Question

multiple choice question
during the stretch reflex, efferent signals in the motor nerve fiber stimulate which muscles to contract, producing a knee jerk?
o calf
o quadriceps
o hamstrings

Explanation:

The stretch reflex (knee - jerk reflex) is a monosynaptic reflex. When the patellar tendon is tapped, it stretches the quadriceps muscle. The sensory neurons detect this stretch and send signals to the spinal cord. In the spinal cord, the sensory neurons synapse directly with motor neurons. The motor neurons (efferent neurons) then send signals back to the quadriceps muscle, causing it to contract. The calf muscles (gastrocnemius and soleus) are mainly involved in plantar - flexion of the foot. The hamstrings are antagonists to the quadriceps (they flex the knee, while the quadriceps extend the knee). In the knee - jerk reflex, the goal is to extend the knee (counteracting the initial stretch), so the quadriceps are the muscles that contract.

Answer:

quadriceps