You’ll love today’s video. Watch and learn from Leslie as he teaches us how to remember more effectively the origins, insertions, and actions of the three deep extrinsic shoulder muscles. Discover a systematic way to make it easier for you to study.
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 deep extrinsic shoulder muscles.
Last video, we talked about the superficial extrinsic shoulder muscles. Now, we got to deal with the deep stuff. So, let’s get right into it.
Those deep muscles are:
1. Levator scapulae
2. Rhomboideus minor
3. Rhomboideus major
And, you might see them (2 and 3) called rhomboid minor and rhomboid major.
We’re going to look at these three muscles. First, let’s look at levator scapulae. You can see that here. I’m not going to give the detail about all of it right now because I want to deal with them together for a specific reason.
This muscle that you see here outlined in red is levator scapulae. Then, we have rhomboideus minor, and we have rhomboideus major. Once again, levator scapulae, rhomboideus minor, and rhomboideus major.
Now, these are going to be really easy to remember the origins, insertions, and the actions because we have a little system for doing so.
Let’s start with levator scapulae. I wan you to remember these numbers: 42 and 24 — 4-2-2-4. If you can remember this, you can remember everything that you need to know when it comes to the origins, the insertions, and the actions. What do I mean?
Okay, here we have the spinal column, and you can see we have our cervical vertebrae, and then, we have our thoracic vertebrae. How many cervical vertebrae do we have? We have seven, and then, we have twelve thoracic. We don’t even need all twelve right now.
But, what I want you to remember is 4-2-2-4, and how that works is very simple.
We have the first cervical vertebrae… C1, C2, C3, and C4. Those are going to be the origins for levator scapulae because levator scapulae, you can’t see it here, but when it projects up or from the origins, there are actually four tendons. It actually splits into four, and then, you have those four tendons. Let me draw that in red. I’m going to try to draw it here. Okay so, we have one, two, three, and four. It’s splitting in four. What that’s going to do is it originates right here on the transverse processes of C1 through C4. You got that first part, right? C1, 2, 3, and 4.
Then, we have the next number, “2.” What’s going to happen is we’re going to skip the next two cervical vertebrae, and we’re going to go down to the next two after that. So, we did 1, 2, 3, and 4, and we’re going to skip 5, and 6. Then, C7 and T1 right here, that’s the origin of rhomboideus minor.
So, the spinous processes of C7 and T1, those are the origins for rhomboideus minor and then, let’s use a different color… Oops! I got rid of the colors. Let’s do that again. So, we have 1, 2, 3, 4. We skipped two and then, we have, let’s do this in red, 1, 2. So then, we have C7 and T1. It’s okay that I have to do it again because then, you have to repeat it.
And then, we have, let’s do another color, green. Okay, I got it right. The next four, that’s going to be T2, T3, T4, and T5, those are going to be the origins of rhomboideus major. So, 42, and then, flip it around, 24. That gives us the origins.
One difference is the first four, that’s going to be the transverse processes, we skip the next two, and then, we have the spinous processes of C7 and T1, and then, the spinous processes of T2 through T5. That’s our origins of these three muscles.
Wasn’t that easy? Well, it’s just as easy when it comes to the insertions. How isit just as easy? Here we go.
Here we have the spine of the scapula, and this is the base of the spine of the scapula. Levator scapulae, it’s going to insert on the medial border. All of these are on the medial border, but it’s going to be right above the base of the scapula so, superior to the base of the scapula, the medial border of the scapula above the base of the spine of the scapula.
Rhomboideus minor, that is going to insert on the medial border but, right at the base of the spine of the basal scapula. Then, rhomboid major, that’s going to be the medial border below the base of the spine of the scapula. So, we have above the base of the spine of the scapula, right at the base of the spine of the scapula, and below the base of the spine of the scapula. All of them are going to be right there on the medial border.
What is it going to do?
Well, if levator scapulae contracts, what’s that going to do? That’s going to elevate the scapula. If rhomboideus minor contracts, what’s that going to do? That’s going to cause retraction, so it’s moving backwards. It’s moving towards the midline. And, rhomboideus major, that’s also going to cause retraction. Depending on how things contract, that can also cause rotation of the scapula.
Pretty easy to remember, right? If it’s levator scapulae, elevation. And then, we have retraction and rotation depending on how these muscles contract.
So, that’s pretty much it. Let’s do our quick review.
The first muscle, that would be levator scapulae. The origins are going to be transverse processes of C1 through C4. The insertion is going to be the medial border of the scapula above the base of the spine of the scapula. And, the action is going to be to elevate the scapula.
The next muscle would be rhomboideus minor. The origin would be the spinous processes of C7 and T1. The insertion would be the medial border of the scapula at the base of the spine of the scapula. The action, that’s going to cause retraction of the scapula.
Lastly, we have rhomboideus major. The origin is going to be the spinous processes of T2 through T5. The insertion is going to be the medial border below the spine of the scapula, and the action, it’s going to cause retraction, and it’s also going to cause rotation of the scapula. When the scapula rotates, I didn’t say that in the last slide, it’s rotating in a way that’s causing the glenoid cavity to be depressed. So, that’s rotating in that direction.
That’s pretty much it for this video. As usual, you want more of this kind of stuff, more videos and more resources to help make Biology fun, you know what to do, and if you don’t, now you know. Head on over to the website at www.interactive-biology.com.
This is Leslie Samuel, that’s all for this video and I’ll see you in the next one.[table “” not found /]