 So here's the scenario. You have, you know those like styrofoam rocks that like why I don't know and okay, whatever. You know those styrofoam rocks that are like decorative things that you put around your lawn, but they're made out of styrofoam? Imagine that you went up to pick up one of those styrofoam rocks. And, but you didn't know it was a styrofoam rock. And you're like, you're trying to impress people around you. And so you're going to be like, dude, I'm the rock instead all my myofibers are filled with lots of myofibrils because I'm the biggest stud on the planet. And so you go over to the rock and you're like, watch me lift this rock. But you think it's a real rock, not a piece of styrofoam. What's going to happen? You're totally kind of like, hopefully not throw the rock into your face, but you're going to apply a great deal of force to the rock and that's actually styrofoam. And you're going to apply too much force to that rock to just lift it. You're actually going to fling it. That's going to be a sad story for you if it hits you in the face, which would be really sad. If you thought it was styrofoam, you're like, I can lift this styrofoam rock. You know, it was actually, actually heavy. Then there's going to be this like, whoa, like your brain does not match the reality and your muscles wouldn't be able to lift the rock if you didn't know that it was actually a rock. Did you follow what I just said? How? How is that possible? Well, first of all, pat your brain because it's amazing. And in the next section of this course, we're going to talk for six lectures all about the nervous system. So we will have a great deal of time to figure out like, how does our brain do this? But at this stage in the game, we can just accept that central nervous system brain sends the message to the skeletal muscle cell to contract. And it sends some kind of a message. And I'm going to tell you that it's going to do it through a neuron. And here's the scoop. One neuron can actually innervate more than one skeletal muscle fiber. Did you hear that? So one, okay, I don't know how I'm going to do this for you. I'm going to imagine I'm doing a cross-section. So here are a whole bunch of myofibers. I'm making you a fascicle. Look at that fascicle. And this is a somatic motor neuron. But look what I'm doing to my neuron. I'm actually making my neuron barf neurotransmitter. And we'll talk about all those details. So don't stress out. But I'm going to have it barf neurotransmitter and send the message. It's time to contract, doggy. It's time to contract to many different myofibers. So the brain says, okay, Joe, Joe, the neuron, please activate one, two, three, four, five myofibers. And all five of those myofibers are going to contract. The brain knows that if we activate Joe, we're going to get five myofibers. The brain also knows that if we activate Larry, Larry only innervates one myofiber. So Larry is going to send, if Larry gets activated, he is sending a message to one. We're going to get a finer message. If Joe gets activated, we're going to throw the rock into the air. If Larry gets activated, we can like draw pictures on Larry. Okay, what is this? This is called a motor unit. A motor unit equals one somatic motor neuron. And the somatic motor neuron is that. There's one. Joe and Larry are somatic motor neurons. Relax. It's one somatic motor neuron plus all the muscle fibers, the myofibers, it innervates. So a motor unit is one neuron and all the myofibers. Now, here's the interesting thing. Now think about this for a second. In your eyes, you have motor units where you have one neuron that's controlling. One message from one neuron that is controlling like 40 different muscle cells. And all this stuff is tiny. In your thigh muscle, you have one motor unit that is, you have one motor neuron that is controlling hundreds of muscle fibers. One message from the neuron to the thigh muscle is going to say 500 of you are contracting. One message from the neuron to the eyeball muscle is going to say 40 of you guys are contracting. Your motor units, the size of the motor unit is going to determine the quality of action that you can do. Your motor units in your hands are small. One motor neuron is controlling a small number of myofibers. Each one is controlling a small number of myofibers. And that means that you can do this kind of fine movement. One motor unit in your feet, well, I mean, some people can solve Rubik's cubes with their feet, play the piano with their feet, do amazing things with their feet. But usually, most of us are quicker with our fingers. I can play the piano with my fingers. And nobody wants to see me trying to play the piano with my feet. That just would be a highly disturbing phenomenon. So motor units let us really fine tune our movements. So think about the brain who's ultimately controlling, the brain and the spinal cord are ultimately controlling how many motor units are activated in any given situation. Hopefully, you're like, holy crud, that's crazy talk. The last thing I want to talk about, I want to zoom way out, like, woo, holy zooming out. We've been right in the middle of the myofibers and we've been looking at proteins and talking about sarcomeres. Let's zoom way out and let's look at pairs of muscles because especially, well, everywhere, we have our muscle organs come in antagonistic pairs.