Transcription
iein in generics. In this video, we are gonna talk about the brachial plexus, super important plexus. So let's go ahead and get started.
First things first, we should know the brachial plexus, right? From what part of the actual spinal cord does it start and at what point does it end? So we say that it generally starts around C5. It might gain some branches from C4, but for the most part, most part, it starts here at C5. And then it goes down C6, C7, C8, and then we can go to T1. And again, we've already explained why this is C8, right? We've said that it's actually running in between the first thoracic vertebrae and the seventh cervical vertebrae. There's not going to be eight cervical vertebrae, but there is going to be eight pairs of cervical spinal nerves.
Alright, anyway, first thing I want you guys to remember about the brachial plexus. On guys, well, I want you guys to remember something. Please remember it. Remember to drink cold beer. Alright? So, first thing I want you to remember is to remember to drink cold beer. Alright, that's the first thing I want you guys to remember.
Next thing I want you guys to remember is what's called MARMU. So remember MARMU. M A R M U. Now, you probably like, what in the world does this stand for? So the R is gonna stand for root. So it's gonna be root. T is for the trunk. D is for the division. C is for the cords. And then the B is going to be for the branches. Okay?
Now, as we come down, down this vertical part here, the MARMU M is for musculocutaneous. Okay? So there's going to be two ends, but the first one is going to be musculocutaneous nerve. Alright. The second one, A is for axillary nerve. So we're just kind of laying the groundwork for our brachial plexus. So then we can have our diagram in there. So we can get this stuff memorized very, very well. So the axillary nerve. Next one, radial nerve. Okay? Then after that, we're gonna have the median nerve. And we'll finish off here with the ulnar nerve. Okay?
Now, in this video, what we're gonna do is, is we're gonna talk about the structure of the brachial plexus, the branches of the brachial plexus, and some minor ones. And then we're gonna talk about the muscles and cutaneous supply. Alright? So let's go ahead and get started here.
First off, the root. First thing I want you guys to remember here is that the C5 nerve root and the C6 nerve roots actually come together. So if we have here the C6 nerve root and the C5 nerve root, these guys will actually come together. When they come together, they're gonna form a nice little trunk right there. Alright?
So now, the next thing is the C7 root actually feeds into its own trunk. Okay? So we're gonna have C5, C6 roots coming together and forming this trunk. The C7 root will feed into its own trunk. And the C8 and the T1 root will come together and form their trunk.
So now let's go ahead and organize this now. So we have C5, C6 roots coming together and forming this trunk. Now the question is, what is this trunk? What is this trunk? What is this trunk? Let's go from top to bottom or upper to lower. Hey, so this should be the upper trunk. Very, very simple here. So this part right here is going to be the upper trunk. This one right here will be the middle trunk. And this bottom one down here is going to be the lower trunk. Very, very self-explanatory for the most part, right?
Now, the next thing that's going to happen here is we're gonna take this upper trunk, middle trunk, and lower trunk, and all of them are gonna break off into divisions. So let's see that now. So now we're gonna have here, here's we're gonna have the upper trunk. He's going to branch into an anterior division and a posterior division. So look here, we're gonna have a posterior division right here. And then over here, same thing. This guy is going to branch out. This guy's going to branch out. Let's have this one as an anterior division. And then up here, we're gonna have an anterior division.
Now, the reason why these divisions are important is because some of these actual divisions are going to combine together and form special cords. And that's why we're mentioning. So again, the upper trunk splits into an anterior division, a posterior division. The middle trunk splits, splits into an anterior division and guess what? Oh, a posterior division. And the last one, same thing here. I'm gonna switch it up though, and I want to have the posterior division here going up. You'll see why it's going to be easier for diagrammatic purposes. We're gonna have the posterior division. And same thing here. What else should we have left over? We should have the anterior division. Okay, sweet deal.
