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Muscles of the foot

Origins, insertions, innervation and functions of the muscles of the foot.

Show transcript

Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, today, we’re going to be talking about the muscles of the foot.

So what I’m going to be doing on this tutorial is walk you through the different muscles that you find on your foot. And I can tell you right now that you can divide the muscles of the foot into four groups specifically, which we will be covering.

So we’re going to be talking about the central muscles of the sole of the foot, the lateral muscles of the sole of the foot, the medial muscles, and the muscle of the dorsum of the foot.

So we’re going to also list all of the muscles that we find within these groups and then describe the different attachment points, which include then the origin points, the insertion points, innervation, and then a little bit on the functions associated to all of these muscles.

Let’s start off with the very first one on the list that I’m now isolating here on this image. So I just removed a few of the muscles of the foot to just isolate the central muscles of the sole of the foot.

And the central muscles of the sole of the foot lie within the central compartment between the muscles of the big and little toes.

This compartment comprises numerous short foot muscles in different layers, and together, they form the central surface of the sole of the foot.

Now, before we talk about these muscles in a little bit more detail, I would like to, then, list them. So the central muscles of the sole of the foot consist of the flexor digitorum brevis, the quadratus plantae, the lumbrical muscles one through fourth. There are three plantar interossei muscles that we’re going to see and also four dorsal interossei muscles.

Let’s start off by talking about the first one on our list that I’m now highlighting here in green, and if you remember from that previous slide, we’re looking now at the flexor digitorum brevis.

And the flexor digitorum brevis muscle lies relatively superficial under the plantar aponeurosis and is the largest muscle in the central compartment.

In terms of its origin point, you can see here on this image that this muscle is originating at the calcaneal tuberosity right here as you can see here. So this projection here is the calcaneal tuberosity or the tuberosity of the calcaneus.

Also, the plantar aponeurosis will serve as an origin point for the flexor digitorum brevis.

When it comes to the different insertion points… yes, insertion points because you can see that, distally, this muscle is dividing into four tendons as you can see here, moving towards, then, the second—so this is the second toe—all the way to, then, the fifth toe.

And notice here that, at the proximal phalanges, these tendons will then separate further into two smaller tendons which finally insert medially and also laterally at the second through fifth middle phalanges.

The flexor digitorum brevis is going to be, then, innervated by the medial plantar nerve, which you see here highlighted in green.

And also, one important point that I want to mention here on this image that we’re looking now, that we’ve been looking at throughout this tutorial, we’re now seeing the plantar side of your foot. So these images that we’re looking now, this is the plantar side of your foot – so the bottom part of your foot where it touches the floor when walking or standing.

Now, I would like to add a few words on the different functions or actions associated to the flexor digitorum brevis. This muscle allows flexion of the second to fifth toes and actively supports the longitudinal arch of the foot.

And you can clearly see here on this image, where we’re looking at the foot from a lateral view, a little bit of the plantar side is clearly seen here, where you see the muscle contracting and
then flexing the second all the way to the fifth toes.

And you can always say that it happens due to the attachment points because, as you remember, the muscle is originating here from the calcaneal tuberosity and then inserting on the middle phalanges of these toes, and when contracting, then, it will cause this movement here: flexion, which is indicated by this arrow.

We’re now ready to move on to the next muscle that you see here highlighted in green. It has a square shape, and for that reason, we’re going to call it the quadratus plantae. And this muscle is going to originate also from the calcaneus, as you can clearly see here from this image.

And then it goes all the way to insert on a tendon of a muscle, the tendon of the flexor digitorum longus muscle, which you see here passing under the plantar or in the plantar side of the foot. And you can see how the quadratus plantae is going to be, then, inserting or using this tendon as an insertion point.

Now, the quadratus plantae is going to be innervated by the lateral plantar nerve, which you see here highlighted in green.

Now, the quadratus plantae muscle does not move any joints but has a rather special function.

By pulling at the tendon of the flexor digitorum longus muscle, it will shift the tendons force effect to the longitudinal direction. And by that, it will increase the effectiveness of the plantar flexion of the flexor digitorum longus.

