It's great to be recording a video again. We've finished the planting season, we've finished the vacation season, and today, well, this year we're all charged up and focused on new projects on this channel. Today we'll talk about the muscles of the hand. We'll finish this video with the myology of the upper limb. I invite you to look for videos on my channel about the muscles of the forearm, muscles of the arm, and muscles of the shoulder.
And as I said, After this I'll focus on making videos about the lower limb. So, as I've been saying, today we'll talk on this Easy Anatomy channel by Juan Jose Sanchez about the muscles of the hand, which we'll divide into four large groups, starting with the intrinsic muscles of the hand, muscles that we find specifically in this region. We're going to talk first about the muscles of the thenar eminence that we'll develop later, which are four muscles.
Then we'll talk about the muscles of the hypothenar eminence, which are three muscles plus an additional one that I'll mention in due time. Finally, we will talk about the interosseous muscles, which are divided into two groups, and the lumbrical muscles. Greetings to Juan Jose Sanchez.
Stay tuned to the video. I invite you to subscribe here in the lower right corner, click on it, and don't forget to like the video. So, let's start with the muscles. First of all the thenar eminence.
Many books will tell you that there are four muscles, but most agree that there are three. It's just that, topographically, in this thenar eminence we will find four muscles, but properly speaking, of the thumb muscles, Only three of the four that are in the region are those that form part of the thenar eminence. So, the thenar eminence is nothing more than the elevation that is found on the lateral part of the hand.
Remember that the lateral part is the one that is facing where the anterior lateral thumb is, specifically of the hand. So, these thumb muscles will be divided into two planes, two superficial and two deep. Let's start with the two superficial muscles first. Let's talk first about the abductor pollicis brevis muscle. This abductor pollicis brevis muscle is the one that is located more laterally and superficially with respect to the other muscle, the superficial group, which is the flexor pollicis brevis muscle.
It is important to give it this second name, which is the word brevis, because there is a flexor pollicis longus and an abductor pollicis longus, which we already saw when we talked about the posterior muscles of the forearm. That is why I invite you to study the myology of the upper limb from the proximal distal point so that you can understand it. So, well, this abductor pollicis brevis muscle and the flexor pollicis brevis have the same origin, it is at the level of what is called the flexor retinaculum, which is this ligamentous structure that you see here. Remember that the flexor retinaculum is also called the anterior annular ligament of the carpus.
In addition to these two, I mean the abductor abductor pollicis brevis and the flexor pollicis brevis originate at the level of the flexor retinaculum, they also originate at the level of the tubercle of the trapezium bone, which is a bone that articulates directly with the first metacarpal which is here, one of the bones of the carpus. In addition to this, listen carefully, only the flexor pollicis brevis also originates at the level of what is, sorry, only the abductor pollicis brevis originates at the level of what is the tubercle of the scaphoid. So both originate at the level of the flexor retinaculum, at the level of the tubercle of the trapezius and apart from that, only the abductor pollicis brevis also originates at what is the tubercle of the scaphoid. So its insertion is going to be at the level of what is the proximal phalanx of the first finger.
Okay? So, in addition to inserting at the proximal phalanx of this first finger, They insert into a small bone located there, which is a sesamoid bone called the external sesamoid bone of the first finger, as well as in the extensor expansion of the first finger. The good thing about the muscles of the thumb is that their name tells you their function. The function of the abductor brevis, which is this one, will be to abduct the thumb and that of the flexor brevis will do what is called flexion of the thumb muscle. Here we see it in a more dissected plane.
This one that is here superficially would then be the abductor brevis and this one that we see more medially would be the flexor brevis. The image is useful to tell you that this one in green is the abductor and that the flexor brevis has two portions, let's say a more lateral portion and a more medial portion. The lateral portion is the one that has the origins that I mentioned at the beginning, and the medial portion is said to have a common origin with this muscle that we will talk about later, which is the adductor pollicis muscle. However, both portions join, the deep and the superficial.
to insert at the level of the proximal phalanx of the first finger and the extensor expansion. What will change in the portions is basically the origin. Now we will talk about the third muscle, which is already the first, which is part of the deep layer of the muscles of the thenar eminence, which is the opponent's pollicis muscle. You should know that this opponent's pollicis muscle is the one that forms the eminence itself, together with the first two that I mentioned. That is to say, the thenar eminence itself is only formed by the abductor brevis, the flexor brevis and the opponent's pollicis.
This fourth muscle that I will talk to you about now, which is the adductor pollicis, although it is a muscle of the thumb, is not part of the eminence itself. So, let's look here at this deeper image. This opponent's pollicis muscle, which would be the one you see here, also originates at the level of the trapezius bone.
which is the one you see here, and at the level of the flexor retinaculum, which is the same anterior annular ligament of the carpus. Basically, then, it has the same origin as the flexor pollicis brevis for this muscle to insert into the first metacarpal. What basically changes is the insertion.
