Anterior Root of First Lumbar Nerve (Right)

Origin

The anterior root of the first lumbar nerve originates as a series of rootlets that emerge from the ventrolateral surface of the spinal cord. These quickly merge to form the anterior root.

Course

The anterior root runs inferiorly and descends through the vertebral column, until it reaches the intervertebral foramen below the corresponding vertebra. In or just lateral to the intervertebral foramen, the anterior and posterior roots merge to form the spinal nerve.

Branches

The anterior root of the first lumbar nerve sends motor axons to the anterior ramus of the first lumbar nerve. These contribute to the lumbar plexus. Specifically, the iliohypogastric, ilioinguinal, and genitofemoral nerves.

Supplied Structures

The anterior root of the first lumbar nerve sends motor axons to the posterior ramus of the first lumbar nerve, which supply the epaxial muscles of the lumbar region, including spinae erector and the transversospinal muscles.

The anterior root of the first lumbar nerve also sends motor axons to the anterior ramus of the first lumbar nerve. These contribute to the lumbar plexus and the following nerves and their targets.

—Small branches innervate the iliopsoas muscle.

—The iliohypogastric nerve supplies innervation to quadratus lumborum, transversus abdominis, and the internal obliquus muscles.

—The ilioinguinal nerve supplies innervation to the quadratus lumborum, transversus abdominis, and internal obliquus muscles.

—The genitofemoral nerve arises from both the first and second lumbar nerves and is almost entirely sensory in females. It may, however, innervate a few vestigial muscle fibers on the round ligament of the uterus.

—Sympathetic innervation from the anterior root of the first lumbar nerve targets the hindgut and genital regions.