Not all the above responses occur simultaneously. The specific responses which are activated depend on the type of emotional stress. For example, embarrassment produces a blushing response resulting from loss of sympathetic activity only to cutaneous vessels. The mechanism is unknown, but may result from release of kinins following activation of cholinergic fibers in the sweat glands. Fainting results from a increase in vagal outflow mediated by the anterior hypothalamus.
Heart rate is reduced, vasodilation occurs, and blood pressure falls.
Fear or excitement produces the alerting reaction , which results in a general increase in cardiovascular sympathetic activity and a decrease in cardiac parasympathetic activity. Increased activity of the preganglionic sympathetic fibers to the adrenal medulla cause secretion of epinephrine into the blood stream. Centers in the posterior hypothalamus are involved. The responses lead to an increased blood pressure and dilation of skeletal muscle and coronary arterioles. The apparent benefit is that it prevents collapse of cranial vessels and preserves adequate blood flow to the brain.