Quick Facts
Origin: In or just medial to the first sacral foramen.
Course: Medially from the sacral foramen and superiorly within the vertebral canal towards the posterior surface of the appropriate spinal cord level.
Branches: Unnamed rootlets just prior to entering the spinal cord.
Supply: Sensory innervation from the buttocks, posterior thigh, leg, and lateral foot.
Origin
The posterior root of the first sacral nerve originates in, or just medial to, the first sacral foramen. It is at this point that the first sacral nerve splits into anterior and posterior roots.
Course
The posterior root of the first sacral nerve runs medially through the first sacral foramen into the vertebral canal. Here, it runs superiorly towards its corresponding spinal cord level in a large bundle of nerve roots called the cauda equina. The posterior root splits into smaller rootlets before entering the dorsal aspect of the spinal cord.
Branches
The posterior root of the first sacral nerve branches into several smaller rootlets shortly before entering the dorsal aspect of the spinal cord.
Supplied Structures
The posterior root of the first sacral nerve carries sensory innervation from the medial buttocks, posterior thigh, leg, and lateral foot.
