okay we're gonna do an overview of the brachial plexus and answer the what questions what is the brachial plexus and what are its routes trunks divisions courts and branches hello everyone my name is dr. Morton and I'm the noted anatomist okay so the brachial plexus is that right there now the c5 and t1 spinal cord levels are what comprise and make up the brachial plexus and there is our spinal cord and those are the c5 to t1 spinal cord levels now brachial plexus is what provides the motor and sensory innervation to the upper limb and so if we zoom in and we take a look at oh there's the dorsal root of the c5 level and there's a sensory neuron coming in with its cell body in the dorsal root ganglion and there's the ventral root with a motor neuron coming out and then the ventral dorsal roots come together to make a spinal nerve trunk and then the spinal nerve trunk is rise to a dorsal and ventral ramus which is the exact same thing as this picture we've used in the past our roots make a spinal nerve trunk and the two ram i this is what occurs at each of the segmental levels between c5 and t1 know the roots trunks divisions cords and branches are the divisions from proximal to distal of the brachial plexus and it looks like this there are the roots there are the trunks in purple there are divisions in red there are the cords in green and there are the terminal branches or branches in blue at the end and so the way I remember this is through Randy Travis drinks cold beer and if you don't know who Randy Travis's then rugby teams drink cold beverages so either way the important thing to remember is that the roots trunks divisions cords and branches are the divisions of the brachial plexus from proximal to distal now let's start with the roots now the roots of the brachial plexus are really another way saying the c5 to t1 ventral remise c5 c6 c7 c8 and t1 and so the roots of the brachial plexus are the same thing as the ventral ramus at each of the segmental level not those roots those roots thank you anatomist for making that so confusing now the c5 to see 8 roots course above their associated vertebra so there we have this picture and there are are the c5 2t1 spinal nerves and their the associated vertebrae sinhala zoom in a little bit and notice that there's a c5 nerve root coursing above the c5 vertebra and the c6 nerve root above the c6 vertebra c7 nerve above the c7 vertebra and then whoo there's a weird thing because we actually have eight cervical spinal nerves and only seven cervical vertebrae and so the c8 nerve courses below c7 and above T 1 and then when we go to the t1 vertebra everywhere below this the nerve associated with the vertebra courses below it so t1 nerve below T when vertebra t2 nerve below t2 vertebra cervical vertebrae and nerves are the exception okay so some of the branches off the roots include one called the dorsal scapular nerve that innervates or levator scapulae and rhomboid muscles and so there is the c5 root and there is the dorsal scapular nerve coming from the c5 root and it innervates our levator scapulae rhomboids minor and rhomboid is major muscles another branch is called the long thoracic nerve that innervates or serratus anterior so there is the c5 c6 and c7 contributions from c5 c6 and c7 roots that then make our long thoracic nerve that descends superficially and innervating the superficial to the serratus anterior and innervates our serratus anterior and i have a hand surgeon colleague who told me that this is how he remembers it roses are red and violets are blue and the serratus anterior is innervated by the long thoracic nerve I thought that was very funny it made me laugh it's like Anatomy laughs not so much Ellen DeGeneres funny but like Anatomy funny okay so a couple of things about the roots to remember first is that each brachial plexus root those things have an Associated dermatome and a dermatomes and area skin innervated by a specific spinal nerve level and so there are dermatomes so the c5 root with the c5 dermatome c6 root c6 dermatome c7 root c7 dermatomes see 8 root CA dermatome t1 root t1 dermatome so the thing to remember is this sensory neurons in each upper limb dermatome course to an associated brachial plexus root another thing to remember is each brachial plexus root have an Associated Maya tome and a Maya tome is a movement associated with a specific spinal nerve level and so there's the c5 root it is associated with a deduction of the shoulder c6 root associated with flexion of the elbow c7 root extension of the elbow c8 root finger flexion t1 root finger a B duction so the thing to remember is this motor neurons from each brachial plexus root course to an associated upper limb Mya tome with an associated movement okay so now let's talk about the trunks of the brachial plexus and so roots give rise to trunks upper middle and lower trunk sometimes known as superior middle and inferior so there's the c5 and c6 roots that go Shi make the upper trunk and then the c8 and t1 roots go shinging and make the lower trunk and then the c7 root well it just continues as the middle trunk the only contribution and so a couple of nerve only one nerve branch we'll focus on is the suprascapular nerve that innervates our