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Muscles of the hand

Origins, insertions, innervation and functions of the intrinsic muscles of the hand.

Show transcript

Hello, everyone. This is Joao from Kenhub and welcome to another anatomy tutorial where this time we’re going to be talking about the muscles of your hands, specifically about the muscles or the intrinsic muscles of the hand as you can see here on this image.

So as you notice here on this image, we just strip all the skin, fat, and a lot of other tissues to just leave the bones and muscles and a lot of the ligaments that you can see. And notice that we’re looking from a palmar view of the hand.

On this tutorial, we’re going to be describing all of these muscles including their attachment points, innervation, and functions.

First point I would like to mention is that the intrinsic muscles of the hand, they can be divided into five groups specifically – the dorsal interossei, the palmar interossei, the lumbricals, the hypothenar, and the thenar muscles. Keep in mind that the first three here on the list, they’re usually included in a different group known as the metacarpal muscles.

Let’s start off with the very first one here on the list, this group. And notice that I just turned the hand to the back.

Now, you’re seeing the back of your hand or the dorsal view of your hand. Now, we’re seeing here the dorsal interossei muscles.

The dorsal interossei muscles are four short muscles of the metacarpals. As you can see, one, two, three, four. And they also are usually numbered, so this one closest to the thumb is number one all the way to the one closest to your little finger. This one is number four.

As every good muscle out there, they have origin points. And the origin points are the adjacent sides of two metacarpal bones which you can see here.

So if you notice, at the dorsal interosseous muscle, number one, it is attached here to this metacarpal bone, the metacarpal bone number one found on the same direction of your thumb.

And then it also attaches or originates from the second metacarpal bone which is in the same direction as your index finger as you notice. And the other muscles are doing the same thing, so attached to the adjacent sides of two metacarpal bones.

Distally, their tendons are going to be inserting at the dorsal aponeurosis and the base of the proximal phalanx of the second to fourth fingers. And for that reason, they will be running towards the middle finger which leads to the following insertion surfaces.

So on number one, you’re going to see that is attaching to the radial side of the index finger specifically on the base of the second proximal phalanx.

Now, the second interosseus muscle, as you can also see here on this image, is attaching on the radial side of the middle finger on the proximal phalanx of the middle finger.

And on the third interosseus, dorsal interosseus muscle, you see here then it’s now attaching to the ulnar side. Notice here the ulna and the radius. That’s why we call it the radial side and the ulnar side.

Same things happening here with the fourth metacarpal when it’s attaching to the ulnar side of the ring finger. So it’s attaching to the proximal phalanx to the ulnar side of the base, this is the base of the proximal phalanx of the ring finger.

In order to contract muscles do need help from nerves, so we have to talk about innervation for the dorsal interossei muscles.

Now, the innervation of all dorsal interossei muscles is carried by the deeper branch of the ulnar nerve. Which you see here the ulnar nerve highlighted in green in this image.

Now, the next topic that we’re going to be talking about is different functions associated to the dorsal interossei muscles. Based on their attachment points, they’re going to be performing different actions in the fingers.

Now, the first and second dorsal interossei muscles are going to be able to pull the index and middle fingers medially to what we call then radial abduction. And you can see here these arrows indicating the movement of these fingers that these muscles are going to be able to perform.

Now, the third and fourth dorsal interossei muscles are going to be able to move your middle and ring fingers laterally to what we then call ulnar abduction. So movement or you’re spreading your fingers towards your ulna.

And notice here that, again, this is your ulna and this is your radius. As a group, these muscles are going to be able to perform flexion in the metacarpal phalangeal joints and also extension in the proximal and distal interphalangeal joints.

We’re now ready to move on to the next group of muscles that you see here highlighted in green. Notice that I now turn the hand back to the palmar view where we’re seeing now the palmar interossei muscles.

The palmar interossei are three muscles located in the metacarpals. They arise from the metacarpal bones of the index finger as you can see here. The ring finger and little finger as well.

