Law & Order and Ionic Current
I know, crazy title, right? I know exactly what’s going on in your head right now. I’ll even outline it for you.
1. You just did the dunh dunh sound from the TV show when you read my title
2. Then you’re like Cool, Mel is gonna talk about something besides science or writing fiction!
3. Then BAM, you see the words ionic current and you realize that alas, Mel is what she is and it’s going to have a science message in there somewhere.
4. Then you close this browser tab. ”No don’t!” I’ll say, ”cmon, you’ve got like 34 other tabs open. Close one of them, not this one! Jesus, reader. You don’t need Amazon open on two tabs.” (I’m pretty sure I’ve nailed this, amirite?)
Anyway, whether or not I was right with any of that, let’s get to the actual blog. Gasp!
Back in college, I was a TA for a physiology class. It was my dream come true. Melinda! I didn’t know you liked physiology, you’ll say, ya sassy thing. Har har, reader, nice one. Yes, it was awesome. I love the human body, and teaching others about it is just about as fun as it gets. Except one of the first lectures I led, when I had to teach about z discs (part of muscle anatomy) and I accidentally said z dicks in front of the class. My face got really red. But hey, it was an opportunity to talk about blood vessel vasodilation in the skin. Anyway, that was a little embarrassing but luckily after a few lectures I hit my stride. Then we got to talk about neuro, my absolute favorite topic. Insert heart eyes emoji, which is just the cutest emoji. I know, I know, it’s wildly anatomically incorrect. But whatevs. It’s still cute.
Anyway, we started talking about neuro. And the thing is with neuro, there are a lot of equations. You have to calculate voltage and current, and neurons form circuits so there’s a bit of math. I had to teach the formula for determining ionic flow across a cell membrane. Neurons are super good at keeping certain ions inside and other ions out. Then they open channels and WHOOSH, you get ions moving. The way they move (their current, I) is dictated by an equation. Current for ion x would be:
Ix = Gx (Vm-Vx)
Yes, I know, it was enough to make a bio major’s head spin. But once you look at the components, it’s actually very easy. G is a number representing the permeability of the membrane to that ion (x). In other words, how many channels are open for that ion to go through. It’s a probability value, from 0 to 1. Most of the time you use the extremes, 0 or 1. Easy, done. Then you get to the parentheses and OMG what the holy hell? Don’t panic. V stands for voltage and this little subtraction gives us the driving force for that ion. It is the difference between the current (bad choice of words, lemme start again), it is the difference between the present membrane voltage and where that ion wants the membrane to be. It‘s called the driving force because it represents the magnitude of push or pull that is acting on the ion.
So as I was teaching this equation I had a realization. Nothing in the world happens unless it has a reason and a way to do it. So think of Law & Order. We’ve all watched one or more versions of that show (my jam was SVU until they brought out the rape instrument and it was an ungodly large candle holder pillar thing and I was like you know I don’t think I can watch this anymore, but I did love Mariska). Anyway, we all know what the lawyers need to prove a crime- motive and opportunity, right? So that’s all this equation is showing us. The driving force for an ion is its motive, what drives it to move. And its conductance, G, is the ion’s opportunity to move. There can be a high driving force, but if the channels are shut, the ion can’t move. Kind of like, you may reeeally have to pee, but if that bathroom door is locked, ya ain’t getting in. You better have worn your astronaut grade diaper or you’re wetting yourself. This is not from personal experience. It happened to my friend, Welinda.
So you see? Even scary math can make sense if we figure out common grounds to begin the dialogue. This is why science communication is so important!
Your average neuroscientist, Melinda