super and infraspinatus muscles so there is the upper trunk so the c5 and c6 levels going into the upper trunk making our suprascapular nerve which then innervates our supra and infraspinatus muscles named according to their association with the spine of the scapula now the roots and Trunks together exit between our anterior middle scalene muscles so there we have our anterior middle scalene muscles and there are the brachial plexus roots and Trunks just above the clavicle and then as well there's the subclavian artery that squeezes between those two muscles as well so we zoom in there's something called an inter scalene block that when we take a look at this surface anatomy and there's our clavicle in the supraclavicular region there's our subclavian artery and there's our brachial plexus and the x marks spot of where you would put this block between our scalenes to knock out the brachial plexus right there this is really good for shoulder arm and elbow not as much for forum in hand because the inferior roots and Trunks are below that but it's really good for an access to at least shoulder and arm and elbow and that's knocking out of for sensation all right next we'll talk about divisions of the brachial plexus and so the trunks give rise to anterior and posterior divisions so the upper trunk has an anterior and posterior division the middle trunk bifurcates into an anterior and posterior division and the lower trunk bifurcates into anterior and posterior divisions as well now why what's the deal here so to answer this let's talk about embryology for a second here's a cross-section through developing embryo and there's the developing limb bud and so in this developing limb bud are bones and in the bones have a dorsal and ventral muscle mass muscles that form ventrally endorsed ly to these bones and so what we see is the following the anterior division of the brachial plexus then sends their axons to the ventral muscle mass which are flexors and the posterior division of the brachial plexus sends its motor neurons to innervate the dorsal muscle mass and so what we see is the anterior division of the brachial plexus innervates flexors and the posterior division of the brachial plexus interface extensors basically muscles in front of and muscles behind the bones and then another thing is the ventral muscle mass forms all the intrinsic can muscles which is why the anterior division of the brachial plexus just innervates hand muscles intrinsic and muscles and the dorsal muscle mass ends in the forearm their tendons go into the hand but no intrinsic muscles of the hand are innervated by the posterior division so there are no branches associated with the divisions of the brachial plexus but I thought it's helpful to know why there are these divisions in the brachial plexus next we're going to talk about cords and so the divisions then give rise to three cords there are named in relation to the axillary artery so there's our actual re artery that's in bloosh I wish I'd drawn it in red but it's there's that axillary artery and then there's a lateral and medial cord named in their relationship to this axillary artery and then deep to it I try to ghost it out is the posterior cord let's do that again except with this picture right here there is our axillary artery and lateral is the lateral cord medial is a medial cord and deep shinging is the posterior cord right there now some of the branches that come off well the lateral cord branches are as follows there is our lateral cord and it gives rise to one branch the lateral pectoral nerve that innervates our pectoralis major lateral pectoral nerve innervates the pectoralis major muscle then the medial cord which is there has the medial pectoral nerve is one of its three branches that innervates both the PEC major and minor there's our medial pectoral nerve and it innervates both PEC major and PEC minor now only on one side it doesn't cross over but this picture shows the PEC major on one side and then on the other side the PEC major is dissected to show the PEC minor so it would go through both and it looks like this so there we have our lateral pectoral nerve here that then courses out an interface our PEC major and then the medial pectoral nerve right there that courses and pierces and innervates our PEC minor and continues out to the pectoralis major and so even though the medial pectoral nerve kind of looks lateral these two nerves are named by their origin on the cords of the brachial plexus now other medial cord branches include the medial cutaneous nerves of the arm and forearm media Katinas nerve of the arm media cattiness nerve of the forearm so when we look at this picture there is our branches of the medial continious nerves of the arm providing sensation to that region it's also called the medial brachial cutaneous nerve and then there's our mediocre taneous nerves of the forearm in that region also called medial antebrachial cutaneous nerve all right so the posterior cord and its branches so there's our posterior cord and there's three branches upper and lower subscapular nerves that innervate ER scubs scapularis muscle there's our upper and lower subscapular nerves and it innervates that muscle the subscapular is one of