Anterior Compartment – Anatomy of the Arm

00:01 So if we look at the anterior compartment of the arm, then they are three muscles that I want you to be aware of in the anterior compartment. These are coracobrachialis, brachialis, and biceps brachii. If we start off with coracobrachialis, this is a relatively short muscle as its name suggests, coracobrachialis is running from the coracoid process of the scapula. Again this is why those bony landmarks on the scapula were important to the shaft of the humerus. And here we can see we have got coracobrachialis running from the coracoid process of the scapula to the middle third of the humerus. It is supplied by the musculocutaneous nerve. The musculocutaneous nerve that was coming from the brachial plexus. This muscle doesn’t cross the elbow joint. It just crosses the glenohumeral joint and because it does that it flexes and also adducts this joint.

01:04 If we go back and look at biceps brachii, we can see on this picture. We can see biceps brachii has two heads as its name suggests. We have a short head that is running up towards the coracoid process and we also have a long head that is running up towards the supraglenoid tubercle, the supraglenoid tubercle, that tubercle above the glenoid cavity. The tendon of the long head actually takes quite a long journey. It passes up within the intertubercular groove.

01:41 The intertubercular groove forms by the greater and lesser tubercles of the humerus. So here we see the long head of biceps passing to the supraglenoid tubercle by passing through the intertubercular groove. The short head here attaches to the coracoid process.

02:02 Here we can see the biceps which is running within the anterior compartment of the arm, the muscle belly of biceps and we can see its main attachment is on to the radius, the radial tuberosity which we can see here. It also gives rise to the bicipital aponeurosis and that blends with the brachial fascia. Another muscle here is brachialis and this muscle like biceps brachii crosses over the elbow joints. But because it is originating from the midshaft of the humerus it doesn't cross the shoulder joint whereas here biceps brachii does. Brachialis coming from the middle 3rd of the shaft of the humerus, it passes all the way down on to the ulnar and we can see brachialis muscle here. This muscle is only going to act on the elbow joint. So if you look at biceps brachii, its long head and short head. We can see it is originating from the supraglenoid tubercle or the coracoid process. It passes through the tuberosity of the radius and it blends with the fascia of the forearm via the bicipital aponeurosis as that continuation of brachial fascia passes down into antebrachial fascia. It is innervated via the musculocutaneous nerve and it has a whole range of functions. It is the chief supinator of the forearm. Because of its attachment on to the radius contraction of biceps will actually supinate the forearm. So from this pronated on mid prone position, the first movement of biceps will be to supinate the forearm. Once the forearm is supinated continued contraction of biceps will then flex the elbow joint. But only once the forearm is in this supinate position will it then flex. Continued contraction of biceps because it crosses the shoulder joint can leads a flexion of the shoulder.

04:03 Brachialis as I mentioned comes from the distal half of the humerus and it attaches to the coronoid process and tuberosity of ulnar. It is also supplied by the musculocutaneous nerve and it flexes the elbow joint. What you notice is that the muscles in the anterior compartment of the arm are all supplied by the same nerve, the musculocutaneous nerve. That terminal branch coming from the lateral coat of the brachial plexus is giving rise to the musculocutaneous nerve that supplies the muscles in the anterior compartment of the forearm. So if we look at these in a bit more anatomical position that actually to see these muscles we need to remove deltoid. So in the slide at the moment we have got a muscle here, an anterior view of the right arm with deltoid in position. We have also removed deltoid on this picture.

05:06 And by removing deltoid we can then see the position of the long head of biceps here.

05:12 We can also see the short head of biceps here. The muscle belly of biceps is in place here and we removed it on this picture to see brachialis lying underneath. So hopefully you could appreciate that brachialis is sitting directly deep to biceps brachii muscle. Its very difficult to see brachialis muscle with biceps brachii still in place. Just see a small bit of it here and here. We can see what we have got the bicipital aponeurosis passing down on to the antebrachial fascia of the forearm. So that we can see if we look at these notes which we have here, that running over the intertubercular groove, we have also noticed the transverse humeral ligament. And that runs over the two tubercles on the head of the humerus and this creates a tunnel for the long head to pass through. As I mentioned distally, the two heads of biceps unite and this continues down as the bicipital aponeurosis. Deep to biceps brachii is brachialis and medial to biceps brachii is coracobrachialis which we can see here.

06:26 So we can see in these pictures all of the muscular put together into one anterior compartment of the arm. If you look at the neurovascular relations of the anterior compartment then we can see in the diagram we have got a brachial plexus again. We can also see we have got some important blood vessels and then neighboring nerves as they descend distally towards the elbow joint. So we can see the muscular cutaneous nerve once again. We can see the median nerve.

07:03 We can see the ulnar nerve and these are running down this medial aspect of the arm. We can see they are running all the way down to medial aspect. We can see actually here the medial intermuscular septum of the arm. I remember that separates the anterior compartment from the posterior compartment. Here we can pick up the axillary artery but we can also see its relationship to the brachial plexus and then as it runs down it becomes the brachial artery.

07:34 And we can see the brachial artery is running in a groove between biceps brachii and brachialis muscle. So here you got biceps and deep to biceps we have got brachialis muscle just here and in the groove between we can see the brachial artery. We can also observe if we go towards the anterior aspects of the elbow, the bicipital tendon which we can see here and that is forming a roof over the brachial artery and the median nerve.

08:05 The brachial artery and the median nerve are running underneath the bicipital aponeurosis and the biceps tendon. And this is the cubital fossa and we will cover that in future slides.