This video was sponsored by Kenhub. More on them at the end of the video. Hello and welcome! My name is Patrick, and in this video I'll teach you some of my tips and tricks for remembering all the skeletal muscles of the upper limb that you would see in an anatomy class.
And to make this lesson more manageable for beginners, I'll present the list in smaller chunks of 4-8 muscles. You can find a list of the sections and timestamps in the description below. And with that out of the way, let's get into the muscles. A few of the muscles that control movement of the arm start all the way back on the spine. So for our first chunk, we'll talk about the muscles that people usually refer to when they say, it's back day.
The trapezius is this big muscle that inserts on the scapula and clavicle, but originates all the way from the base of the skull to the lowest thoracic vertebrae. Sometimes you'll see this described, especially in the fitness world, as the upper, middle, and lower trap muscles, but it's important to remember that they all make up a single muscle. Different sections of it just have different angles of fibers, so this one muscle can move the shoulder in multiple ways. multiple ways, but it's still a single muscle.
The easiest way to remember this one is by looking at both sides of the muscle together, it looks like a trapezoid, which gives it its name, trapezius. The other big superficial muscle is the latissimus dorsi, often just referred to as the lats. It's the widest muscle in the body, spanning from shoulder to shoulder and from the thoracic vertebrae down to the bottom of the sacrum. And all of those fibers meet up to insert on the humerus. If the lat's name doesn't stick for you, then you can use the Latin naming conventions of this muscle.
Latissimus refers to how lateral these muscles are, and dorsi refers to its location, on the back, just like the dorsal fin of a dolphin. If we cut away the superficial trapezius muscles, we'd see three more muscles that originate on the spine and move the shoulder blade. The rhomboid major and rhomboid minor both originate on the spine and insert on the scapula, helping us retract our shoulder blades and maintain good posture.
The rhomboid major is rhomboid-shaped, as the name implies. but the rhomboid minor is really more cylindrical in real life. My tip for this one is to identify rhomboid major first, then look right above it for its little buddy, rhomboid minor.
Also, people tend to mix up the rhomboid major and the serratus posterior superior muscle. Yeah, they're in similar spots, but the rhomboid is more superficial while the SPS is deep. The other big cue is the shape. The rhomboid has those straight geometric edges while the serratus has serrated or jagged attachments.
This is basically a muscle we talked about in the neck unit. The levator scapulae, which does exactly what you think. It elevates the scapula. But be careful. There are lots of neck muscles in this area that run superior to inferior.
The levator scapulae will be the only one that attaches vertebrae way high in the neck to the top of the scapula. The next chunk includes the muscles of the chest, and you probably know the root for this one already, pectoralis. The big familiar one on top is the pectoralis major, literally meaning big chest muscle. But underneath that is the pectoralis minor. It follows a similar path to the pec major, but doesn't extend all the way to the sternum and is clearly much smaller, hence pec minor.
As we move inferiorly, we see this cool looking muscle called the serratus anterior, named so because its jagged pattern makes it look serrated, or sawtoothed like a bread knife. For those who like to find these muscles with touch, you can feel both your pec major and your serratus anterior contract when you punch forward with a straight arm. Your pec is easy to feel, but you may have to press a little harder near your armpits to feel your SA.
Finally, the intercostal muscles are between each rib. Costal is the Latin root for rib, so intercostal literally translates to between the ribs. See this video if you want a little more info on those.
The next big chunk is the shoulder joint, most of the muscles that move the joint made of the glenoid fossa and the head of the humerus, the glenohumeral joint. The biggest and most superficial is the deltoid, named because it looks like the Greek letter D. delta, a triangle. Once you peel away the deltoid, you'll find the four muscles of the rotator cuff, what I learned as the sitz muscles.
The first three, the s-i-n-t, can be easily found on the posterior side of the scapula and use the big bony landmarks to find their name. The supraspinatus is superior to the spine of the scapula, while the infraspinatus is inferior to the spine of the scapula. Meanwhile, the teres minor makes an angle with each humerus that looks kind of like an M for teres minor. Finally, the subscapularis the S in the sits groups, literally means under the scapula.
If you think of the scapula like a rock, you could pick it up, turn it over, and if you looked under the rock, that's where this muscle would be. The last muscle of the shoulder chunk is the teres major, which takes a similar path to the teres minor, but as the name implies, something about it is bigger, and actually I don't bother looking at its size, I look at its position. It originates further down the scapula, and further down the humerus.
which means that this thing has some leverage that the teres minor doesn't have. In fact, the teres major is more like the powerful latissimus dorsi, your pull-up muscle, than it is like a rotator cuff muscle. So the teres major is a major mover of the arm. The muscles of the upper arm are a crash course in Latin names, and as long as you know the regional term brachii for upper arm, everything else is intuitive. You probably already know the biceps brachii, the two-headed muscle of the upper arm, and the triceps brachii.
the three-headed muscle. We got brachii to denote the upper arm, and the bi and tri to denote the number of heads, or seps. The coracobrachialis straight up tells you what it does. It attaches the coracoid process of the shoulder blade to the upper arm. Likewise, the brachioradialis connects the humerus, the upper arm bone, to the radius.
