Question

Explain the biological changes and signs that occur during Walter Cannon's arousal reflex (the fight or flight reflex) and Selye's General Adaptation Syndrome – including the concept of reactivity.

Answer 1

• 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.
• 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.
• The reaction begins in the amygdala, which triggers a neural response in the hypothalamus. The initial reaction is followed by activation of the pituitary gland and secretion of the hormone ACTH.The adrenal gland is activated almost simultaneously, via the sympathetic nervous system, and releases the hormone epinephrine.
• The release of chemical messengers results in the production of the hormone cortisol, which increases blood pressure, blood sugar, and suppresses the immune system.
• Catecholamine hormones, such as adrenaline (epinephrine) or noradrenaline (norepinephrine), facilitate immediate physical reactions associated with a preparation for violent muscular action and :
• Acceleration of heart and lung action
• Paling or flushing, or alternating between both
• Inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops
• General effect on the sphincters of the body

• Constriction of blood vessels in many parts of the body