This article must include a clear description of the startle response. This concern has been noted on the talk page where whether or not to include such information may be discussed.(December 2013)
The startle response or startle reaction is a response to sudden, startling stimuli, such as sudden noise or sharp movement. Usually the onset of the startle response is reflectory. The startle reflex is a brainstem reflectory reaction that serves to protect the back of the neck (whole-body startle) or the eye (eyeblink) and facilitates escape from sudden stimuli. It is found across the lifespan and in many species. An individual's emotional state may lead to a variety of responses.
During neuromotor examination of newborns, it is noted that, for a number of techniques, the patterns of the startle reaction and the Moro reflex may significantly overlap, the notable distinction being the absence of arm abduction (spreading) during startle response.
The pathway for this response was largely elucidated in rats in the 1980s. The basic pathway follows the auditory pathway from the ear up to the nucleus of the lateral lemniscus (LLN) from where it activates a motor centre in the reticular formation. This centre sends descending projections to lower motor neurones of the limbs.