So now we have all our divisions. Here's what I want you guys to remember. Once we have the anterior and posterior divisions, I want you to take all the posterior divisions and combine them together. Alright? So that's what we're going to do now. What I'm gonna do here is I'm going to bring this posterior division up, this posterior division up, and then these guys gonna combine. So now let's bring this guy up a little bit like this. Bring this one like this. And we're gonna have this posterior division like this. All of these guys combine. When they combine, they form a cord. Okay? And that cord is actually going to be a special one that will branch off into these different nerves.
So now the question is, what is this cord here that we're gonna form? So let's actually bring these together a little bit closer so we can have this cord here. This cord is going to be called the posterior cord. Okay? The posterior cord. And it's going to be formed by the posterior division of the upper trunk, middle trunk, and lower trunk. So let's draw like this. Let's have this one like this. And we're gonna have all of these guys combining together here. And then they're gonna split. Okay? And again, flow down like this and then split into this and this. Okay?
So now, what is this cord right here? This cord is called the posterior cord. Okay? It's called the posterior cord. And the posterior cord is going to be formed by the posterior division of the upper trunk, middle trunk, lower trunk. Then it's gonna branch out into the axillary and radial nerve.
Next thing, the anterior division of the upper trunk and the middle trunk are gonna come together. Okay? Now, these guys will come together. Let's do these in a different color so we don't confuse them with these. Let's do it in red. So now the anterior division is gonna come up here and it's gonna combine with the anterior division here. And what these are gonna do is they're gonna form a nice cord that'll go to the musculocutaneous. It'll form the branch of the musculocutaneous. Whereas the posterior cord gave branches to the axillary and the radial. What is this cord called? This cord is actually going to be specifically the lateral cord. Okay? This is called the lateral cord. Okay?
Now, the last and final one here is we're gonna have the anterior division and the anterior division here is actually going to go and supply the ulnar nerve. So let's bring the ulnar nerve down here a little bit. Bring the median down a little bit. Let's bring the ulnar down a little bit. So here's gonna be the median nerve. And then down here a little bit below is gonna be the ulnar nerve. Alright, sweet.
Now, same thing. Let's switch the color up a little bit. Let's do purples. Let's take the anterior division here. And this anterior division is going to basically come and supply the ulnar nerve. So he makes his own cord. What is this cord? So now here's the best way to remember ulnar. Remember it's on there. Gonna be the ulnar bone, right? So the ulnar bone, which is on the pinky side. So that's medial if you're in anatomical position. So this should be the medial cord. Alright?
Now, last one here is we have the median nerve here. The median nerve is going to be formed by branches of the medial cord and the lateral cord. So now look what happens here. The lateral cord is gonna come down here like this. Alright? And the medial cord is gonna come over here like this. And these both will come and supply the median nerve here. So the median nerve is going to be formed by branches of the lateral cord and by branches of the medial cord. That is gonna give us the basic structure of our brachial plexus here.
Now, next thing I want to do before before I start going over all the muscular supply of those nerves is I want to cover some small branches first. So if we come back over here, we had the root back here, right? Let's bring our root over here a little bit more. This is our root. And again, to bring the trunk over a little bit more over here. But the trunk right here. So off of the C5 root, there's a branch, a special little branch coming off of this C5 root. And this guy is gonna go to some special muscles here. Okay? What is this nerve here called? This is called the dorsal scapular nerve. Okay? The dorsal scapular nerve. He's gonna supply two muscles, well actually three if we combine the rhomboids into two different parts. You know the rhomboids, you have the major and then you have the minor. If you guys remember from our muscle anatomy videos, we say that these two are responsible for retraction of the scapula. The other muscle that it's going to supply is going to be what's called the levator scapulae. And the levator scapulae was important for being able to elevate the scapula.
Now, the next one that we should know is a very important one. He's going to be running on the sides there. It makes like those little cutting muscles that you can kind of see serrated edges. And that's called the serratus anterior. The serratus anterior is actually going to be formed by three nerve roots. So you know C5, C5 can actually run down here. He can pick up a branch from C6. And then C6 and C5 will run down here continuously. And they're like, hey, let me pick up another branch. And they pick up one more branch. And that is going to be from C7. This nerve is called the long thoracic nerve. The long thoracic nerve is super important. It goes and supplies a special muscle that helps us to protract that scapula. And that muscle is called the serratus anterior. Okay? So that's gonna be from the C5, C6, and C7 nerve root.
