hello all this is Dr. Alsup and we're talking about one of my favorite areas of the lower limb
and that is the muscles of the thigh you have three compartments muscle compartments that are
divided by fascial plane so you basically have these muscle compartments with similar actions
as well as similar innervation so we're going to talk about those three compartments and
some of the specifics within all right so you can see how we have an anterior,
a medial, and a posterior compartment when we're talking about the thigh region
so let's start with the anterior compartment and this is going to be predominantly composed of one
muscle which is called the quadriceps femoris but there are some other muscles here that are both
powerful or very prominent in terms of being able to locate it and help with identification
and so this first muscle that we have here is very powerful but it's kind of hidden
you can't really see it very well you can see it kind of coming together but when
you're actually in the anterior compartment of the thigh it's going to kind of dive fairly
deep to go insert on this lesser trochanter right here and this is the iliopsoas muscle
this is actually composed of kind of two muscles that are located more in the abdominopelvic
region that come together with this common tendon to the lesser trochanter and that would be the
psoas major which you can see here and the iliacus muscle so they kind of come together
for this common tendon to the lesser trochanter and when this contracts it can play a role in
terms of kind of flexion of the trunk but it's really it's a very powerful and kind of the
main flexor of the hip joint so when it contracts it will cause flexion of the hip joint
this next muscle sartorius I have in here not because it's a powerful muscle in fact it's a very
not powerful muscle it's very much a synergistic muscle but when you're looking at the anterior
thigh it's hard to miss it because it's kind of right it's the most superficial muscle
in the anterior thigh and this is the sartorius muscle sometimes you hear it referred to as the
tailor's muscle you kind of tailors would often sit kind of in a cross-legged position
so things so the sartorius will play a role in a very small role in terms of the actions
that allow you to get into that position so you would have hip flexion, even knee flexion, abduction
abduction, and lateral rotation of the hip joint it will play a role in terms of all those actions
but very much in a synergistic component say the the major muscles that play a role
in terms of those actions were to become de-innervated and not functioning sartorius
really can't take it up in order for you to to get to those powerful movements it
also has the distinction of being the longest muscle of the body so it's
starting way up here on the coxal bone and then it will have its distal attachment on the tibia
all right here's the big one in the anterior compartment and that is the quadriceps femoris
often you hear this referred to as the quads and this is called this because there are
four different heads and these muscles are so large that they're often just described as four
different muscles that come together for this common tendon down here so recall you have that
quadriceps tendon that is going to extend all the way down to the tibial tuberosity so once
you get past the patella it's called the patellar ligament and so the four parts are going to be the
rectus femoris which is the one that runs right down the middle rectus means straight then you'll
have the vastus medialis, the vastus lateralis which is a really powerful component of it
and then deep to the rectus femoris would be the vastus intermedius and again these will have these
muscles will have their distal attachment on the tibial tuberosity of the tibia these muscles are
innervated by the femoral nerve all right so the femoral nerve is not a branch of the sciatic nerve
a lot of the muscles of the lower limb are going to be innervated by the sciatic nerve this is not
one of those examples it's going to have a very unique innervation with the femoral nerve and
the powerful or the main movement of the quadriceps muscles is going to be extension
of the knee joint all four of these heads will play a role in that the rectus femoris
actually will cross the hip joint as well and can play a role in terms of flexion of the hip
joint but really what I want you to focus on here is that the quads will extend the knee
all right moving to the medial compartment of the thigh these are generally
located a little bit on the deeper portion but you can still see it from an anterior
view you can also see some of these muscles from a posterior view as well
and oftentimes this compartment is sometimes just referred to as the adductor compartment
because these muscles main role is going to be adduction or adduction of the hip joint so you
literally have three muscles that have adductor in its name you'll have the adductor longus
and brevis and then you'll have the adductor magnus which as its name would suggest is
quite large but generally you can actually see it a little bit better from a posterior view
you'll also have a muscle that's going to kind of skirt along the most med-
is actually the most medial of the medial compartment and this is the gracilis muscle
it is not a particularly powerful muscle but it is considered part of this group
