Involuntary action – action that doesn’t require thought

An involuntary action is simply the opposite if a voluntary action. It is initiated by the stimulation of a receptor, rather than by the will of the person.

Examples:

Blinking, beating of heart, pupil of eye adjusting to different light levels, sneezing, yawning.

An involuntary action is the opposite of voluntary where stimulation of receptors initiate an action such as yawning or blinking
Yawning is an involuntary action.