Test your understanding with 10 random multiple-choice questions from the question bank.
Introduction
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Alright so in this video we’re going to talk about the Brachial Plexus.
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It’s a super important plexus, so let’s go ahead and get started
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So first we’re gonna go through the topography.
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Just talk a little bit about which nerves feed into the brachial plexus.
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Then after that we’re gonna make a scheme of the brachial plexus.
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And to make this as easy as possible to understand and remember, we’re going to draw the general
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outline first.
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Then we’ll go ahead and go through the supraclavicular parts of the brachial plexus, and then the
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infraclavicular.
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And at the end, there’ll be a little quiz.
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So let’s go ahead and get started with the topography.
Topography of Brachial Plexus
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So here we see the spinal cord within the vertebral canal.
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And here we see the spinal nerve leaving the intervertebral foramen, so there’ll be one
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spinal nerve leaving on each side.
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They’re paired.
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To be specific, though, we’re not really talking about the whole spinal nerve, right?
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We’re actually talking about the anterior branch of the spinal nerve.
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Because the anterior branch is what forms all the plexuses that we’re going to talk
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about in this series of videos.
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So, brachial plexus, formed by the spinal nerves.
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Which branch of the spinal nerves?
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The anterior branch.
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More specifically.
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The brachial plexus is formed by spinal nerve number C5, C6, C7, C8, it’ll also have the
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T1 join in for the brachial plexus.
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So we say that it generally starts at C5, it might get some branches from the C4 but
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for the most part it starts at C5.
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But we’ll add the C4 too so that we cover all the variations.
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Alright.
Scheme of the Brachial Plexus
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Let’s now go ahead and simplify this drawing so that we can actually make a scheme out
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of this.
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Now what I want you to do, is to grab a piece of paper and a pen, and I want you to draw
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this scheme with me.
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Once you do that, I promise you’ll remember this much much easier.
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Aright.
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Now the first thing we can do, is lay down the main topographical areas here so that
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it helps us memorize the scheme.
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Coming from the spinal segments are nerve roots.
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They form Trunks, which form divisions.
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The divisions go together forming cords, which then form the main nerves that supply different
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structures of the upper extremities.
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So Root Trunk, Divisions, Chord, Nerves.
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You’ll find many mnemonics on google for this one, but I remember ‘’Really Tired,
2:26
Drink Coffee Now’’, if you need to memorize.
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Let’s add dividing lines between these landmarks.
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What happens is, C5 and C6 go together forming one Trunk.
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C7 continue forming its own trunk.
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C8 and T1 go together forming one trunk.
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What we have now is a superior trunk, a middle trunk and an Inferior trunk.
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Easy.
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You might find some fibers coming from C4 feeding into the superior trunk sometimes
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as well.
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That’s why C4 is sometimes considered a part of the brachial plexus aswell, even though
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it doesn’t contribute that much to the brachial plexus and its branches.
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So.
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The superior trunk is going to brach out into an anterior division and a posterior division
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The middle trunk is going to branch out into an anterior division and a posterior division.
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And the last one same thing here, but I’m gonna switch it up tho.
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I’m wanna have the posterior division here going up.
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You’ll see why, it’s gonna be easier for diagrammatic purposes.
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We’re gonna have the posterior division and same thing we’re gonna have an anterior
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division.
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Now the reason why these divisions are important is because some of these divisions are gonna
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come together and form actual cords.
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Now.
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Here’s what I want you guys to remember.
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Once we have the anterior and posterior divisions.
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I want you to take all the posterior divisions and combine them together.
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So the posterior divisions go together, combine and form a cord, a Posterior cord formed by
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the posterior divisions of the Upper trunk, middle trunk and the lower trunk.
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The anterior division of the upper trunk and the middle trunk are going to combine and
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form the lateral cord.
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The anterior division of the inferior trunk is gonna go alone and form the medial cord
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of the brachial plexus, traversing on the medial side of the forearm.
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Now.
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The main nerves that the brachial plexus is going to form are the Musculocutaneous Nerve.
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Axillary Nerve.
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Radial Nerve.
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Median nerve and the Ulnar Nerve.
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The lateral cord give a branch forming the musculocutaneous nerve.
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Medial Cord with give a branch going to the Ulnar nerve.
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Ulnar bone, remember is on the same side as your pinky.
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It’s medial, so ulnar nerve goes on the medial sied.
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Posterior cord with split giving off the Radial nerve and the Axillary nerve.
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Now.
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Last one here.
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We got the median nerve here.
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The median nerve is going to be formed by branches coming from the Lateral Cord, and
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the Medial Cord.
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Now.