There's also the brachialis, the stubbiest of elbow flexors. Honestly, I just use the process of elimination to remember this one. The biceps and brachioradialis had more intuitive names, so the last upper arm muscle has to be the brachialis. Finally, there's a small muscle on the backside of the arm that extends the elbow a little bit. It's called the anconius.
It's not as powerful as the triceps, so it's a wee accessory muscle at this point. I remember this one because if you make a cone out of your arm, The very tip is the anconius. I hope you enjoyed the simplicity in this chunk, because the next two are, uh, more involved, you could say. Like, look at this forearm.
All of our human hand dexterity comes at the price of having a lot of tiny muscles. And anatomists didn't want to give them all fun, whimsical names. They get names like the flexor carpi radialis. What's it do? It flexes the carpi, or hand, and it's on the side nearest your radius.
The flexor carpi ulnaris? It does the same thing, but on your ulnar side. Anatomists gave them intuitive names, but that concentrates a lot of multisyllable muscle names into the forearm.
Take the pulmaris longus, a small muscle with a long tendon that inserts at the base of the palm for that pulmaris part. Fun fact, quite a few people don't have this muscle on one of their two hands, and some people don't have it at all. I made a video all about that which you can check out here. The pronator teres has a long but straightforward action name. It pronates the arm, pivoting your hand down.
You can actually palpate it easily if you put your finger in front of your medial epicondyle and pronate your hand. The other pronator is a square-shaped muscle all the way down at your wrist. Its action and square shape give us the name pronator quadratus.
These other muscles also use action plus anatomical region, like the flexor digitorum superficialis. It flexes the digitorum primarily at the proximal interphalangeal joint. this knuckle closest to your wrist here. You have plenty of other muscles to flex and extend the small interphalangeal joints, but we'll get to those later.
Now, as the name implies, if there's a superficial, then there's a deep, or what anatomists call profundus when we're talking about hand muscles. So the flexor digitorum profundus is also a finger flexor, but it's deep to the superficial version. Finally, there's a special Latin root for thumb. It's called pollux, so the flexor pollicis longus is a long muscle that bends the thumb.
Considering how important it is to be able to bend your thumb to grip anything, it makes sense that this muscle would have such a big muscle belly. Now, just like the anterior forearm, the posterior side has superficial and deep sections. Luckily, they follow the same predictable naming patterns.
We'll start from the outside in. The anterior arm had all the flexors, so the posterior side has all the extensors. Most of the time, that leaves us with mirror opposites, like the extensor carpi ulnaris, which follows the same convention.
it extends the wrist joint and inserts on the ulnar side. Or the extensor carpi radialis longus. Same thing, it extends the wrist and inserts on the radial side.
And while this one is a longus, there's also an extensor carpi radialis brevis that follows the same rules, it's just shorter. This muscle is the extensor digitorum, which extends the fingers. It's got a big muscle belly on the forearm and inserts on the dorsal side of the hand. Likewise, the extensor digiti minimi extends a finger but adorably only the tiniest, most minimal finger, the pinky. And you can feel all of these too.
If you put your arm down on the table, you'll feel the different muscles pop up for the whole hand, or just the fingers, or just the pinky. It's a great technique to come back to if you're ever lost on a test. When we go a little deeper, we see more action-specific names.
And the pinky isn't the only finger with its own dedicated muscle. The extensor indice starts on the ulnar side of the forearm and is solely responsible for extending the index finger, or forefinger. Then there's the thumb again. If you spread out your fingers, you'll notice a bunch of tendons around the thumb, which are sometimes called the anatomical snuffbox. Because you could put some cocaine there and snuff it a la Clive Owen's character in The Nick, but there's an anatomic significance too.
This snuffbox is made of the tendons that extend and abduct the thumb, and these long, tendinous muscles originate on the forearm itself. Those muscles are the abductor pollicis longus, extensor pollicis longus, and extensor pollicis brevis. And you'll notice that these muscles insert at different points on the thumb, which helps us identify them. The abductor inserts on the thumb's metacarpal, and has this almost diagonal pull to it. Whereas the extensors, both longus and brevis, cross over the top of the carpometacarpal joint at the base of the thumb.
The abductor pulls sideways, the extensors pull up. From there, the difference between extensor pollicis longus and brevis is just the size. Finally, we already saw the pronator muscles on the anterior forearm, so the muscle that performs the opposite motion must be on the posterior forearm. And it is.
