- Startle reaction
The startle reaction, also called the startle response, startle reflex or alarm reaction, is the
response of mind and body to a sudden unexpectedstimulus , such as a flash oflight , a loud noise (acoustic startle reflex), or a quick movement near the face. Inhuman beings , the reaction includes physical movement away from the stimulus, a contraction of the muscles of thearm s and legs, and oftenblinking . It also includesblood pressure , respiration, andbreath ing changes. Themuscle reactions generally resolve themselves in a matter of seconds. The other responses take somewhat longer. An exaggerated startle reaction is calledhyperexplexia (also hyperekplexia) The exaggerated startle response is often seen in patients withPosttraumatic stress disorder (PTSD).Acoustic Startle Reflex
The pathway for this
response was largely elucidated in rats in the 1980s [Davis, M., Gendelman, D. S., Tischler, M. D., & Gendelman, P. M.(1982). A primary acoustic startle circuit: Lesion and stimulationstudies. Journal of Neuroscience, 6, 791-805. [http://www.jneurosci.org/cgi/content/abstract/2/6/791] ] . In summary the basic pathway follows the audiory pathway from the ear up to the Nucleus of theLateral Lemniscus (LLN) from where it the 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/caudalcolliculus in the reaction that "twitches" the hindlimbs, but these may be important for adjustment ofpinnae , gaze towards the direction of the sound or the associated blink [Castellote, J.M., Kumru, H., Queralt, A. and Valls-Solé, J. (2007) A startle speeds up the execution of externally guided saccades. Exp. Brain Res. 177:129-136 [http://www.springerlink.com/content/d3371924t73mt670] ] .ee also
*
Moro reflex ("Startle reflex")
*Prepulse inhibition - attenuation of the startle response after a weaker preceding stimulus, or "prepulse".
*Surprise (emotion) External links
* [http://www.patrickriley.ca/what-means-exaggerated-startle-response/ "What Means" Exaggerated Startle Response?] From "Riley Down Under: Surviving PTSD And Getting On With Life"
* [http://www.ncptsd.va.gov/ncmain/ncdocs/fact_shts/morgan.html?opm=1&rr=rr107&srt=d&echorr=true Startle Response and PTSD]
Wikimedia Foundation. 2010.