Third Sacral Nerve (Right)

Origin

The third sacral nerve originates within the vertebral canal of the sacrum where the anterior and posterior roots of the third sacral nerve unite.

Course

The third sacral nerve exits the vertebral canal through the sacral foramen. As it exits, the nerve splits into an anterior and posterior ramus.

Branches

The posterior ramus gives rise to small branches that serve the multifidus muscle and skin of the buttocks. The larger anterior ramus contributes to three major nerves: the tibial branch of the sciatic nerve, posterior femoral, and pudendal nerves. Parasympathetic fibers from the anterior ramus of the third sacral nerve also contribute to the pelvic splanchnic nerves.

Supplied Structures

The posterior ramus of the third sacral nerve supplies the multifidus muscle. In addition, it receives cutaneous innervation to the skin above the coccyx.

The anterior ramus of the third sacral nerve contributes to the sacral plexus, and the following nerves and targets.

—The sciatic nerve is the longest nerve in the body. It gives rise to the common fibular, tibial, and sural nerves. The third sacral nerve specifically contributes to the tibial portion of the sciatic nerve. 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 and the anterior and posterior leg and foot. The tibial branch specifically innervates the muscles of the posterior thigh, leg, and foot. Sensory innervation of the sciatic nerve is to the leg and foot. The tibial branch innervates the posterior, medial, and plantar surfaces of the foot.

—The posterior femoral cutaneous nerve, also known as the posterior cutaneous nerve of the thigh, is a sensory nerve that innervates the skin of the posterior thigh, leg, and perineum. It arises from the first, second, and third sacral nerves.

—The pudendal nerve arises from the second, third, and fourth sacral nerves and transmits motor and sensory innervation to the abdomen and pelvic regions. Motor innervation to the muscles of the perineum (bulbospongiosus, ischiocavernosus, superficial transverse perineal, deep transverse perineal, external anal sphincter, and external urethral sphincter). Sensory innervation of the pudendal nerve is to the skin of the perineal region. In females, this includes the skin around the anus, labia, and clitoris.

—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.

Muscles significantly innervated by the anterior ramus of the third sacral nerve include the perineal (through the nerve to levator ani), the external anal sphincter, and urethral sphincter muscles. The sensory dermatome for the third sacral nerve is the skin of the buttocks and perineum.