PNS neurons segregated from the CNS, reflecting the developmental split between neural-crest-derived (PNS) and neural tube-derived (CNS) neurons. The peripheral neurons then split into sensory, sympathetic, and enteric subdivisions, corresponding to functional, anatomical, and developmental differences between the three major divisions of the PNS. CNS neurons generally split first by anteroposterior domain (olfactory, telencephalon, diencephalon, midbrain, hindbrain, spinal cord), and then by excitatory versus inhibitory neurotransmitter. Based on these and similar observations, we propose a data-driven molecular taxonomy arranged in a hierarchy of more than 70 named taxa (Table S5), respecting the dendrogram of Figure 1C. The taxonomy provides an objective structuring principle for exploring the global architecture of the mammalian nervous system.
