External Oblique and Rectus Abdominis

00:01 So now let's have a look at a couple of these muscles quite specifically starting with external oblique.

00:06 So external oblique muscle is a very thin muscle.

00:10 It's the most superficial of those three paired muscles I spoke about a moment or two ago, that originate laterally.

00:17 And here we can see them coming from the outer surface of the ribs.

00:20 Ribs 5 to 12. There can be some variation.

00:23 And forgive me, if some textbooks maybe say things slightly differently.

00:27 But typically, from the outer surface of ribs 5 to 12, you'll find the origin of the external oblique muscle.

00:35 And you can see these fibers are radiating downwards, as if you're just sliding your hands into your pockets on your jacket.

00:42 The direction of your fingers really is the direction of those external oblique muscle fibers.

00:49 They went all the way down to attach to the anterior half of the iliac crest, which can be located on the iliac aspect of the pelvic bone.

00:58 And they also run down as an aponeurosis to help form the inguinal ligament. We'll come back to that in a moment.

01:05 And you can see how the fibers run indicated by these green lines, they run towards the midline. But the muscle themselves, the muscle fibers themselves don't reach the midline, they give rise to a flat tenderness structure.

01:18 So you may recall that muscle say like biceps gives rise to a nice cord like tendon, the tendon of biceps brachii.

01:28 It doesn't happen like this here.

01:30 Here, we can see the muscle fibers give rise to this flat connective tissue sheath which is known as an aponeurosis.

01:36 And that aponeurosis runs towards what we've seen before the linea alba, and then most inferiorly, the pubic tubercle.

01:44 So this is a thin muscle layer that runs towards the midline linea alba pubic tubercle.

01:49 But it does by giving rise to a thin connective tissue sheet called an aponeurosis.

01:56 There you can see it's attached to the inguinal ligament.

01:59 The function of this muscle is relatively straightforward.

02:02 And as those muscles contract, so the distance between the inferior aspect the subcostal region and the midline and the pubic tubercle, the inguinal ligament is going to shorten and obviously that's going to lead to bending to the right.

02:15 So if the right one contract so you bend to the right.

02:18 And then conversely, if the left one contracts, you bend across to the right.

02:22 So very important functions in relation to movement of these muscles.

02:26 But what they also do is they help to compress the abdominal contents.

02:30 So they're always carrying a basic level of tones.

02:34 They're always contracted to a certain extent if all of our muscles were permanently flaccid and relaxed.

02:39 We wouldn't be able to withstand the forces of gravity and will just fall over.

02:42 So all of our muscles even though we may think they're relaxed, do have a basal tone of contraction there.

02:48 And that helps to maintain abdominal pressure.

02:51 Contraction of both of these muscles, the left and right side and simultaneously help to flex the trunk. So helping to move the head forwards.

02:59 So now let's look at the origins and insertions of Rectus Abdominis.

03:04 We can see the rectus Abdominus originates from the pubic symphysis and the pubic crest inferiorly, and it passes all the way up to the xiphoid process superiorly. We also have lateral attachments on the costal cartilages of ribs 5 to 7, and then we actually have within the body of rectus Abdominus a series of what are known as tenderness insertions.

03:25 These are not attachment sites per se, but very much their thickenings of that muscle fiber to help increase the ability for the muscle to contract, running down the midline, separating the two vectors abdominal muscles. We have the linea Alba, a tough connective tissue bead that runs all the way down the midline of the abdomen. Here we can identify the lateral border of the rectus abdominus muscle and we can see here on the surface of the skin where we have that lateral boundary of rectus abdominus demarcated as the semilunar line.

03:58 The function of rectus abdominis is very similar to when both external oblique muscles contract.

04:03 And in addition to that of flexion of the abdomen, it also helps to compress the abdominal contents as well.

04:10 Helps to tense up the abdominal wall, which is important.

04:13 If you were to be attacked, it can have a protective function, not that helpful from a sharp blade or sharp instrument but actually as a muscle band around the abdomen, it can serve some protection to the abdominal contents.

04:26 And as I've alluded to before, contraction of this muscle will help to flex the trunk.

04:33 A muscle I haven't mentioned before, it wasn't in that general overview because we couldn't see it, but a very small muscle that is situated really the inferior aspects of rectus abdominis.

04:43 And a muscle I've only seen a handful of times within the Anatomy Lab is a very small muscle known as pyramidalis.

04:49 And pyramidalis muscle, you can see there is running up from the pubic symphysis and iliac crest, and it runs up into the linea alba.

04:57 It's a very small muscle that is rarely seen within the anatomy lab.

05:01 But it can also serve with you can see that the attachments there.

05:05 It can help to support the rectus abdominis muscle.