Alright so in this video we’re going to talk about the Brachial Plexus. It’s a super important plexus, so let’s go ahead and get started So first we’re gonna go through the topography. Just talk a little bit about which nerves feed into the brachial plexus. Then after that we’re gonna make a scheme of the brachial plexus. And to make this as easy as possible to understand and remember, we’re going to draw the general outline first. Then we’ll go ahead and go through the supraclavicular parts of the brachial plexus, and then the infraclavicular. And at the end, there’ll be a little quiz. So let’s go ahead and get started with the topography. So here we see the spinal cord within the vertebral canal. And here we see the spinal nerve leaving the intervertebral foramen, so there’ll be one spinal nerve leaving on each side. They’re paired. To be specific, though, we’re not really talking about the whole spinal nerve, right? We’re actually talking about the anterior branch of the spinal nerve. Because the anterior branch is what forms all the plexuses that we’re going to talk about in this series of videos. So, brachial plexus, formed by the spinal nerves. Which branch of the spinal nerves? The anterior branch. More specifically. The brachial plexus is formed by spinal nerve number C5, C6, C7, C8, it’ll also have the T1 join in for the brachial plexus. So we say that it generally starts at C5, it might get some branches from the C4 but for the most part it starts at C5. But we’ll add the C4 too so that we cover all the variations. Alright. Let’s now go ahead and simplify this drawing so that we can actually make a scheme out of this. Now what I want you to do, is to grab a piece of paper and a pen, and I want you to draw this scheme with me. Once you do that, I promise you’ll remember this much much easier. Aright. Now the first thing we can do, is lay down the main topographical areas here so that it helps us memorize the scheme. Coming from the spinal segments are nerve roots. They form Trunks, which form divisions. The divisions go together forming cords, which then form the main nerves that supply different structures of the upper extremities. So Root Trunk, Divisions, Chord, Nerves. You’ll find many mnemonics on google for this one, but I remember ‘’Really Tired, Drink Coffee Now’’, if you need to memorize. Let’s add dividing lines between these landmarks. What happens is, C5 and C6 go together forming one Trunk. C7 continue forming its own trunk. C8 and T1 go together forming one trunk. What we have now is a superior trunk, a middle trunk and an Inferior trunk. Easy. You might find some fibers coming from C4 feeding into the superior trunk sometimes as well. That’s why C4 is sometimes considered a part of the brachial plexus aswell, even though it doesn’t contribute that much to the brachial plexus and its branches. So. The superior trunk is going to brach out into an anterior division and a posterior division The middle trunk is going to branch out into an anterior division and a posterior division. And the last one same thing here, but I’m gonna switch it up tho. I’m wanna have the posterior division here going up. You’ll see why, it’s gonna be easier for diagrammatic purposes. We’re gonna have the posterior division and same thing we’re gonna have an anterior division. Now the reason why these divisions are important is because some of these divisions are gonna come together and form actual cords. Now. 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. So the posterior divisions go together, combine and form a cord, a Posterior cord formed by the posterior divisions of the Upper trunk, middle trunk and the lower trunk. The anterior division of the upper trunk and the middle trunk are going to combine and form the lateral cord. The anterior division of the inferior trunk is gonna go alone and form the medial cord of the brachial plexus, traversing on the medial side of the forearm. Now. The main nerves that the brachial plexus is going to form are the Musculocutaneous Nerve. Axillary Nerve. Radial Nerve. Median nerve and the Ulnar Nerve. The lateral cord give a branch forming the musculocutaneous nerve. Medial Cord with give a branch going to the Ulnar nerve. Ulnar bone, remember is on the same side as your pinky. It’s medial, so ulnar nerve goes on the medial sied. Posterior cord with split giving off the Radial nerve and the Axillary nerve. Now. Last one here. We got the median nerve here. The median nerve is going to be formed by branches coming from the Lateral Cord, and the Medial Cord. Now. That is going to give us the basic structure fo our brachial