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Neuro test 2 > 6. Mechanism of Arousal: Brain Arousal Systems > Flashcards

6. Mechanism of Arousal: Brain Arousal Systems Flashcards

1
Q

What is consciousness recognized as?

A

Has two parts: arousal (being awake) vs. awareness (conscious processing of inputs)

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2
Q

What is a coma?

A

neither being awake or aware

has eye/head motions

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3
Q

What is a persistent vegetative state?

A

eye/head motions and physiologically identifiable sleep/wake cycles appear

no evidence of awareness or verbal responses

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4
Q

What is a minimally conscious state:

A

eye/head motions, sleep/wake cycles, awareness, and verbal responses (INCONSISTENT)

reproducible evidence of awareness- ability to respond to simple commands; inconsistency related to plasticity

limited or absent communication

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5
Q

What are the steps in the hierarchy of consciousness (least to most alert)? What does it say about the basis of consciousness?

A

coma–> arousal/wakefullness (sleep/wake)–> awareness–> alertness

  1. different levels of consciousness/awareness are result of diff. levels of cortical excitation
  2. moving from arousal/wakefullnes to awareness requires additional excitation
  3. moving from awareness to alertness (full awareness) takes another layer of excitation to achieve
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6
Q

How does the nature of injuries alter consciousness permanently? what is it usually from?

A

it is a misconception that comatose state results from damage to cerebral cortices; damage must be MASSIVE and bilateral

disruptions of consciousness typically result from smaller lesions in brainstem, midbrain, and hypothalamus (lower brainstem area)

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7
Q

What evidences from patients in persistent vegetative state tells us about the nature of consciousness?

A

you can see marked loss of neurons in Midbrain, pons, etc. (so lesions from lower brainstem, not cortex)

AKA- brainstem regions are CRITICAL for arousing the cortex

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8
Q

Activation of what is required for arousal and awareness?

A

activation of the cortex!!

but cortex lacks an intrinsic mechanism for activation so relies on input from other parts of the brain

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9
Q

What is the function of the arousal systems?

A

5 NTs associated with them
core= EAA system (associated with traditional RAS)

also have cholinergic, noradrenergic, serotonergic, and dopaminergic arousal systems

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10
Q

What is the EAA arousal system associated with? what does it arise from?

A

associated with the traditional RAS

Anatomy: arise from parabrachial nuclei (in mid-ventral portion of medulla and midbrain); loose collection of neurons and fiber tracts; postsynaptic pathways are complex

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11
Q

What are the inputs to the Reticular Activating System?

A

trigeminal, auditory, visual

all ascending sensory tracts send information to the RAS!!

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12
Q

What are the characteristics of inputs to RAS? what is lost?

A

there is sufficient convergence of input to neurons of RAS that MODAL SPECIFICITY is lost!!–> brain only knows something happened, but not what happened (event detector)

so neurons of RAS respond equally well to multiple sensory modalities

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13
Q

What are two output pathways from the RAS? via what?

A
  1. Dorsal pathway– via non-specific nuclei of thalamus (including INTRALAMINAR NUCLEUS OF THALAMUS); from there diffuse pathways to all higher levels
  2. Ventral Pathway– via basal forebrain and hypothalamus (bypasses thalamus); from there, diffuse pathways to all higher levels!
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14
Q

Where is the parabrachial nuclei located? what are they crucial for?

A

in the pons (medial, intermediate, and lateral)

crucial for activation/arousal

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15
Q

What are the inputs for the parabrachial nuclei?

A

similar to RAS–> all/most of sensory inputs to body

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16
Q

What are the outputs from parabrachial nuclei?

A

EXCLUSIVELY via ventral pathway!!

extensive, very diffuse innervation of entire cortex

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17
Q

What is the major NT utilized by both parabrachial and RAS neurons?

A

EAA/glutamate (for both dorsal and ventral pathways)

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18
Q

Within the RAS, what do neurons release?

A

There is a substantial number of interneurons (intrinsic to RAS) that release GABA

Also have neuronal population that releases ACh

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19
Q

What is the EAA systems general role in arousal?

A

regardless of path (dorsal or ventral), it appears to provide a baseline excitation that is crucial to cortical activity

20
Q

Within the cholinergic arousal system, what input and outputs are sent to and from the pedunclopontine tegmental and laterodorsal nuclei (PPT/LDT)?

A

INPUTS: like RAS, receive so much that modality-specifci info is lost

OUTPUTS: via dorsal and ventral pathways used by RAS

21
Q

What is the major neurotransmitter used in the pedunclopontine tegmental and laterodorsal nuclei?

A

part of cholinergic arousal system, so ACh

22
Q

What is the cholinergic arousal systems role in arousal?

