In this episode, we learn more about the first of six intrinsic shoulder muscles, the deltoid muscle. Here, Leslie teaches us again, a better way to remember its origin, insertion and action based on what we’ve learned so far from previous videos.
Transcript of Today’s Episode
Hello and welcome to another episode of Interactive Biology TV where we’re making Biology fun. My name is Leslie Samuel, and in this video, I’m going to be talking about the deltoideus muscle which is the first and the most complicated or complex of the intrinsic shoulder muscles.
We’re going to talk about the origin, insertion, and action. Let’s get right into it.
As I mentioned, this is the most complicated of the shoulder intrinsic muscles but, we’re going to break it down and we’re going to get it. To make it even more simple, I want to let you know that you already know the origins. You may not know that you know the origins, but if you looked at one of the previous videos, you do know the origins because the origins of this muscle is exactly opposite to the insertion of the trapezius muscle.
So, the origin would be and we’re going to go from… let’s go from posterior to anterior just for the fun of it. So, we’ll start from this middle picture here.
The first point of origin would be the inferior margin of the spine of the scapula. Remember with the trapezius, it was the superior margin. So, now we’re dealing with the inferior margin of the spine of the scapula. Then, from there, we have (let’s do that in green) not the medial acromion like the trapezius, but the lateral margin of the acromion. We go around here.
Then, on the other side that you’re not able to see here but you’re ale to see that here, that’s going to be the lateral third of the anterior clavicle. Remember? With the trapezius, that was the posterior clavicle, but here, we’re dealing with the lateral third of the anterior clavicle.
So, that would be the origin.
Now, in terms of the insertion, we already spoke about that in one of the earlier videos. But, right here, on the humerus, we have the deltoid tuberosity, a roughened patch right here. That is where it inserts. It’s coming from the origin point and it’s going down and inserting on this deltoid tuberosity.
Now, when you look at the structure or the make up of this muscle, you’ll see that we have, it’s almost like it’s three separate muscles, but there are three portions or three regions of this muscle. We have the anterior or clavicular section. We have the lateral or the acromial part. So, that would be this region here. Then on the back, we have the posterior or spinal section.
Depending on which aspect of this muscle is contracting, we’re going to get different actions. So, for example, just looking at where it originates and where it inserts, what happens if the anterior portion is contracting?
Well, it’s going to cause elevation of the humerus. So, you’re basically raising the arm forward — elevation of the humerus.
Now, what happen if the acromial or the lateral portion is contracting? What is that going to cause? Well, that’s going to cause abduction. So, you’re basically raising your arm, but you’re raising it horizontally.
Then, what’s going to happen if the posterior or the spinal section is contracting? That’s going to cause the exact opposite of the anterior section, so it’s going to cause not flexion but extension of the arm. So, we can have extension. We can have abduction, and we can have extension. Flexion, abduction and extension depending on what portion of the deltoideus muscle is contracting.
So, quick review. As usual, you can turn the volume down and quiz yourself.
The name of the muscle is the deltoideus muscle. The origin would be, let’s place here, the inferior margin of the spine of the scapula, the lateral acromion, and the lateral third of the anterior clavicle. The insertion would be on the deltoid tuberosity. You can’t see it in the picture, but you know that it’s under here, the deltoid tuberosity.
The action depends on which head you’re dealing with. If you’re dealing with the anterior or clavicular head, that’s going to cause flexion. If you’re dealing with the lateral or acromial head, you’re going to cause abduction. If you’re dealing with the posterior or spinal end, that’s going to cause extension of the arm, extension of the humerus.
That’s pretty much it for this video. As usual, if you want more like this and other resources to help make Biology fun, you know what to do. Head on over to the website. The URL is interactive-biology.com.
That’s it for this video. This is Leslie Samuel and I’ll see you in the next one.[table “” not found /]