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102 The Posterior Compartment Of The Arm

In this video, Leslie talks about the only muscle found in the posterior compartment of the arm, the triceps brachii. He also mentions its parts, innervation, and function.


Transcript of Today’s Episode

Hello and welcome to another episode of Interactive Biology TV where we’re making Biology fun. My name is Leslie Samuel and this video is brought to you by our sponsors over at, the creator of this app and a number of other Anatomy Apps that are pretty amazing. This one is called the Muscle System Pro III. You can find them in the App store for iPad, iPhone and also for Mac.

Check Out Muscle Pro in the App Store

Check Out Muscle Pro in the App Store

In this video, I’m going to be looking at the posterior compartment of the arm. More specifically, first I’m going to talk about the muscle that you find in that posterior compartment. Then, I’m going to talk about the innervation for that muscle and lastly, I’m going to talk about the function of that muscle.

By the end of this video, you’ll have a great understanding of what is going on in that posterior compartment. So, let’s get right into it.

What I’m going to do is I’m going to turn this guy around and then, we’re going to zoom into the region of the arm. We’re going to look at the muscle that you can find in the posterior compartment.

It’s pretty simple! There’s only one muscle. That muscle has three parts but, there’s only one muscle in that posterior compartment and that is called the triceps brachii. All of these that you see here in the posterior compartment, that is your triceps brachii.

Of course, the reason we call it the triceps brachii, triceps refers to the fact that we have three heads. We have a long head that’s going to be this guy, and then, we have a lateral head which is this one. Then, we have a medial head. In order to see that, we need to hide the other two heads. So, I’m going to remove some layers here and there you go. I can see that medial head of the triceps brachii. That is the only muscle, triceps brachii.

Once again, triceps refers to the fact that we have… (Oh, I zoomed out there by mistake. Let me get back in. There we go.) So, the triceps refers to the fact that we have three heads. “Brachii” of course, that refers to the brachium, Latin for arm. That is the muscle that we have in the posterior compartment.

Innervation of that muscle, what is the nerve supply to that muscle? That is done by the radial nerve. Then, when we talk about the function, I don’t just like to talk about the function. I like to show you the function. So, let’s go right here into the media so that, you can see the extension, this motion right here. That’s extension of the elbow. You can see it again right now.

When that contracts, generally speaking, when a muscle contracts, it’s going to pull the bone that’s at the insertion point or the bone that it’s inserting on towards the bone that it’s originating and in this case, we’re going to end up with extension of the elbow.

So, in review, the muscle that we find in the posterior compartment would be the triceps brachii. The innervation of that muscle is the radial nerve and the function of that muscle is extension of the elbow. Extension at the elbow or you can call it extension of the forearm.

That’s pretty much it for this video. I hope you got tons of value from it. If you want more details on this video in particular, this is Episode 102. Come to and you’ll get information on the origins,insertions, innervations, actions, all that fun stuff.

This is Leslie Samuel from You can visit there, visit the website to get more resources just like this and other resources to help make Biology fun.

That’s it for this video and I’ll see you on the next one.

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About The Author

Leslie Samuel

Leslie Samuel is the creator of Interactive Biology. His mission is to use this site to Make Biology fun for people all over the world.