Tapping the patellar tendon with a reflex hammer produces a brief contraction of the knee extensors. What is the cause of the muscle contraction?: (A) Elastic rebound of muscle connective tissue, (B) Golgi tendon organ response, (C) Muscle spindle activation, (D) Muscle spindle unloading
Answer is C. Ans. C. Muscle spindle activationMuscle spindles monitor muscle length. If the muscle is suddenly stretched, the spindle produces action potentials that activate homonymous motor neurons to contract the stretched muscle and resist the length change.