Finally, we will talk about the adductor pollicis muscle, which has two origins or two portions of origin, a transverse portion and an oblique portion. The transverse portion, which is the one you see here lower down, originates at the level of the third metacarpal. But note well that the oblique portion, which would be the one you see shaded in green here, or in the previous image it would be the one that grips upwards, originates at the level of the second metacarpal, at the level of the capitate bone and the trapezoid bone of the Carpus That will be the origin of the deep portion. Both portions of the adductor pollicis, the superficial and deep, join to insert at the level of what is the proximal phalanx of the first finger and its extensor expansion. So, it is basically the same insertion of the abductor pollicis brevis and the afflexor pollicis brevis.
What is going to change with the adductor? That the adductor does it medially. Remember that I told you that the abductor pollicis brevis and the flexor pollicis brevis inserted into the external sesamoid bone, while the adductor does it in the internal sesamoid bone and in the internal part of the proximal phalanx of the first finger.
At the end of the video I will explain the innervation of all these muscles, which is really easy. Right now what I want you to focus on is the origin, the insertion and the function. This is more to tell you then that the function of this adductor pollicis is going to be adduction. to bring my thumb towards the midline.
So, once we've finished with the muscles of the thenar eminence, we'll quickly move on to the muscles of the hypothenar eminence, which are three and a little tip that I'm going to give you, which is the fourth muscle. Before explaining the muscles of the hypothenar eminence itself, which are the muscles that are like the opposite of those of the thenar eminence, which are those of the thumb, these muscles of the hypothenar eminence are related to the little finger. There's one that's superficial and completely covers it, which is the palmaris brevis muscle or in Spanish the palmaris brevis muscle. It's an inconstant muscle, some people have it, others don't. It originates in the medial part of what is the palmar ponorosis and inserts into the skin that covers that portion of the hand.
Basically, what it does is relieve the pressure of the muscles on what is the ulnar artery. It's said that's the function of this palmaris brevis muscle. Now, Once we section the palmaris brevis, we find the muscles of the hypothenar eminence itself, which as I said, there are three. First, we are going to go from superficial to deep or from medial to lateral.
The most superficial would be the abductor digiti minimi. Then the flexor digiti minimi brevis, remembering that there is a long flexor that is at the level of the forearm and the deepest opponent's digiti minimi. So, you know, abductor digiti minimi, Flexor Digity Mini-Me Brevis and Opponents Digity Mini-Me. We are going to start with the Abductor Digity Mini-Me Brevis, which you can see originates at the level of the PIS IV. It seems to be a continuation of this tendon which is the anterior ulnar muscle, also called flexor carpi ulnaris.
So the same insertion of the anterior ulnar muscle is the origin of the reductor digiti minimi. It will be inserted, look at it here, at the proximal phalanx of the fifth finger and its function will be to extend the little finger, that is, to move it to the side. Remember that abduction at the level of the hand is everything that moves away from the midline and the midline here is the third finger. So, Moving the little finger outwards, even though it is moving towards the midline of the body, it is moving away from the midline of the hand. That is why this movement is abduction of the little finger and not adduction, as is stated in some books that are wrong.
Let's talk about the flexor digiti minimi brevis, which would be this more intermediate muscle in relation to depth. This flexor digiti minimi brevis originates at the hook of the hamate bone and inserts into the proximal phalanx of the fifth finger. Very close to the insertion of the abductor digiti minimi. Finally, we will talk about the opponent's digiti minimi, which has the same origin as the flexor digiti minimi brevis, that is, at the level of what is the apophysis of the hamate, or, as it is called, the hook. But this one, unlike the previous one, is not inserted into the proximal phalanx, but rather into the fifth metacarpal.
Its function is to perform the opposition of the little finger. The difference between the opposition or opposition movement that the little finger makes with the thumb is that the thumb opposes the other four fingers, while the little finger only wants to do, can do, my opposition with the thumb, remembering that opposition is nothing more than touching the pads of the fingers together. So, well, these would then be the muscles of the hypothenar eminence. Let's move on to talk about the interosse and the lumbricals, starting with the latter which are the lumbrical muscles.
What is the difference between an interosse and the lumbrical? Something that always confuses students. The lumbricals are muscles that go from tendon to bone, okay? And their functions are flexion.
While the interosseous muscles are muscles that go from bone to bone and their functions are basically either abduction or adduction. Let's start first with the lumbricals, which are four muscles. All four of these muscles originate at the level of what is the flexor muscle or tendon, or rather, The flexor digitorum profundus. Remember that this flexor digitorum profundus was the one that passed at the level of this channel that the flexor digitorum superficialis made and was inserted at the level of what is the distal phalanx of the last four fingers, that is, the four most medial fingers. So, that is the origin of the flexor digitorum profundus tendon.
