/koh"meuh/, n., pl. comas.a state of prolonged unconsciousness, including a lack of response to stimuli, from which it is impossible to rouse a person.[1640-50; < Gk kôma deep sleep]coma2/koh"meuh/, n., pl. comae /-mee/.1. Astron. the nebulous envelope around the nucleus of a comet.2. Optics. a monochromatic aberration of a lens or other optical system in which the image from a point source cannot be brought into focus, the image of a point having the shape of a comet.3. Bot.a. a tuft of silky hairs at the end of a seed.b. the leafy crown of a tree; cluster of leaves at the end of a stem.c. a terminal cluster of bracts, as in the pineapple.[1660-70; < L: hair < Gk kóme]
* * *Complete lack of consciousness, with loss of reaction to stimulus and of spontaneous nervous activity.It is usually associated with cerebral injury of metabolic or physical origin. Simple concussions cause short losses of consciousness. Coma from lack of oxygen may last several weeks and is often fatal. Coma caused by stroke can be sudden, while that caused by metabolic abnormalities (as in diabetes mellitus) or cerebral tumours comes on gradually. Treatment depends on the cause.
* * *state of unconsciousness, characterized by loss of reaction to external stimuli and absence of spontaneous nervous activity, usually associated with injury to the cerebrum. Coma may accompany a number of metabolic disorders or physical injuries to the brain from disease or trauma.Different patterns of coma depend on the origin of the injury. Concussions (concussion) may cause losses of consciousness of short duration; in contrast, lack of oxygen (anoxia) may result in a coma that lasts for several weeks and is often fatal. stroke, a rupture or blockage of vessels supplying blood to the brain, can cause sudden loss of consciousness in some patients, while comas caused by metabolic abnormalities or cerebral tumours (tumour) are characterized by a more gradual onset, with stages of lethargy and stupor before true coma. Metabolic comas are also more likely to have associated brain seizures and usually leave pupillary light reflexes intact, whereas comas with physical causes usually eradicate this reflex.Common causes of metabolic coma include diabetes (diabetes mellitus), excessive consumption of alcohol (alcohol consumption), and barbiturate poisoning. In diabetes, low insulin levels allow the buildup of ketones (ketone), breakdown products of fat tissue that destroy the osmotic balance in the brain, damaging brain cells. Ingestion of large quantities of alcohol over a short period can cause a coma that may be treated by gastric lavage (stomach pump) in its early stages; alcohol combined with barbiturates is a common cause of coma in suicide attempts. Large doses of barbiturates alone will also produce coma by suppressing cerebral blood flow, thus causing anoxia. Gastric lavage soon after the drug is ingested may remove a sufficient amount of the barbiturate to allow recovery. For most metabolic comas, the first step in treatment is to protect the brain cells and attempt to eliminate the cause of coma. Assisted ventilation is often necessary. In some psychiatric conditions, such as catatonic schizophrenia, a comalike state may also occur.
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