Startle reaction

The startle reaction, also called "startle response" or "alarm reaction", is the 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, and breathing 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).

Startles usually elicit a response physically or emotionally.

See also:
Moro reflex