The Sympathetic Branch
of the Autonomic Nervous System
resist giving you the above fancy piece of terminology to casually drop in polite
conversation at school or in your family.
When a stimulus in your
environment is perceived as threatening, or is conjured up in your mind (remember
the section on perception in Chapter 4, What Is Stress,
Anyway?), the specific pathway in the central nervous system that is activated
is the sympathetic branch.
When the sympathetic branch is activated,
all the following occur:
dilate - If your body is reflexively assuming you are in imminent danger, then it is crucial that your eyes are taking in enough light for you to be able to see what the threat is.
Windpipes expand and respiration rate increases - Both changes facilitate the taking in of increased oxygen to burn in your cells for the energy you need to fight for your life or to run away from the danger.
Bladder functions less efficient - Bladder control is a much lower physiological priority if you are in imminent danger, and your very survival is in question.
Digestive functions slowed and blood flow diverted to the heart, brain, and major
- Both of these are significant. Your heart must be functioning efficiently for you to fight or to flee. Your brain needs to be operating at peak efficiency so you can process options. And your major muscle groups, in addition to your heart, need to be operating efficiently so that you can run away from the danger or fight it off. Conversely, if your immediate survival is in question, it does not matter that much if your gastrointestinal system is efficiently processing your most recent meal. In longer-term stressful situations, some persons can point to increased stomach aches and gastrointestinal discomfort.
- If your immediate task is to fight or to run for your life, it is of little consequence that you have a nice moist mouth to facilitate speech (and, in addition, to begin the digestion of carbohydrates). For anyone who has a severe aversion to public speaking, dry mouth or "cotton mouth" when you get up to speak may be something you have experienced.
Sweat glands stimulated to process bodily waste products - With life-saving physiological processes speeded up, more waste products will need to be processed out of the body. We've all seen the movies of people breaking a sweat while being interrogated. They are not fighting or fleeing, but the stress response is doing what it is supposed to be doing to process the waste products.
Adrenal gland stimulated, and adrenaline pumped into blood causing:
heart rate and blood pressure - Sometimes a person even can feel their heart pounding in their chest, right?
blood sugar - Our body needs fuel to fight or to flee.
red cell count
- Red blood cells carry oxygen throughout the body so it can burn the fuel needed to stay alive.
of heart's blood vessels; surface vessels constrict - Another way of pointing out the importance of effective heart functioning — dilated blood vessels facilitate the moving of more blood to the heart. Conversely, surface blood vessels are a lower priority. Are any of you aware that your hands and feet feel colder in stressful situations? The diverted blood flow helps to explain this.
of muscles near surface of skin - In so-called lower forms of animals (including house pets like cats and dogs) one response to a threat is that surface muscles contract, making their fur stand up, which makes them seem larger and more formidable to an attacker. We humans sometimes have an awareness of "the hair standing up on the back of our neck," even feeling it against the inside of a shirt collar. We're not that different from our house cat, except that it doesn't show as much on us. For others of us, a sense of getting goose bumps is related to the same process.