The Sympathetic and Parasympathetic Nervous Systems: How Do They Work Together and Support Each Other?
Let's look at an example of how these two systems function in response to changes in the environment.
When the body is stressed, the SNS contributes to what is known as the "fight or flight" response. The body shifts its energy resources toward fighting off a life threat, or fleeing from an enemy. The SNS signals the adrenal glands to release hormones called adrenalin (epinephrine) and cortisol (Endocrine System). These hormones, together with direct actions of autonomic nerves, cause the heart to beat faster, respiration rate to increase (Respiratory System), blood vessels in the arms and legs to dilate, digestive process to change and glucose levels (sugar energy) in the bloodstream to increase to deal with the emergency. The SNS response is fairly sudden in order to prepare the body to respond to an emergency situation or acute stress, short term stressors. Once the crisis is over, the body usually returns to the pre-emergency, unstressed state. This recovery is facilitated by the PNS, which generally has opposing effects to the SNS. But PNS over-activity can also contribute to stress reactions, for example, by promoting bronchoconstriction (e.g., in asthma) or exaggerated vasodilation and compromised blood circulation. Both the SNS and the PNS have powerful interactions with the immune system, which can also modulate stress reactions. The central nervous system is particularly important in triggering stress-responses, as it regulates the autonomic nervous system and plays a central role in interpreting contexts as potentially threatening. Chronic stress, experiencing stressors over a prolonged period of time, can result in a long-term drain on the body. As the autonomic nervous system continues to trigger physical reactions, it causes wear and tear on the body. It's not so much what chronic stress does to the nervous system, but what continuous activation of the nervous system does to other bodily systems that become problematic.
The signal transmission of the nervous system is fast because neurons are interconnected, but the functions are more short-lived. Signal transmission in the endocrine system is slow, since hormones must travel through the bloodstream, but the responses tend to last longer.
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