Brain arousal systems

Question 1

Consciousness has 2 parts. What are they?

Answer 1

arousal and awareness

Question 2

are there any sleep/wake cycles in the comatose state?

Answer 2

no

Question 3

what is characteristic of the persistent vegetative state?

Answer 3

sleep/wake cycles but no evidence of awareness

Question 4

what is characteristic of the minimally conscious/ awareness state?

Answer 4

there are sleep/wake cycles, the patient has reproducible evidence of awareness (ability to respond to simple commands) but limited or absent communication

Question 5

Most often, disruptions of consciousness result from what?

Answer 5

small lesions in the brainstem, midbrain, or hypothalamus

Question 6

patients in a persistent vegetative state have cortical neurons that are what?

Answer 6

30 mv below threshold than under normal conditions (they are incredibly hyperpolarized)

Question 7

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

Answer 7

different levels of cortical excitation

Question 8

What is critical for arousing the cortex?

Answer 8

brainstem regions

Question 9

What does the cortex require for activation since it does not have an intrinsic mechanism for activation?

Answer 9

it requires input from the midbrain/hindbrain regions

Question 10

What system must be present for a patient to move from a comatose state to at least a persistent vegetative state?

Answer 10

the EAA system

Question 11

What contributes to the EAA system (reticular activating system (RAS)) but if the EAA system it cannot move the patient from the comatose state to the PVS on its own?

Answer 11

the cholinergic system

Question 12

Where is the RAS located?

Answer 12

mid ventral portion of the medulla and midbrain

Question 13

where is the cholinergic system located?

Answer 13

in the pons

Question 14

Where is the noradrenergic system located?

Answer 14

the locus ceruleus

Question 15

where is the serotonergic system located?

Answer 15

raphe nuclei

Question 16

where is the dopaminergic system located?

Answer 16

the ventral tegmental area

Question 17

What inputs does the RAS receive?

Answer 17

all the ascending sensory tracts and also the cranial nerves: trigeminal, auditory, and visual

Question 18

What is the result of the sufficient synaptic convergence of input to the neurons of the RAS?

Answer 18

modal specificity is lost “ I just know something happened not what happened”

Question 19

There are two pathways from the EAAs system to the cortex. What are they?

Answer 19

dorsal pathway and ventral pathway

Question 20

What happens in the dorsal pathway?

Answer 20

a neuron in the RAS sends an axon to the thalamus and then from there it heads to the cortex

Question 21

what happens in the ventral pathway?

Answer 21

an axon goes straight from the RAS to the cortex

Question 22

there is a second group of EAA neurons arising. From where?

Answer 22

from the pons in the parabrachial nuclei

Question 23

What are the output pathways from the parabrachial nuclei?

Answer 23

it is exclusively ventral–> so it bypasses the thalamus and goes straight to the cortex

Question 24

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

Answer 24

EAA/Glutatmate

Question 25

within the RAS there is a substantial number of interneurons (neurons intrinsic to the RAS) that release what?

Answer 25

GABA

Question 26

There are 2 nuclei in the pons that are associated with the cholinergic excitation of the cortex. What are they?

Answer 26

the pedunculopontine tegmental and laterodorsal nuclei (PPT/ LDT)

Question 27

What are the output options for the cholinergic system?

Answer 27

dorsal (goes to the thalamus) or ventral (bypasses the thalamus)

Question 28

What is the major neurotransmitter used by the cholinergic system?

Answer 28

acetylcholine (ACh)

Question 29

What is the main purpose of the cholinergic system?

Answer 29

provides a baseline excitation that is crucial to cortical activity

Question 30

What would damage to the PPT or LDT nuclei result in?

Answer 30

it doesn't necessarily cause coma, but it does produce severe cognitive deficits that are associated with a generalized slowing of cortical processes

Question 31

Where is the locus ceruleus located?

Answer 31

in the pons

Question 32

Once i have moved from the comatose state to the aroused/wakeful state, what is the first NT needed to get closer to being fully aware?

Answer 32

noradrenaline

Question 33

What is different about the input into the locus ceruleus compared to the RAS?

Answer 33

the input to the LC has undergone more neuronal processing

Question 34

What are the pathways used for the outputs from the LC related to consciousness?

Answer 34

they ascend to the cortex using both the dorsal and ventral pathways

Question 35

the locus ceruleus system has a very specific function. What is it?

Answer 35

it is responsible for producing the startle and alerting responses on the EEG (waking you up)

Question 36

Where are the serotenergic nuclei located?

Answer 36

raphe nuclei (in the pons)

Question 37

What is the input into the raphe nuclei?

Answer 37

sensory input from the spinal cord (fine proprioception) and the trigeminal nerve input

Question 38

What are the output pathways of the raphe nuclei in regards to arousal?

Answer 38

both the dorsal and ventral pathways are used

Question 39

What is the function of serotonin in the arousal pathway?

Answer 39

quiet awareness "i'm aware of everything around me"/ general awareness

Question 40

How do we get to the final step of being really alert?

Answer 40

we have to add yet another level of excitation in--> dopaminergic systems

Question 41

the ventral tegmental area provides a dopaminergic input that is important to many functions including what?

Answer 41

cognitive functions, motor activity, and emotion

Question 42

Axons from the thalamus to the cortex are known as what?

Answer 42

thalamocortical neurons

Question 43

in the dorsal pathway, it does not matter what NT is released in the thalamus, the neuron that leaves the thalamus and synapses in the cortex will release what?

Answer 43

EAAs

Question 44

in the ventral pathway, what is the NT that is released once it synapses directly onto the cortical neurons?

Answer 44

the one that is specific to that system

Question 45

The thalamocortical neurons synapse on the cortical neurons and what else?

Answer 45

the intracortical neurons

Question 46

what do the intracortical neurons release on other cortical neurons?

Answer 46

GABA

Question 47

What is believed to lead to the waves recorded on the EEG?

Answer 47

the alternating waves of excitation (due to EAA being released) and inhibition (due to the GABA being released)

Question 48

In Alzheimer's disease, which systems are particularly hit hard?

Answer 48

the cholinergic systems

Question 49

the noradrenergic and serotenergic systems move us from what to what?

Answer 49

from being awake to being more generally aware of incoming information

Question 50

the alerting response on the EEG is an early indicator of what?

Answer 50

that the cortex is looking for sensory input