Mechanisms Of Arousal

Question 1

What are the two parts of consciousness?

Answer 1

Arousal (being awake)

Awareness (conscious processing of inputs, etc)

Question 2

What is a coma?

Answer 2

Neither being awake or aware

No sleep/wake cycles

Question 3

What is a persistent vegetative state?

Answer 3

Physiologically identifiable sleep/wake cycles appear

No evidence of awareness

Question 4

What is 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?

Answer 5

Coma -> arousal/wakefulness -> awareness -> alertness

Question 6

Disruption of consciousness result from what?

Answer 6

Smaller lesions in the brainstem, midbrain or hypothalamus

Question 7

A comatose state can result from damage to what?

Answer 7

The cerebral cortices

But the damage must be massive and bilateral to disrupt consciousness

Question 8

What is the membrane potential of neurons for those in a persistent vegetative state?

Answer 8

Cortical neurons are up to 30 mV below threshold thats under normal conditions

Question 9

Different levels of consciousness/awareness are the result of what?

Answer 9

Different levels of cortical excitation

Question 10

Both arousal and awareness require activation of the what?

Answer 10

Cortex
But the Cortex has not intrinsic mechanism for activation
There are multiple sub-cortical structures that function to provide the activation required for the cortex to function

Question 11

What findings can be present during a coma?

Answer 11

Eye/head movements

No sleep/wake cycle, awareness or verbal response

Question 12

What findings are present during a persistent vegetative state?

Answer 12

Eye/head movements and sleep/wake cycle

No awareness of verbal response

Question 13

What findings are present during minimal consciousness?

Answer 13

Eye/head movements, sleep/wake cycle

Inconsistent or intermittent awareness or verbal responses

Question 14

What findings are present in someone who is aware/alert?

Answer 14

Eye/head movements, sleep/wake cycle, awareness and verbal responses

Question 15

Which NT systems are involved with the arousal system?

Answer 15

EAA (has to be present in order to move from coma to PVS), cholinergic, noradrenergic, serotonergic and dopaminergic
Last 3 move you more and more conscious

Question 16

What is the reticular activating system?

Answer 16

Occupies mid ventral portion of medulla and midbrain
An area of loose collection of neurons and fiber tracts
Associated with the EAA

Question 17

What inputs does the RAS receive?

Answer 17

All ascending sensory tracts send info to the RAS
Trigeminal, auditory and visual inputs also come into RAS
There is so much input to the neurons that modal specificity is lost

Question 18

What does it mean when the neurons of RAS modal specificity is lost?

Answer 18

All the info converges on the same neurons so the brain only knows something happened not what happened
As a result the neurons of the RAS respond equally well to multiple sensory modalities

Question 19

What are the two pathways of output from the RAS?

Answer 19

Dorsal pathway and ventral pathway

Question 20

Describe the dorsal pathway from the RAS

Answer 20

Arousal systems send axons via the non specific nuclei of the thalamus including the intralaminar nucleus of the thalamus
From the thalamus axons diffuse pathway to all higher levels

Question 21

Describe the ventral pathway from RAS

Answer 21

Bypasses thalamus via basal forebrain and hypothalamus and sends axons straight to cortex
Synapse direct onto cortical neurons
From there diffuse pathway to all higher levels

Question 22

What is the parabrachial nuclei (middle, intermediate and lateral)?

Answer 22

Associated with EAA
Located in the pons
Crucial for arousal/activation
Sensory inputs are similar to those seen in RAS (all/most of the sensory inputs to the body)
Outputs are exclusively via the ventral pathway (with extensive very diffuse innervation of the entire cortex)

Question 23

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

Answer 23

EAA/glutamate regardless of the pathway to the brain

Question 24

What other types of neurons are located in RAS?

Answer 24

Substantial number of interneurons (neurons intrinsic to RAS) that release GABA
Also has neuronal population that release ACh

Question 25

Regardless of the dorsal or ventral pathway, the EAA system appears to provide what?

Answer 25

A baseline excitation that is crucial to cortical activity

Question 26

What are the pedunculopontine tegmental and laterodorsal nuclei (PPT/LDT)?

