Dec 21, 2016 11:35 AM
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Coma is a state of unconsciousness in which a person cannot be awakened; fails to respond normally to painful stimuli, light, or sound; lacks a normal wake-sleep cycle; and does not initiate voluntary actions.[1] A person in a state of coma is described as being comatose. A distinction is made in the medical community between a coma and a medically induced coma, the former is a result of circumstances beyond the control of the medical community, while the latter is a means by which medical professionals may allow a patient's injuries to heal in a controlled environment.
A comatose person exhibits a complete absence of wakefulness and is unable to consciously feel, speak, hear, or move.[2] For a patient to maintain consciousness, two important neurological components must function. The first is the cerebral cortex—the gray matter that forms the outer layer of the brain. The other is a structure located in the brainstem, called reticular activating system(RAS).[3][4] Injury to either or both of these components is sufficient to cause a patient to experience a coma. The cerebral cortex is a group of tight, dense, "gray matter" composed of the nuclei of the neurons whose axons then form the "white matter, " and is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.
