Fight-or-flight response
The flight or fight response was first described by Walter Cannon in the 1920s as a theory that animinals react to threats with a general discharge of the sympathetic nervous system.
The response was later associated with specific physiological responses, primarily release of adrenaline and norepinephrine from the medulla of the adrenal glands. The catecholamine hormones facilitate immediate physical reactions by triggering increases in heart rate and breathing, constricting blood vessels and tightening muscles.