You are a neurologist and perform a patellar reflex on each side of the body in one of your patients. You notice that the left side reflex doesn't work. The patient can feel a gentle sweeping motion on the thigh in both legs, cannot voluntarily kick the left leg, and directly applying a current to the quadriceps muscles causes kicking in both legs. Based on these test results, which part of the reflex arc is likely damaged? Explain why you conclude this.