Next is the upper trunk. There's two branches that come off of that one. One of them is gonna be called the suprascapular nerve. The suprascapular. So this one is gonna be called the supra, not sub-par, the suprascapular nerve. And this guy is gonna go to two muscles. It actually supplies around the shoulder joint. But he supplies two muscles around that shoulder joint. And that is going to be called the supraspinatus, which performs weak abduction. So supraspinatus. And another one, which is gonna be below the spine of the actual spine of the scapula. And that's gonna be called the infraspinatus. And he helps to perform like lateral rotation at the shoulder joint. But again, he can also supply the shoulder joint. Okay? So that's a suprascapular.
Now, this is another little minor one, not super, super crazy. But there is a nerve that actually comes off here and supplies the subclavius muscle, which is underneath the clavicle. So they call this the nerve to subclavius. And the nerve to subclavius will, guess what? Do you what do you think it's going to go to? It's gonna go to the subclavius muscle. And the subclavius is important for being able to depress the clavicle. So he depresses the clavicle. Alright, sweet friggin deal.
Now, let's keep going. As we go down here, we're gonna come to the cords. Now, the lateral cord is going to have a special muscle, a special nerve coming off of it. Let's actually keep it in red here. There's a branch coming off of the lateral cord. Let's do that one right here. And this guy is called the lateral pectoral nerve. So this one is gonna be called the lateral pectoral nerve. Now, the lateral pectoral nerve, he is gonna go and supply a special muscle. Okay? That muscle he is gonna supply is going to be called the pectoralis major. The pectoralis major. Okay? So we got the lateral pectoral nerve, which is going to come off the lateral cord and supply the pectoralis major.
Now, we have the posterior cord. The posterior cord has a couple branches that come off there too. So what does the posterior cord give off? Alright, let's keep these in black. The posterior cord has three branches. Boom, boom. Let's do one more. Let's come down here again. Boom. Okay, three branches here. This one right here is called the upper sub. This won't sub-scapular. This is subscapular nerve. This one here, they actually have two names for it. The middle subscapular nerve or the better name, the thoracodorsal. So this one right here is gonna be called the thoracodorsal nerve. And then you have one more. And what do you think this one is, guys? This one right here is specifically the lower subscapular nerve. Okay? So we have one more. And that is going to be called the lower subscapular nerve. Okay? Lower subscapular nerve. Okay? The upper subscapular nerve is gonna be supplying what muscle? The subscapularis. So you pre-easy, right? So this guy is gonna supply the subscapularis. What does the subscapularis do? Well, based upon his origin and insertion, he helps to be able to cause medial rotation of the scapula, okay, or internal rotation of the scapula.
The next one, which is the thoracodorsal nerve, he is gonna go to what's called the latissimus dorsi. The latissimus dorsi has so many different functions. You know, it helps to be able to extend at the shoulder joint, medially rotate at the shoulder joint, and abduct at the shoulder joint. So many functions for this guy.
Now, the lower subscapular nerve is actually going to give off two branches. All right? What's gonna supply two muscles? Okay? It's gonna supply the subscapularis, but it's also going to supply another muscle which performs the exact same functions of this latissimus dorsi. And that is going to be the teres major. Okay? So the teres major is going to perform the exact same functions of latissimus dorsi. And what was that? Extension, adduction, and medial rotation at the shoulder joint. Subscapularis again, medial rotation at the shoulder joint.
Alright, as we are so close, we got this medial cord. Now, the medial cord, it has three branches. Okay? So if you remember up there at the lateral cord, that had the lateral pectoral nerve. The medial cord should have the medial pectoral nerve. So this one should be the medial pectoral nerve. And then this one right here, this is going to be the medial brachial cutaneous. And then the last one is going to be the medial, not that medial antebrachial cutaneous. How many branches off of this son-of-a-gun?
