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Origins and insertions of the muscles of the arm and shoulder.
Building up a strong set of arms and shoulder muscles like these does not come easy. Ask anyone who’s done it. It takes amount enough motivation, plenty of pain, and a bucket load of sweat. But who wants arms like these when you can have arms like these? Of course, if you’re going to go through the trouble of growing muscles like these, you might as well be able to at least name the muscles in question, and that’s exactly what we’re going to be doing today. So whether you’re showing off the fruits of your many, many shoulder and arm workouts or just trying to ace your next upper limb anatomy exams, stay tuned as we explore the muscles of the arm and shoulder.
So to get started, let’s first remind ourselves of the bony framework which provides the attachment points for the muscles that we meet today. As you see here in this illustration, we are looking at the posterior surface of the humerus which, of course, is the long bone of the arm. On the left side, you can see this triangular-shaped bone which we know is the scapula, also commonly referred to as the shoulder blade.
In this tutorial, specifically, we will be introducing you to the muscles that have their attachment points on or between these two bones. The aim of the game today is to help you learn how to identify the muscles by their location and their attachment points. If you need more detailed information in regards to specific functions and innervation of each muscle, please be sure to check out our more in-depth videos on the muscles of the shoulder and muscles of the arm.
We’re going to begin this tutorial now by first exploring the muscles of the arm region. The first point to make here is that these muscles can be split into two groups. The first one belongs to the anterior or ventral compartment of the arm and includes the biceps brachii, coracobrachialis, and brachialis muscles. Also you can find another group which belongs to the posterior or dorsal compartment which includes the anconeus and also the triceps brachii muscle.
Now let’s start with the anterior or ventral group beginning first with this muscle which you see here highlighted in green. This, we all know, is the biceps brachii muscle. Now true to its name, the biceps brachii has two heads – a short head located medially as you can see here and a more lateral long head seen here. Each head of the biceps brachii has a different origin or proximal attachment point. In the case of the long head, you can see it is originating right here from what’s known as the supraglenoid tubercle of the scapula. In regards to the short head, you see that the origin point is located right here on this distinct looking projection of bone which is known as the coracoid process of the scapula.
And as they continue distally, the two heads of the biceps brachii merge into a single belly which continues to insert right here on the radial tuberosity of the radius. The biceps brachii also attaches to some soft tissue of the forearm which is known as the antebrachial fascia.
Now let’s move on to the second member of the anterior group which is this muscle here that you see now highlighted in green. Now, can you guess what this muscle is? I’ll wait a few seconds – tik-tok. Yes, it is indeed the brachialis muscle.
The brachialis originates here from the distal half of the anterior surfaces of the humerus and also the medial and lateral intermuscular septum. In contrast to the biceps brachii, the brachialis has its insertion or distal attachment on the ulna specifically onto its coronoid process and ulnar tuberosity.
The third muscle of the anterior compartment is this small muscle here which is the coracobrachialis muscle, and as its name suggests, the coracobrachialis has its proximal attachment point or origin at the coracoid process of the scapula. And from here, it extends distally along the humeral shaft to then insert along the anteromedial surface of the humerus.
And just like that, my friends, we have discussed the anterior muscles of the arm. It is literally as easy as one-two-three, hopefully. That means, it’s time to turn our attention to the posterior or dorsal group beginning with the first muscle on our list here which is the triceps brachii.
As its name suggests, the triceps brachii muscle has three heads. So, there is the long head seen here which has its origin or proximal attachment at the infraglenoid tubercle of the scapula right here. There is also a medial head which is the smallest of the three arising from the posterior surface of the humerus distal to the radial groove, and medial intermuscular septum. The third one is the lateral head, also has its proximal attachment on the posterior surface of the humerus; however, this time proximal to the radial groove and the lateral intermuscular septum. The three heads of the triceps brachii fuse into then a flat common tendon which crosses the elbow before inserting into the olecranon process of the ulna.
Although the triceps brachii is by far the dominant muscle on your posterior arm, there is another small muscle to be found in this region which is often overlooked, and that muscle is the anconeus muscle now highlighted for you on the screen. As you can see, it is relatively a small triangular-shaped muscle which, in reality, is often blended with the lateral border of the triceps brachii tendon, and it too attaches to the proximal end of the ulna.
We’re going to continue proximally now towards the shoulder joint where we have a number of muscles to examine beginning first with this one here which is, of course, the deltoid muscle. The deltoid muscle is the most superficial muscle of the shoulder joint and therefore it’s this muscle which gives most definition to our shoulders. So if you someone with beautiful shoulders, you know what muscle to blame it on.
The deltoid muscle has three subdivisions or parts based on its origin or proximal attachment points and you will see in a moment that the name of each part gives us a clue to the attachment point in question. Beginning anteriorly, we have the clavicular part of the deltoid which is attached – yeah, you can guess – to the lateral third of the clavicle.