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That is going to give us the basic structure fo our brachial plexus here.
Supraclavicular Branches of Brachial Plexus
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Now.
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Next thing I wanna do before I go through all the muscular supply of those nerves, is
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I wanna cover some small branches first.
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Off of the C5 root, there’s a branch.
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And this guy is going to go to some special muscles here.
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This nerve is the Dorsal Scapular Nerve.
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He’s gonna supply the Rhomboid Major and Minor, which are responsible for retraction
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of the scapula.
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And it’s also gonna supply the levator scapula.
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It elevates the scapula.
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Now the next one that we should know, is a very important one.
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It’s a nerve that’s going to come from C5.
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And on it’s way down, it will pick up a branch from C6, and it’s going to pick up
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a branch from C7.
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This nerve is called the Long thoracic Nerve.
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It’s going to supply the serratus anterior, which help retract the scapula.
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Next one is the suprascapular nerve, coming off the Superior Trunk.
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It’s going to supply the supraspinatus which performs weak abduction of the arm.
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And another one which is going to be below the spine of the scapula, called the infraspinatus.
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Which helps with lateral rotation of the shoulder joint.
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Alright so that is the suprascapular.
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Now there’s another one coming off the superior trunk, called the subclavian nevre.
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Now can you guess which muscle this one goes to?
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It’s going to go to the subclavius muscle and the subclavius is important for being
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able to depress the clavicle.
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Alright, awesome.
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Let’s keep going.
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As we go down here, we’re gonna come to the cords.
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Now the lateral cord is gonna give of a nerve, And this guy is called the Lateral Pectoral
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Nerve.
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Now the lateral pectoral nerve is going to supply the Pectoralis Major.
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Now the Posterior cord has a couple of branches that come off there too.
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Now the posterior cord has three branches.
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We got the Upper Subscapular Nerve, and the Lower subscapular nerve.
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The upper subscapular nerve is gonna supply what muscle?
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The subscapularis!
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Now what does the subscapularis do?
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Well based upon its origin and insertion, he helps to eb able to cause internal rotation
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of the scapula.
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The lower subscapular nerve is going to supply two muscles.
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It’s also going to supply the subscapulais.
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But it’s also going to supply another muscle called Teres Major, causing extension, adduction
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and inner rotation of the shoulder joint.
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The middle branch is called the Thoracodorsal Nerve.
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He’s going to go to the lattisimus dorsi.
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Lattisimus dorsi has exactly the same functions as the teres major.
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You know it helps to be able to extens the shoulder joint, medially rotate the shoulder
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joint and it adducts the shoulder joint.
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Alright guys we are so close!
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Let’s go to the medial cord now.
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The medial cord, it has three branches.
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Ok so remember the lateral cord has the lateral pectoral nerve.
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So this one should have the medial pectoral nerve.
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It’s also going to have the Medial Cutaneous nerve of the arm, and then the last one is
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going to be the medial Cutaneous nerve of the forearm.
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Now the medial pectoral nerve.
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What does it supply?
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The medial pectoral nerve is actually going to supply the pectoralis major, and the pectoralis
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minor.
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Now that begs the question what is the difference between those two muscles?
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The pectoralis major, he performs flexion at the shoulder joint.
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Medial rotation at the shoulder joint and adduction at the shoulder joint.
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The Pectoralis Minor is specific for protraction of that scapula.
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SO these are gonna be supplies by that nerve.
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The medial nerve of the arm is going to supply more of the posterior and the medial surface
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of the brachial region.
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The medial cutaneous nerve of the forearm is gonna supply a little bit anteriorly, and
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then go distally to supply the antebracium.
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So medial brachial cutaneous is gonna be more posterior and medially.
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The medial antebrachial cutaneous is gonna be more anteriorly and down to the forearm.
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So now.
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We covered all of those minor, small nerves.
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So now.
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Let’s shade this diagram in grey.
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There’s a concept that most people use t divide the branches coming off the brachial
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plexus.
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And that is.
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All the nerves you see here highlighted in Yellow.
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Those nerves are called the Supraclavicular part of the brachial Plexus.
Infraclavicular Part of Brachial Plexus
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Whereis.
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The nerves highlighted here in Orange are called the Infraclavicular part of the Brachial
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Plexus.
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Now, we’ve gone through the supraclavicular part of the brachial plexus, which are all
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of these muscular branches coming off here, coming off the roots of the brachial plexus,
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the trunks and the cords.
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Let’s now do the Infraclavicular nerves of the brachial plexus, the main nerves the
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big boys here that innervates most of the actual arm.
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Let’s just start off at the top.
