What is "knee jerk"

Knee jerk \Knee jerk\ (Physiol.) A jerk or forward kick of the lower part of the leg produced by a blow or sudden strain upon the patellar tendon of the knee, which causes a sudden contraction of the quadriceps muscle; the patellar reflex.

Knee jerk \Knee jerk\, n. emotional and predictable; -- of certain people and their reactions to events.

a. (alternative spelling of knee-jerk English) n. (alternative spelling of knee-jerk English)

n. a reflex extension of the leg resulting from a sharp tap on the patellar tendon [syn: knee-jerk reflex, patellar reflex]