God Impulse by Nelson Kevin

Author:Nelson, Kevin [Nelson, Kevin]
Language: eng
Format: epub
ISBN: 9781847378323
Publisher: Simon & Schuster UK

Figure 14: Walter B. Cannon’s journal entry recording when the momentous idea for “fight or run” first came to him.

We now understand that the adrenaline surge that primes the body for fight or flight has been fundamental to our evolutionary development from fish to human beings—its circuitry resides in the evolutionarily oldest and most primitive region of our brain.

Such a powerful system must not go unchecked. The sympathetic nervous system that acts with the adrenal gland is one of two great nerve and chemical systems that Cannon said stood in balanced opposition to each other. The adrenal gland and sympathetic nerves together act against their opposite—the parasympathetic nerves. In the call to action, the sympathetic nervous system dominates; the parasympathetic takes over when we’re resting. The parasympathetic nerves use the chemical acetylcholine to communicate their impulses to other tissues, for example to slow the heart rate or speed the movement of food through the gut.

The sympathetic and parasympathetic combine to form the autonomic nervous system. The autonomic nervous system controls the internal organs or “vegetative” functions, determining the internal milieu. It is “autonomic” because it governs our organs without needing, and rarely benefiting from, our conscious will. We do not have to consciously will each heartbeat or breath—that is the job of the autonomic nervous system. The fight-or-flight response is a fundamental mind-body link—a way that mental stress acts on the body.

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