On receiving fear signals from the amygdalae, the hypothalamus, acts reflexively to control the reproductive, vegetative, endocrine, hormonal, visceral and autonomic functions of the body. Breathing, digestion, blood circulation, brain activity and body fluid flows are instantly affected. The signals from the amygdalae dilate pupils and increase brain wave frequency. They make hairs stand on end. They reduce saliva, drying the mouth. They cause sweating and a decrease in skin resistance. They decrease peripheral blood flow and cause hands to become cold. The signals speed breathing and dilate bronchial tubes to allow more air to the lungs. They tighten stomach muscles, slow digestion and close down the excretory system. They increase acids in the stomach, causing diarrhoea.
The signals travel to the adrenal gland, which produces cortisol, causing an increase in glucose production to provide additional fuel for the muscles and brain to deal with the potential stress. The signals increase blood pressure, release sugar into the blood and increases the tendency for blood clotting. The signals increase red blood cells. They tense postural muscles, causing hand and body tremors. They dilate blood vessels to skeletal muscles to allow greater blood flow. They slow the working of the immune system. The amygdalae trigger a chain of biological events and engulf the mind in the fear emotion, even before the conscious mind can assess the situation. In the modern world, such persistent fear signals are not set off by real physical danger. They are triggered by an instinctive brain, which tries to overcome social and career issues by foolishly preparing the body to freeze, flee or defend itself.
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