So as you can see here, one of the main functions of the quadratus plantae is to actually help the flexor digitorum longus perform its function or its action.

We’re moving on to a next set… a next set of muscles that you see here highlighted in green. These are the lumbricals of the foot. So, we have here four muscles as you can clearly see here, highlighted in green.

And these muscles will be originating from the insertion point of the quadratus plantae. Then, the tendons of the flexor digitorum longus muscle will be serving as an origin point now for the lumbrical muscles. As you can clearly see here, the tendons of the flexor digitorum longus, then, splitting and serving as origin points for the lumbrical muscles.

When it comes to the insertion points for these muscles, as you can clearly see here on this image, the bases of the proximal phalanges of the second all the way to the fifth toes are going to serve as the insertion points for the lumbrical muscles.

Now, when it comes to the innervation of the lumbrical muscles, we’re going to see something interesting here. This is a group of four muscles, and the first lumbrical muscle is going to be innervated by this nerve that you see here highlighted in green, which is the medial plantar nerve.

Now, “What happens to the other three muscles?” you may ask. The second all the way to fourth lumbrical muscles are going to, then, be innervated by this other nerve: the lateral plantar nerve.

So as you can see here, as a group, the lumbrical muscles are innervated by these two nerves specifically.

Now, I would like to add a word on the different function or actions associated to the lumbricals. And I have here this image to show you that we have at least two important functions that are important to highlight here on this tutorial.

The first one is adduction, which you see here indicated by this arrows, just bringing in your toes. So when you have your toes spread and then you bring in or bring them closer together, then you’re performing adduction of your toes. And these muscles are also involved in this action.

Now, we’re moving on to this image now to show you another function that the lumbricals are able to perform (and you have probably guessed). I really love this image here because you can clearly see here the origin point for the lumbricals as well as the insertion points that we talked about.

This image to show that the lumbrical muscles are able to also perform flexion of these toes, all the way from the second to fifth toes.

We’re ready now to move on to the next group of muscles that you see here, highlighted in green. These are only three. They’re known as the plantar interossei muscles.

Now, these muscles are going to have their origin points at the third—as you can see here on this image—at the third all the way to the fifth metatarsal bones. So these are the metatarsal bones of the foot and will be serving as origin points for the plantar interossei muscles.

Now, these will be, then, going all the way to insert at the bases of the proximal phalanges of the corresponding toes – so all the way from the third to your fifth toes, at the bases of the proximal phalanges of these toes as you can see here on this image.

And notice here that they’re inserting at the medial side of the bases of the proximal phalanges.

One reminder here, that this is the medial side of your foot, so the side that is the same direction as your big toe, while the lateral side is on the same direction as your little toe (just for a bit of more reference as we move on throughout this tutorial).

We’re moving on to, then, the innervation of the plantar interossei muscles. And this is an easy one. You just need to know that this group is going to be, then, innervated by the lateral plantar nerve that you see here highlighted in green.

Moving on to the different functions or actions associated to the plantar interossei muscles, these have a very similar functions that we saw on the lumbricals. So we’re going to be seeing flexion of the toes and also adduction of these toes, as you can see here indicated by these arrows.

So these arrows are indicating the movement that I explained before: adduction of the third all the way to the fifth toes, which means that you’re going to be able to bring your toes closer to your foot – so bringing them together thanks to also the plantar interossei muscles.

And now, we’re ready to move on to the next group of muscles that you see here highlighted in green, and right now, we’re looking at the other side of the foot, now, the dorsum of the foot. So we’re looking at, let’s say, the top of your foot, this part that is not in contact with the floor. It’s known as (fancy word) as dorsum of the foot to show you, then, the dorsal interossei muscles.

The dorsal interossei muscles are two-headed muscles that arise from the adjacent sides of the two neighboring metatarsal bones, as you can clearly see here on this image.

So in general, you can say that these muscles are originating from all the metatarsal bones, but you have to clarify that, that they are two-headed muscles that arise from the adjacent sides (adjacent sides!) of the two neighboring metatarsal bones – very important information related to these muscles.

