 A trophic factor can be described as a factor that is associated with providing nourishment to allow for growth.In general they are protein ligands for tyrosine kinase receptors; binding to the specific receptor yields autophosphorylation and subsequent phosphorylation of tyrosine residues on proteins that participate in further downstream signaling to activate proteins and genes involved in growth and proliferation.Neurotrophic factors act through retrograde transport in neurons, in which they are taken up by the growth cone of the injured neuron and transported back to the cell body.