plexus here. Now. Next thing I wanna do before I go through all the muscular supply of those nerves, is I wanna cover some small branches first. Off of the C5 root, there’s a branch. And this guy is going to go to some special muscles here. This nerve is the Dorsal Scapular Nerve. He’s gonna supply the Rhomboid Major and Minor, which are responsible for retraction of the scapula. And it’s also gonna supply the levator scapula. It elevates the scapula. Now the next one that we should know, is a very important one. It’s a nerve that’s going to come from C5. And on it’s way down, it will pick up a branch from C6, and it’s going to pick up a branch from C7. This nerve is called the Long thoracic Nerve. It’s going to supply the serratus anterior, which help retract the scapula. Next one is the suprascapular nerve, coming off the Superior Trunk. It’s going to supply the supraspinatus which performs weak abduction of the arm. And another one which is going to be below the spine of the scapula, called the infraspinatus. Which helps with lateral rotation of the shoulder joint. Alright so that is the suprascapular. Now there’s another one coming off the superior trunk, called the subclavian nevre. Now can you guess which muscle this one goes to? It’s going to go to the subclavius muscle and the subclavius is important for being able to depress the clavicle. Alright, awesome. Let’s keep going. As we go down here, we’re gonna come to the cords. Now the lateral cord is gonna give of a nerve, And this guy is called the Lateral Pectoral Nerve. Now the lateral pectoral nerve is going to supply the Pectoralis Major. Now the Posterior cord has a couple of branches that come off there too. Now the posterior cord has three branches. We got the Upper Subscapular Nerve, and the Lower subscapular nerve. The upper subscapular nerve is gonna supply what muscle? The subscapularis! Now what does the subscapularis do? Well based upon its origin and insertion, he helps to eb able to cause internal rotation of the scapula. The lower subscapular nerve is going to supply two muscles. It’s also going to supply the subscapulais. But it’s also going to supply another muscle called Teres Major, causing extension, adduction and inner rotation of the shoulder joint. The middle branch is called the Thoracodorsal Nerve. He’s going to go to the lattisimus dorsi. Lattisimus dorsi has exactly the same functions as the teres major. You know it helps to be able to extens the shoulder joint, medially rotate the shoulder joint and it adducts the shoulder joint. Alright guys we are so close! Let’s go to the medial cord now. The medial cord, it has three branches. Ok so remember the lateral cord has the lateral pectoral nerve. So this one should have the medial pectoral nerve. It’s also going to have the Medial Cutaneous nerve of the arm, and then the last one is going to be the medial Cutaneous nerve of the forearm. Now the medial pectoral nerve. What does it supply? The medial pectoral nerve is actually going to supply the pectoralis major, and the pectoralis minor. Now that begs the question what is the difference between those two muscles? The pectoralis major, he performs flexion at 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. SO these are gonna be supplies by that nerve. The medial nerve of the arm is going to supply more of the posterior and the medial surface of the brachial region. The medial cutaneous nerve of the forearm is gonna supply a little bit anteriorly, and then go distally to supply the antebracium. So medial brachial cutaneous is gonna be more posterior and medially. The medial antebrachial cutaneous is gonna be more anteriorly and down to the forearm. So now. We covered all of those minor, small nerves. So now. Let’s shade this diagram in grey. There’s a concept that most people use t divide the branches coming off the brachial plexus. And that is. All the nerves you see here highlighted in Yellow. Those nerves are called the Supraclavicular part of the brachial Plexus. Whereis. The nerves highlighted here in Orange are called the Infraclavicular part of the Brachial Plexus. Now, we’ve gone through the supraclavicular part of the brachial plexus, which are all of these muscular branches coming off here, coming off the roots of the brachial plexus, the trunks and the cords. Let’s now do the Infraclavicular nerves of the brachial plexus, the main nerves the big boys here that innervates most of the actual arm. Let’s just start off at the top. Musculocutaneous nerve. Where does it go. The musculocutaneous nerve will mainly pass between the biceps brachii and the brachialis and its terminal