[Music] last week a friend of mine stabbed herself in the finger and she severed one of the nerves here and while we've talked about the nerves that run into the hand and what they do we haven't looked at the branches within the hand and this is a fairly common injury so the question is what nerve did she sever what does that nerve do so what function did she lose how would you test for that where did the nerve come from and what might you do to repair it they take the format on its head we'll do the last bit first but we'll look at we'll review the the median ulnar and radial nerves that go to the hand and what they do and then we'll look at the individual branches but if you say there are different ways of damaging a nerve as in a collection of neurons and you've got to think of a nerve as you know a collection of long sally axons bundled together so surrounded by myelin so they can be crushed or stretched or compressed and you know it's like when you bang one you know that sensations like but if you sever it of course those axons get separated if you get pulled apart they get separated now if you leave that there is an attempt to repair form the severed axons and what tends to form is something called a neuroma which itself can be very painful when it develops over time and then it will kind of exist forever and it all it's very unlikely to join up with the other axons and reconnect and restore any sort of function so something that does need to be looked at and treated and considered but if a skilled surgeon is able to put the end of the nerve back together there is a fair probability of the neurons repairing mending a restoration of function and that neuroma won't fall so you're going to know your Anatomy to be able to do things like that the three major nerves that innervate the hand motor and sensory are the median ulnar and radial nerves these nerves will come from the brachial plexus they run through the upper limb they have various functions within the upper limb but those are the three nerves they enter the hand and then have sensory roles from the skin and some motor roles to the muscles of the hand both the radial nerve doesn't dad doesn't so it's just the ulna and the median nerves have they can innovate these small muscles of the hand that are involved in movements of the digits so those are the three right that was the easy bit okay will do median nerve then on the move and radial nerve we're saving the easy one for the last if I'm really clever I'll draw these on my own hand than how clever I am though so the median nerve either three it's the only one that passes through the carpal tunnel so in the bones of the wrist they form a little U shape which is overlaying by the flexor retinaculum which ties down all the tendons running into the hand and the median nerve runs through that space which means it is a vulnerable to compression within that space so that's how the median nerve gets through the wrist into the hand but before it runs through the carpal tunnel the median nerve gives off a Palomar cutaneous branch that's going to run to the skin kind of in the middle of the palm so that branch isn't gonna throw through the carpal tunnel it's gonna go superficial to the flexor retinaculum to carry sensory innervation back from this region hitch that's kind of the first branch then when the median nerve passes into the into the hand into the palm deep to the flexor retinaculum it gives off three branches it gives off lateral and medial branches and a recurrent branch now this muscle belly here this that we take for granted this is the thenar eminence these are the intrinsic muscles of the thumb intrinsic because they're within the hand these muscles of the thenar eminence are innervated by the median nerve this is your big indicator as to whether the median nerve is happy or not if it's injured or not and it's the recurrent branch of the median nerve that innervates these muscles and that branch branches from the median nerve after is passed through the carpal tunnel right now the medial and lateral branches are well they're going to be sensory so when we talk your medial and lateral we're in our anatomical position right so the anatomical position is so if this is the anatomical position this then is medial and this is lateral now the radius is on this side this is where the radial pulse is so the lateral side also might get called the radial sides that's the side the thumb is on the little finger is on the medial side that might get called the on the side for today we're going to we're going to talk about the lateral and medial size because we're going to talk about lateral and medial branches can you see how if we were to talk about radial branches of the median nerve you would get really confusing really quickly so we're not going to do that right okay from lateral so the lateral branch then of the median nerve in the palm is going to run out laterally towards the thumb sensory so this is going to carry sensory innervation back from the palmar side this side of the skin of the fun and the palmar side of this side of the first finger so it's sensory from the first and second digits this part the second digit the lateral part of the second digit also known as the index finger or the first finger so with hands there's kind of a lot of terminology and you need to know it all first finger index finger second digit all that stuff right also that lateral branch of the median nerve in the hand is motor to the first lumbrical the lumber cause little wormie muscles involved in the fingers go read about those elsewhere so it has a motor job and a sensory job so the medial branch of the median nerve in the hand is going to give off branches that will run up this side of the first finger both sides of the second finger and this side of the third finger it's going to carry sensory innervation back from you know this side and the palmar surface of the index finger the palmar surface of the second finger and the lateral surface and palmar surface or half the palmar surface of the third finger so the medial branch of the median nerve in the hand is going to be sensory to part of the second digit the palmar surface of the third digit and part of the fourth digit and it's also going to have a motor function it's going to be motor to the second lumbrical talked to hand surgeons you'll get some more terms so the the branches the nerves that branch from the lateral and medial branches of the median nerve the run of the fingers will also get called common palmar digital nerves and proper palmar digital nerves so the common palmar digital nerve is one that's going to run up towards the finger and then it's going to give off other branches so it's a common nerve a common palmar digital nerve and then it divides into two proper palmar digital nerves which are going to run up these sides of the fingers either side here do you see what I mean it's a common palmar and proper Palmer common means it's gonna divide proper palmar digital nerve means it is a proper it has divided it's that that are at risk of injury here yes I've got a scar there because the way these these games it is you tend to have a knife in your dominant hand on you and you're opening something cut that's what I did that when I was like 16 17 probably cutting open something and I slipped and I sliced through that the scar still there know that there's two scars there one there one there's another scar there that was from dissecting articular cartilage from some bone samples in a lab and I was rushing and I didn't have a chainmail glove on and I slipped and I cut through to the bone that was