Musculocutaneous Nerve – Nerve Lesion of Upper Limb

00:01 In this lecture, we’re going to look at the nerve lesions of the upper limb. So we’re going to have an initial overview of the nerve supply to the upper limb and then look at some typical location of the lesions, and how this leads to motor and sensory deficits.

00:20 We’re going to look at some nerves that we’ve already covered in the course, so the musculocutaneous, the median and the ulnar nerves. And the radial, axillary and long thoracic nerves. So here we can see just on the screen on this right-hand side, we can see that we have the overview of the brachial plexus and the three cords coming away from the brachial plexus, the medial posterior, and lateral cord, how the medial and the lateral cord give rise to the musculocutaneous, the median, and the ulnar nerves, and how the posterior cord gives rise to the radial and the axillary nerve.

01:00 So we’re going to look at those specific nerves and how damage to those nerves can lead to sensory and motor deficits. It’s important to appreciate that coming off the brachial plexus, we have a whole series of cutaneous nerves that come either from the brachial plexus itself or come from one of those five terminal branches, and they supply the skin of the upper limb, as we spoke about in one of the first lectures.

01:29 We can see here various regions of the upper limb and how they are supplied by various nerves.

01:37 So let’s start by looking at the musculocutaneous nerve. Remember, the musculocutaneous nerve, as we can see on the screen here, is involved in supplying muscles within the anterior compartment of the arm. So damage to the musculocutaneous nerve which can happen as a penetrating injury within the axilla, maybe during a fight perhaps, damage to the musculocutaneous nerve can lead to paralysis of the muscles it supplies. So remember, it supplies coracobrachialis, it supplies biceps brachii, and it supplies brachialis. And if the musculocutaneous nerve is damaged, then, therefore, these muscles are not going to have their innervations. So they will become paralyzed. The effect of that is, well, if you appreciate the effect of these muscles contracting on the elbow joint and on the radio-ulnar joints, then you can appreciate that damage to the musculocutaneous nerve will lead to weakened flexion at the elbow, and also weakened supination of the forearm. So damage to the musculocutaneous nerve can lead to a weakening of the elbow flexion and a weakening of supination.

02:51 Sensory loss, well, if you look at damage to the musculocutaneous nerve, then via the lateral cutaneous nerve of the forearm, you have sensory loss over the lateral arm.

03:02 And we can see here in this region, the musculocutaneous nerve gives rise to the lateral cutaneous nerve of the forearm. So you may well have sensory loss on this region of the forearm.

03:13 This nerve that we can see running along here, the lateral cutaneous nerve of the forearm is originating from the musculocutaneous nerve. So damage here would lead to loss of sensation.