Musculocutaneous Nerve

by Stuart Enoch, PhD

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    00:00 Now, musculocutaneous, other bit. It’s called musculocutaneous. So, what is the cutaneous component in the neck and what is the nerve called? The intercostobrachial nerve. No, not intercostobrachial.

    00:18 Why is it called musculocutaneous? Where is the cutaneous part? It’s the skin, is that what you ask? Yes, yes. Tell me more.

    00:34 Musculocutaneous -- Yes. So which part of the skin? Okay. So the musculocutaneous nerve comes lateral to the artery, then it lies between the coracobrachialis muscle. You have the coracobrachialis here. It lies between the coracobrachialis.

    00:55 Then it does separate all the three BBC muscles and then it becomes cutaneous. At this point, it’s called the lateral cutaneous nerve of the forearm. That’s why it’s called musculocutaneous. Your medial cutaneous nerve of the forearm comes directly from brachial plexus. The lateral cutaneous nerve of the forearm is the continuation of the musculocutaneous nerve. Okay. Coming down here for now to get our median nerve and the ulnar nerve covered in the forearm. We discover the cubital fossa.

    01:34 Very good. Quite important question in the exam. You can take it, boundaries of the cubital fossa. The boundaries of cubital fossa are, one side is the floor which is the brachialis. Floor is the brachialis. What is on the lateral side? Which muscle is this? Coracobrachialis.

    02:08 Coracobrachialis is coming from here. This is brachioradialis.

    02:11 Brachioradialis. Brachioradialis. If you sort of semi pronate your forearm, semi pronate, and then you readily extend the wrist this way, the muscle you’re feeling is the brachioradialis. So semi pronate your forearm and lift your wrist up, that’s the brachioradialis. So that is your lateral boundary -- yeah, that’s the one, yeah.

    02:32 So that’s the lateral border of the cubital fossa. What is the medial side? Pronator teres.

    02:39 So pronator teres, brachioradialis and an imaginary line between the two condyles.

    02:44 So those are the boundaries of the cubital fossa. The floor is formed by the brachialis muscle.

    02:51 What’s on the roof? On the roof, you have the skin, then you have some subcutaneous tissue.

    02:58 On the medial side, you have the medial cutaneous nerve of the forearm. And the lateral side, you have the lateral cutaneous nerve of the forearm. Then the vein you can see here, which vein is that? What is that called? It was a median cubital vein.

    03:16 Median cubital vein. Median cubital vein is a union of the cephalic vein from here and the basilic vein from the medial side. So that’s the median cubital vein. The roof is also reinforced by the tendon of biceps. This is the biceps. From the biceps tendon, there is an aponeurosis which comes up that reinforces the roof. So if you reflect the skin, what are the structures you see from medial to lateral? What’s the most median structure? You’re always cannulating here -- Median nerve. Median nerve. First is at the most median section of the median nerve, after that is -- No. Median cubital vein is on the skin.

    04:03 But now we are reflecting the skin. We've gone into the cubital fossa. Median nerve, brachial artery. Second is the brachial artery, and the third structure is the tendon of biceps.

    04:14 So these are the three important structures in the cubital fossa and the floor is by the brachialis muscle. So, if you imagine the hand, there are eight forearm muscles. As I said, the things we’re covering are quite relevant to your exam.

    04:39 Eight forearm muscles in the hand, out of which, the five are arranged superficial and three are deep in the forearm. So if you tighten and flex your forearm, the muscles you feel, there are eight in total. The first one here is the pronator teres. The next one is flexor carpi radialis. Third one is palmaris longus. Fourth one is flexor digitorum superficialis.

    05:11 And the fifth one is flexor carpi ulnaris. Now, sometimes you know that flexor digitorum superficialis is classified as an intermediate layer. So in exam, if you get the superficial ones, make sure that this one, if at all it is asked separately, just remember that is an intermediate layer, not necessarily the superficial layer, which is called the flexor digitorum superficialis. Now, you go deeper, what do you find? You got three muscles.

    05:41 So you got five muscles superficial, three deep. The three deep muscles are flexor pollicis longus to the thumb, flexor digitorum profundus to the distal interphalangeal joints and the pronator quadratus. So the pronator teres works more proximally, and pronator quadratus more distally. Well, these are the eight muscles out of which the flexor carpi ulnaris and the flexor digitorum profundus to these two fingers are supplied by ulnar nerve. Everything else is by median nerve. So this is clearly our first-year anatomy level. One specific question in your exam will be the anterior interosseous nerve.

    About the Lecture

    The lecture Musculocutaneous Nerve by Stuart Enoch, PhD is from the course Musculoskeletal - Upper Limb.

    Author of lecture Musculocutaneous Nerve

     Stuart Enoch, PhD

    Stuart Enoch, PhD

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