Consciousness can be thought of in two main ways:
obtundation is impaired alertness; stupor is a state of arousability with stimulation, and coma is a total loss of consciousness.
The upper pons and midbrain contain the ascending reticular activating system, containing noradrenergic, serotonergic, cholinergic, and histaminergic pathways that ascend to the thalamus and thereby to the cortex.
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