hippocampus (a part of the brain in the medial temporal lobe). Both the central nucleus of the amygdala and the lateral BNST, when activated, transmit impulses to several other regions of the brain, including the locus coeruleus, which uses norepinephrine (also called noradrenalin) to send signals to numerous other parts of the brain. Several parts of the hypothalamus and many of the same brainstem nuclei activate the sympathetic nervous system, which with the locus coeruleus forms part of the “central stress response,” preparing for fight or flight. The hypothalamus is especially important for regulating the sympathetic nervous system because it receives sensory input from virtually the entire body, including the amygdala and BNST.

FIGURE 4-1 Stress-response pathways. NOTE: ACTH = adrenocorticotrophic hormone, CRH = corticotropin-releasing hormone, RAS = reticular activating system.

The sympathetic nervous system uses epinephrine to stimulate the inner region of the adrenal gland to secrete large amounts of epinephrine and other catecholamines1 into the circulation. The surge of epinephrine floods the brain and peripheral tissues, thereby producing the full-fledged fight or flight response: faster heartbeat, greater energy, more blood flow to skeletal and cardiac muscle, dilation of the pupils and airways, and higher blood glucose concentration and so on. With chronic stress, however, the sympathetic nervous system may


Catecholamines are a class of hormones and neurotransmitters that includes epinephrine and dopamine.

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