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Chromaffin cells contained in the adrenal medulla act as postganglionic nerve fibers that release this chemical response into the blood as a circulating messenger. The sympathoadrenal system can activate and discharge chemical messengers as a single unit to activate an organism's “fight or flight” response.
The fight-or-flight or the fight-flight-freeze-or-fawn [1] (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. [2] It was first described by Walter Bradford Cannon in 1915.
The adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines; epinephrine, norepinephrine, and dopamine. Because the ANS, specifically the sympathetic division, exerts direct control over the chromaffin cells , the hormone release can occur rather quickly. [ 2 ]
Adrenaline is normally produced by the adrenal glands and by a small number of neurons in the medulla oblongata. [14] It plays an essential role in the fight-or-flight response by increasing blood flow to muscles, heart output by acting on the SA node, [15] pupil dilation response, and blood sugar level.
The sympathetic response is colloquially known as the "fight-or-flight response," indicated by accelerated pulse and respiration rates, pupil dilation, and a general feeling of anxiety and hyper-awareness. This is caused by the release of epinephrine and norepinephrine from the adrenal glands.
The adrenal medulla is derived from neural crest cells, which come from the ectoderm layer of the embryo. These cells migrate from their initial position and aggregate in the vicinity of the dorsal aorta , a primitive blood vessel, which activates the differentiation of these cells through the release of proteins known as BMPs .
The SNS is responsible for the fight-or-flight response, which is triggered by experiences such as exercise or fear-causing situations. This response dilates pupils, increases heart rate, mobilizes energy, and diverts blood flow from non-essential organs to skeletal muscle. These effects together tend to increase physical performance momentarily.
If the amygdala perceives a match to the stimulus, i.e., if the record of experiences in the hippocampus tells the amygdala that it is a fight, flight or freeze situation, then the amygdala triggers the HPA (hypothalamic–pituitary–adrenal) axis and "hijacks" or overtakes rational brain function. [5]