Brain Arousal Systems

Question 1

Persistent vegetative state

Answer 1

Physiologically identifiable sleep/wake cycles appear

No evidence of awareness

Question 2

Minimally conscious state

Answer 2

Sleep/wake cycles
Reproducible evidence of awareness- ability to respond to simple commands
Limited or absent communication

Question 3

Most common reason for disruption of consciousness

Answer 3

Lesions in the brainstem, midbrain or hypothalamus

Question 4

Cortex of people in vegetative state

Answer 4

Cortical neurons are usually alive but highly hyperpolarized
Suggests that different levels of consciousness are correlated to levels of cortical excitation
Cortex has no intrinsic mechanism for excitation

Question 5

Excitatory amino acids arise from

Answer 5

Reticular activating system

Parabrachial nuclei

Question 6

Acetylcholine is produced/released by

Answer 6

Pedunculopontine tegmental and laterodorsal nuclei (PPT/LDT)

Question 7

Noradrenergic arousal system

Answer 7

Locus ceruleus

Question 8

Serotonergic arousal system

Answer 8

Raphe nucleus

Question 9

Dopaminergic arousal system

Answer 9

Ventral tegmental area

Question 10

Reticular activating system

Answer 10

Located in ventral portion of medulla/midbrain
All ascending sensory tracts send info to the RAS and so do trigeminal, auditory and visual systems
No modality specificity in RAS post synaptic neurons because there are too many different systems sending info to it (brain knows something has happened, but not what)

Question 11

RAS dorsal pathway

Answer 11

Via non specific nuclei of the thalamus, including the intraluminar nucleus of the thalamus.
From there, diffuse pathway to all higher levels

Question 12

RAS ventral pathway

Answer 12

Bypasses thalamus
Via basal forebrain and hypothalamus
From there, diffuse to higher levels of brain
Uses EAA/glutamate all though some interneurons in system can use GABA/Ach

Question 13

Parabrachial nuclei

Answer 13

Located in the pons
Receives sensory info from pretty much all of body
Only uses ventral pathway (bypassing thalamus and instead synapsing in hypothalamus)
Uses EAA/glutamate although some interneurons in the system can use GABA/Ach
Same function as RAS

Question 14

Pedunculopontine tegmental and laterodorsal nuclei

Answer 14

Receives info from all over body like the others
Outputs via dorsal and ventral pathways like RAS
MAJOR difference is that NT used is Ach
This ventral pathway can be affected in Alzheimer’s

Question 15

PPN/DLT damage

Answer 15

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

Question 16

What do you need to move from coma to arousal/wakeness

Answer 16

Need systems that release EAA and those that release Ach

Question 17

Moving from arousal/wakeness to aware

Answer 17

Need noradrenergic/serotonergic system plus EAA and Ach

Question 18

Noradrenergic-Locus ceruleus

Answer 18

Inputs: paragigantocellularis (in medulla) - sensory info
Periaquaductal gray- pain
Higher centers including the cortex
This information has actually undergone more neural processing than the sensory inputs received by EAA/Ach systems
Outputs: both dorsal and ventral pathways
Function: startle & alerting responses on EEG, sleep/wake cycle, behavioral vigilance

Question 19

Serotonin-Raphe nuclei

Answer 19

Inputs: sensory from spinal cord (fine proprioception from trigeminal nuclei)
Outputs: both dorsal and ventral pathway
Function: produces quiet awareness, plays role in mood and affect

Question 20

Going from aware to alert

Answer 20

Need dopaminergic system as well as all the others

Question 21

Dorsal and ventral pathways

Answer 21

Dorsal arousal systems send axons to the cortex from thalamus using thalamocortical neurons
They synapse on neurons in the cortex including intercortical neurons that release GABA this causes a wave of excitation followed by inhibition

Question 22

The RAS/parabrachial EAA system is crucial for

Answer 22

Increasing general excitability of cortical neurons

This general excitation is also contributed to by Ach systems

Question 23

Persistent vegetative state neuron activity

Answer 23

Rostral regions of pons, midbrain and thalamus show neuronal loss that exceeds that of the cortex

Question 24

Thalamocortical neurons during sleep

Answer 24

Hyperpolarized and show occasional short bursts of action potentials