Brain Arousal Systems Flashcards
Consciousness is recognized as having two parts, which are…
1) Arousal (being awake)
2) Awareness (conscious processing of inputs, etc)
***These are not the same!
This state of consciousness if being neither awake or aware.
Coma
This state of consciousness occurs when physiologically identifiable sleep/wake cycles appear but there is no evidence of awareness.
Persistent vegetative state
***Step up from coma
This state of consciousness has obvious sleep/wake cycles, reproducible evidence of awareness by being able to respond to simple commands, and limited or absent communication.
Minimally conscious state
***Step up from persistent vegetative state
What are the four levels of consciousness?
Coma – Arousal/Wakfulness – Awareness – Alertness
It is a common misperception that the comatose state results from damage to the cerebral cortices. Although this is true, the damage must be…
Massive and bilateral
More often, disruptions of consciousness result from much smaller lesions in the…
Brainstem
Midbrain
Hypothalamus
It has been shown that cortical neurons of people in persistent vegetative states are up to 30 mV below threshold than under normal conditions. What does this mean?
The neurons are hugely hyperpolarized compared to normal, so this means there is no normal stimulus strong enough to activate these neurons.
T/F. Different levels of consciousness/awareness are the result of different levels of cortical excitation.
True
The _________ regions are critical in arousing the cortex. Both arousal and awareness require activation of the cortex, but the cortex has no intrinsic mechanism for activation (aka, the cortex can’t do it on its own, needs help).
Brainstem
This level of consciousness has:
– Inconsistent or intermittent eye/head motions (reflect reflexes)
– No sleep/wake cycle
– No awareness
– No verbal responses
Coma
This level of consciousness has:
- Eye/head motions (reflect reflexes)
- Sleep/wake cycle
- No awareness
- No verbal responses
Persistent vegetative state
This level of consciousness has:
- Eye/head motions
- Sleep/wake cycle
- Inconsistent or intermittent awareness
- Inconsistent or intermittent verbal responses
Minimally conscious
This level of consciousness has:
- Eye/head motions
- Sleep/wake cycle
- Awareness
- Verbal responses
Aware/Alert
What are the 5 arousal systems needed for normal function?
EAA Cholinergic Noradrenergic Serotonergic Dopaminergic
The EAA arousal system originates from where?
Reticular Activating System (RAS)
Parabrachial Nuclei
The Cholinergic arousal system originates from where?
PPT/LDT (Pedunculopontine tegmental and Laterodorsal nuclei)
The Noradrenergic arousal system originates from where?
Locus Ceruleus
The Serotonergic arousal system originates from where?
Raphe nuclei
The Dopaminergic arousal system originates from where?
Ventral Tegmental Area
For the EAA arousal system, the RAS occupies what area?
Mid-ventral portion of the medulla and midbrain
The RAS is a loose collection of neurons and fiber tracts. All ascending sensory tracts send information to the RAS, including ________, ________, and ________.
Trigeminal
Auditory
Visual
The RAS receives so much sensory input, that modal specificity is lost. What does this mean?
Because all this information converges on the same neurons, it knows something sensory is happening, but it can’t process it to know what specifically is happening.
What are the pathways of the output of information from the RAS?
Dorsal Pathway (thalamus) Ventral Pathway (no thalamus)
In the Dorsal Pathway, the RAS outputs information via the non-specific nuclei of the _________, including the _________ nucleus of the _________. From there, it continues to all higher levels.
Thalamus
Intralaminar
Thalamus
In the Ventral Pathway, the RAS outputs via the ________ ________ and ________. It bypasses the Thalamus in this pathway. From there, it continues to all higher levels.
Basal Forebrain
Hypothalamus
In the EAA arousal system, the Parabrachial Nuclei (medial, intermediate, and lateral) are located in the _______. They are crucial for arousal/activation.
Pons
T/F. The RAS and Parabrachial Nuclei contain very different versions of sensory input.
False. The sensory inputs are similar. All/most of the sensory inputs to the body go to both, with no modal specificity.
What is the main difference between the RAS and the Parabrachial Nuclei?
RAS - Uses both the Dorsal and Ventral Pathways
Parabrachial Nuclei – Only uses Ventral Pathway
***Remember, Dorsal utilizes the thalamus while Ventral bypasses it!
The major NT utilized by both the Parabrachial and the RAS neurons is the __________, regardless of pathway to the brain.
