Spinal white matter consists of dorsal and ventral root fibers entering and leaving (not shown) the spinal cord and ascending and descending white matter tracts (fasciculi).

White matter immediately surrounding gray matter consists of fibers that stay within the spinal cord. Collectively these fibers are called fasciculus proprius (FP).

A tract (or fasciculus) refers to group of functionally related nerve fibers. Ascending tracts convey information to the brain and descending tracts convey information from the brain. Tracts are organized so that longer (e.g. sacral) fibers are superficial to shorter (e.g cervical) fibers.

Entering dorsal root fibers form the dorsolateral fasciculus (DL F.) and regionally organized ascending fibers in the dorsal funiculus. Cranial branches of dorsal root fibers form two regional fasciculi: a medial fasciculus gracilis (fibers from the caudal half of the body) and a lateral fasciculus cuneatus (information form the cranial half of the body).