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Musculocutaneous nerve.
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Where does it go.
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The musculocutaneous nerve will mainly pass between the biceps brachii and the brachialis
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and its terminal branch runs on the lateral aspect of the forearm.
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Now.
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The musculocutaneous nerve has two branches, ok so it’s always good to know for these
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big ones.
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They have a cutaneous branch and they have a motor branch.
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So, let’s go ahead and say we first talk about the cutaneous branch.
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The cutaneous branch is pretty easy.
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The cutaneous branch of the musculocutaneous nerve is going to be the lateral forearm.
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So it supplies primarily the lateral forearm where the terminal branches are.
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So it picks up the touch, that pain, the temperature of the lateral forearm.
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The motor branch is gonna go supply the anterior compartment of the arm.
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So three muscles.
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One is the coracobrachialis.
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Which flexes and adducts at the shoulder joint.
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Another one is the Brachialis.
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Which flexes at the elbow joint.
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And the last one is the Biceps Brachii, which is both the short and the long head.
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Which flexes the elbow joint but it can also supinate the palm.
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So that’s that one.
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Next, we have the Axillary Nerve.
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You know it actually run through a space around the shoulder joint it’s called the quadrangular
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space, and then it ends up on the posterior side of the surgical neck of the humerus.
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And what it does it has two branches, again.
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It has a cutaneous branch which supplies a patch of skin on the posterior and the lateral
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surface of the deltoid.
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The Motor branch is gonna supply two muscles.
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It is going to supply the Deltoid Muscle and the Teres Minor.
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So, the deltoid muscle, what can it do?
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It has a bunch of different functions.
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Well technically it has three major functions because you have anterior, lateral and your
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posterior fibres.
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Anterior fibres can help with flexion of the shoulder joint.
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Lateral helps abduction of shoulder joint, and the posterior fibres can help with extension
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at the shoulder joint.
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The teres minor helps with external rotation at the shoulder joint.
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So that is the axillary nerve.
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Now.
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We come to the Radial nerve.
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The radial nerve has so many different muscles that it can supply.
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But first how does the radial nerve go?
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The radial nerve spirals down the radial canal on the posterior surface of the humerus together
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with the deep brachial artery and veins.
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Then it perforates the lateral intermuscular septum to enter the anterior compartment of
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the arm, where it then travels between brachialis and the brachioradialis.
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Then it runs through the cubital fossa, where it divides into the superficial and deep branches.
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They’ll become important in a minute, but the deep branch enters the dorsal forearm
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and the superficial branch runs with the radial artery and veins to the radial fossa, where
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it divides into somatosensory branches for the dorsum of the hand.
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Alright so that was the course.
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Let’s first do the cutaneous, and then the muscular branches.
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The cutaneous branch supplies a good portion of our arm.
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A very very large portion.
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So they say that it generally supplies the posterior, and the lateral surface of the
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upper limb through the posterior cutaneous nerves of the arms and the forearms.
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Again, on it’s way down, it’s going to divide.
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And this is at the elbow region.
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It divides into a superficial branch, and a deep branch.
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The superficial branch is going to go down and give off nerves called dorsal digital
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nerves, giving sensory cutaneous innervation of the of the thumb and the index finger and
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the radial side of the 3rd finger as well.
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So, it’s going to supply the dorsal lateral side of the hand.
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So that’s the cutaneous branch.
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Now what about the motor branch?
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The radial nerve is going to have muscular branches that’s gonna supply many different
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muscles on the extensor side.
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Let’s start top and work our way down.
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So, the first one is that it’s gonna supply the muscles on the posterior upper arm, the
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extensor muscles.
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Specifically, the triceps brachii muscle.
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All the different heads, and these muscles you know plays a role within extension at
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the elbow joint.
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It also supplies another extensor at the elbow joint which is the anconaeus.
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Then if we come down, we’re gonna go to the forearm muscles.
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Easiest way to remember is that it supplies almost all the extensor compartment muscles
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of the forearm.
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And the way it does that is by having muscular branches supplying the extensor compartment,
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and the deep branch of it give off the posterior interosseous nerve, which supplies the deep
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extensor compartment of the forearm.
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So that is mainly the Radial nerve.
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Now we go to the next one, the median nerve.
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Alright so the median nerve follows the brachial artery and veins within the medial brachial
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intermuscular septum, and then in enters the cubital fossa.
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From the cubital fossa, it runs within the pronator canal, and then downwards between
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the flexor digitorum superficialis and profundus in the forearm to then runs more superficially
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in the distal part of the forearm.
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After that, it enters the palm though the carpal tunnel.
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Alright so that was the course.
