Definition of Involuntary

Involuntary: Done other than in accordance with the conscious will of the individual. The opposite of voluntary.

The terms "voluntary" and "involuntary" apply to the human nervous system and its control over muscles. The nervous system is divided into two parts -- somatic and autonomic. The somatic nervous system operates muscles that are under voluntary control. The autonomic (automatic or visceral) nervous system regulates individual organ function and is involuntary. Opening the mouth is voluntary while blushing is involuntary.