Coma

A state of unarousable unconsciousness in which a person cannot be awakened and shows no purposeful response to stimulation. It results from severe disruption of brain function.

Arousal: The brain processes that maintain wakefulness and responsiveness to the environment. Coma occurs when systems supporting wakefulness fail or are disrupted.
Coma scale: A structured clinical instrument for describing a person's level of consciousness. The Glasgow Coma Scale is one widely used way to document coma severity.
Brain death: The irreversible cessation of all functions of the entire brain, including the brainstem, under applicable medical criteria. Unlike coma, brain death is irreversible and is legally recognized as death in many jurisdictions.
Post-coma unresponsiveness: A period of severe impaired consciousness that may follow emergence from coma. Recovery can pass through unresponsive wakefulness before signs of awareness return.
Ascending reticular activating system: Brainstem and forebrain pathways that sustain wakefulness and alertness. Damage to these pathways can prevent arousal even when some cortical tissue remains intact.
Airway management: Measures used to keep the airway open and support breathing. An unconscious person may lose protective reflexes and be unable to maintain a safe airway.
Vegetative state: A disorder of consciousness with wakefulness but no reliable evidence of awareness. Cycles of eye opening distinguish this state from coma, despite absent purposeful responses.
Disorders of consciousness: Conditions in which awareness or wakefulness is impaired after brain dysfunction. Coma is one member of a spectrum that includes several states with different prognoses.
Cerebral cortex: The outer layers of the brain involved in perception, thought, memory, and voluntary action. Widespread cortical dysfunction can abolish purposeful responses and conscious awareness.
Neurological examination: A clinical assessment of nervous-system function using observation and targeted tests. Pupils, reflexes, and motor responses help localize dysfunction and guide urgent care.

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