and most of these muscles will have a distal attachment on that linea
aspera that we talked about which is going to be on the posterior side of the body of the femur
now you may have heard of a groin pull before it's not necessarily a pull of any of like the erectile
bodies or the external genitalia it's generally going to be a pull or a tearing or a strain
of some of those proximal attachments of the muscles of the anteromedial thigh region
a lot of times those adductor muscles are going to to be the portions that are going to be torn
but you can have some of the some of the deeper muscles associated with the anterior compartment
you can see that here anytime you have this glowing red you know something's up and so that's
what's going on here you have a pulled adductor longus muscle which would be colloquially referred
to as a groin pull all right last but not least we have the posterior compartment of the thigh
and these are referred to colloquially as the hamstrings so the hammies in the back of the
thigh these are going to be a collection of three very long very rope-like type muscles
you're going to have the lateral biceps femoris biceps indicating that there are two heads
associated with it but generally you only see the one head pretty well the other one is deeper
and then on the medial side you'll have the semimembranosus and the semitendinosus the
semitendinosus tends to be the more superficial of the two these three muscles will have their
proximal attachment up on the ischial tuberosity that we talked about your sit bones up there
so that is where these hamstrings are going to have their proximal attachment their distal
attachments will either be the the fibula on the lateral side or the tibia on the medial side
medial here all right innervation we're getting into the sciatic world now in fact all the other
muscles that we're going to talk about obviously in this video but in our subsequent videos are
going to be innervated by branches of the sciatic nerve the sciatic nerve is the largest nerve in
the body but really what it is is a collection of two different nerves you'll have a tibial nerve
and a common fibular nerve that are wrapped up together to form the large sciatic nerve
and that they typically are traveling together in this posterior thigh so if you were to get
down to the nerve level you would be looking at the sciatic nerve now the specific motor fibers
that are innervating the hamstrings are almost all going to be tibial nerve or tibial division
okay so we're getting into already I do want you to understand that it is the tibial nerve of the
sciatic nerve that is going to be innervating this muscle sometimes you will just see the
the hamstrings are going to be innervated by the sciatic nerve but I do want you to understand
that it's a bit more complex than that the most powerful movement of the hamstrings is going
to be flexion of the knee joint but they will also play a role in terms of extension of the
thigh because they do cross the hip joint now we talked about the most powerful extender of
the hip joint is going to be the gluteus maximus but when we're talking about extension that
is say in walking or just kind of standing still and keeping you know keeping you upright it's
these hamstrings are going to play a bigger role in terms of that type of extension of the thigh
all right excellent so we got through three of the largest muscle compartments in the whole body
it makes sense these are going the muscles of the thigh need to be robust they need to have
some powerful actions but they also play a role in terms of posture and keeping you upright as well
so let's review a concept we recall that the posterior compartment of the arm and the forearm
are innervated by one nerve you remember me saying over and over again radial nerve equals posterior
well we have a similar pattern in the lower limb and we introduced it here with the hamstrings so
which nerve is going to equal posterior as in it innervates the posterior compartments of both the
thigh and this is a preview of the leg as well so I try to recall what is going to innervate
the posterior compartment of the thigh and that will help you so pause the video if you need to
and when you're ready I hope you have landed on tibial nerve so tibial nerve equals posterior
tibial nerve is going to be the largest branch of the sciatic nerve and it will innervate both the
posterior thigh muscles as well as the posterior leg muscles so tibial nerve equals posterior
obturator nerve is going to innervate the the adductor compartment or that medial compartment of
the thigh femoral nerve not correct either that's going to be the anterior compartment of the thigh
these nerves are not branches of the sciatic nerve the common fibular nerve is a branch of
the sciatic nerve we haven't talked about what it innervates yet but it will certainly come up when
we get down to the leg muscles all right so radial nerve equals posterior when we're talking about
the upper limb tibial nerve equals posterior when we're talking about the lower limb and hopefully
that helps you kind of compartmentalize those and lessen a little bit of that cognitive burden in
terms of memorizing all the muscles and what they innervate or what they're innovated by excuse me
all right excellent thanks so much for your time and attention here i'll see
you in the next video where we talk about the muscles of the leg thanks