nerve tract vs substantia alba

nerve tract and substantia alba both are nouns.

Word	Noun	Adjective	Verb	Adverb
nerve tract	Yes	No	No	No
substantia alba	Yes	No	No	No

As nouns, substantia alba is a hypernym of nerve tract; that is, substantia alba is a word with a broader meaning than nerve tract:

nerve tract: a bundle of myelinated nerve fibers following a path through the brain
substantia alba: whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths

Other hypernyms of nerve tract include white matter.

nerve tract (noun)	substantia alba (noun)
a bundle of myelinated nerve fibers following a path through the brain	whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths