knee jerk vs reflex response

knee jerk and reflex response both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee jerk	Yes	No	No	No
reflex response	Yes	No	No	No

As nouns, reflex response is a hypernym of knee jerk; that is, reflex response is a word with a broader meaning than knee jerk:

knee jerk: a reflex extension of the leg resulting from a sharp tap on the patellar tendon
reflex response: an automatic instinctive unlearned reaction to a stimulus

knee jerk (noun)	reflex response (noun)
a reflex extension of the leg resulting from a sharp tap on the patellar tendon	an automatic instinctive unlearned reaction to a stimulus