Brain Arousal Systems Flashcards
Coma
Neither awake or aware
Persistent vegetative state
Physiologically identifiable sleep/wake cycles.
Not aware.
Minimally conscious state
Sleep/wake cycles
Aware - can respond to commands.
Poor/absent communication.
Hierarchy of consciousness (4)
Coma –> arousal/wakefulness –> awareness –> alertness
Where is the damage in patients that result in loss of consciousness?
Mainly smaller lesions in brainstem, midbrain or hypothalamus.
Less likely, but possible, massive and BL cortical damage.
What NTs are needed to go from coma to arousal/wakefulness?
EAA/ACh
What systems use EAA to induce arousal/wakefulness?
Where are they?
Reticular activating system (RAS)
Parabrachial nuclei
Mid-ventral portion of medulla and midbrain.
What is the function of the RAS?
It alerts the brain that something happened, but not what happened.
Dorsal pathway of output from the RAS?
Via the non-specific nuclei of the thalamus, including the intralaminar nucelus of the thalamus. Then they go to higher levels.
Ventral pathway of output from RAS?
Via basal forebrain and hypothalamus, then to higher levels.
*Avoids the thalamus.
Where are the parabrachial nuclei?
What pathway does it use?
In the pons and are crucial to arousal/activation.
Ventral pathway.
What do the PPT and LDT so?
What pathway?
Which NT?
Function similar to RAS. Baseline excitement to cortex.
Use both dorsal and ventral pathways.
ACh is the NT.
Main role of EAA and ACh?
Baseline excitement to cortex! Initial arousal.
What happens with damage to the PPN/DLT?
No coma, but severe cognitive deficits ensue.
What NTs mediate the transition from arousal/wakefulness to awareness?
NE/serotonin
What is the locus coereuleus (LC)?
It receives more pointed info from the medulla, PAG and cortex that induces awareness. More neural processing than EAA/ACh systems.
Where do outputs from the LC travel?
Ascend or descend.
Ascending tracts travel in dorsal and ventral pathways with RAS.
What is the dorsal noradrenergic bundle?
The ascending fibers from the LC.
What are the main functions of the locus coeruleus and noradrenergic systems? (3)
Startle and alerting.
Sleep-wake cycle.
Behavioral vigilance.
What is the pathway for serotonin in arousal?
What is serotonin’s role?
Inputs from SC, trigeminal, PAG travel in the dorsal and ventral paths (mostly ventral).
Quiet awareness
What mediates the transition from aware to alert?
DA and the ventral tegmental area
What are the functions of DA?
Cognition
Motor activity
Emotion
What happens during sleep between the thalamus and cortex?
They are disconnected.
Thalamocortical neurons are hyperpolarized and no NTs are delivered, but occasioanlly have bursts (spindle-fibers).