our rotator cuff and then also we have the thorkil dorsal nerve they're also called the middle subscapular nerve sometimes it innervates our latissimus dorsi muscle okay so okay we're not going to talk about the branches also known as the terminal branches of the brachial plexus and so the terminal branches are derived bond cords and so when we take a look at the axillary radial musculocutaneous meeting and ulnar nerves they're formed by the courts so there is our posterior cord and it gives rise to our axillary and radial nerves now the lateral cord gives rise primarily to the musculocutaneous nerve for the median nerve goes primarily to the ulnar nerve and together the ulnar the lateral and medial cords give rise to the median nerve and we look at this it kind of looks like an m' and like that the golden arches where we have the musculocutaneous meeting and ulnar nerves muscular Taney's meeting and on their nerves I actually use that golden arches that M when I'm dissecting to find that brachial plexus and so not only is McDonald's good for the terminal branches of the brachial plexus also good for a french fries not so much for the creepy clam so I've never seen the movie it okay so now we're going to talk about each one of these terminal branches starting with the axillary nerve that innervates our deltoid and teres minor muscles and the lateral cutaneous nerve of the arm there's our axillary nerve and it innervates our deltoid muscle and teres minor muscle that Terry's minors part of the rotator cuff and then it also provides cutaneous innervation there to the lateral region of the shoulder so it's called the lateral cutaneous nerve of the arm specifically the superior branch also called the lateral brachial cutaneous nerve next we'll talk about the radial nerve that innervates our triceps and form extensor muscles and has sensory branches primarily the superficial cutaneous branch there's a radial nerve there and then there is our triceps on the back of the arm and our posterior forearm extensor muscles the back of the forearm so again remember that dorsal musculature extensors and then it also provides this superficial cutaneous branch to the back of the hand so the back of the thumb index and square finger there's other sensory distribution of radial nerve but this is the plane main place that we test it next is the musculocutaneous nerve that innervates our biceps and brachialis muscles and gives rise to the lateral cutaneous nerve of the forearm so there's our musculocutaneous nerve coming from that lateral cord and it also innervates her coracobrachialis muscle but it's more because the musculocutaneous nerve pierces that but functionally the biceps and the brachialis are the two functional muscles that we look at for clinically testing this musculocutaneous nerve it also gives rise to this lateral cutaneous nerve of the forum that provides sensation to the lateral forearm it's also called our lateral antebrachial cutaneous nerve okay next is the median nerve that innervates the forum flexors and thenar muscles and has a superficial cutaneous branch there's our median nerve and then it innervates forearm flexors like po nagar Teri's flexor carpi radialis and our palmaris longus muscles it also innervates deep too that the flexor digitorum superficialis and also deep - that it does the flexor digitorum profundus now the radial half and Radio hot because it's the to the belly that's closest to the radius and so the radial half only as well as our flexor pollicis longus that flexes your thumb it also does Athene our muscles that are associated intrinsic muscles of the thumb as well as our first and second lumbrical muscles the sensation are as follows so the superficial gait aeneas branches of the median nerve are there that does the volar or palmar surface of the thumb index where finger and the radial half of your index of your ring finger and then the dorsum of your thumb index where finger and part of the ring finger and finally our older nerve innervates the flexor carpi ulnaris half of the flexor digitorum profundus a bunch of the intrinsic hand muscles and the superficial cutaneous branches so there's our owner nerve coming primarily from that medial cord and it innervates the only muscle in the floor on the flexor compartment of the forum that has the word ulnar in it the flexor carpi ulnaris and the deepest compartment there is our flexor digitorum profundus but specifically only the ulnar half the half that's closest to the ulna bone that goes to your ring in and pinky fingers it also does for intrinsic and muscles the hypothenar muscles these intrinsic muscles that go to the pinkie as well as our third and fourth Lumber Co muscles and in addition to those intrinsic and muscle it does the palmar interossei muscles called the pads because these muscles the palmar interossei addict the digits and dorsal interossei a muscle called ABS because these muscles abduct the digits now sensation the superficial cutaneous branches will do the medial half of the palm the hand the pinky and the owner half of your ring finger on both the front and the back of the hand so there are the terminal branches and that my friends is the brachial plexus in a nut [Music] [Music]