And as you can see here on this image, these muscles have an insertion point or different insertion points at the bases of the proximal phalanges, from the second all the way to the fourth—I’m showing you here—so from the second all the way to the fourth proximal phalanges.

But notice here that some of these muscles are going to be, then, inserting on the lateral (see here) lateral side of these bases of the proximal phalanges, while this one here is going to be inserting on the medial side of the base of the proximal phalanx of the second toe – so, very important information that you need to clarify on your notes, even when you go to an exam, about the insertion points of the dorsal interossei muscles.

The next point that I’m going to be making would be, then, the innervation of the dorsal interossei. Again, this is an easy one. We have to remember that the lateral plantar nerve is going to be innervating all the dorsal interossei muscles.

Moving on to the different functions or actions associated to these muscles, you’re going to see that the dorsal interossei muscles are able to perform, then, flexion of the toes.

And in contrast with some of the other groups that we saw before, these are able to, then, perform abduction of the toes, as you see here represented by these arrows – so when you spread your toes (not bringing them in together but spreading). This is what we call, then, abduction of the toes, and these muscles are able to help you perform this action.

If you remember from previous slides that I talked about, now, we’re going to, then, finish this group of muscles to move on to this one that you see here now on this image. Notice here these group of muscles or this group of muscles that are, then, attached or very close in relation to your little toe. And these are, then, the lateral muscles of the sole of the foot.

Now, the lateral chamber, which is defined by the plantar fascia, contains three muscles that we’re going to talk about. Now, their muscle bellies form the surface of the lateral foot sole – so the ball. We call it the ball of the little toe. And the following muscles lie within this lateral chamber.

So we’re going to be seeing the abductor digiti minimi, the flexor digiti minimi brevis—really interesting names—and then the opponens digiti minimi muscle.

Now, I would like to add an important point here, is that we’re not going to be covering the opponens digiti minimi on this tutorial. This muscle is not as relevant nor found on most of us, so we’re going to skip it for now and leave it for a separate tutorial where we can look into it in a little bit more detail.

But I just wanted to add here to the list, so you can have an idea that, usually, it’s included as part of the lateral muscles of the sole of the foot.

In order to make things really simple here, I’m going to start off by talking about the different… or the innervation related to the lateral muscles of the sole of the foot, which you can see here highlighted in green.

And if you remember well from the previous slides—I’m going to give you one second to remember. See if you can remember which nerve is highlighted here in green—yes, time is up, and this is the lateral plantar nerve.

So, to make things easy, I’m just saying that all muscles found on this compartment on the lateral muscles of the sole of the foot are going to be, then, innervated by the lateral plantar nerve.

And now, we’re ready to move on and talk about the very first one that you see here, highlighted in green. This is the abductor digiti minimi.

This muscle will originate, as you can clearly see here on this image, at the calcaneal tuberosity, and it will also be originating at the plantar aponeurosis.

In terms of insertion points—yes, “points” because we’re going to see two insertion points for the abductor digiti minimi—the first one, as you can see here, it’s going to be, then, inserting at the fifth proximal phalanx as you can see here, specifically at the base of the fifth proximal phalanx, or in other words, the base of the proximal phalanx of your little toe.

But the muscle also inserts on the fifth metatarsal bone, as you can see here on the image.

Now, we’re going to move on and talk about the different function associated to the abductor digiti minimi.

Now, the name of muscles really help us a lot as you can see here: abductor digiti minimi (digiti minimi meaning “little toe”) and abductor, of course, one of the functions that this muscle is able to perform or the main function.

But we’re going to see that this muscle is able to perform flexion of the little toe, as you can see here indicated by this arrow.

Then, the main function would be, then, abduction of the little toe – so, spreading out your little toe, as you can see here indicated by this arrow.

And furthermore, it actively supports the longitudinal arch of the sole of the foot.

We’re now ready to move on to the next muscle that you see here highlighted in green, one that also has an interesting name: the flexor digiti minimi brevis.

