nerves vs mental strain

nerves and mental strain both are nouns.

Word	Noun	Adjective	Verb	Adverb
nerves	Yes	No	No	No
mental strain	Yes	No	No	No

As nouns, mental strain is a hyponym of nerves; that is, mental strain is a word with a more specific, narrower meaning than nerves:

Other hyponyms of nerves include heebie-jeebies, jitters, screaming meemies, nervous strain, strain.

nerves (noun)	mental strain (noun)
control of your emotions	(psychology) nervousness resulting from mental stress
an uneasy psychological state