The nervous system is highly plastic. Its development and maturation is characterised by neuronal proliferation, specialisation and loss and the sorting of synaptic connectivity. Transmission (chemical and electrical), receptor and ion channel transcription and distribution all contribute to the emerging selectivity of action. Numerous factors – especially genetic and autoimmune – and extrinsic factors – synthetic and natural toxic chemicals – disrupt this process of development and maturation or interfere with the function and structure of the mature system. In this review, the response of the peripheral nervous system to such influences is discussed.