Muscles of the Forearm (Nursing)

by Darren Salmi, MD, MS

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    00:01 So let's talk about some of the muscles producing movement at the elbow and wrist.

    00:06 Starting from superficial to deep and starting from the anterior point of view.

    00:13 So we're going to zoom in here actually at the elbow first and kind of go back to some stuff that we saw in the last section, in the shoulder and arm.

    00:22 The big muscle we saw there in the anterior compartment was the biceps brachii and it's coming all the way down and forming a tendon that will cross the elbow joint.

    00:33 So, it had a movement both at both the shoulder and elbow. It was a great flexor of both.

    00:40 That's one of the muscles that the radial tuberosity will receive.

    00:44 Coming off of this tendon is this weird flat sheet of connective tissue.

    00:49 And we have these flat sheets of connective tissue, we give them a special name.

    00:54 We call them aponeurosis and it just is that. It's a flat connective tissue sheet that comes off of this tendon.

    01:03 But deep to the biceps brachii, we also have the brachialis and then posterior in the arm, we had the triceps brachii which was doing basically the opposite stuff of the biceps.

    01:16 But there's something a little fun about this bicipital aponeurosis that's pretty relevant clinically.

    01:22 We find that just deep to the bicipital aponeurosis is the brachial artery which was the continuation of our axillary artery.

    01:32 Fortunately, it turns out that the median cubital vein which is one of the main veins used in venipuncture during a blood draw is just superficial to this bicipital aponeurosis.

    01:45 So there's sort of a built-in protection when you're doing a venipuncture for a blood draw that keeps the artery a little further away behind and deep to this bicipital aponeurosis.

    01:58 So let's keep going on with some compartments of the forearm. So, in general, just like the anterior compartment of the arm, the anterior compartment of the forearm is going to pretty much cause flexion at the wrist and fingers and mostly going to be innervated by a branch of the brachial plexus we saw called the median nerve.

    02:20 So what are some of the muscles in here? Well, there's one that we're going to have to take a pause right away with, pronator teres, and talk about that name.

    02:28 In the shoulder and arm, we saw the word teres and we said that meant round so it tells us something about its shape but what does pronator mean? Well, that's a funny little motion that happens at the forearm called pronation and it's a sort of a rotation where if our palms facing upward and we rotate it so it's facing downward, we call that pronation, and to bring it back is called supination.

    02:53 A good way of remembering that is if you turn it back so that the palm is upward and that's supination and you cup your hand, you can and hold some soup in that hand. At least that's how I remember it.

    03:04 So the pronator teres is a round muscle that causes pronation.

    03:09 Then we have the flexor carpi radialis. That's a mouthful but it's helpful.

    03:15 It tells us it is indeed a flexor of the wrist because carpi means wrist. We saw the carpal bones.

    03:23 And radialis tells us it's going to be out laterally, towards the thumb side because that's where the radius was.

    03:31 We also have something called the palmaris longus which you can guess is a pretty long muscle but it's fairly small and actually fairly ineffective and actually only 80% of people even have it.

    03:44 So it's a redundant muscle in a lot of ways for those who even do have it and that's actually kind of nice because you can use it if you ever need some sort of tendon for a surgery to be transplanted somewhere else.

    03:57 You can take the palmaris longus tendon without really losing any functionality.

    04:03 Then we have the flexor carpi ulnaris which, again, tells us a little something.

    04:08 It's a flexor of the wrist but now more on the ulnar side of the forearm.

    04:13 And if we go down a step to the intermediate layer, we have flexor digitorum superficialis.

    04:21 That, again, tells us everything we need to know.

    04:24 They're flexors of the digits and they're the superficial layer of the flexors of the digits.

    04:31 And by the way, when we say digits, it's kind of confusing because we can count our digits as one, two, three, four, five, we have five digits, but anatomic terms, you'll see that we actually have separate muscles and terms for the thumb so a lot of these are really referring to index, middle, ring, and pinky fingers.

    04:49 But regardless, these are the superficial layer of flexors for those digits and we have to go a level deeper before we can see the flexor digitorum profundus.

    05:01 Profundus meaning deep just like something's very profound, very deep. Here, it means quite literally deep.

    05:08 And then, as you can see, we have a flexor pollicis longus and that's a good example of what I was just talking about.

    05:14 Pollicis actually refers to the thumb so we have a separate muscle with the word pollicis in it for our thumb flexor.

