shrivel up vs atrophy

shrivel up is not a noun while atrophy is a noun.

Word	Noun	Adjective	Verb	Adverb
shrivel up	No	No	Yes	No
atrophy	Yes	No	Yes	No

As verbs, atrophy is a hyponym of shrivel up; that is, atrophy is a word with a more specific, narrower meaning than shrivel up:

Other hyponyms of shrivel up include blast, die back, die down, dry up, mummify.

shrivel up (noun)	atrophy (noun)
	any weakening or degeneration (especially through lack of use)
	a decrease in size of an organ caused by disease or disuse

shrivel up (verb)	atrophy (verb)
wither, as with a loss of moisture	undergo atrophy