonergic: ? • Dopaminergic: ?
- Pedunculopontine tegmental and Laterodorsal
nuclei (PPT/LDT) - Locus Ceruleus
- Raphe nuclei
- ventral tegmental area
Reticular Activating System Location
Occupies “mid-ventral portion” of medulla & midbrain
All ascending sensory tracts send information to the RAS
- Also send info to RAS: ?
As do:
• Trigeminal
• Auditory
• Visual
RAS:
All inputs synapse on the same post synaptic cell
convergence
There is sufficient synaptic convergence of input to the neurons of the RAS that ? is lost
modal specificity
2 pathways for RAS
- ?
- ?
Dorsal and Ventral Pathway
Dorsal Pathway
•Via the non-specific nuclei of the thalamus, including the ?
•From there, diffuse pathway to all higher levels
intralaminar nucleus of the thalamus
Ventral Pathway
•Via ? and ?
•From there, diffuse pathway to all higher levels
Via basal forebrain and hypothalamus
Goal of the Reticular System
To excite the cortex
Parabrachial Nuclei
- Location and Function?
Located in the pons, the parabrachial nuclei (medial, intermediate, and lateral) are crucial for arousal/activation.
What is the one big difference between the Parabrachial Nuclei and RAS?
The outputs for the Parabrachial Nuclei are likely exclusively via the Ventral pathway
- With extensive, very
diffuse innervation
of the entire cortex.
The major neurotransmitter utilized by both the
parabrachial and the RAS neurons is?
EAA/Glutamate
(That is true for both dorsal and
ventral pathways)
Regardless of path (dorsal or ventral), the ? system appears to provide a baseline excitation that is crucial to cortical activity.
EAA
Cholinergic: Pedunculopontine tegmental (PPT) and Laterodorsal nuclei (LDT)
- Like the RAS, the PPT/LDT nuclei receive so much input that all modality-specific information is lost.
- Outputs are via the ? and ? pathways used by the RAS
- Dorsal
- Ventral
Major neurotransmitter of PPT/LDT?
ACETYLCHOLINE!
- The ? pathway skips the thalamus
- The ? pathway goes through the thalamus
- Ventral
- Dorsal
Regardless of path (dorsal or ventral), the ? system ALSO appears to provide a baseline excitation that is crucial to cortical activity.
Cholinergic
Activity in the ? inputs from the pons is ALSO associated with arousal and awareness.
Damage specifically to the ? doesn’t necessarily cause coma, but does produce severe cognitive deficits that are associated with a generalized slowing of cortical processes.
- cholinergic
- PPN/DLT
So from coma –> arousal/wakefulness; what is above the arrow?
EAA/Ach
What does this “hierarchy“ of consciousness suggest about the physiologic basis of consciousness?
(second stage)
- Moving from arousal/wakefulness
to awareness takes additional excitation.
Noradrenergic: Locus Ceruleus
- Releases?
- Location ?
- Releases NE
- Location is Brainstem area
Inputs to the L.C.:
?
• Paragigantocellularis n (in rostral medulla) – sensory information •PAG – periaqueductal grey •Higher centers, including the cortex
Note that this information has undergone more neural processing than the sensory inputs received by the EAA/Ach systems.
(which area are they talking about ?)
Locus Ceruleus
Outputs from the L.C.:
?
•Both ascending & descending
•Ascending:
- dorsal & ventral with the RAS
L.C. :
The ascending fibers from this group of cells become the ?
dorsal noradrenergic bundle
Functions of the L.C. NA system: ?
•Startle & alerting
responses on the EEG **
•Sleep-wake
•behavioral vigilance
Inputs of Raphe nuclei?
• Sensory – from spinal
cord (fine proprioception),
trigeminal, PAG
Outputs of Raphe nuclei?
For Arousal, both the dorsal and ventral paths are used (there other outputs that relate to other functions of the raphe)
Functions of Raphe nuclei?
•Quiet awareness
•Other (non-RAS activities) include:
- Mood and Affect
- Modulation of Pain
Arousal/Wakefulness –> Awareness; what is above the arrow?
NE/5HT
What does this “hierarchy“ of consciousness suggest about the physiologic basis of consciousness?
(third stage)
- Moving to full awareness takes another layer of excitation to achieve.
Dopaminergic: ventral tegmental area (VTA)
- strongly associated with?
Mood and affect
The VTA (along with the Substantia Nigra) provides a dopaminergic input that is important to many functions, including: ?
- Cognitive functions
- Motor activity
- Emotion
? input is important for moving us into awareness
Dopaminergic
Awareness –> Alertness; what is above the arrow?
DA
Which Pathway?
• Arousal systems
send axons to
thalamus
• Synapse
• Axons from
thalamus to
cortex
Dorsal Pathway
goes through thalamus!!
Which pathway?
• Arousal systems
send axons straight to
cortex
• Synapse directly onto
cortical neurons
Ventral Pathway
bypasses thalamus!!
Thalamic Arousal System
• Dorsal pathway synapses in the ?
- non-specific nuclei of the thalamus (e.g. intralaminar)
(Non-specific is a misnomer – it is in contrast to the sensory-specific nuclei of the thalamus and reflects an old belief that these thalamic nuclei did not have specific projections/functions)
Thalamic Arousal System:
- From the thalamus, there is a diffuse projection to the entire cortex, utilizing ? as the neurotransmitter.
EAA
Thalamic Arousal System:
- These neurons (with their EAA input) interact with a series of ? neurons that release ?, to create oscillations that are seen in the EEG.
- intracortical
- GABA
The Function of all Arousal Systems #1
- The RAS/Parabrachial EAA system is crucial for increasing general excitability of cortical neurons
The Function of all Arousal Systems
- In a persistent
vegetative state, the rostral regions of the pons/midbrain/thalamus show neuronal loss that exceeds that of the cortex. - Cortical neurons are 10 – 30 millivolts ? relative to their threshold.
HYPERPOLARIZED
The Function of all Arousal Systems #2
- The cholinergic system adds to that general excitation.
In ? disease, the cholinergic systems are particularly hard hit. Mental processes slow dramatically and memory formation is profoundly impaired.
Alzheimer’s
The Function of all Arousal Systems #3
- The noradrenergic and serotonergic systems move us from being awake to being more generally aware of incoming information.
The ? response in the EEG is an early indicator
that the cortex is ‘expecting’ sensory
‘looking’ for or
input.
alerting
The Function of all Arousal Systems #4
- The dopaminergic system adds to that awareness, particularly focused awareness associated with novel stimuli, but its role is not as well defined.
In a limited number
of people in a
persistent vegetative state, treatment with ? has produced
dramatic increases in cognitive function.
levodopa
Thalamic Arousal Systems
- During sleep, the ? are hyperpolarized and show occasional bursts (spindle-like discharges).
- This hyperpolarization essentially cuts the cortex off from the excitatory influence during the deepest levels of sleep.
- thalamocortical neurons
Coma –> Arousal/Wakefulness
- What is component and function is above the arrow?
- EAA/Ach
- Hyperpolarization/memory
Arousal/Wakefulness –> Awareness
- What is component and function is above the arrow?
- NE/5HT
- Startle/awareness
Awareness –> Alertness
- What is component and function is above the arrow?
- DA
- Agonists improve cognitive function
