. What is the spinal cord?

the cylindrical bundle of nerve fibers and associated tissue which is enclosed in the spine and connects nearly all parts of the body to the brain, with which it forms the central nervous system.

Light microscope uses light to illuminate specimens and glass lenses to magnify images whereas an electron microscope uses a beam of electrons to illuminate specimens and magnetic lenses to magnify images. 

The resolution of electron microscope is very high is compared to that of light microscope. It means, for very small objects like nucleus of cell, virus, we can use electron microscope instead of light microscope.