A tap on the knee just below the kneecap will elicit extension of the leg. This reflex indicates that:
A) muscle spindles have been stretched.
B) Golgi tendon organs have been stretched.
C) neurons have been damaged in the spinal cord.
D) muscle spindles have been relaxed.

Question

Quizplus · Accepted Answer

The knee-jerk reflex is an example of the stretch reflex, which involves the activation of muscle spindles. Muscle spindles detect changes in muscle length and send sensory information to the spinal cord, where a reflexive response is initiated. When the patellar tendon is struck, the quadriceps muscle is lengthened, which activates the muscle spindles. This activates sensory neurons that synapse with motor neurons in the spinal cord, causing the quadriceps muscle to contract and the leg to extend. Therefore, choice A, muscle spindles have been stretched, is the correct answer.

A Tap on the Knee Just Below the Kneecap Will