A

regardless of path (dorsal or ventral), it also appear to provide a baseline excitation that is crucial to cortical activity

activity in cholinergic inputs from pons is also associated with arousal and awareness

23
Q

What happens when there is damage to the PPN/DLT nuclei?

A

doesn’t necessarily cause coma, but does produce SEVERE cognitive deficits that are associated with generalized slowing of cortical processing (can wake tho)

Alzheimers

decline in all cognitive processing

24
Q

What is required for normal arousal and establishment of sleep wake cycles?

A

full function of both EAA and ACh arousal systems

25
Q

Where are the cell bodies of the noradrenergic system located? what is this system the major source of?

A

at the locus coereuleus in the pons

major source of NE in brain

26
Q

Where do the inputs to the locus coereuleus come from?

A

major source= brainstem nuclei, especially Paragigantogocellularis N. (in rostral medulla)= sensory info

PAG= periaqueductal grey

higher centers (hypothalamus, amygdala, cortex)

27
Q

What is different about the inputs coming into the locus coereuleus?

A

the information is processed a bit more, existence of it depends on function of EAA/ACh core already being in place

28
Q

What are the outputs from the locus coereuleus?

A

have both ascending and descending

Ascending fibers: dorsal and ventral axons join axons fof the RAS/parabrachial/PPT/LDT in dorsal and ventral pathways

29
Q

What do the ascending fibers from the Locus coereuleus become?

A

dorsal noradrenergic bundle

30
Q

What are the functions of the locus coreuleus NE Arousal system?

A

STARTLE and ALERTING response on EEG (now aware of specific event**)

sleep-wake

behavioral vigilance

31
Q

Where are the cell bodies of the serotonergic system located?

A

raphe nuclei

32
Q

Where are the inputs to serotonergic system coming from?

A

Sensory- from spinal cord (fine proprioception)

trigeminal sensory nuclei

Periaquaductal grey- pain control

33
Q

What are the outputs from the raphe nuclei/ serotonergic system?

A

both dorsal and VENTRAL* paths are used

ventral strong through hypothalamus!!

34
Q

What are the functions of the serotonergic system?

A

QUIET AWARENESS* (not focused on anything specific, but aware of whats around)

regular awareness

other functions: mood and affect, modulation of pain

35
Q

To get from arousal/Wakefullness to awareness, what do you need?

A

NE and Serotonin arousal systems

36
Q

What is the last layer important to get to full alertness?

A

Dopaminergic Arousal system

37
Q

Where are the cell bodies for the dopaminergic system located?

A

ventral tegmental area

38
Q

What is the function of the ventral tegmental area?

A

VTA (w substantia nigra) provides a dopaminergic input that is important for functions including: cognitive function, motor activity, emotion

alertness in response to novel stimuli (brain arousal function)

39
Q

What illness is associated with a disruption of DA?

A

Parkinsons

40
Q

General: What is the Dorsal pathway?

A

arousal system sends axons to thalamus–> synapse–> axons from thalamus to cortex

non-specific nuclei of thalamus

neurons with EAA input interact with a series of intracortical neurons that release GABA to create oscillations that are seen in EEG

41
Q

General: What is the Ventral pathway?

A

arousal system sends axons straight to cortex–> synapse directly onto cortical neurons

42
Q

What is the function of all arousal systems?

A
  1. RAS/parabachial EAA system crucial for increasing general excitability of cortical neurons
  2. Cholinergic system adds to that general excitation
  3. NA and 5-HT systems move us from being awake to being more generaly aware of incoming information
  4. DA systems adds to that awareness asociated, particularly focused awareness associated with novel stimuli; role not well defined
43
Q

What is the neuronal loss in a persistent vegetative state?

A

in persistent vegetative state, rostral regions of pons/midbrain/thalamus show neuronal loss that exceeds that of cortex (cortical neurons are 10-30 mV hyperpolarized relative to their threshold

44
Q

What is hit hard in Alzheimer’s disease?

A

cholinergic systems!!

mental processes slow dramatically and memory formation profoundly impaired

45
Q

What does the alerting response in the EEG an indicator for? when does this occur?

A

cortex is looking for or expecting sensory input ; more AWARE now

when NA and 5-HT systems active

46
Q

What possible treatment has produced dramatic increases in cognitive function in some patients with a persistent vegetative state?

A

Levadopa

47
Q

what happens during sleep?

what does that do to the cortex?

A

thalamocortical neurons are hyperpolarized and show occasional bursts (spindle-like discharges)

the hyperpolarization essentially cuts cortex off from excitatory influence during deepest levels of sleep, so not releasing EAA

basically: thalamus and cortex disconnected; last thing to come through is auditory

Neuro test 2 (15 decks)

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