(A) In the early embryo, neural stem cells form from a tissue called the neuroectoderm, where various patterning genes (Gsb, En, Msh, Ind and Vnd) are expressed. This spatial patterning process imparts unique molecular identities (different colors) to each of the stem cells. (B) The neural stem cells then start to divide, as shown for two neural stem cells here (red and blue-green). Each division results in a renewed neural stem cell and a ganglion mother cell (GMC; white circle). The GMC then divides to generate two neurons: one of these cells has active Notch signaling (Non; dark green) and the other does not (Noff: light green). In addition, the dividing stem cells express a series of genes sequentially (represented as shades of red and blue). Throughout this temporal patterning process, each stem cell can generate progenies with slightly different identities (hence the different shades of red and blue of the daughter cells). In this way Notch signaling and temporal patterning generate diverse neurons. (C) As they mature, neurons coming from spatially distinct neural stem cells (red or blue) and born over time (shades of red or blue), but which share the same Notch status (light or dark green), often fasciculate together to innervate similar regions in the ventral nerve cord (four such ‘bundles’ of neurons are depicted here: red Noff cells; blue Noff cells; red Non cells; blue Non cells). These complex mechanisms – spatial patterning, temporal patterning and Notch status – create diverse neurons that form the developmental basis of the functional architecture of the ventral nerve cord. Now, Lacin et al. focus on three fast-acting neurotransmitter (Glutamate, or Glu; GABA; Acetycholine, or Ach) and show that all neurons within a hemilineage also share neurotransmitter identity.