Brain Arousal Systems Flashcards by Kristina Assaf

Being awake

Arousal

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Conscious processing of inputs

Awareness

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Neither awake or aware

Coma

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physiologically identifiable sleep/wake cycles appear

* no evidence of awareness

Persistent vegetative state

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sleep/wake cycles
reproducible evidence of awareness – ability to respond to simple commands.
limited or absent communication

Minimally conscious state

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Order of consciousness

Coma –> Arousal/Wakefulness –> Awareness–> Alertness

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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

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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.

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Arousal Systems
EAA:
- ?
- ?

Reticular Activating System (RAS)

* Parabrachial nuclei

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Arousal Systems 
• Cholinergic : ?
• Noradrenergic:  ?
• Serotonergic:  ?
• Dopaminergic: ?

Pedunculopontine tegmental and Laterodorsal
nuclei (PPT/LDT)
Locus Ceruleus
Raphe nuclei
ventral tegmental area

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Reticular Activating System Location

Occupies “mid-ventral portion” of medulla & midbrain

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All ascending sensory tracts send information to the RAS

- Also send info to RAS: ?

As do:
• Trigeminal
• Auditory
• Visual

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RAS:

All inputs synapse on the same post synaptic cell

convergence

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There is sufficient synaptic convergence of input to the neurons of the RAS that ? is lost

modal specificity

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2 pathways for RAS

Dorsal and Ventral Pathway

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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

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Ventral Pathway
•Via ? and ?

•From there, diffuse pathway to all higher levels

Via basal forebrain and hypothalamus

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Goal of the Reticular System

To excite the cortex

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Parabrachial Nuclei

- Location and Function?

Located in the pons, the parabrachial nuclei (medial, intermediate, and lateral) are crucial for arousal/activation.

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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.

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The major neurotransmitter utilized by both the

parabrachial and the RAS neurons is?

EAA/Glutamate
(That is true for both dorsal and
ventral pathways)

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Regardless of path (dorsal or ventral), the ? system appears to provide a baseline excitation that is crucial to cortical activity.

EAA

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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

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Major neurotransmitter of PPT/LDT?

ACETYLCHOLINE!

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- 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)

2. 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)

3. 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?

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

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

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

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

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

Brain Arousal Systems Flashcards

(61 cards)