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George E. Carvell, PhD, PT   University of Pittsburgh
The propriospinal tract is an almost continuous band of axons immediately surrounding the gray matter. Propriospinal (P) Neurons are scattered throughout the intermediate gray. Some cells in the dorsal and ventral horn may also contribute axons to ascend or descend in this tract. P Neurons are influenced by converging inputs from descending pathways, peripheral axons & spinal interneurons. Long propriospinal neurons coordinate 'whole body' integration: bilateral influences are common (interlimb and limb-trunk coordination). Short propriospinal neurons tend to restrict connectivity unilaterally and within that specific level of the cord (intralimb coordination).
The intermediate gray contains a class of relay neurons that connect different segments of the spinal cord; Short Propriospinal Neurons operate within nearby regions, while Long Propriospinal Neurons interconnect segments across many levels of the spinal cord. One set of propriospinal neurons located in the 3rd and 4th cervical segments have a special role in coordination of synergistic actions of the upper extremity (eg., reaching) and others at lower segments assist in coordination of lower extremity/trunk synergistic activity (eg., locomotion & postural control). Commissural interneurons located close to the midline connect the right and left sides. Projection neurons that send their axons into the lateral funiculus are located in the thoracic and lumbar levels.  Local interneurons at all levels influence ventral horn segmental motor centers. Autonomic preganglionic motoneurons live in the lateral aspect of the intermediate gray (sympathetic at thoracolumbar levels, and parasympathetic at                          the sacral level). The sympathetic/parasympathetic motor axons exit the                                            ventral roots to synapse on postganglionic                                                             autonomic                                                          motoneurons in the periphery.
Propriospinal Tract
Autonomic Motoneurons
Propriospinal Neurons