Brain Arousal Systems

Question 1

What are the 2 parts of consciousness?

Answer 1

1) Arousal (being awake)

2) Awareness (conscious processing of inputs)

Question 2

Define a coma in terms of consciousness

Answer 2

Neither awake or aware

Question 3

Define a persistent vegetative state in terms of consciousness

Answer 3

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

Question 4

Define a minimally conscious state

Answer 4

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

Question 5

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

Answer 5

Coma, arousal/wakefulness, awareness, alertness

Question 6

What usually causes a coma or a disruption of consciousness?

Answer 6

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

Question 7

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

Answer 7

30 mV

Question 8

Both arousal and awareness require what?

Answer 8

Activation of the cortex

Question 9

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

Answer 9

Eye/Head Motions: inconsistent or intermittent

Sleep/Wake Cycles: –

Awareness: –

Verbal Responses: –

Question 10

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

Answer 10

Eye/Head Motions: yes

Sleep/Wake Cycles: yes

Awareness: –

Verbal Responses: –

Question 11

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

Answer 11

Eye/Head Motions: yes

Sleep/Wake Cycle: yes

Awareness: inconsistent or intermittent

Verbal Responses: inconsistent or intermittent

Question 12

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

Answer 12

Eye/Head Motions: yes

Sleep/Wake Cycle: yes

Awareness: yes

Verbal Responses: yes

Question 13

What are the different arousal systems?

Answer 13

EAA, cholinergic, noradrenergic, serotonergic, and dopaminergic

Question 14

What makes up the EAA arousal system?

Answer 14

Reticular activating system (RAS) and parabrachial nuclei

Question 15

What makes up the cholinergic arousal system?

Answer 15

Pedunculopontine tegmental and laterodorsal nuclei (PPT/LDT)

Question 16

What makes up the noradrenergic arousal system?

Answer 16

Locus ceruleus

Question 17

What makes up the serotonergic arousal system?

Answer 17

Raphe nuclei

Question 18

What makes up the dopaminergic arousal system?

Answer 18

Ventral tegmental area

Question 19

Where is the RAS found?

Answer 19

Occupies the mid-ventral portion of medulla and midbrain

Question 20

What sends inputs to the RAS?

Answer 20

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

Question 21

What are the 2 outputs from the RAS?

Answer 21

Dorsal pathway and ventral pathway

Question 22

What is the dorsal pathway leaving the RAS?

Answer 22

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

Question 23

What is the ventral pathway leaving the RAS?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

What is the output from the parabrachial nuclei?

Answer 25

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

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

RAS and cholinergic arousal systems

Question 30

What are the inputs to the locus coereuleus?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

What are the outputs from the locus coereuleus?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

What is the source of serotonin?

Answer 34

Raphe nuclei

Question 35

What are the inputs to the raphe nuclei?

Answer 35

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

Question 36

What are the outputs from the raphe nuclei?

Answer 36

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

Question 37

What are the functions of the raphe nuclei?

Answer 37

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

Question 38

What is the ventral tegmental area?

Answer 38

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

Question 39

What are thalamo-cortical neurons?

Answer 39

Axons from the thalamus to the cortex

Question 40

What do thalamo-cortical neurons release as their neurotransmitter?

Answer 40

EAA (excitatory amino acids)

Question 41

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

Answer 41

Synapse on intracortical neurons that release GABA on other cortical neurons

Question 42

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

Answer 42

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

Question 43

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

Answer 43

Neuronal loss; exceeds

Question 44

What happens in Alzheimer's disease?

Answer 44

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

Question 45

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

Answer 45

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

Question 46

Review last 5 slides

Answer 46

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