There’s been a lot written on the subject, so I’m going to talk about from the perspective that matters to most of my patients. This is another background article that will help make future posts make more sense. First, we need to understand the basics:

There’s the Central Nervous System (the brain including the eyes, the spinal cord)
If it’s not central, it’s peripheral right? The Peripheral Nervous System includes the Somatic Nervous System (muscle movements) & our friend the Autonomic Nervous System (ANS)
The ANS, our focus, is then divided into the infamous & unfairly maligned Sympathetic Nervous System and the Parasympathetic Nervous System. There’s also the Enteric Nervous System which innervates the gut, it’s part of the ANS as well.

Let’s start with a forest overview before diving into the branches of the ANS …

What does the ANS do for us? From a practical & clinical standpoint, I see it as the body’s basic approach (PNS) vs. avoid (SNS) system. It’s evolved to help us identify and respond to both danger / activation (SNS) and safety / connection (PNS) to keep us alive. It has wide-ranging effects on our body and mind; e.g. if our brain perceives danger, it can speed our heart rate up by 30 beats per minute + almost immediately or essentially stop the motility of our guts. Psychologically, having an imbalanced ANS is one culprit behind our difficulties letting go of worry or stopping ruminating or our difficulty coping with a strong emotion ~ all of which I call stress recovery.

As you can see in this great graphic below from Healthline (article is really good too), the ANS is connected to (innervates) all of our vital organs. I LOVE showing these types of diagrams to my patients who have trauma, significant anxiety or any other stress-related condition that also (almost without fail) have at least 1 or more symptoms related to the organs innervated by the ANS. In fact, if you really take a look, it might make sense why stress or trauma or anxiety or depression (all of which affect and are affected by the ANS as discussed in the last post) might come with gastrointestinal, visual, breathing or cardiac issues.

Often my patients have what are called “functional disorders.“ What is a functional disorder?? … Here’s a clue: it’s not a disorder that’s working well for you! ;) Traditionally, doctors and patients have thought of functional disorders as those where there isn’t evidence of objective findings of pathology; at its worst, they are thought of as “in your / my head.“

We’re talking about “syndromes”: chronic fatigue, irritable bowel syndrome, POTS (postural orthostatic tachycardia syndrome), fibromyalgia, cyclic vomiting, restless leg, interstitial cystitis, tinnitus, migraine, complex regional pain syndrome. What disorders are included may vary, but the message is clear: “we can’t find why you’re having these symptoms.“ It can be invalidating, frustrating and discouraging to hear these messages when, in reality, it usually reflects a lack of medical understanding (like anxiety used to be hysteria or a wandering womb or before that witchcraft) ~ even if that’s not communicated as well as it should be. If you think about the names that the diagnoses have, it reveals the lack of sophisticated knowledge behind them: “doctor, I just keep vomiting“: “you’ve got cyclic vomiting”; “doctor, I just keep have fatigue all the time“: “you’ve got chronic fatigue.“ Gee, thanks for the information, doc.

So what does functional actually mean if, as I’m suggesting, “made up“ or “it’s just stress“ is not a sufficient definition. It means that multiple bodily systems are not functioning together as they should. One such important system ~ though certainly not the only one ~ that keeps organ systems functioning in a homeostatic (= within a normal range) way is the ANS.

Besides stress-related physical conditions and / or functional disorders, keep in mind that a well-balanced ANS also helps us regulate our emotions which impacts just about everything in life.

So now that you have some context about how the ANS , let’s explore some simple, psychophysiological ways of understanding both the Sympathetic & Parasympathetic Nervous Systems.

https://www.healthline.com/health/parasympathetic-nervous-system#psns-vs-sympathetic

With the Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS), there is no perfect metaphor because of the complexity of these systems. However, I haven’t yet found a metaphor that I like more than the PNS is like the brake of your car and the SNS is like your gas pedal. Let’s flesh that out …

SNS: The SNS has become synonymous with the “fight or flight“ ~ if you haven’t heard of the “fight or flight“ response, it’s our bodies mobilizing for a huge threat (real or imagined) which allows us to be ready for a fight or to flee. Doesn’t sound sympathetic does it? That’s how I remember, it’s the opposite of what it sounds like :)

As it’s usually explained by psychotherapists, the “fight or flight“ response is useful when being chased by a bear but not so much when Jan at the office emails you in that passive aggressive tone again.

