There is overwhelming evidence that environmental factors play a role in the development and progression of a host of central nervous system disorders. Of over 80,000 chemicals are commercially available now, only about 200 have undergone developmental neurotoxicity (DNT) testing according the established guidelines. Human embryonic stem cells based DNT assays mimic neuron development in vitro and have become an alternative to expensive and time consuming animal DNT models. The main focus on this study was to establish in vitro human models for adverse outcome pathway mapping. For this main purpose, first study involved mimicking events associated with early human neurogenesis beginning with proliferating human neuron progenitor cells (hNP), progressing through differentiation and maturation of post mitotic neurite extending neurons at 14 days in vitro. The neuron in vitro differentiation model demonstrated neurotoxicant exposure during a maturation continuum affected human neurogenesis including neuron maturation and neurite outgrowth at substantially lower levels than previously known. The 14 day in vitro neuron was further differentiated to a pure neuron population for high throughput neurite outgrowth toxicity screening. A training set of chemicals including pesticides and endocrine disruptors were tested and their neurotoxicity were validated in the screening, showing the promise of this human model at cellular level for adverse outcome pathway mapping. Finally, these pure neurons were co-cultured with hNP derived astrocytes to study the role of cytochrome P450 in astrocyte neuroprotection. The hNP derived neuron and astroyte co-culture model identify critical role of cytochrome P450 in chlorpyrifos metabolism and indicated cell type specific neurotoxicitity for chlorpyrifos in brain. The hNP derived in vitro cell models in this study showed broad application of hNP derived neurons and astrocytes for DNT study and in the future the cells should be used to replace animal models in order to decrease the uncertainty associated with extrapolating toxicity across species.