For all that, the cerebrum can exert an influence on the knee jerk.
Reflex action persists; the knee jerk is diminished, pointing to relaxation in tone of the muscles; consciousness is suspended.
Cross the knee to be stimulated over the other leg, and tap the tendon just below the knee cap, and the knee jerk appears.
Anxious attention to the knee jerk inhibits it; gritting the teeth or clenching the fist reinforces it.
We see excellent examples of cerebral facilitation and inhibition in the case of the knee jerk.