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What Is Stress?
The release of stress hormones in the fight or flight nervous system state results in a wide-ranging array of physical changes in the body.
Because use and meaning of the word stress can vary, it can be helpful to define stress as a physical response to danger or potential danger in our immediate environment.
Stress has now been shown by a number of researchers to involve physiological mechanisms that change our body and its function in a number of ways. I will not go into great detail about those mechanisms, as they are better described by the researchers themselves in books they have written about the subject. In my resources section, I provide links to these books, the best of which on the physiology of stress are When The Body Says No by Gabor Mate, Why Zebras Don’t Get Ulcers by Robert Sapolsky, and The Stress of Life by Hans Selye, who conducted pioneering research on the stress response.
The broad summary is that, in stress, the brain releases hormones (CRH from the hypothalamus, which triggers ACTH from the pituitary) that trigger the release of the classic stress hormones (mostly glucocorticoids, adrenalin, and cortisol). These trigger additional mechanisms and responses that have wide-ranging effects to on the body that give us an advantage when we are responding to physical danger in our immediate environment.
Why Is Stress Helpful?
The stress response accomplishes a number of things that ideally give us better odds of surviving dangerous situations. This is not an exhaustive list but it covers the basic reasons that the stress response occurs. Stress can:
1. Increase the body’s access to energy.
In stress the body releases its fat stores into the blood stream for immediate access to the energy they provide. Blood flow to the muscles of the arms and legs increases, while water content moves to the center of the body. This allows muscles of the arms and legs to have better access to the energy, which is delivered through blood. Bone to bone contact increases at the joints so that the body has more surfaces to lever off of, which allows for more powerful movement.
2. Alter receipt of sensory information to:
a. Narrow focus to take in information about the immediate danger.
The eye sockets narrow in order to focus either on the sensory information that triggered the stress response, or on the survival situation. Some individuals in survival situations report experiencing tunnel vision, which is a result of extreme narrowing of eye socks in the later stages of the stress response. A less extreme result would be loss of the far ranges of peripheral vision, which often goes unnoticed if attention is not specifically focused on this.
b. Reduce sensory information also to narrow focus, as well as to block signals about pain, etc. that might keep us from continuing to take action for survival purposes.
The same joint compression that increases friction for movement also compresses nerves and blood vessels, decreasing the amount of sensory information that reaches the brain. There is also the phenomenon of stress-based analgesia, in which increased amounts of dopamine are released during stress, helping to dull pain signals to the brain. Robert Sapolsky discusses this phenomenon in Why Zebras Don’t Get Ulcers.
3. Create functional and structural adaptations appropriate to the specific danger being experienced.
The ends of the trigeminal nerve are visible protruding from the jaw and under the eye sockets on either side of the face. They also protrude at the brow bone (not shown here). Compression of this nerve in fight or flight prevents receipt of sensory information from the face, which can be adaptive in a fight.
Hundreds of such changes occur, so I will provide just a couple of examples here. In fight or flight, the jaw dislocates, which causes compression of the trigeminal nerve, which innervates the face and also takes in information about smell and taste. If it were necessary to fight, the body could more easily ignore a punch to the face, due to the lack of neural signals, and continue fighting, fleeing, or reacting to the situation.
This can also reduce other sensory information, such as the ability to taste food, which is usually not necessary in a fight. However, this explains the symptom that some individuals report of not being able to taste food when stressed.
In the collapse stage (read more on the seven stages of the stress response), our valve system – which is a series of pumps whose function allows respiration, circulation, and digestion to occur – stops pumping, which enhances the perception of being dead, which can sometimes cause a predator to lose interest. (Compensatory patterns take over to prevent death in the absence of valve function, but a certain amount of vitality and internal movement are lost).
More examples of structural changes and how they are adaptive for survival are given on the Nervous System page and the Stages of Fight or Flight page.
4. Decrease energy-absorbing activities that are not necessary for survival in the moment.
As one example of this, when the valve system mentioned above stops pumping, this halts digestion, an activity that requires a fair amount of energy.
Sympathetic and Parasympathetic Nervous System States
As discussed in the section on the nervous system, the autonomic nervous system can be in one of two states: the sympathetic or the parasympathetic. The state the nervous system is in when releasing stress hormones and going through the cascade of effects caused by them is the sympathetic, or fight or flight, state. In the parasympathetic nervous system state, this response is shut off, or counter-balanced, by a release of different hormones with a different set of effects on the body. This is sometimes called the “rest and digest” state and allows things such as digestion to occur – as the “rest and digest” term suggests – as well as processes like tissue repair and other things that keep the body in good working order.
Ideally, we would have a balance of these two states and a balance of the hormones released, as well as the ability to flip back and forth quickly and with ease. This balance allows us to maintain vitality and health, as well as the ability to respond and adapt to our environment (internal and external) with ease. This is one of the functions that is disrupted when the sympathetic nervous system is over-activated, which you can read more about on the Why Is Stress A Problem? page.
To dive further into the question of “what is stress?” and explore more of the functional and structural changes that occur during stress, I highly recommend reading about the stages of fight or flight, sometimes also considered the stress / trauma continuum.
Stress Terminology
The term fight or flight response or nervous system has the same meaning as stress, stress response, or sympathetic nervous system – which is to say that these all refer to the activation of the physical changes that allow the body to respond to danger. I will therefore use these terms interchangeably for all discussions related to stress.
Stress Versus Stressor
Hans Seyle, pioneering researcher on stress, made a distinction between the terms “stress” and “stressor”. A stressor is something that activates the stress response mechanism – in other words, the source of the danger or perceived danger. Stress is the physiological response to the stressor. So in other words, being chased by a lion or being exposed to extreme heat or cold would qualify as stressors. The body’s physiological response to these scenarios is stress. In common usage, people may talk about having a certain amount of stress in their lives. In fact, they are probably referring to having a certain amount of stressors in their lives. This is a fine point, but a helpful distinction when discussing stress reduction. One of the techniques utilized by the Fajardo Method of Holistic Biomechanics® is the de-coupling of the stress response from those “stressors” that do not actually involve physical danger. You can read more about this on the How To Reduce Stress page.
Application
Now that you’ve read a little about what stress is, you can learn more about problems that arise from over-activation of the fight or flight nervous system, as well as how to reduce stress to address this.
