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Origins, insertions and innervation of the radial muscles of the forearm.
Hello everyone! Welcome to Kenhub! This is Joao, and I’m very excited to do another tutorial for you guys where we’re going to be talking about the radial muscles of the forearm.
Now, these are a group or a set of muscles that you can find on the forearm, as you can see here on this image on your left. Here, keep in mind that we only have two muscles showing, two of the radial muscles that we’re going to be discussing, because technically, there are three radial muscles that you have to know.
Now, these muscles are found on the lateral portion of the forearm, as you can also see here on this image, and the other muscle, the third muscle that is not present here—but I will show you later on on this tutorial—can be seen a bit better from the anterior view. Now, here you have a dorsal view or a posterior view of the forearm where you can see the other ones a little bit better.
Now, also important to mention that these muscles are inserting, or (sorry) originating somewhere from the lateral epicondyle of the humerus. They go all the way to attach somewhere on your wrist, so as you can see here. And on this tutorial, I'm going to do the job of explaining to you the origins, insertions, and innervation of these muscles.
Now, moving on, what I want to briefly say as well is that, if you look at your forearm, you can easily palpate these muscles because their bellies and tendons lie quite superficially.
Let me now quickly list before we go on and talk about these muscles, the three muscles or the three radial muscles. And these are the brachioradialis, the one that is not seen here right now, and the other two that you can see here are the extensor carpi radialis longus, and the final one that we’re going to talk about is the extensor carpi radialis brevis.
Now, let’s talk about the very first one on the list: the brachioradialis. This muscle is a powerful muscle or relatively powerful that is mainly responsible for the lateral contour of the elbow and the forearm. And you can clearly see here on this portion here on this image where it’s highlighted in green, and you can see that it’s defining this portion or the lateral portion of the forearm.
Now, in terms of origin of this muscle, as I mentioned before, it’s going to come from the lateral portion of the humerus, more specifically the lateral supracondylar ridge of the humerus. Now, write this down. This is also very important that this muscle is going to originate somewhere between the brachio... or the brachialis muscle and the lateral head of the triceps brachii muscle. Write this down. That might be important note for your exam as well. Now, also an extra origin point would be the lateral intermuscular septum. So also have that down, but for now, the main one bony point would be lateral supracondylar ridge as the origin point for the brachioradialis.
Moving on to, of course, now, the insertion point. And the insertion point, as I mentioned, it’s going to insert distally towards the wrist. And it will insert on the styloid process of radius.
Now, let’s move on and talk about the second muscle on our list: the extensor carpi radialis longus. And this muscle is lying underneath the brachioradialis which we talked about on the previous slide. It is also highlighted here in green on both of these images. Now, in terms of origin point, this muscle has one that you need to remember. And as you can see here on this image, keep in mind that we’re looking at the dorsal or posterior portion of the forearm, and right here, you have the lateral part of the humerus on an area here known as the lateral supracondylar ridge. And this is where the extensor carpi radialis is originating from. Now, keep also in mind that somewhere above it, you’re going to have the origin for the brachioradialis. So it’s just right next to it, or the origin point the extensor carpi radialis is slightly below the brachioradialis origin.
Moving on and talking about the insertion point of the extensor carpi radialis, as you can see here on this image, it’s going all the way distally to insert on this bone right here or a portion of this bone that is known as the base of the second metacarpal.
It is time for us to talk about the last one on our list: the extensor carpi radialis brevis. This muscle is shorter and thicker than the extensor carpi radialis longus. The name says it all. “Brevis” meaning “short,” “longus” meaning “long.” Now, that’s the difference between the two muscles.
Now, in terms of origin, and as you can see here, also on the lateral portion of the humerus, this muscle arises from the common extensor tendon of the superficial extensors at the lateral epicondyle of the humerus. Now, in terms of insertion point, it’s also going to insert distally all the way to this bone right here that is known as the base of the third metacarpal bone. Now, keep in mind that this is also the posterior portion of the base of the third metacarpal, and this is where the muscle, the extensor carpi radialis, will be inserting on.
As I promised you, I'm going to do a quick note on the innervation of the radial muscles. What you need to know is that these muscles are going to be supplied by the radial nerve from C5 to C8. All radial muscles are supplied by this nerve which courses between the brachioradialis and the brachialis muscle to the elbow, and there, divides into a deep branch and a superficial branch at the height of the radial head. Now, keep in mind that, here, on both of these images, you can see this nerve both highlighted in green.