Ever wonder how our body knows how to do things and when to do them? There’s an incredibly complex signaling system in our bodies, working ALL THE TIME, without us having to do anything about it. Isn’t that cool?
Before you answer, I should inform you. It’s cool. It’s really cool.
If you say so.
Today I want to talk about the autonomic nervous system. “Autonomic” can be broken down into the roots auto = self, and nomos = arrangement or law. So, it’s the branch of the nervous system that is responsible for self-regulation. And when we’re talking about self-regulation, we’re talking about regulation of all kinds of bodily functions: from how quickly you breathe, to how much you salivate, to how big the pupils of your eyes are.
The autonomic nervous system is divided into two opposing forces: the sympathetic influence, and the parasympathetic influence. Both forces are acting upon every bodily system at all times. It’s like playing tug-of-war between two evenly-matched sides. There’s a balance point between the two opposing forces, and a dynamic system that keeps the balance point in place.
You can see an example of this kind of dynamic equilibrium in the first 25 seconds of this video:
So, what do the sympathetic and parasympathetic systems actually do?
I’ll break it down for you.
The sympathetic system is the “fight or flight” system. I like to remember it as, “everything you want to be doing while you’re running away from a lion.”
(well….hopefully more successfully…..)
So, what would be helpful when you’re running away from a lion?
You want your muscles to work really, really well. So you’re going to make sure they get a really good oxygen supply. You’ll dilate your muscular blood vessels, and your heart will beat faster and stronger to make sure enough oxygen is getting to your muscle cells. You’ll also breathe harder and deeper, making sure you have a lot of oxygen in your blood for maximum delivery.
What else? Well, you’ll want to see really well while you’re running away. So your pupils will dilate to a bigger size to let more light in.
And you’ll also want to inhibit a couple of parasympathetic functions, which… well, you’ll see why in a minute.
The parasympathetic system is responsible for the “rest and digest” functions.
Basically, it’s “everything that your body needs to do…unless you’re running away from a lion!”
The parasympathetic system lowers your heart rate and blood pressure. It slows down your breathing. It constricts your pupils and narrows your blood vessels to direct blood flow from your muscles to other important organ systems. It lets your eyes make tears.
The parasympathetic system increases salivation, which helps in the digestion process. It also increases the movement of the digestive tract, allowing you to digest food and excrete waste.
(Helpful tip: Avoid excreting waste while running away from a lion.)
Usually, these systems find an equilibrium point and stick with it, dynamically pulling against each other to maintain it. And they also react to stimuli, changing the equilibrium point as necessary to adapt to daily needs.
Let’s talk about heart rate as an example. A normal heart will contract about 60-100 times per minute. This represents the physiological balance between the sympathetic and parasympathetic influences. At rest, (such as when you’re sleeping), the influence of the parasympathetic function will increase, and your heart rate will slow. When you’re exercising, the influence of the sympathetic function will increase, and your heart rate will speed up.
Another example: your eyes aren’t completely dilated or completely constricted at any one time; they usually hang out around a particular size (that changes slightly according to age). They use the sympathetic and parasympathetic systems to adapt the diameter of the pupil to the amount of light the eye is receiving.
Then, when the particular condition that’s pulling the system in one direction (say, toward the sympathetic side of things) disappears, the other system (the parasympathetic side, in this case) will exert enough influence to bring the systems back into their favorite physiological set point.
How is that not cool?
Your operational definitions are problematic.
It’s still not cool enough? Fine. I hear sex sells.
Fun with autonomics!
The sympathetic and parasympathetic systems are both involved in sexual activity. The parasympathetic system is responsible for arousal, and the sympathetic system takes care of things such as male ejaculation. The mnemonic to remember which does which? “Point and Shoot”. See, doctors are funny!
“Funny”… “Cool”… “Fun”…. You see, this is what I’m talking about. I’m getting you a dictionary for your birthday.
::Sigh:: Another one?
The other ones clearly haven’t helped.
Okay, fine. It’s not cool and doctors aren’t funny. But I still think it’s pretty awesome. So there.
Oh, Dr. G. We really need to get you a life.
It’s going to have to wait till after residency.