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Fight-or-flight response

The fight-or-flight response, also called hyperarousal or the acute stress response, was first described by Walter Cannon in 1915[1][2]. 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 stresser 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[citation needed]......

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[citation needed].

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
  • General effect on the sphincters of the body
  • Constriction of blood vessels in many parts of the body
  • Liberation of nutrients for muscular action
  • Dilation of blood vessels for muscles
  • Inhibition of Lacrimal gland (responsible for tear production) 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 (Gleitman et al, 2004).

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 complex ways. 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. These responses are triggered by the sympathetic nervous system, but in order to fit the model of fight or flight, the idea of flight must be broadened to include escaping capture in either a physical way or in a sensory way. Thus, flight can be disappearing to another location or just disappearing in place. And often both fight and flight are combined in a given situation.

The fight or flight actions also have polarity - the individual can fight or fly against or away from something that is threatening, such as a hungry lion, or fight or fly for or towards something that is needed, such as the safety of the shore of a raging river.

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.

Behavioral manifestations of fight-or-flight

In prehistoric times when the fight or flight response evolved in humans, fight was manifested in aggressive, combative behavior and flight was manifested by fleeing potentially threatening situations, such as being confronted by a predator. In current times, these responses persist, but fight and flight responses have assumed a wider range of behaviors. For example, the fight response may be manifested in angry, argumentative behavior, and the flight response may be manifested through social withdrawal, substance abuse, and even television viewing (Friedman & Silver 2007).

Behaviorally, the fight or flight response describes men’s reactions to stressful situations better than women’s [1]. That is, men are more likely to cope with stress via social withdrawal, substance abuse, and aggression. Some researchers believe that these aspects of the fight or flight response in men contribute to their earlier mortality, relative to women. Women are more likely to cope with stress through social support, that is, by turning to others to both give and receive instrumental and emotional aid. This pattern of responding has been called “tend and befriend,” and refers to the fact that during stressful times, women are especially likely to show protective responses toward their offspring and affiliate with others for shared social responses to threat (Taylor et al, 2000). This can also be explained as being the tendency of men to direct their fight or flight actions in a away from or against manner while women tend to direct their actions in a towards or for manner.

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. In most modern situations, 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. This activation takes a toll on both our bodies and our minds. Also, simple stresses that can be acted upon quickly are more easily overcome allowing the body to return to homeostasis, but with the more complex stresses of modern societies, with many, many factors and individuals involved, the danger may seem unavoidable, and stress may continue indefinitely, which ends up compromising the system, rather than helping the system.

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


  1. ^ harvardsquarelibrary: W. B. Cannon Bodily Changes in Pain, Hunger, Fear and Rage: An Account of Recent Researches into the Function of Emotional Excitement, Appleton, New York, 1915
  2. ^ Cannon, Walter (1929). Bodily changes in pain, hunger, fear, and rage. New York: Appleton. 

This article incorporates text from, a public domain work of the United States Government.

  • Friedman, H. S., & Silver, R. C. (Eds.) (2007). Foundations of Health Psychology. New York: Oxford University Press.
  • Taylor, S.E., Klein, L.C., Lewis, B.P., Gruenewald, T.L., Gurung, R.A.R., & Updegraff, J.A. (2000). Biobehavioral responses to stress in females: Tend-and-befriend, not fight-or-flight. Psychological Review, 107, 411-429.
  • Thase, M.E.; R.H. Howland (1995). "Biological processes in depression: An updated review and integration", in Beckham & Leber: Handbook of Depression. NY: Guilford Press. 
  • Gleitman, Henry; Alan J. Fridlund, Daniel Reisberg (2004). Psychology, 6, NY: Norton. ISBN 0-393-97767-6. 
  • Sapolsky, Robert M., 1994. Why Zebras Don't Get Ulcers. W.H. Freeman and Company.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fight-or-flight_response". A list of authors is available in Wikipedia.
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