<P> The fight - or - flight response (also called hyperarousal, or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival . It was first described by Walter Bradford Cannon . His theory states that animals react to threats with a general discharge of the sympathetic nervous system, preparing the animal for fighting or fleeing . More specifically, the adrenal medulla produces a hormonal cascade that results in the secretion of catecholamines, especially norepinephrine and epinephrine . The hormones estrogen, testosterone, and cortisol, as well as the neurotransmitters dopamine and serotonin, also affect how organisms react to stress . </P> <P> This response is recognized as the first stage of the general adaptation syndrome that regulates stress responses among vertebrates and other organisms . </P>

In response to an acute stressor epinephrine is released from which structure