Basic Science and Pathophysiology

Fig 1: The reticular system

Consciousness is a continuous physiological variable, [1] dependent on the reticular activating system (RAS) and cerebral cortex (Fig 1).

The RAS lies within the brainstem and midbrain and controls respiration and cardiovascular functions and via the thalamic nuclei causes activation of the cerebral cortex. [3] The cerebral cortex is necessary for conscious awareness and where actions are conceived and initiated. [4]

A decreased consciousness is caused by depression of both cerebral cortices or localised abnormalities of the ascending reticular activating system.

Failure of both cerebral cortices results from:
• Inadequate blood supply
• Inadequate substrate: oxygen or glucose, required for normal metabolism
• Trauma
• Toxins: infection, metabolites, poisons