In response to electrical activity, axon vesicles release growth factors, such as NrgI and BDNF, and glutamate. Receptor tyrosine kinase signaling, activated by growth factors, sensitizes NMDA receptors to glutamate and possibly initiates signal transduction that promotes myelin gene transcription and local myelin protein translation, possibly via PI3K/Akt/mTOR signaling (dashed arrows). NMDA receptor signaling leads to Fyn kinase activity, promoting MBP translation from transcripts that are transported into oligodendrocyte processes on microtubules. MBP production near the point of axon contact initiates disassembly of actin filaments, enabling axon wrapping via membrane spreading.