white matter:  A portion of the brain or spinal cord containing mostly fiber tracts (communicating 'wires') rather than any nerve cell bodies.

 

xenograft:  A graft of tissue from a different species.

 

X-ray:  An image obtained by shining high-energy electrons through a tissue.

 

X-ray myelogram:  An image of the spinal canal obtained with an X-ray machine after first injecting dye into the spinal fluid.

 

yoga:  An exercise-based treatment in use for thousands of years for general health and well being. It is also used for the treatment of some types of spinal pain.