Anterior Root of Fifth Lumbar Nerve (Right)

Origin

The anterior root of the fifth 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 lumbar nerve.

Branches

The anterior root of the fifth lumbar nerve sends motor axons to the anterior ramus of the fifth lumbar nerve. These contribute to the lumbosacral trunk and the sacral plexus. Specifically, the superior gluteal, inferior gluteal, and sciatic nerves.

Supplied Structures

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

The anterior root of the fifth lumbar nerve also sends motor axons to the anterior ramus of the fifth lumbar nerve. These contribute to the lumbosacral trunk, the sacral plexus, and the following nerves and 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 muscles.

—The inferior gluteal nerve arises from the fifth lumbar nerve and the first and second sacral nerves. It innervates the gluteus maximus muscle.

—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. However, the fifth lumbar nerve contributes primarily to the innervation of the gastrocnemius, tibialis anterior, extensor hallucis longus, and extensor digitorum brevis muscles. Of the muscles innervated by the sciatic nerve, extensor hallucis longus, and extensor digitorum muscles are primarily innervated by fibers from the fifth lumbar nerve. The gluteus medius muscle is also primarily innervated by the fifth lumbar nerve.