Involuntary reflexes such as the knee-jerk are controlled at which level?

• A. Brain
• B. Peripheral nerves
• C. The brain and spinal cord
• D. Spinal cord

Answer: (D)

Involuntary reflexes like the knee-jerk are controlled at the level of the spinal cord. When the tendon is stretched, sensory receptors send a signal into the spinal cord, where it directly synapses onto a motor neuron that commands the quadriceps to contract. This monosynaptic arc happens without the brain’s involvement, so the reflex can occur even if the brain isn’t active. The brain can influence reflexes through higher pathways, but the actual reflex action is generated and executed within the spinal cord.