Alright, so now we've covered that, right? Medial pectoral nerve. What is it supply? The medial pectoral nerve is actually gonna supply the pectoralis major and minor. So he's gonna supply the pectoralis major and pectoralis minor. Now, that begs the question, what is the difference in these two muscles? The pectoralis major, he performs flexion at the shoulder joint. He performs medial rotation at the shoulder. So he again, he performs flexion of the shoulder joint, medial rotation at the shoulder joint, and adduction at the shoulder joint. The pectoralis minor is specific for protraction of that scapula. Okay? So these are going to be supplied by that nerve. The medial brachial cutaneous. It's better if I show you on myself here. So if I take here, I'm fat, so don't make fun of you guys. But if you look here, we have the medial brachial cutaneous. It's gonna supply more of the posterior and medial surface of the brachial region. Okay? So that's like right here. If we go a little bit more anteriorly, right? Then you're gonna have the medial antebrachial cutaneous. Key supplies here and continues down the forearm. Okay? So again, medial brachial cutaneous is going to be more posteriorly, medially. And then the medial antebrachial cutaneous is gonna be a little bit more anteriorly on this brachial region and down to the forearm. Okay? It's better if I show you on that, even though I'm fat. Okay?
So now we've covered those minor branches. Now let's get to the meat and potatoes, these big boys here. Okay? Musculocutaneous nerve. What does this sucker do? He has two branches. Okay? So it's always good to know for these big ones, they have a cutaneous branch and they have a motor branch. So let's go ahead and say we talk about first the cutaneous branch. Cutaneous branch is pretty easy. Okay? The cutaneous branch for this mofo is going to be the lateral forearm. So this applies primarily the lateral forearm. And again, it's picking up like touch, it's gonna pick up some of the touch, the pain, the temperature from the lateral forearm. Okay? That's the cutaneous branch. What about the motor branch? The motor branch, again, not a lot for this guy, thankfully. The motor branch is going to go to three muscles. One is the coracobrachialis. Okay? So the coracobrachialis. Another one is the brachialis. The brachialis. And the last one is the biceps brachii, which is both the short and long head. Okay?
Now, what did these muscles do? The coracobrachialis, he has two functions. One is he flexes at the shoulder joint. The other one is he adducts at the shoulder joint. Okay? Don't laugh when I push. I got man boobs. Okay? So brachialis, what does he do? He flexes at the elbow joint. The biceps brachii, he also flexes at the elbow joint. But he can also supinate the palm. Okay? So that's that.
So let's come back to the axillary nerve. The axillary nerve, you know, actually runs through a space where around the shoulder joint called the quadrangular space. And what it does is it supplies, has two components, a cutaneous branch, again, cutaneous branch, and a motor branch. The cutaneous branch is pretty simple. It supplies a patch of skin on the posterior and lateral surface of the deltoid. So posterior and lateral surface of the deltoid. So posterior and lateral surface of deltoid. Alright, that's that guy. What about the motor branch? The motor branch is gonna supply two muscles. Okay? What are those two muscles? It is gonna supply the deltoid muscle. Okay? So the motor branch will give fibers to the deltoid. And another one, which is going to be called the teres minor. So the deltoid muscle, what can it do? Well, it has a bunch of different functions. And I technically three functions because you have your anterior, your lateral, and your posterior fibers. The anterior fibers can help with flexion at the shoulder joint. The lateral fibers can help with abduction at the shoulder joint. And the posterior fibers can help with extension of the shoulder joint. The teres minor plays a role within lateral rotation or external rotation of the shoulder joint. Okay? So that is that guy right there.
