Coma

A coma is a deep state of prolonged 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. The person may experience respiratory and circulatory problems due to the body's inability to maintain normal bodily functions. People in a coma often require extensive medical care to maintain their health and prevent complications such as pneumonia or blood clots. Coma patients exhibit a complete absence of wakefulness and are unable to consciously feel, speak or move. Comas can be the result of natural causes, or can be medically induced.

Clinically, a coma can be defined as the consistent inability to follow a one-step command. For a patient to maintain consciousness, the components of ''wakefulness'' and ''awareness'' must be maintained. Wakefulness is a quantitative assessment of the degree of consciousness, whereas awareness is a qualitative assessment of the functions mediated by the cortex, including cognitive abilities such as attention, sensory perception, explicit memory, language, the execution of tasks, temporal and spatial orientation and reality judgment. Neurologically, consciousness is maintained by the activation of the cerebral cortex—the gray matter that forms the brain's outermost layer—and by the reticular activating system (RAS), a structure in the brainstem. Provided by Wikipedia