branch runs on the lateral aspect of the forearm. Now. The musculocutaneous nerve has two branches, ok 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 first talk about the cutaneous branch. The cutaneous branch is pretty easy. The cutaneous branch of the musculocutaneous nerve is going to be the lateral forearm. So it supplies primarily the lateral forearm where the terminal branches are. So it picks up the touch, that pain, the temperature of the lateral forearm. The motor branch is gonna go supply the anterior compartment of the arm. So three muscles. One is the coracobrachialis. Which flexes and adducts at the shoulder joint. Another one is the Brachialis. Which flexes at the elbow joint. And the last one is the Biceps Brachii, which is both the short and the long head. Which flexes the elbow joint but it can also supinate the palm. So that’s that one. Next, we have the Axillary Nerve. You know it actually run through a space around the shoulder joint it’s called the quadrangular space, and then it ends up on the posterior side of the surgical neck of the humerus. And what it does it has two branches, again. It has a cutaneous branch which supplies a patch of skin on the posterior and the lateral surface of the deltoid. The Motor branch is gonna supply two muscles. It is going to supply the Deltoid Muscle and the Teres Minor. So, the deltoid muscle, what can it do? It has a bunch of different functions. Well technically it has three major functions because you have anterior, lateral and your posterior fibres. Anterior fibres can help with flexion of the shoulder joint. Lateral helps abduction of shoulder joint, and the posterior fibres can help with extension at the shoulder joint. The teres minor helps with external rotation at the shoulder joint. So that is the axillary nerve. Now. We come to the Radial nerve. The radial nerve has so many different muscles that it can supply. But first how does the radial nerve go? The radial nerve spirals down the radial canal on the posterior surface of the humerus together with the deep brachial artery and veins. Then it perforates the lateral intermuscular septum to enter the anterior compartment of the arm, where it then travels between brachialis and the brachioradialis. Then it runs through the cubital fossa, where it divides into the superficial and deep branches. They’ll become important in a minute, but the deep branch enters the dorsal forearm and the superficial branch runs with the radial artery and veins to the radial fossa, where it divides into somatosensory branches for the dorsum of the hand. Alright so that was the course. Let’s first do the cutaneous, and then the muscular branches. The cutaneous branch supplies a good portion of our arm. A very very large portion. So they say that it generally supplies the posterior, and the lateral surface of the upper limb through the posterior cutaneous nerves of the arms and the forearms. Again, on it’s way down, it’s going to divide. And this is at the elbow region. It divides into a superficial branch, and a deep branch. The superficial branch is going to go down and give off nerves called dorsal digital nerves, giving sensory cutaneous innervation of the of the thumb and the index finger and the radial side of the 3rd finger as well. So, it’s going to supply the dorsal lateral side of the hand. So that’s the cutaneous branch. Now what about the motor branch? The radial nerve is going to have muscular branches that’s gonna supply many different muscles on the extensor side. Let’s start top and work our way down. So, the first one is that it’s gonna supply the muscles on the posterior upper arm, the extensor muscles. Specifically, the triceps brachii muscle. All the different heads, and these muscles you know plays a role within extension at the elbow joint. It also supplies another extensor at the elbow joint which is the anconaeus. Then if we come down, we’re gonna go to the forearm muscles. Easiest way to remember is that it supplies almost all the extensor compartment muscles of the forearm. And the way it does that is by having muscular branches supplying the extensor compartment, and the deep branch of it give off the posterior interosseous nerve, which supplies the deep extensor compartment of the forearm. So that is mainly the Radial nerve. Now we go to the next one, the median nerve. Alright so the median nerve follows the brachial artery and veins within the medial brachial intermuscular septum, and then in enters the cubital fossa. From the cubital fossa, it runs within the pronator canal, and then downwards between the flexor digitorum superficialis