The nervous system comprises diverse neurons with many distinctive features including shape, anatomical position, connections to other neurons (their circuitry), the genes they express, patterns of electrical conductivity, and ultimately their function. These unique subpopulations of neurons arise from tightly controlled and precise differentiation processes that direct them to transition from immature nerve stem cells to fully mature, specialized neurons. Because they are so specialized, such distinct “subtypes” of neurons are often particularly vulnerable to, or associated with neurodegenerative injuries or diseases.