1. (noun) a reflex extension of the leg resulting from a sharp tap on the patellar tendon

• knee jerk
• knee-jerk reflex

1. (noun) a reflex extension of the leg resulting from a sharp tap on the patellar tendon

• inborn reflex
• innate reflex
• instinctive reflex
• physiological reaction
• reflex
• reflex action
• reflex response
• unconditioned reflex