Now, we come to the big mama, the radial nerve. The radial nerve has so many different muscles that it can supply. Alright? So first, let's do the cutaneous. Okay? The cutaneous branch is this supplies a good portion of our arm, a very, very large portion. So they say that it generally supplies the posterior, right? The posterior and lateral surface of the upper limb. And it also supplies another area. It supplies the dorsum of the hand. But remember, we always have to assume when we're doing this, when I'm telling you guys this, we're in anatomical position. So this is anatomical position here with my palms facing forward. So when I say dorsum, we're talking about this part here. And this is the radial side. So it should be dorsal and lateral surface of the hand. So it's gonna supply the posterior and lateral surface of the upper limb and the dorsal and lateral surface of the hand. And it also can supply the pollex. Okay? So it also supplies the pollex. And the pollex, pollex is just basically another word for your thumb. Okay?
Now, that's the cutaneous branch. What about that motor branch? Now, this guy, he likes to make a statement. Okay? So now, what I'm gonna do here is I'm gonna move the subscapularis out of the way, but just down here. Okay? So lower subscapular nerve, just remember it's subscapularis and teres major. Okay? Now, this guy here, the motor branch, get ready. This guy supplies so many. Okay? So the radial nerve, start from the top, work your way down. So the first one is going to supply the muscles of the posterior arm, your extensor muscles, specifically the triceps brachii. So we're gonna start at the top and work our way down. So triceps brachii, all the different heads. And these muscles, you know, the triceps brachii plays a role with extension at the elbow joint. It also supplies another extensor at the elbow joint, which is the anconeus.
Then, if we come down, we're gonna come to the forearm muscles. Easiest way to remember is it supplies almost all of the extensor compartment of the forearm. So work our way that way. So now, next muscle is the brachioradialis. So he supplies the brachioradialis. Then, if you go out from that point, we're gonna hit the extensor carpi radialis longus. And right next to it should be brevis. So it's going to supply those two muscles. And remember, brachioradialis is flexion at the forearm by flexion at the elbow joint. And the extensor carpi radialis longus and brevis extend the wrist.
Then, if you go next to that, you have the extensor digitorum. Then there's another one, the extensor indicis, which extends the index finger, the pointer finger, right? Then there's another one, extensor digiti minimi, the little pinky. That is the extensor digiti minimi. What else? Ah, hi. So we're God these guys. Let's go ahead a little bit more. Ours. There's another muscle here which is called the extensor carpi ulnaris. So it supplies another muscle. So what we're going to do is we're going to work over here. Someone box off the cutaneous branches. Okay? And we're gonna continue over here with the motor branches. So we're going to continue from this point and we're gonna stay extensor carpi ulnaris. So extensor carpi ulnaris. Then work your way down here to like the anatomical snuffbox region. I like that name. It's anatomical snuffbox region. You have the abductor pollicis longus. You have the extensor pollicis brevis. And the extensor pollicis longus in that area. It supplies those guys. So supplies the abductor pollicis longus. And it supplies another one, which is the extensor pollicis longus and brevis. The extensor pollicis longus and brevis.
Now, there's another one that I can't forget. You know, um, underneath the brachioradialis is a really deep muscle that helps to supinate the palm, really, really important muscle. He's called the supinator. So it also is going to give a branch here to a deep muscle called the supinator. Okay? So we've covered the radial nerve branches for the motor branch and the cutaneous branch. So again, remember this is the motor branches that we covered. And these are the cutaneous branches that we now.
We go into the next one, the median nerve. It's also a little bit challenging too. So we'll hit that one. Let's do this one in baby blue. Okay? Again, we're gonna have a cutaneous branch. And what is the cutaneous branch? The cutaneous branch for the median nerve is it's actually going to supply the ventral. So if we look here, anatomical position, the ventral and lateral surface of the palm. Okay? And the digits. The ventral surface of digits two and three also. So it's gonna supply the ventral and lateral surface of the palm, the anterior surface of digits two and three, and the dorsum of fingers two and three. Remember that. So cutaneous branch, ventral and lateral. And we can say technically two-thirds of hand and digits two and three on the ventral and dorsal surface. All right, that's the cutaneous branch.
