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This tutorial is on the muscles of the posterior
abdominal wall. So you’ve got five muscles that you need to know about here. You’ve got
the quadratus lumborum. You’ve got the psoas major and minor. You’ve got the iliacus. And
you’ve got the diaphragm. So the psoas major and minor sit medially,
the iliacus is inferiorly. The diaphragm sits at the top, superiorly. And then you’ve got
the quadratus lumborum sitting posteriorly and laterally. So this view that we’re looking at here, I’ve
removed the anterior abdominal muscles and I’ve removed the muscles of the back and the
spine, so we can view these posterior abdominal walls quite nicely. I’ll start off with these
medial muscles, the psoas major and minor. This muscle here, this large muscle is the
psoas major. You can see its attachment here on the vertical bodies. It attaches from the
vertical bodies from T12 down to L5. And if I fade away the other muscle, you can see
its insertion in the lesser trochanter of the femur. So you can see its origins here.
It sits anterolaterally on the vertical body. So it sits in front of the transverse processes
on the bodies of vertebra T12 down to L5. It’s a hip flexor. So it flexes the thigh
at the hip joint. So it brings the thigh up like this. And also in the lying position,
if you imagine this model in the supine position, the muscle can sort of act in the reverse
way. It can flex the vertebra. If it’s in the supine position, the psoas major can contract
to bring the vertebra up (so flexion of the vertebral column). The psoas minor sits on top of it. And this
muscle isn’t always present in everybody, but if it is present, it originates on the
bodies of T12 and L1 and it inserts on the pectineal line and the iliopubic eminence.
So you can see that here. So I’ve just isolated the muscle so you can see its origin on T12
and L1 and it inserts on the iliopubic eminence and pectineal line. So the psoas major is innervated by the anterior
rami of spinal nerves L1-L3. The psoas minor is innervated by the anterior ramus of L1. So the psoas minor acts as a weak flexor of
the vertebral column. If I just get rid of these two muscles now,
we can take a look at the iliacus, which sits just a little bit inferior to it. So the iliacus
muscle sits in the iliac fossa. It joins the psoas muscle to insert into the lesser trochanter.
So you can see its insertion on the lesser trochanter here. You can see how it runs through
and combines with this psoas major muscle. So collectively, the iliacus and the psoas
major are referred to as the iliopsoas. This serves the same function as the psoas
major muscle. It flexes the thigh at the hip joint. It’s innervated by the femoral nerve. So you can see how both the distal ends of
the iliacus and psoas major pass underneath this ligament, the inguinal ligament to insert
onto the lesser trochanter of the femur. So if we just rotate around to the back, we
can see the quadratus lumborum muscle, which is this muscle here. So if I just fade away
the other muscles, we’ll take a look at its origin and insertion. You can see here that it has this origin on
the iliac crest and it also has an origin on the transverse process of lumbar vertebra
L5. Also, if I rotate anteriorly, you can see this ligament connecting the lumbar vertebra
to the inside of the ilium. This is called the iliolumbar ligament and it also originates
on this ligament. It’s not shown very clearly on this model,
but the quadratus lumborum muscle actually inserts onto the transverse processes of lumbar
vertebra L1-L4. So it inserts here, here, here and here as well as the inferior margin
of the 12th rib. So this muscle can laterally flex the spine
and it can also depress the rib. This muscle is innervated by the anterior rami of T12
and also of L1-L4 (spinal nerves T12 and L1-L4). So right at the top, we’ve got the diaphragm.
The posterior parts of the diaphragm contribute to the posterior abdominal wall, the muscular
parts of the posterior abdominal wall. We’ll just take a quick look at the diaphragm.
You can see it’s got this domed shape. It separates the thorax from the abdomen (the
thoracic cavity from the abdominal cavity). It forms the superior aspect of the abdominal
cavity, so it lines the inferior thoracic aperture. It’s attached to the lumbar vertebra by these
two legs. So these two legs are called crura (plural) or crus (singular). This is Latin
for ‘leg’ and you’ve got a right and a left crus. And if I rotate the model around, you can
see that there’s this central tendinous section and there’s a few holes. So various structures
pass from the thorax into the abdominal cavity via these holes. So there’s a lot to talk
about the diaphragm, but I won’t go through all that. I’ll do a separate tutorial. So
it’s the posterior parts of the diaphragm that contribute to the posterior abdominal
wall, the muscular part of the posterior abdominal wall. The diaphragm is innervated by the phrenic
nerve. So those are the five muscles you need to
know that make up posterior abdominal wall. You’ve got the diaphragm at the top (the posterior
parts of the diaphragm), you’ve got the psoas major and minor, you’ve got the iliacus and
you’ve got the quadratus lumborum.

47 thoughts on “Muscles of the Posterior Abdominal Wall – 3D Anatomy Tutorial

  1. thank u very much …great tuts …would u please tell me the name of the 3d programme u are woking with ( if u donnt mind) because i really liked it and i wanna try it

  2. Thanks so much for the tutorials! I've seen a bunch and I am going to see them all… again! As a self-improving/understanding individual, one thing I would like to learn more about is the function of different muscles; especially of muscles with similar functions like the iliacus and psoas major. Keep up the good work please!

  3. amazing tutorials!! after watching these, I don't really feel the need to open my book and memorize stuff all over again.. =D you've made things easier! waaayyy too much!

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  6. You are really doing a great job. Thank You. But i was just wondering if it's possible that I get that model on my desktop/pc.

  7. Is the title of this video correct/accurate, i.e. dost it match the content? For instance, where is the thoracolumbar fascia?

  8. I'm smiling now
    oh ~ I get exam tomorrow and I was hopeless
    thanks for you , they gave hope
    your videos are fast and useful

  9. I know almost nothing about anatomy, but I have this workbook from my physical therapist that I'm trying to understand. I had to keep pausing the video to look up terms, but I slogged through bit by bit and voila … I think I've got it! Thank you. I look forward to watching the others.

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