Second Sacral Nerve (Left)

Origin

The second sacral nerve originates within the vertebral canal of the sacrum, from the union of the anterior and posterior roots.

Course

The second 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 four major nerves: the inferior gluteal, sciatic, posterior femoral, and pudendal nerves. Parasympathetic fibers from the anterior ramus of the second sacral nerve contribute to the pelvic splanchnic nerve.

Supplied Structures

The posterior ramus of the second sacral nerve supplies the multifidus muscle. In addition, it receives cutaneous innervation from the skin over the medial buttocks.

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

—The inferior gluteal nerve arises from the fifth lumbar nerve and the first and second sacral nerves. It sends motor innervation to the gluteus maximus muscle. There is no sensory component to this nerve.

—The sciatic nerve is the longest nerve in the body. It that 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. Sensory innervation of the sciatic nerve is received from the leg and 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. It transmits motor and sensory innervation to the abdomen and pelvic regions. Motor innervation is sent to the muscles of the perineum (bulbospongiosus, ischiocavernosus, superficial transverse perineal, deep transverse perineal, external anal sphincter, and the 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, and reproductive organs, and genitals. Parasympathetic fibers exit the spinal cord via the second, third, and fourth sacral nerves, and unite to form the pelvic splanchnic nerve.

Muscles significantly innervated by the anterior ramus of the second sacral nerve include the gastrocnemius, soleus, abductor hallucis, abductor digiti minimi pedis, and external anal sphincter muscles. The sensory dermatome for the second sacral nerve is the skin of the buttocks and perineum, forming a circle around the anus, posterior thigh and leg, and heel of the foot.