Now, the origin surfaces of these muscles are facing towards your middle finger. And for that reason, we’re going to say that the first palmar interosseus muscle, this one here closes to the thumb, is found on the ulnar side or attaching to the ulnar side of the index finger of the metacarpal bone of the index finger.

While the second, this one right here, the second palmar interosseous muscle is then attaching now to the radial side of the ring finger of the metacarpal bone of the ring finger.

One reminder here that now we’re looking at the palmar view of your hand, this here is the radius, this here is the ulna. That’s why we say that here, this one is attached to the radial side towards the radius, this one is attached to the ulnar side towards the ulna.

Now, the third palmar interosseous muscle is attaching now to the radial side of the metacarpal bone of the little finger.

Now from there, these muscles are going to be inserting at the dorsal aponeurosis and also the bases of the proximal phalanges of their respective finger. One important point, note that the middle finger does not have its own palmar interosseous muscle.

Now, when it comes to the innervation of the palmar interossei muscles, the nerve supply is provided by the deep branch of the ulnar nerve. And right now on this image, you see also the ulnar nerve highlighted in green. And notice that we’re looking at a palmar view of your hand.

Moving on to the different functions associated to the palmar interossei muscles, the most important function of the palmar interossei is closing your spread fingers or open fingers which means that the movement of the fingers towards your middle finger. So this is what we call then adduction in the metacarpal phalangeal joints.

The first one, the first palmar interosseous muscle is going to be pulling the index finger medially as you see here indicated by this arrow.

Now, the second and third interossei muscles, palmar interossei muscles, are going to be pulling the ring and little fingers laterally as you also see here indicated by these arrows.

Now as a group, these muscles are going to be able to perform adduction in the metacarpal phalangeal joints.

We are now ready to move on to the next group of muscles that you see here highlighted in green, these are known as the lumbrical muscles, also known as just the lumbricals of the hand.

Now, they are four short hand muscles located in the metacarpals deep in the palmar fascia.

In terms of origin point and very interesting point that I would like to make here is that one of the feature associated to these muscles is that they originate from a tendon as you can see here on this image.

These tendons here are going to be serving as origin points for these muscles. So they will make the origin surfaces quite movable.

So they usually arise from the radial side of the tendons of the flexor digitorum profundus. So these structures that you see here now looking at the palmar view of your hand. Now these are the tendons of the flexor digitorum profundus.

Now when it comes to the insertion points for these muscles, they’re going to be inserting on the dorsal aponeurosis of their respective finger.

And I would like to also use this image here to show you the first two lumbricals and then the other two. So you always start counting them from your thumb all the way to your little finger.

This to say that in terms of innervation, the first two lumbricals are going to be innervated by the median nerve which you see here highlighted in green on this image; whereas the ulnar nerve is going to be responsible for the innervation of the third and fourth lumbrical muscles.

Now we’re going to be talking about the different functions or actions associated to the lumbrical muscles. The lumbricals are responsible for producing movements on the second all the way to your fifth finger.

And their contraction will lead to that flexion in the metacarpal phalangeal joints which you see here indicated by this arrow, and even this image shows a bit of flexion here on your fingers.

They’re also going to be involved in extension in both proximal and distal interphalangeal joints.

Now these combined movements support a strong hand grip when you’re holding a pen, for example. These muscles will definitely be involved in this action.

We’re going to move on and I’ll talk about the different group of muscles that you see now on the screen, again, looking at the palmar view of your hand. These are known as the hypothenar muscles.

And the list includes the adductor digiti minimi, the flexor digiti minimi, the opponens digiti minimi, and finally the palmaris brevis muscle.

The easiest part about these muscles is their innervation because all of these muscles are going to be innervated by this nerve that you see here highlighted in green, the ulnar nerve.

And knowing that, we’re going to start talking about the very first hypothenar muscle that you see here highlighted in green. This one is known as the abductor digiti minimi and will be originating from the pisiform bone, this really small or the smallest of the carpal bones.

