Nerves of the Posterior Abdominal Wall

Nerves of the Posterior Abdominal Wall

Lumbar plexus

• Is formed by the union of the ventral rami of the first three lumbar nerves and a part of the fourth lumbar nerve.
• Lies anterior to the transverse processes of the lumbar vertebrae within the substance of the psoas muscle

1. Subcostal nerve (T12)

• Runs behind the lateral lumbocostal arch and in front of the quadratus lumborum.
• Penetrates the transverse abdominal muscle to run between it and the internal oblique muscle.
• Innervates the external oblique, internal oblique, transverse, rectus abdominis , and pyramidalis muscles.

2. Iliohypogastric nerve (L1)

• Emerges from the lateral border of the psoas muscle and runs in front of the quadratus lumborum.
• Pierces the transverse abdominal muscle near the iliac crest to run between this muscle and the internal oblique muscle.
• Pierces the internal oblique muscle and then continues medially deep to the external oblique muscle.
• Innervates the internal oblique and transverse muscles of the abdomen and divides into an anterior cutaneous branch , which innervates the skin above the pubis, and a lateral cutaneous branch , which innervates the skin of the gluteal region.

3. Ilioinguinal nerve (L1)

• Runs in front of the quadratus lumborum, piercing the transverse and then the internal oblique muscle to between the internal and external oblique aponeuroses.
• Accompanies the spermatic cord (or the round ligament of the uterus) , continues through the inguinal canal, and emerges through the superficial inguinal ring (see Figure 5-3 ).
• Innervates the internal oblique and transverse muscles and gives off femoral cutaneous branches to the upper medial part of the thigh and anterior scrotal or labial branches.

4. Genitofemoral nerve (L1-L2)

• Emerges on the front of the psoas muscle and descends on its anterior surface.
• Divides into a genital branch , which enters the inguinal canal through the deep inguinal ring to reach the spermatic cord and supply the cremaster muscle and the scrotum (or labium majus), and a femoral branch which supplies the skin of the femoral triangle.

5. Lateral femoral cutaneous nerve (L2-L3)

• Emerges from the lateral side of the psoas muscle and runs in front of the iliacus and behind the inguinal ligament.
• Innervates the skin of the anterior and lateral thigh.

6. Femoral nerve

• Emerges from the lateral border of the psoas major and descends in the groove between the psoas and iliacus.
• Enters the femoral triangle deep to the inguinal ligament and lateral to the femoral vessels, outside the femoral sheath, and divides into numerous branches.
• Innervates the skin of the thigh and leg, the muscles of the front of the thigh, and the hip and knee joints.
• Innervates the quadriceps femoris, pectineal, and sartorius muscles and gives rise to the anterior femoral cutaneous nerve and the saphenous nerve.
  

7. Obturator nerve

• Arises from the second, third, and fourth lumbar nerves and descends along the medial border of the psoas muscle. It runs forward on the lateral wall of the pelvis and enters the thigh through the obturator foramen
• Divides into anterior and posterior branches and innervates the adductor group of muscles, the pectine, the hip and knee joints, and the skin of the medial side of the thigh.

8. Accessory obturator nerve

• Is present in about 9% of the population.
• Descends medial to the psoas muscle, passes over the superior pubic ramus, and supplies the hip joint a the pectineus muscle.

9. Lumbosacral trunk

• Is formed by the lower part of the fourth lumbar nerve and all of the fifth lumbar nerve, which enters into the formation of the sacral plexus.

Autonomic nerves in the abdomen

1. Autonomic ganglia

Sympathetic chain (paravertebral) ganglia

• Are composed primarily of ascending and descending preganglionic sympathetic general visceral efferent (GVE) fibers and general visceral afferent (GVA) fibers with cell bodies located in the dorsal root ganglia.
• Also contain cell bodies of the postganglionic sympathetic fibers.

Collateral (prevertebral) ganglia

• Include the celiac, superior mesenteric, aorticorenal, and inferior mesenteric ganglia, usually located near the origin of the respective arteries.
• Are formed by cell bodies of the postganglionic sympathetic fibers.
• Receive preganglionic sympathetic fibers by way of the greater, lesser , and least splanchnic nerves

Para-aortic bodies

• Are also called aortic bodies, Zuckerkandl's bodies, organs of Zuckerkandl , or aortic glomera.
• Are small masses of chromaffin cells found near the sympathetic chain ganglia along the abdominal aorta and serve as chemoreceptors responsive to lack of oxygen, excess of carbon dioxide, and increased hydrogen ion concentration that help to control respiration.

2. Splanchnic nerves

Thoracic splanchnic nerves

• Contain preganglionic sympathetic (GVE) fibers with cell bodies located in the lateral horn(intermediolateral cell column) of the spinal cord and GVA fibers with cell bodies located in the dorsal root ganglia.
• The greater splanchnic nerve enters the celiac ganglion, the lesser splanchnic nerve enters the aorticorenal ganglion, and the least splanchnic nerve joins the renal plexus.

Lumbar splanchnic nerves

• Arise from the lumbar sympathetic trunks and join the celiac, mesenteric, aortic, and superior hypogastric plexuses.
• Contain preganglionic sympathetic and GVA fibers.

3. Autonomic plexuses

Celiac plexus

• Is formed by splanchnic nerves and branches from the vagus nerves.
• Also contains the celiac ganglia , which receive the greater splanchnic nerves.
• Lies on the front of the crura of the diaphragm and on the abdominal aorta at the origins of the celiac trunk and the superior mesenteric and renal arteries.
• Extends along the branches of the celiac trunk and forms the subsidiary plexuses , which are named according to the arteries along which they pass, such as gastric, splenic, hepatic and suprarenal plexuses.
• Is also called the solar plexus.
• Solar plexus: is the combined nerve plexus of the celiac and superior mesenteric plexuses.

Aortic plexus

• Extends from the celiac plexus along the front of the aorta.
• Extends its branches along the arteries and forms plexuses that are named accordingly superior mesenteric, testicular (or ovarian), and inferior mesenteric.
• Continues along the aorta and forms the superior hypogastric plexus just below the bifurcation of aorta.

Superior and inferior hypogastric plexuses

4. Enteric division

• Consists of the myenteric (Auerbach's) plexus , which is located chiefly between the longitudinal muscle layers, and the submucosal (Meissner's) plexus , which is located in the submucosa. Both parts consist of preganglionic and postganglionic parasympathetic fibers, postganglionic sympathetic fibers, GVA fibers, and cell bodies of postganglionic parasympathetic fibers.
• Have sympathetic nerves that inhibit GI motility and secretion and constrict GI sphincters; parasympathetic nerves stimulate GI motility and secretion and relax GI sphincters.

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