However useful the<unk>  culture has been for biological studies of developmental processes and the functional assay for testing neuronal characteristics, there are several limitations to the method. First, the<unk>  culture formation is highly sensitive to the procedure, as the creation is contingent on the system used to create the culture. Variation in cell density, different constituents or concentrations of factors in the media and method, method and frequency of passaging, and whether the<unk>  is dissociated before differentiation can lead to differences in both the composition of cell types and properties within each<unk> . This poses a problem for consolidating and interpreting data, even within the same study. Another problem with the system arises from the nature of suspension cultures (in vitro) : individual cells cannot easily be carefully monitored. Since the neuronic capacity of the<unk> -expanded cells diminishes after an extended number of passages, the lack of monitoring adds further complexity to the<unk>  method. Finally, only a small percentage of cells within each heterogeneous sphere have the potential to form<unk> s, and even fewer cells actually fulfill the criteria for being neural stem cells.<unk> s each contain cells at multiple stages of differentiation, including stem cells, proliferating neural progenitor cells, postmitotic neurons, and glia. Moreover, the heterogeneity of the<unk>  increases with its size, since more and varied cell types arise with a longer time in culture.
Neurosphere
Neuromatrix
Cortical minicolumn
Chondrocranium
Dinacharya
Tapetum lucidum
Growth cone
Neuroblast