unmyelinated
un·my·elin·at·ed
adj \-ˈmī-ə-lə-ˌnāt-əd\Definition of UNMYELINATED
: lacking a myelin sheath <unmyelinated axons>
Learn More About
Seen & Heard 
What made you want to look up unmyelinated? Please tell us where you read or heard it (including the quote, if possible).
