Walter Cannon: Stress & Fight or Flight Theories

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  • 0:02 Fight or Flight
  • 0:40 Walter Cannon
  • 2:07 Body's Stress Response
  • 3:29 Panic Attacks
  • 4:35 Post-Traumatic Stress Disorder
  • 5:30 Lesson Summary
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Lesson Transcript
Instructor: Sarah Lavoie

Sarah has taught Psychology at the college level and has a master's degree in Counseling Psychology.

The fight or flight response is an instinct designed to keep us alive. Learn about Walter Cannon's discovery of the fight or flight response, what happens during the stress response and how it can help and hurt our bodies in this lesson.

Fight or Flight

More than any other body part, our brains are what keep us safe. A reaction, such as pulling our hand back from a hot stovetop, is an instant reaction designed to protect us. These instincts kept prehistoric people alive. Prehistoric people instinctively knew to fear dangerous situations, such as confrontation with large predators. Humans and animals have maintained those automatic reactions to potentially dangerous situations. In some instances, these reactions are still very useful. When presented with a dangerous situation, our instincts still tell us we must be ready to react swiftly: to fight or to flee.

Walter Cannon

The term fight or flight was first developed by Dr. Walter B. Cannon in 1915. Walter Cannon studied at Harvard University and stayed there to teach in the Department of Physiology. Although he was a physiologist by training, Dr. Cannon became interested in the physical reactions of his laboratory animals when under stress. While studying digestion in his animals, Dr. Cannon noticed that physical changes in the function of the stomach would occur when the animal was frightened or scared. He went on to study all of the various physiological reactions to stress throughout the body.

The fight-or-flight response, also called the acute stress response, is an automatic reaction to a stressful and potentially dangerous situation. Our brains react quickly to keep us safe by preparing the body for action. Just like animals, humans react to the acute stress by either fighting the threat or fleeing from it.

Fight or flight can take many forms, and is often different between species. For example, a snake will generally flee from humans, but if cornered or guarding a nest, they may attack. Some animals, such as frogs or lizards, camouflage themselves in hopes the predator will leave. There can also be differences in reaction based on the sex of the animal. Males are more likely to fight, while females more frequently hide, freeze in place to prevent detection, or flee to safety.

Body's Stress Response

When confronted by a threat, the brain begins to prepare the body for action without conscious thought. The brain activates the sympathetic nervous system, the part of the nervous system that stimulates the body and mobilizes energy resources for action. Changes in the body are just some of the functions of the sympathetic nervous system and can include:

  • Accelerated heart rate
  • Activated sweat glands
  • Blood flow to the muscles
  • Dilated pupils
  • Increased lung capacity
  • Reduced saliva flow and digestive functions
  • Release of energy stores
  • Release of hormones, such as adrenaline
  • Inhibited bladder and excretory functions

Remember the last time you were frightened or startled. Do you remember feeling a rush of energy? Did your heart suddenly beat harder and faster? Did you breathe heavily or start to sweat? These are all symptoms of your body's stress response.

While we no longer have to deal with falling boulders or predatory animals, the fight-or-flight response and the sympathetic nervous system can still become activated in non-life-threatening situations. In some people, the response can occur when confronted with a frightening or stressful situation, such as driving or public speaking. Sometimes, a terrifying or traumatic event can cause these effects weeks, months, or years after the fact.

Panic Attacks

In some people, intense, often debilitating, fear from a normal situation can escalate into what is known as a panic attack. Panic attacks are sudden, unexpected periods of intense fear in which the affected person has a similar reaction as being confronted by a lion. Although the situation is not deadly, the sympathetic nervous system reacts as if it were.

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