Okay, this tutorial is on the intrinsic muscles of the foot.
So the intrinsic muscles are those muscles which originate and insert in the foot.
So these muscles act to produce the fine movements of the toes and they also support the arches
of the foot.
The relationship between some of the intrinsic muscles with the tendons of the leg muscles
which enter the foot means that these muscles can actually change the way that the forces
are produced by some of these muscles and we'll look at that in a bit more detail.
So just like the other groups of muscles that I've talked about, the intrinsic muscles of
the foot can be separated into different layers.
So you've got a plantar group and a dorsal group.
The dorsal group is really simple because there's actually just one muscle in this group,
but the plantar group has four different layers.
So I'll talk you through those.
Just before I start, just a quick mention about the innervation of the foot muscles.
Apart from the extensor digitorum brevis and the first two dorsal interosseous muscles,
all the intrinsic muscles are innervated by branches of the tibial nerve.
So we've got two branches, the medial and lateral plantar branches.
I'll just bring in the nerves and we'll take a look at those quickly.
We're looking posteriorly at the distal leg and foot.
You can see the tibial nerve running medially behind the middle malleolus and entering onto
the flexor retinaculum to enter the tarsal tunnel.
So I'll just fade away the muscles we can have a look at this nerve.
I'm just showing you the plantar surface of the foot.
You can see the tibial nerve running medially in the distal foot and it enters the plantar
surface of the foot and it splits into these two branches.
So laterally, you've got the lateral plantar nerve and medially, we've got the medial plantar
nerve.
So these two branches for the tibial nerve are responsible for innervation of the majority
of the intrinsic muscles of the foot.
So the extensor digitorum brevis muscle is innervated by the deep fibular nerve.
So this is this nerve here which runs anteriorly on the tibia.
It also supports and innervates the anterior muscles of the leg.
So this branch, this nerve, the deep fibular nerve innervates the extensor digitorum brevis
muscle and the first two dorsal interosseous muscles, but all the other intrinsic muscles
are innervated by the medial and lateral plantar nerves, which are branches of the tibial nerve.
So in the dorsal group, you only have one muscle and that's the extensor digitorum brevis
muscle.
I'll just quickly show you that.
I've just isolated the extensor digitorum brevis muscle and you may notice that there's
this other label here, which says extensor hallucis brevis.
This is what the software has brought up, but this muscle is actually often considered
part of the extensor digitorum brevis muscle.
I'm just going to talk about the extensor digitorum brevis as it includes the extensor
hallucis brevis.
So I've removed all the other muscles, so we can take a closer look at this.
Just looking at its origin, you can see it originates superiorly and laterally on the
calcaneus.
And if we look at the insertion, we can see the first tendon of the extensor digitorum
brevis inserts at the base of the proximal phalanx.
And if I bring the rest of the muscles in, we can see the insertion point of the other
three tendons.
You can see that they insert laterally on these tendons.
So these are the tendons of the extensor digitorum longus muscle.
So the extensor digitorum brevis muscle inserts laterally on these tendons.
These three toes here, the extensor digitorum brevis inserts laterally on the tendons of
the extensor digitorum longus muscle.
So you must notice that there's no tendon coming from the extensor digitorum brevis
muscle to the little toe.
It's just the medial four toes that there are tendons to.
So this muscle extends the MPT joint, but it's innervated by the deep fibular nerve.