Coma is a prolonged period of unconsciousness. Unconsciousness is the lack of appreciation of (or reaction to) a stimulus. Coma differs from sleep in that one cannot be aroused from a coma.
Coma involves two different concepts:
1.) Reactivity: Reactivity refers to the innate (or inborn) functions of the brain, i.e., the telereceptors (eyes and ears), the nociceptors (responses to pain), the arousal reaction (wakefulness) and the orienting response (turning one's head toward the source of sound or movement). We could also refer to these as reflexive movements.
2.) Perceptivity: Perceptivity refers to the responses of the nervous system to stimuli, which have been learned or acquired, i.e., language, communication skills, individual methods of movement such as gestures, etc. Perceptivity also refers to less complex learned or acquired reactions such as flinching when threatened. We can also think of these as conscious movements.
