Let’s take a look at three more of the six intrinsic shoulder muscles: suprasinatus, infraspinatus, and teres minor, and learn more about their origins, insertions and actions.
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 talk about three more intrinsic shoulder muscles. That would be supraspinatus, infraspinatus and teres minor.
I wanted to take this together because it’s easy to remember their insertions when you look at the three of them together. Let’s get right into it and deal with the first muscle which would be supraspinatus.
If you remember, when we looked at the scapula, we looked at the fact that on the posterior or the dorsal surface you have the spine of the scapula that we’re showing in this model right here. Above that, we have the supraspinous fossa. Below that, we have the infraspinous fossa.
The supraspinatus muscle is going to originate right there in that supraspinous fossa. From all of the supraspinous fossa, that is the origination point of supraspinatus.
Where is it going to insert? It’s going to actually come through here and go under the acromion and then, insert right here on the superior or the upper facet of the greater tubercle. Remember, we have the upper, the middle and the lower facet. On the upper facet, that’s where we have the isertion point for the supraspinatus.
Now, what’s going to happen when this muscle contracts? It comes from the supraspinous fossa to right here at the top, pretty much of the greater tubercle, the superior and the upper facet of the greater tubercle. When that contracts, what’s that going to do to the humerus?
Well, that’s going to cause abduction. It’s going to actually initiate the process of abduction when the supraspinatus muscle contracts, just based on where it originates, where it attaches. It’s not a huge muscle so it doesn’t do all of the abduction, but it does initiate that process.
Let’s move on to the next one which would be the infraspinatus. You can see that here and it’s originating from the infraspinous fossa, and then, it’s going to insert on the middle facet of the greater tubercle of the humerus. So, we’re going from origin to insertion.
Now, what’s going to happen when this muscle contracts? That’s going to cause external rotation of the humerus. You’re going to externally rotate your arm, and that’s going to be aided by the contraction of infraspinatus.
Then, we’re going to look at the third one which is the teres minor. You can see teres minor over here. I didn’t show infraspinatus on the previous picture like this, but infraspinatus is right here. Teres minor right here, that’s going to be slightly inferior to most of infraspinatus. That’s going to originate… Here we have the lateral border of the scapula, teres minor is going to originate from the upper 2/3 of the posterior surface of the lateral border. Then, it’s going to insert on the lower facet. From the upper 2/3 of the posterior surface, lateral border inserting right here on the lower facet of the greater tubercle of the humerus.
What is that going to do when it contracts? It goes from here to here and remember, we’re moving the bone from the insertion point towards the origin. That’s going to cause some external rotation. Okay some external… Let me try to make that a little round so that, it shows the rotation. And also, it helps with adduction. So, if we have the humerus horizontally here, it’s actually going to cause adduction moving the humerus closer to the trunk.
When we look at these three muscles and we look at the origins and insertions, you can see specifically the insertions, which is why I wanted to put these together, we have the upper, middle, and the lower facet of the greater tubercle, those are the insertion points for the supraspinatus, infraspinatus, and teres minor.
Let’s do a quick review. Here, we have muscle that’s called supraspinatus. The origin would be from the supraspinous fossa and that is going to insert on the superior facet of the greater tubercle of the humerus, and the action is going to be initiating abduction of the humerus.
Then, we have this muscle which is infraspinatus, which is inferior to the spine of the scapula. That’s the name. The origin would be the infraspinous fossa. It’s going to insert on the middle facet of the greater tubercle of the humerus. The action is going to be external rotation.
Lastly, we have teres minor originating on the upper 2/3 of the posterior surface of the lateral border of the scapula (that’s a mouthful). We have it inserting on the lower facet of the greater tubercle of the humerus. In terms of the action, it causes external rotation and adduction of the humerus.
That’s pretty much it for this video. As usual, if you want more, you know what to do. Go to the website, interactive-biology.com for more Biology videos, other resources to help make Biology fun.
This is Leslie Samuel. That’s it for this video, and I will see you on the next one.[table “” not found /]