Now, we got to do the motor branch. The motor branch, it has a decent amount also. So the motor branch, what are some of those? Okay? So with this guy, the median nerve, he's kind of a culprit for a lot of people who are very active and typing and all that kind of stuff. You know, it actually runs in the carpal tunnel underneath the transverse carpal ligament. And as that nerve gets compressed, it can cause carpal tunnel syndrome. The motor branch here supplies a lot of muscles here. So let's go ahead and think about the flexor compartment. So the flexor compartment, what do we have? We have the pronator teres. And then we have the quadratus. So we have the pronator teres and quadratus. If we go a little bit outwards from that, well, then we have the palmaris longus and the flexor carpi radialis. So flexor carpi radialis. And then out from that one is going to be the palmaris longus. Okay?
Now, if you think about another one, you can continue to go deep, right? This is the underneath underneath those muscles. There's another muscle. It's actually called the flexor digitorum superficialis. And then there's another one right there's, you know, there's a muscle really deep under here. It's actually called the flexor digitorum profundus. It's actually gonna supply the radial half of flexor digitorum profundus. All right? So we got that. Now, it'll continue down. As it continues down, it actually is going to supply some of the, you know, they had the lumbricals right here, the second and third lumbricals. So it'll also supply the second and third lumbrical muscles. And it'll also give supply to these thinner muscles, three of them. What are they? Okay? So you have specifically the opponens pollicis brevis. Then another one, which is called the flexor pollicis brevis. And the last one, which is called the abductor pollicis brevis. Whew, a lot of muscles for this guy. Okay? So we got the cutaneous branch and we got the motor branch. Pronator muscles, they pronate the palm. Flexor carpi radialis flexes the wrist. Palmaris longus flexes the wrist. Flexor digitorum superficialis flexes the digits and then eventually the wrist. Flexor digitorum profundus flexes the digits. So most of these are gonna tell you what they need. The lumbricals are intrinsic hand muscles. The opponens pollicis brevis helps with what's called opposition, being able to touch your thumb to all the other different fingers. The flexor pollicis brevis flexes the the actual thumb. And the abductor pollicis brevis abducts with them. So a lot of these muscles, their action is said within their name.
Come to the last one, the ulnar nerve. The ulnar nerve, this guy again has a cutaneous branch and he has a motor branch. Thankfully, this one doesn't have a lot of muscles. The cutaneous branch is actually pretty easy. So think about like this, okay? By taking my hand again, anatomical position, this is the ulnar side, right? Pinky side. If you think about it, this whole side was supplied already. So the ventral two-thirds, right? And the dorsal two-thirds of the hand. So what's left? The ventral and medial one-third of the hand. And the dorsal medial one-third to him. That's it. So it supplies, I got them in my pocket. I got the ventral and dorsal. So ventral and dorsal one-third of the hand. Simple as that. Super easy. Okay?
Now, we come to the motor branch. So remember, the median nerve supplied a lot of the thenar muscles. Well, the ulnar nerve gives off a branch that kind of flies over there and supplies another one. So another branch here off of this guy, it comes over here and supplies the adductor pollicis brevis. Well, let's think about the other muscle over here. What was another muscle that could be right over here? The flexor carpi ulnaris, right? Another one is, remember we had that half of that digitorum profundus, the flexor digitorum profundus? Well, the ulnar half. So we have two muscles now. The ulnar half of flexor digitorum profundus and the flexor carpi ulnaris. Last couple muscles, the hypothenar muscles. So on this side, okay, there's three of them there. The opponens digiti minimi, the flexor digiti minimi, and one more. And that is the abductor digiti minimi. One more. And that is the abductor digiti minimi. Iana.
So I pretty much covered the brachial plexus. I hope it made sense. I really do hope you guys enjoyed. Hope you guys learned something from it. If you guys did, please hit that like button, comment on the comment section, and please subscribe. Also, if you guys get a chance, go check out our Instagram, our Facebook, and even our Patreon. All right, engineers, as always, until next time.
[Music]
[Music]