Startle response

The startle reaction, (also called startle response, alarm reaction or, mistakenly, startle reflex), is the complex, involuntary response of mind and body to a sudden unexpected stimulus, such as a flash of light, a loud noise, or a quick movement near the face.

In human beings, the reaction includes physical movement away from the stimulus, a contraction of the muscles of the arms and legs, and often blinking. It also includes blood pressure, respiration, breathing and hormonal changes.. The muscle reactions generally resolve themselves in a matter of seconds. The other responses take somewhat longer.

An exaggerated startle reaction is called hyperexplexia (also hyperekplexia).