Quick Facts
Origin: Surface of the spinal cord anterior to the ventral horn.
Course: Inferiorly towards the intervertebral foramen between L3 and L4 vertebrae.
Branches: Femoral and obturator nerve.
Supply: Motor innervation to epaxial back muscles, psoas, iliacus, pectineus, sartorius, adductor, and quadriceps muscles.
Origin
The anterior root of the third 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 third lumbar nerve sends motor axons to the anterior ramus of the third lumbar nerve. These contribute to the lumbar plexus. Specifically, the femoral and obturator nerves.
Supplied Structures
The anterior root of the third lumbar nerve sends motor axons to the posterior ramus of the third lumbar nerve, supplying the epaxial muscles of the lumbar region, including erector spinae and transversospinal muscles.
The anterior root of the third lumbar nerve also sends motor axons to the anterior ramus of the third lumbar nerve. These contribute to the lumbar plexus and the following nerves and their motor targets.
—The femoral nerve arises from the second, third, and fourth lumbar nerves. It innervates psoas, iliacus, pectineus, sartorius, and quadriceps muscles (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis).
—The obturator nerve arises from the second, third, and fourth lumbar nerves. It innervates the adductor muscles (gracilis, obturator externus, adductor longus, adductor brevis, and adductor magnus).