Now the muscle is going to be inserting at the ulnar side of the base of the fifth proximal, as you can see here, fifth proximal phalanx, so the proximal phalanx of the little finger. And also it will be inserting at the dorsal aponeurosis of the fifth finger.

Now in terms of the different functions or actions associated to the abductor digiti minimi, this muscle moves the little finger away from the hand in what we call then abduction at the carpometacarpal and metacarpal phalangeal joints.

And as a reminder, the carpometacarpal bones are joints or those joints that form between the carpal bones and the metacarpal bones. And the metacarpal phalangeal joints then will be formed between the metacarpal bones and then the phalanges.

The abductor digiti minimi also will be causing extension in the proximal and distal interphalangeal joints due to its insertion at the dorsal aponeurosis.

We’re ready to move on to the next muscle that you see here highlighted in green, the next hypothenar muscle which is known as the flexor digiti minimi. And it does have a resemblance to the previous muscle.

This muscle is, however, going to be originating at the flexor retinaculum which is then that crosses the wrist and this will be serving then the origin point of one of the origin points for the flexor digiti minimi.

And also the hook of the hamate bone, as you can see here, is hidden by the muscle. But the hook of this bone here, the hamate, is going to be serving as an origin point for the flexor digiti minimi.

Now, distally, the muscle is going to be inserting at the base of the proximal phalanx of the fifth finger as you can see on the image. And note this that this muscle is often very small or even completely missing.

Now a quick word on the different functions or actions associated to the flexor digiti minimi. This muscle is going to be able to bend your finger as you can see here on this image. It bends your little finger and what we call then flexion in the metacarpal phalangeal joints as seen here indicated by this arrow.

Another thing I would like to use here, this image to show you, this then that I talked about before the flexor retinaculum. You notice how this muscle is originating from this structure.

We’re going to move on to the next muscle of the hypothenar group. This is known as the opponens digiti minimi. And this muscle is one of the strongest and deepest of all the hypothenar muscles.

Will be arising also from that bend that I’ve talked about before, the flexor retinaculum and the hook of the hamate bone as you can see here is serving as an origin point for the opponens digiti minimi.

Now the muscle is going to be inserting a bit more proximally at the ulnar surface of the fifth metacarpal bone as you can see here.

When it comes to the different functions or actions associated to this muscle, the contraction of the opponens digiti minimi leads to a combination of flexion, adduction, and lateral rotation in the carpometacarpal joint.

We’re now ready to move on and talk about the last one on the list that you see here highlighted in green. This is known as the palmaris brevis.

Even though this muscle lies superficially as you can see here compared to the other muscles, the other hypothenar muscles, so it’s found above all hypothenar muscles, it cannot be distinguished through palpation due to the fact that it’s quite thin.

Now, the palmaris brevis differs from the other three muscles in many ways which is why it is not often considered as one of the hypothenar muscles. And in terms of origin points, it will be extending from the flexor retinaculum as well as from this structure here that you see on the image, the palmar aponeurosis.

Now, the muscle is going to be inserting also on the palmar aponeurosis and to the skin at the ulnar side of the hands.

Now, the palmaris brevis, in terms of function, is slightly different from the other muscles. Special function is to rather protect the neurovascular halfway from compression which runs underneath it, so all the blood vessels and nerves that will be running underneath it can be protected by the palmaris brevis.

Now we’re ready to move on to the next group of muscles that you find now on the side of your thumb, which you can palpate them. You find like an eminence like elevation which is known as the thenar eminence because these are the thenar muscles.

Now, the thenar muscles consist of four muscles located on the radial side of your palm. Together they form that ball of the thumb known as the thenar eminence as I talked about, and they are listed as following: the abductor pollicis brevis, the adductor pollicis, the flexor pollicis brevis, and the opponens pollicis.

We’re going to start off with the very first one that you see here highlighted in green. This one is known as the abductor pollicis brevis. Lies quite superficially underneath the skin, it arises from the tubercles of the scaphoid and also the trapezium and from the flexor retinaculum which you also see here on this image, this is the flexor retinaculum.

