Here's why:

* Myelin: This fatty substance acts like an insulator around the axon, speeding up nerve impulse transmission.

* White matter: The myelin sheath gives the axons a white appearance, hence the term "white matter."

Important note: The term "white matter" refers to the overall tissue in the brain and spinal cord that is rich in myelinated axons. It's not just a single axon, but rather a collection of them.