Answer 26

Associated with the cholinergic NT system Receive so much input that all modality specific info is lost Output are via the dorsal and ventral pathways by the RAS but the major NT is ACh

Question 27

Regardless of path (dorsal or ventral) the cholinergic system also provides what?

Answer 27

A baseline excitation that is crucial to cortical activity | Does require the EAA (cant act on its own)

Question 28

Activity in the cholinergic inputs from the pons is also associated with what?

Answer 28

Arousal and awareness Damage to the PPN/DLT doesn’t necessarily cause coma, but does produce severe cognitive deficits that are associated with a generalized slowing of cortical processes

Question 29

Moving from arousal/wakefulness to awareness takes what?

Answer 29

An additional excitation | Need EAA and ACh

Question 30

What is the locus ceruleus?

Answer 30

Associated with the noradrenergic system

Question 31

What are the inputs to the locus ceruleus?

Answer 31

Paragigantocellularis n (in rostral medulla) PAG - periaqueductal grey Higher centers including the cortex All sensory info This information has undergone more neural processing than the sensory inputs received by the EAA/ACh systems

Question 32

What are the outputs from the locus ceruleus?

Answer 32

Those related to consciousness ascend to the cortex using both the dorsal and ventral pathways There are unrelated outputs to the SC

Question 33

What are the functions of the locus ceruleus/NE system?

Answer 33

Startle and alerting response identifiable on an EEG* (much more specific, something happened and you want to pay attention to it) Sleep-wake Behavioral vigilance

Question 34

What is the raphe nucleus?

Answer 34

Associated with serotonergic system (release serotonin) | Receives sensory inputs from the SC (fine propioception) and trigeminal N

Question 35

What are the outputs from the raphe nuclei?

Answer 35

For arousal, both the dorsal and ventral pathways are used | There are other outputs that relate to other functions of the raphe

Question 36

What are the functions of the serotonin?

Answer 36

``` Quiet awareness (aware of surroundings) Other (non-RAS activities) including mood and affect, modulation of pain ```

Question 37

What is required for the movement of arousal/wakefulness to awareness?

Answer 37

NE and 5HT

Question 38

What is the ventral tegmental area?

Answer 38

Associated with the dopaminergic system Provides a dopaminergic input that is important to many functions including cognitive functions, motor activity and emotion

Question 39

Dopamine is needed to move from awareness to what?

Answer 39

Alertness | Fully functional

Question 40

What are thalamocortical neurons?

Answer 40

Axons from the thalamus to the cortex

Question 41

Describe the thalamic arousal system

Answer 41

Thalamocortical neurons elease EAA as their NT Also synapse on intracortical neurons that release GABA on other cortical neurons The alternating waves of excitation (due to EAA released) and inhibition (due to GABA released) are believed to lead to the waves recorded on an EEG

Question 42

Describe the function of the arousal systems in creating consciousness

Answer 42

1. RAS/parabrachial EAA system is crucial for increasing general excitability of cortical neurons 2. Cholinergic system adds to that general excitation 3. The NE and serotonergic systems move us from being awake to being more generally aware of incoming info 4. The dopaminergic system seems to add focused awareness associated with novel stimuli

Question 43

What is the state of the thalamocortical neurons during sleep?

Answer 43

During sleep they are hyperpolarized and show occasional short bursts of AP This hyperpolarization essentially cuts the cortex off fro the excitatory influence during the deepest levels of sleep

Question 44

In a persistent vegetative state the rostral regions of the pons, edulla and thalamus show what?

Answer 44

Neuronal loss that exceeds that of the cortex

Question 45

What happens in Alzheimer’s disease?

Answer 45

The cholinergic systems are particularly hard hit | Mental processes slow dramatically and memory formation is profoundly impaired in the absence of excitation

Question 46

The alerting response in the EEG is an early indicator that the cortex is what?

Answer 46

Looking for sensory input

Question 47

In a limited number of people in a persistent vegetative state treatment with levodopa has produced what?

Answer 47

Increases in cognitive function