The flight or fight response, also called the "acute
stress response" was first described by Walter Cannon in the 1920s as a
theory that animals react to threats with a general discharge of the sympathetic
nervous system. The response was later recognized as the first stage of a general
adaptation syndrome that regulates stress
responses among vertebrates and other organisms.
The onset of a stress response is associated with specific
physiological actions in the sympathetic nervous system, primarily caused by
release of adrenaline and norepinephrine from the medulla of the adrenal glands.
The release is triggered by acetylcholine released from preganglionic sympathetic
nerves. These catecholamine hormones facilitate immediate physical reactions
by triggering increases in heart rate and breathing, constricting blood vessels
and tightening muscles. An abundance of catecholamines at neuroreceptor sites
facilitates reliance on spontaneous or intuitive behaviors often related to
combat or escape.
Normally, when a person is in a serene, unstimulated 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. That route of signaling increases the rate of
noradrenergic activity in the locus ceruleus, and the person becomes alert and
attentive to the environment.
If a stimulus is perceived as a threat, a more intense and
prolonged discharge of the locus ceruleus activates the sympathetic division
of the autonomic nervous system (Thase & Howland, 1995). The activation
of the sympathetic nervous system leads to the release of norepinephrine from
nerve endings acting on the heart, blood vessels, respiratory centers, and other
sites. The ensuing physiological changes constitute a major part of the acute
stress response. The other major player in the acute stress response is the
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