The sympathetic nervous system also stimulates the skeletal system and muscular system to pump more blood to those areas to handle the acute stress. Simultaneously, the sympathetic nervous system inhibits the digestive system and the urinary system to optimise blood flow to the heart, lungs, and skeletal muscles. This plays a role in the alarm reaction stage. The parasympathetic response is colloquially known as the "rest and digest" response, indicated by reduced heart and respiration rates, and, more obviously, by a temporary loss of consciousness if the system is fired at a rapid rate. The parasympathetic nervous system stimulates the digestive system and urinary system to send more blood to those systems to increase the process of digestion. To do this, it must inhibit the cardiovascular system and respiratory system to optimise blood flow to the digestive tract, causing low heart and respiratory rates. The parasympathetic nervous system plays no role in acute stress response.Studies have shown that patients with acute stress disorder have overactive right amygdalae and prefrontal cortices; both structures are involved in the fear-processing pathway. Diagnosis
According to the DSM-V, symptom presentation must last for three consecutive days to be classified as acute stress disorder. If symptoms persist past one month, the diagnosis of PTSD is explored. There must be a clear temporal connection between the impact of an exceptional stressor and the onset of symptoms; onset is usually within a few minutes or days but may occur up to one month after the stressor.
Hans Selye was the first to coin the term "general adaptation syndrome" to suggest that stress-induced physiological responses proceed through the stages of alarm, resistance, and exhaustion.The sympathetic branch of the autonomic nervous system gives rise to a specific set of physiological responses to physical or psychological stress. The bodys response to stress is also termed a "fight or flight" response, and it is characterised by an increase in blood flow to the skeletal muscles, heart, and brain, a rise in heart rate and blood pressure, dilation of pupils, and an increase in the amount of glucose released by the liver.The onset of an acute stress response is associated with specific physiological actions in the sympathetic nervous system, both directly and indirectly through the release of adrenaline and, to a lesser extent, noradrenaline from the medulla of the adrenal glands. These catecholamine hormones facilitate immediate physical reactions by triggering increases in heart rate and breathing, constricting blood vessels. An abundance of catecholamines at neuroreceptor sites facilitates reliance on spontaneous or intuitive behaviours often related to combat or escape.Normally, when a person is in a serene, non-stimulated state, the firing of neurons in the locus ceruleus is minimal. A novel stimulus, once perceived, is relayed from the sensory cortex of the brain through the thalamus to the brain stem.