Posterior fasciculus proprius

Posterior fasciculus proprius (a.k.a. posterior propriospinal tract), is a short bundle of propriospinal nerve fibers located within the posterior funiculus, adjacent to the posterior gray horns. These propriospinal neurons originate from cells inside the gray matter of the posterior horn, branching into both ascending and descending fibers within the ventral part of the posterior fasciculus. After travelling up and down a few segments of the cord, they re-enter the gray matter to synapse. This forms the posterior propriospinal tract, an intrinsic spinal cord pathway that links different spinal segments, enabling intersegmental communication.

Similar propriospinal tracts in the lateral and anterior funiculi, named the lateral fasciculus proprius and anterior fasciculus proprius, also play key roles in intersegmental coordination, facilitating integration across spinal cord segments.