External Oblique and Rectus Abdominis – Anterolateral Abdominal Wall

by James Pickering, PhD

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    00:00 membranes, before we get into the viscera. So, if we have a look at this in a little bit more detail then we are just concentrating again on this region here in the male and in the female, this abdominal cavity. And we are stripping away the skin to look at the musculature that lies underneath. And this is where we can see in this cartoon here.

    00:17 We can orientate ourselves again. So, we have got the xiphisternum up here and down inferiorly in this region, here we have got the pubic symphysis and the pubic crest. And we can see a whole arrangement of muscles here. We can see rectus abdominis and we can see some musculature over on this lateral aspect. So, let's go through these muscles individually.

    00:39 Let's start with external oblique. External oblique is an important muscle and its fibers run down within forwards. So, when we see external oblique fibers running in this direction, like you are putting your hands in your pockets like this, running downwards and forwards towards the midline. They originate from the surfaces of the ribs 5 to 12 which we can see here which I have noted and also they insert down into the linea alba, this midline is the umbilicus again, that we spoke about and in this diagram, we have actually opened up this region here. So, we can't exactly see where this muscle inserts, but it passes towards the midline and attaches to the linea alba. It also runs down and attaches to the inguinal ligament which is down here and it runs and attaches to the iliac crest and the pubic tubercle. We will cover this in a more detail as we go through.

    01:39 Previously, I have mentioned some important nerves. And the innervation of this muscle are the thoracoabdominal and subcostal nerves through T7 to 12. And these nerves again importantly run in this direction to supply external oblique and they allow the muscle to contract.

    01:58 The action of these muscles, why do we have these muscles, what is the importance of them, is to flex and to rotate the trunk. So, movement of the trunk enable us to move from side to side, enables to flex our trunk. Importantly, and this is for all of the muscles which we will cover, they enable the internal contents of the abdomen to be compressed. This is important when we defecate and if we vomit. And we can increase the pressure within the abdominal cavity by these muscles contracting, helping to expel faeces, for example. Also by doing this, they are putting pressure on the vertebral column. So, as these muscles contract, they increase the pressure within the abdomen and that effectively is like a football or a bag of air sitting against the base of a tree. The tree being the vertebral column. And that helps to stabilise us and support our vertebral column to keep us upright. So, this muscle, external oblique is important, we have spoke about it before and it?s important in moving and supporting the function of the internal environment.

    03:11 A muscle we can also see on this slide is rectus abdominis and this muscle we have spoken about before. This time we can see it quite clearly. It?s fibers running down in this direction. It?s coming from this xiphisternum and the costal cartilages superiorly and it runs either side of the linea alba. So, we have got some details here of rectus abdominis.

    03:31 It?s coming from the xiphisternum and the costal cartilages which we can see here, but actually originates from the pubic symphysis down here in the pubic crest and its fibers are running vertically, we can see them here. Importantly, we have a whole series of these little cartilaginous breaks within the muscle and here, we can see how they separate this band of muscle into various discreet regions and this gives its characteristics six-pack appearance. And if you have limited amount of subcutaneous fat then these bands can be clearly identified when you generate that six pack appearance like I have mentioned.

    04:15 So, here we have rectus abdominis. Similar nerve supply for this muscle, the thoracoabdominal and subcostal nerves from T6 through to T12 and again, these nerves are coming in this direction and they go to innervate the strap muscles, either side of the linea alba, we have one over on this side as well. The action similar to external oblique, that it helps to compress the internal viscera, but it?s important in flexing the trunk. So, to get a nice six pack, you often do your sit ups and that?s this muscle reducing the space from the xiphisternum down to the pubic symphysis. And by that, you are going to be doing your...

    04:55 your sit ups, your stomach crunches.

    About the Lecture

    The lecture External Oblique and Rectus Abdominis – Anterolateral Abdominal Wall by James Pickering, PhD is from the course Abdomen.

    Included Quiz Questions

    1. It originates from the outer surface of ribs 5–12.
    2. The fibers run superiorly and posteriorly.
    3. It originates from the inner surfaces of ribs 10-12.
    4. It has no relationship to intra-abdominal pressure.
    5. It helps with digestion.
    1. T7–T12
    2. T2–T6
    3. T6–T7
    4. T7–T8
    5. T8–T10
    1. Pubic crest
    2. Xiphisternum and the lowest portion of the body of the sternum
    3. The shaft of ribs 5–7
    4. The costal cartilage of ribs 5–7
    5. Ilium

    Author of lecture External Oblique and Rectus Abdominis – Anterolateral Abdominal Wall

     James Pickering, PhD

    James Pickering, PhD

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