reflex

nouns

an automatic instinctive unlearned reaction to a stimulus
inborn reflex, innate reflex, instinctive reflex, physiological reaction, reflex, reflex action, reflex response, unconditioned reflex

adjectives

without volition or conscious control
"the automatic shrinking of the pupils of the eye in strong light"; "a reflex knee jerk"; "sneezing is reflexive"
automatic, reflex, reflexive