medulla vs myelin sheath

medulla and myelin sheath both are nouns.

Word	Noun	Adjective	Verb	Adverb
medulla	Yes	No	No	No
myelin sheath	Yes	No	No	No

medulla (noun)	myelin sheath (noun)
the inner part of an organ or structure in plant or animal	a layer of myelin encasing (and insulating) the axons of medullated nerve fibers
lower or hindmost part of the brain; continuous with spinal cord; (`bulb' is an old term for medulla oblongata)
a white fatty substance that forms a medullary sheath around the axis cylinder of some nerve fibers