6. Brain Arousal Systems (Karius)

Question 1

What is the general function of the serotonergic pathway in awareness?

Answer 1

“Quiet awareness”

Question 2

What system of awareness is particularly affected in Alzheimers?

Answer 2

The cholenergic system.

Question 3

Where is the start of the cholinergic pathway?

Answer 3

Pedunculopontine tegmental nuclei

laterodorsal nuclei

Question 4

What is the location for the start of the noradrenergic pathway?

Answer 4

Locus ceruleus.

Question 5

What specific part of the thalamus were we asked to remember as a part of the dorsal pathway?

Answer 5

The intralaminar nucleus of the thalamus.

Question 6

What is the general function of the noradrenergic pathway in awareness?

Answer 6

The “startle and alert” functions we can see on an EEG.

Question 7

From where does the raphe nuclei receive stimulus as a part of its awareness pathway?

Answer 7

Spinal cord

Trigeminal nerve

Periaqueductal grey

(Serotonergic pathway)

Question 8

What are the general functions of each of the awareness pathways in order from least aware to most?

Answer 8

EAA / Cholinergic = Awake

Noradrenergic = Startle and alert

Serotonergic = Quiet awareness

Dopaminergic = Alert and focused awareness (not as well defined)

Question 9

Which pathway for activation of the cerebral cortex bypasses the thalamus?

Answer 9

The ventral pathway.

Question 10

What three places provide input to the locus ceruleus and the noradrenergic pathway of awareness?

Answer 10

Paragigantocellularis nuclei

Periaqueductal grey

Cortex itself

Question 11

What pathway of awareness uses only the ventral pathway to activate the cortex?

Answer 11

The excitatory amino acid pathway traveling through the parabrachial nuclei.

Question 12

In a persistent vegitative state, what is the membrane potential of the neurons?

Answer 12

cortical neurons are up to 30mV below threshold than under normal conditions

AKA hyperpolarized, cannot be stimulated at all.

Question 13

Excitatory Amino Acids: Reticular Activating Systems

Answer 13

• mid-ventral portion of medulla and midbrain
• made of neurons and tracts
• ALL ascending TRACTS send information here as does trigeminal/auditory/visual
• Modal specificity is lost
• Dorsal and Ventral pathways

Question 14

Dorsal Pathway

Ventral Pathway

Answer 14

arousal systems send axons to thalamus–>synapse

–>axons from thalamus to cortex are known as thalamocortical neurons

arousal systems send axons straight to cortex –>synapse directly onto cortical neurons

Question 15

Excitatory Amino Acids: Parabrachial Nuclei

Answer 15

• located in pons in parabrachial nuclei
• crucial for arousal/activation
• All Sensory
• Output via ventral pathway
• GLUTAMATE
• crucial for cortical activation

Question 16

Cholinergic: Pedunculopontine Tegmental and Laterodorsal Nuclei

Answer 16

• No modal specificity
• outputs via dorsal and ventral pathways used by RAS
• Main: Ach
• Crucial for cortical activity
• associated with arousal/awakeness

Question 17

Noradrenergic: Locus Ceruleus

Answer 17

• Inputs sensory info via paragigantocellularis and Periaquaductal grey
• undergoes more neural processing than EAA/Ach systems
• Outputs via dorsal and ventral pathways and some unrelated to spinal cord
• Startle/Alert, sleep/wake, behavorial vigilance

Question 18

Serotonin: Raphe Nuclei

Answer 18

• inputs: sensory from spinal cord, fine proprioception, trigem. n.
• outputs: dorsal and ventral paths
• Quiet awareness, mood/affect, modulation of pain

Question 19

Dopaminergic: Ventral Tegmental Area

Answer 19

• cognitive/motor/emotion

Question 20

Thalamic Arousal Systems

Answer 20

• these neurons with EAA input synapse on intracrotical neurons that release GABA on other cortical neurons
• alternating waves of excitement and inhibition (gaba) lead to the waves seen on EEG
• during sleep, thalamocortical neurons are hyperpolarized and shot short bursts of AP.
• Hyperpolarization allows cortex to be cut off from excitation during sleep

Question 21

Four steps of creating consciousness

Answer 21

1. RAS/parabrachial EAA system is crucial for increasing general excitability of cortical neurons
   * in vegetative state-pons, MB, and thalamus show nueronal loss greater than cortex
2. Cholinergic system adds general excitation
   * In Alz. this system is hit, mental processes slow, memory impaired w/o excitation
3. Noradrenergic and seritonergics move from awake to aware
   * “alerting” response on EEG is early indicator that cortex is looking for sensory input “booting up”
4. dopaminergic adds to awareness with novel stimuli
   * Levodopa tx in vegetative pt may help