Dr. Andy Galpin

They are more like a gradient or a toggle.

They're a dimmer switch more so than they are, you know, again, flipped on or flipped off.

So what happens is the intrinsic rate of that SA node is probably higher

than your resting heart rate.

In fact, it probably wants to beat more like 100 to 120 beats per minute.

Most people's resting heart rate is more like 60 to 80 beats per minute.

So you kind of have this vagus nerve that is constantly applying this drip of acetylcholine to naturally slow your heart rate down.

Now, this is actually a really cool mechanism because what it allows you to do is if you want to increase your heart rate, the very first thing you have to do is not necessarily turn on sympathetic drive.

It's just to reduce parasympathetic drive.

Another way to say that is imagine you're driving downhill.

Say you're in San Francisco or someplace that has a ton of hills.

and you're going at 60 miles per hour, and you decide you want to go faster.

Well, the initial instinct is to maybe hit the accelerator or hit the gas.

Think of that as the sympathetic nervous system.

But you don't actually have to do that.

The first step is just to make sure your foot isn't on the brake, the parasympathetic nervous system.

So kind of what's happening is at all times when you're driving, the vagus nerve is slowly keeping its foot just a little bit on that brake to keep you relaxed.

Now it's doing that again so that if you want to go faster really quickly, all we have to do rather than giving out additional resources like epinephrine or adrenaline or

All I actually have to do is stop us from slowing you down.

It's kind of one of those classic double negatives, right?