Startle responses according to the textbook "Introduction to Behavior and Learning" (Powell et al, 2009) is a defensive reaction to a sudden unexpected stimulus. Startle responses cause an automatic tightening of muscles as well as hormone and internal organ changes (Powell et al, 2009.) We have all felt this as some point I am sure, it isn't a pleasant feeling at the time, but if lucky enough to be caught on video watching the response can be quite entertaining. The video I included is my favorite example of startle responses, it also shows how our protective instincts kick in with startle responses.
Our startle responses are tied to our basic instinct to survive, we feel threatened so we respond. When you view the video, how do you think you would have responded? All depending on our own backgrounds and living environments we react differently. From the sources I have listed at the end they talk about how people with Post Traumatic Stress Disorder (PTSD) and/or high anxiety are more likely to have a higher startle response then someone without either of the two. In a study done by Arieh Y. Shalev, M.D., Tuvia Peri, Ph.D., Dalia Brandes, M.A., Sara Freedman, M.Sc., Scott P. Orr, Ph.D., and Roger K. Pitman, M.D, "they looked at the auditory startle response in trauma survivors with post traumatic stress disorder." The study proved that "differences in physiological response to startling tones develop along with PTSD in the months that follow a traumatic event. This pattern supports the theories that associate PTSD with progressive neuronal sensitization" (http://ajp.psychiatryonline.