Here you go, James (Human Anatomy and Physiology, Marieb, 1998): The reticular formation extends through the central core of the medulla oblongata, pons, and midbrain. It is an intricate system composed of loosely clustered neurons in what is otherwise white matter.....The outstanding feature of the reticular neurons is their far-flung axonal connections. Individual reticular neurons project to the hypothalamus, thalamus, cerebellum and spinal cord. Such widespread connections make reticular neurons ideal for governing the arousal of the brain as a whole. For example, certain reticular neurons, unless inhibited by other brain areas, send a continuous stream of impulses (via thalamic relays) to the cerebral cortex, which maintains the cortex in an alert, conscious state and enhances its excitability. This particular arm of the reticular formation is know as the reticular activating system (RAS). Impulses from all the great ascending sensory tracts synapse with RAS neurons, keeping them active and enhancing their arousing effect on the cerebrum. Repetitive, familiar, or weak signals are damped (filtered out), but unusual, significant, or strong impulses do reach our consciousness. For example, you are probably unaware of the slipping of your watch on your wrist, but if the clasp broke, it would immediately gain your attention. Between them, the RAS and the cerebral cortex disregard perhaps 99% of all sensory stimuli as unimportant. If this did not occur, the sensory overload would drive us crazy. The drug LSD removes these sensory dampers, promoting a similar type of sensory overload.....The activity of the RAS is inhibited by sleep centers located in the hypothalamus and other neural regions, and is depressed by alcohol, sleep-inducing drugs, and tranquilizers. Severe injury to this system, as might follow a knockout punch that twists the brain stem, results in permanent unconsciousness (irreversible coma).
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