 Hey everybody, Dr. O here. This video I want to cover some terminology that's going to help you as you learn the musculoskeletal system or your skeletal muscles. We're going to start with origin, insertion, innervation, and action, just so you know this is not a kinesiology class. I'll come back through and do a round of kinesiology videos where I do go through for each muscle, each origin, insertion, innervation, and action. But location and action are the primary focus right now. Like I said, I've done that in the past. I'll come back and do another kinesiology series in the future where I mine even deeper. Now, I do want you to know what the terms mean. So let's start with origin and insertion. So most muscles have two attachment points, and origin and insertion. Here's how I remember them. The origin is usually going to be the most stable ends. Like if you look here, you see the biceps. When the biceps break, I contract, the movement is happening at the elbow. That means the origin of the biceps is going to be up in the shoulder, the part that's not moving when that muscle contracts. The insertion is going to be the more mobile end. So the origin of a muscle is the more stable or fixed end. The insertion is the more mobile end. Another hint, almost always, the origin is usually proximal, and the insertion is going to be distal. So that's how you tell the difference between an origin and insertion. They're both attachment points. Which one's moving more? That's the insertion. Then we have innervation. Innervation is just which nerve controls that muscle. So I'm not asking you to know that at this level right now, but I will come back through and explain the individual nerves that control individual muscles. All right, and then we have action. What does the muscle do? So the action is good. So like I've already mentioned, the biceps brachii is going to flex the elbow, but it also is a supinator. So it actually is going to have two key actions. Some muscles have a whole lot of actions. Some just have one. So that's origin, insertion, innervation, and action. So you're going to see that a lot of times you're going to have several muscles that are going to have the same actions. You can even see here on this one image, the biceps brachii, the brachioradialis, and the brachialis are all involved in elbow flexion. So let's go into a little bit more terminology here. So first, muscles are either going to be an agonist. So the agonist or prime mover when it comes to elbow flexion is the biceps brachii. So the agonist is the muscle that produces a particular movement. Reason agonist is important is because muscles then have antagonist, and antagonist would be any muscle that opposes that movement. So for smooth movement, for me to flex my elbows here, it's just as important that the elbow extensors like the triceps relax as it is the elbow flexors like the biceps contract. So an agonist or prime mover is the key muscle that does some action. The antagonist would be any muscle that opposes that action. So the antagonist to the biceps is the triceps because the triceps extends the elbow, it straightens the arm back out. But we usually only call one muscle the agonist or the prime mover. So other muscles that have the same action are going to be given different names. They're usually going to be called synergists. As you can see here, the brachioradialis and brachialis are both being called synergists. So they're smaller muscles that assist that prime mover, the biceps. Sometimes they initiate the movement like another example is abduction of the shoulders. The deltoid is the most important shoulder abductor. So it'd be the prime mover or agonist. But the little supraspinatus muscle there, one of your rotator cuff muscles, it initiates the action. So I'd call that a synergist. There are other synergists that their job is actually to stabilize an area so they hold an area still so that an agonist or prime mover can do its job. Those would be called fixators. So the key words there are agonist is the muscle that does something, a particular action. Antagonists oppose that muscle and do the opposite action. And then synergists are going to be any muscles that help that prime mover do its job. But then you can use the term fixator if you want, but I won't make a huge deal out of that. So this picture is showing you picking up a cup to take a drink. So obviously to do that, it takes way more than one muscle. If you take kinesiology, you know that lots more muscles than even this is involved. But we're just saying the biceps is the primary muscle to flex that elbow so I can take this drink of milk or whatever it is. So that's going to be the agonist. And you have all these other muscles that are helping. Those would be your synergists. And if they stabilize an area, they're called fixators. So don't fixate too much on those last few terms. But origin and insertion are the two biggest terms. Action, I'll talk about the action of every muscle we talk about. Those are all very important terms. And then agonist versus antagonist also important. Okay. I hope this helps. Have a wonderful day. Be blessed.