challenge: What is Heinrich Wilhelm Gottfried von Waldeyer-Hartz credited with in the field of neuroscience?
  
  A. Discovering the basic structural unit of the nervous system
  B. Developing the silver nitrate method of staining nerve tissue
  C. Conducting the first experiments on neural anatomy
  D. Coining the term 'neuron' to describe the basic structural unit of the nervous system
  Answer: 