Muscles of the Hand and Wrist (Nursing)

00:01 So there's more going on even beyond the forearm. We have to deal with the hand and the wrist.

00:08 So when we look at the hand and we're looking on the palmar side or what we consider an anatomic position, the anterior surface, we see another wide flat sheet of connective tissue which we said those things are called aponeurosis.

00:24 So this is an aponeurosis in the palm holding together all these digits and all of their tendons, and we call that the palmar aponeurosis and we can see some of the tendons for those muscles we already mentioned.

00:40 For example, here are the tendons for flexor digitorum superficialis.

00:45 So even though the muscle that acts on these digits was way up in the forearm, they have to have really long tendons to get to the digits in order to act on them.

00:55 And so, for example, here we see them ending on the middle phalanx but we also had flexor digitorum profundus, a deep layer of muscles that are going to cause flexion of the digits.

01:08 And they're going to go all the way to the distal phalanx.

01:11 And so, that creates a bit of a traffic jam so you'll notice the neat thing that happens is the distal end of the flexor digitorum superficialis, those tendons will split to let the tendon of the flexor digitorum profundus pass through on its way to the distal phalanx.

01:32 So before they get there, they're going to have to go through the wrist and something called the carpal tunnel, something you probably heard of before because it has a lot of clinical significance.

01:43 So here, in cross section, are all of those wrist bones or carpal bones and there's a connective tissue sheet on the anterior or palmar surface called the flexor retinaculum.

01:56 Retinacula are things that sort of keep tendons in place and kind of provide a fulcrum for their action to take place.

02:04 And in the tunnel created by the flexor retinaculum and the carpal bones is the carpal tunnel and we see some important tendons going through here.

02:13 We have the flexor digitorum profundus and flexor digitorum superficialis tendons as well as the flexor pollicis longus going off to the thumb. In addition to all of these tendons, we have our median nerve and this is how you can get carpal tunnel syndrome is with a lot of overuse of these tendons, they can become inflamed and swollen and there's not a lot of room in that tunnel and they can compress the median nerve. And that can cause symptoms distally to that point meaning a lot of numbness and weakness and what we call the thenar compartment which is our other word for the base of the thumb. Which brings us to that compartment.

03:03 So here, we have what are called thenar muscles and they act on the thumb so you'll see the word pollicis, opponens pollicis.

03:13 Opponens is a bit of a weird one. Opponens is something called opposition.

03:19 It's basically a movement where if you're trying to bring your thumb over to your little finger or digiti minimi, that would be called opposition. And we also have the abductor pollicis brevis.

03:32 We also have the flexor pollicis brevis. So these thumb muscles are called the thenar muscles.

03:40 On the opposite side of the hand where we have our little finger, we have the hypothenar muscles.

03:47 And here, we're going to have the opponens digiti minimi doing the same motion we just talked about with the thumb opposition but for the little finger.

03:57 And we also have the abductor digiti minimi and the flexor digiti minimi brevis.

04:03 It's a real fun one to say and because we said the compression of the median nerve in that carpal tunnel can cause thenar weakness, you can assume that, well, that's what innervates these thenar muscles.

04:14 And over on the hypothenar side, that's where we have ulnar innervation.

04:22 So now, we're going to look at some other very tiny muscles that the ulnar nerve also innervates and these are the palmar interossei. They tell us a little bit about where they are because palmar is going to refer to the anterior surface of the hand and what these muscles are going to do is adduction but not quite the same adduction that we're used to in other areas. Here, we're talking about bringing closer to the middle finger.

04:52 So we have this unusual midline that exists only in the hand where the midline of the hand is the middle finger.

05:00 So bringing these three fingers closer to the middle finger is considered adduction and the mnemonic that I'm about to point out starts with PAD, so the palmar interossei adduct.

05:15 So, P-A-D is how you remember that. If we go to the opposite side, we have the dorsal interossei and dorsal is another term for posterior so we're talking about back of the hand.

05:29 And these will have the opposite movement. These are going to be abduction, moving away from the midline created by the middle finger but it creates an unusual situation where since the middle finger is the midline, movement in either direction will be abduction. In this sense, the middle finger can only abduct.

05:51 And to finish off the mnemonic DAB, so DAB, PAD, so dorsals abduct and palmars adduct.