Question

Please describe the patellar reflex and state what the stimulus, receptor, and effector organ(s) are in this reflex.

Answer 1

Patellar reflex is best tested with the subject supine. Examiner's hand is passed under the knee of subject and placed upon the opposite knee, knee to be tested is on the dorsum of examiner's wrist. Patellar tendon is struck midway between origin and insertion with knee hammer. Following the blow, there will be a brief extension of knee caused by contraction of quadriceps. Sometimes the reflex can be conveniently elicited with the subject sitting up, legs hanging freely over the edge of the seat. Sometimes reinforcement will have to be applied to elicit the reflex - Jendrassik's manoeuvre. This is done by asking the subject to make a strong voluntary muscle contraction with upper limbs like locking the fingers of the two hands together and then trying to pull them apart as forcefully as possible and simultaneously eliciting the knee jerk.

• Stimulus : Stretch
• Receptor : Patellar tendon
• Effector organ : Quadriceps