Brain Arousal Systems

Question 1

Coma

Answer 1

Neither awake or aware

Question 2

Persistent vegetative state

Answer 2

Physiologically identifiable sleep/wake cycles.

Not aware.

Question 3

Minimally conscious state

Answer 3

Sleep/wake cycles
Aware - can respond to commands.
Poor/absent communication.

Question 4

Hierarchy of consciousness (4)

Answer 4

Coma –> arousal/wakefulness –> awareness –> alertness

Question 5

Where is the damage in patients that result in loss of consciousness?

Answer 5

Mainly smaller lesions in brainstem, midbrain or hypothalamus.
Less likely, but possible, massive and BL cortical damage.

Question 6

What NTs are needed to go from coma to arousal/wakefulness?

Answer 6

EAA/ACh

Question 7

What systems use EAA to induce arousal/wakefulness?

Where are they?

Answer 7

Reticular activating system (RAS)
Parabrachial nuclei

Mid-ventral portion of medulla and midbrain.

Question 8

What is the function of the RAS?

Answer 8

It alerts the brain that something happened, but not what happened.

Question 9

Dorsal pathway of output from the RAS?

Answer 9

Via the non-specific nuclei of the thalamus, including the intralaminar nucelus of the thalamus. Then they go to higher levels.

Question 10

Ventral pathway of output from RAS?

Answer 10

Via basal forebrain and hypothalamus, then to higher levels.

*Avoids the thalamus.

Question 11

Where are the parabrachial nuclei?

What pathway does it use?

Answer 11

In the pons and are crucial to arousal/activation.

Ventral pathway.

Question 12

What do the PPT and LDT so?
What pathway?
Which NT?

Answer 12

Function similar to RAS. Baseline excitement to cortex.
Use both dorsal and ventral pathways.
ACh is the NT.

Question 13

Main role of EAA and ACh?

Answer 13

Baseline excitement to cortex! Initial arousal.

Question 14

What happens with damage to the PPN/DLT?

Answer 14

No coma, but severe cognitive deficits ensue.

Question 15

What NTs mediate the transition from arousal/wakefulness to awareness?

Answer 15

NE/serotonin

Question 16

What is the locus coereuleus (LC)?

Answer 16

It receives more pointed info from the medulla, PAG and cortex that induces awareness. More neural processing than EAA/ACh systems.

Question 17

Where do outputs from the LC travel?

Answer 17

Ascend or descend.

Ascending tracts travel in dorsal and ventral pathways with RAS.

Question 18

What is the dorsal noradrenergic bundle?

Answer 18

The ascending fibers from the LC.

Question 19

What are the main functions of the locus coeruleus and noradrenergic systems? (3)

Answer 19

Startle and alerting.
Sleep-wake cycle.
Behavioral vigilance.

Question 20

What is the pathway for serotonin in arousal?

What is serotonin’s role?

Answer 20

Inputs from SC, trigeminal, PAG travel in the dorsal and ventral paths (mostly ventral).

Quiet awareness

Question 21

What mediates the transition from aware to alert?

Answer 21

DA and the ventral tegmental area

Question 22

What are the functions of DA?

Answer 22

Cognition
Motor activity
Emotion

Question 23

What happens during sleep between the thalamus and cortex?

Answer 23

They are disconnected.

Thalamocortical neurons are hyperpolarized and no NTs are delivered, but occasioanlly have bursts (spindle-fibers).