nice anyway so these injuries often hit the signs of the hand blockage somebody's usually holding something and it's these nerves here these these these digital nerves or these proper digital nerves we're talking about the polymer one so far we're gonna see some dorsal ones in a minute it's those that are at risk of injury now motor or sensory well all the muscles are in here so by the time you get past this joint the nerves of only got a sensory job to do there's no muscle in here this is tendon and connective tissue that's pulling on the muscles to give us these movements so if the nerve is injured up here then there's going to be a loss of sensory information but if the nerve is injured further down here you can see how some of these branches have got both motor and sensory roles so then you're gonna have both motor and sensory deficits because there are a lot of branches it takes me some careful examination and diagnosis to work out what's going on anyway right that's the medial nerve done those are all its branches superficial palmar recurrent medial sorry lateral lateral and medial branches of the median median nerve in the hand right next to the ulnar nerve so you know that the ulnar nerve runs round the medial epicondyle of the humerus maybe because that's a funny nub that's your funny bone that's the bit you bang and of course what tingles well it's your little finger in this side of your hand so that's the ulnar nerve is gonna run into the hand the medial side this is the hypothenar eminence here this this fleshy bit of muscle here now again okay first of all the ulnar nerve does not run through the carpal tunnel to get into the hand it runs superficial to the flexor retinaculum before the ulnar nerve runs into the hand it gives off two branches it also gives off off a superficial palmar branch which is going to carry sensory innervation back from the medial palm close to the wrist and the skin around here and it gives off a dorsal branch now if this is the palmar side of the hand this is the dorsal side so the dorsal branch is going to run around here now the dorsal branch of the ulnar nerve is gonna carry sensory innervation back from the dorsal hand around here the dorsal skin of the little finger and the dorsal skin on the medial side of this finger here so it's going to be sensory to digits five and half of digit for the ring finger again the actual digital branches that are running up to the fingers are running laterally up here so we have little power Mar Digital branches here and dorsal digital branches on the other side so a lateral injury could injure either of those things dorsally you can feel the bone is very superficial with all of the connective tissue here and on this side of course power on the palmar side with all of the tendons there the nerves get out of the way and they run on either side of the finger not on the front of the back the dorsal branch of the ulnar nerve does not carry sensory innervation back from the tips the the tips that sensory innervation is coming back on the palmar side not the dorsal side right works for the radial nerve over here - we'll get that right okay so only nervous a superficial palmar branch a dorsal branch it then gives off it also gives off superficial and deep branches the superficial and deep branches of the ulnar nerve to the hand branch off after the wrists and the superficial branch is mostly sensory the deep branch is motor right so what have we got left then if we said the median nerve carrier sensory innervation back from these regions of skin then the superficial branch of the ulnar nerve is going to carry sensory innervation back from some of the palmar skin from the from and the power that the power mast skin of the little finger and the palmar skin of the medial side of the third finger so that is the power mask in a digit five and the medial palmar scan of digit for hopefully the pictures are doing a clearer job than maybe my descriptions there's a lot going on here if you look at the pictures and you learn those that's how you hold on to it right but again the superficial branch of the ulnar nerve is carrying sensory innervation back from the tips of these fingers the whole tip here and it shares that job with the median nerve over here okay right the deep branch of the ulnar nerve in the hand and this makes sense right it's going to innervate the muscles muscles a deep skin is superficial right now and the list of muscles well okay the deep branch of the ulnar nerve in the hand is going to innervate all the muscles of the hypothenar eminence it's going to innervate the lumbricals of the fourth and fifth digits it's going to innervate all of the interosseous muscles both Palma and dorsal interosseous muscles it's going to innervate the adductor pollicis muscle and it's gonna in ave one of the heads the short head of flexor pollicis brevis so those motor functions of the ulnar nerve in the hand the you've read about are carried out by that deep branch of the ulnar nerve the branches from the ulnar nerve after is passed into the hand the superficial branch does have a motor role there's a there's a little muscle here called palmar it's brevis Brothers meaning short which goes into the pond that the superficial branch of the ulnar nerve innervates that muscle it's very much a textbook table thing how useful that is as a piece of knowledge I don't know okay then the radial nerve so the superficial branch of the radial nerve leaves the radial nerve at the cubital fossa and works it's what let's do this way it's Thompson works its way all the way back to this region here it's pretty well protected during its root and superficial branches then sensory in the hand it has a sensory role we've covered all the motivates with the other nerves the superficial branch of the radial nerve runs into the hand around here and it's carrying sensory innervation back from the skin of the dorsal hand over on the thumb side so on the lateral side right the radial side a carrier sense renovation back from the dorsal the skin of the dorsal thumb the dorsal hand the dorsal skin of the first finger the second finger and the dorsal skin of the lateral half of the third finger so digits 1 2 3 & 4 but not the tips and that's it's now if you add up all the bits we've done we can account for all of the cutaneous innervation from the skin of the hand and all of the muscles another useful thing that we can do here is we can consider dermatomes right when we're thinking about peripheral nerves we're thinking about bundles of neurons bundled together to travel throughout the body but also we can consider those neurons as they come out of the spinal cord at different levels and then run through whichever route they want to take to get to the regions of the body so we can test the functions of the levels of the cervical spinal cord by remembering that sensory innervation from this region goes back to the c6 level from this finger back to the c7 level from this finger back to the c8 level c6 c7 c8 and there's some overlap in between of course because you've seen how the the proper digital nerves work and how there's some overlap between median on there and radio right good okay there we go that's a tough one there's a lot in there and you can see why there's a lot of detail in there because hands are incredibly important to us we have a lot of fine control we have a huge amount of sensory detail in the hands so not only is there a lot of anatomy in there to account for that but the knowledge of that Anatomy is important to manage maintain repair function in the hand alright see you next time [Music] you [Music]