Anterior Root of Fourth Lumbar Nerve (Right)

Origin

The anterior root of the fourth 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 fourth lumbar nerve sends motor axons to the anterior ramus of the fourth lumbar nerve. These contribute to the lumbar and sacral plexuses. Specifically, the femoral, obturator, superior gluteal, and sciatic nerves.

Supplied Structures

The anterior root of the fourth lumbar nerve sends motor innervation to the posterior ramus of the fourth lumbar nerve, supplying the epaxial muscles of the lumbar region, including erector spinae and transversospinal muscles.

The anterior root of the fourth lumbar nerve also sends motor axons to the anterior ramus of the fourth 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).

The anterior root of the fourth lumbar nerve also contributes to the sacral plexus via the lumbosacral trunk, and subsequently the following nerves and their motor targets.

—The superior gluteal nerve arises from the fourth and fifth lumbar nerves as well as the first sacral nerve. It innervates gluteus medius, gluteus minimus, and tensor fasciae latae.

—The sciatic nerve is the largest nerve in the body. It gives rise to the common fibular, tibial, and sural nerves. It arises from the fourth and fifth lumbar nerves as well as the first, second, and third sacral nerves. The sciatic nerve innervates all the muscles of the posterior thigh, anterior and posterior leg, and foot. Of the muscles innervated by the sciatic nerve, the tibialis anterior muscle is primarily innervated by the fourth lumbar nerve.