This one will be originating at the base of the fifth metatarsal bone, which is hidden here behind the muscle, but the base of the fifth metatarsal bone will be, then, serving as an origin point for the flexor digiti minimi brevis.

Also, the long plantar ligament, as you can see here—this is the long plantar ligament—and you see that the muscle is also using this ligament as an origin point.

Now, the flexor digiti minimi brevis is going to, then, insert at the base of the proximal phalanx of the little toe, as you can see here.

Moving on to the different functions or actions associated to this muscle, now, the flexor digiti minimi is going to be able to perform, then, as you can see here on this image—if you guess—yes, flexion of the little toe (so plantar flexion of the little toe).

But it also supports the longitudinal arch of the sole of the foot.

We’re moving on to the next group of muscles that you see here now isolated on this image. These are known as the medial muscles of the sole of the foot. And as you probably know, the plantar fascia, which surrounds all of these muscles of the sole of the foot, consists of three chambers which, then, eventually will separate all these groups that we’ve been talking about.

Now, the muscles lying within the medial group form a bulge referred to as the ball of the big toe, as you can see here. So all these muscle bellies will be forming a bulge next to or in the same direction as of your toe here, of your big toe, and we call it, then, the ball of the big toe.

You can try and palpate it and feel these muscles right on your foot.

Now, this group will, then, be contributing to the surface anatomy of the medial sole of the foot, and then it’s easy to palpate as I mentioned.

Now, the medial muscles of the sole of the foot consist of the abductor hallucis, the adductor hallucis, and the flexor hallucis brevis.

We’re going to start off with the first one that you see now highlighted in green. This one is the abductor hallucis, which has an origin point on the calcaneal tuberosity as you can see here on the image. But the muscle also originates from the plantar aponeurosis and the superficial layer of the flexor retinaculum.

Now, the abductor hallucis will be inserting, as you can see here on the image, it goes all the way to insert at the base of the first proximal phalanx, or in other words, the base of the proximal phalanx of the big toe.

This muscle is going to be innervated by the medial plantar nerve which you see now, highlighted in green on the image.

When it comes to the function or actions associated the abductor hallucis…

And hallucis means “big toe.” So keep that in mind. And abductor means that this muscle is able to cause abduction.

So the abductor hallucis is able to move this joint here, which is known as the metatarsal phalangeal joint of the big toe, and this leads to, then, the abduction (as you can see here) of the big toe – so when you spread your big toe.

Together with the other two muscles, it’s going to also be able to support plantar flexion and the longitudinal arch of the foot.

We’re moving on to the next muscle that you see here. This is known as the adductor hallucis muscle.

And this muscle has two origin points, two main origin points here because it’s spread here or split into two separate heads. You have here what is known to be as a transverse head and the oblique head.

Now, what we see is that your transverse head is going to be originating from the ligaments of the third to fifth metatarsal phalangeal joints and also the deep transverse metatarsal ligament.

So all these joints that you see here from the third all the way to the fifth toes, these joints here, or the ligaments surrounding these joints, are going to be serving as origin points for the transverse head of the adductor hallucis.

Now, the oblique head of the adductor hallucis will be originating from two bones: the cuboid bone and the lateral cuneiform bone, as well and most importantly the second all the way to the fourth metatarsal bones.

To be a bit more accurate here, the oblique head does not lie within the medial but more on the central group of the plantar fascia.

Now, these two heads will, then, come together to insert at the common tendon which runs along the lateral sesamoid and inserts at the base of the first proximal phalanx or the base of the proximal phalanx of the big toe.

The innervation of the adductor hallucis muscle is going to be, then, provided by this nerve here: the lateral plantar nerve.

Now, in terms of functions or actions associated to this muscle, this muscle is able to move the metatarsal phalangeal joint of the big toe. Again, this joint that I talked about that is now hidden behind these ligaments here.

And as the name indicates, this muscle is able to perform adduction of the big toe, as you see here indicated by this arrow – so bringing your toe in, closing in, not spreading.

Now, the other function it’s able to perform is flexion, and together with the other two muscles, it’s going to be able to support plantar flexion and also the longitudinal arch of the foot.

