In this video, you’ll understand how nerves such as the axillary, suprascapular, upper and lower subscapular nerves innervate the six intrinsic shoulder muscles which include the deltoid muscle, supraspinatus, infraspinatus, teres minor, teres major and subscapularis. Watch to learn more.
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 innervations of the intrinsic shoulder muscles.
Now, if you remember from my previous video, the intrinsic shoulder muscles are muscles that are contained fully within the shoulder. So, they originate mostly from the scapula and insert on the proximal humerus.
Those are the muscles that we’re going to talk about. Those are muscles like the deltoid muscle, supraspinatus, infraspinatus, teres minor, teres major and then, on the anterior surface we have subscapularis. Those are the muscles that we’re going to talk about and what the innervations of those muscles are.
When it comes to innervations, there are three main names I want you to remember:
- Axillary nerve
- Suprascapular nerve
- Subscapular nerves
With the subscapular nerves, of course, they are the upper and lower subscapular or you can call them the superior and inferior subscapular nerves.
So, axillary nerves and then, the other two, makes sense, scapula, right? We’re dealing with the shoulder muscles and the scapula is a big part of that. So, suprascapular nerves and subscapular nerves. These are the nerves that are going to be doing the innervations of the intrinsic shoulder muscles. That’s the order that we’re going to take them.
Let’s first start with the axillary nerve. The axillary nerve, if you remember when we looked at the brachial plexus, that is going to come from the lateral branch of the posterior cord. The lateral branch of the posterior cord is this axillary nerve. That axillary nerve, if you remember when we looked at the gateways of the posterior scapular region, that is going to go through the quadrangular space, and then, it’s going to innervate these two muscles: the deltoid muscle or deltoideus muscle and teres minor.
Let’s move on to the next nerve that is the suprascapular nerve. That suprascapular nerve, you can see it here coming off of the superior trunk and you remember this is a nerve that extends laterally and posteriorly and it goes through the suprascapular notch, the suprascapular foramen, that’s one of the gateways.
This is the nerve, remember? “Army goes over the bridge. Navy goes under the bridge.” The nerve is the navy in this case, and that’s going under the transverse scapular ligament. If that sounds like a totally different language, go back and watch the video where I spoke about the gateways of the posterior scapular region and you’ll get that one time. You’ll understand exactly what I’m talking about.
So, it’s basically coming back and going through that scapular notch, and it’s going to innervate these two muscles, supraspinatus and infraspinatus. So, suprascapular is going to go back and it’s going to go through the suprascapular foramen and innervate supraspinatus and infraspinatus.
Then, we have the subscapular nerve. Remember, we said we have the upper subscapular nerve and the lower subscapular nerve. Or, the superior and the inferior.
Alright, so since these are both subscapular nerves, both of them are actually going to innervate subscapularis which is this one that you see here highlighted in red. Subscapularis, it makes sense if this is named subscapularis for both of the subscapular nerves to innervate that muscle. So, upper and lower or superior and inferior subscapular nerves are going to innervate that subscapularis muscle. If you remember, when we looked at the brachial plexus, these two nerves come off the posterior cord. Alright, so that’s the upper and lower.
Then, the lower by itself, without the help of the upper is going to innervate teres major, which is this muscle shown here. It kind of makes sense. If you look at the arrangement, the teres major is inferior to subscapularis. That’s going to get the inferior scapular nerve. It just makes sense. At least I think it does. So, subscapularis gets innervation from both upper and lower subscapular nerves. Teres major gets innervation from just the lower or the inferior subscapular nerve.
That’s pretty much it. Let’s do our quick review. Here, we have deltoideus, or the deltoid muscle and teres minor. Those are both geting innervated by the axillary nerve. Then, we have supraspinatus and infraspinatus and those are both going to get innervated by the suprascapular nerve. Lastly, we have subscapularis and teres major. Both of them are getting innervated by the lower subscapular nerve, and subscapularis alone is going to get innervated by the upper subscapular nerve.
That’s pretty much it for this video. If you enjoyed this video, you got some value from it, click on the ‘like’ button right beneath if you’re on YouTube and you can also subscribe by clicking on the ‘Subscribe’ button above.
But, most of all, make sure to come over to the website at interactive-biology.com for more Biology videos and many other resources to help make Biology fun. This is Leslie Samuel. That’s it for this video and I’ll see you in the next one.
|Deltoideus||(exact opposite of the insertion of trapezius muscle)|
Inferior margin of the spine of the scapula, lateral margin of the acromion, and lateral third of the anterior clavicle.
|Deltoid tuberosity of humerus.||Axillary nerve (C5, C6)||Middle portion: Abducts arm at shoulder.
Posterior portion: laterally rotates and extends arm at shoulder.
|Suprasipnatus||Supraspinous fossa of scapula.||Superior aspect of greater tubercle of humerus.||Suprascapular nerve (C5)||Helps deltoid abduct arm at shoulder by drawing humerus toward glenoid fossa of scapula.|
|Infraspinatus||Infraspinous fossa.||Middle facet of the greater tubercle of the humerus.||Suprascapular nerve.||External rotation|
|Teres Minor||Upper 2/3 of the posterior surface of the lateral border of the scapula.||Lower facet of the greater tubercle of the humerus.||Axillary nerve.||External rotation and adduction of the humerus.|
|Teres Major||Lower lateral border and inferior angle of scapula.||Medial lip of intertubercular (bicipital) groove of anterior humerus.||Lower subscapular nerve (C5, C6)||Adducts, medially rotates, and extends arm at shoulder.|
|Subscapularis||Subscapular fossa of scapula.||Lesser tubercle of humerus.||Upper and lower subscapular nerves (C5, C6).||Medially rotates arm at shoulder.|