Once the sympathetic nervous system is activated, it stimulates the adrenal glands. The adrenal glands are small hormone producing organs that lie at the top of both kidneys. The adrenal glands release hormones called adrenaline and noradrenaline when stimulated by the sympathetic nervous system. These hormones are known as catecholamines.
Catecholamines have very specific effects on the body. These include:
· Raised heart rate
· Increased breathing rate
· Altered blood flow: blood flows preferentially to the muscles, brains, legs and arms.
· Dilated pupils
· Trembling and shaking as muscles become tense
These effects all make a lot of sense. The body is priming itself for an attack and giving itself the best chance of fighting. The raised heart rate and breathing rate help metabolism and oxygenation in preparation for energy expenditure. The dilated pupils help us become more aware of our surroundings.
Whilst the fight or flight response is undoubtedly useful, chronic stress is attributed to overstimulation of this pathway.
These days, we often experience stress not from an actual physical stressor, but from stressful thoughts. Our ability to learn responses is incredible. Once our body associates a thought with a particular physical response, this pathway becomes more and more streamlined and efficient. It’s this streamlined pathway which can lead someone who once had an unexpected stressful experience with spiders to develop a phobia that can be stimulated by just thinking about them.