hello anatomy friends we are going to get into the muscles of the leg and similar to what we
had in the thigh we have three compartments we're going to talk about and one of those compartments
is so large it's actually split into two so we'll have an anterior compartment a lateral compartment
and then a very large posterior compartment that will have a robust superficial portion and deep so
let's start with the anterior compartment of the leg it is often referred to as the dorsiflexor or
extensor compartment and these muscles are going to be located anterior to the interosseus membrane
so recall that anterior or the interosseous membrane will be between the tibia and the fibula
the shafts or the bodies and so all these muscles are going to be on the anterior side of that
now one important thing to understand about the anterior compartment is that it is going
to be surrounded by very dense deep fascia and all muscle compartments are going to
be surrounded by deep fascia but the the fascia in this particular region is it's notably dense
and so if you have fluid like blood entering into this region due to a fracture
something along those lines this particular compartment is going to be more susceptible
to what's referred to as compartment syndrome and so what will happen as more blood enters into the
region that will increase the pressure it will it will compress the nerves and the arteries
and the muscles in this region it could lead to necrosis of the muscles or death of the muscles
in these regions if not addressed immediately so that is going to be an emergent situation
these muscles are going to pass and insert anterior to the transversely oriented
axis of the ankle and so because of that placement it will allow these muscles to dorsiflex
the ankle which means we're elevating those toes or the forefoot and depressing the heel
those long extensors so particularly these two muscles right here
are going to attach to the dorsal aspect of the digits really i'm kind of spreading out
to create extensor expansions which we'll talk a little bit more about in a moment
so they will play a role in terms of extending the digits or extending the toes
while we have spent the majority of our time when we're talking about the muscles
talking about concentric contractions in this course eccentric contractions of
these muscles in particular are really just as important in proper functioning of locomotion
so let's start with the tibialis anterior often referred to as ta
sometimes you'll even hear it referred to as the anterior tibialis muscle
these this is going to be the most medial so this is your ta right here most medial and superficial
muscle of this compartment it's usually the most prominent muscle of this compartment
and it really has the mechanical advantage for strong dorsiflexion so the strong dorsiflexor
also is tendon does not extend to the digit so it doesn't play a role in terms of extension
it will also play a role in terms of inversion of the ankle just due to its placement or its tendon
placement and that brings up the um kind of the thing that always helps me remember
tibialis muscles will always be the inverters so if it has a tibialis in its name you know that
it's going to be an inverter if it has a fibularis in its name which is on the more lateral side
those will be the inverters so you actually have one muscle in this anterior compartment
that will play a role in eversion whereas the tibialis anterior will play a role in inversion
often times you can have little micro traumas associated with the tibialis anterior meaning
little tears to this muscle and these tears can actually lead to periosteal damage as well
and that's where you get what's referred to as shin splints so that can cause swelling or
edema and pain in this region particularly in the more distal portions of the tibia
the extensor digitorum longus is going to be the more lateral muscle of this compartment
and it is each one of its tendons will extend down to the digits two through five
and it will create what's called the extensor expansions we add something similar on the
digits of the hand and it will allow for extension of those digits two through five
whereas one will be covered by the extensor hallucis longus we had the pollicis when we
were talking about the the thumb region was how is this when we're talking about the big toe
or great toe region so very similar in terms of um what it does but just in terms of the first digit
and it's usually quite difficult to see the house's longest in terms of its muscle belly
because it is going to be deep to these other muscles and lastly you have the fibularis tertius
it does not belong in the lateral compartment like the other fibularis muscles it's actually
just a um it's really only a separated part of the extensor digitorum longus
so it's going to be wrapped up in the fascia associated with the anterior compartment
and like we mentioned it will play a role in terms of e-version of the foot
all right moving to the lateral compartment this is the smallest of the compartments of the leg it
is often referred to as the inverter compartment because really the the major role of these two
muscles the fibularis longus which is the one we can identify but you can also see the fibularis
brevis you can identify this one as well it's just a little bit harder when we're talking about the
laboratory component so these will evert the foot they will also play a role in a very um small role
in terms of plantar flexion of the foot oh and i forgot to mention something on this particular
slide let's go back we can't forget innervation so the anterior compartment is going to be innervated
by the deep fibular nerve so we're kind of remember the sciatic nerve is going to divide into
the tibial division which is mostly those posterior compartments and the common fibular
are going to be the two major divisions of the sciatic nerve the common fibular will
further divide into a deep fibular which is going to innervate this anterior compartment
as well as the superficial fibular and so um so when we're talking about um this anterior
compartment we're talking the deep fibular whereas for this lateral compartment it is the superficial
fibular nerve if you have damage to this deep fibular nerve you can have what is um what's
referred to as foot drop and what happens is if you have a lesion on the deep fibular nerve
this results in the inability to dorsiflex the foot it kind of makes the foot too long you can't
kind of clear the ground when you're trying to step and so that's what's referred to as foot drop
