Anterior Compartment of the Arm

00:00 So, now, let's concentrate on the anterior compartment of the arm.

00:05 So, I'm looking at muscles like the coracobrachialis and the biceps brachii muscles.

00:11 So, here, we can see an anterior view looking at the anterior compartment of those muscles.

00:17 And the most substantial muscle we can see here is biceps brachii.

00:21 We can see it nice and clearly. But here, we have the anterior compartment indicated by the green dotted lines sitting on the anterior surface of the brachium.

00:33 Here, we can start looking at the individual muscles that are forming this compartment.

00:37 And the first one we can see here is a small slender muscle and that is coracobrachialis.

00:43 Coracobrachialis as its name indicates is running from the coracoid process through the brachium and it's running to the humerus of the upper limb. Another muscle we can see here is biceps brachii and then, sitting on top of that most superficially within the anterior compartment, we have brachialis.

01:02 So, let's concentrate in looking at coracobrachialis to start with and here, we can start looking at its origins and its insertions.

01:09 So, where does this muscle start from? As I mentioned a moment ago, it starts from the coracoid process and it runs all the way down to the middle third of the humerus.

01:18 So, the inferior aspects of the humerus is its final third.

01:24 And then, we've got a superior third up towards the head.

01:26 In the middle of the humerus, we have this middle third and that is where the coracobrachialis muscle attaches to.

01:34 So, we've got the coracoid process and the middle third of the humerus.

01:38 And here, we can see coracobrachialis muscle and it helps to do a couple of things.

01:42 First of all, it helps to adduct the shoulder joint.

01:45 So, it adducts the arm at the shoulder joint and that's moving the arm closer to the model body.

01:52 And it also helps to flex the humerus at the shoulder joint.

01:56 So, here, we've got flexion of the arm at the shoulder joint, two functions of the coracobrachialis muscle.

02:05 Now, let's move on to biceps brachii. Biceps brachii as its muscle name suggests has two heads.

02:12 We've got a long head here and we've got a short head which we'll see in a moment.

02:18 The long head, it gives rise to a very long tendon that runs up in the intertubercular sulcus of the humerus before running towards the scapula.

02:27 The intertubercular sulcus is formed between the lesser and greater tubercles of the humerus and here, we can see the intertubercular sulcus formed.

02:37 There is a ligament that runs between the two tubercles forming the roof of this sulcus and that's the transverse humeral ligament.

02:45 And this helps to keep that tendon of biceps brachii, the tendon of the long head of biceps brachii within its location.

02:53 It runs up through the glenohumeral joint and ultimately, runs to the scapula here where we can see, it's attaching to the superior glenoid tubercle of the glenoid fossa.

03:05 The short head of the biceps comes away from the scapula and that runs towards the single muscle belly of biceps brachii where it then gives rise to a common single tendon.

03:19 And here, we can see the bicipital aponeurosis of that tendon.

03:23 The head of the biceps brachii muscle runs down to the radial tuberosity.

03:29 So, now, let's have a look at these origins and insertions in a little more detail.

03:34 So, let's start off with the long head of biceps.

03:37 Long head of biceps passes up through the intertubercular sulcus over the head of the humerus and it attaches to the supraglenoid tubercle.

03:47 The superior aspect of the glenoid fossa of the scapula. The short head of the biceps doesn't take that path.

03:53 It takes a much shorter path, hence, why it's called the short head and that runs up to the coracoid process where it unites with the insertion of coracobrachialis muscle.

04:04 So, we've got the two heads of biceps attaching to the scapula but by two very different pathways.

04:09 These two muscle bellies converge into the primary muscle belly of biceps which then gives rise to a very thick tendon which attaches to the radial tuberosity and also, gives rise to a sheet-like tendon which is the bicipital aponeurosis and that runs over the cubital fossa.

04:28 Let's have a look at the function of biceps brachii.

04:31 Here, we can see it is involved in flexing the arm at the shoulder joint, so, contraction of these muscle bellies will lead to flexion of the shoulder.

04:41 We also then have flexion of the forearm at the elbow joint.

04:45 So, its connection to the radial tuberosity crossing the elbow joint means the flexion, contraction of that muscle will lead to flexion of the forearm at the elbow joint.

04:57 It's also an important supinator of the forearm.

05:00 So, this is where you move your forearm so you're holding a cup of soup, so to speak.

05:05 So, here, we've got the supination process and biceps is involved in supinating the forearm.

05:13 The final muscle in this anterior compartment of the arm is brachialis muscle.

05:18 And the brachialis muscle is running down from the anterior aspect of the humeral shaft, really, in the kind of middle third aspect similar to the attachment site of coracobrachialis.

05:28 But it runs down all the way through the anterior aspect of the arm across the elbow joint to the ulnar tuberosity.

05:37 So, this muscle is important as a flexor of the forearm at the elbow joint.

05:42 And it really is the primary flexor of the forearm at the elbow joint.

05:46 Biceps brachii helps to flex the forearm once it's in that supinated position.

05:51 So, the brachialis muscle is very important in helping to flex the forearm at the elbow joint.

05:58 So, now, let's have a look at the innervation of the anterior compartment.

06:02 And as we saw in the brachial plexus lecture, these muscles are innervated by the musculocutaneous nerve.

06:09 So, coracobrachialis, biceps brachii and brachialis muscles.

06:13 The anterior compartment of the arm are innervated via the musculocutaneous nerve which is that branch that comes from the lateral cord.