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Origins, insertions, innervation and functions of the dorsal muscles of the foot.
Hello, everyone. This is Joao from Kenhub and welcome to another anatomy tutorial where we’re going to talk about the muscles of the dorsum of your foot. And right now, you might be asking, “what is the dorsum of my foot?” Well, this is what we call, this is a fancy word I would say, that we use in anatomy to describe the back of your foot.
Now, what is exactly the back of your foot? You might be asking right now. Well, if you think about there are two main areas that are usually discussed in terms of regions where we find structures within your foot, one of them is the plantar region which is the bottom side, let’s say, of your foot that connects to the floor when you’re walking. This is the plantar side, and then you have this one now seen here on this image right here. This is the back of your foot which is found superiorly, and what we usually call, in a fancy manner, the dorsum of the foot.
Now, what we’re going to be doing is discussing the different muscles that we find here. And I have good news for you. This is going to be a short tutorial because there are only two muscles of the dorsum of the foot.
Now, these muscles lie within a flat fascia called fascia dorsalis pedis, or the dorsal fascia of the foot, and is found like the muscles on the back of your foot. In this area, these muscles or the bellies of these muscles will form the surface of the lateral dorsum of your foot, so you can palpate them on the lateral side of the back of your foot.
And before I list these muscles, I want to briefly talk about the innervation that is now seen highlighted in green. This is going to be the nerve that is going to be innervating the two muscles of the dorsum of the foot. And this nerve is known as the deep peroneal nerve, so L-5 to S-1 and is responsible for the innervation of the two muscles that you find on the back of your foot.
Now, as promised, I'm going to be listing these muscles, and here they are. The two muscles are known as the extensor digitorum brevis muscle and the other one is the extensor hallucis brevis muscle.
Starting off with the very first one here, the extensor digitorum brevis, this muscle has an origin point. And the origin point is going to be the calcaneus. Now, like every muscle in the human body, you have to talk about the different insertion points for the extensor digitorum brevis. Now, this muscle, as you can clearly see here on this image, divides into three muscle bellies whose tendons insert at the dorsal aponeurosis as well as the bases of the middle phalanges of the second to fourth toes. And you can clearly see here the muscle belly dividing into three and then inserting on the bases of the middle phalanges of the second, here, all the way to the fourth toe.
Now, we’re going to continue and talk about the different functions that we find associated to the extensor digitorum brevis. Now, there is one that you need to remember that, when there is contraction here on this muscle, what’s going to happen is the extensor digitorum brevis is going to cause dorsal extension of the second to fourth toes.
And it is always important to remember where the muscle originates from and also where it’s going to be inserting in. If you look here on this image, you notice here that this bone here is serving as the origin point, the calcaneus. And then the muscle is going to go all the way to insert on the bases of the middle phalanges of the second all the way to the fourth toe. Remember from the previous slides. Now, when this muscle is going to contract, it’s going to lift these toes all the way in the direction of your tibia, and this is what we call then the dorsal extension of the second to fourth toes.
Now, in some cases, your professors are going to ask, “What joints are being affected by this action?” And you can say that there is going to be extension of the metatarsal phalangeal and proximal interphalangeal joints on the second to fourth toes.
We’re going to move on now to the next muscle on our list and start off with the origin point for the extensor hallucis brevis. And I have good news that this muscle, as well as the previous one that we talked about, this one is going to be originating from the calcaneus. And then in terms of insertion point, the extensor hallucis brevis is going to insert on the dorsal aponeurosis as well and, now, at the base of the proximal phalanx of the big toe. And you can clearly see here that it goes all the way to insert at the base of the first proximal phalanx on your toe of course… or on your big toe.
Now, let’s talk about the different functions or the main function of the extensor hallucis brevis. And you have probably guessed if we think about also the origin and insertion point that this muscle is going to cause dorsal extension of the metatarsal phalangeal joint of the big toe. Sometimes, you can just abbreviate it and call it the MTP1.
One interesting point I would like to make on this tutorial is that the muscles of the dorsum of the foot have no insertion point at the little toe. This means that the little toe can only be extended by this muscle seen here, highlighted in green, the extensor digitorum longus. And the dorsal aponeurosis of the toes supports the effect of the dorsal muscles of the foot or the muscles of the dorsum of the foot by redirecting the force line of their tendons to the longitudinal axis.