The supinator muscle is found all the way up at the elbow, sprawling across the ulna, radius, and a bit of the humerus too. Here's how I remember this one. All of the other muscles of the forearm control the hand, and you can tell because they have long tendons that insert at the hand.
But the supinator only really interacts with the two forearm bones. So supination is the only thing that it can do. The next chunk is the thenar mass, a group of four short muscles that make up the fleshy mass of your palm.
Collectively, they're special muscles that move the thumb and their names reflect that. Because the muscles are named after their actions, my big The biggest advice is to know your movement terms and look at the angle of pull. The flexor pollicis brevis originates at some of the carpal bones and inserts on the first phalanx. And thumb flexion looks similar to thumb opposition, bringing the thumb and pinky together. Because of that relationship, the muscle responsible for opposition is called the opponent's pollicis and is directly underneath the flexor.
In reality, both of these muscles work together when curling the thumb like during writing, so it's hard to say that this muscle just does the this action. The next muscle gets another movement name, the adductor pollicis. For this one, you just need to know that thumb flexion is more of a bending, while thumb adduction is like bringing your thumb parallel to the other fingers.
From there, you can see how the adductor pollicis just brings the thumb towards the midline. Finally, the abductor pollicis brevis is the odd one out. It abducts the thumb, bringing it away from the palm.
So it runs from the medial carpals to the dorsal side of the thumb, and has this giant muscle belly just slopped along the metacarpal. Look at it, there's no way that muscle is bringing the thumb toward the midline. It must be an abductor. Also pro tip, you can palpate the abductor.
Relax your thumb, put your finger on the thenar mass, abduct your thumb, and it'll pop up. So at this point we've covered a lot of those hand and finger muscles, but there are still a handful left. We had a thenar mass of muscles that control the thumb, but we also have the hypothenar mass. made of muscles that move the pinky. Remember how we said that opposition is touching the thumb to the pinky? Well, it takes two muscles to tango, to finger tango.
What I'm trying to say is that the opponent's digitai minimi is responsible for opposing the pinky, thus completing the motion of opposition. It's easy to see given its diagonal path, especially when you contrast that to the flexor digitai minimi brevis, which pulls directly parallel to the pinky, which curls or flexes it. And it's a short guy, so brevis.
The last in the hypothenar mass is the abductor digiti minimi, this hardy slab of muscle on the medial side of the hand which abducts the pinky. No surprises there. Now there's another misfit muscle near the hypothenar group called the palmaris brevis. It hooks up to a band of connective tissue called the palmar aponeurisis.
And despite its location, it doesn't have anything to do with moving the pinky. It actually pulls on the connecting tissue which lets our hand maintain a strong grip. It's a short muscle connected to the palm, hence palmaris brevis. Finally, there are a few muscles found directly between the fingers that let us spread or bring our fingers together. The lumbricals are tiny muscles that originate on tendons on the palmar side of your hand, and insert on structures at the phalanges called the extensor expansions.
And the fact that they cross multiple joints and twist around from palm to dorsum gives them a unique action. They flex the carpometacarpal joints and extend the interphalangeal joint, giving us a hand that looks like an L. Luckily, that helps us remember the name.
Its action gives you an L for lumbrical. The last two are the interossei muscles, literally translating to between bones. In this case, they're between the metacarpals.
The palmar interossei adduct the fingers or bring them together, while the dorsal interossei abduct the fingers or spread them apart. Unfortunately, they look super similar, so I use the mnemonic pad-dab to remember them. Palmar causes adduction, while dorsal causes abduction. Fun fact, the only reason Spock can do the Vulcan greeting is because of these muscles.
It involves both finger adduction and abduction. Now, these are just the tricks I personally use to remember these muscles, but if you want another great resource for learning anatomy, then you need to check out Kenhub. I use them all the time when researching and writing these videos, and for this series in particular, their written articles and Atlas of Muscles have been extremely helpful in refreshing my knowledge of some of those deeper, smaller muscles.
They've also got an enormous library of in-depth videos about muscles, histology, vasculature, nerves, and everything else you'd need to know in anatomy class. All those beautiful illustrations that you saw in this video came from them. And in addition to their library of content, I also love Kenhub's quiz feature. They allow you to build custom quizzes with different difficulties, and they give you feedback so you can figure out where your weaknesses are. You can use most of Kenhub's features for free, but if you want full access to all of their learning content and quizzes, then go to khub.me slash corporus to get 10% off your subscription.
They've also got a no questions asked seven day money back guarantee. So you can try out the premium version for seven days. And if you don't like it, get your money back. If you want to see the next video in the muscle memorization series, then check out this playlist here. Otherwise, subscribe, leave a like on the video, have fun, be good.
Thanks for watching.