stretch reflex vs reflex action

stretch reflex and reflex action both are nouns.

Word	Noun	Adjective	Verb	Adverb
stretch reflex	Yes	No	No	No
reflex action	Yes	No	No	No

As nouns, reflex action is a hypernym of stretch reflex; that is, reflex action is a word with a broader meaning than stretch reflex:

stretch reflex: reflex contraction of a muscle when an attached tendon is pulled; important in maintaining erect posture
reflex action: an automatic instinctive unlearned reaction to a stimulus

stretch reflex (noun)	reflex action (noun)
reflex contraction of a muscle when an attached tendon is pulled; important in maintaining erect posture	an automatic instinctive unlearned reaction to a stimulus