knee-jerk reflex

1. A sudden involuntary forward movement of the lower leg that can be produced by a firm tap to the tendon located just below the kneecap.

The term is loosely applied to any response or belief that is automatic rather than thoughtful. In this sense, it is usually a term of reproach: “Smith is a knee-jerk liberal.”

Example Sentences

My self-deprecating remarks, a knee-jerk reflex with me, didn’t amuse him.

From Los Angeles Times

Examples include the human knee-jerk reflex and the act of walking.

From Scientific American

“It’s like they go into hibernation from the overwhelming stress. Their brain switches off engagement with their social environment. They don’t respond to pain. Their knee-jerk reflex is absent.”

From Seattle Times

“It’s like they go into hibernation from the overwhelming stress. Their brain switches off engagement with their social environment. They don’t respond to pain. Their knee-jerk reflex is absent.”

From Washington Times

Just as with the knee-jerk reflex, “you have to hit the knee hard enough in the right place, or else nothing happens,” he told me.

From New York Times