Interossei Muscles

00:01 The final muscle group within the hand are what are known as interossei muscles.

00:05 And here, we can see a whole series of interossei muscles that are located deep within the hand.

00:10 These are really wedged in between those metacarpals.

00:14 Here, we can see we have some that are more on the palmar surface.

00:18 We have three of these palmar interossei muscles.

00:21 And then, we have four which are located on the dorsal aspects.

00:25 And these really help to abduct and adduct the digits.

00:30 So, let's concentrate first by looking at the palmar interossei.

00:34 Remember, we have three of these and in the diagram, you can see, they're not attached to that middle digit.

00:39 The third digit there doesn't have an association with these palmar interossei muscles and we'll come to why that is in a moment or two.

00:47 But what we can see here is that these interossei are coming from the metacarpal bones II, IV, and V.

00:55 So, they're coming from the dorsal aspect of metacarpals II, IV, and V.

00:59 And they pass distally to the proximal phalanges, the base of the proximal phalanges II, IV, and V again.

01:07 So, they're completely missing out the middle finger, that third digit.

01:12 And that's because these muscles are associated with moving the fingers towards the midline of the hand which is that middle finger.

01:19 They do this via the innervation of the deep branch of the ulnar nerve which supplies them.

01:24 And here, we can see the function of contraction of these muscles pulls the phalanges towards the midline.

01:30 So, you can imagine that contraction of these pulls the phalanges towards that third digit.

01:37 So, they abduct II, IV, and V fingers towards the midline.

01:42 That's why the middle digit, digit three, doesn't have any of these palmar interossei muscles.

01:49 Because of the function of these adducting, you can call this the pad muscle, the palmar interossei adduct.

01:56 So, the pads bring the fingers together.

02:00 If we then look at the opposite, the dorsal interossei, here, we have four of these dorsal interossei muscles.

02:07 And what these do is they come from the dorsal sides of all of the metacarpals.

02:11 And what they really help to do is to spread the fingers out. So, they have to abduct the fingers.

02:17 So, here, we can see them coming from the dorsal surfaces of all of the metacarpals and they pass towards the base of the proximal phalanges II, III, and IV.

02:28 Obviously, the little finger and the first digit have their own muscles that do this.

02:32 So, these are concentrated on II, III, and IV. So, here, we can see the dorsal interossei muscle being innervated by the ulnar nerve, the deep branch of the ulnar nerve as well.

02:44 And here, we can now see that they help to abduct those fingers II, III, and IV.

02:50 Please bear in mind that the middle digit, digit three, that has its own axial line.

02:54 So, that is where we base the movement of these fingers to.

02:58 So, digit three is the axial line of the hand. So, adducting will bring the fingers towards the middle digit and abducting will move fingers away from that middle digit.

03:09 But what you can also see is that third middle digit, because it has two dorsal interossei muscles going towards it can move both medially and laterally either side of that axial line.

03:23 There's a lot going on in the hand. There's lots of structures, there's lots of muscles, and they have quite an intricate nerve supply. So, please make sure you're familiar with what you need to learn with your learning objectives for your curriculum.

03:34 And hopefully, this lecture will help.