Hello everyone! This is Joao from Kenhub. Welcome to another tutorial!
This time I'm going to be talking about the muscles of the upper arm and the shoulder blade. Like you see here on this image, we have the humerus here, which is the main bony framework of the upper arm. And on your left side (sorry), you have here the triangular-shaped bone known as the scapula or also known as the shoulder blade.
Now, we are going to be discussing the different muscles that you can find within the humerus and also attached somehow to the scapula.
Now, as you know, you may split muscles into several groups based on different criteria, like innervation, functions, or even embryology. But on this tutorial specifically, we will be looking at these muscles or the muscles that have their attachment points, or lay-on, or their bellies are laying on these two bones: the humerus and the scapula.
Now, let’s look at the first topic here on our tutorial, the muscles of the upper arm, which I can tell you that can be also split into two groups. The first one, the ventral group, which includes the biceps brachii and also the bracialis muscle. Also, you can find another group known as the dorsal group, which includes the anconeus and also the triceps brachii.
Now, let’s start with the very first group here, the ventral group and with the first muscle of this list which you see here, highlighted in green. This is known as the biceps brachii. Now, the biceps brachii has, like the name indicates, is divided into two heads—now, the short head, as you can see here, and the long head of the biceps brachii.
Now, as you see here on these images where we highlighted the heads in green as well, you notice that the long head is originating right here from the supraglenoid tubercle of the scapula. And on the short head, you see that the origin point is right here on the coracoid process of the scapula. Now, these two heads will merge, then, to insert right here on the radial tuberosity of the radius. And also, as you can see, this portion right here, this is on the antebrachial faschia.
Now, let’s move on the second one on our list. This muscle here that you see highlighted on both of these images in green. Now, on the left side on this image, it’s found on its relaxed position, while on the right side is where you see it contracted. Now, can you guess what this muscle is? Well, it is, indeed, the brachialis muscle. Now, the brachialis originates right here on this point that you can see here—from the distal half of the anterior portion of the humerus and also the medial and lateral intermuscular septum. Now, it goes all the way to insert right at this point here on the ulnar tuberosity.
Now, taking a second look here on the list of the muscles of the upper arm to say that we just concluded the ventral group and going to move on to dorsal group to the first muscle on our list here, the anconeus muscle. You also see two images here where this muscle is highlighted and found on its contracted version and also relaxed version.
Now, this muscle originates from the lateral epicondyle of the humerus as you can see right here, and it goes all the way to insert on the olecranon of the ulna, right about here.
Now, the second muscle on the dorsal group is this muscle here that defines the dorsal portion of your upper arm. So a lot of people go to the gym to work on this muscle, and as you probably guess, this is the triceps brachii. Now, as the name indicates and as we’ve seen on the biceps brachii, the triceps brachii has three heads.
Now, the first one is seen here highlighted in green. This is known as the long head. The long head originates right about here on the infraglenoid tubercle of the scapula.
Now, a little bit more medially, you will find then the medial head which is also highlighted here in green. And you can see that this head is originating from the posterior surface of the humerus, a little bit distal from the radial groove. It also inserts on the intermuscular septum, more specifically on the medial portion of the intermuscular septum.
Now, the third head is seen here and, of course, found more laterally, and we call it then the lateral head of the triceps brachii, and it is originating right about here on the posterior surface of the humerus as well, but this time proximal to the radial groove. This head is also attaching to or originating from the lateral intermuscular septum.
Now, the three heads are merging as you can see on either of these three images. They will merge into this flat, relatively flat tendon and then insert on this portion right here on your elbpw on the olecranon of the ulna.
With the triceps brachii, we just concluded the last group of the muscles of the upper arm. We’re going to move on to another set of muscles that you can find attached between the scapula and the humerus. Now, keep in mind, like I mentioned in the beginning, these muscles are included in this list based on the fact that they are attached between the scapula and the humerus—nothing else. They can also be seen included in other groups if we define their function, and innervation, and so on.
