Muscles of the Posterior Abdominal Wall – Abdominal Walls and Inguinal Canal

by Craig Canby, PhD

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    00:01 Next, let’s look at the muscles of the posterior abdominal wall individually. Our first one will be the psoas major. So, we want to understand its attachments, its innervation and actions or functions. The origin of the psoas major and we can see several points of origin in the illustration. Here is the right psoas major, the left one is shown over in through here. The points of origin of the psoas major will be the vertebral bodies, the lateral aspects of T12, L1, L2, L3, L4 and L5, the intervening intervertebral disc and then it also will originate from the transverse processes of your lumbar vertebrae, all five of them.

    00:50 The insertion will extend underneath the inguinal ligament to then insert on the lesser trochanter of the femur. The innervation of your psoas major muscle will be the anterior rami of lumbar spinal nerves L1, 2 and 3. And the primary function of the psoas major is to flex the femur at the hip. It is a very powerful flexor of the hip.

    01:26 The psoas minor is a small muscle that runs on the superficial aspect of the psoas major.

    01:36 This muscle may be absent in some individuals. Its points of attachment would be the lateral surfaces of the bodies of T12 through L1 and the intervening intervertebral disc. Its insertion is more inferior and will be to the pectineal outline region of the pubic bone. It’s innervated by the anterior ramus of the first lumbar spinal nerve and its action is to produce a weak flexion of the vertebral column.

    02:17 The next muscle to take a look at is our quadratus lumborum. It’s a quadrate shaped muscle in the lumbar area and that is visualized in the illustration right in through here.

    02:31 The attachment of this would be to the transverse process of L5, the ileal lumbar ligament and then the iliac crest. It also attaches for its points of insertion to the transverse processes of L1 down through L4 and also has an attachment for its insertion to the 12th rib.

    03:01 This muscle is innervated by the anterior rami at T12, L1, L2, L3 as well as L4 and its main function is most likely to stabilize the 12th rib during respiratory movements.

    03:19 Diaphragm also has an attachment to the 12th rib. And so, when it’s contracting during inspiration, it wants to pull that 12th rib superiorly. What will happen then to counteract that is that your quadratus lumborum will contract and stabilize that 12th rib to keep it from being pulled more superiorly by the action of the diaphragm.

    03:47 The last muscle to point out with respect to the posterior abdominal wall is your iliacus muscle. It is shown right in through here. It is originating from the internal surface of the iliac ala or the wing of the ilium. Also has a partial attachment to the sacrum and some associated ligaments in this region.

    04:18 It has the same point of insertion as does the psoas major. It inserts onto the lesser trochanter of the femur. Collectively, the psoas major and the iliacus are known as the iliopsoas and since they both contract to the same point, the function of the iliacus is the same as the psoas major, a powerful flexor of the femur at the hip. The nerve that innervates your iliacus will be the femoral nerve and the femoral nerve would run on the lateral margin of the psoas major.

    About the Lecture

    The lecture Muscles of the Posterior Abdominal Wall – Abdominal Walls and Inguinal Canal by Craig Canby, PhD is from the course Abdominal Wall.

    Included Quiz Questions

    1. Quadratus lumborum
    2. Psoas major
    3. Psoas minor
    4. Iliacus
    1. Iliopsoas
    2. Quadriceps femoris
    3. Rectus femoris
    4. Sartorius
    5. Pectineus
    1. L1, L2, and L3
    2. L2, L3, and L4
    3. L4 and L5
    4. L2 and L3
    5. L1 and L2

    Author of lecture Muscles of the Posterior Abdominal Wall – Abdominal Walls and Inguinal Canal

     Craig Canby, PhD

    Craig Canby, PhD

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