The spinal nerve emerges from the spinal column through an opening (intervertebral foramen) between adjacent vertebrae.

The rest of the spinal cord, however, is oriented differently, so a symptomatic posterolateral herniation between two vertebrae will actually impinge on the nerve exiting at the next intervertebral foramen down.

Each intercostal gives off a posterior branch which goes to the posterior vertebral muscles, and sends a small spinal branch through the corresponding intervertebral foramen to the medulla spinalis and its membranes.