Here’s the truth though: it’s actually not nearly as common as people think, or therapists describe it as, to be in “fight or flight.“ “Fight or flight“ is actually a major mobilization of the SNS ~ think full-blown panic attack, not getting anxious before a meeting. Believe it or not, the SNS is slower to activate than the PNS and it does take some time to recover from it when it’s in full bloom (i.e. “fight or flight“)

While the SNS is much maligned, if you didn’t have your body’s version of the gas pedal, you wouldn’t get very far! As I said, a lot has been written about what the SNS to prepare us for action that is easy to understand: it increases our heart rates, constricts our blood vessels (leading to colder extremities), increases our blood sugar, sends out the troops of the immune response, etc.

But for our purposes, it’s the gas pedal … it’s activation. And for many people coming to see me, it’s revving a little too much. Or … there’s something awry with the brake pedal …

PNS: The PNS is often called “rest & digest“ or is associated with the “relaxation response.“ It’s responsible for normal functioning of organs and does have the ability to “put the brake“ on the SNS. In fact, what’s usually happening physiologically when people (or therapists) say that you’re in “fight or flight“ is actually your PNS (brake) withdrawing. Here’s a more extreme example to make the point: a hot flash (so I’m told) can feel pretty similar to a panic attack … but studies show that it’s actually PNS withdrawal, not “fight or flight.“

The main thoroughfare, anatomically, for the PNS is through the Vagus Nerve (which one of my patients calls the “Las Vegas nerve“ :) … it’s pronounced the same). The Vagus Nerve may be familiar, perhaps, for anyone who knows about severe depression ~ people with Treatment-Resistant Depression may be able to have a surgically-implanted device that electrically stimulates the Vagus Nerve to relieve their depression if other treatments have failed. The Vagus Nerve is fairly synonymous with the PNS (Parasympathetic).

So now we can talk about concepts like Vagal Tone (i.e. the strength of your PNS). As it turns out, your Vagal Tone is a pretty incredible predictor of lots of important things: how likely you might be to die after a cardiac event, whether you have debilitating PTSD or a major depressive disorder, how compassionate you are (!), how likely you are to do your sport incredibly well and your ability to successfully regulate your emotions. How could that be?? Well, all of these abilities involve the ability to balance stress and activation on a physiological level … and that’s an ANS function.

While there are lots of medications to quiet down the SNS, there are no medications or even many non-invasive ways to improve the Vagus Nerve. However, there’s a simple breathing technique (Resonant Frequency breathing) that’s been shown to directly improve the tone (think about this like improving your muscle tone) of the Vagus Nerve and, if you read the first post this will be review, activate the all-important Pre-Frontal Cortex … all of which improves symptoms of stress-related conditions. That’s the big picture of why we care about this: to improve stress-related mental & physical health conditions, improving ANS functioning can be very helpful.

OK, here’s my bottom line:

the ANS has to do with our organ functioning and our mental / emotional functioning
the SNS is our gas pedal and the PNS is our brake pedal; usually, when people come to see me, the brake pedal needs some work
When we improve that imbalance (more on how in the future), we see better emotion regulation and improvements in stress-related mental & physical health conditions

Congratulations to you! That was a lot of science! My philosophy is that normal, non-scientifically trained people are capable of understanding all of this; the more it’s out there, the more it becomes part of the cultural conversation. For example, when I started practicing clinically, I think it’s unlikely my patients would have been able to understand and identify the function of the amygdala, now nearly every single one can. Beyond that, they use it to understand what is happening for them and elevating their mindfulness about emotional stress, how to identify it and respond skillfully.

That’s what I hope happens with the ANS, understanding the role of the PreFrontal Cortex in emotion regulation and topics like my next post on Heart Rate Variability …

References:

Pereira, V. H., Campos, I., & Sousa, N. (2017). The role of autonomic nervous system in susceptibility and resilience to stress. Current Opinion in Behavioral Sciences, 14, 102-107.
Kreibig, S. D. (2010). Autonomic nervous system activity in emotion: A review. Biological psychology, 84(3), 394-421.