That Neuroscience Guy - Neuroscience Bites-Primary Motor Cortex
Episode Date: November 10, 2022Next in our series of Neuroscience Bites, we discuss the Primary Motor Cortex: a brain area important for controlling muscles all over the body. ...
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Hi, my name is Olov Krigolson and I'm a neuroscientist at the University of Victoria.
And in my spare time, I'm that neuroscience guy. Welcome to another neuroscience bite.
Today I want to tell you about one of my favorite parts of the brain, which a lot of people think
is pretty straightforward, but it's actually really amazing.
And that's the primary motor cortex.
Now, the primary motor cortex is located at the back of the frontal lobe,
right up against the central sulcus.
And like the name implies,
its main role is to control muscles.
So when neurons fire in the primary motor cortex,
basically muscles fire.
There's a pathway down that goes to the spinal cord and then out on the alpha motor neurons
to contract actual muscles.
So if you stimulate the correct part of the primary motor cortex, you'll get activity
and contraction in the corresponding muscle.
Now, in case you didn't know, I think most of you do, the organization is a little bit
backwards, as you say.
The left primary motor cortex controls the right-hand side of the body, and the right
primary motor cortex controls the left-hand side of the body.
So there's a crossover happening there.
Now, the other thing that's cool, and I'd encourage you to check out the blog.
So if you go to thatneuroscienceguy.com and you find the blog,
I'm going to put up a picture of the primary motor cortex where it is, but I'm also going to put up
a picture of something called the homunculus. Now, what that means is literally little man,
but in terms of the primary motor cortex, it has to do with representation. So some parts of our
body require tons of fine motor control and other parts not as much. So if you look
at the homunculus within the primary motor cortex, what you'd see is that a massive number of neurons
are dedicated to the face. And the reason for that is quite simple. The face is comprised of tons of
tiny little muscles or muscle fibers that basically allow you to have facial expression. So if you think about all of
the complexities of facial expression, it's because the primary motor cortex has this massive
representation for the face. Now, on the other hand, the representation for the shoulder isn't
that big because while the shoulder muscles are massive, the actual jobs they do don't
require the same amount of fine motor control as the face does. And conversely, the hands have
massive representation because of all the dexterity we have with our hands. So the organization of the
primary motor cortex is functional. Lots of neurons dedicated to things that need fine control,
is functional. Lots of neurons dedicated to things that need fine control, fewer neurons dedicated to things that don't need as much control. Now the input to the primary motor
cortex comes from motor planning regions, such as the supplementary motor area or the premotor
cortex, but it's been shown recently that the primary motor cortex can initiate simple movements,
very simple movements, without any input from the higher level motor planning
regions. And one last thing about why I think the primary motor cortex is so cool. There are several
teams of researchers in the United States and around the world that are using the primary motor
cortex to control robots. Imagine that. So basically, imagine you have a robot that has a
simulated biceps muscle. So what they do is they put a wire into the primary motor cortex that would correspond to that biceps muscle. So they'd find the part of the primary motor cortex that represents the biceps muscle. And when that neuron fires on there or that group of neurons in the bicep region, the primary motor cortex, the robot arm actually moves. And this has progressed
to the point where they have people wearing exoskeletons, so a complete skeleton of the body,
and they're mapping it into the brain. Now, you might wonder, why would you do that? Well,
what if you have someone that's a quadriplegic? They've lost their ability to move their arms and
their legs, and all of a sudden, they can move them again. Now, that's so
interesting that I'm going to do a full episode on that later. So this is a bit of a teaser.
Anyway, that is a little neuroscience bite on the primary motor cortex. Remember, check out the
website, thatneuroscienceguy.com. It's got links to Patreon, our Etsy store. It's got links to the
blog. And of course, please subscribe to the podcast. Thank you so much for listening.
I'll be back on Sunday for another full episode.
My name is Olaf Krigolsen, and I'm that neuroscience guy.
See you soon.