Ilioinguinal nerve

Origin

The ilioinguinal nerve arises from the anterior ramus of the first lumbar spinal nerve (L1). It originates as a single trunk, shared with the iliohypogastric nerve, from L1. This trunk typically splits into the ilioinguinal and iliohypogastric nerves either before or shortly after emerging from the lateral border of the psoas major muscle.

Course

After its origin, the ilioinguinal nerve traverses the anterior surface of the quadratus lumborum muscle, running posterior to the kidney. It parallels and lies inferior to the iliohypogastric nerve along much of its course. As it moves anteriorly, the ilioinguinal nerve crosses part of the iliacus muscle. Near the anterior iliac crest, it pierces the transversus abdominis muscle. From there, it enters the inguinal canal while traveling anteriorly, positioned deep to the internal oblique muscle. Within the inguinal canal, the ilioinguinal nerve accompanies the spermatic cord in men or the round ligament of the uterus in women. Finally, it exits the inguinal canal through the superficial inguinal ring.

Branches and Innervation

1. Motor Innervation

The ilioinguinal nerve provides motor branches to portions of the abdominal wall musculature, including the transversus abdominis and internal oblique muscles, as it travels through the abdominal cavity.

2. Sensory Innervation

Beyond the superficial inguinal ring, the ilioinguinal nerve supplies cutaneous innervation to the following areas:

• The upper medial thigh.

• In men: the root of the penis and the anterior surface of the scrotum (via the anterior scrotal nerves).

• In women: the anterior portion of the mons pubis and labium majus (via the anterior labial nerves).

Fiber Types and Neural Pathways

The ilioinguinal nerve is a mixed nerve, containing both motor and sensory fibers:

1. General Somatic Afferent (GSA)

These sensory fibers carry information from the aforementioned cutaneous regions (e.g., the upper medial thigh and anterior external genitalia) to the spinal cord.

• Pathway: Sensory signals travel through the ilioinguinal nerve → anterior ramus of L1 → spinal nerve L1 → posterior root of L1 → dorsal gray horn of the L1 spinal segment.

2. General Somatic Efferent (GSE)

These motor fibers originate in the anterior gray horn of the spinal cord at the L1 segment. They traverse the spinal nerve L1 and its anterior ramus to reach the ilioinguinal nerve, ultimately supplying the abdominal wall muscles (e.g., transversus abdominis, internal oblique) during its course.