Now, but on this list, specifically, I will include the coracobrachialis, which sometimes can be also listed as an upper arm muscle. The second one will be the deltoid, and the third one, the teres major. Now, we are going to talk about another group of four muscles that is quite well-known, and you hear a lot about this group of muscles, especially in clinical anatomy, and this is the rotator cuff mucles.
So first on our list of muscles, we have this one here highlighted in green on both of these images. And if you guessed it well, yes, this is the coracobrachialis. The coracobrachialis, as you can see here, originates from this portion of the scapula known as the coracoid process, and then it goes all the way to insert in line, as you can see here, in line with the lesser tuberosity of the humerus. You can also see here that it’s inserting right in-line with the lesser tuberosity of the humerus and goes to insert on the anterior surface of this bone, the humerus, on the middle third medial anterior surface of the humerus.
The second muscle on our list is one that clearly defines your shoulder, and this muscle, of course, is known as the deltoid. The deltoid is divided into three parts. You need to know this—very important. And these parts are divided depending on the insertion point.
The first one is this that I'm showing you right now. This is the clavicular part that is originating from the lateral third of the clavicle. The second part is known as the acromial part, which you can slightly see here a portion of the origin point on the acromion of the scapula, which you can see a little bit better here on the posterior view of the deltoid. Now, the third part is clearly seen here also on the posterior view, and this is originating from the spine of the scapula. Now, this muscle has one insertion point which is right here on the deltoid tuberosity of the humerus.
Now, the third muscle on our list is the one seen here highlighted in green, and this is the teres major. Now, on a posterior view here on your left, you can see that the muscle is originating from the inferior angle of the scapula and goes all the way to insert—and you can see a bit better here on the anterior view—on the crest of the lesser tuberosity of the humerus, right about here.
Now, let’s move on and talk about the last group of muscles here on our list, the rotator cuff muscles. And as I’ve mentioned, this is a group of four muscles including the supraspinatus, the infraspinatus, the teres minor, and the subscapularis.
Starting off with the supraspinatus muscle, right here, also highlighted in green, you notice that this muscle is originating right here from the supraspinous fossa of the scapula, and keep in mind that we’re looking at these images both on the dorsal view of the muscle. So their origin point is here on the supraspinous fossa of the scapula and goes all the way to insert—and you can see a little bit better here—on the greater tuberosity of the humerus.
Now, the second muscle of the list is the infraspinatus, also seen on a posterior view, and you notice here that the origin point of this muscle is the infraspinous fossa of the scapula, so all of this portion here of the scapula, and goes all the way to insert on the greater tuberosity of the humerus as well.
Still on the infraspinatus, I just wanted to add here the other muscles that you will see nearby, and you find here on the dorsal or defining the dorsal portion of your upper arm, the muscle that we talked about, the triceps brachii. Now, here, you’ll also find another one that we discussed, the teres major, and then this one here that will be discussed on the next slide, the teres minor.
Now, as I promised, let’s talk about the teres minor which will be originating from the scapula, more specifically on the lateral border of the scapula and goes all the way here to insert on the greater tuberosity of the humerus.
Now, keep in mind… I can also show you another image of the teres minor, and keep in mind that, throughout this tutorial, I’ve been showing you images of these muscles either contracted or relaxed, and here, you see clearly that. So this is not a different image of another muscle. This is still the teres minor that is originating from the lateral border of the scapula and goes all the way to also insert—you see here—on the greater tuberosity of the humerus. Also, see here, the triceps, and here, the teres major.
Last on our list is going to be this muscle here, highlighted in green, and this time we’re going to look at the anterior view of the humerus and scapula and anterior view, of course, of this muscle. This is the subscapularis, which originates from the subscapular fossa of the scapula, right here, and goes all the way to insert on the lesser tuberosity of the humerus.
I can show you also another image here of the subscapularis, and you notice here, this muscle, if you can guess which muscle this is, this is the teres major which is inserting in line with the lesser tuberosity of the humerus, like I talked about before.