EAA/Glutamate
Within the RAS, there is a substantial number of interneurons (neurons intrinsic to the RAS) that release ________. The RAS also has a neuronal population that releases _________.
GABA
Acetylcholine
***Just FYI, if you see RAS always think EAA/Glutamate first!
Regardless of path (dorsal or ventral), the ______ and _______ systems appear to provide a baseline excitation that is crucial to cortical activity.
EAA
Cholinergic
Like the RAS/Parabrachial, the ________ nuclei receive so much input that all modality-specific information is lost.
PPT/LDT
In the PPT/LDT nuclei, the outputs are via the dorsal and ventral pathways just like RAS, but the NT is _________.
Acetylcholine (ACh)
T/F. Activity in the Cholinergic inputs from the Pons is also associated with arousal and awareness. Damage specifically to the PPT/LDT doesn’t necessarily cause coma, but does produce severe cognitive deficits that are associated with generalized slowing of cortical processes.
True
To go from coma to arousal/wakfulness, what is required?
EAA and ACh systems
***If you lose one or the other, it won’t cause coma but will result in slowed cortical processes
Paragigantocellularis N. (in rostral medulla) receives sensory information, the Periaqueductal Grey (PAG), and higher centers including the cortex, all send info to the ________ ________ which is noradrenergic. This information has undergone more neural processing than the sensory inputs received by the EAA/ACh systems (which has no modal specificity).
Locus Ceruleus
Outputs from the Locus Ceruleus (noradrenergic) related to consciousness ascend to the cortex using what pathways?
Ventral and Dorsal pathways
***There are unrelated outputs to the Spinal Cord
What are the functions of the Locus Ceruleus (noradrenergic) system?
- Startle and alerting responses on the EEG
- Sleep-wake
- Behavioral vigilance
What is the source of the Serotonergic system?
Raphe Nuclei
The outputs of the Serotonergic system (via Raphe Nuclei) for arousal is via which pathways?
Doral and Ventral pathways
***There are other outputs related to other functions of raphe
What are the functions of the Serotonergic system?
- Quiet awareness
- - Other (non-RAS activities) include: Mood and Affect, Modulation of Pain
In order to go from arousal/wakefulness to awareness, what systems are needed?
Noradrenergic (Locus Ceruleus) and Serotonergic (Raphe Nuclei)
***Need both!
This area provides a dopaminergic input that is important to many functions, including cognitive functions, motor activity, and emotion.
Ventral Tegmental Area (VTA)
This system is required to go from awareness to alertness (full normal function).
Dopaminergic (Ventral Tegmental Area)
In this pathway, arousal systems send axons to the thalamus to synapse.
Dorsal pathway
In the Dorsal pathway, axons from the thalamus to the cortex are known as __________ neurons.
Thalamocortical
In this pathway, arousal systems send axons straight to the cortex. They synapse directly onto the cortical neurons.
Ventral pathway
Dorsal pathway synapses in the non-specific nuclei of the thalamus, like the _________ nuclei.
Intralaminar
From the thalamus, there is a diffuse projection to the entire cortex. These thalamocortical neurons release _______ as their neurotransmitter. These neurons (with their NT input) also synapse on intracortical neurons that release _______ on other cortical neurons.
EAA
GABA
***These excitatory/inhibitory waves are what make the waves recorded on EEG!
The alternating waves of excitation (due to the EAA released) and inhibition (due to the GABA released) are believed to lead to the waves recorded on the ______.
EEG
The ________ ________ system is crucial for increasing general excitability of cortical neurons. The ________ also adds to that general excitation.
RAS/Parabrachial EAA
Cholinergic
In a persistent vegetative state, the rostral regions of the _______, _______, and _______ show neuronal loss that exceeds that of the cortex.
Pons
Midbrain
Thalamus
In this disease, the cholinergic systems are particularly hard hit. Mental processes slow dramatically and memory information is profoundly impaired in the absence of the excitation.
Alzheimers
These systems move us from being awake to being more generally aware of incoming information.
Noradrenergic
Serotonergic
T/F. The alerting response in the EEG is an early indicator that the cortex is ‘looking’ for sensory input.
True
This system seems to add to focused awareness associated with novel stimuli.
Dopaminergic
In a limited number of people in a persistent vegetative state, treatment with ________ has produced dramatic increases in cognitive function.
L-Dopa
During sleep, ___________ neurons are hyperpolarized and show occasional short bursts of action potentials. This hyperpolarization essentially cuts the cortex off from the excitatory influence during the deepest levels of sleep.
Thalamocortical