Its insertion, see it here in this section. Remember that this is anterior and this is posterior, that is, this is palmar and this is dorsal. Its insertion will be at the level of the aponeurotic expansion. Obviously it will be from the second to the fifth finger, because remember that the first finger did not have a lumbrical muscle.
So that insertion at the level of what is the extensor expansion of the second to fifth fingers is what will give it its function, because the function of this muscle is going to be the extension of the interphalangeal joints. The extension, although it is not inserted into the tendon of the extensor itself, when this muscle contracts, when the flexor digitorum communis muscle or the flexor digitorum profundus muscle relaxes, it helps with the extension of the fingers by inserting at the level of what is that extensor expansion. That is why this muscle, despite, listen carefully, that it originates from a flexor, Its function is to extend the interphalangeal joints, don't forget that.
Now, now the interosseous muscles, which are deeper, are divided into two large groups, an anterior group, which is the palmar group, and a posterior group, which is the dorsal group. Just like the lumbricals, there are four, that is, there are four lumbricals, four palmar interosseae, and four dorsal interosseae. Let's start first with the palmar interosseae muscles.
Although this image you see is an image taken from the anatomy class, in theory it insists that there are four palmar interoche muscles. These muscles originate at the level of the first, which is the one missing from the image, the second, fourth, and fifth metacarpals. Note that they do not touch the third metacarpal.
Why don't they touch it? Because their function is to adduct the four fingers where they are inserting, that is, the first, second, fourth, and fifth. I just explained to you that the midline of the hand passes at the level of the third finger. So, it would not make sense for the third finger to have a palmar interosse muscle, because the function of the others is to bring it closer to the third finger.
Note the insertion, this one down here would be the lumbrical, this would be the palmar interosseum, and this would be the dorsal interosseum. Note that these palmar interosseums are also inserted into the extensor expansion of the fingers where they originate, that is, the first, second, fourth, fifth, and sixth fingers. and fifth. And their function is basically going to be adduction, that is, bringing those four fingers that are the outermost ones closer to the third finger.
The opposite happens with the dorsal interosseums, which are four. First, what difference do you see between these dorsal interosseums and the palmar interosseums? These dorsal interosseums have two bones of origin, all of them, and there are also four of them.
Note that the first interosseum, remember that you always find it taking into account the thumb, originates in the first metacarpal and the second metacarpal. The second dorsal interosseum is between the second and third, and the third is between the third and fourth. And the fifth dorsal interosseous muscle is between the fourth and fifth metacarpals.
These muscles also join both portions of origin and are also inserted into the extensor expansions. How will they vary? Listen carefully. How will they vary with the palmar muscles? Well, The first dorsal interosseous is inserted into the second metacarpal, into the second finger, into the trefoil of the second finger.
The third and fourth reach the third finger, so that the third finger is the only one that has insertion of two dorsal interosseous, while the fourth dorsal interosseous is inserted into the fourth finger, into the extensor expansion of the fourth finger, so that the first and fifth fingers do not have a dorsal interosseous muscle as insertion. The function of these dorsal interosseous is the opposite of that of the palmar interosseous. If the palmar interossary muscles abduct my fingers, the dorsal interossary muscles do the opposite, that is, they abduct my fingers, moving them all away from the third finger.
Okay? Remember that the midline, as I remind you, passes at the level of the third finger. So, to finish, we will talk about the innervation of these muscles of the hand in the form of diagrams. Those of the thenar eminence, the three that make up the thenar eminence itself, are innervated by the median. The only muscle in this region, of the thumb muscles, that is not innervated by the median, is the only one that is not part of the thenar eminence, as I said, which is the adductor pollicis.
It is innervated by the deep branch of the ulnar nerve. Now, regarding the hypothenar muscles, which I told you there were three, and I also mentioned here what the palmaris brevis is, They are all supplied by the ulnar nerve, but specifically by the superficial branch of the ulnar nerve. Now, regarding the interosse, both the palmaris and the dorsal muscles are innervated by the deep branches of the ulnar nerve, as is the adductor pollicis.
While the lumbricals vary, the first and second lumbricals are innervated by the median because they are the ones that innervate that portion of the flexor digitorum profundus muscle. While the third and fourth lumbricals are innervated by the deep branch of the ulnar because it is, listen carefully, the one that innervates, I mean, the ulnar, which is that portion of those tendons of the flexor digitorum profundus. Remember that this flexor digitorum profundus is the origin of these lumbrical muscles.
So friends, this has been the entire video on the muscles of the hand. Don't forget to subscribe in the little circle that appears here. Like the video which is very important and don't forget to follow me on Instagram at ajanpisoseacuteenches1315. Here are the videos of forearm muscles, arm muscles and shoulder muscles.
Also so you can watch my videos of bones in the hand, forearm bones and have complete information.