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Neuro Exam 2 - JLJ > Brain Arousal Systems > Flashcards

Brain Arousal Systems Flashcards

1
Q

What are the 2 parts of consciousness?

A

1) Arousal (being awake)

2) Awareness (conscious processing of inputs)

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2
Q

Define a coma in terms of consciousness

A

Neither awake or aware

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3
Q

Define a persistent vegetative state in terms of consciousness

A

Physiologically identifiable sleep/wake cycles appear; no evidence of awareness

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4
Q

Define a minimally conscious state

A

Sleep/wake cycles; reproducible evidence of awareness (ability to respond to simple commands); limited or absent communication

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5
Q

What is the hierarchy of consciousness from least conscious to most conscious?

A

Coma, arousal/wakefulness, awareness, alertness

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6
Q

What usually causes a coma or a disruption of consciousness?

A

Usually smaller lesions in brainstem, midbrain, or hypothalamus; it takes massive, bilateral damage in the cerebral cortices to alter consciousness or cause a coma

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7
Q

How much further below threshold are neurons in people in a persistent vegetative state?

A

30 mV

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8
Q

Both arousal and awareness require what?

A

Activation of the cortex

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9
Q

For patients in a coma, what are their eye/head motions, sleep/wake cycle, awareness, and verbal responses?

A

Eye/Head Motions: inconsistent or intermittent

Sleep/Wake Cycles: –

Awareness: –

Verbal Responses: –

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10
Q

For patients in a persistent vegetative state, what are their eye/head motions, sleep/wake cycle, awareness, and verbal responses?

A

Eye/Head Motions: yes

Sleep/Wake Cycles: yes

Awareness: –

Verbal Responses: –

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11
Q

For patients in a minimally conscious, what are their eye/head motions, sleep/wake cycle, awareness, and verbal responses?

A

Eye/Head Motions: yes

Sleep/Wake Cycle: yes

Awareness: inconsistent or intermittent

Verbal Responses: inconsistent or intermittent

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12
Q

For patients who are aware/alert, what are their eye/head motions, sleep/wake cycle, awareness, and verbal responses?

A

Eye/Head Motions: yes

Sleep/Wake Cycle: yes

Awareness: yes

Verbal Responses: yes

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13
Q

What are the different arousal systems?

A

EAA, cholinergic, noradrenergic, serotonergic, and dopaminergic

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14
Q

What makes up the EAA arousal system?

A

Reticular activating system (RAS) and parabrachial nuclei

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15
Q

What makes up the cholinergic arousal system?

A

Pedunculopontine tegmental and laterodorsal nuclei (PPT/LDT)

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16
Q

What makes up the noradrenergic arousal system?

A

Locus ceruleus

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17
Q

What makes up the serotonergic arousal system?

A

Raphe nuclei

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18
Q

What makes up the dopaminergic arousal system?

A

Ventral tegmental area

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19
Q

Where is the RAS found?

A

Occupies the mid-ventral portion of medulla and midbrain

20
Q

What sends inputs to the RAS?

A

Trigeminal, auditory, visual, and all ascending sensory tracts; so much convergence that modal specificity is lost, so the brain knows something happened but not what happened

21
Q

What are the 2 outputs from the RAS?

A

Dorsal pathway and ventral pathway

22
Q

What is the dorsal pathway leaving the RAS?

A

Information leaves via non-specific nuclei of the thalamus, including the intralaminar nucleus of the thalamus; from there, diffuse pathway to all higher levels

23
Q

What is the ventral pathway leaving the RAS?

A

Bypasses thalamus via basal forebrain and hypothalamus; from there, diffuse pathway to all higher levels

24
Q

Where is the parabrachial nuclei located? What is it crucial for?

A

Pons; crucial for arousal and activation; has medial, intermediate, and lateral parts and inputs are the same as the RAS

25
Q

What is the output from the parabrachial nuclei?

A

Strictly the ventral pathway with extensive, very diffuse innervation of the entire cortex

26
Q

What is the major neurotransmitter used by the RAS and parabrachial nuclei?

A

EAA/glutamate; RAS also has interneurons that release GABA and a neuronal population that releases acetylcholine

27
Q

What are the similarities and differences between the RAS and cholinergic (PPT/LDT) arousal systems?

A

Same: receive input from lots of modalities, so specific information is lost; outputs are via the dorsal and ventral pathways used by RAS

Different: major neurotransmitter is acetylcholine

28
Q

What does damage to the PPT/LDT (pedunculopontine tegmental and laterodorsal nuclei) cause?

A

Causes cognitive deficits that are associated with a generalized slowing of cortical processes, but not necessarily a coma

29
Q

What 2 pathways provide baseline excitation that is crucial to cortical activity?

A

RAS and cholinergic arousal systems

30
Q

What are the inputs to the locus coereuleus?

A

Paragigantocellularis (in rostral medulla), which carries sensory information; periaqueductal grey (PAG); higher centers including the cortex

31
Q

What is the key difference in information going to the RAS/cholinergic (EAA/Ach) arousal systems and the noradrenergic arousal system?

A

The information going to the locus coereuleus has undergone more neural processing than the sensory inputs received by the EAA/Ach systems

32
Q

What are the outputs from the locus coereuleus?

A

Those related to consciousness that ascend to the cortex using the ventral/dorsal pathways and unrelated outputs to the spinal cord

33
Q

What are the functions of the locus coereuleus (noradrenergic) arousal system?

A

Startle and alerting responses on EEG, sleep-wake cycles, and behavioral vigilance

34
Q

What is the source of serotonin?

A

Raphe nuclei

35
Q

What are the inputs to the raphe nuclei?

A

Sensory, from the spinal cord (fine proprioception and trigeminal nerve)

36
Q

What are the outputs from the raphe nuclei?

A

For arousal, both dorsal and ventral paths are used; there are other outputs related to other functions of the raphe

37
Q

What are the functions of the raphe nuclei?

A

Quiet awareness and other (non-RAS activities) such as mood and affect and modulation of pain

38
Q

What is the ventral tegmental area?

A

Provides a dopaminergic input that is important to many fucntions, including cognitive functions, motor activity, and emotion

39
Q

What are thalamo-cortical neurons?

A

Axons from the thalamus to the cortex

40
Q

What do thalamo-cortical neurons release as their neurotransmitter?

A

EAA (excitatory amino acids)

41
Q

Where do thalamo-cortical neurons synapse? What do those neurons release?

A

Synapse on intracortical neurons that release GABA on other cortical neurons

42
Q

What leads to the waves that are recorder on an EEG?

A

Alternating waves of excitation, due to EAA being released through the dorsal pathway and thalamo-cortical neurons, and inhibition, due to GABA being released in the cortex by intracortical neurons

43
Q

In a persistent vegetative state, the rostral regions of the pons, midbrain, and thalamus show ______ ______ that _______ that of the cortex.

A

Neuronal loss; exceeds

44
Q

What happens in Alzheimer’s disease?

A

Cholinergic systems are particularly hard hit; mental processes slow dramatically and memory formation is profoundly impaired in the absence of the excitation

45
Q

What does the heirarchy of consciousness suggest about the physiological basis of consciousness?

A

1) Different levels of consciousness/awareness are the result of different levels of cortical excitation
2) Moving from arousal/wakefulness to awareness takes additional excitation
3) Moving to full awareness takes another layer of excitation to acheive

46
Q

Review last 5 slides

A

!!!!!!!

Neuro Exam 2 - JLJ (16 decks)

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