so that would be a lesion of this deep fibular all right so lateral compartment as i mentioned is
going to be the fibularis longus and the fibularis brevis um fibularis longest tendon if you can kind
of see here sure says a muscle belly um the tendon will kind of extend down to this fifth
metatarsal region over here it's going to the the tendon here will be palpable
and actually observable on that proximal and posterior portion of the lateral malleolus so
here's that lateral mallealist of the fibula until you can actually feel that tendon right there
the posterior compartment is the largest of the leg compartments it's actually so large that it's
subdivided into a superficial and deep part and the superficial part is by far the the
most dominant the strongest portion it is going to have the two muscles the gastrocnemius and
the soleus muscles that are playing the largest role in terms of plantar flexion of the ankle
plantar flexion is a very powerful movement it's four times stronger than dorsiflexion as you
might can just kind of test on yourself and it's really used to propel the body forward or kind of
push off a portion of locomotion so the the superficial muscles or the superficial parts of
the posterior compartment as i mentioned will be made of the gastrocnemius and the soleus muscles
these two muscles will actually have a combined tendon with the small plantaris muscle
called the calcaneal tendon but you have probably heard it referred to as the achilles tendon
and this is the the largest um thickest strongest tendon in the body
if they are going to as mentioned they will share this common tendon but the gastrocnemius and the
soleus muscles actually connect independently um you may have heard the kind of mnemonic or kind of
phrase to help understand the difference between these two muscles actions so you can stroll with
soleus so not as powerful a movement or it's a very powerful movement but kind of more of a
workhorse type of movement so you can stroll with soleus but win the lung jump with gastrocnemius so
gastronemius is for that kind of really powerful strong contraction for those quicker movements
whereas a longer um a longer more workhorse type of plantarflexion would be the soleus muscle
that count um that calcaneus is and the size of the the calcaneal tendon as well as
the gastrocnemius and the soleus are really just directly proportional to our bipedal stance so the
fact that these are so large is because of that bipedal stance you can see here the gastrocnemius
has two heads they actually will cross the knee joint so you can it does gastronemius can play
a role in terms of flexion of the knee soleus does not cross the knee it is a much flatter
muscle it's actually named after the sole fish which is a really flat type fish and you
can actually see a bit of the soleus on either side the medial and lateral side of this region
you can see this very large very prominent calcaneal tendon
the deep posterior compartment of the leg
is going to be made up of muscles that will play a role in terms of plantar flexion
but um only about seven percent of the total force of plantar flexion comes from these
deep muscles of the posterior compartment and the fibularis muscles in the lateral compartment
so that tells you how important that superficial compartment is for plantar flexion so if you have
a calcaneal tendon rupture these muscles in this particular compartment or those fibularis muscles
in the lateral compartment cannot generate the power necessary to really lift the body's weight
um so plantar flexion is going to be one of the roles of this deep compartment you
do have a tibialis posterior here it will play a role in terms of inversion of the
foot because it is a tibialis muscle and then you will also have flexion of the digits so
you have a flexor digitorum longus and a flexor hallucis longus so these would be two through
five and this would be one in terms of the digits that they will flex and you do have a muscle up
here that is within the sheath of the posterior deep posterior compartment called the popliteus
and that can play a role in terms of flexion of the knee both of these compartments the deep and
the superficial will be innervated by the tibial nerve because we know that tibial nerve
equals posterior compartments when we're talking about the lower limb
okay question damage to the superficial fibular nerve could most greatly affect which action
would it be dorsiflexion eversion extension of toes um inversion of foot or plantar flexion
of ankle ankle okay so for me when i'm working through this so i i know that there's damage
to the superficial fibular nerve so i want to think about what compartment does that innervate
well we know the deep compartment or excuse me the the posterior compartments are going
to be the tibial nerve so it's not posterior compartments of the leg and we know that the
anterior compartment is innervated by the deep fibular nerve so that's not it either
so that only leaves the lateral compartment and we remember the lateral compartment is going to be
composed of the fibularis longus and brevis fibularis equals eversion so eversion is the
correct answer here dorsiflexion would be more affected by a deep fibular um a deep fibular
injury so recall we were talking about the foot drop extension would be more deep fibular as well
inversion there is um an inversion would be any of the tibialis muscles so you do have one in
the deep posterior compartment as well as the anterior compartment and then plantar flexion
would be tibial in terms of its major role now we do know that the superficial fibular nerve and the
lateral compartment that lateral compartment does play a role in terms of plantar flexion but as we
talked about not as significant a role so really it's that tibial nerve that would have the the
biggest issues we also recall that in the anterior compartment we do have the fibularis tertius
and that does play a role in terms of eversion and that anterior compartment is innervated by
the deep fibular so that could play a small role in terms of eversion and allowing some of it
but if you're knocking out both of the fibularis longus and brevis
you would likely notice some type of disruption to the full range of motion
of eversion okay excellent we have one video left in terms of our lecture component of the
musculoskeletal system and so we are finishing off our discussion with the muscles of the foot thank
you for your time and attention here always reach out if you have any questions early and often
and i uh thank you for um for your attention and i hope you have a great rest of your day