Coma Health Article

Definition

Coma, from the Greek word koma, meaning deep sleep, is a state of extreme unresponsiveness, in which an individual exhibits no voluntary movement or behavior. Furthermore, in a deep coma, even painful stimuli (actions which, when performed on a healthy individual, result in reactions) are unable to cause any response, and normal reflexes may be lost.

Description

The important characteristics of the conscious state is defined by two fundamental elements: awareness and arousal.

Awareness allows one to receive and process all the information communicated by the five senses. Awareness has both psychological and physiological components. The psychological component refers to an individual's mind and mental processes. The physiological component refers to the functioning of an individual's brain, and the physical and chemical condition of the brain. Awareness is regulated by cortical areas within the cerebral hemispheres, the outermost layer of the brain.

Arousal is regulated solely by physiological functioning and consists of more primitive responsiveness to the world, as demonstrated by predictable reflex (involuntary) responses to stimuli. Arousal is maintained by the reticular activating system (RAS), a network of brain structures, including the brainstem, the medulla, and the thalamus, and nerve pathways that function together to produce and maintain arousal.

Causes and symptoms

Coma is the result of something that interferes with the functioning of the cerebral cortex and/or the functioning of the structures that comprise the RAS. Several conditions can result in coma. Anatomic causes of coma are those conditions that disrupt the brain structures responsible for consciousness, either at the level of the cerebral cortex or the brainstem, while metabolic causes of coma consist of those conditions that change the chemical environment of the brain, thereby adversely affecting function.

There are many metabolic causes of coma, including:

• a decrease in the delivery to the brain of substances necessary for appropriate brain functioning, such as oxygen, glucose (sugar), and sodium• the presence of certain substances such as drugs, alcohol, carbon dioxide, and ketones that disrupt the functioning of neurons
• changes in chemical levels in the brain caused by seizures