First Sacral Nerve (Left)

Origin

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

Course

The first 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 superior gluteal, inferior gluteal, sciatic, and posterior femoral nerves.

Supplied Structures

The posterior ramus of the first sacral nerve supplies the multifidus muscle. In addition, cutaneous innervation is received from skin over the medial buttocks.

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

—The superior gluteal nerve arises from the fourth and fifth lumbar nerves, in addition to the first sacral nerve. It innervates gluteus medius, gluteus minimus, and tensor fasciae latae muscles. This nerve has no sensory component.

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

—The sciatic nerve is the longest 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. 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.

Muscles largely innervated by the anterior ramus of the first sacral nerve include the gastrocnemius, soleus, peroneus longus, peroneus brevis, and gluteus maximus muscles. The sensory dermatome for the first sacral nerve is the posterior and lateral leg, and foot.