Looking now from a posterior perspective, we can see the acromial part that originates from the acromion of the scapula. You can see how the naming here works. We’re very – we like to simplify things in anatomy. And finally, the scapular spinal part which again true to its name presents its origin along then the spine of the scapula.
Now, if we remove the large deltoid muscle like this, we can now get a better view of the muscles lying deep to it. There are five muscles here for us to consider – four of which belong to what’s known as the famous rotator cuff which, if you’ve ever had a shoulder injury, you’ll probably know all about it. The muscles of the rotator cuff share a common feature in the sense that they all insert or have their distal attachments somewhere on the proximal end of the humerus, and because of that, they help support the shoulder joint by keeping the head of the humerus in its correct position within the glenoid cavity.
From an anterior perspective, we have just one rotator cuff muscle to consider and that is the subscapularis muscle. As its name suggests, the subscapularis muscle has its origin across the entirety of the subscapular fossa of the scapula. As you can see in the illustration, the large belly of the subscapularis tapers off as it reaches its insertion which is generally located on the lesser tubercle of the humerus.
Flipping over to the posterior aspect now, the second member of the rotator cuff is the infraspinatus muscle, which originates from the infraspinous fossa of the scapula. It extends laterally where it has its distal attachment along the posterior aspect of the greater tubercle of the humerus. And moving inferiorly, we find our third member of the rotator cuff which is known as the teres minor muscle. It originates from the infraspinous fossa and lateral border of the scapula and finds its insertion just distal to that of the infraspinatus on the posterior aspect of the greater tubercle of the humerus.
And, finally, muscle number four of the rotator cuff is this one here highlighted in green for you and it’s called the supraspinatus muscle. This muscle originates from the supraspinous fossa of the scapula and reaches across over the head of the humerus to insert here at the greater tubercle.
And there you have the four muscles of the rotator cuff. A little tip to help you remember the four members of this group is to always remember that the head of the humerus SITS in the glenoid cavity with SITS being a handy little mnemonic for you to use here.
We have just one more muscle to discuss here and that is the big brother of the teres minor which is appropriately known as the teres major muscle. As we can see in the illustration, the teres major muscle has its origin right here around the inferior angle of the scapula. It has a longer belly than its little brother which reaches anterosuperiorly to insert along the anterior aspect of the humerus specifically the crest of the lesser tubercle.
And that concludes our introduction to the muscles of the shoulder and arm. Before we finish our tutorial, let’s have a final look at some of the muscles we saw today from a clinical perspective.
So just a few moments ago, we identified these four muscles as the members of the rotator cuff and for those of you who work out, play sports, or physically use your arms a lot in your work, you’re probably very familiar with the term rotator cuff injury.
There are three main types of rotator cuff injury. Tendinitis which is usually caused by overuse of the rotator cuff. This results in inflammation of the rotator cuff tendons. Tennis players and painters are commonly affected in this way and typically experience a consistent dull, aching pain around the shoulder joint.
The second type is bursitis which involves inflammation of the subacromial and subdeltoid bursae. And, finally, we have strains and tears of the rotator cuff which are caused by overuse or acute trauma to the shoulder joint. The tendons of the rotator cuff muscles may be overstretched or torn partially or completely.
Now these types of rotator cuff injury cause the most immediate and intense pain for sure and sometimes require surgical intervention.
There are some actions which we can take in order to prevent rotator cuff injury starting off with daily shoulder stretches to increase flexibility of the shoulder joint. Also many people who work out tend to focus on the anteriorly positioned muscles of the chest, arm and shoulders; however, if you remember from earlier, many of the rotator cuff muscles are located posterior to the shoulder joint. And this means it’s important to strengthen the muscles around the shoulder blade and posterior shoulder specifically to optimize the muscle balance of the rotator cuff.
And with that, we have reached the end of our tutorial. Let’s wrap up with a quick summary of what we have learned today.
We began our study with the muscles of the anterior compartment of the arm which included three members – the biceps brachii with its long and short heads. And we looked at the brachialis muscle, and finally the coracobrachialis muscle. We then flipped over and identify two muscles of the posterior compartment of the arm which were the triceps brachii with its long medial and lateral heads and the small anconeus muscle located here in the distal arm.
We then quickly went on to the muscles of the shoulder joint beginning of course with the large and superficial muscle of the shoulder that is the deltoid muscle. We identified its three parts which were the clavicular, acromial, and spinal scapular parts. We then looked at four muscles which together form the rotator cuff group. These included the subscapularis muscle, we also saw the infraspinatus muscle, the teres minor muscle, and finally the supraspinatus muscle. And don’t forget that these muscles can be remembered using the mnemonic SITS or S I T S.
This left us with just one last muscle to identify which was the teres major muscle.
And that’s it. I hope you enjoyed this introductory tutorial to the muscles of the arm and shoulder. Remember to check out our other videos at Kenhub and as well as other quizzes, articles, cross-section, and lots, lots more that you can use to learn anatomy and histology.
Thanks for watching and I will see you next time.