The autonomic nervous system has two primary components: sympathetic (“fight or flight”) and parasympathetic (“rest and digest”). Each of these states can profoundly affect nearly every organ in the body.

There is one nerve more associated with the parasympathetic state than any other: the vagus nerve, or cranial nerve X.

Organs the Vagus Nerve Stimulates

Vagus means “wanderer”, and the nerve is so named because it innervates most of the body’s major organs. It has a strong effect on the gut especially (hence “rest and digest”), increasing stomach acid, pancreatic enzyme release, and bile release from the gallbladder, as well as increasing gut motility—making the intestines “move”.

It also encourages the liver and pancreas to keep your blood sugar balanced—makes sense, since the stress hormone cortisol encourages the liver to mobilize glucose.

As you might imagine, it also has a powerful effect on the cardiovascular system in terms of heart rate and blood pressure: our blood pressure and heart rates are lower when we’re relaxed, and higher when stressed.

The vagus nerve also increases blood flow to the kidneys, assisting with filtration and electrolyte balance. Vagus stimulation to the bladder encourages urine retention—which is one reason why urine release can occur in times of high stress or fear (that’s a function of the sympathetic nervous system, the opposite of the parasympathetic).

Hormones that Stimulate the Vagus Nerve (Or Vice Versa)

The functions of the vagus nerve are closely tied to a number of hormonal cues. What this means: balancing hormones can have a powerful effect on the body’s ability to moderate stress. If you’re constantly in “fight or flight,” here are some of the systems and hormones that are likely out of balance… or conversely, balancing these systems might help you to find a new set point nearer to “rest and digest.”

Relaxation Techniques: Stimulating the Vagus Nerve Directly

Perhaps even more useful in the moment of crisis are relaxation techniques that can hit all the organ systems at once, getting you you out of “fight or flight” mode and instead into “rest and digest” quickly.

All of the stress management techniques here will put you into a parasympathetic state. But perhaps the most profound approach is deep breathing. Any stress management technique worth its salt will put you in a state of deep breathing, such as yoga, meditation, or massage.

You also might try eating something, or even just chewing gum—the act of chewing “tricks” your body into thinking you’re about to eat, which stimulates the parasympathetic nervous system to get ready to digest.

Hydrotherapy is also a great way to calm down your nervous system—particularly the cold phase. You might think this would have the opposite effect—after all, an acute cold shock to the system isn’t exactly the most relaxing idea in the world. But because your body is a living system always seeking homeostasis (or balance), an initial sympathetic shock of this kind will apparently give way to a parasympathetic backlash. So try splashing your face with icy water, or even end your shower on cold!

The Upshot

You want to spend as much of your time in a parasympathetic state as possible—“fight or flight” should be relatively rare. These autonomic nervous states affect nearly every organ system, and they affect or are affected by quite a few hormone systems. So if you spend too much time in “fight or flight,” don’t ignore any hormone imbalance you might also have—it’s all interconnected!

Also, pick one or a few of the relaxation techniques to try for a quick exit the next time you find yourself in an escalating “fight or flight” state.