Myelination of axons by glial cells called oligodendrocytes is essential for regulating axon conduction velocity in the central nervous system of vertebrates. However, the ways that axons and oligodendrocytes respond to each other during myelination are still poorly understood. One of the best-characterized responses of neurons to myelin is myelin-induced cytoskeletal collapse in the growth cone, or tip, of an elongating axon, which inhibits neuron outgrowth -- but the role of this inhibitory relationship during normal development is not known. I propose to combine the techniques of glial biology with biophysics and super-resolution microscopy to characterize how the axonal cytoskeleton responds to myelination. This could pave the way to improved understanding of the dysregulation involved in common diseases like epilepsy and multiple sclerosis.