Median Nerve

00:01 Let's then move on to the median nerve. So, let's remind ourselves of the course of the median nerve.

00:08 The median nerve is formed by the lateral and the medial roots that are coming from the lateral and the medial cords of the brachioplexus.

00:18 And here, they combine to form the median nerve.

00:21 The median nerve then leaves the axilla at the inferior margin of teres major and it runs alongside the brachial artery, lateral to it as it descends through the arm.

00:33 As it caries on, it passes medial to the brachial artery which we can see now in the cubital fossa.

00:39 And then, it passes all the way down into the forearm.

00:42 So, it runs deep to flexor digitorum superficialis and on top of flexor digitorum profundus.

00:48 So, by separating those two muscle bellies, you'll be able to locate the median nerve on its course.

00:54 It innervates all of the flexors of the forearm except for a couple.

00:59 All of the flexors of forearm except for flexor carpi ulnaris and the ulnar head of flexor digitorum profundus.

01:07 So, damage to this nerve is really going to prevent those muscles from performing their movement.

01:15 If we then, continue following the course of the median nerve down into the hand, we see it gives off a palmar branch from the median nerve that supplies the skin over the central palm.

01:25 It also then passes through the carpal tunnel and as it emerges, it gives rise to the recurrent branch and that supplies the thenar muscles.

01:34 It then, continues on its course providing some palmar digital nerves that go and supply two lumbricals and also the skin around the first, second, third, and half of the fourth digits.

01:48 So, it supplies the skin of these three-and-a-half digits and also, the thumb which we can see here.

01:55 If we look at the posterior aspect, we can see the median nerve also covers the dorsal aspect of the distal phalanges of some of the fingers as we can see here.

02:04 So, this sensory and motor supply of the median nerve is a lot more involved than that of the muscular cutaneous nerve but the principle remains.

02:13 Lesions to the median nerve will impact on the motor function and also, the sensory function.

02:20 There's a number of places the median nerve can be damaged and the closer to the spinal cord where this damage occurs will mean there's more widespread impact.

02:30 If we were to have traumatic injury at the elbow, then, all of the muscles that the nerve supplies within the forearm would be impacted.

02:37 So, here, we can see we'd have paralysis of the lateral two tendons or flexor digitorum profundus.

02:43 We'd have paralysis of flexor digitorum superficialis.

02:49 We'd have paralysis of the thenar muscles and we'd have paralysis of the lumbricals one and two.

02:55 And on the screen, you can actually see all of the reduction in movement that would occur because of the paralysis of these muscles.

03:04 I don't necessarily have to read that out because you can read it on the screen yourselves.

03:08 But please take some time to recognize the lack of movement that would occur due to paralysis of those muscles.

03:16 We'll see an example of this in a moment or two.

03:19 If we move on, we can also see that if you've got damage to the median nerve in the elbow, you would have complete sensory loss over the cutaneous innervation of that nerve.

03:30 So, here, we'd see loss of sensation from the first three, and then, a half of the fourth digit.

03:37 This means you end up with something like the hand of benediction.

03:40 Now, what's going on here is the patient is asked to form a grip to draw their fingers together.

03:47 Now, because you've got innervation of flexor digitorum profundus and superficialis to those second and third digits, remember, the ulnar nerve supplies the fourth and fifth.

04:01 When the patient is asked to form a grip, obviously, you cannot have flexion of those second, third, and the first digit because the nerve is being interrupted.

04:10 But the ulnar nerve is still intact. So, you still have flexion of the fourth and fifth digits.

04:17 And this leads to a presentation known as hand of benediction where you have a permanently extended first, second, and third digit.

04:26 If we then carry on looking at lesions of the median nerve but this time, associated with the carpal tunnel, then, you can have carpal tunnel syndrome or a laceration impacting the median nerve here.

04:37 But this time, it's going to affect everything distal to that trauma or to that syndrome that's impacting the nerve.

04:45 So, here, if it was to occur at the carpal tunnel level, we'd have an inability to oppose the thumb and we'd have paralysis of those first and second lumbricals.

04:54 You would also have loss of that sensation.

04:57 But this time, specifically, the digits, not the surface, the palmar surface of the hand.

05:02 And that's because where the nerves are emerging in relation to where the trauma or the syndrome is located means that some of those will still be preserved.

05:14 So, because the central palm is served by a branch that emerges proximal to the carpal tunnel, this is still intact.

05:22 Also, innervation to the muscles because they occur within the forearm, they will still be intact.

05:28 So, you won't get hand of benediction.

05:30 So, that's important to differentiate and find out the level of which this lesion has occurred.

05:37 If it's quite proximal, then, you'll have more widespread impact.

05:40 If it's more distal, you'll have a smaller cluster of symptoms.