Posterior Compartment of the Arm

00:01 So, now, let's have a look at the posterior compartment of the arm.

00:05 We've looked at the anterior compartment. We've looked at the cubital fossa.

00:08 Now, let's have a look at the posterior compartment.

00:12 So, here, looking at the posterior aspect of the two upper limbs, you can see a large muscle mass which is of triceps.

00:19 And we're going to spend a bit of time looking at the three muscle bellies of triceps brachii which we can see here.

00:25 Another important muscle in this space is known as anconeus.

00:29 This is a very small muscle and depending on your curricula, you may not need to know too much about it.

00:34 But it's within this posterior compartment of the arm. So, triceps brachii.

00:40 Triceps brachii as its name suggest has three heads. It has a long head. It has a lateral head.

00:48 And it has a medial head. Has three heads which are running in the posterior aspect of the humerus.

00:56 So, let's have a look at these in more detail because although they have one large common tendon that goes and attaches in the forearm, it actually has three different locations for its origin.

01:08 So, let's have a look at these in a little bit more detail. Let's start off by looking at the long head.

01:13 The long head has a long tendon that passes from the infraglenoid tubercle.

01:18 Remember, the long head of biceps went from the supraglenoid tubercle.

01:23 Here, the long head of triceps runs from the infraglenoid tubercle.

01:27 The medial and lateral heads, these come from the posterior surface of the humerus.

01:32 We can see they come from the radial groove. This is an important space that occupies the profundabrachii artery that's coming along from the posterior aspect of the humerus and the radial groove. And also, the radial nerve.

01:46 Either side of that radial groove, we have the medial head coming from it medially or inferior to the radial groove.

01:54 And then, coming superior or lateral to the radial groove, we have the lateral head.

01:59 So, the two heads of triceps, not including the longhead, is coming from the posterior surface of the humerus, separated by the radial groove that's containing the radial nerve.

02:11 And here, we have the lateral head coming from superior to the radial groove and the medial head coming inferiorly from the radial groove.

02:19 All those muscles come away and they converge on this large common tendon.

02:25 And that large tendon goes and attaches to the olecranon and that is positioned within the ulna.

02:31 So, an important part of triceps is actually doing the opposite.

02:35 It's a counter balance to the muscles in the anterior compartment.

02:40 So, these muscles in the posterior compartment, its function is going to be important in extending the arm at the shoulder joint.

02:47 So, I'm moving the arm backwards, extending the arm at the shoulder joint.

02:51 And also, because it attaches to the forearm, it crosses the elbow joint and it's important, extends the forearm at the elbow joint.

02:59 And important to know is because of only the long head crossing the shoulder joint is only the long head that contributes to extension of the arm, at the shoulder joint.

03:09 But posterior compartment of the arm is important in counteracting the work of the anterior compartment.

03:14 So, rather than flexion which biceps and brachialis, coracobrachialis does, this is working in extending these bony structures.

03:23 So, now, let's look at the final muscle in the posterior compartment of the arm and this is anconeus.

03:28 Anconeus is a small muscle and I've only seen it a handful of times within the dissecting room.

03:33 And here is anconeus. It originate from the lateral epicondyle of the humerus, looking at the posterior aspect of the elbow.

03:42 And we can see it running from the lateral epicondyle of the humerus to the olecranon.

03:46 The lateral aspect of the olecranon which we can see indicated here.

03:52 This helps to extend the forearm at the elbow joint. As the muscle crosses the elbow joint when it contracts, it's going to extend the forearm at the elbow joint.

04:04 So, the innervations of these muscles in the posterior compartment is by the radial nerve.

04:09 Remember, the radial nerve is the direct terminal branch of the posterior cord and it leaves the axilla via the triangular interval to enter into the posterior compartment of the arm.

04:22 It runs along the radial groove, separating the two heads of the medial and lateral heads of triceps and it goes on to supply these two muscles.