I just came across this succinct and informative site in Scholarpedia curated by Christof Koch and Florian Mormann at Cal. Tech. It has some useful instructional graphics.
Midline structures in the brainstem and thalamus necessary to regulate the level of brain arousal. Small, bilateral lesions in many of these nuclei cause a global loss of consciousness. (From Koch, 2004, The Quest for Consciousness: A Neurobiological Approach. Roberts, Denver, CO.)