Anterior Root of Fourth Sacral Nerve (Right)

Origin

The anterior root of the fourth sacral 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. At lumbar and sacral levels, the anterior root descends through the vertebral column until it reaches the fourth sacral foramen. Just before entering this foramen the anterior and posterior roots merge to form the nerve.

Branches

There are no named branches; however fibers do contribute to the sacral plexus (see supplied structures).

Supplied Structures

The anterior root of the fourth sacral nerve contributes to the sacral plexus, particularly the pudendal nerve.

The pudendal nerve arises from the second, third, and fourth sacral nerves. It transmits motor and sensory innervation to the abdomen and pelvic regions. Motor innervation is to the muscles of the perineum (bulbospongiosus, ischiocavernosus, superficial transverse perineal, deep transverse perineal, external anal, and urethral sphincter muscles). In addition, the anterior root of the fourth sacral nerve innervates the levator ani and coccygeus muscles.

The pelvic splanchnic nerve carries parasympathetic innervation to the hindgut organs, kidneys, reproductive organs, and genitals. Parasympathetic fibers exit the spinal cord via the second, third, and fourth sacral nerves, and combine to form the pelvic splanchnic nerve.