Important safety tip: "Brain death," "coma" and "vegetative state" each have a distinct medical meaning. Keep this in mind next time you're in the hospital. Trace Dominguez approaches the very portal of death in this edition of DNews.
We'll start with the condition known as vegetative state, in which the brain stem is functioning but the body is on auto-pilot. In this state, people can breathe on their own, have a sleep-wake cycle, and can respond to stimuli. But they're unaware of their environment and can't hold a conversation. Neurologists define consciousness by awareness and wakefulness, and people in a vegetative state are awake but not aware.
Those in the coma, however, are neither awake nor aware. It's a state of deep unconsciousness in which the reticular activating system is damaged -- the part of the brain stem responsible for wakefulness isn't working. But the brain is still sending out some signals. It's possible to recover from a coma, move through the vegetative state, and regain awareness.
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With brain death, however, all neural activity ceases and the brain no longer has any input on the body's functions. Brain death is irreversible, and is essentially synonymous with death itself. The body can be kept alive, kinda-sorta, with advanced life support technology. But without assistance, nothing works.
Total cessation of neural activity means that the lungs stop operating entirely. All of the brain's other regulatory functions -- over things with blood pressure and body temperature -- also go offline. Those hormones that manage organ functions stop circulating, too.
Keeping the body alive after brain death requires extraordinary measures, and because the condition is irreversible, doctors go through a series of tests known as the brain death examination before officially making a determination. If the patient fails these tests, he or she is declared legally dead.
-- Glenn McDonald
How Stuff Works: How Brain Death Works
Live Science: Life After Brain Death: Is The Body Still 'Alive'?
The Dana Foundation: Disorders of Consciousness: Brain Death, Coma, And The Vegetative And Minimally Conscious States