and profundus in the forearm to then runs more superficially in the distal part of the forearm. After that, it enters the palm though the carpal tunnel. Alright so that was the course. Again we’re going to have a cutaneous branch, for the median nerve. It’ll supply the ventral and the lateral surface of the palm. And the digits, the ventral surface of the digits two and three. And the dorsum of fingers two and three. Going to the ventral and dorsal surface. Alright so that is the cutaneous branch. What about the motor branch? The median nerve is actually a culprit for many people who’re active and typing and all that kinda stuff, because you know it actually lies within the carpal tunnel. Superficially to the tendons of the flexor digitorum superficialis, and underneath the transverse carpal ligament. Sometimes this nerve can get a whole lot of pressure on it or irritation which can cause the so called „carpal tunnel syndrome”. And if that happens, usually, there’s weakness or paralysis of the thenar muscles, as well as sensory changes in the region supplied by the median nerve. Alright so, motor branches. What do we got? So let’s go ahead and think about the flexor compartment. The median nerve, also has Muscular branches and anterior interosseous nerve. And they will give motor innervation for almost all of the anterior antebrachial muscles. Like the flexor carpi radialis, palmaris longus, pronator teres, flexor digitorum superficialis, flexor pollicis longus, flexor digitorum profundus (for the 2nd and 3rd finger), and also the pronator quadratus. And we also got the common palmar digital nerves number I, II and III, which provide motor branches for the muscles of the thenar eminence. Which remember are the abductor pollicis brevis, opponens pollicis and the superficial head of the flexor pollicis brevis. It also gives off motor branches for the 1st and 2nd lumbricals And, it also split into the proper palmar digital nerves which innervate the skin of the digits 1–3 and the radial side of the 4th digit and reach the distal phalanges on both the palmar and the dorsal sides. Let’s come to the last one. The Ulnar nerve. The ulnar nerve, alright, so course. How does it travel? It travels in the medial brachial intermuscular septum. Then it passes through the groove for the ulnar nerve behind the medial epicondyle of the humerus, which is where it’s only covered by fascia and skin. That’s why it hurts so much when you hit the medial side of the elbow. After the medial epicondyle fo the humerus, it passes through the cubital canal and enters the palm via the ulnar canal. Alright. Innervations. Again it has a cutaneous branch, and a motor branch. Thankfully this one doesn’t have a lot of muscles. Um, the cutaneous branch is actually pretty easy. So think about like this. Ok. So this is the hand, anatomical side this is the ulnar side, the pinky side. IF you think about it, this whole side was supplies already. Sot he ventral 2/3s and the dorsal 2/3s of the hand. SO what’s left? The ventral medial 1/3 of the hand and the dorsal medial 1/3 of the hand. That’s it. Now we come to the motor branch. The ulnar nerve has muscular branches in the forearm. And they provide motor innervation for the flexor carpi ulnaris and the part of the flexor digitorum profundus that acts on the 4th and 5th digits. When the ulnar nerve go through the ulnar canal, it then divides into two branches. A superficial branch that travels in the palm of the hand. This one is mostly a sensory branch, giving off the common and proper palmar diginat nerves that provide sensory innervation for the 5th and the ulnar side of the 4th singer. But it do have a motor branch that innervates the palmaris brevis as well. The deep branch of the ulnar nerve innervates all hypothenar muscles, palmar and dorsal interossei, lumbricals number III and IV, adductor pollicis and deep head of the flexor pollicis brevis. Alright guys so that pretty much covers the brachial plexus. Now what I want to do, is change all the labels with numbers, and sort them out in this table. And here is where this video gets scary. I am going to make all these labels disappear. And can you, from the beginning, tell me what is the name of number 1? What is the name of number 2? Where does number 3 go? And so on. If you can do that, then you’ve grasped this topic fully. There you have it my friends, thank you so much for watching another one of my videos. If you enjoyed, learned something from it, please remember to like, comment your favourite moment, subscribe. Turn on those notifications. 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