Knee-jerk reflex and Reflex action

Knee-jerk reflex noun - A reflex extension of the leg resulting from a sharp tap on the patellar tendon.

Reflex action and knee-jerk reflex are semantically related. In some cases you can use "Reflex action" instead a noun phrase "Knee-jerk reflex".

Reflex action noun - An automatic instinctive unlearned reaction to a stimulus.

Knee-jerk reflex and reflex action are semantically related. Sometimes you can replace phrase "Knee-jerk reflex" with "Reflex action", this phrases are similar.