Somatic Nerves of Posterior Abdominal Wall

00:01 Now, let's have a look at the somatic nerves and how they are situated on the posterior abdominal wall.

00:10 So this is quite a complex area and there's a number of nerves here and they together form what's known as the lumbar plexus.

00:18 So here we have a whole series of nerves, the spinal nerves, so they're somatic in nature, although they will carry a very small amount of sympathetic nerves.

00:28 But these are spinal nerves that are coming away from the spinal cord through the intervertebral foramen at numerous levels.

00:35 They go on to form the lumbar plexus.

00:37 And here we can see the anterior rami of those spinal nerves coming away from T12, we have the subcostal nerve.

00:45 This runs along the inferior border of the 12th rib.

00:50 We can see it has a connection with L1 and we can see that there is the anterior rami of the spinal nerves.

00:57 It gives rise to ramus, which is a branch and that goes to L1.

01:02 Coming away from L1, we have the iliohypogastric nerve, and that may have contributions coming from T12.

01:09 And then we have the ilioinguinal nerve as well coming away.

01:12 So note really that we have two named nerves coming from this L1 region.

01:18 You'll be familiar with these as they ran along the anterior lateral abdominal wall between transversus abdominus muscle and internal oblique.

01:28 If we look at L2, again, we can see a connecting ramus is running down from L1 to L2, but now we can pick out another nerve, which is the genitofemoral nerve.

01:38 The genitofemoral nerve goes down to supply running down the posterior abdominal wall to supply part of the external genitalia and the side.

01:47 Here we can see another branch known as the lateral femoral cutaneous nerve.

01:51 And here we can see the femoral nerve, these are running down to supply the lower limb.

01:57 The final nerve we can see here is the obturator nerve.

02:00 And that's passing down to help supply some regions through the pelvis and then on to the side.

02:07 So let's have a closer look at the iliohypogastric nerve that's coming away from L1.

02:14 So here we can see the iliohypogastric nerve is emerging with quadratus lumborum muscle posteriorly and the kidney is sitting anterior to it.

02:23 Sometimes you'll need to clear away the perinephric fat surrounding the kidney and move the kidney anterior to see this structure.

02:30 But you can see that it's running between the layers of transversus abdominus muscle here, as you can see, it's superficial to this muscle and internal oblique will be superficial to it.

02:41 Again, it gives rise to a number of branches.

02:43 Remember, it's a somatic nerve, so it's going to give branches that go to the surface of the skin, so cutaneous branches.

02:50 here we're gonna see the lateral cutaneous branch and that's taking sensation from the surface of the skin and even seen anterior branch go into more anterior regions to supply sensation.

03:01 As we move down into the inferior aspect of the abdominal wall, we can see that iliohypogastric nerve is now piercing internal oblique muscle.

03:11 And now it's running towards the inferior aspect of the abdominal wall.

03:16 We can see it occurs slightly anterior to the anterior superior iliac spine, which is an important landmarks to help recognize if you're looking for this nerve.

03:26 And then it runs all the way down piercing external oblique muscle.

03:29 So again, supply the skin on the surface of the abdomen.

03:34 Now, let's have a look at the ilioinguinal nerve.

03:36 This nerve carries a very similar course to iliohypogastric.

03:41 It's running here with quadratus lumborum, running posterior to it, and it's running along the superior edge of the iliac crest which we can see here.

03:50 It then passes through anteriorly piercing transversus abdominus muscle.

03:55 And then we can remember it has this intimate association with the spermatic cord and the inguinal canal.

04:01 It now pierces the internal oblique muscle, which means it happens to be located within the inguinal canal.

04:09 But it doesn't end to the inguinal canal like the spermatic cord is formed with the vas deferens the genital branch the genitofemoral nerve, etc.

04:17 Passing through transversalis fascia.

04:20 So that's important to remember.

04:22 The ilioinguinal nerve is located within the inguinal canal, but it's not actually within the sheath of the spermatic cord.

04:30 So here we can see the ilioinguinal nerve within the inguinal canal.

04:35 It will ultimately pass out of the superficial inguinal ring and here we can see it goes on to supply parts of the root of the penis, the medial thigh, and the anterior surface of the scrotum.

04:46 Now, let's turn to the genital femoral nerve.

04:48 The genital femoral nerve takes a different course.

04:51 In that it descends through the posterior abdominal wall, sitting very anterior to the psoas major muscle.

04:58 We can see it here running down inferiorly.

05:00 with psoas major muscle directly behind it and it splits into a genital branch, which pierces transversalis fascia, and it runs within the spermatic cord.

05:11 So although it's an inguinal canal, it is different from the ilioinguinal nerve.

05:17 As it's called the genital femoral nerve, we've concentrated on the genital branch passing through the deep inguinal ring, but it also has a femoral branch that passes deep to the inguinal ligament and goes and supplies the skin over the upper anterior aspect of the thigh.

05:33 Now let's talk about the lateral cutaneous nerve.

05:36 Here we can see the lateral cutaneous nerve that escapes lateral to the lateral border of psoas major muscle and it runs along the surface of iliacus we can see.

05:46 So again, go deep to the inguinal ligament most laterally within the inguinal region.

05:52 Here we can see it passes all the way down to supply parts of the thigh.

05:57 The alternator nerve is an important nerve, and here it's emerging near the medial border of psoas major, and it runs along the lateral wall of the pelvic cavity.

06:07 It then passes through the pelvis to enter into the thigh by passing through the obturator canal.

06:15 The femoral nerve is a really important nerve that supplies lots of the structures within the lower limb, specifically within the anterior compartment of the thigh.

06:24 Here we can see the femoral nerve, leaving against the lateral border of the psoas major muscle.

06:30 Again, coursing alongside iliacus muscle to pass into the thigh deep to the inguinal ligament.

06:37 We can see it runs alongside the femoral artery here, and you'll also find the femoral vein in this location as well.