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Again we’re going to have a cutaneous branch, for the median nerve.
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It’ll supply the ventral and the lateral surface of the palm.
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And the digits, the ventral surface of the digits two and three.
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And the dorsum of fingers two and three.
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Going to the ventral and dorsal surface.
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Alright so that is the cutaneous branch.
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What about the motor branch?
15:59
The median nerve is actually a culprit for many people who’re active and typing and
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all that kinda stuff, because you know it actually lies within the carpal tunnel.
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Superficially to the tendons of the flexor digitorum superficialis, and underneath the
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transverse carpal ligament.
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Sometimes this nerve can get a whole lot of pressure on it or irritation which can cause
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the so called „carpal tunnel syndrome”.
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And if that happens, usually, there’s weakness or paralysis of the thenar muscles, as well
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as sensory changes in the region supplied by the median nerve.
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Alright so, motor branches.
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What do we got?
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So let’s go ahead and think about the flexor compartment.
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The median nerve, also has Muscular branches and anterior interosseous nerve.
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And they will give motor innervation for almost all of the anterior antebrachial muscles.
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Like the flexor carpi radialis, palmaris longus, pronator teres, flexor digitorum superficialis,
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flexor pollicis longus, flexor digitorum profundus (for the 2nd and 3rd finger), and also the
17:05
pronator quadratus.
17:07
And we also got the common palmar digital nerves number I, II and III, which provide
17:13
motor branches for the muscles of the thenar eminence.
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Which remember are the abductor pollicis brevis, opponens pollicis and the superficial head
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of the flexor pollicis brevis.
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It also gives off motor branches for the 1st and 2nd lumbricals
17:29
And, it also split into the proper palmar digital nerves which innervate the skin of
17:35
the digits 1–3 and the radial side of the 4th digit and reach the distal phalanges on
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both the palmar and the dorsal sides.
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Let’s come to the last one.
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The Ulnar nerve.
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The ulnar nerve, alright, so course.
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How does it travel?
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It travels in the medial brachial intermuscular septum.
17:56
Then it passes through the groove for the ulnar nerve behind the medial epicondyle of
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the humerus, which is where it’s only covered by fascia and skin.
18:05
That’s why it hurts so much when you hit the medial side of the elbow.
18:10
After the medial epicondyle fo the humerus, it passes through the cubital canal and enters
18:15
the palm via the ulnar canal.
18:17
Alright.
18:18
Innervations.
18:19
Again it has a cutaneous branch, and a motor branch.
18:22
Thankfully this one doesn’t have a lot of muscles.
18:25
Um, the cutaneous branch is actually pretty easy.
18:28
So think about like this.
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Ok.
18:30
So this is the hand, anatomical side this is the ulnar side, the pinky side.
18:35
IF you think about it, this whole side was supplies already.
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Sot he ventral 2/3s and the dorsal 2/3s of the hand.
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SO what’s left?
18:44
The ventral medial 1/3 of the hand and the dorsal medial 1/3 of the hand.
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That’s it.
18:50
Now we come to the motor branch.
18:52
The ulnar nerve has muscular branches in the forearm.
18:55
And they provide motor innervation for the flexor carpi ulnaris and the part of the flexor
19:01
digitorum profundus that acts on the 4th and 5th digits.
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When the ulnar nerve go through the ulnar canal, it then divides into two branches.
19:10
A superficial branch that travels in the palm of the hand.
19:14
This one is mostly a sensory branch, giving off the common and proper palmar diginat nerves
19:20
that provide sensory innervation for the 5th and the ulnar side of the 4th singer.
19:25
But it do have a motor branch that innervates the palmaris brevis as well.
19:29
The deep branch of the ulnar nerve innervates all hypothenar muscles, palmar and dorsal
19:35
interossei, lumbricals number III and IV, adductor pollicis and deep head of the flexor
19:41
pollicis brevis.
QUIZ
19:42
Alright guys so that pretty much covers the brachial plexus.
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Now what I want to do, is change all the labels with numbers, and sort them out in this table.
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And here is where this video gets scary.
19:53
I am going to make all these labels disappear.
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And can you, from the beginning, tell me what is the name of number 1?
20:01
What is the name of number 2?
20:04
Where does number 3 go?
20:05
And so on.
20:06
If you can do that, then you’ve grasped this topic fully.
20:09
There you have it my friends, thank you so much for watching another one of my videos.
20:13
If you enjoyed, learned something from it, please remember to like, comment your favourite
20:18
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20:19
Turn on those notifications.
20:20
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20:32
box.
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Have fun ya’ll.
20:34
Peace.
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