In this video extrinsic back muscle innervations of some nerves namely accessory, thoracodorsal and dorsal scapular nerves are discussed. Muscles involved include  trapezius, latissimus dorsi, levator scapulae, rhomboid minor and rhomboid major.

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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. In this video, I’m going to talk about the extrinsic back muscle innervations. So, let’s get right into it.

The first extrinsic back muscles, the superficial extrinsic back muscle, the first one would be the trapezius muscle. You can see that right here in both these pictures. You can see trapezius here and you can see trapezius on both sides here.

That is the only muscle that’s NOT innervated by a nerve from the brachial plexus. That’s actually innervated by the accessory nerve which is a cranial nerve, cranial nerve number 11 (CNXI). Alright, so the innervation for the trapezius is cranial nerve XI, the accessory nerve.

The other superficial extrinsic muscle as we’ve looked at before is latissimus dorsi. Latissimus dorsi is actually innervated by the thoracodorsal nerve. You can see that nerve coming off right here, coming off the posterior cord, the thoracodorsal nerve. It’s coming off right there between the upper and lower subscapular nerve.

Alright, so the innervation for latissimus dorsi is the thoracodorsal nerve coming off the posterior cord. Just by the name of it, “thoraco” it’s going to the thoracic region; “dorsal,” latissimus dorsi. It just makes sense. It’s one of the easier ones to remember.

Then, let’s go to the deep extrinsic muscles. Those deep extrinsic muscles would be levator scapulae as you see over here to the left, rhomboid minor and rhomboid major. These are all innervated by THE SAME nerve. You can see that nerve here. That would be the dorsal scapular nerve. What happens is that comes off of the C5 root and then, that goes through the middle scalene muscle and then goes back to innervate levator scapulae, it goes through levator scapulae and then, goes down to rhomboid minor and rhomboid major.

Those are the extrinsic back muscles. Let’s review that really quick. As usual, you can turn the sound down and then, quiz yourself.

The trapezius muscle is innervated by the CNXI (cranial nerve XI) which is the accessory nerve. Then, we have the latissimus dorsi which is innervated by the thoracodorsal nerve coming off the posterior cord between the upper and lower subscapular nerve. Then, we have levator scapulae, rhomboid minor, and rhomboid major which are all innervated by the dorsal scapular nerve which comes off of the C5 root.

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That’s it for this video. This is Leslie Samuel and I’ll see you in the next one.

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