Startle response

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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.[1]

Neuromotor examination[edit]

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.[2]

Acoustic startle reflex[edit]

The pathway for this response was largely elucidated in rats in the 1980s.[3] 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.

In slightly more detail this corresponds to Ear (cochlea) -> Cranial Nerve VIII (auditory) -> Cochlear Nucleus (ventral/inferior) -> LLN -> Caudal pontine reticular nucleus (PnC). The whole process has a less than 10ms latency. There is no involvement of the superior/rostral or inferior/caudal colliculus in the reaction that "twitches" the hindlimbs, but these may be important for adjustment of pinnae, gaze towards the direction of the sound or the associated blink.[4]

See also[edit]


  1. ^ "Peter J. Lang, Margaret M. Bradley, Bruce M Cuthbert. "Emotion, attention, and the startle reflex" 1990". Retrieved 2011-10-01. 
  2. ^
  3. ^ Davis, M; Gendelman, Ds; Tischler, Md; Gendelman, Pm (Jun 1982). "A primary acoustic startle circuit: lesion and stimulation studies" (Free full text). Journal of Neuroscience 2 (6): 791–805. ISSN 0270-6474. PMID 7086484. 
  4. ^ Castellote, Jm; Kumru, H; Queralt, A; Valls-Solé, J (Feb 2007). "A startle speeds up the execution of externally guided saccades". Experimental brain research. Experimentelle Hirnforschung. Experimentation cerebrale 177 (1): 129–36. doi:10.1007/s00221-006-0659-4. ISSN 0014-4819. PMID 16944110. 

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