Motoneurons extend long axons peripherally to innervate skeletal muscle. These motoneurons receive information from descending tracts of the brain both directly and indirectly via interneurons in the spinal cord gray matter. Axons of dorsal root ganglion cells connect peripheral sensory receptors to spinal interneurons, to motoneurons, and to brain centers. Radial glia enclose the cord like the rim and spokes of a wheel, defining compartments for ascending and descending fiber systems. Astrocytes contribute to the blood-spinal cord barrier and provide a wide variety of support functions.
Oligodendrocytes myelinate axons, and provide for rapid conduction of neuronal signals.
Traumatic injury disrupts all of these cell types and changes their functions. Axons degenerate, neurons die, astrocytes proliferate and become reactive, radial glia enclose large cysts, and oligodendrocytes cannot remyelinate damaged areas. The anatomy of an injured spinal cord shows profound pathology, but also reveals the sprouting of uninjured fibers, the regeneration of damaged populations, the reorganization of glia, and clearing away of debris. The neurophysiology of the spinal cord also changes, reflected by altered responses to stimulation. Without appropriate ascending and descending input, remaining neural circuits change over time, and this plasticity may contribute to permanently impaired function.