knee jerk vs instinctive reflex

knee jerk and instinctive reflex both are nouns.

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

As nouns, instinctive reflex is a hypernym of knee jerk; that is, instinctive reflex 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
instinctive reflex: an automatic instinctive unlearned reaction to a stimulus

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