We’re moving on to the next muscle that you see here now, highlighted in green. This is known as the flexor hallucis brevis.

And this one will be originating from the lateral cuneiform bone, the cuboid bone, which you can’t see exactly here because it’s hidden behind the muscle, and also the ligaments, and other muscles that you see on this image, and also the plantar calcaneocuboid ligament will be serving as an origin point for the flexor hallucis brevis.

Now, this muscle has an interesting insertion point or insertion points. As you can see here, it will be splitting into two, inserting at the base of the first proximal phalanx or the base of the proximal phalanx of the big toe via two sesamoid bones, so via the medial sesamoid bone. So the medial head will be, then, inserting at the base of the first proximal phalanx via the medial sesamoid bone.

And the lateral head, as you can see here, will be then inserting at the base of the first proximal phalanx, but this time, via the lateral sesamoid bone.

Now, in terms of innervation, the flexor hallucis brevis is going to be innervated on one side. The medial head is going to be innervated by the medial plantar nerve, while the lateral head will be, then—if you can guess. This is an obvious one—then innervated by the lateral plantar nerve which you see here highlighted… both of these nerves highlighted in green on this images.

So you can say that the flexor hallucis brevis is double-innervated or has double innervation.

We’re moving on to talk about the different functions or actions associated to the flexor hallucis brevis.

This muscle is able to move the metatarsal phalangeal joint of the big toe, leading to flexion of the big, which you see here indicated by this arrow.

Notice here the metatarsal phalangeal joint of the big toe, and also, I like this image because you can see here the two sesamoid bones: the medial and the lateral sesamoid bones, which will be, then, involved in the insertion points of the flexor hallucis brevis.

And together with the other two muscles, the flexor hallucis brevis is going to be able to also support plantar flexion and the longitudinal arch or the foot.

We’re now ready to move on to the last group of muscles that you see here on this image of the dorsum of the foot. So as you probably guessed already, these are the muscles of the dorsum of the foot.

This is a group of two muscles which, together, represent the dorsal foot musculature, and they lie within a flat fascia called fascia dorsalis pedis at the back of the foot.

And hereby, their muscle bellies form, then, the surface of the lateral dorsum of the foot.

Now, these muscles will be the extensor digitorum brevis muscle, and the extensor hallucis brevis.

Now, before we talk about these, also a clarification here and something very easy, all you need to know about the innervation of the muscles of the dorsum of the foot, they’re going to be innervated by this nerve that you see here highlighted in green, which is known as the deep peroneal nerve or the deep fibular nerve (both names are used).

Let’s start with the very first one that you see here highlighted in green. This is known as the extensor digitorum brevis, and this muscle is going to originate at the calcaneus, and then in terms of insertion points, it will be dividing into three muscle bellies as you can see here on this image, and the tendons will be, then, inserting at the bases of the middle phalanges or the second all the way to the fourth middle phalanges or bases of the middle phalanges.

This muscle also uses the dorsal aponeurosis as an insertion point.

And when it comes to the functions associated to the extensor digitorum brevis, you can see here the muscle in action on this lateral view, this image of the lateral view of the extensor digitorum brevis.

You see here that the contraction of this muscle will result into dorsal extension of the second to fourth toes.

And now, we’re ready to move on to the next muscle that you see here highlighted and the last one that we’re going to be covering on this tutorial. This is the extensor hallucis brevis.

And just like the extensor digitorum brevis, its origin point is going to be the calcaneus, and then it’s going to insert all the way to the base of the first proximal phalanx of the big toe as you can see here.

This muscle also uses the dorsal aponeurosis as an insertion point.

When it comes to its functions or actions, you could also see here an image of the lateral side of the muscle in action, showing that the extensor hallucis brevis muscle causes dorsal extension of the metatarsal phalangeal joint of the big toe here.

So you notice here the metatarsal phalangeal joint of the big toe, and how or when this muscle is contracting, it’s going to cause movement at this joint here, and then it’s able to pull the big toe up and causing what we call, then, dorsal extension.

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