    05:24 And then, finally, we have at the distal end, another pronator muscle, pronator quadratus.

    05:30 Quadratus because it looks sort of like a rectangle and we already know that pronation is to cause the palm to point downwards when we're rotating our wrists like this.

    05:41 If we look at the lateral compartment, we see it's actually got this funny name called the mobile wad which is really confusing when you hear that meaning.

    05:49 What does that mean? It moves something? Don't all the muscles move something? Well, Mobile wad refers to its ability to be easily retracted during surgery and that's probably not very intuitive when you see this name but these lateral muscles are still pretty interesting.

    06:05 We have some good names for them. Extensor carpi radialis brevis. A lot of words there but we can break it down.

    06:13 Extensor carpi, well, that's going to do the opposite of the flexor carpi in terms of extending the wrist.

    06:19 We know radialis means towards the radial bone and so out towards the lateral and then brevis meaning short.

    06:27 Then we have extensor carpi radialis longus and that's the longer equivalent.

    06:34 Then, finally, one that is a little funny because it doesn't really act on the wrist is the brachioradialis.

    06:41 Brachio, Remember, brachio meant arm and in anatomic terms arm wasn't the whole upper limb, it's just the part between the shoulder and the elbow.

    06:51 And so, brachioradialis means it's going from the arm to the radial bone which means it's only crossing the elbow joint and really having an action, flexion, specifically, at the elbow joint but since it's not crossing the wrist, it's not doing anything at the wrist.

    07:08 If we swing all the way around to the posterior compartment, these are going to be generally the opposite of the anterior compartment.

    07:15 They're generally going to cause extension of the wrist and fingers and they're going to be innervated by the radial nerve which was the one that innervated the posterior compartment of the arm with the triceps.

    07:27 The first thing is kind of a funny one, the anconeus.

    07:32 I'd say it's kind of a funny one because it's actually really hard to distinguish from the rest of the triceps.

    07:36 So it kind of gives you an idea that if you think of it as a distal extension of the triceps, you have a good idea of where it is and what it's doing. Extensor carpi ulnaris.

    07:47 Hopefully, by now, you're starting to get to the swing of things.

    07:49 Extensor carpi is extending the wrists on the ulnar side of the forearm. Extensor digiti minimi. It's a great one.

    07:59 Digiti minimi, that's a fun one because that's the word for little finger, digiti minimi.

    08:06 We have the extensor digitorum for the other digits.

    08:10 And then, we move to the deep layer to see some more. We have extensor indicis for the index finger.

    08:20 Extensor pollicis longus, again, pollicis means thumb and longus means, there's probably a brevis somewhere and there it is. And then, we finally have the abductor pollicis longus.

    08:34 Adductor, so we have mentioned a lot of those but we have abduction as well of the digits.

    08:39 Now, the rest of the digits are going to have some smaller ones in the hand themselves but for right now here's a good example of a way to move the thumb with a forearm muscle.

    08:52 And together, these three have a little funny name. They're considered the outcropping muscles because their tendons emerge from the deep compartment and pop out onto the posterior lateral surface of the wrist and if you move your thumb around, you can actually see those tendons pop out and form a little divet that used to be called the anatomic snuff box because long ago people would powder snuff in this little divet caused by the outcropping of these tendons.

    09:19 So, sometimes these three muscles together are called the outcropping muscles.

    About the Lecture

    The lecture Muscles of the Forearm (Nursing) by Darren Salmi, MD, MS is from the course Anatomy of the Musculoskeletal System (Nursing).

    Included Quiz Questions

    1. Brachial artery
    2. Ulnar artery
    3. Radial artery
    4. Bicipital artery
    1. Median cubital vein
    2. Brachial vein
    3. Axillary vein
    4. Cephalic vein
    5. Radial vein
    1. Biceps brachii
    2. Palmaris longus
    3. Anconeus
    4. Brachioradialis
    5. Flexor carpi radialis
    1. Extensor carpi radialis longus
    2. Extensor carpi radialis brevis
    3. Brachioradialis
    4. Palmaris longus
    5. Biceps brachii
    1. Flexor digitorum profundus
    2. Flexor pollicis longus
    3. Pronator quadratus
    4. Anconeus
    5. Extensor carpi ulnaris

    Author of lecture Muscles of the Forearm (Nursing)

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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