Fight-or-flight response
The fight-or-flight response, also called the acute stress response, was first described by Walter Cannon in 1929. His theory states that animals react to threats with a general discharge of the sympathetic nervous system, priming the animal for fighting or fleeing. This response was later recognized as the first stage of a general adaptation syndrome that regulates stress responses among vertebrates and other organisms.
Biology of the Stress Response
Normally, when a person is in a serene, unstimulated state, the "firing" of neurons in the locus ceruleus is minimal. A novel stimulus (which could include a perception of danger or an environmental stressor signal such as elevated sound levels or over-illumination), 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. Similarly, an abundance of catecholamines at neuroreceptor sites facilitates reliance on spontaneous or intuitive behaviors often related to combat or escape.
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). This activation is associated with specific physiological actions in the system, both directly and indirectly through the release of epinephrine (adrenaline) and to a lesser extent norepinephrine from the medulla of the adrenal glands. The release is triggered by acetylcholine released from preganglionic sympathetic nerves. The other major player in the acute stress response is the hypothalamic-pituitary-adrenal axis.
Physiology of the Stress Response
These catecholamine hormones facilitate immediate physical reactions associated with a preparation for violent muscular action. (Gleitman, et al, 2004). These include the following:
- Acceleration of heart and lung action
- Inhibition of stomach and intestinal action
- Constriction of blood vessels in many parts of the body
- Liberation of nutrients for muscular action
- Dilation of blood vessels for muscles
- Inhibition of tear glands and salivation
- Dilation of pupil
- Relaxation of bladder
- Inhibition of erection
Psychology of the Stress Response
A typical example of the stress response is a grazing zebra, calmly maintaining homeostasis. If the zebra sees a lion closing in for the kill, the stress response is activated. The escape requires intense muscular effort, supported by all of the body’s systems. The sympathetic nervous system’s activation provides for these needs. A similar example involving fight is of a cat about to be attacked by a dog. The cat shows accelerated heartbeat, piloerection (hair standing on end, normally for conservation of heat), and pupil dilation, all signs of sympathetic arousal.
Though Cannon, who first proposed the idea of fight-or-flight, provided considerable evidence of these responses in various animals, it subsequently became apparent that his theory of response was too simplistic. Animals respond to threats in many ways, not only by fighting and fleeing. Rats, for instance, try to escape when threatened, but will fight when cornered. Some animals stand perfectly still so that predators will not see them. Others have more exotic self-protection methods. Some species of fish change color swiftly, to camouflage themselves. Although these responses are triggered by the sympathetic nervous system, they do not fit the simple model of fight or flight. The only thing that would generate the fight method in these animals would be the law of self-preservation. This means that if the animal was attacked while camouflaged, it would instinctively counter-attack its assailant.
Furthermore, it is relatively rare that a threat from another animal results immediately in fight or flight. Usually there is a period of heightened awareness, during which each animal interprets behavioral signals from the other. Signs such as paling, piloerection, immobility, sounds, and body language communicate the status and intentions of each animal. There may be a sort of negotiation, after which fight or flight may ensue, but which might also result in playing, mating, or nothing at all. An example of this is kittens playing: each kitten shows the signs of sympathetic arousal, but they are aware of each other’s intent not to inflict real damage.
Negative Effects of the Stress Response in Humans
Although the emergency measure of the stress response is undoubtedly both vital and valuable, it can also be disruptive and damaging. Most humans rarely encounter emergencies that require physical effort, yet our biology still provides for them. Thus we may find our stress response activated in situations where physical action is inappropriate or even illegal. This activation takes a toll on both our bodies and our minds.
Disruption of the sexual response and the digestive system are common negative results. Diarrhea, constipation, and difficulty maintaining sexual arousal are typical examples. These are functions which are controlled by the parasympathetic nervous system and therefore suppressed by sympathetic arousal. Prolonged stress responses may result in chronic suppression of the immune system, leaving the sufferer vulnerable to infection by bacteria and viruses. Repeated stress responses can be caused not only by real threats, but also by mental disorders such as post-traumatic stress disorder, in which the individual shows a stress response when remembering a past trauma, and panic disorder, in which the stress response is activated apparently by nothing.
See also
External links
References
- Thase, M.E. (1995). "Biological processes in depression: An updated review and integration". In Beckham & Leber (ed.). Handbook of Depression. NY: Guilford Press.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - Gleitman, Henry (2004). Psychology (6 ed.). NY: Norton. ISBN 0-393-97767-6.
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