Now, its short tendon will be coursing all the way to the base of the first proximal phalanx to just so via the radial sesamoid bone and the dorsal aponeurosis of the thumb.

When it comes to the innervation of the abductor pollicis brevis, the recurrent branch of the median nerve is responsible for innervating the abductor pollicis brevis. You see here the nerve highlighted in green.

Moving on to the different functions or actions associated to the abductor pollicis brevis, and you see here an image of the muscle contracting or in action. The abductor pollicis brevis moves the thumb away from the hand on what we call abduction at the carpometacarpal joint of the thumb.

We’re now ready to move on to the next muscle that you see here highlighted in green known as the adductor pollicis, which is the deepest of all thenar muscles.

It has two heads as you can see here. This one is known as the oblique head, and this one known as the transverse head.

Now, in terms of origin points, these heads are going to be attaching to different areas, different bones including the transverse head which comes from the third metacarpal bone as you can see here. While the oblique head is going to be originating from one carpal bone, the capitate as you can see here as well as the base of the second metacarpal bone and the base of the third metacarpal as you can see here. So base of the second metacarpal and base of the third metacarpal bone will be origin points for the oblique head of the adductor pollicis.

Now, the common tendon, these two heads will be joining forces in forming a common tendon which will be inserting at the base of the first proximal phalanx, as you can see here, and also the dorsal aponeurosis of the thumb via the ulnar sesamoid bone.

When it comes to the innervation of the adductor pollicis, this muscle is going to be innervated by the deep branch of the ulnar nerve. As every good muscle, this muscle is going to be involved in different functions.

Now, the function of the adductor pollicis, again the name says everything about these muscles. Adductor pollicis meaning thumb, “pollicis” – thumb, “adductor” coming from adduction when you bring your fingers in.

Now, what happens is the powerful contraction of the adductor pollicis moves the thumb towards the hand to what we call then adduction at the carpometacarpal joint. You see here the image, this image on the far right showing then adduction at the carpometacarpal joint.

We’re going to move on to the next muscle here that you see here highlighted in green in action. This one is known as the flexor pollicis brevis.

Now this muscle has two heads separated by the tendon of the flexor pollicis longus. In terms of origin points, the superficial head originates from the flexor retinaculum and the deep head from the both the capitate bone and the trapezium bone.

The tendon of this muscle will be running towards the base of the first proximal phalanx as you can see here on this image where it is going to be inserting then, this all through then the radial sesamoid bone.

The innervation of the flexor pollicis brevis, the flexor pollicis brevis is the only thenar muscle receiving double innervation by both nerves due to its formation during the course of embryogenesis.

Now, most frequently, the median nerve supplies the superficial head as you can see here highlighted in green, the median nerve highlighted in green; while the deep head is going to be innervated by the ulnar nerve which you now see on the far right image.

However, one note here that the innervation pattern is quite variable.

We’re going to move on and talk about the different functions associated to the flexor pollicis brevis. Now, the flexor pollicis brevis is mainly responsible for bending the thumb or what we call then the flexion of the carpometacarpal joint. You see here, this arrow indicating movement of the thumb caused by the flexor pollicis brevis.

We’re moving on to the next one that you see here highlighted in green. Next muscle, this is known as the opponens pollicis. This muscle is mostly covered by the adductor pollicis brevis.

It’s going to be coursing from the tubercle of the trapezium bone. And also, the flexor retinaculum will be serving as an origin point for the opponens pollicis then goes all the way to insert to the radial surface of the first metacarpal bone which you can see here.

The innervation of the opponens pollicis is going to be carried by the recurrent branch of the median nerve.

The final topic on this tutorial will be the functions or actions associated to the opponens pollicis muscle. Now, it does a combination of flexion, abduction, and medial rotation in the carpometacarpal joints which altogether resulting to what we call “opposition,” hence the name opponens pollicis. And thanks to that, your thumb is able to touch the other fingers and fulfill grip movements.

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